Anti-contamination Device Research Articles

Peltier cooling for the reduction of carbon contamination in scanning electron microscopy

We used a novel Peltier anticontamination device (PAC) to reduce carbon contamination upon electron beam irradiation in scanning electron microscopy through a reduction of hydrocarbon molecules in the specimen chamber. Unlike liquid-nitrogen based cold traps, the PAC operates free of user maintenance and is suitable for lengthy imaging sessions without degradation of the anticontamination performance. Its performance as an alternative cold trap method provides considerable reduction of electron beam-assisted carbon build-up. We compared the thickness of carbon contamination deposited upon prolonged electron beam scans with the PAC system on and off. Topographical structures of the carbon build-up were characterized using atomic force microscopy. We report that under identical beam parameters, thickness of the carbon contamination was reduced by over 79 % for area scans (1.2 × 1.2 µm2), and by two orders of magnitude for stationary point scans when the PAC cooling mode is engaged.

Quantitative FE-EPMA measurement of formation and inhibition of carbon contamination on Fe for trace carbon analysis.

Hydrocarbon contamination introduced during point, line and map analyses in a field emission electron probe microanalysis (FE-EPMA) was investigated to enable reliable quantitative analysis of trace amounts of carbon in steels. The increment of contamination on pure iron in point analysis is proportional to the number of iterations of beam irradiation, but not to the accumulated irradiation time. A combination of a longer dwell time and single measurement with a liquid nitrogen (LN2) trap as an anti-contamination device (ACD) is sufficient for a quantitative point analysis. However, in line and map analyses, contamination increases with irradiation time in addition to the number of iterations, even though the LN2 trap and a plasma cleaner are used as ACDs. Thus, a shorter dwell time and single measurement are preferred for line and map analyses, although it is difficult to eliminate the influence of contamination. While ring-like contamination around the irradiation point grows during electron-beam irradiation, contamination at the irradiation point increases during blanking time after irradiation. This can explain the increment of contamination in iterative point analysis as well as in line and map analyses. Among the ACDs, which are tested in this study, specimen heating at 373 K has a significant contamination inhibition effect. This technique makes it possible to obtain line and map analysis data with minimum influence of contamination. The above-mentioned FE-EPMA data are presented and discussed in terms of the contamination-formation mechanisms and the preferable experimental conditions for the quantification of trace carbon in steels.

Characterization of a highly efficient chevron-shaped anti-contamination device

This paper is devoted to the characterization of an optimized chevron-shaped anti-contamination device (ACD). This device can prevent efficiently the propagation of turbulence from the fuselage along the attachment line (hypothetical streamline that spreads the flow going to suction side and the one going to pressure side) of swept wings and enables the development of a new laminar boundary layer downstream. More specifically, the aim is to prevent boundary-layer transition along the attachment line by a contamination process. This process is characterized by the typical Reynolds number $$\overline{R}$$ and the associated Poll’s criterion. Thus, ACD efficiency will be expressed in terms of $$\overline{R}$$ values. Some experiments performed on a new numerically optimized ACD have shown its ability to prevent leading-edge contamination up to $$\overline{R}$$ values close to the natural transition process of the laminar boundary layer along the attachment line. The corresponding stability analysis of the laminar boundary layer is made using the Gortler–Hammerlin stability approach. The study is completed with the different transition processes that can occur downstream the attachment line, around the airfoil, especially with crossflow analysis.

Anti-contamination device for cryogenic soft X-ray diffraction microscopy

Cryogenic microscopy allows one to view frozen hydrated biological and soft matter specimens with good structural preservation and a high degree of stability against radiation damage. We describe a liquid nitrogen-cooled anti-contamination device for cryogenic X-ray diffraction microscopy. The anti-contaminator greatly reduces the buildup of ice layers on the specimen due to condensation of residual water vapor in the experimental vacuum chamber. We show by coherent X-ray diffraction measurements that this leads to fivefold reduction of background scattering, which is important for far-field X-ray diffraction microscopy of biological specimens.

Effect of Cleaning Parameters on Cleaning Effectiveness in an SEM Equipped with an RF Plasma Anti-Contamination Device

Effect of Cleaning Parameters on Cleaning Effectiveness in an SEM Equipped with an RF Plasma Anti-Contamination Device

Monitoring Contamination Rate in an SEM Equipped with an Evactron Anti-Contamination Device

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

The First Experience with new Small-Sized Commercial Tem (TEM -100) and Biological Specimens

Conventional electron microscope TEM -100 (Made by “ELECTRON”, Sumy, USSR; Fig. 1) was presented at the XI Int. Congress on Electron Microscopy (Kyoto) by I.S. Lyalko et al. (1,2). The purpose of the microscope constructors were to design a small-sized general conventional TEM for various application fields. The microscope have mini lenses, which winding is placed in closed casing and soaked in working liquid (low boiling temperature) but upper part of the casing being water cooled.In this communication we gave our first experience and impression as a customer, beginning from the montage, the instruction and the testing of the microscope to our application in the field of biological specimens. Just after montage of the microscope on the second floor, the test of the point resolution power was performed by Ir specimen. It was achieved 0.5 nm (Fig. 2 and 3) on the roll film (ORWO 22 DIN) with 300 OOOx magnification and anticontamination device. The ultimate vacuum (about 10exp-6 mm Hg, ion discharge pump) also achieved using large trap cooled by liquid nitrogen.

Reduction of contamination using a specimen heating holder in an ultra high resolution Scanning Electron Microscope

In general, various improvements have been made to SEM vacuum systems, and clean high vacuum specimen chambers are now routinely available. However, in the ultra high resolution scanning electron microscope, the prevention or reduction of contamination on the specimen surface has recently become an important subject when SEM imaging is done at higher than 200,000x magnification using a very fine electron probe. Typically, the specimen carries hydrocarbon gas molecules which are the source of the contamination, into the SEM. They adhere not only to the specimen surface but may also incorporated in the specimen, most typically in biological specimens, and cannot be reduced by the anti-contamination device of the SEM. Recently, a specimen heating holder was used in a JSM-890 ultra high resolution SEM, to reduce the contamination deposition on the specimen surface during SEM imaging. Using this holder, the specimen can be heated up to 300°C inside the SEM. Images 1 to 4 in Fig. 1 are the secondary electron images showing the cone-shaped deposition of contamination on a platinum-coated carbon film at different heating temperatures. This platinum-coated film, which had been kept in wet and oily atmosphere for several weeks to insure it was well covered with hydro carbon gas molecules, was irradiated by an electron probe in a spot mode for 30sec. with 1×10−11 Amp. of probe current at 20kV. After the electron probe irradiation, the platinum-coated carbon film was tilted 45° for imaging. Image 1 in Fig. 1 shows the cone-shaped deposition of contamination when the specimen was not heated. Image 2 was at 35°C, Image 3 was at 55°C, and Image 4 in Fig. 1 was at 115°C. At higher than 120°C specimen heating temperature, the cone-shaped deposition of contamination could not be observed any more. On the other hand, we can heat up the specimen outside the SEM before we put the specimen into the SEM. Image 5 in Fig. 1 shows the results of specimen heating by a hair dryer. The same platinum- coated carbon film was heated by a hair dryer for 1 minute before it was intro- duced into the SEM, and was irradiated by the electron probe for 15, 30, and 45sec. in a spot mode. This 1 min. heating by a hair dryer shows almost same result as 55°C specimen heating in the SEM.

High resolution cryo system designed for JEM 100CX electron microscope

A high resolution (3.5 Å) cold stage operated at 123 K and an improved anti-contamination device have been constructed and operated in a top-entry JEM 100CX electron microscope. High resolution electron diffraction patterns and images of hydrated tobacco mosaic virus particles in vitrified ice have been recorded with the use of this cryo system.

Mechanism of contamination build-up induced by fine electron probe irradiation

Abstract To clarify the transfer mechanism of contaminating molecules and the dominant source of them, carbon thin films were irradiated with a fine electron probe of 12 nm dia using three types of anti-contamination devices, individually. No contamination deposit was observed for a certain period or an incubation time after the specimen was pretreated by an electron beam shower. After the incubation time, the growth rate increased gradually with the elapsed time after the electron beam shower treatment and reached the saturated rate. The incubation time and the saturated growth rate depended largely on the type of the anti-contamination device used. It can be concluded that hydrocarbon molecules being adsorbed on the specimen surface are transferred to the irradiated area by surface diffusion. The dominant source of contaminating molecules is the residual gas molecules in the vicinity of the specimen even in a clean high vacuum.

The Uptake and Distribution of Potassium in Roots of Duckweed (Lemna Minor L) As Measured using Low Temperature X-Ray Microanalysis

Lemna minor L. plants were grown in a 14 H light and 10 H dark regime at 298 K in a medium containing 2 mM [K+]. Roots, 20 mm long and photosynthetically active, were removed and prepared for low temperature microscopy using methods described elsewhere. Fracture faces were made using the AMRAY Biochamber and the analysis carried out using an AMRAY 1000A SEM fitted with an LaB6 gun and a Kevex Si (Li) x-ray detector at 15-17 kV and a beam current of 1-2 nA. A reduced raster (1.0 μm2) was placed at the centre of the cell being analysed, care being taken to avoid any contact with the cell walls. Samples were maintained at 100-110 K throughout analysis and an LN2 cooled anti-contamination device was inserted close to the specimen. The spectra were analysed using the peak/background (P/B) ratio technique following use of background subtraction and peak de-convolution routines. Between eight and twelve fracture faces were analysed for each of the ten sites along the length of the root and the data pooled and presented in Table I.

分析電子顕微鏡における試料汚染の改善

This paper describes the method to measure quantitatively the contamination caused by the use of a micro electron probe, and instrumental improvements for reducing it. These improvements include the adoption of a new type of vacuum grease and the development of a new type anti-contamination device. Since the weight of contamination deposits changes lineally with the probe irradiation time, a highly accurate method of contamination measurement has been established by indicating the contamination rate in g/min. Thus, it has become possible to correctly evaluate instrumental improvements for reducing contamination. The partial pressure of hydrocarbon gases in the specimen chamber was reduced by approx. one order, through various instrumental improvements. This resulted in a drastic reduction of the contamination rate and therefore in the performance improvement of the analytical electron microscope. In this experiment, any specimen pre-treatment that eliminates contamination source existing in a specimen itself, was not carried out. But it is now important to establish such a treatment in order to further reduce the contamination.

Sources of background X-radiation in analytical electron microscopy

It is well known that a major barrier to quantitative energy dispersive (EDS) measurements of thin films is the background X-radiation generated from stray electrons and X-rays from a variety of internal sources. A number of sources have been reported in a variety of microscopes and there is disagreement over their relative importance. Clearly the sources from each type of microscope must be systematically investigated and suppressed. We report here one such study of a JEM 100C/SEG microscope. Although our data are specific to this instrument, analogous results should be obtained from other analytical transmission microscopes. The major sources of spectral background in the JEM 100C were found to be: 1) the fixed condenser (Cl) aperture, 2) the variable condenser (C2) aperture, and 3) the specimen holder. Other potential background sources such as the objective lens pole pieces and the anticontamination device did not contribute a measurable signal. Still others, such as the objective aperture, could be eliminated simply by prudent operation (e.g. removal during EDS counts).

Progress In The Practical Application Of Automated Image Analysis To Tem Negatives

In our initial publication on this subject1) we reported results demonstrating that contrast is the most important factor in producing the high image quality required for reliable image analysis. We also listed the factors which enhance contrast in order of the experimentally determined magnitude of their effect. The two most powerful factors affecting image contrast attainable with sheet film are beam intensity and KV. At that time we had only qualitative evidence for the ranking of enhancing factors. Later we carried out the densitometric measurements which led to the results outlined below.Meaningful evaluations of the cause-effect relationships among the considerable number of variables in preparing EM negatives depend on doing things in a systematic way, varying only one parameter at a time. Unless otherwise noted, we adhered to the following procedure evolved during our comprehensive study:Philips EM-300; 30μ objective aperature; magnification 7000- 12000X, exposure time 1 second, anti-contamination device operating.

Silicon-containing granules of rat liver, kidney and spleen mitochondria. Electron probe X-ray microanalysis.

Isolated rat liver mitochondria containing granule aggregates (25-75 nm in diameter) and small (5-10 nm) electron opaque granules were examined by electron probe X-ray microanalysis. The granule aggregates gave an intense Si signal, while the small granules gave both Si and P signals. Isolated mitochondria of rat liver, spleen and kidney, subjected to detergent solubilization and differential centrifugation, produced two granule fractions: (1) a 10,000 g fraction consisting predominantly of granule aggregates (25--75 nm) composed of smaller granules (5--10 nm in diameter), and (2) a 10,000--30,000 g fraction of non-aggregated small granules (5-10 nm). Thin sections of isolated granule aggregates gave Si X-ray signals similar to those obtained from in situ granules. In addition S, Cl, Mg, Cr and Fe X-ray signals were observed. Cr occurred only in the large kidney granules, while Fe occurred in both fractions of the spleen and kidney granules. The presence of Si in the granules was confirmed by chemical analysis of the isolated granules and in vivo radiolabeling of the granules with 31Si and 68Ge. Contamination within the electron microscope was eliminated by a liquid nitrogen anticontamination device.

Energy dispersion quantitative X‐ray microanalysis on a scanning electron microscope

AbstractIn this work quantitative measurements performed by EDX on SEM, abd by WDX on EPMA are compared. The commerical SEM has been improved by the addition of a beam regulation and an anticontamination device. The spectra are detected by a Si(Li) detector (FWHM = 180 eV) and digitalized by an analog‐to ‐digital converter. The spectra obtained are treated by an on‐line minicomputer PDF 11/05 included in a NS 880 system. A teminal byilt‐in magnetic tape cassette functions as a storage device for the computer. The dialogue between the system and the operator and programmation are possible through a keyboard and a visualization screen. The programs used include: spectrun smoothing, background subtaction selected area totalizing and spectrum stripping. The count rate is maintained at the order of 3000 counts per second to avoid pulse pile up and dead time losses. The experimental intensities are then corrected through a ZAF method by the profgram C ø R on an IBM 360. Binary alloys TiA1, FeA1, ZrNi, NbA1 and TiZr have been studied by K and L lines at different values of the excitation voltage. Alloys MgA1, FeMn and TiVCr Presenting overlapping peaks, and a glass, have also been analysed. The errors, advantages and limits of the method are discussed: in a homgeneous bulk material the minimum detectable limit calculated by C(DL)A = 3I CA/IA is of the order of 0.03 wt % with WDX and 0.2 Wt % with EDX for 100 seconds counting time. It could be improved by increasing the counting time and by using better electronics. The precision of the result is comparable to that obtained by WDX. With EDX on SEM the rapid and simultaneous quentitative micro analysis of all the elements of 11 < Z ≤ 92 can be performed with good precision. This method is very interesting for thin targets and dispersion of precipitates.

Electron diffraction studies of biological membrane and lipids

IN diffraction studies of biological membranes, X-ray diffraction has been used more frequently than electron diffraction in spite of certain advantages inherent in the latter technique. Electron diffraction enables the study of a small area (about 1 µm2) of a very thin specimen, and the collection of experimental data within a short time. Moreover, the morphology and degree of purity of the specimen can often be investigated. It seems possible to overcome the main problems arising from the application of the electron diffraction technique to biological materials, namely the difficulty of studying hydrated materials and the damage caused to the specimen by the electron beam, and a study of wet biological membranes has been reported1. In this investigation dry specimens have been studied. Radiation damage was largely overcome by using minimum beam current, by maximally overfocusing the first condenser of the electron microscope, and by moderately overfocusing the second condenser. To minimise the temperature rise of the specimen, caused by inellastically scattered electrons, a cooled specimen holder was used. To facilitate heat transport, the specimen grids were covered with aluminium instead of carbon. A Philips 301 G electron microscope equipped with an anti-contamination device was used and the diffraction patterns were recorded at 100 kV on a highly sensitive X-ray film, Kodirex. All diffractograms were recorded at a specimen holder temperature of about −60 °C, which was regarded as a fair estimate of the temperature of the specimen itself.

Reduction of Contamination Rates in Electron Microscopes

In scanning and transmission electron microscopes anti-contamination coldfingers at the specimen are usually limited in design or use because of available space. An anti-contamination device has been developed which takes advantage of the space provided by the long evacuation pipes employed on many SEMs and TEMs. This device consists of a long U shaped copper tube inserted into the vacuum line used to evacuate the emission chamber and column. Liquid nitrogen is circulated through the copper tube for cooling. The cooled tube provides a trapping surface for contamination with a minimum restriction to gas flow. A “top hat” configuration, as shown in the figure, was used to prevent freezing of-the o-ring. The purpose of the cup is to increase the heat conduction path between the feed-thru and the o-ring.Two such devices were installed in electron microscopes; one in a JSM II SEM and one in a Philips EM 200 TEM.

Hydration Stages—Achievements and Obstacles

As we have previously reported our laboratory has developed and perfected a dynamically pumped hydration stage. The stage consists of four collinear apertures: two 100μ and two 200μ. The two 100μ apertures straddle the specimen and define the specimen chamber. The two 200μ apertures define the intermediate chamber which is independently pumped by a normal cryotrapped forepump. The whole stage is translated in order to move the apertures collinear with the beam by the normal specimen translation mechanism, through the bore of the upper polepiece. The specimen may be moved within its 1.2mm gap by an independent translation mechanism thereby allowing the full area of the grid to be examined. Water vapor evaporates from the source and continuously flows out of the apertures thereby providing a very effective anticontamination device.

An electron-microprobe technique for detecting low carbon concentrations in iron

A technique is described for detecting low carbon concentrations in iron alloys. A detectibility limit of less than 0.03% C is achieved routinely using relatively standard procedures on an instrument which also must meet varied service requirements. The key development, an effective anticontamination device, is described and its effectiveness demonstrated quantitatively using carefully prepared standard specimens and established statistical procedures.