Fabrication and characterization of nanopore-based electrodes with radii down to 2 nm

We report on the fabrication and characterization of gold nanoelectrodes with carefully controlled nanometer dimensions in a matrix of insulating silicon nitride. A focused electron beam was employed to drill nanopores in a thin silicon nitride membrane. The size and shape of the nanopores were studied with high-resolution transmission electron microscopy and electron-energy-loss two-dimensional maps. The pores were subsequently filled with gold, yielding conically shaped nanoelectrodes. The nanoelectrodes were examined by atomic and electrostatic force microscopy. Their applicability in electrochemistry was demonstrated by steady-state cyclic voltammetry. Pores with a radii down to 0.4 nm and electrodes with radii down to 2 nm are demonstrated.     

In Situ Thermocouples in Macro-Components Fabricated Using SALD and SALDVI Techniques. I. Thermochemical Modeling

To fabricate macro-structural SiC components containing an In Situ SiC/C thermocouple using an integrated SALD and SALDVI technique, thermodynamic analyses on the involved reactant gases have been performed with the CET89 code based on the minimization of the system free energy. The gaseous precursors considered include tetramethylsilane (TMS) and methyltrichlorosilane (MTS) for the deposition of silicon carbide, and methane, ethylene and acetylene for the deposition of carbon. Reactions between disilane and acetylene and between TMS and ammonia have also been thermodynamically calculated for the deposition of silicon carbide and silicon nitride (for use as an insulation layer between the thermocouple and the matrix), respectively. Based on these analyses, four characteristic temperature zones have been defined for the decomposition of silicon carbide from TMS. A silicon nitride deposition map has been built for the TMS and ammonia system. The deposition temperature range of silicon nitride is found to increase with the total pressure of TMS plus ammonia and the addition of hydrogen, and be affected by the ratio of TMS to ammonia. The addition of hydrogen also introduces a stable silicon carbide and silicon nitride mixture zone that otherwise does not exist. The co-deposition of graphite with silicon carbide and silicon nitride is found in the TMS-containing systems at certain conditions. However, the threshold temperature at which graphite co-deposition occurs can be increased by the addition of hydrogen, thereby eliminating or reducing the graphite co-deposition. Based on these thermodynamic analyses, the gaseous precursors for the deposition of silicon carbide, silicon nitride and carbon have been selected for further experimental evaluation, the result of which is reported in part II of this series.     

Synthesis of crystalline carbon nitride with enhanced photocatalytic NO removal performance:An experimental and DFT theoretical study

The pristine carbon nitride derived from the thermally-induced polymerization of nitrogen-containing precursors(e.g.cyanamide,dicyanamide,melamine and urea)displays low crystallinity because of the predominantly kinetic hindrance.Herein,we reported a modified molten-salts method to fabricate the crystalline carbon nitride under ambient pressure,which is expected to the large-scale production of crystalline carbon nitride.The obtained crystalline carbon nitride displayed about 3.0 times higher pho-tocatalytic NO removal performance than that of pristine carbon nitride under visible light irradiation(λ＜400 nm).Detailed experimental characterization and theoretical calculation revealed the crucial roles of crystallinity in crystalline carbon nitride for the enhanced photocatalytic NO removal performance.This research provided deep insights into the crystallinity of carbon nitride for the enhanced photocatalytic performance.     

A wurtz-like reaction to silicon nanowires

Silicon nanowires have been successfully synthesized via wurtz-like reaction, using silicon tetrachloride and sodium in the presence of Co/Ni catalyzer at 500 °C In this process the sodium was used as reductant and flux. Transmission electron microscopy (TEM) shows that the nanowire cluster is about 10 nm in diameter and length up to several microns, and well aligned along their longitude direction. High-resolution transmission electron microscopy (HRTEM) images demonstrates that as-synthesized nanowires interlayer spacing are around 0.31 nm, corresponding well to the (111) lattice parameter of diamond-like crystalline silicon. Based on the experimental results, the possible wurtz reaction mechanism of the silicon nanowires (SiNWs) has been properly proposed.     

Planar silver nanowire,carbon nanotube and PEDOT:PSS nanocomposite transparent electrodes

Abstract

Highly conductive, transparent and flexible planar electrodes were fabricated using interwoven silver nanowires and single-walled carbon nanotubes (AgNW:SWCNT) in a PEDOT:PSS matrix via an epoxy transfer method from a silicon template. The planar electrodes achieved a sheet resistance of 6.6 ± 0.0 Ω/□ and an average transmission of 86% between 400 and 800 nm. A high figure of merit of 367 Ω^?1 is reported for the electrodes, which is much higher than that measured for indium tin oxide and reported for other AgNW composites. The AgNW:SWCNT:PEDOT:PSS electrode was used to fabricate low temperature (annealing free) devices demonstrating their potential to function with a range of organic semiconducting polymer:fullerene bulk heterojunction blend systems.     

Directed Fabrication of Ceramic Nanostructures on Fragile Substrates Using Soft-electron Beam Lithography (soft-eBL)

We demonstrate the use of a facile nanopatterning scheme known as soft electron beam lithography (soft-eBL) to fabricate and site specifically position a variety of functional ceramic nanostructures onto two fragile substrates: a 75-nm-thick electron-transparent silicon nitride membrane and suspended microhotplates with embedded heaters. The patterned nanostructures on nitride membranes can be readily probed with a variety of characterization tools without any postfabrication sample preparation, allowing observation of the nanostructures in near-pristine condition. We demonstrate this by characterizing the structural, chemical, and optical properties of several ceramic nanostructures patterned on membranes using electron microscopy and surface scanning probe tools such as atomic force microscopy and near- field scanning optical microscopy. We further demonstrate that such nanostructures, upon integration with microelectromechanical systems (MEMS) microhotplate platforms, can function as gas-sensing elements; we evaluate their sensing performance at micromoles per mole target analyte concentration levels.     

Characterization of silicon oxynitride films prepared by the simultaneous implantation of oxygen and nitrogen ions into silicon

Silicon oxynitride films about 5 nm in thickness were prepared by simultaneously implanting 5 keV oxygen and nitrogen ions into silicon at room temperature up to saturation. These films with concentrations ranging from pure silicon oxide to silicon nitride were characterized using Auger electron spectroscopy, electron energy loss spectroscopy and depth-concentration profiling. The different behaviour of the silicon oxynitride films compared with those of silicon oxide and silicon nitride with regard to thermal stability and hardness against electron and argon ion irradiation is pointed out.     

Nucleation and growth mechanism of diamond during hot-filament chemical vapour deposition

High-resolution transmission electron microscopy (HRTEM) was employed to study the nucleation and subsequent growth mechanism of crystalline diamond grown on copper TEM grids by the hot-filament chemical vapour deposition process. The HRTEM revealed direct evidence for the formation of a diamond-like amorphous carbon layer 8–14 nm thick, in which small diamond microcrystallites about 2–5 nm across were embedded. These diamond microcrystallites were formed as a result of direct transformation of the diamond-like carbon into diamond. Large diamond crystallites were observed to grow from these microcrystallites. The diamond surface was found to be non-uniform. It is envisaged that the diamond microcrystallites present in the amorphous, diamond-like carbon layer provide nucleation sites on which the large diamond crystallites grew. A mechanism of diamond growth has been proposed, based on the experimental findings, and is consistent with available theoretical models and numerous experimental observations reported in the literature.     

Fabrication and performance analysis of film bulk acoustic wave resonators

In this paper, a radio frequency reactive sputtering deposition technique for piezoelectric aluminum nitride (AlN) thin film formation on a gold (Au) bottom electrode and its successful application in a film bulk acoustic resonator (FBAR) are investigated. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements show that the AlN films were deposited onto an Au bottom electrode with highly c-axis-preferred orientation, well-textured columnar structure with a fairly uniform grain size of approximately 83 nm. The roughness is measured at a root-mean square (RMS) value of 5.4 nm and the average peak to valley of each grain column is 46.3 nm. The FBAR consists of an AlN piezoelectric thin film sandwiched between Au electrodes, all of which lie on a thin low-stress silicon nitride which serves as a support membrane on silicon. The performance of FBAR device exhibits a significant of the series quality factor (Q_s), the parallel quality factor (Q_p), the effective electromechanical coupling coefficient (k_eff²), and the bandwidths are 97, 120, 5.1%, and 24 MHz, respectively.     

Sub-50 nm positioning of organic compounds onto silicon oxide patterns fabricated by local oxidation nanolithography

We present a process to fabricate molecule-based nanostructures by merging a bottom-up interaction and a top-down nanolithography. Direct nanoscale positioning arises from the attractive electrostatic interactions between the molecules and silicon dioxide nanopatterns. Local oxidation nanolithography is used to fabricate silicon oxide domains with variable gap separations ranging from 40?nm to several microns in length. We demonstrate that an ionic tetrathiafulvalene (TTF) semiconductor can be directed from a macroscopic liquid solution (1?μM) and selectively deposited onto predefined nanoscale regions of a 1?cm(2) silicon chip with?an accuracy of 40?nm.     

Enhanced photoelectrochemical activity of the TiO2 /ITO nanocomposites grown onto single-walled carbon nanotubes at a low temperature by nanocluster deposition

High-resolution transmission electron microscopy (HRTEM) is used to observe a TiO2/ITO-coated composite nanostructure grown onto single-walled carbon nanotubes (SWCNTs). The SWCNTs, indium tin oxide (ITO), and TiO2 mixtures of anatase (A) and rutile (R) are clearly distinguished in the HRTEM images. The thickness of the SWCNT was about 3 nm, and the TiO2 shell included different polycrystalline structures.     

Electrical Characterization of Ordered Si:P Dopant Arrays

We report on the ability to fabricate arrays of planar, nanoscale, highly doped phosphorus dots in silicon separated by source and drain electrodes using scanning tunneling microscope lithography. We correlate ex situ electrical measurements with scanning tunneling microscope (STM) images of these devices and show that ohmic conduction can be achieved through the disordered array with a P coverage of 0.8times10¹⁴ cm^-2. In comparison, we show that an ordered array of P dots ~6 nm in diameter and containing ~50 P atoms separated by ~4 nm shows nonlinear I-V, characteristic of a series of metallic dots separated by tunnel barriers. These results highlight the use of STM lithography to pattern ordered dopants in silicon down to the sub-10 nm scale     

Correlating Raman-spectroscopy and high-resolution transmission-electron-microscopy studies of amorphous/nanocrystalline multilayered silicon thin films

The nanostructure of multilayered silicon thin films was studied using Raman spectroscopy (RS) and high-resolution transmission electron microscopy (HRTEM). Since the properties of nanocrystalline silicon layer depend on the size of the nanocrystals, an accurate determination of the crystallite sizes and the crystalline fraction is of primary importance. The average sizes of the nanocrystals estimated by RS, assuming bi-modal distribution of crystal sizes, were close to 2 nm and above 5-20 nm. HRTEM confirmed the existence of nanocrystals with a mean square value of around 2 nm and certain number of larger nanocrystals, embedded in an amorphous matrix. The correlation between the results obtained by these two techniques is discussed. The optical properties of measured samples corresponded to an amorphous-crystalline mixture with indication of confinement effects compatible with 2 nm nanocrystals.     

Planar silver nanowire,carbon nanotube and PEDOT:PSS nanocomposite transparent electrodes

Highly conductive, transparent and flexible planar electrodes were fabricated using interwoven silver nanowires and single-walled carbon nanotubes (AgNW:SWCNT) in a PEDOT:PSS matrix via an epoxy transfer method from a silicon template. The planar electrodes achieved a sheet resistance of 6.6 ± 0.0 Ω/□ and an average transmission of 86% between 400 and 800 nm. A high figure of merit of 367 Ω⁻¹ is reported for the electrodes, which is much higher than that measured for indium tin oxide and reported for other AgNW composites. The AgNW:SWCNT:PEDOT:PSS electrode was used to fabricate low temperature (annealing free) devices demonstrating their potential to function with a range of organic semiconducting polymer:fullerene bulk heterojunction blend systems.     

Use of anodic tantalum pentoxide for high-density capacitor fabrication

In this work we report on very thin (10 to 100 nm) tantalum oxide fabricated by anodic oxidation of tantalum nitride and tantalum silicide to be used as the dielectric of high density MIM and MIS capacitors. These films exhibit greatly improved leakage currents, breakdown voltage and very low defect density, thus allowing the fabrication of large area capacitors. Several counter and bottom electrodes have been used and compared. The effects of the different processing conditions (top-electrode metals, annealing conditions, bottom electrode stoichiometry) on the capacitor performances are extensively discussed throughout this work. The nitrogen content of tantalum nitride films seems to have an important influence on the insulator quality. Leakage currents in the insulator have been carefully studied in order to determine the nature and physical origin of the dominant conduction mechanisms in the insulator. The electrical behaviour of the resulting high-density MIM capacitors has been extensively characterized. Finally, we describe a new method to fabricate MIS diodes with anodic tantalum oxide as insulator.     

A novel submicron-gap electrode fabrication technology using thermal oxidation

A novel and reproducible method to fabricate submicron-gap electrodes using thermal oxidation has been presented. In this method, oxidation process determines the gap distance. The micron-level silicon electrode gaps with different shapes were first generated on the silicon wafer by conventional photolithography followed by deep reactive ion etching process. Then thermal oxidation was conducted to realize the transition from silicon to silicon dioxide, i.e. reduce the gap width. Finally, the planar electrodes with sub-micron spacing were formed by metallization and photolithography. Scanning electron microscopy (SEM) was used to examine the electrode configuration and the electrical properties of as-prepared electrode pairs were also characterized. The results showed that using the method investigated in this work, Au electrodes with a submicron-sized gap could be easily fabricated, with good uniformity and reproducibility.     

Suspended multiwalled carbon nanotubes as self-aligned evaporation masks

We describe the nanofabrication study of self-aligned electrodes on suspended multiwalled carbon nanotube structures. When metal is deposited on a suspended multiwalled carbon nanotube structure, the nanotube acts as an evaporation mask, resulting in the formation of discontinuous electrodes. The metal deposits on the nanotubes are removed with lift-off. Using Al sacrificial layers, it was possible to fabricate self-aligned contact electrodes and control electrodes nanometers from the suspended carbon nanotubes with a single lithography step. It was also shown that the fabrication technique may also be used to form nano-gapped contact electrodes. The technique should prove useful for the fabrication of nano-electromechanical systems.     

Design and fabrication of nanofluidic devices by surface micromachining

Using surface micromachining technology, we fabricated nanofluidic devices with channels down to 10?nm deep, 200?nm wide and up to 8?cm long. We demonstrated that different materials, such as silicon nitride, polysilicon and silicon dioxide, combined with variations of the fabrication procedure, could be used to make channels both on silicon and glass substrates. Critical channel design parameters were also examined. With the channels as the basis, we integrated equivalent elements which are found on micro total analysis (μTAS) chips for electrokinetic separations. On-chip platinum electrodes enabled electrokinetic liquid actuation. Micro-moulded polydimethylsiloxane (PDMS) structures bonded to the devices served as liquid reservoirs for buffers and sample. Ionic conductance measurements showed Ohmic behaviour at ion concentrations above 10?mM, and surface charge governed ion transport below 5?mM. Low device to device conductance variation (1%) indicated excellent channel uniformity on the wafer level. As proof of concept, we demonstrated electrokinetic injections using an injection cross with volume below 50?attolitres (10(-18)?l).     

Synthesis of nanozirconooligocarbosilanes

We describe the first chlorine-free synthesis of nanozirconooligocarbosilanes through thermal cocondensation of low-molecular oligocarbosilanes and zirconium tetrakis(diethylamide). The starting reagents, reaction intermediates, and final products have been characterized by ¹H, ¹³C, and ²⁹Si nuclear magnetic resonance, UV and IR spectroscopy, gel-permeation chromatography, thermogravimetry, transmission electron microscopy (TEM), and elemental analysis. The synthesized nanozirconooligocarbosilanes have been used to fabricate ceramic fibers and matrices through thermal and chemical processing. TEM results demonstrate that the particles of zirconium and products of its reactions with silicon, carbon, and nitrogen range in size from 10 to 20 nm in the oligomers and from 20 to 30 nm in the ceramics.     

纯化处理对碳纳米管脱盐性能的影响

利用未经纯化处理和纯化处理后的碳纳米管分别压制成电极片并分别组装成脱盐器,对两种脱盐器的脱盐性能进行了测试,并且利用氮气吸附-脱附、透射电子显微镜、原子力显微镜、拉曼光谱及接触角测试仪等表征手段测试了影响电极脱盐性能的主要性能参数.研究表明,纯化处理使得碳纳米管电极的比表面积大大增加,孔径结构得到了很大的改善,并且含氧官能团的引入使得浸润性能得到了大大的提高,其脱盐性能得到很大改善.