Chemical bonding in native oxides of GaAs, before and after etching, is detected by X-Ray Photoelectron Spectroscopy (XPS). It is correlated with surface energy engineering (SEE), measured via Three Liquid Contact Angle Analysis (3LCAA), and oxygen coverage, measured by High Resolution Ion Beam Analysis (HR-IBA).

Before etching, GaAs native oxides are found to be hydrophobic with an average surface energy, γT, of 33 ± 1 mJ/m2, as measured by 3LCAA. After dilute NH4OH etching, GaAs becomes highly hydrophilic and its surface energy, γT, increases by a factor 2 to a reproducible value of 66 ± 1 mJ/m2. Using HR-IBA, oxygen coverage on GaAs is found to decrease from 7.2 ± 0.5 monolayers (ML) to 3.6 ± 0.5 ML. The 1.17 ratio of Ga to As, measured by HR-IBA, remains constant after etching.

XPS is used to measure oxidation of Ga and As, as well as surface stoichiometry on two locations of several GaAs(100) wafers before and after etching. The relative proportions of Ga and As are unaffected by adventitious carbon contamination. The 1.16 Ga:As ratio, measured by XPS, matches HR-IBA analysis. The proportions of oxidized Ga and As do not change significantly after etching. However, the initial ratio of As2O5 to As2O3, within the oxidized As, significantly decreases after etching from approximately 3:1 to 3:2.

Absolute oxygen coverage, as a function of surface processing, is determined within 0.5 ML by HR-IBA. XPS offers insight into these modifications by detecting electronic states and phase composition changes of GaAs oxides. The changes in surface chemistry are correlated to changes in hydro-affinity and surface energies measured by 3LCAA.

We present theoretical calculations of the line shapes of emission spectra of ZnO micro spheres (MSs), including the exciton-polariton and Purcell effect. Our calculation explains the red shift of emission peaks of whispering gallery modes (WGMs) in UV range commonly observed in ZnO MSs. We show that the red shift of the UV emission peak is caused by the combination of cavity effect and the polariton dispersion. The positions and relative strengths of sharp peaks arising from WGMs are also simulated by our calculation, and theoretical predictions match well with experimental data. Our calculation provides useful guide lines for the design of MS cavities for applications in white-light illumination, optical communication, and biosensing.

Electrical properties such as conductivity and permittivity of biological material have notable dependency on frequency. These frequency dependent changes in biomaterial properties can play a prominent role in impedance signature of Electrical Impedance Myography (EIM). EIM is a non-invasive painless four electrode measurement tool, measuring the impedance based on the response of the low amplitude alternating current. In this study, multifrequency Electrical impedance Myography assessment was performed using an applied range of frequencies for getting valuable insight of the biomaterials. In this paper, the objective of our study is to explore the effects of different sized malignant tumor in female breast tissue on the multi-frequency signature of EIM. In this study, a finite element model of a female breast has been developed based on electro-biophysical data for each malignant tissue within a frequency range of 2 GHz to 3 GHz and log frequency vs resistance and log frequency vs reactance of EIM have been analyzed for various sized tumor on breast. It is found that the slope of log reactance vs. frequency and resistance vs log frequency decrease with increasing tumor size. For instance, the percentage deviation of log reactance slope for 8 mm tumor and 6mm tumor from 2 mm (1mm radius) tumor size is 4.12% and 0.412% respectively. The study provides evidence that evaluation of the frequency dependent impedance data can provide rich assessment of the abnormal biological tissue.

Effects of nitrogen impurity on ZnO crystal growth on Si substrates have been investigated. The quantitative analysis on the surface morphology deriving height-height correlation function indicates that adsorbed nitrogen atoms suppress the secondary nucleation and enhance adatom migration. The resultant films have smooth surface as well as large grain size up to 24 nm even for small thickness of 10 nm. ZnO films fabricated by using such films as buffer layers possess high crystal quality, where the full width at half maximum of (002) rocking curve is 0.68°, one-fourth of that for films fabricated without nitrogen.

In this study, we report developments towards the application of large zeolite particles, with diameter ca. 40 μm, as tracers in Positron Emission Particle Tracking (PEPT) imaging using 68Ga. The influence of intrapore Na+ and TEA+ (tetraethylammonium) cation concentrations and framework Si/Al ratio on the morphology of mordenite particles has been investigated, advancing understanding of the relationship between these factors. Moreover, the influence of ethanol concentration in the gel during aging on intrapore cation concentration, Si/Al ratio and particle morphology has also been investigated. Additionally, facile ion-exchange between aqueous Ga3+ and intrapore H+ in mordenite has been demonstrated. The influence of pH and gallium speciation on ion-exchange has been investigated to determine favourable conditions for 68Ga3+ uptake by the zeolite.

Poly(ε-caprolactone) (PCL) is one of the leading biocompatible and biodegradable polymers. However, the mechanical property of PCL is relatively poor as compared with that of polyolefins, which has limited the active applications of PCL as an industrial material. In this study, to enhance the mechanical property of PCL, cellulose nanofibers (C-NF) with high mechanical property, were employed as reinforcement materials for PCL. The C-NF were fabricated via the electrospinning of cellulose acetate (CA) followed by the subsequent saponification of the CA nanofibers. For the enhancement of the mechanical property of the PCL composite, the compatibility of C-NF and PCL was investigated: the surface modification of the C-NF was introduced by the ring-opening polymerization of the ε-caprolactone on the C-NF surface (C-NF-g-PCL). The polymerization was confirmed by the Fourier transform infrared (FTIR) spectroscopy. Tensile testing was performed to examine the mechanical properties of the C-NF/PCL and the C-NF-g-PCL/PCL. At the fiber concentration of 10 wt%, the Young’s modulus of PCL compounded with neat C-NF increased by 85% as compared with that of pure PCL, while, compounded with C-NF-g-PCL, the increase was 114%. The fracture surface of the composites was analyzed by scanning electron microscopy (SEM). From the SEM images, it was confirmed that the interfacial compatibility between PCL and C-NF was improved by the surface modification. The results demonstrated that the effective surface modification of C-NF contributed to the enhancement of the mechanical property of PCL.

Since ancient times, lubricants have been used to reduce friction and wear problems of mechanical systems. However, nowadays, there is a constant effort to improve their performance through additives so that they can accomplish properly in this modern world. In that sense, in this study, it was proposed the use of Poly(ε-Caprolactone) (PCL) as a biodegradable additive in Castor oil. The effect that this additive has on the tribological properties of AISI 4140 steel/Al2O3 tribosystem was analyzed. For this purpose, PCL was dissolved in Castor oil at 65 °C for 15 minutes. Later, once the lubricant formulations got into room temperature, friction tests were conducted with a ball-on-disk configuration. Several experiments were systematically carried out in order to study the factors that could influence the performance of the tribological system, for instance: additive concentration, velocity, temperature, and wear track radius. The kinetic friction coefficient was used to analyze the results as an output variable. The parameters in which the best friction behavior was observed were employed again to compare the efficiency of the polymeric additive by profoundly analyzing and comparing the wear response of the system. The PCL additive showed great results by decreasing friction up to 30% compared to the neat Castor oil. Nevertheless, as the opposite effect, this additive increased the steel wear to almost half an order of magnitude. Given the above, this investigation showed that, with further studies, Poly(ε-Caprolactone) could be used as an additive in vegetable oil-based lubricants for the improvement of friction performance.

Natural structural materials (NSMs) such as nacre, teeth, bones and crustacean exoskeleton are usually made of weak biomaterials arranged in specific structural design imparting them remarkable mechanical characteristics. Such hierarchical structural layouts found in nature encourage designing of mechanically desirable synthetic structural materials (SSMs). Among variety of natural hierarchical layouts, this paper specifically focuses on helicoidal architectural design found in the tough dactyl club of mantis shrimp. We first decode the mechanics behind helicoidal microstructural design and document the development of impact resistant macroscale helicoidal architectured synthetic structural materials (HA-SSMs). Next, near-field electrospinning technique (NFES)- both melt (polycaprolactone) and solution (polyvinylidene fluoride) type has been discussed in detail, as a novel method for developing lab scale 3D biomimetic HA-SSMs in micro-nanoscale. Further, the effect of the helical arrangement, size of substructures and surface treatment on strength and toughness of NFES fabricated HA-SSMs samples is analysed.

Biodegradable material was prepared from cassava starch in combination with zinc oxide nanoparticles (ZnO NPs) to give the properties of microbial growth resistance, glycerin concentrations were varied to 5%, 10%, and 20% (w/v) for the study of the rheological properties. The nanoparticles were characterized by a spectrophotometer where an exciton peak at 370 nm was obtained. The different samples were subjected to a thermomechanical study through an AR-G2 hybrid rheometer, using a parallel plane geometry of 20 mm, a weak gel behavior is observed, it is a slimming material and it is thermostable, it is also established that the zinc oxide concentration nanoparticles do not affect the mechanical behavior of the material.

Single-phase multiferroic materials have attracted considerable attention among scientists, due to the strong drive in industry towards device miniaturization, addition of new functionalities, etc. Currently, most of the discovered materials have at-least one ferroic order active only at low temperatures, thereby hindering their induction into practical devices. κ-Al2O3-type AlxFe2-xO3 (x-AFO) oxides belong to a new class of metastable multiferroic compounds (space group: Pna21), with relatively high Curie temperatures. The current work investigates the effect of thin film deposition conditions on the ferroelectric and ferrimagnetic properties of Al0.5Fe1.5O3 (0.5-AFO). Substrate temperature and oxygen partial pressure during deposition were found to be the critical parameters in obtaining high quality films. Optimizing the deposition conditions of 0.5-AFO enabled observation of both ferroelectricity and ferrimagnetism at room temperature.

This work presents the mesoscale step of a theoretical study of a Polymer-Clay Nanocomposite (PCN) composed by starch, pequi vegetable oil and montmorillonite (MMT), a phyllosilicate. In the present study, amylose oligomers, oleic, palmitic and stearic acids in the proportion found in that vegetable oil and MMT were studied, as a simplified model, in order to simulate in multiscale their structural and behavioral correlations. The calculations were carried out by Dissipative Particle Dynamics (DPD), at 363 K, using Materials StudioTM suite. The DPD model had its interaction parameters calculated from previous MD simulations. It was observed that the organic material concentrated near the MMT surfaces, which correlated with the MD results, implying in the validity of the model. The new knowledge acquired about those molecular systems, works as a starting point to build more complex models and, if the theoretical work converge with the experimental findings, encourages further studies in the design of PCNs with biopolymers.

Fully inorganic lead halide perovskite nanocrystals (NCs) are of interest for photovoltaic and light emitting devices due to optoelectronic properties. Understanding the surface chemistry of these materials is of importance as surface defects can introduce trap-states which reduce their functionality. Here we use Density Functional Theory (DFT) to model surface defects introduced by Pb2+ on a CsPbBr3 NC atomistic model. Two types of defects are studied: (i) an under-coordinated Pb2+ surface atom and (ii) Pb2+ atomic or molecular adsorbents to the NC surface. From the DFT calculations we compute the density of states (DOS) and absorption spectra of the defect models to the pristine fully-passivated NC model. We observe that for the low surface defect regime explored here that neither (i) or (ii) produce trap-states inside of the bandgap and exhibit bright optical absorption for the lowest energy transition. From the models studied, it was found that the Pb2+ atomic absorbent provides broadening of the conduction band edge, which implies chemisorption of Pb2+ to the NC surface. At higher defect densities it would be expected that Pb2+ atomic absorbents would introduce trap-states and degrade the opto-electronic properties of these materials.

We describe the use of immobilized deoxyribonucleic acid (DNA) in a silica matrix as a biorecognition agent for the detection of albendazole sulfoxide (ASU), the primary metabolite of albendazole and a suspected teratogenic and embryotoxic agent. The biomaterial (DNA-containing gel) was synthesized by physical entrapment of salmon sperm in an inorganic silicate matrix by the sol-gel method. Functionality of the DNA-containing gel was evaluated by comparative offline frontal chromatography followed by HPLC analysis of ASU and caffeine (CAF, control) using DNA-containing gel and DNA-free gel. The DNA-containing gel showed relatively high specific retention for ASU, while CAF showed no retention using frontal analysis. We anticipate that the DNA-containing gel can be implemented to identify the interactions of DNA with other active pharmaceutical ingredients (APIs) and their metabolites in a readily available, sensitive and selective frontal chromatography experiment.

Even though AA 7075 is an aluminum alloy with high mechanical properties, it is not often applied in manufacturing. This is so, because it is considered as very difficult to produce defect free welded joints. This is so, because this alloy has a tendency to hot cracking. The metallurgical problems that appear during welding of AA 7075 have not been fully solved but they have been reduced by applying alloys such as: 4043 and 5356 as filler metals. However, in literature there is little information about the metallurgical effects of these types of filler metals applied in arc welded joints of AA7075. This is especially true for Tungsten Inert gas welding. Therefore, this work is focused in comparing the microstructure and Vickers microhardness in weldments of AA 7075 with ER4043, ER5356 and AA7075 as filler metals. Besides, a set of welded joints with the three different filler metals were quenched after welding in order to modify the final microstructure. The results were evaluated by microstructural analysis focused on the Heat Affected Zone and Vickers microhardness and they were compared among them.

Periodontitis, or conventionally “Gum Disease,” is the infection and inflammation of gingival tissue, and is currently the leading cause of tooth loss in the United States. One of the most effective treatments of periodontitis is guided bone regeneration (GBR); however, current GBR barrier membranes lack high biocompatibility and cell impermeability. The authors of this study evaluated the in vitro viability of previously synthesized Gelatin-Pluronic® F127 hybrid hydrogels as potential GBR barrier membranes through a novel three-partition test involving migration of fluorescent-dyed human dermal fibroblasts. Results showed that cells were unable to migrate across the Gelatin-Pluronic® F127 hybrid hydrogel barrier, whereas control setups with gelatin hydrogel barriers showed cell permeability. In addition, cytotoxicity tests were conducted with fibroblasts plated in both cell mediums that had been incubated while in contact hybrid gels and cell mediums suspended on the surface of hybrid gels during swelling procedures. Fluorescence cell plate readings showed similar cell viability across data from both tests, indicating that Gelatin-Pluronic® F127 hybrid hydrogels are not toxic to cells, and thus biocompatible.

van der Waals (vdW) magnetic materials show promise in being the foundation for future spintronic technology. The magnetic behavior of Fe2.7GeTe2 (FGT), a vdW itinerant ferromagnet, was investigated before and after proton irradiation. Proton irradiation of the sample was carried out at a fluence of 1×1018 cm-2. The magnetization measurements revealed a small increase of saturation magnetization (Ms) of about 4% upon proton irradiation of the sample, in which, the magnetic field was applied parallel to the c-axis. X-ray photoelectron spectroscopy for pristine and irradiated FGT revealed a general decrease in intensity after irradiation for Ge and Te and an increase in peak intensity of unavoidable surface iron oxide. Furthermore, no noticeable change in the Curie temperature (TC =152 K) is observed in temperature dependent magnetization variation. This work signifies the importance of employing protons in tuning the magnetic properties of vdW materials.

Lithium-rich layered oxides such as Li2MnO3 have shown great potential as cathodes in Li-ion batteries, mainly because of their large capacities. However, these materials still suffer from structural degradation as the battery is cycled, reducing the average voltage and capacity of the cell. The voltage fade is believed to be related to the migration of transition metals into the lithium layer, linked to the formation of O-O dimers with a short bond length, which in turn is driven by the presence of oxygen holes due to the participation of oxygen in the redox process. We investigate the formation of O-O dimers for partially charged O1-Li2MnO3 using a first-principles density functional theory approach by calculating the reaction energy and kinetic barriers for dimer formation. Next, we perform similar calculations for partially charged O1-Li2IrO3, a Li-rich material for which the voltage fade was not observed during cycling. When we compare the stability of the oxygen framework, we conclude that the formation of O-O dimers is both thermodynamically and kinetically viable for O1-Li0.5MnO3. For O1-Li0.5IrO3, we observe that the oxygen lattice is much more stable, either returning to its original state when perturbed, or resulting in a structure with an O-O dimer that is much higher in energy. This can be explained by the mixed redox process for Li2IrO3, which is also shown from the calculated magnetic moments. The lack of O-O dimer formation in O1-Li0.5IrO3 provides valuable insight as to why Li2IrO3 does not demonstrate a voltage fade as the battery is cycled, which can be used to design Li-rich battery cathodes with an improved cycling performance.

We present an information-based total-energy optimization method to produce nearly defect-free structural models of amorphous silicon. Using geometrical, structural, and topological information from disordered tetrahedral networks, we have shown that it is possible to generate structural configurations of amorphous silicon, which are superior than the models obtained from conventional reverse Monte Carlo and molecular dynamics simulations. The new data-driven hybrid approach presented here is capable of producing atomistic models with structural and electronic properties which are on a par with those obtained from the modified Wooten-Winer-Weaire (WWW) models of amorphous silicon. Structural, electronic, and thermodynamic properties of the hybrid models are compared with the best dynamical models obtained from using machine-intelligence-based algorithms and efficient classical molecular dynamics simulations, reported in the recent literature. We have shown that, together with the WWW models, our hybrid models represent one of the best structural models so far produced by total-energy-based Monte Carlo methods in conjunction with experimental diffraction data.

This paper presents a novel way to obtain reinforced pores by the dissociation of mixed carbides during sintering. Porous materials have a wide range of applications such as dampeners, light structures, etc. But usually pores act as points of stress concentration and crack nucleation, harming the mechanical properties of these materials. Methods have been developed to control the shape and size of pores but, until now, there are no techniques that allow reinforcing the material around the pores. To address this, steels were prepared by adding 1, 3 and 5 wt.% of Mo1.5Cr0.5C mixed carbide particles to a iron matrix by metal injection moulding. The results showed that during sintering, the dissociation of the carbide followed by the dissolution of the elements in the matrix generated rounded secondary pores with a reinforced vicinity, which increased the mechanical strength of the materials. The presence of rounded pores encircled by an enriched vicinity can allow the production of porous materials with exceptional fatigue strength and fracture toughness.

Frequent switching of resistive memory cell may lead to a local accumulation of Joules heat in the device. Since the ReRAM cells are arranged in crossbar arrays with the two electrodes running perpendicular to each other, the heat generated in one device spreads via common electrode metal lines to the neighboring cells causing their performance degradation. Also cells that do not share any of the two electrodes (e.g. the diagonal array cells) with the hot device may also degrade provided the intermediate cells are set to an on-state establishing thus a continuous thermal conduction path between the heated and the probed device. It is found that the heat conduction along the active Cu electrode is more pronounced than that along the inert Pt electrode. Devices with Rh inert electrode performed better than those with Pt electrode due to better heat conductivity properties of Rh vs Pt. The heat dissipation is also found worse for a heated device with narrow and thin lines causing, however less degradation of more distant neighbor cells than for wide and thick metal lines. Finally, there is a trade-off between dissipating the heat quickly form the heated device to increase its maximum switching cycles and the heat exposure of the neighboring devices.