Scanning Optical Microscopy via a Scanning Electron Microscope

We have described in detail the principles of operation of a commercially available SEM-based scanning optical microscope. The stage consists of a cathodoluminescent material which converts the scanning electron beam into a scanning optical beam and an optical system to focus the light beam onto the specimen. The resolution attainable with such a stage is discussed as well as the efficiency of electron-to-photon conversion. Simplified formulae are given and a set of curves plotted which can be used to determine the appropriate tradeoff between resolution and optical power. Examples of the imaging ability in the optical beam induced current mode from various semiconductor devices are presented.     

Versatile optical access to the tunnel gap in a low-temperature scanning tunneling microscope

We developed a setup that provides three independent optical access paths to the tunnel junction of an ultrahigh vacuum low temperature (4.2 K) scanning tunneling microscope (STM). Each path can be individually chosen to couple light in or out, or to image the tunnel junction. The design comprises in situ adjustable aspheric lenses to allow tip exchange. The heat input into the STM is negligible. We present in detail the beam geometry and the realization of lens adjustment. Measurements demonstrate the characterization of a typical light source exemplified by emission from tip-induced plasmons. We suggest employing the Fourier transforming properties of imaging lenses and polarization analysis to obtain additional information on the light emission process. Performance and future potential of the instrument are discussed.     

一款新型LED台灯的设计

为了设计一款配光简单、光照均匀的LED台灯,从抛物线的光学特性出发,详细说明了LED光源的放置位置对出光效果的影响。证明了把LED面光源放置在中心轴上焦点与抛物线顶点之间的适当位置,可以使光线均匀发散。利用抛物线的这个特性,经过多次实验把单颗LED面光源放在旋转抛物反光镜顶点与焦点之间的正确位置,在距台灯400 mm、面积为1 000mm×1 000mm的平面得到了均匀的光照。在总体光通量基本不变的情况下,把10个如此配光组合按一定尺寸排列成2×5分布的光源模块,能很好地达到台灯的标准配光要求。     

Integration of a high‐NA light microscope in a scanning electron microscope

We present an integrated light‐electron microscope in which an inverted high‐NA objective lens is positioned inside a scanning electron microscope (SEM). The SEM objective lens and the light objective lens have a common axis and focal plane, allowing high‐resolution optical microscopy and scanning electron microscopy on the same area of a sample simultaneously. Components for light illumination and detection can be mounted outside the vacuum, enabling flexibility in the construction of the light microscope. The light objective lens can be positioned underneath the SEM objective lens during operation for sub‐10 μm alignment of the fields of view of the light and electron microscopes. We demonstrate in situ epifluorescence microscopy in the SEM with a numerical aperture of 1.4 using vacuum‐compatible immersion oil. For a 40‐nm‐diameter fluorescent polymer nanoparticle, an intensity profile with a FWHM of 380 nm is measured whereas the SEM performance is uncompromised. The integrated instrument may offer new possibilities for correlative light and electron microscopy in the life sciences as well as in physics and chemistry.     

Research and development of VUV optical coatings for micro mirror applications

1Introduction Duringthelastthreedecades,thedevelop mentofpowerfulUVlightsourcessuchasexci merlasers,frequencymultipliedsolidstatela sersorstoragefreeelectronlasershavegathered increasingresearcheffortsinthefieldsofUV photoninteractionwithmatteraswellasrising industrialapplicationssuchasintegratedcircuit manufacturing,microandnano materialpro cessingormedicine.Adominantdrivingforce downtotheshortestwavelengthsinthevacuum ultraviolet(VUV)spectralregionisthesemi conductormanufacturingwiththeopt…     

Auger microanalysis in a conventional scanning electron microscope

We have coupled an Auger spectrometer to a conventional scanning electron microscope. Specimens were examined without an ultrahigh vacuum by maintaining a high partial pressure of argon in the vicinity of the specimen. It was possible to examine the specimens by means of both Auger and x-ray microanalysis. Sputtering profiles could be recorded by removing surface layers by ion bombardment. Examples of the application of the method are drawn from studies of surface layers on metals, and are compared with XRMA results.     

Optical sectioning microscope with a binary hologram based beam scanning

We describe the development of a beam scanning microscope that can perform optical sectioning based on the principle of confocal microscopy. The scanning is performed by a laser beam diffracted from a dynamic binary hologram implemented using a liquid crystal spatial light modulator. Using the proposed scanning mechanism, unlike the conventional confocal microscopes, scanning over a two-dimensional area of the sample can be obtained without the use of a pair of galvo mirror scanners. The proposed microscope has a number of advantages, such as superior frame to frame repeatability, simpler optical arrangement, increased pixel dwell time relative to the time between two pixels, illumination of only the sample points without pulsing the laser, and absolute control over the amplitude and phase of the illumination beam on a pixel to pixel basis. The proposed microscope can be particularly useful for applications requiring very long exposure time or very large working distance objective lenses. In this paper we present experimental implementation of the setup using a nematic liquid crystal spatial light modulator and proof-of-concept experimental results.     

Compact non‐contact total emission detection for in vivo multiphoton excitation microscopy

We describe a compact, non‐contact design for a total emission detection (c‐TED) system for intra‐vital multiphoton imaging. To conform to a standard upright two‐photon microscope design, this system uses a parabolic mirror surrounding a standard microscope objective in concert with an optical path that does not interfere with normal microscope operation. The non‐contact design of this device allows for maximal light collection without disrupting the physiology of the specimen being examined. Tests were conducted on exposed tissues in live animals to examine the emission collection enhancement of the c‐TED device compared to heavily optimized objective‐based emission collection. The best light collection enhancement was seen from murine fat (5×–2× gains as a function of depth), whereas murine skeletal muscle and rat kidney showed gains of over two and just under twofold near the surface, respectively. Gains decreased with imaging depth (particularly in the kidney). Zebrafish imaging on a reflective substrate showed close to a twofold gain throughout the entire volume of an intact embryo (approximately 150 μm deep). Direct measurement of bleaching rates confirmed that the lower laser powers, enabled by greater light collection efficiency, yielded reduced photobleaching in vivo. The potential benefits of increased light collection in terms of speed of imaging and reduced photo‐damage, as well as the applicability of this device to other multiphoton imaging methods is discussed.     

The tandem scanning reflected light microscope

Reflected light microscopy of biological material has been a very difficult task and many different but hardly successful attempts have been made to get usable images. The main reasons for this state are: Weak reflections from the biologically important structures in the object as against strong reflection at its surface; reflections at optical surfaces in the microscope which cause a deterioration of contrast; and the mixing together of reflections from many levels in the object so that the signal coming from the focussed-on level is lost in noise and d.c. components. We tried, and successfully, to reverse this situation and to make it possible for the signal to overwhelm spurious and scattered light using double, or, as we call it, tandem scanning. The object is illuminated only in small patches lying in one plane and moving across this plane, and only the light reflected from these illuminated patches is allowed to pass into the image plane and participate in image formation. The image consists of points which travel over the image plane and which are geometrical images of the illuminated patches in the focussed-on object plane. To ensure that only the light belonging to these geometrical images be allowed to enter the image, the image plane is covered with an opaque diaphragm having holes in locations exactly corresponding to the locations of the geometrical images of the illuminated object points; this diaphragm travels in concordance with the first scanning and so the complete image of the focussed-on object plane is formed successively. Both scans are performed by a single device, a Nipkow disc carrying in its annular periphery several ten thousands of holes arranged in Archimedean spirals. The disc is 100 mm in diameter and rotates about 100 rpm driven by an electric motor. On one side the disc is illuminated in a circle 18 mm in diameter, and the light transmitted through several hundred holes and reflected in a mirror system passes a microscope objective which forms the images of the disc holes in the object plane. The light reflected here passes through the same objective and mirror system (one mirror being a “limitlessly thin” beam splitter) to pass conjugate aperture holes on the observation side of the Nipkow disc. As the disc lies at the intermediate image plane of the objective lens on both its illuminating and observation sides, only light emanating from reflection or fluorescence in the plane of focus can contribute to the image. High contrast images of very thin focussed-on layers are thus formed. The practical arrangements are such that very large specimens can be examined: The specimens for this microscope need not themselves be microscopic.     

A low-temperature scanning tunneling microscopy investigation of single electron effects

The design and the performance of a low-temperature scanning tunneling microscope (STM) operating in ultrahigh vacuum (UHV) is described. The sample and the STM are cooled by means of a helium bath cryostate. The STM consists of a “beetle”-type microscope, which is mounted on a spring suspension stage that can be operated between room temperature and 30 K. We present the results of tunneling spectroscopy on ligand-stabilized Au₅₅-clusters on a thiol-covered gold substrate. I(V)-curves taken at 100 K clearly show coulomb staircase structures, which agree well with theoretical predictions for these structures.     

Refined tip preparation by electrochemical etching and ultrahigh vacuum treatment to obtain atomically sharp tips for scanning tunneling microscope and atomic force microscope

A modification of the common electrochemical etching setup is presented. The described method reproducibly yields sharp tungsten tips for usage in the scanning tunneling microscope and tuning fork atomic force microscope. In situ treatment under ultrahigh vacuum (p ≤10(-10) mbar) conditions for cleaning and fine sharpening with minimal blunting is described. The structure of the microscopic apex of these tips is atomically resolved with field ion microscopy and cross checked with field emission.     

The near-field scanning thermal microscope

We report on the design, characterization, and performance of a near-field scanning thermal microscope capable to detect thermal heat currents mediated by evanescent thermal electromagnetic fields close to the surface of a sample. The instrument operates in ultrahigh vacuum and retains its scanning tunneling microscope functionality, so that its miniature, micropipette-based thermocouple sensor can be positioned with high accuracy. Heat currents on the order of 10(-7) W are registered in z spectroscopy at distances from the sample ranging from 1 to about 30 nm. In addition, the device provides detailed thermographic images of a sample's surface.     

Atomic friction studies on well-defined surfaces

Atomic friction studies have been performed by means of a friction force microscope (FFM) in ultrahigh vacuum, where well-defined surfaces can be prepared. A home-built FFM allows us to study lateral forces as low as 0.05 nN using rectangular silicon cantilevers. Furthermore, comparison with dissipation measurements performed in non-contact mode are possible. Recent experimental results are presented and discussed in the framework of a one-dimensional Tomlinson model which includes thermal activation. Atomic-scale stick–slip processes on a metallic surface could be repeatedly measured on Cu(111), while the Cu(100) surface was distorted by the tip during the scanning process. A logarithmic velocity dependence of atomic friction has been measured on Cu(111) and NaCl(100) for low scanning velocities. The dissipation found in stick–slip measurements is compared to the power loss detected in dynamic non-contact measurement.     

A confocal fibre scanning microscope for magnetic domain imaging

A compact confocal single-mode optical fibre scanning microscope for imaging magnetic domain structures, based on the polar magneto-optic Kerr effect, has been developed. The images obtained correspond to those obtained using single mirror scanning but this design offers a more compact structure and can be made more immune from system depolarization which makes two-axis mirror scanning difficult to implement when very small changes in polarization need to be detected.     

Electron optical characteristics of a concave electrostatic electron mirror for a scanning electron microscope

Numerical computer calculations are used to explore the design characteristics of a concave electrostatic electron mirror for a mirror-attachment for a conventional scanning electron microscope or an instrument designed totally as a scanning electron mirror microscope. The electron paths of a number of set-ups are calculated and drawn graphically in order to find the optimum shape and dimensions of the mirror geometry. This optimum configuration turns out to be the transition configuration between two cases of electron path deflection, towards the optical axis of the system and away from it.     

A new design approach for solar concentrating parabolic dish based on optimized flexible petals

Large parabolic dish concentrator mirrors are an important component of many solar energy systems. They need to be relatively precise and are expensive to fabricate and to transport. Here, a new concept for designing and fabricating large parabolic dish mirrors is presented. The dish mirror is formed from several optimal-shaped thin flat metal petals with highly reflective surfaces. Attached to the rear surface of the mirror petals are several thin layers whose shapes are optimized to have reflective petals form into a parabola when their ends are pulled toward each other by cables or rods. An analytical model to optimize the shape and thickness of the petals is presented. The validity of the concept is demonstrated using Finite Element Analysis and laboratory experiments. The concept would permit flat mirror elements to be easily fabricated and efficiently packaged for shipping to field sites where they can be assembled into the parabolic dish concentrators. The concept has the potential to provide precision solar parabolic solar collectors at a substantially lower cost than conventional methods.     

Fundamental differences between micro- and nano-Raman spectroscopy

Electric field polarization orientations and gradients close to near-field scanning optical microscope (NSOM) probes render nano-Raman fundamentally different from micro-Raman spectroscopy. With x -polarized light incident through an NSOM aperture, transmitted light has x, y and z components allowing nano-Raman investigators to probe a variety of polarization configurations. In addition, the strong field gradients in the near-field of a NSOM probe lead to a breakdown of the assumption of micro-Raman spectroscopy that the field is constant over molecular dimensions. Thus, for nano-Raman spectroscopy with an NSOM, selection rules allow for the detection of active modes with intensity dependent on the field gradient. These modes can have similar activity as infra-red absorption modes. The mechanism can also explain the origin and intensity of some Raman modes observed in surface enhanced Raman spectroscopy.     

校准能见度仪用标准散射体定标系统装调技术

为了实现校准能见度仪用标准散射体的快速高精度定标,依据标准散射体校准前向散射式能见度仪的校准原理,提出了一种新型的校准能见度仪用标准散射体定标系统,重点研究了该系统的装调技术。根据定标系统的组成与工作原理,建立了定标系统装调光学模型,并提出由抛物面反射镜与全景成像能量检测系统相对位置装调以及抛物面反射镜与低反射率球形屏幕系统相对位置装调组成的定标系统装调方案。建立校准能见度仪用标准散射体定标系统极限误差计算模型,在入射光线角度为45°的情况下,计算出装调过程中抛物面反射镜与低反射率球形屏幕系统平移误差与倾斜误差的极限装调误差分别为3.18°和0.847°,抛物面反射镜与全景成像能量检测系统平移误差与倾斜误差的极限装调误差的极限装调误差均为2.14 pixel。实验证明装调后的校准能见度仪用标准散射体定标系统的最大角度检测误差为0.795°,满足定标系统的角分辨率是1°的使用要求。     

Mirrorlike pulsed laser deposited tungsten thin film

Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10(-5) Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness ～782 nm.