Impurities removal by laser blow-off from in-vacuum optical surfaces on RFX-mod experiment

An in situ window cleaning system by laser blow-off through optical fiber has been developed on the basis of a feasibility study previously presented. The beam generated by a Q-switched Nd:YAG laser is launched in a vacuum box into a high damage threshold optical fiber through a lens. The fiber output is focused on the impurities-coated surface of a vacuum window exposed to the plasma of the RFX-mod experiment, and it is remotely controlled with an xy motion system to scan the entire surface. We first investigate the energy density threshold necessary to ablate the deposited impurity substrate on removed dirty windows: above threshold, a single laser pulse recovers ～95% of the window transmission before its exposure to the plasma, while below it the efficiency of the cleaning process is too poor. The system so conceived was then used to clean the three collection windows of the Main Thomson scattering diagnostic on RFX-mod. We also present results obtained applying the same technique to the SiO-protected Al mirror used for the Z(eff) diagnostic: an energy threshold for efficient impurity removal without mirror damage is first identified, then ablation tests are executed and analyzed in terms of recovered reflectivity. The SIMS technique is used both with windows and mirror to study the composition of surfaces before and after the ablation.     

Atom-probe for FinFET dopant characterization

With the continuous shrinking of transistors and advent of new transistor architectures to keep in pace with Moore's law and ITRS goals, there is a rising interest in multigate 3D-devices like FinFETs where the channel is surrounded by gates on multiple surfaces. The performance of these devices depends on the dimensions and the spatial distribution of dopants in source/drain regions of the device. As a result there is a need for new metrology approach/technique to characterize quantitatively the dopant distribution in these devices with nanometer precision in 3D.In recent years, atom probe tomography (APT) has shown its ability to analyze semiconductor and thin insulator materials effectively with sub-nm resolution in 3D. In this paper we will discuss the methodology used to study FinFET-based structures using APT. Whereas challenges and solutions for sample preparation linked to the limited fin dimensions already have been reported before, we report here an approach to prepare fin structures for APT, which based on their processing history (trenches filled with Si) are in principle invisible in FIB and SEM. Hence alternative solutions in locating and positioning them on the APT-tip are presented. We also report on the use of the atom probe results on FinFETs to understand the role of different dopant implantation angles (10° and 45°) when attempting conformal doping of FinFETs and provide a quantitative comparison with alternative approaches such as 1D secondary ion mass spectrometry (SIMS) and theoretical model values.     

Versatile system for the temperature-controlled preparation of oxide crystal surfaces

We present a versatile system for the preparation of oxide crystal surfaces in the ultra-high vacuum (UHV) at temperatures up to 1300 K. Thermal treatment is accomplished by direct current heating of a tantalum foil in contact with the oxide sample. The sample temperature is measured by a thermocouple at a position close to the crystal and its reading is calibrated against the surface temperature determined by a second thermocouple temporarily attached to the surface. The design of the sample holder is based on a transferable plate originally developed for a commercial UHV scanning probe microscope. The system is, however, also suitable for the use with electron spectroscopy or electron diffraction based surface analytical techniques. We present results for the high-temperature preparation of CeO(2)(111) surfaces with atomically flat terraces exhibiting perfect atomic order and cleanliness as revealed by non-contact atomic force microscopy (NC-AFM) imaging. NC-AFM imaging is, furthermore, used to demonstrate the temperature-controlled aggregation of gold atoms on the CeO(2)(111) surface and their evaporation at high temperatures.     

Design and performance of a combined secondary ion mass spectrometry-scanning probe microscopy instrument for high sensitivity and high-resolution elemental three-dimensional analysis

State-of-the-art secondary ion mass spectrometry (SIMS) instruments allow producing 3D chemical mappings with excellent sensitivity and spatial resolution. Several important artifacts however arise from the fact that SIMS 3D mapping does not take into account the surface topography of the sample. In order to correct these artifacts, we have integrated a specially developed scanning probe microscopy (SPM) system into a commercial Cameca NanoSIMS 50 instrument. This new SPM module, which was designed as a DN200CF flange-mounted bolt-on accessory, includes a new high-precision sample stage, a scanner with a range of 100 μm in x and y direction, and a dedicated SPM head which can be operated in the atomic force microscopy (AFM) and Kelvin probe force microscopy modes. Topographical information gained from AFM measurements taken before, during, and after SIMS analysis as well as the SIMS data are automatically compiled into an accurate 3D reconstruction using the software program "SARINA," which was developed for this first combined SIMS-SPM instrument. The achievable lateral resolutions are 6 nm in the SPM mode and 45 nm in the SIMS mode. Elemental 3D images obtained with our integrated SIMS-SPM instrument on Al/Cu and polystyrene/poly(methyl methacrylate) samples demonstrate the advantages of the combined SIMS-SPM approach.     

创新设计的K-Alpha电子能谱仪

本文简单介绍新型高性能、一体化结构的K-Alpha型X射线光电子能谱(XPS)仪的主要特点,包括:全自动样品分析能力,先进的样品导航系统和摄像系统,独特的样品照明方式,用专利技术设计的样品荷电自动补偿装置,方便的谱仪自动校准功能,快速的XPS成像分析能力和高质量的深度剖析,紧凑的组装和小巧的体积,以及高性能价格比等等。这些特点相结合不仅简化XPS操作,而且提高XPS谱仪的分析能力和使用效率,满足用户对现代XPS分析的需求。     

Lubrication of carbon coatings with MoS2 single sheet formed by MoDTC and ZDDP lubricants

The fuel economy and reduction of harmful elements of lubricants are becoming important issues in the automotive industry. One approach to these requirements is the potential use of low‐friction coatings in engine components exposed to boundary lubrication conditions. Diamond‐like carbon (DLC) coatings, extensively studied as ultra‐low friction films to protect ductile metals surfaces for space applications, are expected to fit the bill. The main purpose of this work is to investigate the friction and wear properties of DLC coatings lubricated with molybdenum dithiocarbamate (MoDTC) and zinc dithiophosphate (ZDDP) under boundary lubrication conditions. The mechanisms by which MoDTC reduces the friction in the centirange were studied using ultra‐high vacuum (UHV) analytical tribometer. The UHV friction tests were performed on a tribofilm previously formed on selected DLC material with MoDTC and ZDDP containing oil. Ex‐situ characterizations show that the composition of this tribofilm is similar to that of a tribofilm obtained on steel surfaces in the same lubrication conditions with MoS₂ single sheets dispersed inside zinc phosphate zones. However, analyses by X‐ray photoelectron spectroscopy (XPS) indicate that MoDTC and ZDDP additives seem to be more active on steel surfaces than carbonaceous ones. After UHV friction with the tribofilm formed on selected DLC and steel pin counterpart, the wear scars of both sliding surfaces were characterized by in‐situ analytical tools such as Auger electron spectroscopy, scanning Auger microscopy and micro‐spot XPS. Low friction is associated with the transfer of a thin MoS₂ film to the steel pin counterpart. Copyright © 2006 John Wiley & Sons, Ltd.     

高分辨二次离子质谱超高真空样品台的研制

目前,微束类分析仪器的一次离子束斑越来越精细,直径已达到微米级甚至亚微米级,仪器真空度也已达到稳定的超高真空水平,因此,亟需研制一种与之相匹配的高分辨样品台,提高在超高真空环境下的分辨力及定位精度。新研制的样品台,通过置于真空腔体外部的高精度滑台驱动小型焊接波纹管的伸缩传递三维运动,解决了大尺寸焊接波纹管表面放气及承受较大大气压力的问题;通过使用适用于超高真空的材料和固体润滑、无动态密封,解决了高真空中摩擦偶件的润滑问题。实验数据表明：在40 mm行程范围内,运动平台三轴定位重复性为0.94、1.83、0.38 μm,分辨力为0.10 μm,并已成功地应用在1.19×10^-6 Pa超真空环境下。外置的高精度滑台不仅克服了真空电机在真空腔体内发热及绝缘材料放气的问题,而且不需要引入任何电子电气元件及导线,不会在分析腔室内产生电磁干扰,行程不受装置本身的限制。这些特性不仅可满足二次离子质谱仪的要求,也适用于具有高分辨、超高真空环境、无污染要求的其他分析测试仪器。     

Techniques for the compositional and chemical state analysis of surfaces and thin films

In this review we will make a brief comparison of analytical techniques yielding information on the composition and chemical states of surfaces and thin films. We will include in this discussion CBS (charged particle backscattering spectroscopy), IIXS (ion induced X-ray spectrometry), EMP (electron microprobe), AM (analytical microscopy), AES (Auger electron spectroscopy), XPS (X-ray photoelectron spectroscopy), XRF (X-ray fluorescence spectroscopy) and SIMS (secondary ion mass spectroscopy). The major accent of this treatment is on the fundamental physical processes of each technique as these affect both the sensitivity and our quantitative understanding.     

Effect of electrical current on the tribological behavior of the Cu-WS2-G composites in air and vacuum

As the traditional graphite-based composites cannot meet the requirement of rapid developing modern industry, novel sliding electrical contact materials with high self-lubricating performance in multiple environments are eagerly required. Herein a copper-based composite with WS2 and graphite as solid lubricant are fabricated by powder metallurgy hot-pressed method. The friction and wear behaviors of the composites with and without current are investigated under the condition with sliding velocity of 10 m/s and normal load of 2.5N/cm 2 in both air and vacuum. Morphologies of the worn surfaces are observed by optical microscope and compositions of the lubricating films are analyzed by XPS. Surface profile curves and roughness of the worn surfaces are obtained by 2205 surface profiler. The results of wear tests show that the friction coefficient and wear volume loss of the composites with current are greater than that without current in both air and vacuum due to the adverse effects of electrical current which damaged the lubricating film partially and roughed the worn surfaces. XPS results demonstrate that the lubricating film formed in air is composed of oxides of Cu, WS2 , elemental S and graphite, while the lubricating film formed in vacuum is composed of Cu, WS2 and graphite. Because of the synergetic lubricating action of oxides of Cu, WS2 and graphite, the composites show low friction coefficient and wear volume loss in air condition. Owing to the fact that graphite loses its lubricity which makes WS2 become the only lubricant, severe adhesive and abrasive wear occur and result in a high value of wear rate in vacuum condition. The formation of the lubricating film on the contact interface between the brush and ring is one of the factors which can greatly affect the wear performance of the brushes. The low contact voltage drop of the composites in vacuum condition is attributed to the high content of Cu in the surface film. This study fabricated a kind of new sliding electrical contact self-lubricating composite with dual-lubricant which can work well in both air and vacuum environments and provides a comprehensive analysis on the lubrication mechanisms of the composite.     

The use of X-ray photoelectron spectroscopy to estimate the stability of primary mass standards

Because it is still defined in terms of an artefact, the limit on the accuracy with which the SI unit of mass can be realised is largely limited by the surface stability of the kilogram standard. Not only is this true on the case of the International Prototype used to define the unit but also for national standard copies and indeed for mass standards in general. This paper describes the use of X-ray photoelectron spectroscopy (XPS) to study the accretion of contamination of the surfaces of standard masses. Angle Resolved X-ray photoelectron spectroscopy (AR XPS) was used to characterise the surfaces of platinum–iridium and stainless steel mass standards stored either in air or in vacuum, or which have been transferred between the two media. Various analysis methods for XPS data have been compared both in terms of providing an overlayer thickness on the mass standard and in terms of analysing the composition of this layer of contamination.     

Ultrahigh vacuum chamber for Raman studies of gases adsorbed on metals

An ultrahigh vacuum chamber is described which is being used to study laser Raman spectra associated with gas adsorption on clean metal surfaces. The system enables sample temperatures from -85 degrees to 600 degrees C to be obtained, and besides surface cleaning capabilities associated with high-temperature oxidation or reduction, it incorporates an Ar(+) sputter gun for surface cleaning. Initial experiments of CO+H(2) adsorption on crystalline Ni surfaces are described and the effects of H(2) and O(2) exposure shown for the 80 cm(-1) band which results from CO+H(2) adsorption.     

颗粒物塑形负压吸盘的设计与研究

 在气压传动系统中，负压吸盘是实用有效的真空元件。大多数负压吸盘针对平面形接触面而设计，无法保证粗糙表面的气密性。为解决这一问题，提出一种基于颗粒物塑形原理的负压吸盘。该吸盘利用刚度可控的阻塞技术，将颗粒物填充于硅胶软膜内，并在软膜内部镶嵌类软骨结构。当吸盘与平面物体接触时，硅胶气囊充气膨胀并贴合物体表面三维轮廓。完全贴合后固化颗粒物并利用负压实现适形吸附式夹持，适用于多种材质和形状的表面。通过对光滑表面物体和粗糙表面物体的吸附测试，验证了吸盘的气密性和适形能力。负压塑形吸取技术方案可为气动真空元件的设计提供有益参考。     

A chamber attached to the SEM for fracturing and coating frozen biological samples

A chamber for introducing, fracturing and coating frozen biological samples has been developed as an attachment to the sepcimen chamber of a scanning electron microscope. Together with a eucentric-tilt cold-stage, this chamber constitutes a complete system for viewing fractured biological surfaces of the type normally only seen by replica techniques. An air-lock on the chamber accepts a transfer module to allow insertion of the frozen sample without frost build-up. Fracturing is carried out with a precisely adjustable cooled knife under a 10--100X binocular microscope. The sample can tilt and rotate while being coated with carbon or metals evaporated from rechargeable sources introduced through the air-lock. Cooling in the chamber is provided by a cylindrical copper tank filled with liquid nitrogen. The chamber has its own LN2 trapped high vacuum system. After preparation the sample can be placed directly into the SEM through an isolation valve. The cold-stage utilizes a Joule-Thomson refrigerator. The sample can be kept below 103 K at all times though there are provisions for heating it in the fracturing and cold-stage positions. A system of controls, sensors and interlocks simplifies the operation of the system.     

XPS在测量薄膜样品中的应用——一种非破坏性XPS深度剖析测量

通过改变XPS探测掠角,对硅表面的氧化层和富锗氧化硅表层薄膜样品进行非破坏性深度剖析测量,得到了有意义的结果。本文详细介绍了这一原理,并对这一分析方法的深度分辨等进行了讨论,为进行其它类型的薄膜XPS深度剖析测试提供了借鉴。     

Tribological Characteristics and Tribochemical Reactions of Various Ceramics Lubricated with HFC-134a Gas

The role of tribochemical products in the friction and wear reduction of ceramics with different fractional ionic character in CF₃CH₂F (HFC-134a) gas was investigated using a ball-on-disk type tribometer. Without exposure to air, the wear tracks on the disks were characterized with the aid of a micro-spot X-ray Photoelectron Spectroscope (XPS) whose analytical chamber was connected to the friction chamber of the tribometer. Further, the adsorption and desorption behaviors of HFC-134a molecules on the nascent surfaces of the ceramics were studied using an adsorption test apparatus in high vacuum. It was found that the lubricating effect of HFC-134a gas was closely related to the fractional ionic or covalent characters of the ceramics. HFC-134a gas was more effective in lubricating ionic ceramics than the covalent ceramics. XPS analysis revealed that metal fluorides were mainly formed on the frictional surfaces of the ionic ceramics, whereas the composition of the tribochemical products on the frictional surfaces of the other ceramics was complicated. The adsorption tests proved that HFC-134a was decomposed to an olefin CF₂=CHF on the nascent surfaces of the ionic ceramic Al₂O₃ and the covalent ceramics. However, the formation of organic fluorine-containing compounds was not detected on the frictional surfaces of the ionic ceramics by XPS. This result implies that the mechanism of tribochemical reactions is strongly dependent on the bond type of ceramics. It is concluded that the low friction and wear of the ionic ceramics in HFC-134a gas result from the metal fluorides formed with high surface concentration on the sliding surfaces.     

Surface and Tribological Chemistry of Water and Carbon Dioxide on Copper Surfaces

The tribological chemistry of carbon dioxide and water vapor is studied on copper surfaces at high pressures, with a view to understand the gas-phase lubrication of copper–copper sliding contacts. The adsorption and film formation properties are studied on vapor-deposited copper films in an ultrahigh vacuum chamber using a quartz crystal microbalance. The nature of the reactively formed film is studied after reaction by ex situ X-ray photoelectron spectroscopy (XPS). Carbon dioxide adsorbs reversibly on copper, while water vapor adsorbs both reversibly and irreversibly, where XPS reveals that the irreversibly formed film consists of a mixture of cuprous oxide/hydroxide. Measuring the thickness of the cuprous oxide/hydroxide film as a function of water vapor pressure and temperature reveals that its thickness varies between about 6 and 14 Å and is proportional to the total amount of water adsorbed on the surface. This results in a cuprous oxide/hydroxide film that is thinner at higher temperatures. Measurements of the friction coefficient as a function of temperature and pressure in the presence of water vapor shows that it correlates with film thickness, reaching a limiting value of ~0.35 for thicker films.     

Imaging mass spectrometry

Imaging mass spectrometry combines the chemical specificity and parallel detection of mass spectrometry with microscopic imaging capabilities. The ability to simultaneously obtain images from all analytes detected, from atomic to macromolecular ions, allows the analyst to probe the chemical organization of a sample and to correlate this with physical features. The sensitivity of the ionization step, sample preparation, the spatial resolution, and the speed of the technique are all important parameters that affect the type of information obtained. Recently, significant progress has been made in each of these steps for both secondary ion mass spectrometry (SIMS) and matrix-assisted laser desorption/ionization (MALDI) imaging of biological samples. Examples demonstrating localization of proteins in tumors, a reduction of lamellar phospholipids in the region binding two single celled organisms, and sub-cellular distributions of several biomolecules have all contributed to an increasing upsurge in interest in imaging mass spectrometry. Here we review many of the instrumental developments and methodological approaches responsible for this increased interest, compare and contrast the information provided by SIMS and MALDI imaging, and discuss future possibilities.     

An ultrahigh vacuum fast-scanning and variable temperature scanning tunneling microscope for large scale imaging

We describe the design and performance of a fast-scanning, variable temperature scanning tunneling microscope (STM) operating from 80 to 700 K in ultrahigh vacuum (UHV), which routinely achieves large scale atomically resolved imaging of compact metallic surfaces. An efficient in-vacuum vibration isolation and cryogenic system allows for no external vibration isolation of the UHV chamber. The design of the sample holder and STM head permits imaging of the same nanometer-size area of the sample before and after sample preparation outside the STM base. Refractory metal samples are frequently annealed up to 2000 K and their cooldown time from room temperature to 80 K is 15 min. The vertical resolution of the instrument was found to be about 2 pm at room temperature. The coarse motor design allows both translation and rotation of the scanner tube. The total scanning area is about 8 x 8 microm(2). The sample temperature can be adjusted by a few tens of degrees while scanning over the same sample area.     

Overcoat Free Magnetic Media for Lower Magnetic Spacing and Improved Tribological Properties for Higher Areal Densities

Surface modification with shallow embedding (≤1 nm) of carbon in the top layer of magnetic media is evaluated for its tribological and anti-oxidation properties. Cobalt is used as the magnetic material and carbon embedding is achieved by using the filtered cathodic vacuum arc technique at different ion energies, specifically of 20, 90, and 350 eV, in order to study the effect of ion energy on the embedding profiles. Simulations using the transport of ions in Matter software and X-ray photoelectron spectroscopy (XPS) are used to characterize the embedded layer and their surface chemical composition. XPS and transmission electron microscopy depth profiling results confirm the presence of a shallow mixed layer of carbon and cobalt for all three types of ion energies tested. However, embedding carried out at the ion energy of 90 eV produced a more uniform overcoat free mixed layer (≤1 nm) with improved anti-oxidation properties. Ball-on-disk wear tests and atomic force microscopy based scratch tests are conducted on the bare cobalt and modified cobalt surfaces. It is observed that the wear life and scratch resistance of the cobalt surface improved considerably after surface modification at the ion energy of 90 eV.     

An ice lithography instrument

We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines.