Photo-Electron Emission Microscopy of Semiconductor Surfaces

1998 ◽  
Vol 4 (S2) ◽  
pp. 606-607
Author(s):  
R.J. Nemanich ◽  
S.L. English ◽  
J.D. Hartman ◽  
W. Yang ◽  
H. Ade ◽  
...  
Keyword(s):  
Electron Emission ◽  
Imaging System ◽  
Uv Light ◽  
Ultra Violet ◽  
Objective Lens ◽  
Electron Optics ◽  
Light Sources ◽  
Emission Microscopy ◽  
Electron Imaging ◽  
Crucial Part

The technique of photo-electron emission microscopy (PEEM) is based on imaging of photo excited electrons from a surface. Typically ultra violet (UV) light above the work function of a metal will cause electrons to be emitted from a surface. Since photo excited electrons originate very near to the surface, they essentially reflect the electronic structure of the surface. These electrons may be accelerated and imaged, and the image will reflect the properties of the surface.While the PEEM technique has been understood in a basic sense for many years, it has been limited by the lack of high intensity UV light sources. The most crucial part of the electron imaging system for PEEM, the objective lens, is essentially the same as for the sister technique of low energy electron microscopy (LEEM), and advances in electron optics capabilities have been exploited both for LEEM and for PEEM.

scholarly journals Beeporter: a high-throughput tool for non-invasive analysis of honey bee virus infection

2021 ◽  
Author(s):  
Jay D. Evans ◽  
Olubukola Banmeke ◽  
Evan C. Palmer-Young ◽  
Yanping Chen ◽  
Eugene V. Ryabov
Keyword(s):  
Virus Infection ◽  
Honey Bee ◽  
High Throughput ◽  
Honey Bees ◽  
High Throughput Screening ◽  
Fluorescent Protein ◽  
Imaging System ◽  
Uv Light ◽  
Light Sources ◽  
Deformed Wing Virus

ABSTRACTHoney bees face numerous pests and pathogens but arguably none are as devastating as Deformed wing virus (DWV). Development of antiviral therapeutics and virus-resistant honey bee lines to control DWV in honey bees is slowed by the lack of a cost-effective high-throughput screening of DWV infection. Currently, analysis of virus infection and screening for antiviral treatments in bees and their colonies is tedious, requiring a well-equipped molecular biology laboratory and the use of hazardous chemicals. Here we utilize a cDNA clone of DWV tagged with green fluorescent protein (GFP) to develop the Beeporter assay, a method for detection and quantification of DWV infection in live honey bees. The assay involves infection of honey bee pupae by injecting a standardized DWV-GFP inoculum, followed by incubation for up to 44 hours. GFP fluorescence is recorded at intervals via commonly available long-wave UV light sources and a smartphone camera or a standard ultraviolet transilluminator gel imaging system. Nonlethal DWV monitoring allows high-throughput screening of antiviral candidates and a direct breeding tool for identifying honey bee parents with increased antivirus resistance. For even more rapid drug screening, we also describe a method for screening bees using 96-well trays and a spectrophotometer.

scholarly journals Effect of UV-Light Treatment on Efficiency of Perovskite Solar Cells (PSCs)

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1069 ◽  
Author(s):  
Sangmo Kim ◽  
Hoang Van Quy ◽  
Hyung Wook Choi ◽  
Chung Wung Bark
Keyword(s):  
Solar Cells ◽  
Conversion Efficiency ◽  
Uv Light ◽  
Perovskite Solar Cells ◽  
Ultra Violet ◽  
Light Treatment ◽  
Light Sources ◽  
Perovskite Layer ◽  
Solar Conversion ◽  
Solar Conversion Efficiency

We employed ultra-violet (UV) light treatment on the TiO2 layer prior to coating the perovskite layer to improve the solar conversion efficiency of perovskite solar cells (PSCs). A laboratory-made UV treatment system was equipped with various UV light sources (8 W power; maximum wavelengths of 254, 302, and 365 nm). The UV light treatment improved the power conversion efficiency (PCE) while coating the uniformity layer and removing impurities from the surface of cells. After the PSCs were exposed to UV light, their PCE developed approximately 10% efficiency; PBI2 decreased without changing the structure.

Electron emission microscopy in retrospect and prospect

1986 ◽  
Vol 318 (1541) ◽  
pp. 219-241 ◽  
Keyword(s):  
Magnetic Field ◽  
Chemical Analysis ◽  
Electron Emission ◽  
Photoelectron Spectroscopy ◽  
Energy Analysis ◽  
Photoelectron Spectra ◽  
Electron Optics ◽  
Small Object ◽  
Emission Microscopy ◽  
Conventional Electron Microscopy

Photoelectron microscopy developed as part of the general advance in electron optics and conventional electron microscopy. The recent emphasis on energy analysis through photoelectron spectroscopy has led to several related developments in which the possibility of obtaining photoelectron spectra from very small object areas has emerged. Either chemical analysis, and especially molecular chemical analysis, becomes possible from areas less than a square micrometre, or magnified images may be obtained by using closely selected electron energies. Both of these possibilities are realized in the Oxford photoelectron spectromicroscope, which is described. Other means of producing electron images include the use of metastable or fast atoms. The use of a magnetic field, which is an essential part of the Oxford instrument, introduces the opportunity for a number of novel techniques, which are also described.

UV-C LEDs for Sterilization Applications

2014 ◽  
Vol 2014 (DPC) ◽  
pp. 002132-002166
Author(s):  
Joe Grzyb
Keyword(s):  
High Voltage ◽  
High Efficiency ◽  
Lattice Mismatch ◽  
Uv Light ◽  
High Reliability ◽  
Ultra Violet ◽  
Device Fabrication ◽  
Light Sources ◽  
Wafer Processing ◽  
Uv C

HexaTech has developed a proprietary, patented process for manufacturing bulk aluminum nitride (AlN) crystals and semiconductor wafers. HexaTech is leveraging this unique capability to develop and commercialize high-performance, long-lifetime Ultra Violet Light Emitting Diodes (UV-C LEDs) for disinfection applications (particularly clean water) and high-voltage, high-efficiency power semiconductors for power conversion applications (particularly smart grid). Deep-ultraviolet light with wavelength in the range of 250 to 280nm (UV-C) has been used to sterilize liquids, air and surfaces for over a century. UV-C light is absorbed by and damages the DNA of harmful bacteria, either outright killing the bacteria or preventing their ability to replicate. Traditionally, high voltage mercury tubes have been used to generate such UV light. While mercury tubes have enabled UV-C use bulk disinfection applications such as drinking water and waste water, they have proven impractical in point-of-use applications where small size, elimination of harmful mercury, and high reliability under intermittent use conditions are required. The solution is to generate UV-C light using LEDs. In spite of numerous efforts, the power output and reliability of UV-C LEDs is still not sufficient for their adoption as practical and reliable UV-C light sources. Traditionally, AlGaN-based UV-C LEDs have been fabricated on sapphire substrates. Because of huge number of defects caused by the lattice mismatch between the AlGaN active layers and the sapphire substrate, these sapphire-based UV-C LEDs show performance and reliability of limited interest to sterilization system manufacturers. HexaTech's AlN crystal growth and wafer processing technology results in single crystal wafers with extremely high quality. HexaTech and its development partners have fabricated UV-C LEDs that have shown performance dramatically superior to other devices in the market in terms of output power, power density and lifetime. In this presentation, we will discuss the market requirements for UV-C LEDs, the challenges of UV-C device fabrication, package and test, and the solutions that are being pursued.

Navigation of Lutzomyia longipalpis (Diptera: Psychodidae) under dusk or starlight conditions

2003 ◽  
Vol 93 (4) ◽  
pp. 315-322 ◽  
Author(s):  
H.E. Mellor ◽  
J.G.C. Hamilton
Keyword(s):  
Uv Light ◽  
Ultra Violet ◽  
Lutzomyia Longipalpis ◽  
Light Sources ◽  
Trap Design ◽  
Low Intensity ◽  
Violet Light ◽  
Males And Females ◽  
The Difference ◽  
And Control

AbstractThe responses of male and female Lutzomyia longipalpis (Lutz & Neiva) to different wavelengths of light was tested by presenting the sandflies with two light sources simultaneously, a series of test wavelengths between 350–670 nm and a 400 nm control. To test whether L. longipalpis could discriminate between the test and control, three sets of experiments were carried out in which the test wavelengths were presented at higher, equivalent or lower intensity than the control. In all three experiments, ultra-violet (350 nm) and blue-green-yellow (490–546 nm) light was more attractive to L. longipalpis than the control wavelength. However, at low intensity, UV was less attractive, than equivalent or higher intensity UV light. At intensities equivalent to or higher than the control wavelength, ultra-violet light was more attractive than blue-green. Furthermore, at low intensity, green-yellow (546 nm) light was more attractive to males whereas blue-green (490 nm) was more attractive to females. Blue-violet (400 nm) and orange-red (600–670 nm) light were least attractive in all three sets of experiments. Response function experiments indicated that the responses were dependent on both intensity and wavelength and that therefore more than one photoreceptor must be involved in the response. The results indicated that L. longipalpis can discriminate between different wavelengths at different intensities and thus have true colour vision. It also suggests that L. longipalpis may be able to navigate at dusk or under moonlight or starlight conditions using light in the blue-green-yellow part of the spectrum. The difference in response of males and females to light in this region is interesting and may indicate the different ecology of the sexes at night. Overall, these results may have important implications for sandfly trap design.

New Aspects in the Design of Electron Optical Magnification Systems

1972 ◽  
Vol 30 ◽  
pp. 606-607
Author(s):  
Willem H.J. Andersen
Keyword(s):  
Electron Microscope ◽  
Imaging System ◽  
Chromatic Aberration ◽  
Research Tool ◽  
Energy Losses ◽  
Objective Lens ◽  
Theoretical Limit ◽  
Optical Magnification ◽  
Chromatic Aberrations ◽  
High Degree

Electron microscope design, and particularly the design of the imaging system, has reached a high degree of perfection. Present objective lenses perform up to their theoretical limit, while the whole imaging system, consisting of three or four lenses, provides very wide ranges of magnification and diffraction camera length with virtually no distortion of the image. Evolution of the electron microscope in to a routine research tool in which objects of steadily increasing thickness are investigated, has made it necessary for the designer to pay special attention to the chromatic aberrations of the magnification system (as distinct from the chromatic aberration of the objective lens). These chromatic aberrations cause edge un-sharpness of the image due to electrons which have suffered energy losses in the object.There exist two kinds of chromatic aberration of the magnification system; the chromatic change of magnification, characterized by the coefficient Cm, and the chromatic change of rotation given by Cp.

Rocking Beam Microarea Diffraction Applied to Metallic thin Films

1976 ◽  
Vol 34 ◽  
pp. 396-397
Author(s):  
R. H. Geiss
Keyword(s):  
Thin Films ◽  
Electron Diffraction ◽  
Small Area ◽  
Objective Lens ◽  
Electron Optics ◽  
Metallic Thin Films ◽  
Transmission Electron Diffraction ◽  
Transmission Electron ◽  
Sample Height ◽  
Scanning Transmission

The theory and practical limitations of micro area scanning transmission electron diffraction (MASTED) will be presented. It has been demonstrated that MASTED patterns of metallic thin films from areas as small as 30 Åin diameter may be obtained with the standard STEM unit available for the Philips 301 TEM. The key to the successful application of MASTED to very small area diffraction is the proper use of the electron optics of the STEM unit. First the objective lens current must be adjusted such that the image of the C2 aperture is quasi-stationary under the action of the rocking beam (obtained with 40-80-160 SEM settings of the P301). Second, the sample must be elevated to coincide with the C2 aperture image and its image also be quasi-stationary. This sample height adjustment must be entirely mechanical after the objective lens current has been fixed in the first step.

Tandem scanning confocal light microscopy as compared with x-ray diffraction for characterizing the behavior of clays in fluid-saturated petroleum reservoir rock

1989 ◽  
Vol 47 ◽  
pp. 148-149
Author(s):  
C.J. Stuart ◽  
B.E. Viani ◽  
J. Walker ◽  
T.H. Levesque
Keyword(s):  
Light Microscopy ◽  
Image Plane ◽  
Reservoir Rock ◽  
Depth Of Field ◽  
Objective Lens ◽  
Scanning System ◽  
Light Sources ◽  
Petroleum Reservoir ◽  
Image Recording ◽  
Scan Speed

Many techniques of imaging used to characterize petroleum reservoir rocks are applied to dehydrated specimens. In order to directly study behavior of fines in reservoir rock at conditions similar to those found in-situ these materials need to be characterized in a fluid saturated state.Standard light microscopy can be used on wet specimens but depth of field and focus cannot be obtained; by using the Tandem Scanning Confocal Microscope (TSM) images can be produced from thin focused layers with high contrast and resolution. Optical sectioning and extended focus images are then produced with the microscope. The TSM uses reflected light, bulk specimens, and wet samples as opposed to thin section analysis used in standard light microscopy. The TSM also has additional advantages: the high scan speed, the ability to use a variety of light sources to produce real color images, and the simple, small size scanning system. The TSM has frame rates in excess of normal TV rates with many more lines of resolution. This is accomplished by incorporating a method of parallel image scanning and detection. The parallel scanning in the TSM is accomplished by means of multiple apertures in a disk which is positioned in the intermediate image plane of the objective lens. Thousands of apertures are distributed in an annulus, so that as the disk is spun, the specimen is illuminated simultaneously by a large number of scanning beams with uniform illumination. The high frame speeds greatly simplify the task of image recording since any of the normally used devices such as photographic cameras, normal or low light TV cameras, VCR or optical disks can be used without modification. Any frame store device compatible with a standard TV camera may be used to digitize TSM images.

Observation of GaAs/AlAs Superlattice Structures in both Secondary and Backscattcred Electron Imaging Modes with an Ultrahigh Resolution Scanning Electron Microscope

1990 ◽  
Vol 48 (1) ◽  
pp. 404-405
Author(s):  
K. Ogura ◽  
A. Ono ◽  
S. Franchi ◽  
P.G. Merli ◽  
A. Migliori
Keyword(s):  
Gaas Layer ◽  
Objective Lens ◽  
Superlattice Structure ◽  
Backscattered Electron ◽  
Instrumental Resolution ◽  
Electron Microscopes ◽  
Superlattice Structures ◽  
Electron Imaging ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

In the last few years the development of Scanning Electron Microscopes (SEM), equipped with a Field Emission Gun (FEG) and using in-lens specimen position, has allowed a significant improvement of the instrumental resolution . This is a result of the fine and bright probe provided by the FEG and by the reduced aberration coefficients of the strongly excited objective lens. The smaller specimen size required by in-lens instruments (about 1 cm, in comparison to 15 or 20 cm of a conventional SEM) doesn’t represent a serious limitation in the evaluation of semiconductor process techniques, where the demand of high resolution is continuosly increasing. In this field one of the more interesting applications, already described (1), is the observation of superlattice structures.In this note we report a comparison between secondary electron (SE) and backscattered electron (BSE) images of a GaAs / AlAs superlattice structure, whose cross section is reported in fig. 1. The structure consist of a 3 nm GaAs layer and 10 pairs of 7 nm GaAs / 15 nm AlAs layers grown on GaAs substrate. Fig. 2, 3 and 4 are SE images of this structure made with a JEOL JSM 890 SEM operating at an accelerating voltage of 3, 15 and 25 kV respectively. Fig. 5 is a 25 kV BSE image of the same specimen. It can be noticed that the 3nm layer is always visible and that the 3 kV SE image, in spite of the poorer resolution, shows the same contrast of the BSE image. In the SE mode, an increase of the accelerating voltage produces a contrast inversion. On the contrary, when observed with BSE, the layers of GaAs are always brighter than the AlAs ones , independently of the beam energy.

Electron Holography Improving Transmission Electron Microscopy

1990 ◽  
Vol 48 (1) ◽  
pp. 208-209
Author(s):  
Hannes Lichte
Keyword(s):  
Electron Microscopy ◽  
Transfer Functions ◽  
Imaging System ◽  
Spherical Aberration ◽  
Image Plane ◽  
Chromatic Aberration ◽  
Object Wave ◽  
Objective Lens ◽  
Electron Holography ◽  
Wave Aberration

Generally, the electron object wave o(r) is modulated both in amplitude and phase. In the image plane of an ideal imaging system we would expect to find an image wave b(r) that is modulated in exactly the same way, i. e. b(r) =o(r). If, however, there are aberrations, the image wave instead reads as b(r) =o(r) * FT(WTF) i. e. the convolution of the object wave with the Fourier transform of the wave transfer function WTF . Taking into account chromatic aberration, illumination divergence and the wave aberration of the objective lens, one finds WTF(R) = Echrom(R)Ediv(R).exp(iX(R)) . The envelope functions Echrom(R) and Ediv(R) damp the image wave, whereas the effect of the wave aberration X(R) is to disorder amplitude and phase according to real and imaginary part of exp(iX(R)) , as is schematically sketched in fig. 1.Since in ordinary electron microscopy only the amplitude of the image wave can be recorded by the intensity of the image, the wave aberration has to be chosen such that the object component of interest (phase or amplitude) is directed into the image amplitude. Using an aberration free objective lens, for X=0 one sees the object amplitude, for X= π/2 (“Zernike phase contrast”) the object phase. For a real objective lens, however, the wave aberration is given by X(R) = 2π (.25 Csλ3R4 + 0.5ΔzλR2), Cs meaning the coefficient of spherical aberration and Δz defocusing. Consequently, the transfer functions sin X(R) and cos(X(R)) strongly depend on R such that amplitude and phase of the image wave represent only fragments of the object which, fortunately, supplement each other. However, recording only the amplitude gives rise to the fundamental problems, restricting resolution and interpretability of ordinary electron images:

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