Controlled collapse of high-aspect-ratio nanostructures

Capillary-force-induced collapse of high-aspect-ratio (HAR) micro- and nanostructures is common in the evaporation-drying process and a number of applications based on the collapse have been proposed. However, the collapse of small HAR structures is usually uncontrollable, which has prevented it from being used in engineering applications. Here, the collapse of 10-nm-scale structures is separately controlled through engineering an asymmetric cross section, curvature, and tilt in the structures prior to collapse. It is shown that this deterministic-collapse approach can be used to create linear structures from collapsed pillars and planar rectangular structures from collapsed fencelike linear structures, and can further be used to create small gaps by controlling the collapse of nearby structures. These techniques could be used to improve the performance of beam-based lithography methods for certain types of patterns by increasing throughput and resolution, reducing the proximity effect, and reducing irradiation damage. In addition, this controlled-collapse concept provides a possible platform with which to study mechanical behavior at the 10-nm scale.     

电子束焦点位置对TC4板材焊接接头显微组织的影响

目的针对厚板TC4合金真空电子束焊缝组织不均匀的问题,通过改变不同焦点位置,分析焊接接头显微组织特征。方法采用真空电子束对厚度为20 mm的TC4板进行对接试验,用光学显微镜和显微硬度计对焊缝不同位置的显微组织进行观察与分析。结果采用表面聚焦时,可获得成形良好的"I"型焊缝;焊缝显微组织由柱状β相转变组织组成;表面聚焦状态下电子束流密度大,气孔较少,截面成形最好;接头显微硬度沿熔深方向上呈梯度分布,接头底部显微硬度最高,顶部硬度最低。结论不同聚焦状态下焊缝中部晶粒存在较大差别,表面聚焦晶粒最为细小。接头沿熔宽方向上的显微硬度呈"W"型分布,沿熔深方向呈梯度分布。     

Quantitative analysis of the combined effect of substrate rigidity and topographic guidance on cell morphology

Live cells are exquisitely sensitive to both the substratum rigidity and texture. To explore cell responses to both these types of inputs in a precisely controlled fashion, we analyzed the responses of Chinese hamster ovary (CHO) cells to nanotopographically defined substrata of different rigidities, ranging from 1.8 MPa to 1.1 GPa. Parallel arrays of nanogrooves (800-nm width, 800-nm space, and 800-nm depth) on polyurethane (PU)-based material surfaces were fabricated by UV-assisted capillary force lithography (CFL) over an area of 5 mm × 3 mm. We observed dramatic morphological responses of CHO cells, evident in their elongation and polarization along the nanogrooves direction. The cells were progressively more spread and elongated as the substratum rigidity increased, in an integrin β1 dependent manner. However, the degree of orientation was independent of substratum rigidity, suggesting that the cell shape is primarily determined by the topographical cues.     

Filling in of Fraunhofer lines in the ocean by Brillouin scattering

We have investigated the relative contribution of Brillouin scattering to the filling in of both narrow and wide Fraunhofer lines in the ocean. The spectral behavior of the filling in was studied in two ways. First we studied Fraunhofer lines of variable width, such as the 455-nm Ba line with full-width at half-maximum (FWHM) = 0.02 nm, the 486-nm H(β) line (FWHM = 0.08 nm), and the 518-nm Mg line (FWHM = 0.11 nm). We then used the 455-nm Ba line as a narrow-line model to calculate the spectral dependence of the filling in. We found that Brillouin scattering can play a significant role in the filling in of narrow Fraunhofer lines in the ocean. We have also shown that, compared with the filling in caused by Raman scattering, the filling in caused by Brillouin scattering has less dependence on both the wavelength and ocean depth but is strongly dependent on the linewidth of the Fraunhofer line.     

高温合金GH4169电子束熔丝增材制造工艺研究

目的 研究GH4169合金电子束熔丝增材制造过程中电子束流参数的选择方法及组织特征.方法 在其他工艺参数不变的条件下,分析电子束流的大小对单层成形形貌的影响,寻找最佳电子束流参数值;采用光学显微观察增材制造GH4169合金柱状晶组织.结果 获得了不同电子束流条件下,单熔覆层表面形貌、横截面形貌、熔覆宽度和高度数据,以及...     

Model-based approach for quality improvement of electron beam welding applications in mass production

A model-based approach is presented to obtain a definite geometry of the seam as well as to find the regimes where the results will repeat with less deviation from the desired values in the electron beam welding. Using the response surface methodology, polynomial regression models for the behaviour of weld depth and the weld width are found. In order to improve the quality of the process in mass production, by a decrease of the deviation from a target value of the performance characteristic, parameters in two models describing the mean value and the variance for the weld depth and for the weld width in mass production are estimated. Using these models quality improvement, defined as an optimisation problem to produce reproducible welds while keeping the mean value of weld depth or/and width constant, is discussed. This approach is applied to the electron beam welding of stainless steel, for beam powers in the region of 4.2-4.8 kW and welding speeds of 3.333-13.333 mm/s.     

Evaluation of annular pupil for scanning transmission electron microscope formed by focused ion beam technique

Annular pupils for electron optics were developed using a focused ion beam (FIB) technique to realize an increase in the depth of focus, aberration-free imaging and separation of amplitude and phase images under scanning transmission electron microscopy (STEM). A tantalum plate 30 μm thick was used as the annular pupil material in the present experiment. The annular pupils were designed with various outer diameters from ?120 μm to ?40 μm. The inner diameter was designed at 60 to 80% of the outer diameter. The fabricated annular pupils were inspected by scanning ion beam microscopy and scanning electron microscopy. Annular pupils were successfully obtained at the designed size, although the slits of the pupils were slightly tapered by the ion beam etching process. These annular pupils were loaded on a STEM and confirmed to display no charge-up phenomenon by observation of the projection image on a scintillator using a CCD camera. We confirmed the image taken by annular pupil with narrow width was able to suppress the influence of the normal illumination.     

Subwavelength-resolvable focused non-gaussian beam shaped with a binary diffractive optical element.

The diffraction-limited spot size limits the optical disk storage capacity and microscopic resolution. We describe a technique to shape a focused Gaussian beam into a superresolving beam by using a diffractive optical element fabricated by laser-assisted chemical etching. The focused shaped beam has a smaller width and a longer depth of focus than a similarly focused Gaussian beam. Using the diffraction-limited shaped beam along with threshold writing, we achieved a written pit size of less than 0.33 mum at a 695-nm laser wavelength, compared with a 0.7-mum focused Gaussian spot size (full width at e(-2) of the peak) with the same focusing lens. The energy conversion efficiency for the beam shaping was ~81%.     

In situ high resolution transmission electron microscopy investigation of deformation mechanism in sub-10-nm Au crystals

Abstract

In situ high resolution transmission electron microscopy investigations were performed on sub-10-nm Au crystals. The effects of tensile loading direction and crystal size on the deformation mechanism of Au crystals were analysed. For the Au crystals with a width below 2 nm, the surface atom diffusion with a phenomenon of layer by layer peeling is the main deformation mechanism and the tensile loading direction plays negligible effect. For the Au crystals with a width over 7 nm, the dislocations generated form surface and gliding into crystal dominate the plastic deformation and the tensile loading direction plays important role. Lomer dislocations are produced and destructed by dislocation reaction during tensile strain process in <001> oriented Au crystal. The Schmid law is the key intrinsic issue controlling the deformation mechanism for the nanowires with a size larger than 7 nm.     

Effects of thin-film structural parameters on laser desorption/ionization from porous alumina

Nanoporous aluminum oxide layers, grown by anodization of aluminum thin films on glass and then sputter-coated with gold, were used to study the effects of the thin-film structural parameters on laser desorption/ionization (LDI) mass spectrometry (MS) of peptides. Variation of MS signal intensity was examined as a function of alumina pore depth, pore width, and gold layer thickness. Peptide molecular ion intensity was optimal with porous alumina formed from aluminum films of approximately 600-nm thickness; thinner or thicker films gave significantly lower signals. Signals decreased when pore sizes were increased beyond the as-formed width of approximately 100 nm. The MS signal also varied with the thickness of the sputtered gold layer with an optimum thickness being approximately 90 nm. The results of these studies provide values for empirical optimization of LDI MS performance as well as potential clues to the LDI mechanism.     

Origin of non-uniformity in MBE grown nanometer-sized InGaAs ridge quantum wires and its removal by atomic hydrogen-assisted cleaning

The origin of non-uniformity of MBE-grown InGaAs ridge quantum wires (QWRs) in sub 10-nm wire width range was investigated in detail by SEM, in situ XPS, TEM and PL measurements. InAlAs/InGaAs/InAlAs wires were selectively grown on InGaAs ridge structures prepared also by MBE on 10 stripe patterned (001) InP substrates. The main source of non-uniformity was thermal cleaning of InP in As₄ done prior to InGaAs ridge formation which produced ridges having irregular sized InGaAs islands due to an initial As–P exchange reaction. Low temperature atomic hydrogen cleaning removed this problem, and led to successful formation of sub 10-nm QWRs.     

Electron beam weld parameters and thermal efficiency improvement

Thermal efficiency is considered in connection with welding regimes and seam parameters by applying a statistical approach. This approach allows one to establish empirically (by fitting a mathematical model) the type of relationship that is present between performance characteristics and its influencing factors. Optimal regimes are found through thermal efficiency optimisation. The study leads to new proposals for the position of the focus with respect to the surface of the welded material, under conditions of maximum thermal efficiency or maximum welding depth. The values of the ratio of power to weld depth (P/H) and weld width times velocity of weld front (vB) are confirmed to be the main characteristic parameters of electron beam welding, considered as a self-organising process.     

Tailoring the Performances of Lead Halide Perovskite Devices with Electron‐Beam Irradiation

Lead halide perovskites are intensively studied in past few years due to their potential applications in optoelectronic devices such as solar cells, photodetectors, light‐emitting diodes (LED), and lasers. In addition to the rapid developments in material synthesis and device fabrication, it is also very interesting to postsynthetically control the optical properties with external irradiations. Here, the influences of very low energy (10–20 keV) electron beam of standard electron beam lithography are experimentally explored on the properties of lead halide perovskites. It is confirmed that the radiolysis process also happens and it can selectively change the photoluminescence, enabling the direct formation of nanolaser array, microsized light emitter array, and micropictures with an electron beam writer. Interestingly, it is found that discontinuous metallic lead layers are formed on the top and bottom surfaces of perovskite microplate during the radiolysis process, which can act as carrier conducting layers and significantly increase the photocurrent of perovskite photodetector by a factor of 217%. By using the electron beam with low energy to modify the perovskite, this method promises to shape the emission patterns for micro‐LED with well‐preserved optical properties and improves the photocurrent of photodetector.     

Edge localization of subwavelength structures by use of polarization interferometry and extreme-value criteria

A polarization interferometric method is presented for the quantitative microscopy of topographical structures with subwavelength linewidths. A liquid-crystal phase shifter is inserted into the imaging optics of a reflected-light microscope, and the principles of phase-shifting interferometry are applied to measuring the phase and the contrast of the TE-polarized image (E parallel edge) with the TM-polarized image (E perpendicular edge) as the reference. This common-path interferometric method provides selective edge detection for line structures because the polarization difference is localized at the structure edges. Two different threshold criteria for linewidth determination are discussed: distance of the contrast minima and distance of the points of the steepest phase change. Linewidths as small as 300 nm were measured at a 635-nm wavelength. The dependence on the illumination numerical aperture, as well as on the material, the width, and the depth of the structure, is investigated both experimentally and by rigorous numerical simulations.     

Electronic and magnetic properties of ultra-thin epitaxial magnetite films on MgO(001)

The electronic and magnetic properties of epitaxial Fe₃O₄ (001) films on MgO(100) substrates were studied throughout the 2.5- to 30-nm thickness range using conversion electron Mössbauer spectroscopy. Despite the superparamagnetism that was observed for film thickness below 5 nm, the Verwey transition persisted even for the thinnest film. Temperature-dependent Mössbauer measurements between 80 K and 400 K revealed that the activation energy for the magnetic moment fluctuations in the 3-nm magnetite film is higher than the magnetic anisotropy energy by an order of magnitude.     

Effects of nano-structured photonic crystals on light extraction enhancement of nitride light-emitting diodes

The light extraction efficiency of an InGaN/GaN light-emitting diode (LED) can be enhanced by incorporating nano-structured photonic crystals inside the LED structure. We employed plane wave expansion (PWE) method and finite difference time domain (FDTD) method to reveal the optical confinement effects with the relevant parameters. The results showed that band-gap modulation could increase the efficiency for light extraction at the lattice constant of 200 nm and depth of 200 nm for the 468-nm LED. Focused ion beam (FIB) using Ga created the desired nano-structured patterns. The LED device micro-PL (photoluminescence) results have demonstrated that the triangular photonic crystal arrays could increase the peak illumination intensity by 58%. The peak wavelength remained unchanged. The integrated area under the illumination peak was increased by 75%. As the patterned area ratio was increased to 85%, the peak intensity enhancement was further improved to 91%, and the integrated area was achieved at 106%.     

Free vibrations of solid and hollow wedge beams with rectangular or circular cross‐sections and carrying any number of point masses

Since the literature relating to the natural frequencies and mode shapes of the double‐tapered wedge beams carrying multiple point masses is rare, the object of this paper is to present some information in this aspect. First of all, the closed‐form solutions in terms of the Bessel functions for the natural frequencies and normal mode shapes of the ‘bare’ wedge beams (without carrying any point masses) were determined. Next, the partial differential equation of motion for the ‘loading’ wedge beams (carrying any number of point masses) were transformed into the matrix equation by using the expansion theorem and the foregoing natural frequencies and normal mode shapes of the ‘bare’ wedge beam. Finally, the eigenvalue equation associated with the last matrix equation was solved to give the natural frequencies and the mode shapes of the ‘loading’ wedge beams. The formulation of this paper is available for the solid and hollow wedge beams with square, rectangular or circular cross sections. In other words, the taper ratio for the width and that for the depth may be equal or unequal. All the numerical results were compared with the existing literature or the conventional finite element method results and good agreement was achieved. Copyright © 2004 John Wiley & Sons, Ltd.     

基于电子注嵌入光栅的0.55 THz返波振荡器的结构设计与注波互作用的分析

根据矩形栅慢波结构的色散公式初步确定各结构参数, 并分析了各结构参数的变化对色散曲线的影响, 用CST微波工作室仿真, 计算并对比分析嵌入与未嵌入圆形电子注的高频特性的变化趋势, 得出前者对应的色散曲线和耦合阻抗曲线要大于后者的结论。利用CST粒子工作室进行注波互作用模拟, 权衡起振时间和输出功率关系, 确定整管的仿真长度。研究了电子注嵌入深度、填充比、电流大小对输出功率的影响, 优化结构参数, 最终得到14. 6 W的稳定输出功率, 与Magic计算出的结果相吻合。     

Spatial distribution of copper vapour from a two-dimensional source using a strip electron beam at aspect ratio greater than 3

We present results on the spatial distribution of copper vapour as a function of temperature, from a 2D evaporating source generated using 130 mm strip electron beam at aspect ratio >3. At this aspect ratio vapour flow is expected to appear approximately as a point source flow. The 2D evaporating source during these studies can be described in terms of inverse Knudsen number (1/K_n) that is proportional to source temperature, ranging from 0.75 to 6.67. These experimental results could be fitted with accuracy of ±5% using a spatial distribution function with different beaming coefficients along the width and the length of a 2D source. It is observed that the beaming exponent along the width of a 2D source saturates at about 2, which is marginally higher than that observed for the aspect ratio in the range of 1 to 2 for the similar range of 1/K_n, whereas, the beaming exponent along the length direction of a 2D source was observed to increase up to 6.34, which is substantially higher than that observed at the aspect ratio in the range of 1-2 for the similar range of 1/K_n. These results clearly indicate that, for given evaporating source conditions, the widthwise atomic collisions, collimation of atomic beam and beaming exponent along the width remains constant. At the same time lengthwise collisions, atomic beam collimation and hence beaming coefficient do not freeze and the wedge-shaped atomic beam does not run out of collisions in the lengthwise direction even at aspect ratio >3. Thus, the atomic vapour from a 2D source does not attain the free molecular regime even at radial distance in excess of 390 mm above the source.     

Electron‐Beam‐Driven III‐Nitride Plasmonic Nanolasers in the Deep‐UV and Visible Region

Plasmonic nanolasers based on wide bandgap semiconductors are presently attracting immense research interests due to the breaking in light diffraction limit and subwavelength mode operation with fast dynamics. However, these plasmonic nanolasers have so far been mostly realized in the visible light ranges, or most are still under optical excitation pumping. In this work, III‐nitride‐based plasmonic nanolasers emitting from the green to the deep‐ultraviolet (UV) region by energetic electron beam injection are reported, and a threshold as low as 8 kW cm^?2 is achieved. A fast decay time as short as 123 ps is collected, indicating a strong coupling between excitons and surface plasmon. Both the spatial and temporal coherences are observed, which provide a solid evidence for exciton‐plasmon coupled polariton lasing. Consequently, the achievements in III‐nitride‐based plasmonic nanolaser devices represent a significant step toward practical applications for biological technology, computing systems, and on‐chip optical communication.