Effect of high energy ion irradiation on silicon substrate in a pulsed plasma device

We have performed an experimental analysis on the investigation of high energy ion beam irradiation on Si(1 0 0) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The surface modifications induced by the ion beams are characterized using standard surface science diagnostic tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive X-ray (EDX) analysis and atomic force microscope (AFM) and the results are reported. In particular, it has been found that with silicon targets, the application of PF carbon ion beams results in the formation of a surface layer of hexagonal (6H) silicon carbide, with embedded self-organized step/terrace structures.     

Surface Erosion of GaN Bombarded by Highly Charged 208Pbq+-Ions

Surface change of gallium nitride specimens after bombardment by highly charged Pbq^＋-ions （q = 25, 35） at room temperature is studied by means of atomic force microscopy. The experimental results reveal that the surface of GaN specimens is significantly etched and erased. An unambiguous step-up is observed. The erosion depth not only strongly depends on the charge state of ions, but also is related to the incident angle of Pbq^＋-ions and the ion dose. The erosion depth of the specimens in 60° incidence （tilted incidence） is significantly deeper than that of the normal incidence. The erosion behaviour of specimens has little dependence on the kinetic energy of ion （Ek = 360, 700 keV）. On the other hand, surface roughness of the irradiated area is obviously decreased due to erosion compared with the un-irradiated area. A fiat terrace is formed.     

Ion beam induced crystal-edge nanoclusters at the origin of poly(ethylene glycol) film stabilization

PEG films stabilized by noble gas ion beam irradiation showed characteristic clustering at the crystal edges. These structures appear in determined ion beam conditions after exposure to Ar and Kr ions. Atomic force microscopy exploration indicates that, rather than presenting drastic topographic features, the nanostructures show radically different elastic properties. Within the concerned set of ion beam conditions, the surface properties are observed to vary according to the absorbed energy as suggested by X-ray photoelectron spectroscopy and contact angle measurements. These analyses predict that Ar irradiation in the 500-600 V extraction potential range is an appropriate condition for PEG stabilization.     

Influence of ion-irradiation parameters on defect formation in silicon films

It is shown that unlike bulk silicon, for which amorphization is observed at an irradiation dose of 5 × 10¹⁶ ion/cm², thin silicon films on sapphire are amorphized at lower critical doses (10¹⁵ ion/cm²). An undamaged surface layer remains when the silicon films are irradiated with Si⁺ ion beams. Its thickness depends on the current density of the incident beam. Rutherford backscattering studies show that annealing at 950°C improves the crystallinity of the irradiated silicon film. Annealing of the films at 1100°C leads to mixing of the silicon-sapphire interface.     

制备多孔硅的一种新方法

自从Canham观察到多孔硅(PS)的可见光致发光后,由于其可望成为可与Ⅲ—Ⅴ族半导体材料相媲美的新型光电子材料而引起了科学界极大的兴趣.目前,制备多孔硅一般都采用电化学腐蚀方法.     

Effect of polarization on femtosecond laser pulses structuring silicon surface

Arrays of conical-like spikes can be formed on silicon surface after irradiated with femtosecond laser pulses in ambient of SF₆ or N₂. In this article, we report our observations on how the shape of the spikes formed on silicon surface varies with the polarization of laser beam. The experimental results show that, with circular polarized laser irradiation, the shape of the spikes is conical; however, with linearly polarized laser irradiation, the spikes show elliptic conical shape, and the long-axes are perpendicular to the direction of the polarization of laser beam. The asymmetric shape of spikes produced by linearly polarized laser beam can be explained by considering the polarization dependence of Fresnel-refraction.     

Nanoporous structures of polyimide induced by Ar ion beam irradiation

The surface morphology evolution of polyimide (PI) that was treated with an Ar ion beam was explored using a hybrid ion beam system. A hole-like nanostructure formed on PI during the Ar ion beam treatment at a lower fluence, but PI formed 3D porous nanostructures with a mean diameter of ∼90 nm at a higher fluence. The chemical binding energy and the composition of the Ar ion irradiated PI were analyzed using FT-IR and XPS spectra, which revealed that the polymer chain scissioning increased with increasing Ar ion treatment duration, i.e., fluence. The surface hardness and the elastic modulus of PI increased from 1.17 to 1.62 GPa and 4.06 to 5.41 GPa, respectively, with respect to the Ar ion beam treatment duration.     

Ion beam mixing of AG on glass

A series of Ag-glass samples have been studied. They were irradiated as a function of bombarding ion species, dose, temperature, and energy. The results by RBS indicate that ion beam mixing of Ag-glass takes place not only at higher energy irradiation (I. OMeV Xe+), but also at lower energy irradiation (120KeV Ar+ and Kr+). The effective diffusion lengths squared, Dt, were introduced for comparison. It is found that Dt is dependent on the nuclear stopping power, dose and irradiation temperature.     

Role of an oxide layer in the long-range effect upon irradiation of silicon by light and ions with medium energy

Correlations between the modes of silicon irradiation with light, as well as the thickness of an oxide layer on the surface of the sample, and the character of changes in the microhardness in the long-range effect are experimentally established. The results are interpreted from the standpoint of the effect of processes that take place in the oxide layer upon irradiation and cause the generation of two types of hypersonic waves that determine the regularities of the effect. It is shown that an oxide layer on the irradiated silicon surface is a mandatory condition for manifestation of the long-range effect not only in the case of irradiation with light, but also upon ion irradiation.     

Irradiation induced modifications in morphology and magnetic property of Mn/Si structure

Mn films of ∼50 nm has been deposited by electron beam evaporation technique on cleaned and etched Si [(1 0 0), 8–10 Ω cm] substrates to realize a Mn/Si interfacial structures. The structures have been irradiated from energetic (∼100 MeV) ion beam from Mn side. The irradiated and unirradiated structures have been characterized from atomic force microscopy, X-ray diffractometry, magnetic force microscopy, and vibrating sample magnetometer facilities. It has been found that surface/interfacial granular silicide phases (of Mn_xSi_y) are formed before and after the irradiation with a irradiation induced modifications of surface morphology and magnetic property. The surface/interface roughness has been found to increase on the irradiation from the atomic force microscopy data. The magnetic property on the irradiation shows an interesting and significant feature of an increased coercivity and a ferromagnetic like behavior in the Mn–Si structure. The observed increased coercivity has been related to the increased roughness on the irradiation. The ferromagnetism after the irradiation is a curious phenomenon which seems due to the formation of Mn–C–Si compound from the carbon dissolved in silicon.     

基于直接胶体晶体刻蚀技术的高度有序纳米硅阵列的尺寸及形貌控制

以自组装单层胶体小球阵列为掩模，采用直接胶体晶体刻蚀技术在硅表面制备二维有序尺寸可控的纳米结构.在样品制备过程中，首先通过自组装法在硅表面制备了直径200nm的单层聚苯乙烯(PS)胶体小球的二维有序阵列；然后对样品直接进行反应离子刻蚀(RIE)，以氧气为气源，利用氧等离子体对聚苯乙烯小球和对硅的选择性刻蚀作用，通过改变刻蚀时间，制备出不同尺寸的PS胶体小球的有序单层阵列；接着以此二维PS胶体单层膜为掩模，以四氟化碳为气源对样品进行刻蚀；最后去除胶体球后得到二维有序的硅柱阵列.SEM和AFM的测量结果表明：改变氧等离子体对胶体球的刻蚀时间和四氟化碳对硅的刻蚀时间，可以控制硅柱的尺寸以及形貌，而硅柱阵列的周期取决于原始胶体球的直径. 关键词： 胶体晶体刻蚀 纳米硅柱阵列     

Spectroscopic observation of the plasma produced by a CO2 laser beam interacting with titanium target under helium and/or argon atmosphere

In many laser applications such as drilling, welding and cutting, the role of the plasma in the transfer of energy between the laser beam and the metal surface appears to be rather important. It depends on several parameters such as laser wavelength, irradiation time and deposited energy but especially on the buffer gas nature. In this work the plasma is initiated by a TEA-CO₂ laser beam perpendicularly focussed onto a Ti target (100 MW/cm²), in a cell containing He, Ar or a He-Ar mixture as buffer gas. The plasma is studied by time and space resolved spectroscopic diagnostics. The results show that helium allows target erosion whereas a highly absorbing breakdown plasma develops in argon shielding the target from the subsequent laser heating. With only 20% Ar in He, a strong quenching of the He plasma by Ar occurs, and the Ar plasma effect is dominant.     

Electrical transport characteristic of carbon nanotube after mass-separated ultra-low-energy oxygen ion beams irradiation

Mass-separated ultra-low-energy oxygen ion beams were irradiated to the single-walled carbon nanotubes (SWCNTs) under an ultra-high-vacuum pressure of 10⁻⁷ Pa for the purpose of achieving n-type conduction of nanotubes. The ion beam energy was 25 eV, which was close to the displacement energy of graphite. The incident angle of the ion beam was normal to the target nanotube. The ion dose ranged from 3.3 × 10¹¹ to 3.8 × 10¹² ions/cm². The structure of SWCNTs after the ion irradiation was investigated. The CNTs still have a clear single-walled structure after the ion irradiation. The graphite structure is distorted and some defects are induced in the nanotube by the oxygen irradiation. The oxygen ions with the ion energy of 25 eV are irradiated to the field effect transistor (FET) device with the nanotube channel. The n-type characteristic appears upon the oxygen ion irradiation, and the device exhibits ambipolar behavior. The defects induced by the ion irradiation may act as the n-type dopants.     

Silicon enhanced carbon nanotube growth on nickel films by chemical vapor deposition

Silicon enhances carbon nanotube growth on nickel films by chemical vapor deposition using methane and hydrogen. Nanotube growth characteristic is significantly improved on nickel films patterned by argon plasma etching on silicon oxide layers. Auger electron spectroscopy shows that a reduced silicon phase forms in the surface silicon oxide layer by Ar ion bombardment used for patterning. The enhanced growth of carbon nanotubes could be ascribed to an oxygen removal effect by silicon in the process of synthesis.     

A low temperature surface preparation method for STM nano-lithography on Si(1 0 0)

Registration markers are crucial in connecting scanning tunneling microscope (STM) lithographed nano- and atomic-scale devices to the outside world. In this paper we revisit an ultra high vacuum annealing method with a low thermal budget that is fully compatible with etched registration markers and results in clean 2 × 1 reconstructed Si(1 0 0) surfaces required for STM lithography. Surface contamination is prevented by chemically stripping and reforming a protective silicon oxide layer before transferring the sample to the vacuum system. This allows for annealing temperatures of only 900 °C, where normally carbon contaminants result in the formation of SiC clusters on the surface at annealing temperatures below 950 °C. Reactive ion etched marker structures with an etch depth of 60 nm and a typical lateral dimension of only 150 nm survive a 900 °C flash anneal.     

Broadband antireflection gratings fabricated upon silicon substrates

We fabricated a two-dimensional subwavelength structured (SWS) surface upon a crystal silicon substrate. The SWS surface was patterned by electron beam lithography and etched by an SF(6) fast atom beam. The SWS grating had a conical profile, the period was 150 nm, and the groove was approximately 350 nm deep. The reflectivity was examined at 2002500-nm wavelengths. At 400 nm the reflectivity decreased to 0.5% from the 54.7% of the silicon substrate. We also used HeNe laser light to examine the reflectivity as a function of the incident angle.     

Enhancement of oxygen adsorption on silicon following electron irradiation

While electron-stimulated adsorption of oxygen on silicon during electron irradiation is well known, we here report enhanced adsorption of oxygen on both crystalline and hydrogenated amorphous silicon following electron irradiation. The adsorption enhancement is proportional to the energy dissipation at the irradiated surface, and thus is inversely related to the beam energy. Electronic excitation processes are thought to cause bonding changes and thus enhanced adsorption.     

Low-energy ion emission from a xenon gas-puff laser-plasma X-ray source

We have measured low-energy ion emission from a gas-puff laser-plasma X-ray source. The ions may cause the degradation of the condenser mirror of the extreme ultra-violet projection lithography system. A 0.7 J in 8 ns Nd:YAG laser at 1.06 μm was focused onto the xenon gas-puff target with an intensity of ∼10¹² W/cm². The silicon (111) plates, placed at a distance of 32 mm from the laser-interaction region, were exposed with the xenon ions. The average ion energy was measured to be less than 50 eV with a Faraday-cup detector placed close to the silicon plates. The xenon deposition occurred in the silicon plates with a depth of less than 40 nm. The deposition density was measured with a quadrupole secondary ion mass spectrometer to be 10²¹ /cm³ after 1500 laser shots. The energy-conversion efficiency from the laser energy into the ions is ∼0.1%/4 π sr/shot. For the lithography system, if we can remove such ion bombardment completely using novel techniques such as electro-magnetic devices or gas flow curtain techniques, the lifetime of the condenser mirror will be extended significantly. Received: 20 November 2000 / Published online: 9 February 2001     

Large area laser surface micro/nanopatterning by contact microsphere lens arrays

Laser surface micro/nanopatterning by particle lens arrays is a well-known technique. Enhanced optical fields can be achieved on a substrate when a laser beam passes through a self-assembled monolayer of silica microspheres placed on the substrate. This enhanced optical field is responsible for ablative material removal from the substrate resulting in a patterned surface. Because of the laser ablation, the microspheres are often ejected from the substrate during laser irradiation. This is a major issue impeding this technique to be used for large area texturing. We explored the possibility to retain the spheres on the substrate surface during laser irradiation. A picosecond laser system (wavelength of 515 nm, pulse duration 6.7 ps, repetition rate 400 kHz) was employed to write patterns through the lens array on a silicon substrate. In this experimental study, the pulse energy was found to be a key factor to realize surface patterning and retain the spheres during the process. When the laser pulse energy is set within the process window, the microspheres stay on the substrate during and after laser irradiation. Periodic patterns of nanoholes can be textured on the substrate surface. The spacing between the nanoholes is determined by the diameter of the microspheres. The depth of the nanoholes varies, depending on the number of laser pulses applied and pulse energy. Large area texturing can be made using overlapping pulses obtained through laser beam scanning.     

Sub-microns period grating couplers fabricated by silicon mold

This paper describes a novel simple process suitable for fabrication of micro-periodic structure in optical waveguide. The mold was fabricated using electron beam lithography and fast atom beam etching. Sub-micron-scale patterns were transferred from silicon mold to polymer layer. Grating coupler was fabricated by the mold and normal optical mask. In the proposed method, no press which is needed for imprint lithography is required and the mold structure can be duplicated with high aspect ratio. Experimental coupling efficiency is about 25%. This technique can also be used to fabricate other nanometer-scale structures.