Biography:

Kirk J Ziegler has joined the Chemical Engineering Department at the University of Florida in 2005. His work on SWCNTs has focused on understanding the effect of surfactant-nanotube interactions on dispersion and separation processes. His work on nanowire arrays has applications in energy-related devices, which require high surface area to maximize energy generation or storage.

Abstract:

The post synthesis separation of single wall carbon nanotubes (SWCNTs) is needed for their inclusion in novel electronic devices. For example, semiconducting SWCNTs have unique optoelectronic properties that can be utilized in photovoltaics and biosensors. The high surface area of nanomaterials dictates that the interface with their surroundings is important in determining their properties or functionality. For example, all atoms in SWCNTs exist on the surface and therefore, have excellent sensing capabilities. The interface of SWCNTs with their surroundings is also important to their application in polymer composites, devices, drug delivery, bioimaging and biosensing. SWCNT interfaces are often altered with surfactants to improve their dispersion in aqueous suspensions. Understanding and ultimately controlling these surface layers is important because of its influence on reactivity, adsorption of pollutants and interaction with materials. Our group has focused on characterizing and controlling SWCNT interfaces for high-fidelity separations of semiconducting SWCNTs by the n, m type. Here we report the high-fidelity desorption of single-chirality SWCNTs from hydrogels through surfactant structure modulation. High-purity fractions of (n, m) SWCNTs are obtained with high yield once a specific ratio of sodium dodecyl sulfate (SDS)/sodium deoxycholate (DOC) co-surfactant solution is used as the eluent. The elution of only one n, m type at a specific co-surfactant ratio while other types are exposed to more surfactant suggests that each n, m type forms a thermodynamically-stable surfactant structure in the co-surfactant solution.

Biography:

Avinash Baji focuses on bio-inspired materials research using electrospun polymer fibers. His current research interests include fabrication of electrospun fibers for dry adhesion applications. He aims to mimic the geometry and adhesive mechanisms of natural materials using electrospinning enabled techniques. He has authored over 35 journal articles with additional papers in conference proceedings.

Abstract:

In this study, hierarchical structures for dry-adhesive applications were fabricated using electrospinning combined with template wetting method. Briefly, in the first step, electrospinning technique was used to produce micron sized fibers which were directly deposited on porous anodized aluminum oxide (AAO) template. Following this step, the setup consisting of the AAO template along with the fibers was heated above the glass transition temperature of polymer. This enabled the flow of polymer within the porous channels and resulted in the growth of nanometer sized pillars on the surface of the fibers. Based on this fabrication technique, we produced hierarchical structures using two different polymeric systems, viz. poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). A representative scanning electron microscopy (SEM) image of the fibers is shown in Figure-1. The SEM image shows that this approach led to the growth of sub-nano structures on the surface of the fibers. These samples were used to investigate the normal as well as shear adhesion behavior of hierarchical structures. The normal adhesion was characterized using a nanoindenter. A flat circular indenter tip (diameter=10 µm) was used to indent the surface of the samples and then retracted back. The pull-off required to separate the indenter tip from the samples was recorded. This pull-off force gave an indication of its normal adhesion. Similarly, the samples were finger pressed onto sandpaper with varying degree of roughness. The samples were then pulled in shear and the shear adhesion force was characterized. Fibers without any surface structures were also tested and their adhesion behavior was compared with that of hierarchical samples. The samples with surface nanostructures exhibited increased pull-off force compared to neat control samples due to its improved van der Waals interactions.

Biography:

Abstract:

Biography:

Er. Neeru Chaudhary is an Assistant Professor in Department of Physics, Panjab University, Chandigarh. She got her B.E. in Instrumentation in 1999 from Dr. B.A.M. University, Aurangabad (M.S.) and M.Tech in Instrumentation from University Centre of Instrumentation and Microelectronics, Panjab University Chandigarh in 2001. Currently Er. Neeru Chaudhary’s research is focused on studying Electrical and Optical properties of Semiconductor materials to be used in solid state electronic devices. The rapid growth in the field of MEMS and NEMS has led to production of variety of new materials. Hence the study of properties of the materials under different stresses is very important field in Material Science Engineering. She is life member of two national professional bodies; Indian Society of Technical Education (ISTE) and Indian Association of Physics Teachers (IAPT).

Abstract:

To understand the behavior of materials for applications in solid state electronic devices, the materials are to be exposed to different stresses such as thermal, electrical, humidity, optical, nuclear radiations, pressure (static or dynamic) etc. to better understand their structural, morphology, conduction, optical and sensing properties. The Se_85-xTe₁₅Ag_x compositions prepared from melt-quench technique were exposed to high pressure (0-10 GPa) and temperature (300K-373K). The results depict the change in resistivity with respect to pressure in forward as well as backward pressurization. These results depicts that there is very small change in resistivity with change in pressure and the change in resistivity with respect to pressure follows the same pattern, when the pressure is applied from atmospheric pressure to 10 GPa and vice versa. The results of resistivity change with the variation of silver in the compositions is also reported in this study. Similar results are observed in case of resistivity change with respect to temperature. Some deviation is observed in the results which is well explained with average coordination number, fermi level change and crystallinity.

Biography:

Naser Qamhieh has received his PhD in Physics in 1996 from the University of Leuven, Belgium, where he worked with professor Guy Adriaenssens. He has joined the Department of Physics at United Arab Emirates University (UAEU) in 1999 where he is presently a full Professor. His research interest centers on experimental study of the electronic properties and density of states of amorphous semiconductors and chalcogenide glasses and among materials of interest is phase change materials used in memory devices. His research also involves fabrication and characterization thin films and nanoclusters by the existing techniques in UAEU labs. He has published over 50 research articles in refereed international journals and conferences. He was honored a Research Project Award by the Research Affairs at UAE University in 2009. Moreover, he has rich experience in teaching and developing general physics courses in UAEU. He had several contributions to pedagogical journals and conferences. For research in pedagogy, he was honored the 2009-2010 Faculty of Science Recognition Award for Excellence in Teaching and Learning.

Abstract:

Thin films of amorphous Germanium antimony sulfide (Ge30Sb10S60) doped with cobalt (Co) have been deposited on glass substrates by thermal evaporation technique. The composition and amorphous structure of the deposited films have been characterized by X-ray diffraction and energy dispersive X-ray analysis (EDX) techniques. Optical transmission spectra measured by UV-VIS spectrophotometer showed that Co-doped Ge30Sb10S60 have 2.0 eV optical band gap. Raman spectroscopy was used to characterize the composition and phase structure of the prepared film and shows a wide band spectrum from 300 to 410 cm^-1 centered at 355 cm^-1. The Raman shift peaks at 325 cm^-1 and 350 cm^-1 are assigned to the bond stretching mode Sb-S and Ge-S, respectively. The capacitance and conductance versus voltage measurements were performed at different temperatures. The results show a slight increase in the capacitance with temperature and it reaches a maximum value around 150 ^oC and eventually it becomes negative. This behavior is interpreted in terms of the nucleation-growth process and the thermally activated conduction process with measured activation energy of 0.79 eV. This value of activation energy together with the measured optical gap indicates that the Fermi level is unpinned in the gap which could be attributed to gap states induced by cobalt doping.

Biography:

Single layer (SL) transition metal dichalcogenides (TMDCs) (MX₂; M=transition metal such as Mo, W and X= S, Se, Te) have attracted a lot of attention due to their intriguing electronic and optical properties. SL TMDCs are direct band gap semiconductors, which can be used to produce smaller and more energy efficient devices such as transistors and integrated circuits. Moreover, the band gap lie in the visible region, which makes them highly responsive when exposed to visible light, a property with potential applications in optical detection. In contrast to graphene, SL TMDCs exhibit large spin-orbit coupling (SOC) originating from the d orbitals of the transition metal atoms. The presence of the giant SOC makes them great candidates for exploring spin physics and for spintronic devices. Defects usually play an important role in tailoring electronic, optical and magnetic properties of semiconductors. We performed standard first-principle study to evaluate the electronic and optical properties of single-layer (SL) transition metal dichalcogenides (TMDCs), in the presence of vacancy defects (VDs). We consider three types of VDs in SL TMDCs (1) X-vacancy, (2) X₂-vacancy, and (3) M-vacancy. We find that VDs lead to localized defect states (LDS) in the band structure, which in turn give rise to sharp transitions in in-plane and out-of-plane optical susceptibilities, c_II and c_^, respectively. The effects of spin orbit coupling (SOC) are also considered. We find that SOC splitting in LDS is directly related to the atomic number of the transition metal atoms. Apart from electronic and optical properties we also find magnetic signatures (local magnetic moment of ~µ_B) in MoSe₂ in the presence of Mo vacancy, which breaks the time reversal symmetry and therefore lifts the Kramers degeneracy. We use group theory to derive the optical selection rules for both c_II and c_^.

Abstract:

Michael N Leuenberger has received his PhD degree in Theoretical Physics in 2002 from the University of Basel in Switzerland. After his Postdoctoral positions at the University of Iowa and at the University of California, San Diego he joined in 2005 the NanoScience Technology Center at the University of Central Florida and became tenured Associate Professor in 2011. In 2008, he has received the DARPA/MTO Young Investigator Award. His current research areas include quantum information processing in topological insulators, optoelectronics in 2D materials and solar energy harvesting in nanoparticles. He has published more than 60 peer-reviewed papers and 4 book chapters.

Biography:

Pankaj Sharma is currently pursuing his PhD degree in Electrical Engineering at Indian Institute of Technology Indore since 2014. He has completed his Masters in VLSI Design from Delhi, India. His research work includes fabrication and characterization of ZnO thin films using dual ion beam sputtering technique for optoelectronic applications. He is presently working on realizing low resistive and high hole concentration ZnO thin films by using various acceptor dopants.

Abstract:

In the last decade, Zinc oxide (ZnO) based optoelectronic devices have attracted much attention due to their superior material properties such as wide direct band gap energy, large exciton binding energy, high radiation resistance and chemical and thermal stability. However, the lack of availability of reliable and stable p-type ZnO has always remained a concern in order to fabricate these devices. Various groups have reported p-type ZnO by doping with different elements of group V, whereas others have also used co-doping approach for achieving p-type conduction in ZnO. Unfortunately, the high resistivity and low hole concentration still poses limitations for high performance devices. In this work, we report the fabrication of high hole concentration, low resistive and stable Li-P co-doped ZnO (LPZO) thin films. LPZO thin films were fabricated by DIBS technique on low resistive n-type Si substrates. The deposition was performed using high quality ceramic target having Li and P content of 5% and 3% respectively, in oxygen rich ambient at 300 ^oC and 500 ^oC. Post deposition annealing was carried out in N₂ ambient at 800 ^oC for 20 minutes to activate the acceptor dopants. The XRD pattern of annealed LPZO film confirmed that crystal structure was preferentially oriented in c-axis (002) direction. FWHM of (002) peak was calculated to be 0.24^o resulting in a crystallite size of ~35 nm. Figure 1(a) shows the schematic structure of p-LPZO/n-Si heterojunction with linear I-V curves of ohmic contacts. Hall measurement was performed in the van der Pauw configuration to measure the electrical parameters e.g., carrier concentration, resistivity and mobility. The annealed LPZO films clearly depicted p-type conduction as observed from the rectifying behavior shown in Figure 1(b). A relatively higher hole concentration of the order 2×10²⁰ cm^-3 and resistivity of 8×10^-3 Ω.cm were calculated. The turn-on voltage of the diode was determined to be 1.6 V whereas the rectification ratio of forward to reverse current at ±3 V was 76.