InSb has been considered as a promising material for spintronic applications owing to its pronounced spin effects as a result of large intrinsic electronic g-factor. In addition, embedding InSb quantum nanostructures in a GaAs matrix could create type-II band alignment, where radiation lifetimes are longer than those of the typical type-I systems. Such characteristics are promising for memory devices and infrared photonic applications. The growth of InSb/GaAs quantum nanostructures by strain driven mechanism using molecular beam epitaxy with low growth temperature, slow growth rate, Sb soaking process prior to In deposition, and small amount of In deposition typically creates a mixture of twin and single nano-stripe structures with truncated pyramid shape. In this work, we further investigate the growth mechanism of such twin InSb/GaAs nano-stripes by controlling the growth conditions, consisting of nanostructure growth duration and growth temperature. When the growth temperature is kept to less than 300°C and In deposition is set to only a few monolayers, we found that 25-40% of formed nanostructures are twin InSb/GaAs nano-stripes. However, when the In deposition is stopped immediately after the spotty reflection high-energy electron diffraction patterns are observed, the ratio of twin nano-stripes to single ones is increased to 50-60%. We therefore describe the growth mechanism of twin nano-stripes as the early state of single nano-stripe formation, where the twin nano-stripes are initially formed during the first monolayer of InSb formation as a result of large lattice mismatch of 14.6%. When In deposition is increased to a few monolayers, the gap between twin nano-stripes is filled up and consequently forms the single nano-stripes instead. With this particular twin nano-stripe growth mechanism, the preservation of high ratio of twin nano-stripe formation can be expected by further reducing the growth temperature, i.e. less than 260°C. These twin nano-stripes may find applications in the fields of spintronics and novel interference nano-devices.

The advent of graphene created a revolution in materials science. Because of this there is a renewed interest in other carbon-based structures. Graphene is the ultimate (just one atom thick) membrane. It has been proposed that graphene can work as impermeable membrane to standard gases, such argon and helium. Graphene-like porous membranes, but presenting larger porosity and potential selectivity would have many technological applications. Biphenylene carbon (BPC), sometimes called graphenylene, is one of these structures. BPC is a porous two-dimensional (planar) allotrope carbon, with its pores resembling typical sieve cavities and/or some kind of zeolites. In this work, we have investigated the hydrogenation dynamics of BPC membranes under different conditions (hydrogenation plasma density, temperature, etc.). We have carried out an extensive study through fully atomistic molecular dynamics (MD) simulations using the reactive force field ReaxFF, as implemented in the well-known Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. Our results show that the BPC hydrogenation processes exhibit very complex patterns and the formation of correlated domains (hydrogenated islands) observed in the case of graphene hydrogenation was also observed here. MD results also show that under hydrogenation BPC structure undergoes a change in its topology, the pores undergoing structural transformations and extensive hydrogenation can produce significant structural damages, with the formation of large defective areas and large structural holes, leading to structural collapse.

In0.06Ga0.94N/GaN superlattices (SLs) grown on sapphire (0001) by metalorganic chemical vapor deposition were studied before and after europium (Eu) ion implantation to understand the strain induced-effects in the SL structure. The implanted SLs were investigated as a function of the thermal annealing temperature up to 1000 °C in nitrogen ambient. Temperature dependent photoluminescence spectra showed a red-shift of the SL emission peaks due the quantum confined Stark effect, followed by a blue-shift due to In atoms out-diffusion from the In0.06Ga0.94N quantum well, for both Eu ions implanted and unimplanted SLs. The amplitude of observed spectral shifts was smaller and the line width of the SLs emission peaks were narrower in the SLs:Eu3+ as compared to the unimplanted SLs. It is concluded that Eu3+ ions modified the strain in the SLs acting like impurity and/or defects getter in implantation degraded SLs resulting in material phase purification and improvements of SLs optical properties.

The dynamics of gas evolution during the thermal oxidation of 30% solutions of tri-n-butyl phosphate (TBP) in Isopar-M saturated with 4.3, 8.2 and 12.0 mol/L nitric acid was investigated in open vessels in the temperature range of 70°C to 150°C. The volume of the released gases has been measured. The influence of the pre-irradiation by accelerated electrons has been determined for the thermolysis and accumulation of liquid products of TBP degradation in the system TBP-Isopar-M-HNO3. The temperature borders of oxidation processes transition to autocatalytic regime have been estimated. It has been shown, that the conditions resulting in growth of autocatalytic oxidation do not exist under heating of single-phase systems in open vessels.

Electron transfer in molecular wires are of fundamental importance for a range of optoelectronic applications. The impact of electronic coherence and ionic vibrations on transmittance are of great importance to determine the mechanisms, and subsequently the type of wires that are most promising for applications. In this work, we use the real-time formulation of time-dependent density functional theory to study electron transfer through oligo-p-phenylenevinylene (OPV) and the recently synthesized carbon bridged counterpart (COPV). A system prototypical of organic photovoltaics is setup by bridging a porphyrin-fullerene dyad, allowing a photo-excited electron to flow between the Zn-porphyrin (ZnP) chromophore and the C60 electron acceptor through the molecular wire. The excited state is described using the fully self-consistent ∆-SCF method. The state is then propagated in time using the real-time TD-DFT scheme, while describing ionic vibrations with classical nuclei. The charge transferred between porphyrin and C60 is calculated and correlated with the velocity autocorrelation functions of the ions. This provides a microscopic insight to vibrational and tunneling contributions to electron transport in linked porphyrin-fullerene dyads. We elaborate on important details in describing the excited state and trajectory sampling.

In the present investigation, AA7075-T6 alloys and AZ31B-H24 were joined by the FSW process using the following range of parameters: rotational speed between 200 and 800 rpm, welding speed from 30 to 60 mm/min and a tilt angle from 1° to 3°. In some cases, a tool offset of 1 mm was used into Mg-based alloy. The experimental results show that sound and good joints can be obtained by positioning the tool in the middle of the joint-line using a rotational speed of 200 rpm, a welding speed of 30 mm/min and a tool tilt angle of 1°. The hardness and ultimate tensile strength in the stir zone were 122 Hv and 61.35 MPa, respectively. Also, it is important to mention that the Al3Mg2 and Al12Mg17 intermetallics compounds were observed in the this zone besides some defects like cavities and tunnel.

The Ga-doped ZnO (GZO) were deposited by magnetron reactive sputtering on glass substrates at room temperature with different deposited times to obtain various thickness. The root-mean-square (RMS) roughness obtained from the atomic force microscopy (AFM) images is observed to shift linearly with the deposited time, the fractal geometry and multi-resolution signal decomposition (MRSD) based on wavelet transform were applied on the surface profiles and the results does not synchronously changes as the thickness, which is related to the profile’s frequency. The calculated compressive in-plane stress of highly c-axis oriented GZO films also shows an irregular variation as the increase of film thickness, what’s more, the in-plane stress and fractal dimension exhibit a polynomial relationship and the two parameters can be used for describing the surface morphology.

Borate is present in natural groundwaters and borate is also released into groundwaters when borosilicate glass, waste form for high level nuclear waste, is corroded. Borate can form an aqueous complex, AmHB4O72+, with actinides in +III oxidation state. In this work, we present our evaluation of the equilibrium constant for formation of AmHB4O72+ and the associated Pitzer interaction parameters at 25°C.

Using Nd(III) as an analog to Am(III), solubility data of Nd(OH)3(s) in NaCl solutions in the presence of borate ion from the literature, is used to determine Am(III) interactions with borate. The log10K for the formation reaction is 37.34. This evaluation is in accordance with the Waste Isolation Pilot Plant (WIPP) thermodynamic model in which the borate species include B(OH)3(aq), B(OH)4–, B3O3(OH)4–, B4O5(OH)42–, and NaB(OH)4(aq). The WIPP thermodynamic database uses the Pitzer model to calculate activity coefficients of aqueous species.

In addition, the equilibrium constant for dissolution of AmB9O13(OH)4(cr) at 25oC is evaluated from the solubility data on NdB9O13(OH)4(cr) in NaCl solutions, again using Nd(III) as an analog to Am(III). The log10K for the dissolution reaction is –79.30. In the evaluation for log10K for the dissolution reaction, AmHB4O72+ is also considered.

The equilibrium constant and Pitzer parameters evaluated by this study will be important to describe the chemical behavior of Am(III) in the presence of borate in geological repositories.

Single-walled carbon nanotubes (SWNTs) possess superior electronic properties that make them ideal candidates for making next-generation electronic circuits. However, the commercially available SWNTs that obtained directly from the viable synthesis procedures are the mixtures of semiconducting (s-) and metallic (m-) SWNTs. That shortcoming of present technologies hinders further studies and limits the scalable applications for a series of promising SWNT-based electronics. Separation of the two species is the way to solve the present dilemma. Herein, this review highlights “in situ” approaches towards selective growth of s-SWNT. The methods and techniques used for the enrichment of s-SWNTs are reviewed. Based on the understanding of the growth mechanism of those strategies, we try to propose the general guideline on that how can we develop the optimal method for the growth of s-SWNTs.

Magnetocaloric materials have gained significant interest as an environment friendly and efficient refrigeration technology. We have been working on Heusler alloys, primarily the Ni-Mn-Ga system for improved magnetocaloric effect (MCE). We have observed significant MCE increase in stress assisted thermally cycled samples and demonstrated that one primary mechanism is texture change. More recently, we have observed volumetric decrease as well as anisotropy changes due to stressed cycling. The influence of these parameters on magnetic anisotropy and MCE are discussed. We have also utilized isoelectronic Al substitution at the Ga lattice sites for optimizing atomic distances and exchange interactions in an effort to bring about magnetostructural transformation closer to room temperature (RT) while retaining high MCE. The results show that Al substitutions can bring about large decreases (50 – 70K) in both the Curie (TC) and martensite start (Ms) temperatures, and permit fine tuning the magnetostructural transformation temperature.

Two-dimensional (2D) materials are very promising with respect to their integration into optoelectronic devices. Monolayer tungsten diselenide (WSe2) is a direct-gap semiconductor with a bandgap of ∼1.6eV, and is therefore a complement to other two-dimensional materials such as graphene, a gapless semimetal, and boron nitride, an insulator. The direct bandgap distinguishes monolayer WSe2 from its bulk and bilayer counterparts, which are both indirect gap materials with smaller bandgaps. This sizable direct bandgap in a two-dimensional layered material enables a host of new optical and electronic devices. In this work, a comprehensive analysis of the effect of optical excitation on the transport properties in few-layer WSe2 is studied. Monolayer WSe2 flakes from natural WSe2 crystals were transferred onto Si/SiO2 (270nm) substrates by mechanical exfoliation. The flakes were observed under an optical microscope. A FET based on mechanically exfoliated WSe2 was fabricated using photolithography with Molybdenum as metal contact and Silicon as back gate and the electronic properties were measured in a wide range of temperatures. The mobility of our device was found to be 0.2 cm /V-S at room temperature. The schottky barrier height was found to decrease from 80 meV to 25 meV as the gate voltage increases.

The deformation behavior and shape recovery of an Fe-added AuCuAl shape memory alloy micropillar were investigated. XRD analysis revealed that Au-28Cu-22Al-2Fe (at.%) alloy contained a second phase which was evaluated to be α-Fe (bcc). SEM observation also confirmed the second phase at the surface of the micropillar specimen. A polycrystalline micropillar with 20 x 20 x 40μm rectangular was fabricated by a focused ion beam (FIB) system, and micro compress test was performed at room temperature. It was found that the yield stress of micropillar showed 50MPa, which must correspond to stress for inducing martensite. After the heating of the compressed micropillar, 1.75% shape recovery was recognized which is comparable to the transformation strain. Then, the Fe-added AuCuAl micropillar was concluded to possess good shape memory property, and thus this alloy may be suitable for small endovascular treatment which requires good X-ray radiography.

Multiferroic materials are of great interest from the scientific and technological viewpoints based on their multifunctional behavior involving ferroelectricity, ferromagnetism, ferroelasticity and strong electromagnetic coupling properties. Among these materials, BiFeO3 (BFO), is a well-known multiferroic with simultaneous ferroelectricity (TC=1103K) and G-type antiferromagnetism (TN=643K). In this work, we doped BiFeO3 with Mn species and studied the doping effect on the corresponding magnetic properties, expected from the substitution of Bi3+ by Mn2+. Additionally, the optimum processing conditions to minimize the formation of any impurity phase were also identified. X-Ray Diffraction (XRD) characterization confirmed the formation of powdered impurity-free BFO in pure and 7 at.% Mn-BFO only after annealing of the precursor compounds at suitable temperatures and time (700°C, 15 minutes). Scanning Electron Microscopy (SEM) analyses were used to determine the size and morphology of synthetized powders. Vibrating sample magnetometry (VSM) measurements showed that maximum magnetization values increased with doping and reached a maximum value in the 7 at.% Mn-doped BFO annealed at 700°C for 15min; the corresponding magnetization in the non-saturated MH loops reached 0.68 emu/g. This behavior can be attributed to the actual incorporation of Mn species into the BFO lattice and the substitution of non-magnetic Bi species.