Copper Indium Sulfide (CIS)-based quantum dots (QDs) are considered as a safer alternative compared to carcinogenic cadmium- and lead-based QDs. Here, we present a facile, high throughput, and non-injection method of synthesizing CIS-based QDs. The structure, shape, size, and crystalline structure of the synthesized QDs were studied using high resolution transmission electron microscopy (HRTEM). The effects of temperature and compositional dependency on the structure and optical properties of the resulting QDs were investigated using elemental, absorption, photoluminescence (PL), and time-resolved spectroscopic analyses. We observed that a gradient increase of temperature during the core growth, as well as addition of excess indium (In) and zinc (Zn) precursors during core and core/shell synthesis, at low growth temperatures, resulted in QDs with improved PL and lifetime. The large Stokes shift, broad emission spectra, and long-lived emission of the synthesized QDs reveal their potential applicability to third generation photovoltaic and optoelectronic devices.

Kinetic Monte Carlo (KMC) methods have been a successful technique for accelerating time scales and increasing system sizes beyond those achievable with fully atomistic simulations. However, a requirement for its success is a priori knowledge of all relevant reaction pathways and their rate coefficients. This can be difficult for systems with complex chemistry, such as shock-compressed materials at high temperatures and pressures or phenolic spacecraft heat shields undergoing pyrolysis, which can consist of hundreds of molecular species and thousands of distinct reactions. In this work, we develop a method for first estimating a KMC model composed of elementary reactions and rate coefficients by using large datasets derived from a few molecular dynamics (MD) simulations of shock compressed liquid methane, and then using L1 regularization to reduce the estimated chemical reaction network. We find that the full network of 2613 reactions can be reduced by 89% while incurring approximately 9% error in the dominant species (CH4) population. We find that the degree of sparsity achievable decreases when similar accuracy is required for additional populations of species.

The multiferroic material YbMnO3 has been reported to exhibit bothferroelectric and antiferromagnetic orders in the ground state. Of these twoorders, the ferroelectric order is associated with theP63/mmc-to-P63cm structural transition, which occursaround 1270 K. The interesting feature of the ferroelectric state is that acloverleaf domain structure with a pseudo-six-fold symmetry is observed intransmission electron microscopy images with the beam incidence parallel to thehexagonal axis. To understand the origin of the formation of the cloverleafdomain structure, we have examined the crystallographic features of theferroelectric state in YbMnO3 by transmission electron microscopy. Inthis study, particularly, we adopted the experimental condition that electronbeam incidences are perpendicular to the hexagonal axis. It was, as a result,found that there existed various ferroelectric domain structures including thecloverleaf domain structure under the present condition. The notable feature ofdomain structures found in this study is that each domain structure basicallyconsists of six domains, whose domain boundaries are terminated at one point.Because this feature makes us reminiscent of a discommensurate structure in anincommensurate state, we took high-resolution electron micrographs of areasincluding domain boundaries. Their analysis indicated that a domain boundarycould be identified as a discommensuration with a phase slip of π/3.It is thus understood that the cloverleaf domain structure should be one ofdomain morphologies for a discommensurate structure, which is related to thebreak of the translational symmetry.

While graphene has unique electrical and mechanical properties, it is not soluble in most common solvents. Partially reducing graphene oxide (prGO) will remove some of the functional groups while still maintaining solubility, producing an intermediate between graphene oxide and reduced graphene oxide. This research investigated the properties of prGO as well as those of prGO sheets incorporated with gold and platinum nanoparticles (Au/Pt-prGO) using FTIR, Raman, TEM and HRTEM.

Glucose sensor based on ITO/ZnO NRs/GOx/nafion is fabricated and tested under different glucose concentrations. Hydrothermal growth method along with sol-gel technique is used to grow high quality ZnO nanorods that have well-alignment and high density with an acceptable aspect ratio. The as-grown of ZnO nanorods are used to fabricate a working electrode that can be used for glucose detection in blood after a modification process with GOx and nafion membrane. Annealing at 110 °C helped in improves the crystallinity of the seed layer and as a result, a high density and well alignment as-grown ZnO nanorods were obtained. High sensitivity and short response time were obtained from the fabricated device with an acceptable lower limit of detection.

This study presents a combine experimental and analytical investigation of the toughening behavior in natural fiber-reinforced earth-based composites. A specially designed single fiber pullout apparatus was used to provide a quantitative determination of interfacial properties that are relevant to toughening brittle materials through fiber reinforcement. The parameters investigated included a specially designed high strength earth-based matrix comprising of 60% laterite, 20% clay and 20% cement. The toughening behavior of whisker-reinforced earth-based matrix is analyzed in terms of a whisker bridging zone immediately behind the crack tip and interface strength. This approach is consistent with microscopy observations which reveal that intact bridging whiskers exist behind the crack tip as a result of debonding of the whisker-matrix interface. Debonding with constant frictional stress was obtained and this formed the basis for the analytical model considered and the underlying crack-microstructure interactions associated with Resistance-curve behavior was studied using in situ/ex situ optical microscopy to account for the bridging contribution to fracture toughness. The effect of multiple toughening mechanisms (debonding and crack bridging) was elucidated and the implications of the results are considered for potential applications in the design of robust earth-based building materials for sustainable eco-friendly homes.

The paper presents the results of numerical modeling of thermomechanical stresses and thermal fields for conditions of erosion-resistant electrode coatings of vacuum and gas discharge switching devices with W-Ti-Cu and W-Mo-Cu structures at local temperature and electric current influence in axially symmetrical approximation. The efficiency assessment of intermediate layers introduction by comparison of interlaminar mechanical stresses is carried out. It is shown that introduction of titanium interlayer in the coating with W Cu structure results in considerable (more than two times) decrease of internal thermomechanical stresses between layers that increases coating resistance to delamination. The optimum value of interlayer thickness at which the minimum thermomechanical stresses are provided is determined.

The reaction pathway for shallow arsenic doping of silicon by methylarsenic acid molecules directly grafted on oxide-free, H-terminated Si(111) surfaces is unraveled combining Infrared absorption spectroscopy, X-ray Photoelectron Spectroscopy, Low Energy Ion Scattering and ab initio Molecular Dynamics simulations. The overall driving force is identified as a thermodynamic instability of As+5 in contact with silicon, which initiates a self-decomposition of chemisorbed methylarsenic molecules at ∼600 K. As the temperature is increased, the As-C bond breaks -- the weakest link of the adsorbed molecule -- with release of the organic ligand and a rearrangement from a monodentate to a bidentate bonding configuration. In this process, oxygen atoms evolve by partial desorption as H2O and partial incorporation into the surface Si atom backbonds. At ∼1050 K, diffusion of As into the sub-surface region of silicon is observed. There is no evidence for As desorption and no remaining C contamination.

Thin-film transistors (TFT) were fabricated at room-temperature (RT) utilizingzinc oxide (ZnO) channel and indium molybdenum oxide (IMO) electrodes. Thecommon bottom-gate TFTs were fabricated on commercially available thermalsilicon oxide (100 nm thick) coated silicon wafers. A total of 100 devices weremade in a 1 inch square area as 10 × 10 matrix, by varying the channelwidth and length, between 5 µm and 300 µm. Output and transfercharacteristics of the fabricated devices were extracted from a semiconductorparameter analyzer. A threshold voltage (V Th) of 10 V and an I ON/I OFF ratio of 1 × 10-5 were obtained. The impact ofchannel dimensions on the device performance was investigated, confirming thatthe saturation current (I sat) is directly proportional to the channel width (W), andinversely proportional to channel length (L), in agreement withfield effect device theory.

A wurtzite-strained nitride Quantum Well Laser has been characterized for short distance communication wavelength. InN and In0.25Ga0.75N have been chosen as well material and barrier material respectively with In0.4Al0.6N SCH layers at the end of barrier layers to improve the carrier and photon confinement within the active region. This structure shows less compressive strain (7.33%) with respect to previously proposed structure which makes the structure more suitable for fabrication. To obtain the electronic band structure, self-consistent method with k.p formalism has been performed where valence band mixing effect, strain effect and spontaneous and piezoelectric polarization effect has been included. From the electronic characteristics, the optical properties have been performed with numerical model. From the optical properties, the structure has been found as TE polarized with C1-HH1, C1-LH1, C2-HH1 and C2-LH1 dominating transition elements. From the performance of the numerical model, 4731.98 cm−1 optical gain for TE polarization at 1315.5 nm emission wavelength and 8.017×1027 cm−3s−1eV−1 spontaneous emission rate at 1301.7nm wavelength have been found for 12Å well width, 17Å barrier width and 52Å SCH layer width at 5×1019 cm−3 carrier density. The obtained properties have been shown a good agreement with previously published works.

Polyethylene terephthalate (PET) is an interesting flexible substrate material for many applications in electronics since it is inexpensive and has good mechanical and electrical properties. Due to these good properties there is increasing interest in using PET in applications involving harsh environments. However, PET has relatively poor thermal properties, which may cause reliability concerns in demanding conditions. Above its glass transition temperature, Tg, PET is susceptible to hydrolysis, which may considerably restrict its use. Hydrolysis breaks the molecular structure of PET and makes the material mechanically unreliable. This paper reports the reliability of PET films in an LCD display application and in RFID tags in thermal and humid conditions. Additionally, neat PET films were studied. Several thermal cycling and humidity tests were used. The results clearly showed that above the Tg of PET the combined effect of humidity and high temperature caused PET to become brittle leading to considerable reliability problems. However, in dry thermal cycling conditions and in humid conditions below the Tg of PET, the reliability of PET was found to be excellent even under prolonged exposure.

We are reporting the formation of free-standing graphene foam (GF) via a noveltwo-step process, in which a polyurethane (PU) foam is first dip-coated withgraphene oxide (GO) and subsequently the dried GO-coated-PU is heated innitrogen atmosphere at 1000°C. During the pyrolysis of theGO-coated-PU, GO is reduced to GF whereas PU is simultaneously decomposed andreleased completely as volatiles in a step wise mass-loss mechanism. Morphologyof the formed GF conforms to that of the pure PU foam as indicated by thescanning electronic micrographs. Polydimethylsiloxane (PDMS) was successfullyinfiltrated inside the GF to form flexible and stretch-able conductors. TheGF-PDMS composite was tested for it’s pressure and strain sensingcapabilities. It is shown that a 30% compressive strain changes resistance ofthe GF-PDMS composite to about 800% of it’s original value. Sincedensity of the formed GF is tunable, therefore, the pressure/strain sensivity ofthe GF-PDMS composite is also tunable.

A water-developable sugar-based negative resist material was developed. This material enables the use of pure water in the development process of electron beam (EB) green lithography instead of conventionally used aqueous alkaline developers and organic solvents. The sugar-based negative resist material was developed by replacing the hydroxyl groups in alpha-linked disaccharides with EB-sensitive 2-methacryloyloxyethyl groups. The sugar-based negative resist material features highly efficient crosslinking and low film thickness shrinkage under EB irradiation. It is demonstrated to be applicable to green lithography with a 100– 500 nm line-and-space pattern and an EB exposure dose of 18 μC/cm2.

An investigation of the electronic structure of charged vacancies and X(C), X=(As, Sb, P) substitutional centers in diamond has been carried out by means of ab initio density functional theory. The revised Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE06) was utilized for the total energy calculation. The equilibrium geometry, defect charge transition levels and energetics of the vacancies and substitutional centers were determined. It is found that substitutional As and Sb introduce a donor level into the band gap about 0.5 eV with respect to the conduction band minimum (CBM), therefore, these elements may be a good choice for achieving n-type diamond. From a technological point of view, however, fabrication of As and Sb doped diamond would be challenging due to its high, positive formation energy.

Mn-Ga alloys have shown promising hard magnetic properties, even though thesealloys contain no rare-earth metals. However, much work is needed before Mn-Gaalloys become viable permanent magnets for applications. One of the challengesis to enhance the remanence. One technique to improve this property is applyinga magnetic field during the heat treatment process. Magnetic annealing canpromote phase transformation of the phases with high magnetic moment. Thisresults in an increased remanence. Bulk samples of Mn-Ga alloys were made bymechanically alloying in order to create a nanostructured composite, followed byheat treatments in the presence of a 31 T magnetic field. The heat treatmenttemperatures were kept low in order to keep the refined microstructure. All thealloys exhibit hard magnetic properties at room temperature with largecoercivity. This work reports findings of magnetic field annealed Mn-Ga bulkthat exhibit high coercivities up to 19.4 kOe and increased remanence of 50%over the binary system, achieving values up to 6.9 emu/g. This is the highestcoercivity reported in bulk Mn-Ga samples.

We performed dynamical cluster analysis in a Cu-Zr-Al based glass-forming metallic liquid using an unsupervised machine learning algorithm. The size of the dynamical clusters is used to quantify the onset of cooperative dynamics as the underlying mechanism leading to the Arrhenius dynamic crossover in transport coefficients of the metallic liquid. This technique is useful to directly visualize dynamical clusters and quantify their sizes upon cooling. We demonstrate the robustness of this algorithm by performing sensitivity analysis against two key parameters: number of mobility groups and inconsistency coefficient of the hierarchical cluster tree. The results elucidate the optimized range of values for both of these parameters that capture the underlying physical picture of increasing cooperative dynamics appropriately.

TlBr crystals have superior radiation detection properties; however, their properties degrade in the range of hours to weeks when an operating electrical field is applied. To account for this rapid degradation using the widely-accepted vacancy migration mechanism, the vacancy concentration must be orders of magnitude higher than any conventional estimates. The present work has incorporated a new analytical variable charge model in molecular dynamics (MD) simulations to examine the structural changes of materials under electrical fields. Our simulations indicate that dislocations in TlBr move under electrical fields. This discovery can lead to new understanding of TlBr aging mechanisms under external fields.

Effects of defect on ferroelectric stability in PbTiO3 (PTO) thinfilms have been investigated using molecular dynamics with first-principleseffective Hamiltonian. In this paper, oxygen vacancy (Vo) has been considered tostudy the hysteresis loop, spontaneous polarization as a function of filmthickness. Vo has been modeled as a charged point defect. Density functionaltheory (DFT) calculations are performed to determine the Vo-induced localizedfields (both mechanical and electrical) and the calculated DFT results are usedas inputs to molecular dynamics simulations in a large system. The strain fieldinduced by the Vo is calculated by DFT calculations and fitted by the continuumstrain modeling, and the electrostatic field is given by the superposition ofthe Vo-induced field and the external field. Vo significantly reduces thespontaneous polarization and increases the critical thickness.

Poly(ε-caprolactone) (PCL) biopolymer nano- and micro-fibers have been fabricated at high rates up to 14.0 grams per hour using a needleless and collectorless alternating current electrospinning technique. By combining the ac-voltage, glacial acetic acid (AA) as the solvent and sodium acetate (NaAc) as an additive, beadless PCL fibers with diameters tunable from 150 nm to 2000 nm, varying surface morphology and degree of self-bundling were obtained. In this new approach, the addition of NaAc plays a crucial role in improving the spinnability of PCL solution and fiber morphology. NaAc revealed the concentration-dependent effect on charge transfer and rheological properties of the PCL/AA precursor, which results in broader ranges of spinnable PCL concentrations and ac-voltages suitable for rapid manufacturing of PCL-based fibers with different textural properties.

We employ a combination of the density-functional theory and the dynamical mean-field theory to study the electronic structure of selected rare-earth sesquioxides and dioxides. We concentrate on the core-level photoemission spectra, in particular, we illustrate how these spectra reflect the integer or fractional filling of the 4f orbitals. We compare the results to our earlier calculations of actinide dioxides and analyze why the core-level spectra of actinide compounds display a substantially reduced sensitivity to the filling of the 5f orbitals.