Qualification: 
Ph.D, MSc
Email: 
t_rajagopalan@cb.amrita.edu

Dr. T. Rajagopalan currently serves as Associate Professor at Department of Electronics and Communication Engineering, School of Engineering. His areas of research include Synthesis, Processing, Characterization and Application Development of Carbon Nanotubes and Graphene.

Dr. Rajagopalan has recently joined Amrita Vishwa Vidyapeetham in the Department of Electronics and Communication Engineering. Prior to joining Amrita in May 2014, Dr. Rajagopalan was a Research Assistant Professor in University of Missouri (MU) – Columbia, USA since October 2007 after pursuing a post doctoral fellowship in the same University from June 2006 to Sept 2007.

He also worked as a Senior Project Manager in NEMS/MEMS Works LLC in 2012-13. During this period, he worked on a number of research projects related to the synthesis, characterization, testing and application aspects of nanoenergetic materials.

He has authored/co-authored more than 10 publications on various aspects related to nanoenergetic materials in prestigious international journals such as Combustion and Flame, Journal of Propulsion and Power, Langmuir etc. These works have resulted in two US patents besides several invention disclosures.

Previously, he also worked at the Department of Chemical Engineering, Ben Gurion University of the Negev (BGU), Israel as a visiting scientist from Jan 2004 to May 2006, with the research focused on the synthesis and characterization of a host of nanomaterials including carbon nanotubes and cadmium sulfide nanostructures. One of these works on the alignment of carbon nanotubes in liquid crystal matrix appeared in noteworthy chemistry in the American Chemical Society (ACS) homepage.

From 2001 to 2003, he worked on the development of new generation interleveland intermetal low k dielectric materials for ultra-large scale integration (ULSI) devices and the research was funded by IBM and Tokyo Electron America among others. He received Ph.D. on the study of Chalcogenide thin films as ‘phase change optical recording material’ from Indian Institute of Technology (IIT) Delhi and M.Sc.in Physics from Loyola College, Chennai in 2001 and 1989 respectively.

Dr. Rajagopalan has authored/co-authored more than 35 peer-reviewed papers in international journals with a citation count of more than 750 till date. He has also recently authored a book chapter on Energetic Materials published by CRC Press. Besides, he has delivered several oral and poster presentations at national and international conferences.

Dr. Rajagopalan’s current research interests include nanomaterials’ synthesis, characterization and testing for application-specific performance, specifically carbon nanotubes and graphene. Besides he is a regular reviewer for international journals like Materials Science in Semiconductor Processing, Combustion and Flame, Journal of the Electrochemical Society, Journal of Applied Physics, Chemistry of Materials, etc. He is a member of ACS and Materials Research Society (MRS). He was a core-member of the technology team at MU that received the Nanotech Briefs’ Nano50 - 2007 Technology Award for pioneering work on Nanoengineered Superthermites and Shock Wave and Energy Generation.

Publications

Publication Type: Journal Article

Year of Publication Publication Type Title

2017

Journal Article

S. S. Prabhu, Bhavani, R., Dr. Gireesh K. T., and Dr. T. Rajagopalan, “A computational approach to determine shielding effectiveness of carbon nanotube-based nanocomposites for \EMC\ application”, Computational Materials Science, vol. 126, pp. 400 - 406, 2017.[Abstract]


Abstract A computational method to determine the shielding effectiveness against electromagnetic interference of carbon nanotube (CNTs)-based nanocomposites through modelling of its electrical properties is presented. Specifically, simulations based on Ant Colony Optimization (ACO) were implemented to evaluate the electrical conductivity (σ) of \{CNTs\} (used as a filler in a polymer matrix) that formed electrical network inside a representative cuboid volume of the sample. A pseudo three-dimensional (3D) percolation model was developed to study the effects of random connectivity of \{CNTs\} to one another on the conductivity of nanocomposites. In our approach, both contact and intrinsic resistances were taken into account. The tunneling resistance between \{CNTs\} was also taken into account while dealing with single-walled \{CNTs\} (SWCNTs). A resistor network recognition method that optimizes connective paths was built using \{ACO\} method and conductivity was subsequently computed as a function of \{CNTs\} concentration. Then, the shielding effectiveness was computed using the conductivity data. It is remarkable that the calculated \{SE\} values as a function of frequency of \{EM\} waves at a constant weight percent of \{CNTs\} were in agreement with the experimental data for CNT-based nanocomposites reported in literature. More »»

2015

Journal Article

Dr. T. Rajagopalan, Staley, C., Geeson, J. M., Chung, S., Raymond, K. E., Gangopadhyay, K., and Gangopadhyay, S., “Enhanced Combustion Characteristics of Bismuth Trioxide-Aluminum Nanocomposites Prepared through Graphene Oxide Directed Self-Assembly”, Propellants, Explosives, Pyrotechnics, vol. 40, pp. 729–734, 2015.[Abstract]


We present a facile, spontaneous, and surfactant-free method to controllably self-assemble aluminum and bismuth trioxide nanoparticles through the introduction of graphene oxide as a self-assembly directing agent. The self-assembled nanocomposites demonstrate significant combustion performance improvements in comparison to randomly mixed aluminum and bismuth trioxide nanoparticles with enhanced pressure generation from 60 to 200 MPa, pressurization rate from 3 to 16 MPa μs−1, burning rate from 1.15 to 1.55 km s−1, and specific impulse from 41 to 71 s. The sensitivity of the self-assembled aluminum and bismuth trioxide to electrostatic discharge was reduced by four orders of magnitude, without decreasing the combustion performance. Graphene oxide directed self-assembly can be used to synthesize nanocomposites with diverse combustion properties and controlled ignition sensitivity, which lays the foundation for preparing multi-functional, highly-reactive, combustion systems in the future. More »»

2014

Journal Article

Dr. T. Rajagopalan, Chung, S. W., Basuray, S., Balasubramanian, B., Staley, C. S., Gangopadhyay, K., and Gangopadhyay, S., “A Versatile Self-Assembly Approach toward High Performance Nanoenergetic Composite Using Functionalized Graphene”, Langmuir, vol. 30, pp. 6556-6564, 2014.[Abstract]


Exploiting the functionalization chemistry of graphene, long-range electrostatic and short-range covalent interactions were harnessed to produce multifunctional energetic materials through hierarchical self-assembly of nanoscale oxidizer and fuel into highly reactive macrostructures. Specifically, we report a methodology for directing the self-assembly of Al and Bi2O3 nanoparticles on functionalized graphene sheets (FGS) leading to the formation of nanocomposite structures in a colloidal suspension phase that ultimately condense into ultradense macrostructures. The mechanisms driving self-assembly were studied using a host of characterization techniques including zeta potential measurements, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), particle size analysis, micro-Raman spectroscopy, and electron microscopy. A remarkable enhancement in energy release from 739 ± 18 to 1421 ± 12 J/g was experimentally measured for the FGS self-assembled nanocomposites. More »»

2014

Journal Article

C. S. Staley, Raymond, K. E., Dr. T. Rajagopalan, Herbst, J. J., Swaszek, S. M., Taylor, R. J., Gangopadhyay, K., and Gangopadhyay, S., “Effect of Nitrocellulose Gasifying Binder on Thrust Performance and High-g Launch Tolerance of Miniaturized Nanothermite Thrusters”, Propellants, Explosives, Pyrotechnics, vol. 39, pp. 374–382, 2014.[Abstract]


Nanothermites are promising propellants for miniaturized thruster applications, but in their pure state can be very sensitive to ignition stimuli and prone to phase separation. Consequentially, a need exists for desensitizing binders that do not inhibit nanothermite thrust performance. We investigate the effects of incorporating small weight concentrations of nitrocellulose as a gasifying binder in bismuth trioxide-aluminum nanothermites. Thrust measurements revealed improvements in specific impulse up to 63.2 s using nitrocellulose. The launch tolerance of the nanothermites in response to high-g acceleration was also explored and substantial improvements were realized for nanothermites prepared with nitrocellulose. As small as 5 % nitrocellulose content suppressed the sensitivity of the nanothermites to less than 1 % ignition probability after exposure to 30 kg acceleration events. Some nanothermite charges experimentally survived up to 90 kg loads. Most importantly, nitrocellulose predictably modulated the thrust performance and ignition sensitivity of the nanothermites as a function of weight content. Employing nitrocellulose as a binder, high performance nanothermite propellants can be synthesized for miniaturized thruster applications with tailored impulse generation and ignition sensitivity. More »»

2013

Journal Article

Dr. T. Rajagopalan, Korampally, V., Ghosh, A., Chanda, N., Gangopadhyay, K., and Gangopadhyay, S., “Nanomaterial processing using self-assembly-bottom-up chemical and biological approaches”, Reports on Progress in Physics, vol. 76, p. 066501, 2013.[Abstract]


Nanotechnology is touted as the next logical sequence in technological evolution. This has led to a substantial surge in research activities pertaining to the development and fundamental understanding of processes and assembly at the nanoscale. Both top-down and bottom-up fabrication approaches may be used to realize a range of well-defined nanostructured materials with desirable physical and chemical attributes. Among these, the bottom-up self-assembly process offers the most realistic solution toward the fabrication of next-generation functional materials and devices. Here, we present a comprehensive review on the physical basis behind self-assembly and the processes reported in recent years to direct the assembly of nanoscale functional blocks into hierarchically ordered structures. This paper emphasizes assembly in the synthetic domain as well in the biological domain, underscoring the importance of biomimetic approaches toward novel materials. In particular, two important classes of directed self-assembly, namely, (i) self-assembly among nanoparticle–polymer systems and (ii) external field-guided assembly are highlighted. The spontaneous self-assembling behavior observed in nature that leads to complex, multifunctional, hierarchical structures within biological systems is also discussed in this review. Recent research undertaken to synthesize hierarchically assembled functional materials have underscored the need as well as the benefits harvested in synergistically combining top-down fabrication methods with bottom-up self-assembly. More »»

2013

Journal Article

C. S. Staley, Raymond, K. E., Dr. T. Rajagopalan, Apperson, S. J., Gangopadhyay, K., Swaszek, S. M., Taylor, R. J., and Gangopadhyay, S., “Fast-impulse nanothermite solid-propellant miniaturized thrusters”, Journal of Propulsion and Power, vol. 29, pp. 1400–1409, 2013.[Abstract]


Highly reactive nanothermites prepared by mixing bismuth trioxide or cupric oxide nanoparticles with aluminum nanoparticles were evaluated as solid propellants for small-scale propulsion applications. Miniaturized engines were fabricated from steel in three-piece configurations without a converging/diverging nozzle. Bismuth trioxide-aluminum generated 46.1 N average thrusts for 1.7 ms durations with a specific impulse of 41.4 s. Cupric oxide-aluminum generated 4.6 N thrusts for 5.1 ms durations with a specific impulse of 20.2 s. Convective and conductive reaction regimes were identified as functions of bulk packing density and confinement geometry. Average thrusts and burning durations differed by greater than an order of magnitude for equivalent nanothermites dependent on the reaction regime. Adding small amounts of nitrocellulose to the nanothermites increased specific and volumetric impulses to maximum values of 59.4 s and 2.3  mN⋅s/mm32.3  mN·s/mm3 while controllably reducing average thrusts and prolonging burning durations. The energy-conversion efficiencies of the thrusters were evaluated using a rotary-arm measurement, and a maximum efficiency of 0.19% was observed. Last, a miniaturized four-engine array was fabricated with micromachined initiators and sequentially fired. The high specific and volumetric impulses, fast combustion, and tailored reactions of nanothermites are appealing for many small-scale propulsion applications. More »»

2013

Journal Article

B. - D. Lee, Sengupta, S., Gangopadhyay, S., and Dr. T. Rajagopalan, “Ultra-rapid elimination of biofilms via the combustion of a nanoenergetic coating”, BMC Biotechnology, vol. 13, p. 30, 2013.[Abstract]


Background Biofilms occur on a wide variety of surfaces including metals, ceramics, glass etc. and often leads to accumulation of large number of various microorganisms on the surfaces. This biofilm growth is highly undesirable in most cases as biofilms can cause degradation of the instruments and its performance along with contamination of the samples being processed in those systems. The current “offline” biofilm removal methods are effective but labor intensive and generates waste streams that are toxic to be directly disposed. We present here a novel process that uses nano-energetic materials to eliminate biofilms in < 1 second. The process involves spray-coating a thin layer of nano-energetic material on top of the biofilm, allowing it to dry, and igniting the dried coating to incinerate the biofilm. Results The nanoenergetic material is a mixture of aluminum (Al) nanoparticles dispersed in a THV-220A (fluoropolymer oxidizer) matrix. Upon ignition, the Al nanoparticles react with THV-220A exothermically, producing high temperatures (>2500 K) for an extremely brief period (~100 ms) that destroys the biofilm underneath. However, since the total amount of heat produced is low (~0.1 kJ/cm2), the underlying surface remains undamaged. Surfaces with biofilms of Pseudomonas aeruginosa initially harboring ~ 107 CFU of bacteria /cm2 displayed final counts of less than 5 CFU/cm2 after being subjected to our process. The byproducts of the process consist only of washable carbonaceous residue and gases, making this process potentially inexpensive due to low toxic-waste disposal costs. Conclusions This novel method of biofilm removal is currently in the early stage of development. However, it has potential to be used in offline biofilm elimination as a rapid, easy and environmentally friendly method. More »»

2012

Journal Article

M. Korampally, Apperson, S. J., Staley, C. S., Castorena, J. A., Dr. T. Rajagopalan, Gangopadhyay, K., Mohan, R. R., Ghosh, A., Polo-Parada, L., and Gangopadhyay, S., “Transient pressure mediated intranuclear delivery of FITC-Dextran into chicken cardiomyocytes by MEMS-based nanothermite reaction actuator”, Sensors and Actuators B: Chemical, vol. 171–172, pp. 1292 - 1296, 2012.[Abstract]


We have developed a novel, operator-friendly, nanothermite reaction actuator which generates transient pressures comprised of a shock wave superimposed on a broad pressure pulse to facilitate intranuclear molecular transport. The actuator demonstrates the delivery of ∼70 kDa FITC-Dextran into chicken cardiomyocytes with cytoplasmic delivery efficiency greater than 90%, maximum intranuclear delivery efficiency of 84%, and cell survival rates exceeding 95% in minimum operating pressure conditions. Tunable nanothermite reactions enable versatile pressure generating characteristics which can extend the technology to a spectrum of biomedical molecular delivery applications. More »»

2012

Journal Article

Dr. T. Rajagopalan, Belarde, G. Maria, Bezmelnitsyn, A., Shub, M., Balas-Hummers, W., Gangopadhyay, K., and Gangopadhyay, S., “Combustion Characteristics of Silicon-Based Nanoenergetic Formulations with Reduced Electrostatic Discharge Sensitivity”, Propellants, Explosives, Pyrotechnics, vol. 37, pp. 359–372, 2012.[Abstract]


This paper details the synthesis and combustion characteristics of silicon-based nanoenergetic formulations. Silicon nanostructured powder (with a wide variety of morphologies such as nanoparticles, nanowires, and nanotubes) were produced by DC plasma arc discharge route. These nanostructures were passivated with oxygen and hydrogen post-synthesis. Their structural, morphological, and vibrational properties were investigated using X-ray diffractometry, transmission electron microscopy (TEM), nitrogen adsorption-desorption analysis, Fourier transform infrared (FTIR) spectrometry and Raman spectroscopy. The silicon nanostructured powder (fuel) was mixed with varying amounts of sodium perchlorate (NaClO4) nanoparticles (oxidizer) to form nanoenergetic mixtures. The NaClO4 nanoparticles with a size distribution in the range of 5–40 nm were prepared using surfactant in a mixed solvent system. The combustion characteristics, namely (i) the combustion wave speed and (ii) the pressure-time characteristics, were measured. The observed correlation between the basic material properties and the measured combustion characteristics is presented. These silicon-based nanoenergetic formulations exhibit reduced sensitivity to electrostatic discharge (ESD). More »»

2011

Journal Article

Dr. T. Rajagopalan, Bezmelnitsyn, A., Apperson, S., Staley, C., Redner, P., Balas, W., Nicolich, S., Kapoor, D., Gangopadhyay, K., and Gangopadhyay, S., “Combustion characteristics of novel hybrid nanoenergetic formulations”, Combustion and Flame, vol. 158, pp. 964 - 978, 2011.[Abstract]


This paper presents the combustion characteristics of various copper oxide (CuO) nanorods/aluminum (Al) nanothermite compositions and hybrid nanoenergetic mixtures formed by combining nanothermites with either ammonium nitrate (NH4NO3) or secondary explosives such as \{RDX\} and CL-20 in different weight proportions. The different types of nanorods prepared in this study are referred to as CuO-VD (dried under vacuum at 25 °C for 24 h), CuO-100 (at 100 °C for 16 h) and CuO-400 (short time (1 min) calcination at 400 °C). The physical and chemical characteristics of these different kinds of CuO nanorods were determined using a variety of analytical tools such as X-ray diffractometer, transmission electron microscope (TEM), Fourier transform infrared spectrometer (FTIR), surface area analyzer and simultaneous differential scanning calorimeter (DSC)/thermogravimetric analyzer (TGA). These measured characteristics were correlated with the combustion behavior of the nanoenergetic compositions synthesized in this work. The use of different drying and calcination parameters produced the synthesis of CuO nanorods with varying amount of hydroxyl (OH) and \{CHn\} (n = 2, 3) functional groups. The experimental observations confirm that the presence of these functional groups on the surface of CuO nanorods enabled the formation of assembled nanoenergetic composite, upon mixed with Al nanoparticles. A facile one-step synthesis of assembled composite through surface functionalization is reported and it can be extended to large-scale preparation of assembled nanoenergetic mixtures. The combustion behavior was studied by measuring both combustion wave speed and pressure–time characteristics. Pressurization rate was determined by monitoring the pressure–time characteristics during the combustion reaction initiated by a hot wire in a fully-confined geometry. Different amounts of nanothermite powder were packed in the same volume of combustion chamber by applying different packing pressures and the pressure–time characteristics were measured as a function of varying percent theoretical maximum density (% TMD). The experimental setup used in this work enabled us to study the functional behavior of initiating explosives such as \{NH4NO3\} nanoparticles, \{RDX\} and CL-20 using nanothermites under fully-confined test geometry. The dent tests performed on lead witness plates support the experimental observations obtained from pressure–time and combustion wave speed measurements of hybrid mixtures. More »»

2011

Journal Article

C. S. Staley, Morris, C. J., Dr. T. Rajagopalan, Apperson, S. J., Gangopadhyay, K., and Gangopadhyay, S., “Silicon-based bridge wire micro-chip initiators for bismuth oxide–aluminum nanothermite”, Journal of Micromechanics and Microengineering, vol. 21, p. 115015, 2011.[Abstract]


We present a micro-manufacturing process for fabricating silicon-based bridge wire micro-chip initiators with the capacity to liberate joules of chemical energy at the expense of micro joules of input electrical energy. The micro-chip initiators are assembled with an open material reservoir utilizing a novel 47 °C melting point solder alloy bonding procedure and integrated with a bismuth oxide–aluminum nanothermite energetic composite. The electro-thermal conversion efficiency of the initiators is enhanced by the use of a nanoporous silicon bed which impedes thermal coupling between the bridge wire and bulk silicon substrate while maintaining the structural integrity of the device. Electrical behaviors of the ignition elements are investigated to extract minimum input power and energy requirements of 382.4 mW and 26.51 µJ, respectively, both in the absence and presence of an injected bismuth oxide–aluminum nanothermite composition. Programmed combustion of bismuth oxide–aluminum nanothermite housed within these initiators is demonstrated with a success rate of 100% over a 30 to 80 µJ range of firing energies and ignition response times of less than 2 µs are achieved in the high input power operation regime. The micro-initiators reported here are intended for use in miniaturized actuation technologies. More »»

2010

Journal Article

A. Bezmelnitsyn, Dr. T. Rajagopalan, Barizuddin, S., Tappmeyer, D., Apperson, S., Gangopadhyay, K., Gangopadhyay, S., Redner, P., Donadio, M., Kapoor, D., and Nicolich, S., “Modified Nanoenergetic Composites with Tunable Combustion Characteristics for Propellant Applications”, Propellants, Explosives, Pyrotechnics, vol. 35, pp. 384–394, 2010.[Abstract]


This work reports on the synthesis and tunable characteristics of nanothermite compositions based on mesoporous Fe2O3 as an oxidizer and Al nanoparticles as a fuel. The reactivity (rate of increase of pressure) and the combustion wave speed were determined to evaluate the performance of these composites for various applications. A gas generating polymer, (acrylamidomethyl) cellulose acetate butyrate (AAMCAB), was loaded in the mesopores of Fe2O3 matrix following wet-impregnation technique. The samples prepared in this work were characterized by a number of analytical techniques such as Fourier transform infrared (FTIR) absorption spectroscopy, transmission and scanning electron microscopy (TEM, SEM), energy dispersive X-ray analysis, X-ray diffraction, and nitrogen adsorption–desorption isotherms. Then, mesoporous Fe2O3 powder was mixed with Al nanoparticles to prepare nanoenergetic composites. The main characteristics such as peak pressure, reactivity, combustion wave speed, and pressure sustenance were determined as a function of polymer loading. The dependence of combustion wave speed on the pressure was established following the well-known Vieille's law. The small value of 0.408 for the pressure exponent indicates the suitability of these nanothermite compositions for propellant applications. By reducing the percentage of polymer, the characteristic properties of nanoenergetic composite can be suitably tuned for other applications. More »»

2010

Journal Article

Dr. T. Rajagopalan, Bezmelnitsyn, A., Apperson, S. J., Tappmeyer, D., Redner, P., Balas, W. A., Nicolich, S., Kapoor, D., Gangopadhyay, K., and Gangopadhyay, S., “Combustion behavior of nanoenergetic material systems”, Energetic Materials: Thermophysical Properties, Predictions, and Experimental Measurements, p. 221, 2010.

2010

Journal Article

M. Korampally, Apperson, S. J., Korampally, V., Bok, S., Dr. T. Rajagopalan, Bezmelnitsyn, A., Polo-Parada, L., Gangopadhyay, K., and Gangopadhyay, S., “Shock Wave Based Cell Transfection and Fluorescent Organosilicate Nanoparticles for Targeted Drug Delivery [abstract]”, Abstracts (Missouri Regional Life Sciences Summit 2010), 2010.

2010

Journal Article

Dr. T. Rajagopalan, Lee, B. Doo, Smith, B., Sengupta, S., Polo-Parada, L., Gangopadhyay, S., and Gangopadhyay, K., “Applications of Energetic Materials and Copper Oxide Nanorods for Decontamination [abstract]”, 2010.

2010

Journal Article

Dr. T. Rajagopalan, Bezmelnitsyn, A., Apperson, S. J., Staley, C., Gangopadhyay, K., and Gangopadhyay, S., “Design and development of nanoenergetic materials with tunable combustion characteristics [abstract]”, Abstracts (Missouri Technology Expo 2010), 2010.[Abstract]


In recent years, nanoengineered thermites with tunable and tailored characteristics have attracted a great deal of attention owing to their enormous potential as excellent reactive materials, green primers, and structural energetic materials etc. Nanothermites are typically composed of metal oxide (oxidizer) and metal (fuel) nanoparticles. A variety of nanostructured oxidizers such as Fe2O3, CuO, Bi2O3 and MoO3 etc have been prepared in our laboratory. Various morphologies of oxidizers include nanorods, nanoparticles, and mesoporous structures exhibiting high surface area. Surfactant templating method has been developed for the synthesis of ammonium nitrate (NH4NO3) nanoparticles with a size distribution of 10–100nm. The physical and the chemical properties such as morphology, surface area, purity, composition, crystal structure of these metal oxide nanostructures have been determined by a host of characterization tools. Among the nanothermites, CuO nanorods/Al nanoparticles exhibit the best combustion performance measured in terms of combustion wave speed of 2600 ± 100 m/s and reactivity of 11± 1 MPa/msec. Nanothermites based on CuO nanorods/Al nanoparticles were then modified by mixing with polymers such as nitrocellulose (NC) and/or explosives such as (NH4NO3) nanoparticles, RDX (micron and nano size) and CL20 and the reaction rates of these nanocomposites were determined. Among the polymers, nitrocellulose coating of nanothermites is very interesting. Both the NC and the Teflon coated CuO/Al based nanothermite systems exhibit the ability to generate shock waves during their fast combustion. The NC coating has shown tremendous potential to reduce the high sensitivity of nanothermites to electrostatic discharge (ESD), friction and impact. Experimentally measured combustion characteristics are found to correlate very well with the physical and chemical characteristics of metal oxide nanostructures. The developed technology in our lab demonstrates the potential to tune and tailor the combustion characteristics of nanothermites to the desired level by proper choice and combination of fuel and oxidizer materials, their dimensions, and the process of self-assembly with reduced sensitivity. Potential Areas of Applications: * Microthrusters; * Propellants; * Propellant Initiators; * Suitable Replacements for Lead and Sulfur based Primers; * Shockwave drug delivery systems; More »»

2010

Journal Article

S. Gangopadhyay, Apperson, S. J., Gangopadhyay, K., Dr. T. Rajagopalan, and Bezmelnitsyn, A., “Multi-mode nanothermite thrusters with tunable impulse”, Abstracts (Missouri Technology Expo 2010), 2010.[Abstract]


Microthrusters have applications in projectile guidance systems, and micro-nano-satellite control. Thrusters are an integral part of a guidance system that includes orientation and trajectory sensors and target recognition components. The thrusters provide the actuation force to move the projectile. Nanothermite composites containing metallic fuel and inorganic oxidizer have unique combustion properties that make them potentially useful for microthruster applications. The nanothermite formulation can be tuned to achieve specific impulse characteristics. Depending on the application of the thruster, nanothermite formulation and motor design can be chosen to meet the application requirements. If properly configured, the reaction can have a velocity of <3mm/s or >1000m/s. The efficiency of the thrusters is not drastically affected by the duration of reaction More »»

2009

Journal Article

S. J. Apperson, Bezmelnitsyn, A. V., Dr. T. Rajagopalan, Gangopadhyay, K., Gangopadhyay, S., Balas, W. A., Anderson, P. E., and Nicolich, S. M., “Characterization of nanothermite material for solid-fuel microthruster applications”, Journal of Propulsion and Power, vol. 25, pp. 1086–1091, 2009.

2009

Journal Article

V. Korampally, Yun, M., Dr. T. Rajagopalan, Dasgupta, P. K., Gangopadhyay, K., and Gangopadhyay, S., “Entropy driven spontaneous formation of highly porous films from polymer–nanoparticle composites”, Nanotechnology, vol. 20, p. 425602, 2009.[Abstract]


Nanoporous materials have become indispensable in many fields ranging from photonics, catalysis and semiconductor processing to biosensor infrastructure. Rapid and energy efficient process fabrication of these materials is, however, nontrivial. In this communication, we describe a simple method for the rapid fabrication of these materials from colloidal dispersions of Polymethyl Silsesquioxane nanoparticles. Nanoparticle–polymer composites above the decomposition temperature of the polymer are examined and the entropic gain experienced by the nanoparticles in this rubric is harnessed to fabricate novel highly porous films composed of nanoparticles. Optically smooth, hydrophobic films with low refractive indices (as low as 1.048) and high surface areas (as high as 1325 m 2 g −1 ) have been achieved with this approach. In this communication we address the behavior of such systems that are both temperature and substrate surface energy dependent. The method is applicable, in principle, to a variety of nanoparticle–polymer systems to fabricate custom nanoporous materials. More »»

2008

Journal Article

R. Shende, Subramanian, S., Hasan, S., Apperson, S., Dr. T. Rajagopalan, Gangopadhyay, K., Gangopadhyay, S., Redner, P., Kapoor, D., Nicolich, S., and , “Nanoenergetic Composites of CuO Nanorods, Nanowires, and Al-Nanoparticles”, Propellants, Explosives, Pyrotechnics, vol. 33, pp. 122–130, 2008.[Abstract]


This paper reports on the synthesis of the nanoenergetic composites containing CuO nanorods and nanowires, and Al-nanoparticles. Nanorods and nanowires were synthesized using poly(ethylene glycol) templating method and combined with Al-nanoparticles using ultrasonic mixing and self-assembly methods. Poly(4-vinylpyridine) was used for the self-assembly of Al-nanoparticles around the nanorods. At the optimized values of equivalence ratio, sonication time, and Al-particle size, the combustion wave speed of 1650 m s−1 was obtained for the nanorods-based energetics. For the composite of nanowires and Al-nanoparticles the speed was increased to 1900 m s−1. The maximum combustion wave speed of 2400 m s−1 was achieved for the self-assembled composite, which is the highest known so far among the nanoenergetic materials. It is possible that in the self-assembled composites, the interfacial contact between the oxidizer and fuel is higher and resistance to overall diffusional process is lower, thus enhancing the performance. More »»

2008

Journal Article

M. Jin, Chen, P., Boolchand, P., Dr. T. Rajagopalan, Chopra, K. L., Starbova, K., and Starbov, N., “Origin of giant photocontraction in obliquely deposited amorphous $\textGe}_x\textSe}_1\ensuremath-x}$ thin films and the intermediate phase”, Phys. Rev. B, vol. 78, p. 214201, 2008.[Abstract]


Obliquely deposited amorphous GexSe100−x thin films at several compositions in the 15%25%, the stressed rigid phase, and at x<20%, the flexible phase. IR reflectance confirmed absence of photo-oxidation of films under these conditions. The IP represents a range of compositions across which stress-free networks form. Columns observed in SEM reveal a high aspect ratio, with typical lengths in the 1–2−μm range and a lateral width in the 50-nm range. We observe a blueshift (up to 0.38 eV) in the optical band gap of oblique films (α=80°) in relation to normally deposited (α=0°) ones, a result we identify with carrier confinement in nanofilaments (<10 nm) that form part of columns observed in SEM. In the IP, the large PC results due to the intrinsically stress-free character of filaments, which undergo facile photomelting resulting in film densification. Ge-rich films (25% More »»

2008

Journal Article

Dr. T. Rajagopalan, Lahlouh, B., Chari, I., Othman, M. T., Biswas, N., Toma, D., and Gangopadhyay, S., “Hexamethyldisilazane vapor treatment of plasma damaged nanoporous methylsilsesquioxane films: Structural and electrical characteristics”, Thin Solid Films, vol. 516, pp. 3399 - 3404, 2008.[Abstract]


Repair of plasma damaged nanoporous organosilicate films carried out by hexamethyldisilazane (HMDS) vapor treatment was investigated as a function of temperature. Capacitance–voltage measurements were carried out before and after \{HMDS\} vapor treatment. The dielectric constant measurements confirm that the \{HMDS\} vapor treatment facilitates only partial curing of the plasma damaged films, as also observed from the Fourier transform infrared absorption measurements. Bias temperature stress measurements for samples with copper (Cu) metal electrodes reveal a shift of − 35 V in the capacitance–voltage curve for samples cured at 55 °C whereas negligible shift is observed for samples treated above 80 °C. This behavior suggests the existence of a dense solid layer on the top surface of the samples treated above 80 °C, hindering the diffusion or movement of Cu ions into the dielectric. Direct imaging of the \{HMDS\} vapor treated plasma damaged films using scanning electron microscope clearly shows the existence of two distinct layers, with the top layer (at the film–air interface) being denser than the bottom layer at the film–substrate interface. More »»

2008

Journal Article

M. Jin, Chen, P., Boolchand, P., Dr. T. Rajagopalan, Chopra, K. L., Starbova, K., and Starbov, N., “Inhomogeneous, disordered, and partially ordered systems-Origin of giant photocontraction in obliquely deposited amorphous GexSe1-x thin films and the intermediate phase”, Physical Review B Condensed Matter And Materials Physics, vol. 78, p. 214201, 2008.

2007

Journal Article

N. Geblinger, Dr. T. Rajagopalan, and Regev, O., “Preparation and characterization of a double filler polymeric nanocomposite”, Composites Science and Technology, vol. 67, pp. 895 - 899, 2007.[Abstract]


Single walled carbon nanotubes (SWNTs) with an anisotropic morphology (rod) are currently being employed as fillers in polymer matrix to produce novel nanocomposites with enhanced properties and performance in a wide variety of applications. We investigate the effect of the addition of second isotropic (spherical) filler, antimony tin oxide (ATO) particles to the anisotropic SWNT-polymer composites. Cryogenic transmission electron microscope (cryo-TEM) and scanning electron microscope (SEM) were employed to image the aqueous dispersions of the SWNTs–ATO–Latex solution and composite thin films respectively. The \{SEM\} imaging of these films shows that \{SWNTs\} (rods) tend to aggregate in the presence of \{ATO\} clusters, indicating depletion interactions between the rods and the spheres. The difference in the value of electrical conductivity of the films measured along the radial and the tangential directions to the spinning lines is probably due to the preferred orientation of the \{SWNTs\} in the matrix during the spin coating process. More »»

2007

Journal Article

Dr. T. Rajagopalan, Levi-Kalisman, Y., and Regev, O., “Synergetic effect of ultrasound and sodium dodecyl sulphate in the formation of CdS nanostructures in aqueous solution”, Ultrasonics Sonochemistry, vol. 14, pp. 398 - 404, 2007.[Abstract]


High aspect ratio (>1000) CdS nanostructures were prepared via ultrasound treatment of parent nanowires (NWs) dispersed in sodium dodecyl sulfate (SDS) aqueous solution. The CdS parent \{NWs\} were prepared using ordered mesoporous silica, SBA-15, as a template. The elongated nanostructures (ENS), namely, NWs, nanoribbons and nanotubes, form stable dispersions in aqueous solutions. Electron microscopy and X-ray diffraction techniques were used to characterize both the parent \{NWs\} and the ENS. While the structure of the parent \{NWs\} is crystalline cubic, the \{ENS\} are amorphous. We show that the amorphous \{ENS\} bud from the parent bundled NWs. Ultrasound power and duration, presence of commensurate surfactant and calcination temperature of the templating SBA-15 are critical parameters in the formation of \{ENS\} in aqueous solution. More »»

2007

Journal Article

D. Tappmeyer, Dr. T. Rajagopalan, Shende, R., Gangopadhyay, K., Apperson, S. J., and Gangopadhyay, S., “Nano-synthesis of Energetic Materials”, 2007.[Abstract]


Energetic materials are defined as substances in which fuel and oxidizer react chemically to release energy. The amount and rate of energy released by this reaction can be improved by increasing the amount of interfacial contact between fuel and oxidizer. In conventional energetic materials macroscopic particles of fuel and oxidizer are mixed randomly. In this arrangement energy is lost due decreased contact between fuel and oxidizer as a result of the large particle size and random distribution. To reduce the amount of energy lost much smaller nano-particles can be used. The smaller particles allow for increased interfacial contact between fuel and oxidizer, resulting in improved performance. Even with smaller particles some energy is still lost due to the random arrangement. In order to further improve performance it is necessary to order the arrangement of fuel and oxidizer. Utilizing a method known as surfactant templating ordered structures such as nanorods, nanowires, and nanowells (similar to a honeycomb) can be created from oxide materials such as Copper Oxide, and Iron Oxide. When Aluminum Nano-particle fuel is mixed with these ordered oxide materials the resulting material has greatly increased interfacial contact between fuel and oxidizer. When reacted, these materials have minimal energy loss and greatly improved energetic performance. The increased performance of this type of material has created the possibility of many new applications for energetic materials. The potential uses for this material range from on chip power generation, to shockwave generation for medical imaging. More »»

2006

Journal Article

S. Attal, Dr. T. Rajagopalan, and Regev, O., “Determination of the concentration of single-walled carbon nanotubes in aqueous dispersions using UV-visible absorption spectroscopy”, Analytical Chemistry, vol. 78, pp. 8098-8104, 2006.[Abstract]


Stable, homogeneous, aqueous dispersions of single-walled carbon nanotubes (SWNTs) are prepared by nonspecific physical adsorption of surfactants enhanced by sonication. Upon centrifugation, supernatant and precipitate phases are obtained. The initial weights of the SWNTs and the surfactant are divided between these two phases, and the respective SWNT concentration in each phase is unknown. The focus of this work is on the determination of the true concentration of raw, exfoliated HiPCO SWNTs in the supernatant phase. A UV−visible absorption-based approach is suggested for a direct measurement of the SWNT and the surfactant concentration in the supernatant. UV−visible absorbance spectra of SWNTs−surfactant dispersions and surfactants alone reveal that the intensity of a certain peak, attributed to the π-plasmon resonance absorption, is unaffected by the presence of most surfactants. A calibration plot is then made by monitoring the intensity of the peak as a function of the true concentration of the exfoliated SWNTs. Thus, we are able to determine the unknown concentration of surfactant-dispersed HiPCO SWNTs in the supernatant solution, simply by measuring its optical absorbance. Moreover, we can now calculate the surfactant efficiency in dispersing SWNTs. Cryogenic-transmission electron microscopy and thermogravimetric analysis techniques are used for the characterization of these dispersions and to complement the UV−visible measurements. More »»

2006

Journal Article

V. Weiss, Dr. T. Rajagopalan, and Regev, O., “Preparation and characterization of a carbon nanotube-lyotropic liquid crystal composite”, Langmuir, vol. 22, pp. 854–856, 2006.[Abstract]


We present a detailed study on the integration of individual single-walled carbon nanotubes (SWNTs) within a lyotropic hexagonal liquid crystal (LC) for the first time. Two systems are studied in this work; in the first, the same surfactant is used for both the dispersion of the SWNTs and the formation of the LC. In the second system, we use different surfactants for the dispersion of SWNTs and LC formation. Light microscopy imaging combined with small-angle X-ray scattering (SAXS) indicates that the nanotubes (NTs) are well dispersed and aligned along the LC director. The macroscopic property, namely, the viscosity, is strongly enhanced by the presence of the NTs. More »»

2006

Journal Article

Dr. T. Rajagopalan, Lahlouh, B., Lubguban, J. A., Biswas, N., Gangopadhyay, S., Sun, J., Huang, D. H., Simon, S. L., Toma, D., and Butler, R., “Investigation on hexamethyldisilazane vapor treatment of plasma-damaged nanoporous organosilicate films”, Applied Surface Science, vol. 252, pp. 6323 - 6331, 2006.[Abstract]


Hexamethyldisilazane (HMDS) vapor treatment of plasma-damaged nanoporous organosilicate thin films has been studied as a function of treatment temperature in this work. Although, the \{HMDS\} vapor treatment facilitated incorporation of methyl (CH3) groups subsequent to the removal of free hydroxyl (OH) groups in the damaged films at treatment temperature as low as 55 °C, the bonded \{OH\} groups were not removed. More significantly, detailed analysis of the results reveals that \{HMDS\} vapor modified only the surface of the plasma-damaged samples and not the entire film as expected. This is attributed to the formation of a thin solid layer on the surface, which effectively prevents penetration of \{HMDS\} vapors into the bulk. The Fourier transform-infrared (FT-IR) absorption and dielectric constant measurements confirm that the vapor treatment assists only partial curing of the plasma-damaged films. Alternative processes of curing the films with \{HMDS\} dissolved in supercritical carbon dioxide (SCCO2) as a medium of reaction in static and pulsed modes were also attempted and the results are presented in this paper. More »»

2006

Journal Article

B. Lahlouh, Dr. T. Rajagopalan, Biswas, N., Sun, J., Huang, D., Simon, S. L., Lubguban, J. A., and Gangopadhyay, S., “Post treatments of plasma-enhanced chemical vapor deposited hydrogenated amorphous silicon carbide for low dielectric constant films”, Thin Solid Films, vol. 497, pp. 109 - 114, 2006.[Abstract]


Post treatments by annealing or supercritical carbon dioxide (SCCO2) exposure of plasma-enhanced chemical vapor deposited hydrogenated amorphous silicon carbide (a-SiC:H) films are reported to reduce the dielectric constant up to 2.1. The a-SiC:H films were prepared using diethylsilane diluted in methane. The deposition precursors and conditions were chosen to fabricate a thermally unstable a-SiC:H film with a high concentration of \{CHn\} (n = 1, 2, 3) functional groups. The Fourier transform infra-red spectroscopy measurements of as-deposited films show a-SiC:H networks and presence of a-C:H moieties throughout the film. The films were then annealed in vacuum up to 450 °C to remove thermally unstable \{CHn\} as well as other species. After annealing, the dielectric constant of the films decreased from 4.2 up to 2.1 due to the decrease in film density. The reduction suggests the presence of molecular voids/pores. Annealing produced a stable film with thickness decreasing by a maximum of 6% only. \{SCCO2\} treatment was also explored and found to be more effective in the extraction of \{CHn\} and other species at 200 °C. More »»

2005

Journal Article

Dr. T. Rajagopalan and Regev, O., “Hierarchically ordered cadmium sulfide nanowires dispersed in aqueous solution”, Chemistry of Materials, vol. 17, pp. 3281-3287, 2005.[Abstract]


The paper reports on the preparation, characterization, and dispersion of cadmium sulfide (CdS) nanowires using ordered mesoporous silica, SBA-15, as a template. A homogeneous and stable dispersion of hierarchically ordered CdS nanowires in water solubilized with sodium dodecyl sulfate (SDS) has been obtained. Direct imaging of the nanoconnectors (templated by the micropores in SBA-15) between the bundled nanowires has been accomplished by high-resolution transmission electron microscope (HRTEM). Cryogenic-TEM (cryo-TEM) measurements carried out on the dispersed samples complemented by small-angle X-ray (SAX) diffraction and HRTEM examination of the dry CdS powder clarify the role played by the micropores in the formation of a hierarchically ordered array of nanowires in the meso- and atomic scale. The amount of nanoconnectors is controlled by varying the calcination temperature of SBA-15, which tunes the formation of either bundled or individual CdS nanowires. The effect of such organizations is discussed in view of optical absorption and fluorescence measurements. More »»

2005

Journal Article

Dr. T. Rajagopalan, Levi-Kalisman, Y., and Regev, O., “Templating nanostructures by mesoporous materials with an emphasis on room temperature and cryogenic \TEM\ studies”, Current Opinion in Colloid & Interface Science, vol. 10, pp. 280 - 286, 2005.[Abstract]


Rapid strides realized in the field of ordered mesoporous silica (OMS) with a well-defined pore shape and nanometric sizes, provide new gateways for the preparation of nanostructured materials having controlled shape and size with a very narrow distribution. The focus of the current review is on the synthesis of nanostructures templated by \{OMS\} either in bulk or in thin film form. The importance of electron microscopy as an indispensable technique in the structural characterization of \{OMS\} templated nanostructures, including cryo-TEM, electron tomography and HR-SEM, is highlighted in this review. More »»

2004

Journal Article

S. Gangopadhyay, Lubguban, J. A., Lahlouh, B., Sivaraman, G., Biswas, K., Dr. T. Rajagopalan, Biswas, N., Kim, H. - C., Volksen, W., and Miller, R. D., “Supercritical CO2 Treatments for Semiconductor Applications”, MRS Proceedings, vol. 812, 2004.[Abstract]


Supercritical fluids (SF) have been used in a wide variety of applications: in industrial processes, analytical, waste detoxification, etc. Recently, its usefulness extends to the semiconductor industry. Researches have shown that supercritical CO2 (SCCO2) can be used to remove photoresists and significantly reduce the amount of waste from solvents in comparison to conventional stripping techniques. SF will also find its usefulness in cleaning high aspect ratio vias and deep trenches as semiconductor features shrink to submicron levels. We will report here the use of supercritical CO2 treatments in extraction of porogens from a nanohybrid film fabricated via templated-porogen approach. Its use as a medium to repair the damage in porous films from plasma ashing will also be presented. The ability to tune the solvation and diffusion power of SCCO2 and to swell the film matrix make it a good medium for silylation to restore hydrophobicity and functionalize the film. More »»

2003

Journal Article

Dr. T. Rajagopalan, Wang, X., Lahlouh, B., Ramkumar, C., Dutta, P., and Gangopadhyay, S., “Low temperature deposition of nanocrystalline silicon carbide films by plasma enhanced chemical vapor deposition and their structural and optical characterization”, Journal of applied physics, vol. 94, pp. 5252–5260, 2003.[Abstract]


Nanocrystalline silicon carbide ~SiC! thin films were deposited by plasma enhanced chemical vapor deposition technique at different deposition temperatures (Td) ranging from 80 to 575 °C and different gas flow ratios ~GFRs!. While diethylsilane was used as the source for the preparation of SiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. The effects of Td , GFR and dilution gases on the structural and optical properties of these films were investigated using high resolution transmission electron microscope ~HRTEM!, micro-Raman, Fourier transform infrared ~FTIR! and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in the amorphous matrix of the films deposited at a temperature of 300 °C. The degree of crystallization increases with increasing Td and the crystalline fraction (f c) is 65%62.2% at 575 °C. The f c is the highest for the films deposited with hydrogen dilution in comparison with the films deposited with argon and helium at the same Td . The Raman spectra also confirm the occurrence of crystallization in these films. The HRTEM measurements confirm the existence of nanocrystallites in the amorphous matrix with a wide variation in the crystallite size from 2 to 10 nm. These results are in reasonable agreement with the FTIR and the micro-Raman analysis. The variation of refractive index ~n! with Td is found to be quite consistent with the structural evolution of these films. The films deposited with high dilution of H2 have large band gap (Eg) and these values vary from 2.6 to 4.47 eV as Td is increased from 80 to 575 °C. The size dependent shift in the Eg value has also been investigated using effective mass approximation. Thus, the observed large band gap is attributed to the presence of nanocrystallites in the films. More »»

2003

Journal Article

Dr. T. Rajagopalan, Lahlouh, B., Lubguban, J. A., Biswas, N., Gangopadhyay, S., Sun, J., Huang, D. H., Simon, S. L., Mallikarjunan, A., Kim, H. - C., and , “Supercritical carbon dioxide extraction of porogens for the preparation of ultralow-dielectric-constant films”, Applied physics letters, vol. 82, pp. 4328–4330, 2003.[Abstract]


Supercritical carbon dioxide extraction of poly(propylene glycol) porogen from poly(methylsilsesquioxane) (PMSSQ) cured to temperatures adequate to initiate matrix condensation, but still below the decomposition temperature of the porogen, is demonstrated to produce nanoporous, ultralow-dielectric-constant thin films. Both closed and open cell porous structures were prepared simply by varying the porogen load in the organic/inorganic hybrid films. 25 and 55 wt % porogen loads were investigated in the present work. Structural characterization of the samples conducted using transmission electron microscope, small angle x-ray scattering, and Fourier transform infrared spectroscopy, confirms the extraction of the porogen from the PMSSQ matrix at relatively low temperatures (⩽200 °C). The standard thermal decomposition process is performed at much higher temperatures (typically in the range of 400 °C–450 °C). The values of dielectric constants and refractive indices measured are in good agreement with the structural properties of these samples. More »»

2003

Journal Article

Dr. T. Rajagopalan, Wang, X., Lahlouh, B., Ramkumar, C., Dutta, P. S., and Gangopadhyay, S., “Low temperature deposition of nanocrystalline SiC films by PECVD and their structural and optical characterization”, J. Applied Physics, vol. 94, pp. 5252–5260, 2003.

2003

Journal Article

B. Lahlouh, Dr. T. Rajagopalan, Lubguban, J. A., Biswas, N., Gangopadhyaya, S., Sun, J., Huang, D., Simon, S. L., Kim, H. C., Volksen, W., and Miller, R. D., “Creating Nanoporosity by Selective Extraction of Porogens Using Supercritical Carbon Dioxide/Cosolvent Processes”, MRS Proceedings, vol. 766, 2003.[Abstract]


AbstractThis work presents a novel approach using supercritical carbon dioxide (SCCO2) to selectively extract poly(propylene glycol) (PPG) porogen from a poly(methylsilsesquioxane) (PMSSQ) matrix, which results in the formation of nanopores. Nanoporous thin films were prepared by spin-casting a solution containing appropriate quantities of PPG porogen and PMSSQ dissolved in PM acetate. The as-spun films were thermally cured at temperatures well below the thermal degradation temperature of the organic polymer to form a cross-linked organic/inorganic polymer hybrid. By selectively removing the CO2 soluble PPG porogen, open and closed pore structures are possible depending upon the porogen load and its distribution in the matrix before extraction. In the present work, two different loadings of PPG namely 25 wt.% and 55 wt.% were used. Both static SCCO2 and pulsed SCCO2/cosolvent treatments were used for PPG extraction. The initial results indicate that the pulsed SCCO2/cosolovent treatm" # "ent was more efficient. Fourier transform infrared spectroscopy (FTIR) and refractive index measurements further corroborate the successful extraction of the porogens at relatively low temperatures (2000C). For the pure PMSSQ film, the k value is 3.1, whereas it is 1.46 and 2.27 for the open and closed pore compositions respectively after the static SCCO2 extraction and 430°C subsequent annealing. The reduction in the k-value is attributed to the formation of nanopores. The pore structure was verified from transmission electron microscopy (TEM), and from small-angle x-ray scattering (SAXS) measurements, the pore size was determined to be 1-3 nm for these films. More »»

2002

Journal Article

J. Lubguban, Dr. T. Rajagopalan, Mehta, N., Lahlouh, B., Simon, S. L., and Gangopadhyay, S., “Low-k organosilicate films prepared by tetravinyltetramethylcyclotetrasiloxane”, Journal of Applied Physics, vol. 92, pp. 1033-1038, 2002.[Abstract]


Low-kfilms with k of 2.5–2.9 were deposited under different conditions of pressures and temperatures using a plasma-enhanced chemical vapor deposition(PECVD) system. These films were prepared using a new liquid precursor, tetravinyltetramethylcyclotetrasiloxane (TVTMCTS) and H2H2 carrier gas. The rf power was kept as low as possible to maintain the original ring structure in the films. The as-deposited films were annealed and the dielectric and optical properties were investigated. Identification of the absorption bands in the IR spectra for as-deposited films reveals a broadband around 950–1200 cm−1cm−1 arising from the Si–O stretching mode of the ring (1065 cm−1)cm−1) and chain structure (1000 cm−1),cm−1), respectively; a band at 750–900 cm−1cm−1 due to Si–O bending (790 cm−1);cm−1); Si–CH3Si–CH3 rocking mode (760 cm−1);cm−1); a sharp band centered at 1260 cm−1cm−1 due to a Si–CH3Si–CH3 bending mode; and a broadband at 2800–3000 cm−1cm−1 due to the CH group. A comparison of the IR spectra of the PECVDfilm and TVTMCTS liquid reveals that vinyl vibrations (Si–CH=CH2)(Si–CH=CH2) at 960, 1410, and 3030–3095 cm−1cm−1 for CH2CH2 and at 1598 cm−1cm−1 for C=C present in the liquid were not detected in the CVDfilms. Hence C=C bonds were broken in the plasma polymerization process. As the pressure and the depositiontemperature(TD)(TD) increased, the intensity of the Si–O vibration arising from the ring structure increased and decreased, respectively. Thus by tuning the pressure and TDTD we can control the structure of the film. There is a good correlation found between the Si–CH3Si–CH3 and Si–O ring intensities and k values; the increasing Si–CH3Si–CH3 and Si–O ring is accompanied by decreasing k. The films were thermally stable up to 400 °C400 °Cannealingtemperature. More »»

2000

Journal Article

Dr. T. Rajagopalan and Reddy, G. B., “Thermal and optical properties of Ge5Bi18Se77 films”, Journal of Materials Science: Materials in Electronics, vol. 11, pp. 397–400, 2000.[Abstract]


Amorphous films of Ge5Bi18Se77 deposited by vacuum evaporation have been studied for their thermal and optical properties. Differential scanning calorimetry (DSC) has been used to perform the thermal analysis to estimate the activation energy for crystallization (Ec) and the order of crystallization (m) of this material. The high value of (Ec), 1.672 eV, indicates good stability of the amorphous phase. The optical constants of the as-deposited, amorphous and the thermally annealed crystalline films indicate semiconducting behavior and the band gap (Eg) determined from Tauc's plot are 0.92 eV and 0.8 eV for the amorphous and crystalline films, respectively. The value of the absorption coefficient ($\alpha$) is of the order of 104cm-1 in the optical range for both amorphous and crystalline films. The studies on optical and thermal properties confirm the suitability of these firms in phase change optical recording. More »»

2000

Journal Article

Dr. T. Rajagopalan and Reddy, G. B., “Formation of highly oriented GeBiSe films from the as-deposited amorphous state by annealing”, Thin Solid Films, vol. 377–378, pp. 501 - 506, 2000.[Abstract]


As-deposited amorphous GeBiSe films were crystallized by thermal and laser annealing. Their structural properties were studied using a glancing angle X-ray diffractometer (GAXRD) and a transmission electron microscope (TEM). Films were crystallized into either a polycrystalline or a highly oriented state, depending on the choice of parameters, such as annealing temperature, rate and duration, and substrate nature and composition. All phases have been identified. The effect of annealing conditions on the relative proportion of these phases has been investigated. A wide range of surface topographical features, such as pyramidal needle shapes of 3 μm length and spherical crystallites with average sizes of 0.35–2 μm, were observed on annealing. The laser scan parameters have been optimized to only obtain crystallization. The film composition and annealing parameters have been optimized in order to obtain strongly oriented crystalline films with a smooth surface topography. More »»

1999

Journal Article

Dr. T. Rajagopalan and Reddy, G. B., “Effect of annealing rate on the crystallization process in Ge5Bi18Se77 films”, Thin Solid Films, vol. 353, pp. 254 - 258, 1999.[Abstract]


Amorphous Ge5Bi18Se77 thin films deposited by thermal evaporation were crystallized by thermal annealing at their crystallization temperature (Tc). The composition, determined using EDAX, does not indicate any significant variation in both as-deposited films and films annealed with different annealing rates from that of bulk alloy. The effect of annealing rate on the nature and the degree of crystallization has been investigated by studying the structure using TEM/XRD and the surface morphology using SEM. It is found that the annealed films crystallized into a face centred cubic (FCC) phase with a lattice constant of 6.2084±0.0015 Å. Further, it is also seen that depending on the annealing rate, the as-deposited films crystallized into either single crystal films or polycrystalline films. A detailed analysis of the structural properties has been presented. More »»

1998

Journal Article

Dr. T. Rajagopalan and Reddy, G. B., “Study of surface topography and optical properties of Ge15Bi38Se47 films”, Journal of Materials Science: Materials in Electronics, vol. 9, pp. 133–137, 1998.[Abstract]


Adherent and smooth amorphous GeBiSe films deposited by vacuum evaporation at substrate temperatures less than 30 °C have been studied for their structural and optical properties. The films were crystallized by thermal annealing and they were found to be polycrystalline in nature. A correlation between X-ray diffraction (XRD) data and surface topography is reported. Optical constants calculated from reflectance and transmittance data indicate semiconducting behaviour. The optical band gap of the as-deposited film is 1.0 eV. The measured optical contrast at 0.8 $μ$m is 44{%}. No significant changes in the optical parameters have been observed after exposing the samples to laboratory ambient for a period of six months. More »»

Publication Type: Conference Paper

Year of Publication Publication Type Title

2017

Conference Paper

Dr. T. Rajagopalan and Dr. Shanmugha Sundaram G. A., “Electromagnetic fields for propagation and confinement of high current heavy ion beam towards conformal thin film deposition”, in 2016 IEEE Asia-Pacific Conference on Applied Electromagnetics, APACE 2016, 2017, pp. 68-72.[Abstract]


Uniform thin layers of heavy elements such as niobium (Nb) have been found to possess superior superconductivity characteristics in applications like radio frequency cavity resonators. The experimental process to realize conformal coating with reproducible characteristics especially on non-planar, cavity resonators rests on the generation of high-current beam of Nb ions. Here, the fundamental principles that govern the motion of such ions in an electromagnetic (e-m) field are investigated. An electric quadrupole is designed via modelling so as to generate desired e-m fields that support parallel propagation as well as confinement of the Nb ions to a desired beam size and shape in ultrahigh vacuum (UHV) conditions. The simulation study presented here considers the case of Nb ions whose currents are of the order of 5 A, that traverse a length of 130 cm and have a cross-section radius of 3.75 cm. The trajectories for Nb ions are simulated, and the effect of external fields on the trajectory of ions is evaluated using appropriate performance metrics. © 2016 IEEE.

More »»

2008

Conference Paper

D. Tappmeyer, Gangopadhyay, S., Gangopadhyay, K., Dr. T. Rajagopalan, Bezmelnitsyn, A., Apperson, S., and Newport, N., “Electric Arc Production of Nanoparticles for Energetic Materials”, in The 2008 Annual Meeting, 2008.

2008

Conference Paper

P. E. Anderson, Balas, W., Dr. T. Rajagopalan, Bezmelnitsyn, A. V., Gangopadhyay, K., and Gangopadhyay, S., “Sensitivity and Performance of Solution-phase synthesized Nanothermite Materials”, in INTERNATIONAL ANNUAL CONFERENCE-FRAUNHOFER INSTITUT FUR CHEMISCHE TECHNOLOGIE, 2008.

2007

Conference Paper

Dr. T. Rajagopalan, Apperson, S., Bezmelnitsyn, A., Gangopadhyay, K., Gangopadhyay, S., Redner, P., Balas, W., Kapoor, D., and Nicolich, S., “Reduced Electrostatic Discharge Sensitivity Of Nanothermites”, in The 2007 Annual Meeting, 2007.[Abstract]


Nanoenergetic materials with very high combustion speeds are ideal for use as green primers, kinetic rods, and reactive materials. However, their high sensitivity to ESD remains a major challenge for practical applications. These static sensitive materials may cause accidental ignition posing a major safety hazard. It is known that Al nanoparticles are typically used as the fuel component along with nano-sized metal oxides as oxidizers to prepare nanothermites. These Al nanoparticles are highly sensitive to the ESD, thereby making nanothermites vulnerable to ignition at extremely very low ESD energy. We explore the possibility of reducing the ESD sensitivity of Al nanoparticles through coating with fluoropolymers such as Teflon. Teflon being an energetic fluoropolymer is expected to sustain the reactivity of nanothermite while helping to reduce the ESD sensitivity. Well dispersed Al nanoparticles in Teflon were obtained by coating the surface of Al nanoparticles first with perfluorooctal mono-functional trimethoxy silane and then with teflon AF solution. Our measurements show that uncoated Al nanoparticles have a very low ESD energy of 0.98mJ. On the other hand, Al nanoparticles coated with 1 and 2 % of teflon have ESD energy 2.6 mJ and 4.7 mJ respectively. With increasing teflon weight to 4% and 10 %, the ESD energy increases to 25 mJ and 60mJ respectively. We have also studied the combustion properties and reactivity of the Teflon coated nanoparticles with copper oxide nanorods. Although there is a reduction in the burn rate due to Teflon coating, the peak pressure and reactivity of the material increases with the increase in percent of Teflon coating. In conclusion, our results clearly demonstrate that coating with fluoropolymers is very effective in reducing the ESD sensitivity of nanothermite materials. More »»

2007

Conference Paper

S. Apperson, Bezmelnitsyn, A., Dr. T. Rajagopalan, Tappmeyer, D., Chen, Z., Gangopadhyay, K., and Gangopadhyay, S., “Characterization Of Shock Waves Produced By Nanothermites”, in The 2007 Annual Meeting, 2007.

2007

Conference Paper

A. Bezmelnitsyn, Dr. T. Rajagopalan, Apperson, S., Shende, R., Gangopadhyay, K., Gangopadhyay, S., Redner, P., Balas, W., Kapoor, D., and Nicolich, S., “Reactivity of Conventional and Modified Nanothermites”, in The 2007 Annual Meeting, 2007.[Abstract]


Nanoengineered composites of metal oxide (oxidizer) and metal(fuel)have shown to exhibit enhanced combustion properties. More specifically, when the sizes of oxidizer and fuel particles are in nanoscale, the heat and the mass transport length scales are drastically reduced, leading to enhanced combustion speeds and reaction rates. Thus, it is quite possible to achieve tunable reaction rates by proper choice and combination of fuel, oxidizer and other chemicals, their dimensions in nanoscale and the mixing ratio. The present work is devoted to the study of reaction rates of conventional and modified nanothermites. We have used a variety of metal oxides, namely, Fe2O3, CuO and MoO3 and Al as the fuel. The conventional nanothermites were also modified by mixing with ammonium nitrate (AN) nanoparticles. The reactivity was determined by monitoring the pressure as a function of time generated during the energetic reaction. The rate of increase in the pressure generated during combustion process is a measure of the reactivity of the material system. Reactivity rate tests were performed in a closed volume using a typical mass of 20 mg in a milli-well with a packing density of 0.33g/cm3. Among the conventional nanothermites studied in this work, CuO-Al system possesses the highest reactivity. The rate of pressure increase is about 3.23MPa/�s and the peak pressure recorded is 40MPa. In comparison, it is 0.01MPa/s for Fe2O3/Al nanocomposite. The reactivity of self-assembled CuO nanorod (NR) - Al nanoparticle composite (3.81 MPa/�s) is higher than that of the one prepared by random mixing of CuO NR and Al nanoparticle (3.23MPa/�s). The CuO NR � Al based conventional nanothermites were modified by mixing with low-grade explosives, such as ammonium nitrate (AN) nanoparticles. These nanoparticles were prepared by employing microemulsion route. The reactivity increases to about 250 MPa/�s and the peak pressure to 600 MPa for the modified thermite composition with 60 % AN nanoparticles. Mixing of micron size AN particles reduced the reactivity drastically. Our studies clearly show that nanoscale mixing of thermites with explosives is necessary to enhance the reactivity of the mixture. More »»

2007

Conference Paper

D. Tappmeyer, Dr. T. Rajagopalan, Bezmelnitsyn, A., Apperson, S., Gangopadhyay, K., Gangopadhyay, S., Redner, P., Balas, W., Kapoor, D., and Nicolich, S., “Novel Nanoenergetic Material Using Porous Copper Oxide Nanoparticles and Aluminum Nanoparticles”, in The 2007 Annual Meeting, 2007.[Abstract]


We are currently developing nanoengineered thermites (nanothermite) with tailored properties that are expected to replace lead azide and lead styphnate primers in the near future. Nanothermites are comprised of a mixture of nanoscaled fuel and oxidizer. Typically Al nanoparticles are used as fuel and metal oxides like CuO, MoO3, Bi2O3 are used as oxidizers. Herein we combine two methodologies namely surfactant templating and sol-gel approach to synthesis porous CuO nanoparticles. The formation and the stability of the gel were optimized by varying the proportions of the precursors. The gel was then washed and heated for complete removal of surfactant. The nanoparticles were characterized using Transmission Electron Microscopy and Fourier transform infrared (FTIR) spectroscopy. Micrographs revealed the formation of nano-porous particles with a diameter of 75-100 nm with 4-6 nm pores. FITR was performed on all samples to confirm the formation of copper oxide and the successful removal of impurities. The combustion characteristics were determined by performing burn rate and reactivity measurements. Burn rate was measured using an optical method. The inner walls of a lexane tube were coated with nanothermite slurry. The combustion speed of the energetic material was obtained from the propagation distance traveled and measured time of propagation. The porous nanoparticles exhibit very high combustion speeds of 1900 m/s. In conclusion, the results clearly reveal that the nanothermites prepared with porous CuO nanoparticles (oxidizer) and Al nanoparticles (fuel) are indeed very promising for both military and civilian applications. More »»

2006

Conference Paper

M. Jin, Boolchand, P., Dr. T. Rajagopalan, and Chopra, K. L., “Giant photocontraction effects in obliquely-deposited chalcogenide glass thin-films”, in APS Meeting Abstracts, 2006.[Abstract]


GexSe1-x thin-films at several obliqueness angles α (= 0, 20, 45, 60, 80) and compositions x ( = 0.15, 0.20, 0.23, 0.25 and 0.33) were vapor-deposited, and examined in Raman scattering and SEM measurements both in the pristine and illuminated state. The films, placed in an inert ambient, were exposed to Hg lamp radiation, and photo-contraction of the films established using a profilometer. Raman scattering of the pristine and exposed films were studied as a function of depth using a confocal microscope attachment. Our results show (i) Raman scattering of the normally deposited (α = 0) films in the pristine state are similar to those of corresponding bulk glasses, (ii) obliquely deposited films at x = 1/3 reveal Raman lineshapes that change qualitatively with α, suggestive of nanoscale phase separation of the films, while those at x = 0.23 show Raman lineshapes that are largely independent of α, (iii) the photocontraction effect maximizes in the 0.20< x < 0.25 range, confirming the earlier finding (ref1) (iv) light illumination partially undoes effects associated with nanoscale phase separation. Possible interpretation of these results in relation to origin of photocontraction effects will be presented. More »»

2004

Conference Paper

S. Gangopadhyay, Lahlouh, B., Dr. T. Rajagopalan, Biswas, N., Mehta, N., and Lubguban, J. A., “Creating Voids by Annealing a-SiC: O: H Films Prepared by Plasma-enhanced Chemical Vapor Deposition”, in APS March Meeting Abstracts, 2004.[Abstract]


Hydrogenated amorphous silicon carbide (a-SiC:H) films were prepared by plasma-enhanced chemical vapor deposition from diethylsilane (C4H12Si) diluted in methane (CH4). The deposition conditions resulted in a highly unstable a-SiC:H film, which reacted with oxygen when exposed to air, forming Si-OH and H-OH bonds and Si-O networks as well. The Rutherford Back Scattering analysis shows 15incorporation. The Fourier transfom infra-red (FT-IR) measurement suggests the presence of a-SiC:O:H component and a-C:H moieties throughout the film. The films were then thermally annealed in vacuum at 450C to removed unstable C-H bonds and Si-OH and H-OH groups creating voids in the film. The removal of C-H, Si-OH and H-OH is evident from the FT-IR spectra. During the annealing process, the film also cross-links and formed a stable a-SiC:O:H film. After annealing, the dielectric constant of the films decreased from 4.2 to 2.1 suggesting the presence of voids/pores in the films. More »»

2003

Conference Paper

J. A. Lubguban, Lahlouh, B., Biswas, N., Dr. T. Rajagopalan, and Gangopadhyay, S., “Selective Extraction of Porogens in Hybrid Films by Supercritical Carbon Dioxide”, in APS Meeting Abstracts, 2003.[Abstract]


The need for low dielectric constant materials with k < 2 for devices with feature sizes below 130 nm has generated interest to develop a variety of nanoporous materials. One such class is the organic/inorganic hybrid films where nanopores are formed/incorporated by thermal decomposition of porogens in organosilicate matrix at high temperatures up to 430oC. Our process is selective extraction of different types of porogens in organic matrix like methylsilsesquioxane (MSSQ) via supercritical carbon dioxide (SCCO2). In contrast with thermal decomposition, we have demonstrated that SCCO2 extraction occurred at much lower temperature (160oC) and 6000 psi pressure. The present work will demonstrate SCCO2 extraction at lower temperatures and pressures. Introducing certain modifiers in the SCCO2 process can help attain this goal. Furthermore, a pulse or dynamic SCCO2 system will be utilized to reduce the extraction time drastically. Fourier transform infrared spectroscopy (FTIR) is extensively used to monitor the extraction process. The measured values of refractive index and dielectric constant and the calculated values of porosity will confirm the successful extraction of porogens using SCCO2. More »»

2003

Conference Paper

B. Lahlouh, Dr. T. Rajagopalan, Lubguban, J., Biswas, N., Gangopadhyay, S., Sun, J., Huang, D. H., Simon, S. L., Toma, D., and Butler, R., “Supercritical Carbon Dioxide/Hexamethyldisilazane Treatment of Plasma-Damaged Low Dielectric Constant Films”, in APS Meeting Abstracts, 2003.[Abstract]


Etching, ashing and cleaning are very essential processes in semiconductor manufacturing. During these processes porous low dielectric constant (low-k) materials can be heavily damaged with a concomitant increase in dielectric properties. Fourier transform infrared spectroscopy (FTIR) measurements of the nanoporous films exposed to these manufacturing processes show that the methyl groups in these films were replaced by the silanol group during the plasma process. The highly polar silanol group increases the film's dielectric constant and makes the film more hydrophilic. In this work, supercritical carbon dioxide (SCCO2) with hexamethyldisilazane (HMDS) is used as a potential treatment to fix the plasma-damaged porous low-k films. Comparing the FTIR spectra for the films before and after SCCO2/HMDS treatment shows that it was successful in replacing silanol groups with methyl groups. The dielectric constant of the films was measured before and after the plasma treatment, as well as before and after the SCCO2/HMDS treatment, using CV measurements on a metal/insulator/semiconductor (MIS) structure. The dielectric constant of the plasma-damaged films was 3.71. When the sample was treated with SCCO2/HMDS, the dielectric constant decreased to 2.49. The dielectric constant and the FTIR measurements of the SCCO2/HMDS treated samples are comparable to those of the undamaged films. More »»

Publication Type: Patent

Year of Publication Publication Type Title

2015

Patent

S. Gangopadhyay, Chung, S. W., Dr. T. Rajagopalan, Staley, C. S., Gangopadhyay, K., and Raymond, K. E., “Hierarchical self-assembled energetic materials and formation methods”, 2015.

2013

Patent

S. Gangopadhyay, Tappmeyer, D., Bezmelnystin, A., Dr. T. Rajagopalan, Shende, R., Mehendale, B., Apperson, S., Barizuddin, S., and Gangopadhyay, K., “Homogeneous mesoporous nanoenergetic metal oxide composite fabrication methods”, 2013.

2011

Patent

S. Gangopadhyay, Apperson, S., Gangopadhyay, K., Bezmelnitsyn, A., Dr. T. Rajagopalan, Kraus, M., Shende, R., Hossain, M., Subramanian, S., Bhattacharya, S., and , “Shock wave and power generation using on-chip nanoenergetic material”, 2011.[Abstract]


A method of generating power uses a nanoenergetic material. The nanoenergetic material comprising thermite is obtained and deposited on a substrate. An igniter is placed on the nanoenergetic material. When power is desired, the nanoenergetic material is ignited. A transducer receives thermal, sonic, magnetic, optic and/or mechanical energy from combustion of the nanoenergetic material and converts it into electrical energy. Preferably, the transducer is a thermoelectric, piezoelectric or magneto device. Preferably, multiple transducers are integrated in one power generators to maximize the power from nanoenergetic thermites. More »»

2011

Patent

S. Gangopadhyay, Apperson, S., Gangopadhyay, K., Dr. T. Rajagopalan, and Bezmelnitsyn, A., “Nanothermite thrusters with a nanothermite propellant”, 2011.

2008

Patent

S. Gangopadhyah, Dr. T. Rajagopalan, Bezmelnytsin, A., Apperson, S., and Gangopadhyay, K., “Reducing electrostatic discharge ignition sensitivity of MIC materials”, 2008.[Abstract]


The invention provides metastable intermolecular composites that have good thermite properties while also being relatively insensitive to electrostatic discharge ignition. A preferred embodiment metastable intermolecular composite has a metal oxide nanostructure, which can be coated with an energetic polymer via a molecular linker or loaded with a gas generating polymer. Metal fuel nanoparticles coated with an energetic polymer via a molecular linker are closely associated with said metal oxide nanostructure. Methods of making metastable intermolecular composites are also provided by the invention. More »»

Publication Type: Thesis

Year of Publication Publication Type Title

2001

Thesis

Dr. T. Rajagopalan, “STUDY OF STRUCTURAL AND OPTICAL PROPERTIES OF AS-DEPOSITED AND THERMAL/LASER ANNEALED GeBiSe THIN FILMS”, INDIAN INSTITUTE OF TECHNOLOGY, DELHI, 2001.[Abstract]


Phase change optical recording (PCOR) medium is considered as a potential replacement for conventional magnetic recording medium due to its large data storage and archival stability. The basic principle of PCOR is based on the r&versible switching of the structure, usually, between amorphous and crystalline states using the heat of a focused laser beam. The difference in optical reflectivity of these states, defined as optical contrast, is utilized to know the data status ('0'or'1'). For a material to be an ideal PCOR medium it. More »»

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