Recent achievements in nanostructured photovoltaic devices

This mini-review summarizes some key interesting applications and perspectives of nanostructured devices for future nanoelectronics, among them are photonic circuits, carbon nanostructures for chemisensors, unique Ag-Cu-nanocluster contacts for high-effective solar cells. Recent patents in the field are also discussed.     

Local field effects on electron transport in nanostructured TiO2 revealed by terahertz spectroscopy

We study electron mobilities in nanoporous and single-crystal titanium dioxide with terahertz time domain spectroscopy. This ultrafast technique allows the determination of the electron mobility after carrier thermalization with the lattice but before equilibration with defect trapping states. The mobilities reported here for single-crystal rutile (1 cm2/(V s)) and porous TiO2 (10(-2) cm2/(V s)) therefore represent upper limits for electron transport at room temperature for defect-free materials. The large difference in mobility between bulk and porous samples is explained using Maxwell-Garnett effective medium theory. These results demonstrate that electron mobility is strongly dependent on the material morphology in nanostructured polar materials due to local field effects and cannot be used as a direct measure of the diffusion coefficient.     

Inorganic photovoltaics – Planar and nanostructured devices

Since its invention in the 1950s, semiconductor solar cell technology has evolved in great leaps and bounds. Solar power is now being considered as a serious leading contender for replacing fossil fuel based power generation. This article reviews the evolution and current state, and potential areas of near future research focus, of leading inorganic materials based solar cells, including bulk crystalline, amorphous thin-films, and nanomaterials based solar cells. Bulk crystalline silicon solar cells continue to dominate the solar power market, and continued efforts at device fabrication improvements, and device topology advancements are discussed. III–V compound semiconductor materials on c-Si for solar power generation are also reviewed. Developments in thin-film based solar cells are reviewed, with a focus on amorphous silicon, copper zinc tin sulfide, cadmium telluride, as well as nanostructured cadmium telluride. Recent developments in the use of nano-materials for solar power generation, including silicon and gallium arsenide nanowires, are also reviewed.     

Geometrical effects in adhesive joints

This paper is concerned with determining the effects of the geometry of the adherends, near the end of the bond line, upon the strength of a shear lap adhesive joint. The particular two dimensional elasto-static boundary value problem of a wedge bonded to a half plane along a finite length is considered in detail. The connection transmits a resultant normal and shear force as well as a moment. A dual integral equation formulation is used and the mathematical problem is reduced to the numerical solution of simultaneous Fredholm integral equations of the second kind. Numerical results are presented for all of the stress intensity factors and the character of the stress field is discussed in detail. It is shown that if the moment, shear and normal resultants transmitted across the bond line satisfy certain relations, then the singular stress field at the ends of the bond line can be eliminated.     

Simulation of thermal debinding: effects of mass transport on equivalent stress

A simulation of thermal debinding in polymer removal from a PIM compact, based on integrated control volume finite difference and finite element methods, is proposed. Polymer pyrolysis, heat transfer, multi-phase fluid movement, as well as stress, deformation, and their interactions are simultaneously considered. The key phenomena of mass transport, i.e., the mass flux fields of total polymer, liquid polymer, polymer vapor, vapor diffusion, and vapor convection are analyzed. The effects of mass transport on the equivalent stress, which describes the distortion energy and is responsible for the yielding of a material, are investigated. The simulated results revealed that the equivalent stress, which might lead to failure of the compact, results mainly from the polymer liquid saturation gradient, i.e., the non-uniform distribution of polymer residue, which is attributed to the non-uniform flow of the polymer.     

Size effects in nanostructured ferroelectric films

The dependence of the effective dielectric permittivity of a nanostructured ferroelectric film on the grain size and the thickness of a dead (nonferroelectric) surface layer in inhomogeneous grains has been theoretically studied.     

Geometrical resonance effects in HTSC break junctions

A periodic structure has been observed in the tunneling characteristics of HTSC break junctions. This structure is explained in terms of the electron-hole interference effect in the surface layer, which causes the formation of bound states in the normal regions N of the SNINS-type junctions. Good qualitative agreement has been found between experimental data and the predictions of the Arnolds proximity model. Several parameters of the SNINS-type structures have been derived from studies of Fiske resonances in HTSC Josephson break junctions in weak magnetic fields.     

Energy dissipation and transport in nanoscale devices

Understanding energy dissipation and transport in nanoscale structures is of great importance for the design of energy-efficient circuits and energy-conversion systems. This is also a rich domain for fundamental discoveries at the intersection of electron, lattice (phonon), and optical (photon) interactions. This review presents recent progress in understanding and manipulation of energy dissipation and transport in nanoscale solid-state structures. First, the landscape of power usage from nanoscale transistors (∼10⁻⁸ W) to massive data centers (∼10⁹ W) is surveyed. Then, focus is given to energy dissipation in nanoscale circuits, silicon transistors, carbon nanostructures, and semiconductor nanowires. Concepts of steady-state and transient thermal transport are also reviewed in the context of nanoscale devices with sub-nanosecond switching times. Finally, recent directions regarding energy transport are reviewed, including electrical and thermal conductivity of nanostructures, thermal rectification, and the role of ubiquitous material interfaces.      

The thermal stability of high-energy ball-milled nanostructured Cu

The thermal stability of nanostructured (NS) Cu prepared by high-energy ball milling was investigated. The as-prepared samples were isothermal annealed for 1 h in the temperature range of 200–1000 °C. Effects of annealing on NS Cu samples were studied by means of Vickers hardness test, differential scanning calorimetry (DSC) and stress relaxation test. The exceptional high microhardness of as-prepared Cu sample of 1.7 GPa was not detected to decrease after annealing at 500 °C for 1 h with corresponding small value of activation volumes V^* of 22.6b³ and high value of strain rate sensitivity m of 0.0176. A prominent decrease of microhardness was detected after higher temperature annealing with a rapidly increase of activation volume and decrease of strain rate sensitivity. The present investigation demonstrates that the thermal stability of NS Cu prepared by high-energy ball milling is determined by not only the grain size but also the microstructure of grain boundaries, and during annealing process, the strain release process occurred prior to the grain growth process, therefore, the NS Cu has a relatively high thermal stability.     

Spin transport in high-quality suspended graphene devices

We measure spin transport in high mobility suspended graphene (μ ≈ 10(5)cm(2)/(V s)), obtaining a (spin) diffusion coefficient of 0.1 m(2)/s and giving a lower bound on the spin relaxation time (τ(s) ≈ 150 ps) and spin relaxation length (λ(s) = 4.7 μm) for intrinsic graphene. We develop a theoretical model considering the different graphene regions of our devices that explains our experimental data.     

Conditions preventing thermal breakdown in semiconductor devices

We present results facilitating the prediction of the possibility of thermal breakdown in semiconductor devices and selection of the working parameters preventing such breakdowns.     

喷雾干燥YPSZ纳米结构热喷涂粉末材料制备及表征

YPSZ纳米结构粉末材料的研究是热喷涂制备YPSZ纳米结构涂层必须首先进行研究的问题。本文采用喷雾干燥方法制备适合于热等离子体喷涂的YPSZ纳米结构粉末原料,同时采用等离子体喷涂制备涂层。利用扫描电子显微镜分析晶粒大小、颗粒形貌,X射线衍射分析相组成,对喷雾干燥后粉末进行热重-差热分析,测定粉末的松装密度、振实密度及流动性。结果表明制备的YPSZ粉末材料具有实心、流动性好、松装密度高、振实密度高、球形度高、单斜相少等优点,采用热等离子体喷涂沉积制备YPSZ纳米结构涂层。     

Geometrical effects of positional errors in integral photography

The effects of misarrangement of elements (elemental lenses and elemental images) that construct three-dimensional (3-D) images in integral photography are presented. If the lens arrays of the capturing system and the display system are not aligned accurately, positional errors of elements may occur, causing the 3-D image to be reconstructed in an incorrect position. The relation between positional errors of elements and the reconstructed image is derived. As a result, it is shown that a 3-D image is separated by local positional errors and blurred by global positional errors. In both local and global positional errors, 3-D images reconstructed far from the lens array are greatly affected.     

Innovative aspects in thin film technologies for nanostructured materials in gas sensor devices

This work reports on the use of two innovative techniques in the field of gas sensors for preparing nano-structured materials: sol-gel and supersonic cluster beam deposition. By means of sol-gel, nano-structured In₂O₃ thin films have been prepared and deposited under different deposition parameters on silicon wafer. In this way the results have shown a good compatibility of the method with silicon technology, then potentially suitable to be used in the fabrication of integrated devices. The second technique has been applied for the preparation of nano-structured TiO₂ thin films showing its capability to be used in the fabrication of gas sensor devices, mainly when a good control of the grain dimension is required.     

Ab initio correlation effects on the electronic and transport properties of metal(II)-phthalocyanine-based devices

Using first-principles calculations in the framework of density functional theory, we investigated the electronic and transport properties of metal(II)-phthalocyanine (M(II)Pc) systems, both in a single-molecule configuration and in a model device geometry. In particular, using copper(II)-Pc and manganese(II)-Pc as prototypical examples, we studied how electronic correlations on the central metal ion influence the analysis of the electronic structure of the system and we demonstrated that the choice of the exchange-correlation functional, also beyond the standard local or gradient corrected level, is of crucial importance for a correct interpretation of the data. Finally, our electronic transport simulations have shown that M(II)Pc-based devices can act selectively as molecular conductors, as in the case of copper, or as spin valves, as in the case of manganese, demonstrating once more the great potential of these systems for molecular nanoelectronics applications.     

Structured graphene devices for mass transport

The reversible atomic-mass transport along graphene devices has been achieved. The motion of Al and Au in the form of atoms or clusters is driven by applying an electric field between the metal electrodes that contact the graphene sheet. It is shown that Al moves in the direction of the applied electric field whereas Au tends to diffuse in all directions. The control of the motion of Al is further demonstrated by achieving a 90° turn, using a graphene device patterned in a crossroads configuration. The controlled motion of Al is attributed to the charge transfer from Al onto the graphene so that the Al is effectively charged and can be accelerated by the applied electric field. To get further insight into the actuation mechanism, theoretical simulations of individual Al and Au impurities on a perfect graphene sheet were performed. The direct (electrostatic) force was found to be ～1 pN and dominant over the wind force. These findings hold promise for practical use in future mass transport in complex circuits.     

Atomic structure and thermal stability of nanostructured Y-Fe alloys

We present results of an X-ray and EXAFS study of nanostructured Y-Fe alloys with 0.05 ≤ _XFe ≤ 0.77. Because the atomic size mismatch implies a large elastic contribution to the heat of solution of Fe in the Y lattice, the alloy system is a potential candidate for the stabilization against grain-growth by grain boundary segregation. For _XFe ≤ 0.3, the majority of Fe is segregated to the grain boundaries of crystalline Y. The grain-size of the Y-crystals in asprepared and annealed samples decreases with increasing x_Fe ⩾ 0.45, the alloys are amorphous. Upon annealing, the grain-size of the low-x_Fe crystalline samples increases significantly, whereas high-x_Fe crystalline samples show little grain-growth. Annealing is accompanied by a progressive increase of the concentration of Fe dissolved in the Y crystal lattice to values considerably beyond the equilibrium solubility.     

Microelectromechanical devices for satellite thermal control

Future space missions will include constellations of spacecraft, including nano- and picosatellites, where adaptive thermal control systems will be needed that fit the constraints of space applications with limited power and mass budgets. A microelectromechanical systems (MEMS) solution has been developed that will vary the emissivity on the surface of the small satellite radiator. The system is based on louver thermal controllers, where panels are mechanically positioned to modulate the effective radiator surface area. This system consists of MEMS arrays of gold-coated sliding shutters, fabricated with the Sandia ultraplanar, multilevel MEMS technology fabrication process, which utilizes multilayer polycrystalline silicon surface micromachining. The shutters can be operated independently to allow digital control of the effective emissivity. This first demonstrator technology is limited in the possible emittance range to a 40% change. Early prototypes of MEMS louvers that open away from the structure have shown the capability of a much wider dynamic range. The first generation of this active thermal management system will be demonstrated on NASA's New Millennium Program ST-5 spacecraft. With the opportunity to validate the MEMS thermal control technology in space on ST-5, lightweight, low-power MEMS radiators offer a possibility for flexible thermal control on future nanosatellites.     

Macro- and nanoscopic capillary effects on nanostructured real surfaces

The measurements of capillary forces on different diamond-like materials and carbon allotropic modifications taken using a scanning force microscope have been discussed. The amplitude-frequency characteristics of the nanorelief surfaces studied have been widely varied by plasma chemical treatments. The measurements of capillary forces have been compared with the macroscopic values of a wetting angle. It has been shown that a macroscopic wetting angle depends on the averaged surface energy only and is slightly dependent on the nanorelief characteristics, and nanocapillary forces correlate with both surface relief parameters and the local angle of wetting. Criteria for multimeniscus mode of capillary forces measurement in the surface force spectroscopy and the prospects of this procedure application for mapping the real surface energy have been considered in detail.     

Charge-gated transport of proteins in nanostructured optical films of mesoporous silica

The admission into and diffusion through nanoscale pores by molecules is a fundamental process of great importance to biology and separations science. Systems (e.g., chromatography, electrophoresis) designed to harness such processes tend to remove the separation process from the detection event, both spatially and temporally. Here, we describe the preparation and characterization of thin optical Fabry-Pe?rot films of mesoporous silica (pSiO(2)) that can detect protein infiltration by optical interferometry, which probes the separation process in real time and in the same ultrasmall physical volume (5 nL). Admission of a protein into the pores is controlled by the diameter (～50 nm) and the surface charge of the pores, and both the rate and the degree of protein infiltration are a function of solution pH. Test proteins bovine serum albumin (BSA, 66 kDa), bovine hemoglobin (BHb, 65 kDa), and equine myoglobin (EMb, 18 kDa) are admitted to or excluded from the nanophase pores of this material based on their size and charge. The rate of protein transport within the pores of the pSiO(2) film is slowed by 3 orders of magnitude relative to the free-solution diffusion values, and it is maximized when pH = pI.