We have developed a thermodynamic model that predicts the heat distribution in a stack of PECVD SiO2 and a-Si:H on crystalline Si after laser irradiation. The model is based on solving the total enthalpy heat equation with a finite difference scheme. The laser used in the model is a frequency doubled Nd:YVO4 green laser with pulse duration in the nanosecond range. The modeling was done with the aim of getting a better understanding of our newly developed laser ablation process for making local contacts on back-junction silicon solar cells. Lasers with pulse duration within the nanosecond range are usually believed to induce too much thermal damage into the underlying silicon to make them suitable for high efficiency solar cells. In our case, insertion of a thin layer of a-Si:H between the SiO2 and the Si absorbs much of the laser irradiation both optically and thermally. This makes it possible to form local contacts to Si in a damage-free way. In addition, the residual a-Si:H serves as an excellent surface passivation layer for the Si substrate. We have also developed a simple static model to determine the onset of SiO2 ablation on a-Si:H layers of varying thickness. The models, both the static and the dynamic, are in good agreement with experimental data.

We have studied the variable range hopping (VRH) mechanism for polarons in DNA structures using an exponential density of states. Due to the electron-phonon interaction localized polarons are formed in the DNA helix. The unwinding of DNA increases molecular orbital overlap between bases while decreasing the base-to-base distance. These types of vibrations create phonons. We consider that DNA has a band tail which has an exponential density of states and we have calculated the temperature- and the electric field dependence of the conductivity. We compare our model with the experiments of the electrical conductivity of samples of double-stranded H5N1 genes of avian Influenza virus DNA. Our theory is able to explain their data.

High quality strained Ge (s-Ge) epitaxial layers are a promising candidate to achieve high mobility channel MOSFETs suitable for the 22 nm technology node and beyond, due to the intrinsically higher mobility of Ge compared to Si, and the additional performance enhancements from strain [1]. In order to achieve an s-Ge channel more than a few monolayers thick it is necessary to engineer a relaxed Si1-xGex buffer with a high Ge content (x > 0.5). We have recently reported high quality s-Ge layers grown by RP-CVD at low temperature (T ≤ 450 °C), on a fully relaxed Si0.2Ge0.8 buffer [2]. By using a reverse-grading approach, we achieved a high Ge composition in the buffer, with a smooth surface (rms surface roughness of ~2 nm), low threading dislocations density (~ 4 x 106 cm-2) and much thinner (~ 2.1 μm) than can be achieved with conventional linear grading [3].

In this work, the thermal stability of s-Ge epilayers (up to 80 nm thick) grown on relaxed Si0.2Ge0.8 buffers has been investigated by in-situ annealing in H2 ambient at temperatures up to 650 °C. These temperatures are similar to those currently used during fabrication of advanced CMOS devices. All s-Ge layers were grown at 400 °C using GeH4 gaseous precursor. The relaxation of the annealed layers has been studied using high-resolution XRD reciprocal space maps (RSMs), and was found to depend strongly on both annealing temperature and thickness of the Ge epilayer. Strained Ge layers up to 50 nm thick remained fully strained after annealing at 450 °C, whereas after annealing at 550 °C s-Ge layers thicker than 20 nm were on the onset of relaxation; after annealing at 650 °C all s-Ge layers showed significant relaxation with defects clearly visible at the Si0.2Ge0.8/Ge interface. All annealed s-Ge layers exhibited higher surface roughness than s-Ge control samples without annealing (rms ~ 2 nm). Annealing at 450 °C resulted in only a slight increase in surface roughness (rms ~ 3 nm), almost independent of s-Ge thickness. However, annealing at 550 °C and 650 °C resulted in significant surface roughening (with maximum rms values of 5 nm and 35 nm, respectively) due to the formation of Ge islands, which were observed by AFM. At these higher temperatures, the surface roughness of the s-Ge layers was found to be thickness dependent, with a Ge smoothing effect observed for layers greater than 50 nm.

These results are particularly important for the fabrication of s-Ge MOSFETs, for which the surface passivation prior to gate stack formation is critical to the performance of the device. Based on the results presented here, the thermal budget should be kept below 550 °C to avoid relaxation and roughening of the s-Ge epilayer, which could degrade the device performance.

High-resolution piezoresponse force microscopy (PFM) was used to measure the out-of-plane (effective longtitudinal) and in-plane (effective shear) piezoresponse of zinc oxide films and microrods. Thin films were deposited by pulsed laser deposition (PLD) and micro rods formed from solution. Measurements of three components of piezoresponse, one out-of-plane (OPP) and two in-plane (IPP) signals, allowed the construction of 3D piezoelectric maps reflecting the polycrystalline nature of the films. Both the IPP and OPP piezoresponse signal distributions are analyzed based on the particular texture of the films. It was observed that the central part of microrods contains polarization inversion with head-to-head ferroelectric-like domains. The as-grown domain boundaries were always parallel to the (0001) basal plane. Analysis of the PFM piezoresponse images was done based on the hexagonal structure of ZnO and topographic features along the hexagonal axis.

This paper describes the results from static leach tests using the ASTM International standard Materials Characterisation Centre (MCC-1) and Product Consistency Test (PCT) protocols for inactive High Level Waste (HLW) glasses fabricated at full scale on the Sellafield Vitrification Test Rig. The samples comprised monoliths and powders of a 75:25 Oxide:Magnox Blend glass with 31 wt% waste incorporation and a Magnox-only glass with 35 wt% waste incorporation. The tests were carried out in de-ionized water at 90 °C for durations up to 42 days and normalized mass losses calculated.

The results of MCC-1 and PCT tests on both 31 wt% Blend and 35 wt% Magnox glasses, showing measurable differences to the corresponding standard 25 wt% waste incorporation glasses, are presented. A series of Scanning Electron Microscopy (SEM) investigations were also undertaken. The variation in composition and thickness of the alteration layer with sample type and duration is reported.

Well-controlled architectures (aligned or horizontally suspended) of CuO nanowire (average diameter ~75±18 nm)-Co3O4 nanoparticle (average diameter ~7±1 nm) heterostructures were fabricated in a simple and surfactant-free growth approach. This approach coupled microfabrication methods with a thermal growth method and wet-coating technique. The fabricated heterostructures were characterized by high resolution electron microscopy (SEM and TEM) and X-ray Photoelectron Spectroscopy (XPS) for their size, morphology, phases, interfaces, and composition of heterostructures. Finally, CuO nanowire–Cox3O4 nanoparticle heterostructures were utilized as photocatalyst to degrade organic dye (methyl orange) under a wide range of wavelengths (from UV, 265 nm, to visible region, 580 nm).

In this paper, the fabrication of Ge-NCs embedded in Al2O3 and HfO2 layers by ion-beam-synthesis for memory applications is investigated. Structural properties of the high-k layers before and after implantation and annealing were studied by TEM observation and EELs analysis. Spherical Ge-NCs 5nm in diameter were observed in Al2O3 implanted layers after furnace annealing at 800°C in nitrogen. Annealing studies in the range 700-1050°C in nitrogen revealed the evolution of the charge storage properties of these structures utilizing MIS capacitors test structures. No NCs were observed in HfO2 implanted layers. However, significant negative-differential-resistance regions were observed in I-V characteristics of the related MIS structures. These may be attributed to the formation of conductive paths made of hafnium germanide (HfGe2) or hafnium germanate (HfGeO) regions.

A three-dimensional numerical model capable of predicting structural behavior of concrete under various loading conditions is developed. Concrete, as a composite material, is represented by the mechanically strong aggregates of various shapes and sizes incorporated into a cement matrix. The most important aspect of concrete modeling involves an accurate representation of the spatial distribution of the aggregate particles.

A micromechanical heterogeneous model based on prescribed spatial distribution of aggregates is developed. This model allows to compute the effective material properties of concrete using a representative cell homogenization approach. The results of numerical analysis of this model are compared to the models of particulate composite material.

WO3 doped TiO2 nanotube(WO3-doped TNT) thin film was fabricated by anodizing the TiO2 nanotube (TNT) film in an NH4F electrolyte containing WO4- ions. The sample was characterized by Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance spectroscopy (DRS). The results show that WO3 was successfully doped into TiO2 nanotubes and the absorption edge of WO3 doped TNT appeared to be red shifted. The photoelectrocatalytic (PEC) activity of WO3 doped TNT electrode was evaluated through the PEC degradation of aqueous Acid Blue 80. The experimental results demonstrated that the PEC degradation rate of WO3 doped TNT is increased by 48% and by 167% over that of non-doped TNT under UVA light irradiation and visible-light irradiation, respectively, at an applied potential of 1.54V. The degradation rates of WO3 doped TNT under photocatalytic (PC), electrochemical (EC), and PEC processes were compared. The results reveal the synergetic effect of PC and EC processes.

A new computational algorithm is introduced for packing simulation of spherical elements/particles into an imaginary container with three main possible geometries, cubic, cylindrical and spherical. The performance of the algorithm depends directly on the strategy or logic considered to solve the problem and the quality of its computational implementation. The combination of these two factors let the packing algorithm here presented and named as Octant Packing Random Algorithm (OPRA) to reduce the computation time between 2 and 127 times, when compared with the simplest or classical Packing Algorithm. OPRA is designed to reduce the number of comparisons needed to accept or reject a new position for an element/particle to be allocated into the virtual container. OPRA considers the container as if it were divided into 8 equal cells or octants limiting the overlap detection for a new position.

To explore higher, farther, and faster, scientists and engineers have developed advanced materials for manned spacecraft and satellites for a range of sophisticated applications in transportation, global positioning, exploration, and communication. Materials used in space are exposed to vacuum, intense ultraviolet radiation from the sun, and ionizing radiation that results in material damage as well as charging (electrostatic discharge effects), micrometeoroids and debris impacts, and thermal cycling (typically from -175 to 160°C). In terms of materials degradation in space, the low Earth orbit (LEO), where LEO is defined as 200—1000 km above the Earth’s surface, is a particularly challenging synergistic environment, since atomic oxygen (AO) is present along with all other environmental elements. Hence, this special issue focuses primarily on the materials issues experienced in LEO by space environmental exposure, such as on the exterior of the International Space Station and the Hubble Space Telescope, and the challenges and opportunities of ground-based laboratory sources to mimic LEO. The combination and comparison of both in-flight and groundbased experiments are needed for the development of predictive understanding of the materials degradation and AO passivation mechanisms in LEO. Such insights are essential for the development of advanced materials and coatings to ensure the longterm durability and performance of vehicles employed in space.

Controlled reaction conditions in simple, template-free hydrothermal processes yield Tm-Lu2O3 and Tm-GdVO4 nanocrystals with well-defined specific morphologies and sizes. In both oxide families, nanocrystals prepared at pH 7 reaction media exhibit photoluminescence in ∼1.95 μm similar to bulk single crystals. For the lowest Tm3+ concentration (0.2 % mol) in GdVO4 measured 3H4 and 3F4 fluorescence lifetimes τ are very near to τrad.

We present recent developments in rolled-up helical nanobelts in which helical structures are fabricated by the self-scrolling technique. Nanorobotic manipulation results show that these structures are highly flexible and mechanically stable. Inspired by the helical-shaped flagella of motile bacteria, such as E. coli, artificial bacterial flagella (ABFs) are a new type of swimming microrobot. Experimental investigation shows that the motion, force, and torque generated by an ABF can be precisely controlled using a low-strength, rotating magnetic field. These miniaturized helical swimming microrobots can be used as magnetically driven wireless manipulators for manipulation of microobjects in fluid and for target drug delivery.

Carbon nanotube (CNT)-nickel/nickel oxide (Ni/NiO) core/shell nanoparticles (CNC) heterostructures were prepared in a unique single-step synthetic route by direct chemical precipitation of nanoparticles on CNT surface. Chemical vapor deposition (CVD)-grown CNTs (average diameter ˜42.7±12.3 nm) allowed for direct nucleation and uniform coating of Ni/NiO core/shell nanoparticles (average diameter ˜11.8±1.7 nm). The crystal structure, morphology, and phases in CNC heterostructures were studied using high resolution transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Subsequently, the as-produced CNC heterostructures were incorporated into polyvinyl alcohol (PVA) hydrogel resulting in CNC heterostructure-PVA hydrogel with ˜ 75% water absorbing capability. These novel hydrogels were also characterized by SEM and showed actuation under 0.2 T magnet. They are promising for smart analytical devices and platform.

A chain FeRAMTM is the best solution to realize high-speed and high-bandwidth nonvolatile RAM with low power dissipation. In this paper, the overview of chain FeRAM, the technical trend for FeRAM scaling and the marketing strategy are presented. First of all, the concept and performance of chain FeRAM are described. Secondly, the status and history of chain FeRAM development are presented. Thirdly, four kinds of scaling strategies for chain FeRAM are presented; (1) A shrink trend of chain cell including a capacitor plug shared with twin cells, and process techniques including Ir/TiAlN-barrier metal and MOCVD-PZT with SrRuO3 electrode, which are installed in 16Kb, 8Mb, 32Mb, 64Mb and 128Mb chain FeRAMs, (2) Capacitor damage suppression processes to reinforce step coverage and protect H2 damage even in 0.1μm2 capacitor of 128Mb, (3) A scalable array architecture such as an octal / quad bitline architecture to reduce bitline capacitance and ensure enough cell signal in scaled ferroelectric capacitor, and (4) A ferroelectric capacitor overdrive technique by driving shield-bitlines to enlarge tail-to-tail cell signal in low voltage operation of 1.3V. Fourthly, future direction of chain FeRAM is discussed. The vertical capacitor is one of candidates for gigabit-scale chain FeRAMs, and solves signal problem and achieves small 4F2 cell without contact formation. Finally, the marketing strategy to take full advantage of chain FeRAM is presented. A nonvolatile FeRAM cache is the promising candidate to achieve high bandwidth memory systems. Applications of chain FeRAM to solid-state drive (SSD) and hard-disk drive (HDD) and their system performance improvements are demonstrated.

We have developed a novel surface treatment process using vacuum ultraviolet (VUV) light with a wavelength of 172 nm and formic acid vapor. A previous study showed that the VUV process can help remove the organic contaminants on the bonding surfaces and improve the shear strength. This new work focuses on studying the effects of VUV/O3 and formic acid treatments. The formic acid (HCOOH) vapor removes the metal oxides from the surfaces before the bonding process. Evaporated Cu/Sn and immersion Au were used for the bonding micro-bumps and bonding pads in our evaluations. Different cleaning conditions with VUV/O3, formic acid vapor, or both were compared and evaluated. X-ray Photoelectron Spectroscopy (XPS) was used to study the surface elemental composition of the micro-bumps and pad surfaces before and after the cleaning process. The photoelectron spectra of C1s, Sn3d, and Au4f were obtained with XPS. The XPS results showed the atomic carbon concentrations were significantly decreased by the VUV/O3 treatment process, while the Sn and Au concentrations were increased by the VUV/O3 and formic acid treatment because of the removal of the organic contaminants and metal oxides from the surfaces. The bonding strength of the Cu/Sn bumps was evaluated using a shear test tool. The results shows that the combination of VUV/O3 and formic acid treatment obtains the highest average shear strength among the treatments tested, with a shear strength almost 2.5 times stronger than the untreated samples.

We report on high transversal relaxivity values of composite iron oxide-silica nanoparticles. To obtain the material, pre-formed maghemite nanoparticles were coated with silica by sol-gel chemistry, using supercritical fluids as the reaction media. The composite particles were monodisperse and consisted of a core of several maghemite nanoparticles, surrounded by a thick silica shell. The high pressure and high temperature process did not affect the iron oxide particle size but induced an increase on their saturation magnetization values, possibly due to an improvement of the particle crystallinity. These iron oxide-based materials present very high transversal relaxivity values which can be correlated to the magnetic moment and to the silica shell width of the composite particles. Moreover, composite particles are not cytotoxic and they are dispersable in polar solvents.

The study focuses on the adhesion and friction coefficient of DLC (Diamond Like Carbon) coating on a metallic surface AISI-316L. A DC technique was used in order to develop DLC coatings, while a silicon interface allowed a better adhesion of those coatings, having variations of time during the deposit to allow different thickness in anchoring coating. The adhesion and friction coefficient were measure through Scratching Test while the sheets were analyzed through Atomic Force Microscope (AFM) to visualize its surface morphology. Besides, it was used Raman spectroscopy to study sp3/sp2 ratio of DLC coatings. The tests show that the sample with the largest period of time of deposit has a better adhesion and the highest surface roughness.

Recent efforts in investigating the mechanism of ion beam assisted deposition (IBAD) of biaxially textured thin films of magnesium oxide (MgO) template layers have shown that the texture develops suddenly during the initial 2 nm of deposition. To help understand and tune the behavior during this initial stage, we pre-deposited thin layers of MgO with no ion assist prior to IBAD growth of MgO. We found that biaxial texture develops for pre-deposited thicknesses < 2 nm, and that the thinnest layer tested, at 1 nm, resulted in the best qualitative RHEED image, indicative of good biaxial texture development. The texture developed during IBAD growth on the 1.5 nm pre-deposited layer is slightly worse and IBAD growth on the 2 nm pre-deposited layer produces a fiber texture. Application of these layers on an Al2O3 starting surface, which has been shown to impede texture development, improves the overall quality of the IBAD MgO and has some of the characteristics of a biaxially texture RHEED pattern. It is suggested that the use of thin (<2 nm) pre-deposited layers may eliminate the need for bed layers like Si3N4 and Y2O3 that are currently thought to be required for proper biaxial texture development in IBAD MgO.

In this work we propose a particle agglomeration model for chemical mechanical planarization (CMP) under the primary motivation of understanding the creation and behavior of the agglomerated slurry abrasive particles during the CMP process, which are a major cause of defectivity and poor consumable utility due to sedimentation.

The proposed model considers the slurry composition as a colloidal suspension of charged colloidal silica in an electrically neutral aqueous electrolyte. First, a theoretical relationship between the measurable chemical parameters of the slurry's aqueous electrolyte, the surface potential of the abrasive particles, and corresponding zeta potential between the agglomerated abrasive particles is presented. Secondly, this zeta potential is used in a modified DVLO interaction potential model to determine the particle interaction potentials due to both the attractive van Der Waals forces and repulsive electrostatic interactions. Finally, the total interaction potential created is then used to define a stability ratio for slow versus fast agglomeration and corresponding agglomeration rate equations between particles; these are used in a discrete population balance framework to describe the final particle size distribution with respect to time and agglomerate composition.

The proposed model will provide both a qualitative and quantitative description of agglomeration of abrasive slurry particles during CMP that can be extended to account for slurry composition or abrasive particle type, enabling more accurate process control, increased consumable utility, and possible defectivity reduction.