Tunable visible and near-IR emission from sub-10 nm etched single-crystal Si nanopillars

Visible and near-IR photoluminescence (PL) is reported from sub-10 nm silicon nanopillars. Pillars were plasma etched from single crystal Si wafers and thinned by utilizing strain-induced, self-terminating oxidation of cylindrical structures. PL, lifetime, and transmission electron microscopy were performed to measure the dimensions and emission characteristics of the pillars. The peak PL energy was found to blue shift with narrowing pillar diameter in accordance with a quantum confinement effect. The blue shift was quantified using a tight binding method simulation that incorporated the strain induced by the thermal oxidation process. These pillars show promise as possible complementary metal oxide semiconductor compatible silicon devices in the form of light-emitting diode or laser structures.     

Optical gain and stimulated emission in periodic nanopatterned crystalline silicon

Persistent efforts have been made to achieve efficient light emission from silicon in the hope of extending the reach of silicon technology into fully integrated optoelectronic circuits, meeting the needs for high-bandwidth intrachip and interchip connects. Enhanced light emission from silicon is known to be theoretically possible, enabled mostly through quantum-confinement effects. Furthermore, Raman-laser conversion was demonstrated in silicon waveguides. Here we report on optical gain and stimulated emission in uniaxially nanopatterned silicon-on-insulator using a nanopore array as an etching mask. In edge-emission measurements, we observed threshold behaviour, optical gain, longitudinal cavity modes and linewidth narrowing, along with a collimated far-field pattern, all indicative of amplification and stimulated emission. The sub-bandgap 1,278 nm emission peak is attributed to A-centre mediated phononless direct recombination between trapped electrons and free holes. The controlled nanoscale silicon engineering, combined with the low material loss in this sub-bandgap spectral range and the long electron lifetime in such A-type trapping centres, gives rise to the measured optical gain and stimulated emission and provides a new pathway to enhance light emission from silicon.     

Scaling down lateral dimensions of silicon nanopillars fabricated by reactive ion etching with Au/Cr self-assembled clusters as an etch mask

Nanodot and nanopillar structures and precisely controlled reproducible fabrication thereof are of great interest in common nanoelectronic devices, including photonic crystals and surface plasmon resonance instruments. In this work, fabrication process of the silicon nanopillar structures is described. It includes self-organization of gold and chromium clusters at thickness close to that of one atomic diameter to serve as etching masks followed by the reactive ion etching to form silicon nanopillars. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize self-organized gold and chromium clusters as well as the final silicon nanopillars. This method was found to produce silicon nanopillars of sub-10 nm lateral dimensions and the diameter-to-height aspect ratio of up to 1:14.     

Understanding the kinetics and nanoscale morphology of electron-beam-induced deposition via a three-dimensional Monte Carlo simulation: the effects of the precursor molecule and the deposited material

The electron-beam-induced deposition of silicon oxide from tetraethyorthosilicate and tungsten from tungsten hexafluoride is simulated via a Monte Carlo simulation. Pseudo one-dimensional nanopillars are grown using comparable electron-beam parameters and a comparison of the vertical and lateral growth rate and the pillar morphology is correlated to the precursor and deposited material parameters. The primary and secondary electrons (type I) are found to dominate the vertical growth rate and the lateral growth rate is dominated by forward and secondary electrons (type II). The resolution and morphology of the nanopillars are affected by the effective electron interaction volume and the resultant surface coverage of the precursor species in the effective electron interaction region. Finally, the simulated results are compared to previously reported experimental results.     

Enhanced free exciton and direct band-edge emissions at room temperature in ultrathin ZnO films grown on Si nanopillars by atomic layer deposition

Room-temperature ultraviolet (UV) luminescence was investigated for the atomic layer deposited ZnO films grown on silicon nanopillars (Si-NPs) fabricated by self-masking dry etching in hydrogen-containing plasma. For films deposited at 200 °C, an intensive UV emission corresponding to free-exciton recombination (~3.31 eV) was observed with a nearly complete suppression of the defect-associated broad visible range emission peak. On the other hand, for ZnO films grown at 25 °C, albeit the appearance of the defect-associated visible emission, the UV emission peak was observed to shift by ~60 meV to near the direct band edge (3.37 eV) recombination emission. The high-resolution transmission electron microscopy (HRTEM) showed that the ZnO films obtained at 25 °C were consisting of ZnO nanocrystals with a mean radius of 2 nm embedded in a largely amorphous matrix. Because the Bohr radius of free-exictons in bulk ZnO is ~2.3 nm, the size confinement effect may have occurred and resulted in the observed direct band edge electron-hole recombination. Additionally, the results also demonstrate order of magnitude enhancement in emission efficiency for the ZnO/Si-NP structure, as compared to that of ZnO directly deposited on Si substrate under the same conditions.     

Thermal-and field-treatment induced reconstruction of a carbon fiber crystal

A carbon (PAN) fiber crystal was studied in a field electron microscope equipped with a dispersive energy analyzer. Annealing of the emitter crystal at a temperature of 750° C lead to a tenfold decrease in the emission current and to the appearance of an additional low-energy peak (shifted by 0.5 eV from the main peak toward lower energies) in the field electron energy distribution. An increase in the anode voltage restored both the initial emission current and the electron energy distribution.     

Electron field emission from microtip arrays

Electron field emission measurements from structurized cathodes was reported. Silicon (Si) and boron-doped silicon carbide (SiC:B) had been chosen as a base materials for microtip field emission arrays (FEA). Each of single silicon FEAs has been covered by a thin metal layer using chromium (Cr), titanium (Ti) or platinum (Pt) to reduce the threshold voltage of electron emission. Surface of boron-doped silicon carbide and silicon FEAs have also been modified by deposition of multi-walled carbon nanotubes (MWNT). These efforts let improved the emission currents and bring down the turn-on field down to 1.2 V/μm. In contrast to the above, plain cold cathodes prepared as porous silicon (PS) substrates covered by thin MWNTs have also been measured.     

Field-emission electron source for vacuum micropump

In the work a conception of a miniature, orbitron ion vacuum micropump for an integration with vacuum MEMS devices is presented. It is made of silicon and glass using microengineering technology. The main part of the device is a lateral field-emission source of electrons, which has been fabricated on oxidized silicon wafer. Both, cold cathode and anode of the source are made of thin gold layer using only one photolithography process. Fabrication process and the preliminary results of electrical tests of the field-emission electron source are presented. Experimental studies have shown its good emission parameters: a low threshold voltage (over a dozen Volts), a high electron current (from tens to several hundred micro amperes), and field enhancement coefficient from 10⁷ to 10⁸ cm⁻¹. These results are promising and give possibility to fabricate orbitron micropump as an integrated part of vacuum MEMS.     

Field-emission electron source for vacuum micropump

In the work a conception of a miniature, orbitron ion vacuum micropump for an integration with vacuum MEMS devices is presented. It is made of silicon and glass using microengineering technology. The main part of the device is a lateral field-emission source of electrons, which has been fabricated on oxidized silicon wafer. Both, cold cathode and anode of the source are made of thin gold layer using only one photolithography process. Fabrication process and the preliminary results of electrical tests of the field-emission electron source are presented. Experimental studies have shown its good emission parameters: a low threshold voltage (over a dozen Volts), a high electron current (from tens to several hundred micro amperes), and field enhancement coefficient from 10⁷ to 10⁸ cm⁻¹. These results are promising and give possibility to fabricate orbitron micropump as an integrated part of vacuum MEMS.     

电子束蒸发制备纳米硅锥及其场发射性能研究

应用超高真空电子束蒸发方法，以铁作为催化剂，在硅和多孔硅衬底上生长纳米Si锥阵列。采用原子力显微镜表征生长在不同衬底上纳米硅的形貌特征，测试和比较了不同衬底上纳米硅的电子场发射性能。实验结果表明用这种方法形成了高度为10—35nm的锥状纳米结构，并且这些纳米硅锥阵列的场发射性能良好。比较生长不同衬底上的纳米锥形貌与场发射性能，发现多孔硅衬底上更适合生长这种纳米硅锥。     

An electron source with a multiarc plasma emitter for obtaining submillisecond pulsed megawatt beams

An electron source with a plasma emitter based on an arc-discharge system with six cathodes and a common cylindrical hollow anode is described. Upon synchronous initiation of vacuum-arc discharges, the space of the hollow anode is filled by dense low-temperature plasma, the emission boundary of which is stabilized by a fine-structure metal grid with a 150-cm² area. The arc-current amplitude for each cathode amounts to 100–300 A. Under the action of a constant accelerating voltage applied between the plasma emitter and grounded accelerating electrode combined with the drift tube, electrons are extracted from plasma and accelerated. At a working pressure of 0.04 Pa, an electron beam with a maximum current amplitude of 1 kA has been obtained at an initial accelerating voltage of 80 kV and pulse duration (FWHM) of 100 μs, which has been transported in a longitudinal magnetic field of 0.035 T over a distance of 80 cm.     

Electron emission characterization of diamond thin films grown from a solid carbon source

Diamond films of various morphologies and compositions have been deposited on silicon substrates by a plasma-enhanced chemical transport (PECT) process from a solid carbon source. Electron emission efficiency of these diamond films is related to their morphology and composition. The electric field required to excite emission in a boron-doped polycrystalline diamond film ranged between 20 to 50 MV m⁻¹. In an undoped conducting nanocrystalline diamond composite film, the field was as low as 5–11 MV m⁻¹. The cold field electron emission of these films is confirmed from the Fowler-Nordhelm plots of the data. Enhancement of electron emission by band-bending and by the nanocrystalline microstructure are discussed. New diamond emitters made of nanocrystalline boron-doped diamond composite are proposed.     

Cell adhesion and migration on nanopatterned substrates and their effects on cell-capture yield

With scanning electron microscopy analysis, we investigated the role of nanoscale topography on cellular activities; e.g.?cell adhesion and spreading by culturing A549 cells (human lung carcinoma cell line cells) for 1-48?h on three sets of nanostructures; quartz nanopillars (QNPs), silicon nanopillars and silicon nanowire (SiNW) arrays, along with planar glass substrates. We found that cells on QNP arrays developed a longer shape than those on SiNW arrays. In addition, we studied how cell morphologies influence the cell-capture yield on the three sets of nanostructures. This research showed that the filopodial formations were directing the cell-capture yield on nanostructured substrates. This finding implies the possibility of using nanoscale topography features to control the filopodial formation including extension and migration from the cells. Using streptavidin-functionalized SiNW substrate, we further demonstrated a substantially higher yield (～91.8?±?5.9%) than the planar glass wafers (～24.1?±?7.5%) in the range of 200-3000 cells.     

Mathematical modeling of the electron beam formatting systems on the basis of field emission cathodes with various shapes

In the present paper we solve some problems of field emission cathodes mathematical modeling and the electron guns for vacuum electronics. The supposed shape of the field emission cathode was either “sphere-on-cone” or “sphere-on-spindle” (as a cathode) on the sphere substrate and the spherical segment (as an anode).     

Thermal effect on anode during field electron emission from cathode

It is demonstrated that, during field electron emission from the cathode, the amount of heat evolved in the anode can differ from the classical value, provided that the translational energy of electrons reaching the anode does not exceed the Fermi energies of electrons in the dissimilar electrode pair. This effect is related to the fact that each electron emitted from the cathode brings the corresponding Fermi energy to the anode, in addition to the energy of the applied field. Therefore, under-or overheating of the anode is possible due to a difference between the Fermi energies.     

A model of electron emission from a wedge in the space-charge-limited current regime

The process of electron emission from a wedge-shaped cathode in the space-charge-limited current regime has been theoretically studied. The field distribution in the interelectrode gap is described using a simple analytical model, which is based on the matching of self-similar solutions for electron flows at the vertex region and at the periphery. The dependence of the perveance on the wedge angle in the wedge cathode-flat anode system is determined.     

Nanocrystal-semiconductor interface: Atomic-resolution cross-sectional transmission electron microscope study of lead sulfide nanocrystal quantum dots on crystalline silicon

We report on a cross-sectional high resolution transmission electron microscope study of lead sulfide nanocrystal quantum dots （NCQDs） dispersed on electron-transparent silicon nanopillars that enables nearly atomically-resolved simultaneous imaging of the entire composite： the quantum dot, the interfacial region, and the silicon substrate. Considerable richness in the nanocrystal shape and orientation with respect to the substrate lattice is observed. The average NCQD-substrate separation is found to be significantly smaller than the length of the ligands on the NCQDs. Complementary photoluminescence measurements show that light emission from PbS NCQDs on silicon is effectively quenched which we attribute to intrinsic mechanisms of energy and charge transfer from PbS NCQDs to Si.     

常开型后栅极场致发射显示板工作特性的研究

常开型后栅极场致发射显示板是一种新型的场致发射器件.它直接利用阳极使阴极产生场致电子发射,而通过埋在阴极之下的栅极上施加负电压来阻止阴极产生场致电子发射来调制显示所需的图像.为了研究该场致发射显示板的阴极发射特性,本文采用有限元法对场致发射区域内的电场分布进行了模拟计算,用Fowler-Nordheim(F-N)公式计算了阴极表面的发射情况.并研究了阳极电压、阴极电压、阴调距、阴极宽度和阴极厚度等参数的改变对阴极发射特性和栅极调制能力的影响.计算结果显示阴极发射特性和栅极调制能力与上述电参数和结构参数关系密切,从而为优化设计这种显示器件提供了方向.     

Enhanced emission during submillisecond low-energy electron beam generation in a diode with grid-stabilized plasma cathode and open anode plasma boundary

We have experimentally studied the phenomenon of emission enhancement in a gas-filled diode with grid-stabilized plasma cathode and open (mobile) anode plasma boundary at an accelerating voltage of up to 20 kV. As the working gas pressure is increased to p ≥ 10⁻² Pa and the longitudinal magnetic field is increased to B _z ≥ 20 mT, the current in the accelerating gap exhibits significant growth, sometimes by a factor of two or more. Experimental data show that the most probable mechanism responsible for this effect is ion-induced secondary electron emission from the emitting electrode surface bombarded by ions from plasma generated by the electron beam in the drift space. These ions are accelerated in the space charge layer between the emitting electrode surface and the mobile boundary of the beam-generated (anode) plasma.     

Three-dimensional metal scaffold supported bicontinuous silicon battery anodes

Silicon-based lithium ion battery anodes are attracting significant attention because of silicon's exceptionally high lithium capacity. However, silicon's large volume change during cycling generally leads to anode pulverization unless the silicon is dispersed throughout a matrix in nanoparticulate form. Because pulverization results in a loss of electric connectivity, the reversible capacity of most silicon anodes dramatically decays within a few cycles. Here we report a three-dimensional (3D) bicontinuous silicon anode formed by depositing a layer of silicon on the surface of a colloidal crystal templated porous nickel metal scaffold, which maintains electrical connectivity during cycling due to the scaffold. The porous metal framework serves to both impart electrical conductivity to the anode and accommodate the large volume change of silicon upon lithiation and delithiation. The initial capacity of the bicontinuous silicon anode is 3568 (silicon basis) and 1450 mAh g(-1) (including the metal framework) at 0.05C. After 100 cycles at 0.3C, 85% of the capacity remains. Compared to a foil-supported silicon film, the 3D bicontinuous silicon anode exhibits significantly improved mechanical stability and cycleability.