A compact sub-Kelvin ultrahigh vacuum scanning tunneling microscope with high energy resolution and high stability

We designed a scanning tunneling microscope working at sub-Kelvin temperatures in ultrahigh vacuum (UHV) in order to study the magnetic properties on the nanoscale. An entirely homebuilt three-stage cryostat is used to cool down the microscope head. The first stage is cooled with liquid nitrogen, the second stage with liquid (4)He. The third stage uses a closed-cycle Joule-Thomson refrigerator of a cooling power of 1 mW. A base temperature of 930 mK at the microscope head was achieved using expansion of (4)He, which can be reduced to ≈400 mK when using (3)He. The cryostat has a low liquid helium consumption of only 38 ml/h and standing times of up to 280 h. The fast cooling down of the samples (3 h) guarantees high sample throughput. Test experiments with a superconducting tip show a high energy resolution of 0.3 meV when performing scanning tunneling spectroscopy. The vertical stability of the tunnel junction is well below 1 pm (peak to peak) and the electric noise floor of tunneling current is about 6fA/√Hz. Atomic resolution with a tunneling current of 1 pA and 1 mV was achieved on Au(111). The lateral drift of the microscope at stable temperature is below 20 pm/h. A superconducting spilt-coil magnet allows to apply an out-of-plane magnetic field of up to 3 T at the sample surface. The flux vortices of a Nb(110) sample were clearly resolved in a map of differential conductance at 1.1 K and a magnetic field of 0.21 T. The setup is designed for in situ preparation of tip and samples under UHV condition.     

一种快速超高真空保护系统

为了满足同步辐射光源光束线和实验站真空联锁保护系统的需要,本实验室研制出超高真空计、快阀及快阀控制器。本文超高真空计及快阀控制器设计,给出了束线和实验站真空联锁保护系统的应用实例。     

Reducing the infiltration at vacuum chambers to obtain ultrahigh vacuum

The design of electric heaters in ultrahigh-vacuum chambers is considered. Effective heat shielding of the tested product is proposed. The permissible operating time of the heating elements is determined.     

Visible-infrared window assembly for ultrahigh vacuum systems

A window assembly for ultrahigh vacuum systems is described which uses Irtran 4 visible-infrared transmitting optical material. The assembly is made in a standard ultrahigh vacuum flange. The window is sealed in place with Pyroceram. The assembly can be repeatedly heat-cycled up to 200 degrees C without failure.     

Note: reliable and reusable ultrahigh vacuum optical viewports

We report a simple technique for the realization of ultrahigh vacuum optical viewports. The technique relies on using specially designed thin copper knife-edges and using a thin layer of Vacseal(?) on tip of the knife-edges between the optical flat and the ConFlat(?) (CF) flange. The design of the windows is such that it gives uniform pressure on the flat without breaking it. The assembled window is a complete unit, which can be mounted directly onto a CF flange of the vacuum chamber. It can be removed and reused without breaking the window seal. The design is reliable as more than a dozen such windows have survived several bake out and cooling cycles and have been leak tested up to 10(-11) Torr l/s level with a commercial Helium leak detector. The advantages of this technique are ease of assembly and leak proof sealing that survives multiple temperature cycling making the windows reliable and reusable.     

BNC-JJ coaxial floating shield bakable and coolable vacuum feedthrough useful from dc to 4 GHz

A floating (10(11) Omega), bakable (300 degrees C), coolable (liquid helium temperature) BNC-JJ-type coaxial vacuum feedthrough is described. It has a VSWR < or =1.22 from dc to 1.3 GHz and < or =1.35 from 2.0 to 4.0 GHz.     

High-resolution microscope for tip-enhanced optical processes in ultrahigh vacuum

An optical microscope based on tip-enhanced optical processes that can be used for studies on adsorbates as well as thin layers and nanostructures is presented. The microscope provides chemical and topographic informations with a resolution of a few nanometers and can be employed in ultrahigh vacuum as well as gas phase. The construction involves a number of improvements compared to conventional instruments. The central idea is to mount, within an UHV system, an optical platform with all necessary optical elements to a rigid frame that also carries the scanning tunneling microscope unit and to integrate a high numerical aperture parabolic mirror between the scanning probe microscope head and the sample. The parabolic mirror serves to focus the incident light and to collect a large fraction of the scattered light. The first experimental results of Raman measurements on silicon samples as well as brilliant cresyl blue layers on single crystalline gold and platinum surfaces in ultrahigh vacuum are presented. For dye adsorbates a Raman enhancement of approximately 10(6) and a net signal gain of up to 4000 was observed. The focus diameter ( approximately lambda2) was measured by Raman imaging the focal region on a Si surface. The requirements of the parabolic mirror in terms of alignment accuracy were experimentally determined as well.     

Magneto-optical near-field microscopy of ultrathin films in ultrahigh vacuum

In this study, guiding of surface plasmon polaritons excited at a gold film surface along corrugation‐free channels in regions that are covered with randomly located surface scatterers, is considered using near‐field microscopy for imaging of surface plasmon polariton intensity distributions at the surface. In the wavelength range 713–815 nm, we observed complete inhibition of the surface plasmon polariton propagation inside the random structures composed of individual (≈ 70 nm high) gold bumps (and their clusters) placed on a 55 nm thick gold film with a bump density of 75 µm^?2. We demonstrate well‐defined surface plasmon polariton guiding along corrugation‐free 2 µm wide channels in random structures and, in the wavelength range 738–774 nm, low‐loss guiding around 20° bends having a bend radius of ≈ 15 µm.     

Antenna-based ultrahigh vacuum microwave frequency scanning tunneling microscopy system

The instrumental synthesis of high resolution scanning tunneling microscopy (STM) with the ability to measure differential capacitance with atomic scale resolution is highly desirable for fundamental metrology and for the study of novel physical characteristics. Microwave frequency radiation directed at the tip-sample junction in an STM system allows for such high-resolution differential capacitance information. This ability is particularly critical in ultrahigh vacuum environments, where the additional parameter space afforded by including a capacitance measurement would prove powerful. Here we describe the modifications made to a commercial scanning tunneling microscope to allow for broad microwave frequency alternating current scanning tunneling microscopy (ACSTM) in ultrahigh vacuum conditions using a relatively simple loop antenna and microwave difference frequency detection. The advantages of our system are twofold. First, the use of a removable antenna on a commercial STM prevents interference with other UHV processes while providing a simple method to retrofit any commercial UHV-STM with UHV-ACSTM capability. Second, mounting the microwave antenna on a translator allows for specific tuning of the system to replicate experimental conditions between samples, which is particularly critical in sensitive systems like organic thin films or single molecules where small changes in incident power can affect the results. Our innovation therefore provides a valuable approach to give nearly any commercial STM, be it an ambient or UHV system, the capability to measure atomic-scale microwave studies such as differential capacitance or even single molecule microwave response, and it ensures that experimental ACSTM conditions can be held constant between different samples.     

A compact vacuum UV excilamp on argon dimers

The energy and spectral characteristics of the argon dimer emission with the maximum at a wave-length of ∼126 nm under excitation by a pulse-periodic discharge in a gas flow with pressures higher than the atmospheric pressure are studied. A compact excilamp has been designed for obtaining radiation in the vacuum ultraviolet spectrum region. The minimal argon flow velocities are determined, at which cooling is effected by convective gas ejection from the discharge region. This allows one to form a diffusion discharge with a stable radiation power density. It is shown that, when the flow velocity is 0.5 m³/h, the radiation power density of an Ar₂* molecule is >100 μW/cm² behind a LiF window with ∼10% transmission at a wavelength of 126 nm. It is shown that the use of a windowless design and an increase in the gas flow velocity allows an increase in the radiation power density up to 10 mW/cm².     

Highly sensitive,precise, and traceable measurement of force

Force in the micronewton range may be traced to the International System of Units by an electrostatic force balance weight system. However, there is a conflict between range and sensitivity. To solve this problem, a lever-type force metrology system based on the null-balance method is reported. The force is loaded on one end of the lever, causing elastic torsion of the central rod, and an electrostatic force is applied to the other end. With a variety of mass loading positions and standard weights, a wide range of moments may be produced to calibrate the system. The electrostatic force was generated by a pair of coaxial cylindrical capacitors where the applied voltage was converted into electrode displacement. The design of the inner and outer cylindrical capacitors was deduced considering the material and miniaturization requirements, and concentric alignment was ensured by a vision system. The null balance was achieved by a proportion-integration-differentiation control system, so that the external force was compensated by the electrostatic force. A method to increase the center of gravity was used to improve the resolution. The mechanism was analyzed based on stiffness, strength, stability, and frequency. Furthermore, the impact on the capacitance gradient due to the capacitor tilt caused by the applied force was estimated. Standard weights were utilized to evaluate the system performance. The results showed that a stiffness of 0.8 N/m and a force resolution of 10^?8 N were achieved.     

Dynamic behavior of amplitude detection Kelvin force microscopy in ultrahigh vacuum

The acquisition rate of all scanning probe imaging techniques with feedback control is limited by the dynamic response of the control loops. Performance criteria are the control loop bandwidth and the output signal noise power spectral density. Depending on the acceptable noise level, it may be necessary to reduce the sampling frequency below the bandwidth of the control loop. In this work, the frequency response of a vacuum Kelvin force microscope with amplitude detection (AM-KFM) using a digital signal processing (DSP) controller is characterized and optimized. Then, the main noise source and its impact on the output signal is identified. A discussion follows on how the system design can be optimized with respect to output noise. Furthermore, the interaction between Kelvin and distance control loop is studied, confirming the beneficial effect of KFM on topography artefact reduction in the frequency domain. The experimental procedure described here can be generalized to other systems and allows to locate the performance limitations.     

Tribological behavior of a multialkylated cyclopentane oil under ultrahigh vacuum conditions

An ultrahigh vacuum, ball-on-flat test apparatus has been built to study the performance of candidate oils intended for spacecraft applications. Tests have been conducted on a multialkylated cyclopentane base oil using steel balls and disks. Different results are obtained when this oil is tested under vacuum conditions than when it is tested under a nitrogen environment. These differences are dramatic when the tests are conducted under starved conditions. Analyses of gases evolved during rubbing reveal that large quantities of methane are evolving from the process. A mechanism is proposed whereby oxide-free steel surfaces combine with tribological activity to crack the hydrocarbon oil to produce CH _x radicals. These CH _x radicals abstract hydrogen from the surrounding oil to produce methane. The increased volatility of the oil fragments remaining after methane formation leads to material loss by evaporation, thereby explaining the differences in vacuum and nitrogen performance of the oil.     

Adaptation of an ultrahigh vacuum angle-resolving photoemission chamber for sample manipulation and rotation

A sample-manipulator attachment to a UHV angle-resolving photoemission system is described which permits the sample to be rotated azimuthally and to be transported to a LEED/Auger optics. The manipulator may be assembled from readily available commercial parts.     

精密数控回转工作台位置控制的研究

在基于工业控制计算机（IPC）的开放式数控系统中。为实现精密数控回转工作台的位置控制,文中提出了半闭环智能PID控制方法,并针对转台中蜗轮蜗杆传动机构的特点,提出了精密数控回工作台的双向螺距误差补偿方法。该控制算法和补偿算法已经应用在某航天火箭喷管铣槽加工控制系统中。     

Study on physical and technological effects of precise turning with self-propelled rotary tool

This study is focused on some physical and technological aspects of a precise turning with Self-Propelled Rotary Tool (SPRT). As part of experiment, the cutting forces, on-line insert run-out and machined surface topography were investigated. Turning tests were carried in the range of variable feeds, depths of cut and cutting speeds for a hardened 41Cr4 steel with the use of a coated carbide round indexable inserts. The effect of cutting conditions on the tool rotation and the dynamics of cutting force signal were evaluated. In particular, changes of cutting forces vs. cutting lengths for different cutting parameters were analyzed in terms of the cutting insert rotation, and Power Spectral Density (PSD) analysis. Moreover, the original method based on cutting force oscillations was employed to estimate the on-line insert run-out. Ultimately, the analysis of a machined surface topography was conducted, considering the interactions between the process inputs and outputs. It was shown that application of high cutting speeds and feeds during SPRT turning can lead to the improvements in surface finish, as well as the stabilization of cutting force values.     

A cooling system for samples for studying their surfaces in ultrahigh vacuum

The device described is designed to cool samples with liquid nitrogen to T=?165°C during low-energy electron diffraction (LEED) studies at an ultra-high-vacuum MALTIPROBE Compact system (Omicron) and versions thereof equipped with a scanning tunneling microscope and an LEED system. The efficiency of the system is demonstrated using the example of a low-temperature 2×1 ? c(4×2) phase transition on a (100)-oriented silicon surface observed using the LEED technique.     

高精度卫星激光通信地面验证系统

为了在地面高精度评估激光通信终端对卫星平台扰动以及轨道姿态变化的适应能力,研究了卫星扰动模拟技术和卫星随动仿真模拟技术,据此提出了激光通信系统地面验证方案。首先开展了激光通信链路随动探测误差对系统随动性能影响分析、卫星扰振源特性分析及建模工作。其次,分析了卫星扰动模拟和随动模拟的关键技术及解决措施。最后,结合目前卫星激光通信及卫星平台技术水平,利用典型数据开展了扰动和随动仿真,完成了激光通信系统测试。实验结果证明:基于双反馈环路的高精度光束瞄准控制能够大幅提高卫星扰动模拟器光束瞄准的控制精度,光束控制精度优于0.1″;采用高低频联合卫星扰动模拟设计方法,实现了控制带宽优于1kHz的高精度光束控制;高精度随动系统在全卫星运行区域内对卫星光通信终端随动性能的检测精度可达0.1″。     

Highly precise and stable displacement-measuring laser interferometer with differential optical paths

To achieve sub-nm precision of a displacement-measuring laser interferometer, its optical systematic error should be made as small as possible. In this paper, methods to reduce the optical path length changes and stray light reflections, as well as materials appropriate for main optical elements in the optical layout and the holders, are discussed. As a solution, a complete differential interferometer using a quartz plate inclined 45° to the optic axis is presented. This interferometer has null dead path length, fewer and smaller optical elements, and fewer boundary surfaces with air than conventional differential interferometers. Adopting the athermal glass (Ultran30) for interferometric prisms and aluminum alloy (A5056) for the interferometric prism holder was effective in reducing the drift of measurement caused by thermal changes. The interferometer made of Ultran30 glass with a A5056 holder achieved 0.31 nm/K thermal drift in the displacement measurement.