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.

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 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.

Photolithographically patterned thin films often possess unwanted spikes along the side edges. These spikes are a significant issue for the development of spinvalve memory, tunnel junction based molecular devices, and micro-electromechanical systems. Here, we report a very simple, economical, and fast way of creating an optimum photoresist profile for the production of spike-free patterned films. This approach is based on performing a soaking step in the positive-photoresist’s developer solution before the UV exposure. However, the success of this method depends on multiple photolithography factors: photoresist thickness (governed by spin speed), soft baking temperature, soaking time in developer, and exposure time. In this paper, we report our systematic experiments to study the effect of these factors by following the L9 experimental scheme of the Taguchi Design of experiment (TDOE) approach. The L9 experiment scheme effectively accommodated the study of four photolithography factors, each with three levels. After performing photolithography as per L9 TDOE scheme, we sputter deposited 20 nm Tantalum to check the side edge profile of the patterned film by atomic force microscope (AFM). We measured the heights of the spikes along the thin film edges. We utilized spike height as the desired property and chose “smaller the better” criteria for the TDOE analysis. TDOE enabled us to understand the relative importance of the parameters, relationship among the parameters, and impact of the various levels of the parameters on the thin film edge profile. TDOE analysis yielded an optimum combination of levels for the four photolithography factors. The optimum combination of photolithography factors included spin speed 4000 rpm, 100 °C soft baking temperature, 60 sec pre-soaking in the developer solution, and 15 sec UV exposure. We validated the TDOE by AFM and observed spike free patterned films. We also made complete tunnel junction devices by utilizing the optimized photolithography factors for the bottom electrode and obtained excellent tunneling behavior. In summary, this study provides a very simple, economical, and fast photolithography approach for creating optimum photoresist profile for the micro-nano scale devices and electromechanical structures.

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.

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.

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.

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.

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.

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.

This work describes the electrical behavior of dye sensitized solar cells manufactured with TiO2-nanocrystalline semiconductor sensitized with diverse natural tints. A number of natural sensitizers have been tested, including red fruits as blackberries, hibiscus and beet in order to comprehend the relationship between anthocyanin and electron transfer and green vegetables as spinach and grass, as well as for known the relationship between chlorophyll and electron transfer. The nanocrystalline semiconductor was characterized by XRD, FTIR and SEM. The bands observed at 931, 667 and 514 cmˉ1 in the FTIR spectrum confirmed the presence of Ti-O-Ti bonds. From DRX analysis it is confirmed the presence of TiO2 in its anatase form. This study confirms the great potential of the use of organic dyes for sensitized the TiO2-semiconductor. Principally, in blackberries it has reached values around 300 mV owing to high concentrations of purple pigment due to the molecule called anthocyanin and the anchoring properties of the anthocyanin with the TiO2-nanocrystalline semiconductor.

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.

We report on a wide-range Density Functional Theory (DFT) investigation of the g-C3N4 photocatalysis systems combined with metals/nonmetals, especially those available in plants and involved in the natural photosynthesis process, such as K, Mg, Mn, Mo, Fe, Co, Cr, S and B. It is found that doping increases the range at which light absorption occurs to significantly large regions of the visible spectrum. These findings suggested that the g-C3N4 can be a promising system for the photosynthesis process.