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.     

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.     

Highly precise and compact ultrahigh vacuum rotary feedthrough

The precision and rigidity of compact ultrahigh vacuum (UHV) rotary feedthroughs were substantially improved by preparing and installing an optimal crossed roller bearing with mounting holes. Since there are mounting holes on both the outer and inner races, the bearing can be mounted directly to rotary and stationary stages without any fixing plates and housing. As a result, it is possible to increase the thickness of the bearing or the size of the rolling elements in the bearing without increasing the distance between the rotating and fixing International Conflat flanges of the UHV rotary feedthrough. Larger rolling elements enhance the rigidity of the UHV rotary feedthrough. Moreover, owing to the structure having integrated inner and outer races and mounting holes, the performance is almost entirely unaffected by the installation of the bearing, allowing for a precise optical encoder to be installed in the compact UHV rotary feedthrough. Using position feedback via a worm gear system driven by a stepper motor and a precise rotary encoder, the actual angle of the compact UHV rotary feedthrough can be controlled with extremely high precision.     

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.     

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.     

Note: mounting ultra-high vacuum windows with low stress-induced birefringence

We have developed a way to mount ultra-high vacuum windows onto standard ConFlat(?) vacuum systems with very low stress-induced birefringence. Each window is sealed to a stainless steel flange with a compressed indium wire, and that flange is connected to a vacuum chamber with another indium seal. We find that deformation of a standard ConFlat flange during indium sealing dominates the stress on the window, so an extra-rigid flange is needed for minimal birefringence. With this mounting scheme, the typical residual birefringence is Δn = 2.3 × 10(-7) and is unchanged by a 120 °C bake.     

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.     

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.     

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.     

Friction force microscopy in ultrahigh vacuum: an atomic-scale study on KBr(001)

We present an atomic-scale study on friction performed by a bidirectional atomic force microscope operated in ultrahigh vacuum. Experiments on surfaces of in situ cleaved KBr crystals are presented. On a m scale the cleavage structure with monoatomic steps of 3.5 ± 0.3 Å is revealed. On the atomically flat terraces, atomic-scale resolution is achieved. The resolved square lattice shows a periodicity of 4.7 Å and corrugations of 0.3–0.7 Å and exhibits the cubic symmetry of KBr(001). The lateral (frictional) force map shows all characteristics of the stick-slip movement of the probing tip. From analysis of the friction loops, the kinetic friction force was determined as a function of load. For a load regime of -4 to 10 nN, lateral force corrugations ranging from 1 to 5 nN were found. A comparison with a novel theoretical model is discussed qualitatively.     

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.     

A pulse-type evaporator for ultrafast deposition of thin films in ultrahigh vacuum

The design of a simple pulse-type evaporator ensuring a high rate (up to ～10⁴ nm/s) of deposition of thin films (0.01–100 nm thick) onto a solid surface in ultrahigh vacuum is described. The evaporation pulse is created by discharge of a capacitor bank via a fast-response evaporator produced from a tungsten foil. Results illustrating the efficiency of this device are presented.     

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.     

超高真空电子束蒸发系统ULS400的技术改造及新应用

本文主要介绍安装在超高真空电子束蒸发系统ULS4 0 0中———自行设计、研制的恒温控制系统以及它在纳米科技领域发挥出的新作用 :制备多种特殊结构的纳米材料 ,包括首次在超高真空条件下制备出高品质的一维单晶硅纳米线等     

Low temperature ultrahigh vacuum noncontact atomic force microscope in the pendulum geometry

A noncontact atomic force microscope (nc-AFM) operating in magnetic fields up to ±7 T and liquid helium temperatures is presented in this article. In many common AFM experiments the cantilever is mounted parallel to the sample surface, while in our system the cantilever is assembled perpendicular to it; the so called pendulum mode of AFM operation. In this mode measurements employing very soft and, therefore, ultrasensitive cantilevers can be performed. The ultrahigh vacuum conditions allow to prepare and transfer cantilevers and samples in a requested manner avoiding surface contamination. We demonstrate the possibility of nc-AFM and Kelvin force probe microscopy imaging in the pendulum mode. Ultrasensitive experiments on small spin ensembles are presented as well.     

Analyzer system capable of determining energy and direction of charged particles in ultrahigh vacuum

We have constructed and tested a system capable of measuring the energy of charged particles emitted from a sample at any angle relative to the sample or the incident beam of exciting particles. The energy analysis is accomplished by a 180 degrees spherical deflecting-type analyzer, operated at constant pass energy with a series of electrostatic lenses. The analyzer system is properly apertured to accept incoming particles from a spot of 1.5 mm diameter at the sample and within a cone of 2.5 degrees half-angle. The lens system used has constant transmission independent of the incident energy. The energy analyzer is independently rotatable about two orthogonal axes, giving it complete freedom of access to any angle of collection relative to the sample orientation. The sample can rotate about two orthogonal axes so that any angle of incidence can be used. Specific examples are given of the performance of the system when used for the measurement of the angular distribution of photoelectrons excited by synchrotron radiation.     

Note: High-speed optical tracking of a flying insect

We developed a video recording system with the capability of tracking moving objects and used it to track the flight of an insect. The system consists of two galvano mirrors, which redirect the light coming from the object in two orthogonal directions toward a high-speed camera to capture the image. An additional high-speed camera, which views the same object through a beam splitter placed between one of the galvano mirrors and the observation camera, detects the position of the object. The mirror angle is controlled to maintain the position of the object at the center of the view, allowing the object to be tracked. In order to validate this system, images of a live fly in flight were recorded along a flight path that was much longer than the field of view of the stationary camera. A high-resolution video image of a rapidly moving live fly was successfully captured.     

Note: fast and reliable fracture strain extraction technique applied to silicon at nanometer scale

Simple fabrication process and extraction procedure to determine the fracture strain of monocrystalline silicon are demonstrated. Nanowires/nanoribbons in silicon are fabricated and subjected to uniaxial tensile stress along the complete length of the beams. Large strains up to 5% are measured for nanowires presenting a cross section of 50 nm × 50 nm and a length of 2.5 μm. An increase in fracture strain for silicon nanowires (NWs) with the downscaling of their volume is observed, highlighting the reduction of the defects probability as volume is decreased.