Specimen Chamber Research Articles

Image Noise Reduction Using Vibration Mode Shaping for Scanning Electron Microscope

This paper addresses Scanning Electron Microscope (SEM). There is the quality problem that the image noise caused by the acoustic noise disturbs observation for correct shape of the specimen. Thus, SEM be less influenced by the acoustic noise is expected.This paper approaches to this image noise problem from the mode shapes of the base plate, and the transmission path of the acoustic noise and vibration. Firstly, the mode shapes of the base plate with conventional rib are compared to those of the plain base plate, and no remarkable increase in natural frequencies and no change in mode shapes are shown. Secondary, new base plate, which has two twisting mode as 1st and 2nd mode by arranging position of the rib, is developed. In those two twisting modes, vibration amplitude around the center of the base plate is smaller than that in bending modes. Thus, less vibration is transmitted to the specimen chamber and to the specimen in twisting modes than bending ones. Finally, the developed base plate is assembled to SEM, and remarkable reduction of the image noise under the condition of the acoustic noise below 250Hz is shown. This base plate has already applied to the products on the market.

Image Noise Reduction Using Electron Beam Deflection for Scanning Electron Microscope

This paper addresses Scanning Electron Microscope (SEM). In detail, the image noise caused by the transient vibration due to the step moving of the specimen stage disturbs high throughput of the inspection, and the acoustic noise disturbs the correct shape observation of the specimen.This paper shows a way to solve this image noise problem with the feedforward compensator using the electron beam deflection that has no risk of the oscillation. Firstly, the mechanisms how those vibrations cause the image noises are explained, and it is shown that the signal to compensate the transient vibration by step moving of the stage can be made from the low path filtered acceleration of the specimen chamber, and the signal to compensate the acoustic noise can be made from the band path filtered displacement of the specimen stage. Secondary, an electron beam deflection compensator, which uses two signals of the accelerometers, is designed. Finally, this feedforward compensator is implemented to SEM, and remarkable reductions of the image noises in the step moving of the stage and under the condition of the acoustic noise, are shown.

Fabrication and Corrosion Property of Novel Ti-Based Bulk Glassy Alloys without Ni

New Ni-free bulk glassy alloys in the Ti47:5Zr2:5þxCu37:5� xPd7:5Sn5 (x ¼ 0; 5; 7:5) system were fabricated by copper mold casting with diameters from 1 to 3 mm, which are expected to be applied as biomaterials. The structure, thermal stability and corrosion resistance were investigated by X-ray diffraction, differential scanning calorimetry and electrochemical measurement, respectively. Surface information after immersion in Hanks' solution was also characterized by using XPS. The results indicate that the bulk glassy alloys examined are spontaneously passivated. By anodic polarization, they show the passive current densities between 10 � 2 and 10 � 3 A/m 2 . The higher corrosion resistance for the Ti-based bulk glassy alloys is attributed to the formation of stable and protective passive films enriched with titanium and zirconium. (doi:10.2320/matertrans.48.515) size were chosen. The structure of the cast alloys was examined by X-ray diffraction (XRD) with Cu Kradiation. Thermal stability was characterized by differential scanning calorimetry (DSC) under an argon atmosphere with a heating rate of 0.67 K/s. The samples for thermal analyzing were the bottom parts of the as-cast rod samples. The corrosion behavior of the bulk glassy alloys was evaluated by electrochemical measurements. Prior to corro- sion testing, the samples were mechanically polished in cyclohexane with silicon carbide papers up to frit 1500, degreased in acetone, washed in distilled water, dried in air and further exposed in air for 24 h. Each condition testing was performed at least three times for good reproducibility. Electrolyte used was Hanks' solution with pH 7.4 at 37 � C open to air, which was prepared from reagent grade chemicals and deionized water. The composition of Hanks' balance saline solution (g/L) is 8.00 NaCl, 0.40 KCl, 0.35 NaHCO3, 0.19 CaCl2� 2H2O, 0.09 Na2HPO4� 7H2O, 0.2 MgSO4� 7H2O, 0.06 KH2PO4, 1.00 Glucose. Electrochemical measurements were conducted in a three-electrode cell using a platinum counter electrode and a saturated calomel reference electrode (SCE). Potentiodynamic polarization curves were measured with a potential sweep rate of 0:83 � 10 � 3 V/s in Hanks' solution after immersing the specimens for 600 s, when the open-circuit potentials became almost steady. X-ray photoelectron spectroscopy (XPS) for the surface of the bulk glassy alloys after immersion in Hanks' solution at 37 � C for 7 days were measured by means of a SSI SSX-100 photoelectron spectrometer with monochromatized Al Kexcitation (h� ¼ 1486:6 eV). The vacuum of the specimen chamber for XPS measurements was ca. 7 � 10 � 8 Pa during the measurements. Binding energies of electrons were calibrated by a method described elsewhere. 11,12) The angle between the specimen surface and the direction of the photoelectron to the detector (take-off angle) was fixed at 35 � . Alloy compositions were estimated from the integrated

Studying vesicle cycling in presynaptic terminals using the genetically encoded probe synaptopHluorin

Genetically encoded fluorescent probes have become indispensable tools in the biological sciences. Studies of synaptic vesicle recycling have been facilitated by a group of GFP-derived probes called pHluorins. These probes exploit changes in pH that accompany exocytosis and recapture of synaptic vesicles. Here we describe how these synaptic tracers can be used in rodent hippocampal neurons to monitor the synaptic vesicle cycle in real time and to obtain mechanistic insights about it. Synapses can be observed in living samples using a wide-field fluorescence microscope and a cooled charge-coupled device camera. A simple specimen chamber allows electrical stimulation of synapses to evoke exocytosis in a precisely controlled manner. We present protocols to measure various parameters of the synaptic vesicle cycle. This technique can be easily adapted to study different classes of synapses from wild-type and mutant mice. Once cultured neurons expressing synaptopHluorin are available, the whole procedure should take about 2 h.

Environmental Scanning Electron Microscope study of SiO 2 heterogeneous material with helium and water vapor

The analysis and the structural characterization of heterogeneous materials are usually difficult to perform using conventional techniques and only global information may be obtained. A comparative study in the Environmental Scanning Electron Microscope with different gases is carried out on a heterogeneous and insulating SiO 2 material. Electron beam scattering effect on the resolution of microanalysis due to the introduction of two gases: water vapor and helium within the specimen chamber of the Environmental Scanning Electron Microscope is studied. The best results are obtained with helium. The use of this gas enabled a better focusing the electron beam on the micronic zones which led to better distinguish the chemical species present in our material. This study deals with the diffusion of some cations such as Ca 2+ and K + inside the SiO 2 aggregate. The results show that calcium and potassium do not belong to the same phase.

Cutting of carbon nanotubes assisted with oxygen gas inside a scanning electron microscope

The authors report a cutting technique for carbon nanotubes (CNTs) assisted by the presence of oxygen gas. The cutting procedure is conducted in less than 1min using a low-energy electron beam inside a scanning electron microscope. The oxygen gas was regulated by a mass flow controller and was injected at 1SCCM. It was found that although the total pressure inside the specimen chamber reached 10−2Pa, high-speed cutting occurred only in an area close to the oxygen gas nozzle. They assume that the CNTs are cut only under a low acceleration voltage since the CNT molecules are easily excited and ionized by the low-energy electron beam.

The trajectories of secondary electrons in the scanning electron microscope

Three-dimensional simulations of the trajectories of secondary electrons (SE) in the scanning electron microscope have been performed for plenty of real configurations of the specimen chamber, including all its basic components. The primary purpose was to evaluate the collection efficiency of the Everhart-Thornley detector of SE and to reveal fundamental rules for tailoring the set-ups in which efficient signal acquisition can be expected. Intuitive realizations about the easiness of attracting the SEs towards the biased front grid of the detector have shown themselves likely as false, and all grounded objects in the chamber have been proven to influence the spatial distribution of the signal-extracting field. The role of the magnetic field penetrating from inside the objective lens is shown to play an ambiguous role regarding possible support for the signal collection.

1P1-C16 Oxygen Gas Assisted Nanofabrication and Nanoassembly of Carbon Nanotubes

We report the cutting technique of carbon nanotubes (CNTs) assisted with oxygen gas, the cutting procedure occurred in less than 1 minute by a low-energy electron beam inside a field emission scanning electron microscope (FESEM). The oxygen gas was regulated by a digital mass flow controller and was injected at 1 seem from a glass nozzle. It is found that although the total pressure of specimen chamber reached 10^<-2> Pa, but high speed cutting occurs only in the area close to the nozzle. We assume that CNTs are cut only under the low acceleration voltage, because the carbon molecules were easily exited and ionized by the low-energy electron beam. A logo consisting of two letters was assembled with 6 CNTs assisted with cutting process. We think that the cutting CNTs inside SEM will be widely used for rapid prototyping of CNT nanodevices and characterization of nanomaterials.

Modeling of imaging processes in the low‐vacuum SEM

AbstractThe presence of a gas in the specimen chamber of low‐vacuum scanning electron microscopes (SEMs) gives rise to a number of interactions that are not found in their high‐vacuum counterparts. Many of these interactions are integral to the specimen charge neutralizing capabilities of these instruments. However, these interactions, and the electronic charge state of the specimen, give rise to a number of processes that influence, and sometimes even dominate, secondary electron contrast. As many of the processes are stochastic in nature, and depend on discrete interactions between electrons, gaseous ions, neutral molecules, and the specimen surface, modeling can offer important insights for contrast interpretation. This paper discusses these interactions and the mechanisms through which contrast is influenced. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Wet STEM: A new development in environmental SEM for imaging nano-objects included in a liquid phase

Environmental scanning electron microscopy (ESEM) enables wet samples to be observed without potentially damaging sample preparation through the use of partial water vapour pressure in the microscope specimen chamber. However, in the case of latices in colloidal state or microorganisms, samples are not only wet, but made of objects totally submerged in a liquid phase. In this case, under classical ESEM imaging conditions only the top surface of the liquid is imaged, with poor contrast, and possible drifting of objects. The present paper describes experiments using a powerful new Scanning Transmission Electron Microscopy (STEM) imaging system, that allows transmission observations of wet samples in an ESEM. A special device, designed to observe all sorts of objects submerged in a liquid under annular dark-field imaging conditions, is described. Specific features of the device enable to avoid drifting of floating objects which occurs in the case of a large amount of water, thus allowing slow-scan high-definition imaging of particles with a diameter down to few tens of nm. The large potential applications of this new technique are then illustrated, including the imaging of different nano-objects in water. The particular case of grafted latex particles is discussed, showing that it is possible to observe details on their surface when submerged in water. All the examples demonstrate that images acquired in wet STEM mode show particularly good resolution and contrast, without adding enhancing contrast objects, and without staining.

Application of 10-μm thin stainless foil to a new assembly of the specimen carrier in high-pressure freezing

High-pressure freezing (HPF) has been accepted generally as the most reliable method for cryoimmobilization of biological samples. However, the depth of vitreous freezing in biological samples was less than expected, probably because of the poor thermal conductivity with high water contents. In this study, we introduce a new assembly of the specimen carrier using a 10-microm thin stainless foil for the specimen chamber cover in the HPF technique and describe the fine structure of rat gastric glands processed with the assembly. A low-magnification view of the gastric surface region showed a well-preserved morphology in which the vitreous freezing reached deeper than 100-microm from the freezing face. The present results prove that the 10-microm thin stainless foil is useful in HPF, providing deep vitrification in biological samples.

Secondary electron contrast in low-vacuum∕environmental scanning electron microscopy of dielectrics

Low vacuum scanning electron microscopy (SEM) is a high-resolution technique, with the ability to obtain secondary electron images of uncoated, nonconductive specimens. This feat is achieved by allowing a small pressure of gas in the specimen chamber. Gas molecules are ionized by primary electrons, as well as by those emitted from the specimen. These ions then assist in dissipating charge from the sample. However, the interactions between the ions, the specimen, and the secondary electrons give rise to contrast mechanisms that are unique to these instruments. This paper summarizes the central issues with charging and discusses how electrostatically stable, reproducible imaging conditions are achieved. Recent developments in understanding the physics of image formation are reviewed, with an emphasis on how local variations in electronic structure, dynamic charging processes, and interactions between ionized gas molecules and low-energy electrons at and near the sample surface give rise to useful contrast mechanisms. Many of the substances that can be examined in these instruments, including conductive polymers and liquids, possess charge carriers having intermediate mobilities, as compared to metals and most solid insulators. This can give rise to dynamic contrast mechanisms, and allow for characterization techniques for mapping electronic inhomogeneities in electronic materials and other dielectrics. Finally, a number of noteworthy application areas published in the literature are reviewed, concentrating on cases where interesting contrast has been reported, or where analysis in a conventional SEM would not be possible. In the former case, a critical analysis of the results will be given in light of the imaging theory put forth.

Photoluminescence and reversible photo-induced spectral change ofSrTiO3

When strontium titanate (SrTiO3) single crystal is irradiated at room temperature with a 325 nm laser light in anevacuated specimen chamber, the luminescence intensity increases, creating abroad visible luminescence centred at about 2.4 eV. Then, introducing oxygen gasinto the specimen chamber, the photoluminescence spectrum returns reversiblyto the original weak luminescence under the same laser light irradiation. Afterremoving the laser light irradiation, each photoluminescent state is stored fora long time at room temperature under room light, regardless of any changesof atmosphere. Such photo-induced spectral change has been observed also atdifferent temperatures from 13 K to room temperature. The observed phenomenon isexplained by means of the photo-induced oxygen defect formation at the surfaces ofSrTiO3 crystal. Forthe same SrTiO3 single crystal, we have studied the photoluminescence properties. Besides the2.4 eV luminescence band, we have observed new two luminescence bandscentred at about 3.2 eV and about 2.9 eV. The energy, 3.2 eV, is close to both thephotoluminescence excitation edge energy and the reported band edge energy ofSrTiO3 crystal. Both the 3.2 eV luminescence and the 2.9 eV luminescence decay rapidly after a pulsedphotoexcitation, while the 2.4 eV luminescence lasts for several seconds at 13 K. The excitationlight intensity dependence of these luminescence bands has been also measured at 13 K. The2.4 eV luminescence increases in intensity with increasing excitation intensity up to4 mJ cm−2, and then it becomes decreased with further increase in the excitation intensity.On the other hand, both the 3.2 eV luminescence and the 2.9 eV luminescenceincrease in intensity with increasing excitation intensity, without any saturation.Although the 2.4 eV luminescence had been assigned to the radiative decay ofintrinsic self-trapped excitons in a superparaelectric state by several workers, thepresent studies have clarified that the luminescence originates mainly from crystaldefects (oxygen defects and chemical heterogeneity in the surface region). Boththe 3.2 eV luminescence and the 2.9 eV luminescence are discussed qualitatively.

Photo-induced phenomena in SrTiO3

When different SrTiO3 single crystals are irradiated at room temperature with a continuous wave 325 nm laser light in an evacuated specimen chamber, their luminescence increase in intensity, creating a broad visible luminescence band centred at about 2.4 eV. Then, introducing oxygen gas into the specimen chamber, the photoluminescence spectra return reversibly to the original weak luminescence with the same laser light irradiation. After removing the laser light irradiation, each photoluminescent state is stored for a long time at room temperature under room light, regardless of any changes of atmosphere. Such photoinduced spectral change has been also observed at different temperatures from 6 K to room temperature. The observed phenomenon is explained by the photo-induced oxygen defect at the surfaces of SrTiO3 crystal. The observed photo-induced optical phenomena are discussed in the light of both the crystal defect chemistry of SrTiO3 and the exciton theory.

Low pressure mode combined with OsO4 vapor fixation and sputter-coating for the preservation of delicate aerial hyphae and conidia in the ESEM

The newer generation of environmental scanning electron microscopes (ESEMs) allows samples to be viewed under a range of different vacuum conditions. No specific sample preparation protocols are required with the ESEMs, as fresh, unfixed samples are used and discarded later. We have worked out a method that preserves aerial hyphae on biltong that closely resemble fresh specimens and may be stored for viewing at a later date. Another advantage is that fixed samples are more resilient to the variable vacuum encountered in the ESEM. When biltong samples with fungal growth were first studied, we observed that vacuum-related artifacts were induced unless vacuum conditions and changes in pressure were carefully controlled. Damage readily occured in conidia and its delicate hyphae. Fresh, unfixed samples are very vulnerable to these artifacts. In addition, biltong proved to be a problematic study sample because of its high salt content, its hygroscopic nature as well as being laden with spices. To eliminate these artifacts, the preservation of specimens by OsO4 vapor fixation combined with a special sputter-coating technique is described. Previous studies confirmed that OsO4 vapor fixation is superior to traditional immersion fixation methods for the examination of hyphae and conidia of various fungi in a conventional SEM. However, both preparation methods induce sample shrinkage. We observed that OsO4 vapor fixation followed by Au coating under strictly controlled vacuum conditions induced fewer artifacts and gave the best images with minimum distortion in low pressure (LP) mode. The proposed method allows samples to be viewed both in ESEM and LP mode. There are however some disadvantages inherent to ESEM mode. Even when viewing fixed, coated samples, care should be taken to maintain a pressure of not lower than 0.2 Torr in the specimen chamber. It is critical that different samples have the same vacuum exposure history, as shrinkage and collapse were found to be directly related to the lowest pressure the samples were subjected to, both in the sputter coater chamber and in the electron microscope specimen chamber.

Morphological characteristics of oxide scales grown on H11 steel oxidised in dry or wet air

The oxidation behaviour in dry and wet air of H11 steel was studied at 600 and 700°C by Thermo Gravimetric Analysis (TGA) and in situ oxidation in the specimen chamber of an Environmental Scanning Electron Microscope (ESEM) equipped with a hot stage specimen holder. The oxidation kinetics of H11 steels are quite sensitive to the presence of water vapour and, although the final mass gains show a good overall reproducibility, they are locally rather irregular. The morphology and microstructure of oxide scale are complex and often heterogeneous, particularly at 700°C. In situ oxidation tests permit to follow the evolution of oxide scales and to observe several growth modes of oxide scales. The diversity of the observed scale growth modes can explain the complexity and irregularity of scale growth mechanisms. Some additional in situ oxidation tests were performed in wet nitrogen. Morphology and growth modes of oxide scale grown in wet air and wet nitrogen differ strongly.

Electron scattering by gas in the Environmental Scanning Electron Microscope (ESEM): Effects on the image quality and on the X-ray microanalysis

In this work, we studied the electron beam scattering due to the introduction of two gases : water vapour and helium within the specimen chamber of the Environmental Scanning Electron Microscope (ESEM) and the effects of this phenomenon on the image quality and on the microanalysis results. An increase in the pressure involves an amplification of the electron beam scattering phenomenon up to 160 microns when water vapour is used. The best results are obtained with helium. The use of this gas allowed a better focusing of the electron beam on the micronic particle which led to an improvement of the chemical contrast of the images, like the stability of the results of microanalysis X. In addition, with helium we showed an improvement in the signal-to-noise ratio which not only leads to obtain images of good quality but also to improve the limit of detection of the microanalysis system. In spite of the advantages of the use of helium, an important focusing of the electron beam, can induce an increase in the temperature of the surface of the sample by causing its degradation especially for fragile materials or a dehydration of hydrated samples.

Measurement of X-ray emission efficiency for K-lines.

Results for the X-ray emission efficiency (counts per C per sr) of K-lines for selected elements (C, Al, Si, Ti, Cu, Ge) and for the first time also for compounds and alloys (SiC, GaP, AlCu, TiAlC) are presented. An energy dispersive X-ray spectrometer (EDS) of known detection efficiency (counts per photon) has been used to record the spectra at a takeoff angle of 25 degrees determined by the geometry of the secondary electron microscope's specimen chamber. Overall uncertainty in measurement could be reduced to 5 to 10% in dependence on the line intensity and energy. Measured emission efficiencies have been compared with calculated efficiencies based on models applied in standardless analysis. The widespread XPP and PROZA models give somewhat too low emission efficiencies. The best agreement between measured and calculated efficiencies could be achieved by replacing in the modular PROZA96 model the original expression for the ionization cross section by the formula given by Casnati et al. (1982) A discrepancy remains for carbon, probably due to the high overvoltage ratio.

The effect of beam diameter on the electron skirt in a high pressure scanning electron microscope

Helium gas and air are commonly used in the high pressure scanning electron microscope (HPSEM). The presence of a gaseous environment in the specimen chamber modifies the electron beam profile. In order to fully understand the beam-gas interaction, we have investigated the beam-diameter effect for two gases (helium and air) by Monte Carlo simulation. In this calculation, we have assumed that the electron beam is Gaussian and we have explored the influence of the nature of the gas at low voltage. When the beam diameter varies between 1 and 100 nm, there is no influence on the beam profile for these two gases. The resolving power of the HPSEM is not affected by the beam-gas interaction. These theoretical results have been compared with experimental images obtained at low voltage under air and helium gases. The variation of image quality at low voltage has confirmed the interest of helium for use in a Field Emission Gun SEM (FEGSEM) in high pressure (or low vacuum) conditions.

Image-processing approach to vibration isolation of a scanning electron microscope

We propose a new approach to estimating a pointing error of the electron probe of a scanning electron microscope. The approach is formulated to estimate the pointing errors using a specimen image. Specimen images are numerically simulated by a mathematical model and identified with measured images of the specimen using a least-squares procedure to determine the pointing errors. The pointing errors are estimated by the proposed approach and used to design a controller for vibration isolation of a scanning electron microscope. Acceleration sensors are located at the root of the specimen chamber and are used to detect any environmental disturbance into the microscope. The designed controller is based on a transfer function from the sensor outputs to the pointing errors, and the transfer function is determined by sinusoidal excitation tests for the microscope. The controller is implemented as a digital filter on a PC and is used to move the electron probe to cancel the pointing errors using image-shifting coils. The pointing errors are successfully reduced by the controller in a lower frequency region that contains the first four natural frequencies.