Piezoresistors are commonly used in microsystems for transducing force, displacement, pressure and acceleration. Silicon piezoresistors can be fabricated using ion implantation, diffusion or epitaxy and are widely used for their low cost and electronic readout. However, the design of piezoresistive cantilevers is complicated by coupling between design parameters as well as fabrication and application constraints. Here we discuss analytical models and design optimization for piezoresistive cantilevers, and describe several applications ranging from studying electron movement using scanning gate microscopy to measuring the biomechanics of whole organisms.

Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm CMOS technology. We present results for crystalline gadolinium oxides on silicon in the cubic bixbyite structure grown by solid source molecular beam epitaxy. On Si(100), crystalline Gd2O3 grows usually as (110)-oriented domains, with two orthogonal in-plane orientations. Layers grown under best vacuum conditions often exhibit poor dielectric properties due to the formation of crystalline interfacial silicide inclusions. Additional oxygen supply during growth improves the dielectric properties significantly. Layers grown by an optimized MBE process display a sufficiently high-K value to achieve equivalent oxide thickness values < 1 nm, combined with ultra-low leakage current densities, good reliability, and high electrical breakdown voltage. A variety of MOS capacitors and field effect transistors has been fabricated based on these layers. Efficient manipulation of Si(100) 4° miscut substrate surfaces can lead to single domain epitaxial Gd2O3 layer. Such epi-Gd2O3 layers exhibited significant lower leakage currents compared to the commonly obtained epitaxial layers with two orthogonal domains. For capacitance equivalent thicknesses below 1 nm, this differences disappear, indicating that for ultrathin layers direct tunneling becomes dominating. We investigated the effect of post-growth annealings on layer properties. We showed that a standard forming gas anneal can eliminate flatband instabilities and hysteresis as well as reduce leakage currents by saturating dangling bond caused by the bonding mismatch. In addition, we investigated the impact of rapid thermal anneals on structural and electrical properties of crystalline Gd2O3 layers grown on Si with different orientations. The degradation of layers can be significantly reduced by sealing the layer with amorphous silicon prior to annealing.

Magnesium and its alloys are used as implants because of their biocompatibility and high strength-to-weight ratio. In contrast to other commonly used implantable materials such as stainless steel and Co-Cr-alloys, which may release toxic metallic ions, magnesium belongs to the natural composition of the human body. Our work is focused on engineering a cellular carrier system based on biodegradable magnesium and magnesium alloy substrates, which are decorated with gold nanoparticles to form magnesium-gold (Mg-Au) hybrid materials. Specifically, we deposited gold nanoparticles on MgO single crystals (100 orientation) and on AZ31-Mg alloy substrates using diblock copolymer micelle nanolithography. The gold nanoparticles were arranged in ordered arrays with controllable interparticle distances of 25 to 300 nm and were further functionalized with RGD-thiols or fibronectin. This method allowed the deposition of a protein carpet on top of the surface and facilitated the initial adhesion of cells on the magnesium substrates. In order to determine the stability of the substrates in a physiological environment, their corrosive behavior was studied by comparing the weight of the substrates before and after a 24h-long submersion in water, PBS, or cell culture medium and by studying the post-submersion surface morphology with scanning electron microscopy. Corrosion rates of magnesium substrates in PBS and cell culture medium were significantly higher than in water. The spreading and survival of C2C12 mouse myoblasts and human mesenchymal stem cells cultured on MgO single crystals and AZ31-alloys were investigated with fluorescence and phase contrast microscopy. The spreading and survival of C2C12 myoblasts on the Mg-Au hybrid materials were different than on non-functionalized Mg substrates. Additionally, cells on non-functionalized MgO crystals showed reduced filopodia activity. Our results show that biofunctionalized and engineered magnesium-based substrates can be used as carriers for different cellular systems and promising initial steps have been taken towards an implantable device with a defined biological surface activity made from magnesium materials.

Spin-polarized currents across an insulating tunnel barrier, needed for the development of efficient magnetic tunneling junctions (MTJs), may be obtained using hard spin injector electrodes. Thin films of CoCr solid solutions have been fabricated involving two main steps: 1) deposition of Co/Cr alternated layers via RF magnetron sputtering both onto silicon (100) substrates and thermally oxidized wafers and 2) thermal annealing in a partial Ar pressure of 1 mTorr at 450°C for 1 hour and cooling treatment in a uniform magnetic field (600 Oe). The deposition of stacks of pure elements and subsequent diffusion treatment has been preferred instead of the direct deposition of the native alloy because in the former case the right composition and magnetic bias may be tuned more easily playing on the layer thicknesses and number of repetitions.

A detailed numerical correlation of field effect SEM images and EDX micro-maps was used to evaluate the oxygen diffusion on the magnetic film, while an alternating gradient force magnetometer (AGFM) allowed us to evaluate at room temperature both coercivity and magnetic bias obtained after the field cooling treatment. The effect of standard thermal treatment on the homogeneity of the films is discussed, and a possible alternative heating technique is proposed.

In situ, real time spectroscopic ellipsometry (RTSE) has been used to study the growth processes and optical properties of Cu2-xSe - an important binary compound in the fabrication of high efficiency copper indium gallium diselenide (CIGS) photovoltaic devices. It was found that the high surface roughness of the Cu2-xSe layers necessitated a “graded” optical model in order to extract meaningful dielectric functions at both 550 °C and room temperature. The optical model was verified at room temperature against SEM micrographs and reflectance measurements carried out ex situ. The growth temperature dielectric functions presented in this study are expected to allow for a greater level of control and understanding of the so-called 2- and 3-stage processes for CIGS fabrication in which a Cu2-xSe phase, present at the CIGS grain boundaries, acts as a fluxing agent for the growth of photovoltaic quality CIGS. Real time optical feedback via RTSE combined with the growth temperature dielectric functions presented here could play an important role in improving material fabrication on both the laboratory and industrial scales.

Nanostructured hematite thin film for photoelectrochemical (PEC) splitting of water has great potential in the design of low-cost, environmental friendly solar-hydrogen production. Presently, solar-to-hydrogen conversion efficiency of PEC cell using iron oxide is limited by its poor charge transport due to high recombination losses and mismatch of band edges position with the redox level of water. High energy heavy ion irradiation provides the researchers a new dimension to introduce the desired changes in the behaviour of the material, which largely influence their properties. In order to get efficient PEC system, spray-pyrolytically deposited nanostructured hematite thin films were modified by irradiating the samples with 120 MeV Ag9+ ions with fluences ranging from 5×1011 to 1×1013 ions/cm2. Irradiated samples exhibited a partial transition from the hematite to the magnetite phase and reduction in particle size as indicated by XRD and Raman analysis. SEM picture showed a decrease the thickness and porosity of the films after irradiation. These irradiated films, when used in PEC cell showed significantly higher photocurrent density than unirradiated α-Fe2O3.

The unique one-dimensional electronic and optical properties attributed to single-walled carbon nanotubes (SWCNTs) are mainly related to the peculiar local arrangement of sp2 hybridised carbon atoms. This structural configuration gives raise to interesting features, which can be identified with various spectroscopic techniques. In the case of SWCNTs, high energy spectroscopy methods represent effective key tools to analyse the modifications of the underlying basic correlation effects in the bonding environment, the charge transfer between functionalized nanotubes, and on-wall doping. More specifically, in this article we review the shape of the C1s photoemission (PES) response related to the density of states (DOS) of the valence band (VB) in SWCNTs and its changes upon on-wall functionalization and metallicity-sorting. In the last, the progress in the identification of changes in the site selective valence-band electronic structure is clarified in detail.

A new process, based on melt processing has been investigated with oxide thermoelectrics to achieve long-range grain alignment for low resistivity as well as to embed secondary phase precipitates and associated crystal defects for low thermal conductivity. Melt-processing of Bi2Sr2Co2Ox and CaMnO3 has been studied. A high degree of (00l) grain alignment has been achieved by melt processing. Good values of Seebeck coefficient of nearly -250 μV/K were measured in the melt-processed CaMnO3. Secondary phases of Ca4Mn3O10 and CaMn2O4 are found to be trapped between the aligned grains which led to high electrical resistivity values and limited the figure of merit in our initial samples.

Emulating the ECM microenvironment of natural tissue and understanding how such an environment affects integrin function is a major goal of regenerative medicine and tissue engineering. In this work we have combined laser and aerosol techniques to create nanoengineered substrates comprising calcium phosphate nanoparticles of well controlled size on atomically flat SiO2 layers. In our process, gas suspended calcium phosphate nanoparticles are generated by ablation of solid a hydroxyapatite target inside a tube furnace at 800-900°C in presence of Argon/H2O flow using a KrF excimer laser and deposited on a silicon substrate via electrostatic precipitation.

Immobilization of DNA/RNA, onto various metal and metal oxide surfaces is of great importance for the development of future microarray, gene mapping, DNA sequencing, nanoparticle targeting, and sensor applications. Attachment of DNA to solid interfaces typically occurs through either electrostatic interactions or covalent bonds to functional groups introduced to nucleic acid termini. Previously, we and others have demonstrated that alkanephosphates and terminal phosphate groups present on nucleic acids play an important role in the interaction with group IV metal oxides such as zirconium and hafnium, providing a stable linkage to the surface. Titanium dioxide (TiO2), which is frequently employed in various nanoscale applications, belongs to the same group and similar interactions with phosphate are expected. Various adsorption studies have demonstrated binding of nucleic acids to TiO2 surfaces, although the influence of terminal phosphate versus electrostatic interaction (via the DNA/RNA backbone) on the surface interaction is unclear. The research presented here investigates the effect of nucleic acid length, presence of terminal phosphates, and differences between dsDNA and ssDNA on their binding to TiO2 nanoparticles. TiO2 nanoparticles (20 nm) were used to study the adsorption of Lambda DNA (˜48 kbp), and shorter (21 bp) ssDNA and dsDNA oligonucleotides with and without a 5’ phosphate group. Initial adsorption of DNA to nanoparticles was calculated via UV absorption. Results showed that all types of nucleic acids (Lamda DNA, ssDNA and dsDNA) initially bind to nanoparticles, independent of molecular weight single/double strandedness, or phosphorylation state. The total amount of DNA initially adsorbed to nanoparticles (ng/particle) differs between ssDNA and dsDNA, as well as the length of the DNA used. These results show that nucleic acid interactions with TiO2 nanoparticles are not dependent upon the presence of a terminal phosphate group. These results provide valuable data for future applications based on DNA-nanoparticle constructs including nanoelectronics, photovoltaics, and biotemplated synthesis of semiconducting materials.

The hot embossing properties of Cyclic Olefin Copolymer (COC) have been examined as a function of comonomer content. Six standard grades of COC with varying norbornene content (61-82 wt%) were used in these experiments in order to provide a range of glass transition temperatures, Tg. All grades of COC exhibited sharp increases in embossed depth over a critical range of temperature. The transition temperature in embossed depth increased linearly with norbornene content for both 35 and 70 μm deep structures. At temperatures above this transition, the dimensions of the embossed patterns were essentially independent of COC grade, the applied pressure and duration of loading. Channels formed above the transition in a regime of viscous liquid flow were extremely smooth in morphology for all grades. The average surface roughness, Ra, measured at the base of the channels decreased sharply at the transition temperature, with a levelling off at higher temperatures. Grades of COC with higher norbornene content exhibited extensive micro-cracking during embossing at temperatures close to the transition temperature.

We have carried out a TEM investigation of the micromechanisms of deformation in these nanoporous gold specimens after compression testing. We find that the nanoporous specimens show deformation localised to the nodes between the ligaments of the foamed structure, with very high densities of microtwins and Shockley partial dislocations in these regions. These deformation structures are very different from those seen after solid nanowires are tested in compression, which show very low dislocation densities and a few sparsely distributed twins. However, similar dislocation structures to those found in the nanoporous specimens are observed in the larger nanowires when they are deformed in bending. The currently accepted model for the deformation of nanoporous gold, implicitly assumes that the deformation of these structures is by bending near the nodes where ligaments intersect. We hypothesis that the much higher dislocation densities seen in both the nanoporous gold and the nanowires deformed in bending are evidence for the presence of geometrically necessary dislocations in these deformed structures.

Seeding a layer of cells at specific depths within scaffolds is an important optimization parameter for bi-layer skin models. The work presented investigated the effect of fiber diameter and its mechanical property on the depth of cell seeding for electro-spun fiber scaffold. Polycaprolactone (PCL) is used to generate scaffolds that are submicron (400nm) to micron (1100nm) using electro-spinning. 3T3 fibroblasts were seeded on the electro-spun fiber scaffold mat of 50-70 microns thickness in this study. In order to investigate the effect of fiber diameter on cell migration, first, the electrospun fiber scaffold was studied for variation of mechanical properties as a function of fiber diameters. Atomic force microscopy (AFM) was used to investigate the Young’s modulus (E) values as a function of fiber diameter. It was identified that as the fiber diameter increases, the Young’s modulus values decreases considerably from 1.1GPa to 200MPa. The variation in E is correlated with cell seeding depth as a function of vacuum pressure. A higher E value led to a lower depth of cell seeding (closer to the surface) indicating that nanofibrous scaffolds offer larger resistance to cell movement compared to microfibrous scaffolds.

We report on the growth of high-permittivity (k) TiO2 thin films on In0.53Ga0.47As channels by chemical beam deposition with titanium isopropoxide as the source. The films grew in a reaction-limited regime with smooth surfaces. High-resolution transmission electron microscopy showed an atomically abrupt interface with the In0.53Ga0.47As channel that indicated that this interface is thermally stable. Measurements of the leakage currents using metal-oxide-semiconductor capacitors with Pt top electrodes revealed asymmetric characteristics with respect to the bias polarity, suggesting an unfavorable band alignment for CMOS applications. X-ray photoelectron spectroscopy was used to determine the TiO2/In0.53Ga0.47As band offsets. A valence band offset of 2.5 ± 0.1 eV was measured.

Mg has 7.6 mass% of high gravimetric hydrogen density, an abundance of resources and inexpensive price compared with other functional materials. Owing to these merits, it has been the major subject of hydrogen storage study. However, it is unsuitable for practical application due to thermodynamic stability and slow kinetics of Mg hydride. Therefore, many ways such as fabrication of nanocrystalline or addition of catalyst have been proposed to solve the problems of Mg hydride system. Copper and aluminum are inexpensive and can obtain easily as well as Mg. Each eutectic alloy could be produced by sintering process and observed improvement of reaction with hydrogen. Mg2Cu laminate, one phase of Mg-Cu eutectic alloy, could also be produced by cold-rolling process, and it showed reversible reaction with hydrogen, at this study.

Experiments on the reactivity of CO for Au nanoclusters have shown a local maximum in the adsorption of the first molecule for Au18 and its cation, whereas O2 adsorption has been observed in Au18 -1. In this work we present a theoretical analysis of the preferential sites for the adsorption of the CO and O2 molecules on neutral and single ionized Au18 clusters with C2v symmetry, which has been shown both theoretical and experimentally, to be the most stable isomer of the Au18 cluster. We report the results of the calculation for the binding energies of CO and O2 for non-equivalent sites and compare with the available experimental values. The oxidation mechanism is studied in first instance by the subsequent adsorption of the CO on the O2 molecule, which was previously adsorbed on the respective gold cluster. The study is based on a DFT-GGA calculation with the PW91 functional.

In this paper, we present a systematic study of the transient cooling in different Si/SiGe superlattices as well as bulk silicon microrefrigerators. Transient thermoreflectance imaging is used to obtain the temperature map of the device with sub micrometer spatial, 100ns temporal and 0.1C temperature resolution. It is shown that Peltier cooling dominates in the first 10-30 microseconds before Joule heating in the active and buffer layers reach the top surface. The transient characterization shows that at the optimum current for maximum steady-state cooling, the response of bulk silicon cooler is 25% faster than the 3 microns thick superlattice device and that of the 6 microns thick superlattice is 25% slower. However, it is possible to increase the cooling speed by a factor of two or three, down to 3.6 microseconds, by overdriving the current at the expense of the reduced steady-state cooling.

Mms6 is a small acidic protein which is tightly bound to magnetite in the bacterium Magnetospirillum magneticum AMB-1. Mms6 has been previously shown to promote iron-binding capacity as well as modulate the size and morphology of magnetic iron oxide crystals in vitro. In this study, we synthesized iron oxide crystals by using a monolayer-modified substrate. A self-assembled monolayer of octadecyltrimethoxysilane was modified on a silicon substrate. Recombinant Mms6 protein was attached to the substrate through the hydrophobic interactions between the protein molecules and the monolayer. The immobilization of protein molecules on the substrate surface was confirmed by fluorescent labeling of these molecules and subsequent fluorescence microscopy. This protein-modified substrate was then used as a template for iron oxide crystal formation in a ferrous solution. Scanning electron microscopy revealed site-specific formation of iron oxide crystals in substrate regions with immobilized proteins. This use of proteins might provide an alternative method for the bottom-up fabrication of nano-sized magnetic particles.

In this study, we report on the diffusion of neodymium (Nd) and erbium (Er) into n-type and undoped GaN and subsequent measurements of the room-temperature (RT) magnetic and optical properties. The diffusion profile has been measured via secondary ion mass spectroscopy (SIMS) with rare-earth (RE) concentration yields of up to 1×1018/cm3. The ferromagnetic properties were measured using an alternating gradient magnetometer (AGM) giving a saturation magnetization (Ms) of up to 3.17emu/cm3 for the RE-diffused layer. The photoluminescence (PL) emission of the Nd-diffused and Er-diffused GaN is observable in the near-infrared (NIR) and infrared (IR) regions of the spectrum, respectively. The Nd-diffused GaN samples show NIR emission at 1064nm and 1350nm, while Er-diffused GaN samples have IR emission at 1546nm. This appears to be the first successful result of Nd diffusion doping into GaN crystals, and the first demonstration of above RT ferromagnetism involving GaN diffused with Nd. Details of our ferromagnetic and optical emission studies, related to the RE diffusion into GaN, are presented.

Understanding interaction of ultrafast pulsed laser with matter is critical for probing ultrafast processes in materials science, understanding the physics of laser ablation and the laser induced non-equilibrium carrier dynamics in metals and semiconductors, including plasmonics. When an intense laser pulse of femtoseconds (fs) in duration hits the surface of a targeted matter, it excites a hot electron gas. Part of the hot electrons is emitted from the surface in a way similar to thermionic emission. Electrons can also be emitted through multiphoton photoemission (MPPE) or thermally assisted MPPE. The emitted electrons travel at speeds that create transient electric fields (TEFs). To detect TEFs and study the dynamics of emitted electrons, we have developed a time resolved electron beam imaging technique that allows us to measure TEFs above a sample surface at picoseconds time resolution. We have also developed a model of the TEFs based on the propagation of emitted electrons and the percentage of electrons escaping from the surface. We examine the significance of TEFs for ultrafast reflection electron diffraction by examining anomalous effects in ultrafast reflection high energy electron diffraction (RHEED) of silicon surfaces.