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We report synthesis of some binary and ternary metal oxide nanostructures using microwave irradiation-assisted chemical synthesis, either in the presence or absence of a surfactant/structure directing agent. The method is simple, inexpensive, and yields nanoparticles of desired metal oxides in minutes, and requires no conventional templating. Nanoparticles of some functionally advanced binary/ternary metal oxides (MnO2, ZnO, CuO, ZnMn2O4 etc) have been synthesized using metal acetylacetonates as the starting precursor material and microwave as the source of energy, in a process developed in detail in our laboratory. The nanoparticle size varies from 7-50 nm. Emphasis has been placed on the synthesis of ZnO nanostructures, particularly ZnO nanoshells, which do not require any surfactant/structure-directing agent for synthesis. There is a systematic variation in the morphology of the ZnO nanostructures with variation of process parameters, such as microwave power, microwave irradiation time, type of solvents, surfactants/structure-directing agents and its type and concentration. The as-prepared powder sample may either need a very brief exposure to heat to remove the surfactant or no post-synthesis processing, and is found to be well-crystallised. Determination of their crystallinity, actual shape, and orientation was made using X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Phase-change materials undergo a change in bonding mechanism upon crystallization, which leads to pronounced modifications of the optical properties and is accompanied by an increase in average bond lengths as seen by extended x-ray absorption fine structure (EXAFS), neutron and x-ray diffraction. The reversible transition between a crystalline and an amorphous phase and its related property contrast are already employed in non-volatile data storage devices, such as rewritable optical discs and electronic memories. The crystalline phase of the prototypical material GeSb2Te4 is characterized by resonant bonding and pronounced disorder, which help to understand their optical and electrical properties, respectively. A change in bonding, however, should also affect the thermal properties, which will be addressed in this study. Based on EXAFS data analyses it will be shown that the thermal and static atomic displacements are larger in the meta-stable crystalline state. This indicates that the bonds become softer in the crystalline phase. At the same time, the bulk modulus increases upon crystallization. These observations are confirmed by the measured densities of phonon states (DPS), which reveal a vibrational softening of the optical modes upon crystallization. This demonstrates that the change of bonding upon crystallization in phase-change materials also has a profound impact on the lattice dynamics and the resulting thermal properties.
The aim of this paper is to focus attention on some current developments in the physical examination of decorative ceramic thin coatings performed in France and in Europe. Thanks to the recent progress in instrumentation and the implication of material science teams, significant new results were obtained concerning the finishing coatings of ceramic ware, and specially regarding the luster decorations of Islamic medieval potteries and the high gloss coatings of Greek and Roman ceramics.
Solar cells based on Cu(In, Ga)Se2 (CIGS) have made significant strides in the past decades with a record efficiency of over 20% [1]. A problem with CIGS modules is the high resistive losses along the transparent top contact. One solution is to deposit highly-conductive metal grids to collect the current. We use finite-element analysis to determine the effectiveness of the metal grid under a variety of parameters. We identify the resistance of the top contact and the width of the scribes as the most important factors in determining whether a metal grid would present a significant efficiency gain. Using the same model, we also investigate methods to optimize the design of the grid.
Hydrogen absorption in metallic nanoparticles was investigated by classical molecular dynamics (MD) simulation. We used a simple model composed of an isolated f.c.c. or b.c.c. nanoparticle of 1, 1.4, 2, 4, 6, 8 and 10 nm in diameter and surrounding hydrogen atoms. The simulated particle sizes are which correspond to about 50 to 44000 atoms. In the case of f.c.c. nanoparticles, atomic configuration with five-fold symmetries was observed in both hydrogenfree and hydrogenated particles smaller than 2 nm. The f.c.c. structure was maintained in larger particles than 4 nm with lattice deformation which varies with M-H interaction. The b.c.t. structure was observed in hydrogenated b.c.c. nanoparticles. Number of H atoms absorbed in a nanoparticle varies depending on particle size and M-H interaction: it increases with increasing particle size and M-H bond strength.
Integration of nanomaterials (in the form of quantum dots, nanotubes, nanowires, nanocrystalline thin films, and nanocomposite films) with micromachined structures and devices has the potential to enable the development of microelectromechanical systems (MEMS) with enhanced functionality and improved performance. Here, we present a fabrication approach that combines spray-coating of electron beam resist with direct-write electron beam lithography to pattern nanomaterials on fragile micromachined components. Polymers and metallic structures in the form of arrays of holes, concentric circles, and arrays of lines, with critical dimensions ranging from 135 nm to 500 nm, were patterned directly on various micromachined structures including commercial metal-coated silicon microcantilevers used for atomic force microscopy, and commercial plate-mode SiC/AlN microresonators used for sensing.
In this paper, the degradation processes of commercial supercapacitors aged at 2.7 V and 65 °C for 2000 h were studied. The crystallinity, thermal stability, and specific surface areas of the carbon electrodes of the supercapacitors were measured. Significant changes and degradations in the carbon electrodes were observed for the aged supercapacitors. New functional groups were also found on the surface of the electrodes. The degradation of the lattice structures and the reduction in the specific surface area were as well observed for the aged supercapacitors. It was suggested that the aging of supercapacitors significantly changed the electrode surface which affects considerably electrical properties and functionality of supercapacitors. We have also performed experiments which suggest that the aging effect on the electrode is not uniformly distributed through its length.
We report a low-cost and high-throughput method to fabricate large-area light emitting pattern via thermal evaporation of organic molecules on the patterned self-assembled monolayer of homogenous 3-aminopropyltrimethoxysilane. This method is based on the selective deposition of the organic light emitting molecules on the template of self-assembled monolayer (SAM), which is patterned with nanoimprinting lithography. The selectivity can be controlled by adjusting the design of the pattern, the storage duration and the substrate temperature. The deposition selectivity of the molecules may be caused by the different binding energy of the molecules with the SAM and the substrate surface.
One potential application for Bulk Metallic Glasses (BMGs) is in dies with micro- and nano-sized features. Three basic characteristic sets inherent to BMGs make them ideal materials for micro/nano-tooling applications: (1) excellent compressive strength, wear and corrosion resistance; (2) amorphous structure which presents no microstructural length scale limitation to cutting and forming operations; (3) the presence of a glass transition temperature above which they can be easily formed. There are many potential applications for multi-scale BMG tooling, including in production of microfluidic and other precision biomedical devices. In the current work, discs were cut from 5 mm diameter cylindrical specimens of Zr44Cu40Al8Ag8 BMG produced via arc melting and casting into water-cooled copper molds. The cylindrical specimens were then thermoplastically formed into thin coin-like disc samples. The thin disc-shaped plates were then ground and polished to create a smooth flat surface. Sub-micron-sized features were patterned into the plates via a focused ion beam. We demonstrated that such feature sizes are not achievable in conventional crystalline metallic tool materials. The patterned BMG tools were then set in a compression press where the platen temperature was precisely controlled and a series of load-controlled embossing trials were carried out in which the features of the BMG tooling were replicated in poly(methyl methacrylate) (PMMA) sheet. An exercise in mapping out the size limitation of such a multi-scale embossing operation is reported.
To counteract plasma instabilities like Neoclassical Tearing Modes (NTM-modes) in nuclear fusion reactors (JET, ITER, DEMO) high power microwaves are used for the Electron Cyclotron Resonance Heating (ECRH) and for the plasma current drive (CD). The foreseen power level for ITER (Cadarache, France) is Ptot = 24 MW at f = 170 GHz. Each transmission line is designed for a maximum of 2 MW power. The vacuum and tritium barrier to the ITER vacuum vessel is realized by a CVD diamond disk window assembly. Diamond has an extremely high thermal conductivity of about k = 2100 W/Km and a very low loss tangent of tan δ < 10-5 for this frequency and shows therefore a very small microwave absorption. The normalized absorbed power A=Pabs/P0 can be calculated as A = (f/c) • π • (1+εr‘) • tan δ • t (with the rule of thumb estimate: (f/c)=0.5 mm-1; π • (1+εr‘) = 20; tan δ =10-5; A=10-4 • t [mm]); i.e. each t = 1 mm thickness of diamond absorbs Pabs = 100 W of Po = 1 MW microwave power transmitted through the CVD diamond window with an effective tanδ of 10-5.
Poly(3-hexylthiophene) (P3HT) nanofibers were fabricated with an association of poly(vinyl pyrrolidone) (PVP) by electrospinning. A mixture of P3HT/PVP in a mixed solvent of chlorobenzene and methanol was electrospun to form composite fibers with 60 nm - 2 μm in diameter, followed by getting rid of PVP by selective extraction. After extraction, pure P3HT nanofibers were obtained as a spindle-like structure with wrinkled surface. The nanofibers obtained exhibit specific features of strong interchain contribution as investigated by UV-vis, fluorescence spectroscopic, X-ray diffraction (XRD), and photo-electron investigations. Bulk heterojunction P3HT:PCBM nanofibers with ~200 nm in diameters were also successfully fabricated by using the same technique. The preliminary results from the study of P3HT:PCBM nanofiber-based photovoltaic cells with conversion efficiency over 0.2% could be achieved.
Spectroscopic techniques such as IR and Raman are very powerful to understand guest-host interactions. Although these techniques are complementary, Raman spectroscopy has not been widely implemented as a tool to characterize these interactions. This study illustrates the use of Raman spectroscopy not only to probe the interactions experienced by a guest molecule but also to detect structural changes occurring in the framework upon loading. Weak interactions of adsorbed molecules with the framework are reflected in frequency and intensity variations in both Raman and IR absorption lines, as shown for the case of CO2, N2 and CH4 with Zn(bdc)(ted)0.5.
Titanium oxide thin films were deposited at 250 – 400 °C on amorphous SiO2 prepared on n-type Si substrates by chemical vapor deposition (CVD) using a novel precursor, ethene-1,2-diylbis(tert-butylaminido)diisopropoxotitanium [Ti[N(tBu)C=CN(tBu)](OiPr)2 , Ti-DOT], with oxygen gas as an oxidant. Deposition characteristics of thin films were compared with those using titanium tetraisopropoxide [Ti(OiPr)4, TTIP]. As a result, the deposition amount of TiO2 thin films using Ti-DOT was larger than that of TTIP because of the shorter incubation time in the case of Ti-DOT. Smaller surface roughness was observed for the films using Ti-DOT. In addition, a good conformability was obtained on amorphous SiO2 hole prepared on n-type Si substrate substrate with aspect ratio of 5.
A feedback control mechanism based on infrared radiation monitoring coupled with reflectivity information was developed to control the temperature of a laser assisted chemical vapor deposition process for the growth of carbon nanotube forests. An infrared laser operating at 808 nm is focused on a silicon substrate containing a 20 nm-aluminum-oxide layer and a 1.5 nm-iron catalyst layer. The growth takes place in an argon/ hydrogen/ ethylene gaseous environment. SEM and Raman spectroscopy analysis show that good controllability and reproducibility is achieved over multiple experiments.
Radiation hard monolithic particle sensors can be fabricated by a vertical integration of amorphous silicon particle sensors on top of CMOS readout chip. Two types of such particle sensors are presented here using either thick diodes or microchannel plates. The first type based on amorphous silicon diodes exhibits high spatial resolution due to the short lateral carrier collection. Combination of an amorphous silicon thick diode with microstrip detector geometries permits to achieve micrometer spatial resolution beneficial for high accuracy beam positioning. Microchannel plates based on amorphous silicon were successfully fabricated and multiplication of electrons was observed. This material may solve some of the problems related to conventional microchannel devices. Issues, potential and limits of these detectors are presented and discussed.
Proton conducting ceramics are considered as promising membranes for medium temperature fuel cells, water stream electrolyzers and CO2/syngas converters. Materials for these applications have to be mechanically and chemically stable at corrosive conditions of temperature and water vapor pressure in order to ensure the long life-time operation. Our comprehensive Raman, infrared, thermogravimetric, thermal expansion and neutron diffraction studies have shown that the choice of A and B elements as well as the material processing (synthesis, geometry, density, etc.) are crucial to control aging of material. We will consider an example of BaZr0.25In0.75O3 perovskite to show that several factors such as the carbonation, the traces of secondary AO phases at the grain boundaries as well as the use of samples with highly active surface, i.e. powders or lightly densified ceramics can cause: i) preferential adsorption of surface protonic species such as hydroxides, (hydro)carbonates, water, ii) decreased incorporation of bulk protonic species responsible for the proton conduction, iii) significant modification of the host perovskite structure up to complete crumbling of the material. We will show how to improve potential application of perovskites by understanding and controlling these processes.
Nanotechnology, a field interested in materials with features smaller than 100 nanometers and possessing novel properties, is a field that is unquestionably in a period of rapid growth. As the limits of existing technologies are pressed, the need arises for faster, better, and stronger materials and devices. Manipulation of matter on the nanoscale is quickly becoming the next frontier of materials and technology. Due to the scale of the phenomena and the exploratory nature of nanoscience and nanotechnology, a high degree of knowledge in many diverse fields is required. This requires a centralized presentation to students in order to best teach them the required knowledge.
In the past, knowledge has mostly been transferred hand-to-hand on an active level. However, in modern education, the classroom and lectures take a more active role. With this rise, the position and focus of hands-on work has diminished [1], while at the same time undergraduates remain isolated from research being conducted at universities [2]. With the broad nature of nanoscience and nanotechnology, it is becoming more important to maximize students’ learning ability in order to train future researchers and workforce. This paper explores the impact of a hands-on research experience in undergraduate nanotechnology education. This experience is presented to show the importance of student involvement on hands-on projects for their learning process.