Due to the increasing complexity of thin-film silicon solar cells, the role of computer modeling for analyzing and designing these devices becomes increasingly important. The ASA program was used to study two of these advanced devices. The simulations of an amorphous silicon solar cell with silver nanoparticles embedded in a zinc oxide back reflector demonstrated the negative effect of the parasitic absorption in the particles. When using optical properties of perfectly spherical particles a modest enhancement in the external quantum efficiency was found. The simulations of a tandem micromorph solar cell, in which a zinc oxide based photonic crystal-like multilayer was incorporated as an intermediate reflector (IR), demonstrated that the IR resulted in an enhanced photocurrent in the top cell and could be used to optimize the current matching of the top and bottom cell.

Kesterite Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) compounds are candidate low-cost absorber materials for thin-film solar cells, and a light-to-electricity efficiency as high as ~10% has been achieved in the solar cell based on their alloys, Cu2ZnSn(S,Se)4 (CZTSSe). In this paper, we discuss the crystal and electronic structure of CZTSSe alloys with different composition, showing that the mixed-anion alloys keep the kesterite cation ordering, and are highly miscible with a small band gap bowing parameter. The phase stability of CZTS and CZTSe relative to secondary compounds such as ZnS and Cu2SnS3 has also been studied, showing that chemical potential control is important for growing high-quality crystals, and the coexistence of these secondary compounds is difficult to be excluded using X-ray diffraction technique. Both CZTS and CZTSe are self-doped to p-type by their intrinsic defects, and the acceptor level of the dominant CuZn antisite is deeper than Cu vacancy. Relatively speaking, CZTSe has shallower acceptor level and easier n-type doping than CZTS, which gives an explanation to the high efficiency of CZTSSe based solar cells.

In the last years more and more effort has been put into the development of thin-film organic solar cells using conductive and semi-conductive polymers. A great advantage of these polymers is the possibility to deposit them in high throughput print and coating processes. This feature provides huge potential for future production of low cost photovoltaics. While TCO layers form the transparent front contact, polymers are used for the buildup of the active layer and the design of the interface between active layer and front contact. The polymer materials have to be patterned in order to allow for a row connection of the solar cell work (typically by structured deposition, e.g. printing). In addition the bulk hetero junction (BHJ) of the active layer consisting of poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) requires an annealing step to optimize the layers structure and therewith the efficiency of the solar cell (typically by thermal treatment, e.g. oven). 3D-Micromac used ultra-short pulsed lasers to evaluate the applicability of various wavelengths for the selective ablation of the BHJ consisting of P3HT:PCBM on top of a Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and indium tin oxide (ITO) film system on glass substrates. The process of laser annealing was investigated using a short-pulsed laser with a wavelength close to the absorption maxima of the BHJ.

In this paper we present a novel approach for interface bilayer formation inwhich the uptake of an aqueous lipid vesicle solution by two polymerichydrogels contained in a substrate causes the gels to swell so as to comeinto contact within an internal oil-filled region of the device. Aninterface bilayer, similar to those formed using the droplet interfacebilayer (DIB) method, forms upon contact in oil between the lipid-encasedends of the two gels. Experimental measurements provide initial evidencethat gel swelling enables automatic bilayer formation within a few minutesafter the addition of lipid solution. The approach presented herein workstoward the development of a new portable, easy-to-use screening platformthat features tailored interface bilayers for a wide variety of screeningapplications.

Well-crystallized AlN nanorods have been produced by mechanical milling and subsequent annealing treatment of the milling powders (mechanothermal process). High purity AlN powders were used as the starting material. Mechanical milling was carried out in a vibratory SPEX mill for 30 h, using vials and balls of silicon nitride. The annealing treatment was carried out at 1200 ºC for 10 min. The characterization of the samples was performed by X-ray diffractometry and transmission electron microscopy (TEM). TEM observations indicated that the synthesized nanorods consisted of 30 nm in diameter and 100 nm in length. High resolution electron microscopy observations have been used in the structural characterization. AlN nanorods exhibit a well-crystallized structure. The growing direction of the nanorods is close to the [001] direction. The structural configurations have been explored through comparisons between experimental HREM images and theoretically simulated images obtained with the multislice method of the dynamical theory of electron diffraction.

We investigate the electronic structure of interstitial Li and Li vacancy in Li7P3S11 by first principles calculations. We find that Li7P3S11 is a good insulator with a wide band gap of 3.5 eV. We find that the Li vacancy and interstitial Li+ ion do not introduce states in the band gap hence they do not deteriorate the electronic properties of Li7P3S11. The calculated formation energies of Li vacancies are much larger than those of Li interstitials, indicating that the ion conductivity may arise from the migration of interstitial Li.

A new plasma deposition system was built with the capability of varying the electrode spacing in the DC Saddle Field plasma enhanced chemical vapor deposition system. An ion mass spectrometer was installed just below the substrate holder to sample the ion species travelling towards the substrate. Silane plasma and amorphous silicon film studies were conducted to shed light on the impinging ion species, ion energy distributions, and film properties with varying electrode spacing. The results indicate that decreasing the distance between the substrate and cathode leads to a reduction in the high energy ion bombardment.

The effects of ion irradiation damage on dislocation generation and propagation in austenitic stainless steels were studied by means of in situ transmission electron microscopy and electron tomography. Tensile samples were irradiated in situ to a dose on the order of 1017 ions/m2 with 1MeV Kr+ and strained at 300 K as well as 673 K. Dislocation motion through the irradiation-obstacle field was jerky and discontinuous, dislocation pile-ups formed in grain interiors and at boundaries, long straight dislocations were generated decorating the channel-matrix walls, and dislocation cross-slip within the channel created debris along the channel leading to channel widening. Electron tomography was applied for the first time to reveal new detail about the dislocation reactions in the channel wall.

A technique to improve and accelerate aluminum induced crystallization (AIC) by hydrogen plasma is proposed in this paper. Raman spectroscopy and Secondary Ion Mass Spectrometry of crystallized poly-Si thin films show that hydrogen plasma radicals reduce the crystallization time of AIC. This technique shortens the annealing time from 10 hours to 4 hours and increases the Hall mobility from 22.1 cm2/V·s to 42.5 cm2/V·s. The possible mechanism of AIC assisted by hydrogen radicals will also be discussed.

Recently, the first molecular nanowheel was synthesized and characterizedfrom Scanning Tunneling Microscope (STM) experiments. It was demonstratedthat a specifically designed hydrocarbon molecule (C44H24) could roll on a copper substrate along the[110] surface direction. In this work we report a preliminary theoreticalanalysis of the isolated molecule and of its rolling processes on differentCu surfaces. We have used ab initio and classical moleculardynamics methods. The simulations showed that the rolling mechanism is onlypossible for the [110] surface. In this case, the spatial separation amongrows of copper atoms is enough to ‘trap’ the molecule and to create thenecessary torque to roll it. Other surface orientations ([111] and [100])are too smooth and cannot provide the necessary torque for the rollingprocess.

Nanotechnology is an area of research that is highly intriguing because of the novel properties often observed for materials whose sizes are reduced to the nanoscale. However, one of the biggest challenges is understanding the underlying principles that dictate the particles resulting properties. The atomic level structure for nanoparticles is suspected to vary from that for the corresponding bulk materials, however, direct observation of this phenomenon has proven difficult. Until recently only indirect information on the atomic level structure of such materials could be obtained with techniques such as XRD, HR-TEM, XPS, etc… However, recent advances in Transmission Electron Microscopy techniques now allow true atomic scale resolution, leading to definitive confirmation of the atomic structure. Namely, Scanning Transmission Electron Microscopy coupled with a High-angle Annular Dark Field detector (STEM-HAADF) has been demonstrated to be capable of achieving a nominal resolution of 0.8 nm (the JEOL JEM-ARM200F instrument). The ability is highly exciting because it will lead to an enhanced understanding of the relationship between atomic structure of nanoparticles and the resulting novel properties. In our own study, we focus on the analysis of the atomic level structure for nanoparticles composed of bismuth, antimony and tellurium for thermoelectric materials. This area has recently received much interest because of the realization that nanotechnology can be employed to greatly enhance the efficiency (dimensionless figure of merit ZT) of this class of materials. One of the most intriguing parameters leading to the enhanced TE activity is the relationship between composition and structure that exists within individual nanoparticles. We report our results on a study of the atomic level structure for both nanowires and nanodiscs composed of bismuth, antimony and tellurium. It was found that the nanoparticles have a complex structure that cannot be elucidated by conventional techniques such as XRD or HR-TEM. In addition, by employing Energy Dispersive Spectroscopy (EDS), a greater understanding of the composition-structure dependence was gained. The results are primarily discussed in terms of the atomic level resolution images obtained with the STEM-HAADF technique.

Glancing angle deposition (GLAD) was used to deposit ordered arrangements of Si/Ge-nanocolumns applying the ion beam sputter technique. After substrate preparation by electron beam lithography as well as nanosphere lithography the deposition behavior of GLAD nanocolumns in regular arrangements with different symmetries was studied. The nanocolumns exhibited distinct morphology regions which are correlated to their temporal evolution during deposition. Furthermore, the customization of the column morphology by non-uniform substrate rotation is considered. Axial Si/Ge-heterojunctions were incorporated by sequential deposition.

The actuation of ionic polymer actuators is mainly caused by the ion transport and excess ions storage in the membrane and electrodes. To quantify the charge transport behavior, a time domain method based on Poisson-Nernst-Planck equations was applied. The time domain transient current in response to a step voltage can provide insights on the charge transport and storage behaviors in the membranes. In this study, we investigate the charge transport behavior of Aquivion ionomer with different uptakes of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf). A critical uptake and voltage independent of charge transport behavior were observed. The results also show that bending actuations of the Aquivion membrane with 40wt% EMI-Tf is much larger than that of Nafion, indicating that the shorter flexible side chain ionomer possesses a better electromechanical coupling between the excess ions and the membrane backbones, while not affect the actuation speed.

First-principles density functional calculations are performed to investigate the electronic properties of O-vacancy defects in high-k HfO2, Si/HfO2 interface, and amorphous oxide semiconductors. The role of O-vacancy in device performance is discussed by comparing the results of the GGA, hybrid density functional, and quasiparticle energy calculations.

Pt/Pb(Zr0.4Ti0.6)O3 (PZT)/Pt capacitors were prepared by the sol-gel technique and their electric properties were analyzed. The asymmetry of polarization-electric field (P-E) and capacitor-voltage (C-V) curves exhibits existence of an interface layer (dead-layer) between top Pt electrode and PZT thin film. By conducting temperature dependant measurement, the Pt/PZT/Pt capacitor was confirmed to be Schottky emission conduction. In addition, barrier height of PZT contact calculated 0.67eV. On basic a series capacitors model and Schottky contact of Pt/PZT interface, the thickness and the dielectric constant of this dead-layer were estimated to be 6.4 nm and 170, respectively. Moreover, the dielectric constant of 900 was obtained for the real PZT ferroelectric layer. The existence of the dead-layer was also confirmed by the high resolution transmission electron microscopy (HR-TEM) observation and the energy dispersive X-ray (EDX) analysis on PZT ferroelectric layer in the Pt/PZT/Pt structure. Based on EDX analysis result, a 10-nm layer at Pt/PZT contact was suggested to be the dead-layer.

In this work, the damage formation subsequent to Eu implantation at 300 keV has been investigated by coupling the TEM, XRD and RBS/C techniques. It has been found that GaN exhibits a specific damage buildup in three main steps: (i) clustering of point defects and formation of a network of stacking faults defects in the bulk, (ii) propagation of the planar defect network towards the surface and (iii) breakdown of the surface layer. This occurs through different strain saturation regimes. Around 5x1014 Eu/cm2, the strain along the implantation direction saturates to 0.6%. At higher fluence, whereas the peak at 0.6% is maintained, there is an increase of the strain throughout the implanted layer which probably continues to extend. A second saturation occurs when the stacking fault network reaches the layer surface.

The low loss coefficient and high elastic energy storage of amorphous metals may provide novel opportunities in the design of stringed musical instruments. To produce prototypes for metallic glass music wire, bulk metallic glass pre-forms were reheated into the supercooled liquid region and stretched into wires. Investigations of these wires’ geometrical, mechanical, and physical properties are reported. The process is relatively simple and could be practical for producing continuous wire. A theoretical analysis shows the importance of the interaction between heating power input, radiative and convective cooling, and area reduction in determining the wire’s final properties.

Semiconductor epitaxial CVD single crystal diamond is considered a potential material for power devices because of its unique characteristics. In the discussion on the relationship between crystal quality and device performance, the atomic purity and defect concentration have been considered; however, the information on the local stress-strain distribution in a single crystal is not sufficient. In this paper, the local stress-strain distribution of the epitaxial CVD single crystal diamond is quantitatively examined using the birefringence and cathodoluminescence images and the Raman peak-shift map. From the Raman peak-shift map, the local stress-strain is estimated and the stress is found to range from -67 MPa to +160 MPa in the observed area.

The National Science Foundation (NSF) evaluates grant applications based on two criteria: intellectual merit and broader impact. The broader impact criterion (BIC), or the science outreach criterion, is intended to connect science, technology, engineering, and math (STEM) research to the general public, and has grown in its relevance for successful grants. A method to increase the competitiveness of a grant application and, in turn, the quality of science outreach programs is to suggest successful science outreach models for connecting scientists to the public. Science Saturdays is a fun science lecture series for the general public that is a simple, scalable, and transferable model. Its main mission is to introduce participants to excellent communicators of science and to shatter stereotypes about those who do science. It aims to inspire and motivate children as they traverse the STEM pipeline by emphasizing that science is fun. This paper discusses the elements needed to create this outreach program and the lessons learned from its development.