We have investigated the diffusion mechanisms of Li-ion in amorphous lithium phosphite (LiPO3) with the addition of sulphur. By applying the nudge elastic band (NEB)1 method in crystal LiPO3 and Li3PO4, we have confirmed the ease in diffusion pathways for Li ions in LiPO3 which is quite consistent with the previous theoretical finding. From our diffusion study in 0.5 Li2O- 0.5 P2O5 and 0.4 Li2SO4 –0.6 (Li2O-P2O5) melts above 3000K investigated with ab-initio molecular dynamics (AIMD) has been confirmed by experiments at lower temperatures, we have demonstrated the benefit of S addition in increasing the Li+ mobility. We have also found that the Li2SO4 addition into the glass result in a characteristic shift in Li-ion vibration to a lower vibrational frequency. In addition, the presence of oxygen surrounding the diffusion pathways appears to be essential in assisting the Li+ mobility in both crystalline and amorphous structures.

The kinetics of silver nanoparticles release from chitosan spheres is addressed experimentally and theoretically in this work. From the experimental viewpoint, the study of silver nanoparticles release is performed by measuring the time-dependent UV-Vis spectra of solutions where spheres were dispersed. The UV-VIS spectra intensity reflects the concentration of nanoparticles in the solution. Despite simple expressions for drug release are found in the literature, as those that relate the amount of drug release with the square root of time, a proper modeling might require the inclusion of several phenomena such as the presence of stagnant layers, swelling or erosion of the matrix, accumulation of particles in the medium, amongst others. The experiments show that chitosan/silver nanoparticles complexes are actually released, indicating that both swelling and erosion of the matrix takes place during the release process. The simplest model for drug release, i.e., the Higuchi’s model, fits the observed results surprisingly well, which is a relevant result due to the lack of mathematical modeling for the release of nanoparticles.

Traditional lecture-centered approaches alone are inadequate for preparing students for the challenges of creative problem solving in the STEM disciplines. As an alternative, learnercentered and other high-impact pedagogies are gaining prominence. The Wabash College 3D Printing and Fabrication Center (3D-PFC) supports several initiatives on campus, but one of the most successful is a computer-aided design (CAD) and fabrication-based undergraduate research internship program. The first cohort of four students participated in an eight-week program during the summer of 2015. A second group of the four students was successfully recruited to participate the following summer. This intensive materials science research experience challenged students to employ digital design and fabrication in the design, testing, and construction of inexpensive scientific instrumentation for use in introductory STEM courses at Wabash College. The student research interns ultimately produced a variety of successful new designs that could be produced for less than $25 per device and successfully detect analytes of interest down to concentrations in the parts per million (ppm) range. These student-produced instruments have enabled innovations in the way introductory instrumental analysis is taught on campus. Beyond summer work, the 3D-PFC staffed student interns during the academic year, where they collaborated on various cross-disciplinary projects with students and faculty from departments such as mathematics, physics, biology, rhetoric, history, classics, and English. Thus far, the student work has led to three campus presentations, four presentations at national professional conferences, and three peer-reviewed publications. The following report highlights initial progress as well as preliminary assessment findings.

Ancient silver artifacts, when exposed to environments that contain sulfides (H2S), become tarnished and a black film is formed on the surface. The current study deals with the role of copper content and oxygen in the formation of tarnishing in the silver alloys 0.925, 0.800 and 0.720. An ammonium sulfide solution was used as an accelerator of the tarnishing process for different immersion conditions. The analysis of the tarnishing layer in silver alloys was performed by Raman Spectroscopy, Scanning Electron Microscopy - Energy Dispersive X-ray spectroscopy (SEM-EDS) and X-Ray Fluorescence (XRF). The formation of the tarnishing layer was found to be influenced by copper and oxygen contents. The corrosion products under the conditions studied were found to be mainly acanthite and jalpaite.

Corundum-structured α-In2O3 was grown by mist chemical vapor deposition (CVD) on sapphire substrates with the use of α-Ga2O3 buffer layers. The use of ozone (O3) and thermal annealing in air were effective for improved surface morphology and electrical properties of the α-In2O3 layer. MOSFETs were fabricated using the α-In2O3 layer, where the residual electron concentrations were temporary reduced by doping Mg acceptors. Nevertheless the MOSFETs showed the best field-effect mobility of as high as 187 cm2/V⋅s and the best effective mobility of as high as 240 cm2/V⋅s, suggesting high potential of α-In2O3 MOSFETs.

Carbon nanotube (CNT) sock formation is required for the continuous synthesis of CNT thread or sheet using the gas phase pyrolysis method. Nanometer diameter CNTs form and are carried along the reactor tube by gas flow. During the flow, the CNT stick to each other and form bundles of about 10-100 nm diameter. Coupling of the CNT bundles in the flow leads to the formation of a centimeter diameter CNT sock with a wall that is hundreds of nanometers thick. Understanding the multiscale phenomena of sock formation is vital for optimizing the CNT synthesis and manufacturing process. In this work, we present a multiscale model for the CNT bundle agglomeration inside a horizontal gas phase pyrolysis reactor. The interaction between CNT bundles was analyzed by representing the attraction forces between CNTs using a discrete phase modeling method. Flow in the synthesis reactor was studied using a computational fluid dynamics (CFD) technique with multiphase flow analysis. A model was proposed to represent the coupling between CNT bundles and the gas flow. The effect of different CNT bundles on the agglomeration phenomenon was analyzed. The modeling results were also compared with experimental observations.

Two dimensional (2D) thin transition metal dichalcogenides are being widely investigated for optoelectronics applications. Here, we report on the interfacial study of WSe2 with photo-absorber materials for efficient charge transport using Kelvin Probe Force Microscopy (KPFM) for solar cell applications. The WSe2 in these experiments was synthesized using Chemical Vapor Deposition (CVD) with a WO3 powder and Se pellets as the precursors, where the selenium was placed upstream in an Ar carrier gas within the furnace at a temperature zone of 260-270°C. For the interfacial analysis, nanoscale KPFM measurements show an average surface potential of 125 meV for the CVD synthesized WSe2 flakes. KPFM measurements signify that a thin layer of WSe2 can be used to suppress back recombination of carriers between the electron transport layer (ETL) and the absorber layer. A proper band alignment between ETL and absorber layer helps to increase the overall device performance, which we will elaborate upon in this work. Capacitance-voltage and capacitance-frequency measurements were measured to study the role of defects.

We fabricate and characterize metal-oxide-semiconductor (MOS) devices with graphene as the gate electrode, 5 or 10 nm thick silicon dioxide as the insulator, and silicon as the semiconductor substrate. We find that Fowler-Nordheim tunneling dominates the gate current for the 10 nm oxide device. We also study the temperature dependence of the tunneling current in these devices in the range 77 to 300 K and extract the effective tunneling barrier height as a function of temperature for the 10 nm oxide device. Furthermore, by performing high frequency capacitance-voltage measurements, we observe a local capacitance minimum under accumulation, particularly for the 5 nm oxide device. By fitting the data using numerical simulations based on the modified density of states of graphene in the presence of charged impurities, we show that this local minimum results from the quantum capacitance of graphene. These results provide important insights for the heterogeneous integration of graphene into conventional silicon technology.

An ultra-thin LiF layer in conjunction with an Al layer is employed as the electron collector for the a-Si:H based single-junction thin film photovoltaic cell. The cell has the structure of boron doped μ-SiOx (hole collector) - intrinsic a-Si:H (photoactive layer) - LiF / Al (electron collector and back electrode). The substrate used is U type Asahi glass, which is also acting as the transparent front electrode. For the cell with the 1.5 nm thick LiF layer, annealed at 120°C, the open current voltage (VOC) of 0.936 V, the short current density (JSC) of 13.598 mA/cm2, and the fill factor (FF) of 0.690 are achieved. The JSC and VOC values are comparable to the values measured for the a-Si:H based p-i-n reference cell, but the FF value is found to be lower, which is attributed to the losses due to recombination at the intrinsic a-Si:H / LiF / Al junction. The current versus voltage measurements are carried out under the standard test conditions. The JSC values are corrected according to the external quantum efficiency measurements of the cells in the AM1.5 spectrum region between 270 nm and 800 nm.

Two-dimensional group IV layers beyond graphene, as silicene, germanene and the Sn-based stanene, have been recently synthesized by molecular beam epitaxy. Density Functional Theyory (DFT) calculations predict low-buckled structures for these 2D nanosheets, with a hexagonal honeycomb conformation, typical of the graphene-like surfaces. The buckling parameter δ increases from Si to Sn-based layers, with a maximum predicted of 0.92 Å for stanene. High-buckled structures for these materials resulted to be unstable. We have previously shown that for silicene and germanene, the origin of the buckled structure resides on the pseudo Jahn-Teller puckering distortion, resulting from non-adiabatic effects. It has been shown that hexagermabenzene, the single hexagonal unit of germanene, is subject to a strong vibronic coupling whose origin is the pseudo Jahn-Teller effect. This coupling resulted to be around ten times larger than the one obtained for hexasilabenzene. For stanene, an additional effect needs to be considered to understand the origin of buckling: the spin-orbit coupling (SOC). This SOC contributes to open an electronic band gap, enabling the use of these layers as nanoelectronic components. In this work, we present an analysis based on DFT in the Zeroth-Order Regular Approximation (ZORA) for both scalar relativistic and spin-orbit versions that quantify the influence of the spin-orbit coupling in the puckering of Sn6H6. Also, under the linear vibronic coupling model between the ground and the lowest excited states, we present the pseudo Jahn-Teller contribution. The scalar ZORA approximation is used to perform time-dependent DFT calculations to incorporate the low-energy excitations contributions. Our model leads to the determination of the coupling constants and predicts simultaneously the Adiabatic Potential Energy Surface behavior for the ground and excited states around the maximum symmetry point. These values allow us to compare the Jahn-Teller relevance in buckling with the other group IV layers.

LaFe13−xSix compounds display a giant magnetocaloric effect near 200 K. The insertion of light elements (H, C) is used to improve the Curie temperature near ambient temperature for magnetic refrigeration applications. We have developed a synthesis method with a short annealing treatment compared to classical melting techniques. The parent intermetallic alloys were synthesized by high energy ball milling. The insertion of H atoms was carried out using a Sievert apparatus and the carbon atom was inserted by solid/solid reaction. Moreover, structural and magnetic results were carried out by neutron diffraction and Mössbauer spectrometry for H content (y = 0.7,1.5) and C content (y = 0.7). The cell parameter and the Fe magnetic moments versus temperature are determined. The misunderstanding on interstitial site is clarified. The magnetovolume effect on the Curie temperature is explained by combination of the structural and magnetic properties. The advantages and drawbacks of each type of element insertion are discussed.

Diamond is a promising wide band-gap semiconductor material for use in devices; therefore a thorough understanding of the surface electronic structure is important. The Kelvin Probe (KP), Surface Photovoltage / Surface Photovoltage Spectroscopy (SPV/SPS) and Ambient Pressure Photoemission Spectroscopy (APS) techniques are commonly applied to traditional and organic semiconductor materials. The application of these techniques to synthetic and natural diamond samples provides some challenges: surface charge on the samples and atypical capacitive interaction with the KP tip. In this study, measurements using a combination of KP, SPV/SPS and APS techniques are taken of samples of natural and synthetic diamond samples to investigate their surface electronic structure and compare their different properties. These techniques are all non-contact and non-destructive. The Fermi Level position of the diamond samples was found to vary, typically between 4.3 – 4.9 eV, depending on the light illumination. For example, when a natural diamond sample was illuminated with 400 nm light from a 150W Quartz Tungsten Halogen light source, there was a surface photovoltage response of ∼250 mV. The oxygen terminated synthetic diamond sample required near continuous illumination at low visible wavelengths in order to retain sufficient conductivity to allow measurement with the Kelvin Probe. By contrast, the natural diamond samples measured showed good conductivity in the layers underneath the top surface. In summary, the KP, SPV/SPS and APS measurement techniques provided some interesting information on the diamond samples and an initial investigation of their surface electronic states is performed.

Semiconducting iron disilicide (β-FeSi2) island grains of 50-100 nanometers in size were formed on the surface of Au-coated 3C-SiC powder by metal-organic chemical vapor deposition. On the surface of 3C-SiC powder, the Au-Si liquidus phase was obtained via a Au-Si eutectic reaction, which contributed to the formation of the β-FeSi2 island grains. This β-FeSi2/SiC composite powder could evolve hydrogen (H2) from methyl-alcohol aqueous solution under irradiation of visible light with wavelengths of 420-650 nm.

Mechanical damage of non-metallic nuclear wasteforms can be caused by electrical fields induced by decaying clusters of radionuclides surrounded by an insulating matrix. We assess the electric fields near clusters with decaying radionuclides 244Cm, 241Am, 238,239Pu and 137Cs in a glass matrix determining that matrix destruction can gradually occur via electric breakdown discharges and diffusion-controlled change in form of clusters. The most important parameters that control potential matrix destruction are the radioactive cluster (inhomogeneity) size, radionuclide specific radioactivity and effective electrical conductivity of the matrix.

Aluminum alloys have increased their use due to the properties such as low density, resistance to corrosion under environmental conditions and mechanical properties. In this work, the alloying elements are immiscible promoting dendrites formation with different phases attributed to zinc and tin. The applied mechanical stresses promoted the modification of the dendrite sizes (interdendritic space) as well as pore sizes and shapes. The microhardness decreased in the ternary Al-Zn-Sn alloy with a subsequent increase caused by microstructural changes after cold work. By XPS, the metallic elements were detected with an aluminum oxide layer.

In this work, we have demonstrated the light concentration from zero-contrast gratings (ZCG) subwavelength structures and compared the light concentration properties of previously proposed high-contrast gratings (HCG) to the ZCG micro concentrating lenses. To address the challenges of potential HCG fabrication, the difference between ZCG and HCG micro lenses is investigated numerically and found both of these subwavelength grating structures have similar light concentration characteristics. To gain deeper understanding of this phenomenon, we have explored the light concentration formation process and discussed the concentration mechanism in detail. Our work will be promising to provide a new ZCG micro lens potentially with easier and more controllable fabrication and could be utilized for various integrated nanophotonics applications, from optical cavities, read/write heads and concentrating photovoltaics.

Monitoring and understanding of corrosion on nuclear sites is key to safe asset management (predicting plant life, assessing efficacy of corrosion inhibitors for plant lifetime extension) and supporting informed choice of decontamination methods for steels due for decommissioning. Recent advances in Quartz Crystal Nanobalance (QCN) technology offer a means to monitor corrosion in-situ in radiologically harsh environments, in real time and with high sensitivity.

Oxalic acid has been widely used in nuclear facilities as a corrosion inhibitor for carbon steels and as a decontamination cleaning agent due to its ability to remove rust from the surface of ferritic metals and alloys. As an exemplar system for decontamination, the corrosion behavior of pure iron samples in 1 wt% oxalic acid solution has, for the first time, been measured in simulated radioactive environments in real time, in situ using the QCN. Results show that the QCN is a promising tool for studying the efficacy of oxalic acid decontamination agent formulations with the sensor providing useful mechanistic information regarding decontaminating agent mode-of-action derived from the mass change (gain or loss) in real time when a quartz crystal is immersed in oxalic acid solution in simulated and non–simulated radioactive environments.