Things That Go “Bump” in the VPSEM - and How We Image with Them

Variable pressure scanning electron microscopes (VPSEM) differ from conventional SEM by operating at pressures ranging from the ‘high vacuum’ SEM levels of 10-6 torr up to typically around 2 torr. The environmental SEM or ESEM is a commercial variant which employs an unique multistage pressure-limiting aperture (PLA) system to attain specimen chamber operating pressures of up to 50 torr. Early instruments used air or argon as the imaging gas but more commonly today water vapour is used. A wide range of gases have been employed, including potentially explosive hydrogen-methane mixtures. The choice of gas is operator-based and can be varied during the imaging session.Early VPESM were restricted to backscattered electron imaging (BSE) until the development of the gaseous secondary electron detector in the ESEM. Gaseous secondary electron detectors are now available for all models of VPSEM and together with compatible cathodoluminescence and EDS XRay detectors, the full range of SEM-based imaging options is present.The principal distinguishing feature of VPSEM is, of course, that samples can be examined uncoated. Gas-electron interaction generates a positive ion supply that can minimise conventional charging artefacts, in a simple imaging model.

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Towards Optimal Imaging and Microanalysis in Variable Pressure and Low Voltage SEM

Microscopy Today ◽

10.1017/s1551929500051415 ◽

2005 ◽

Vol 13 (2) ◽

pp. 18-19

Author(s):

Brendan J Griffin

Keyword(s):

Pressure Range ◽

Secondary Electron ◽

Low Voltage ◽

Variable Pressure ◽

X Ray ◽

Electron Microscopes ◽

Electron Imaging ◽

Scanning Electron Microscopes ◽

Optimal Imaging

Image quality of 'secondary electron imaging' has been an ongoing operational issue with the variable pressure range of scanning electron microscopes (VPSEM), including the extended pressure range environmental or SEM. A second question that has received considerable attention concerns charge cancellation on insulators in VPSEM with particular reference to effects of charging on x-ray microanalytical results.

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Analysis of Interesting Materials in the Environmental SEM: You Put What in Your Microscope?

Microscopy and Microanalysis ◽

10.1017/s1431927600029950 ◽

2001 ◽

Vol 7 (S2) ◽

pp. 776-777

Author(s):

John F. Mansfield

Keyword(s):

Electron Microscope ◽

Chemical Engineering ◽

Materials Science ◽

Variable Pressure ◽

Environmental Scanning ◽

Specimen Preparation ◽

Wide Range ◽

Electron Microscopes ◽

Scanning Electron Microscopes ◽

Scanning Electron

The environmental scanning electron microscope (ESEM™) and variable pressure electron microscope (VPSEM) have become accepted tools in the contemporary electron microscopy facility. Their flexibility and their ability to image almost any sample with little, and often no, specimen preparation has proved so attractive that each manufacturer of scanning electron microscopes now markets a low vacuum model.The University of Michigan Electron Microbeam Analysis Laboratory (EMAL) operates two variable pressure instruments, an ElectroScan E3 ESEM and a Hitachi S3200N VPSEM. The E3 ESEM was acquired in the early 1990s with funding from the Amoco Foundation and it has been used to examine an extremely wide variety of different materials. Since EMAL serves the entire university community, and offers support to neighboring institutions and local industry, the types of materials examined span a wide range. There are users from Materials Science & Engineering, Chemical Engineering, Nuclear Engineering, Electrical Engineering, Physics, Chemistry, Geology, Biology, Biophysics, Pharmacy and Pharmacology.

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Low Vacuum SEMs: Latest Generation Technologies and Applications

Microscopy Today ◽

10.1017/s1551929500055681 ◽

2007 ◽

Vol 15 (4) ◽

pp. 20-25

Author(s):

William Neijssen ◽

Ben Lich ◽

Pete Carleson

Keyword(s):

Focused Ion Beam ◽

Electron Backscatter Diffraction ◽

Ion Beam ◽

High Vacuum ◽

Ease Of Use ◽

Wide Range ◽

Sample Chamber ◽

Electron Microscopes ◽

Scanning Electron Microscopes ◽

Backscatter Diffraction

Since becoming popular more than a decade ago, low vacuum scanning electron microscopes (SEM) have continued to evolve. The latest systems offer uncompromised performance over an unprecedented range of sample chamber vacuum conditions. Instruments are now available that provide near-nanometer resolution in all vacuum modes and the ability to operate at pressures as high as 4000 Pascals (~30 Torr). Low vacuum operation eliminates much of the sample preparation required for conventional (high vacuum) SEM. Insulating samples can be imaged without conductive coatings. Wet, dirty, outgassing samples can be examined without drying and fixing. Systems can also be configured with a wide range of ancillary capabilities for imaging, analysis, and sample manipulation, including advanced secondary, backscattered, and transmitted electron detection, X-ray spectrometry, electron backscatter diffraction, and focused ion beam (FIB) manipulation. The current generation of systems combine speed, flexibility, repeatability, and ease of use, making them the ideal solution for any laboratory that must satisfy a wide range of imaging and analytical demands.

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Secondary Electron Detector with the Unipotential Lens Structure for Variable Pressure/Environmental SEM

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.186.24 ◽

2012 ◽

Vol 186 ◽

pp. 24-27

Author(s):

Witold Słówko ◽

Michał Krysztof

Keyword(s):

Main Part ◽

Secondary Electron ◽

High Vacuum ◽

Variable Pressure ◽

Original Structure ◽

Intermediate Chamber ◽

Wide Range ◽

Optimum Solution ◽

Environmental Sem ◽

Gas Pressures

To extend capabilities of classic instruments toward the VP/E technique, authors designed the vacuum-detector system in the form of a simple attachment, which can be mounted to a classic SEM, without changes in its original structure. The main part of the system is the vacuum and detection head, combining the intermediate chamber and electron detectors of chosen kinds. Authors investigate the SE detector showing the unipotential lens structure to find optimum solution for a wide range of gas pressures from high vacuum to pressures exceeding 10 mbar.

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

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010018077x ◽

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.

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Studies of Ge/Si(100) and Observation of Atomic Steps on Si(100) using Biassed Secondary Electron Imaging in a UHV STEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010018029x ◽

1990 ◽

Vol 48 (1) ◽

pp. 308-309

Author(s):

Mohan Krishnamurthy ◽

Jeff S. Drucker ◽

John A. Venablest

Keyword(s):

Secondary Electron ◽

Critical Thickness ◽

Surface Defects ◽

Film Growth ◽

Growth Parameters ◽

High Vacuum ◽

Ultra High Vacuum ◽

Surface Steps ◽

Epitaxial Crystal Growth ◽

Electron Imaging

Secondary Electron Imaging (SEI) has become a useful mode of studying surfaces in SEM[1] and STEM[2,3] instruments. Samples have been biassed (b-SEI) to provide increased sensitivity to topographic and thin film deposits in ultra high vacuum (UHV)-SEM[1,4]; but this has not generally been done in previous STEM studies. The recently developed UHV-STEM ( codenamed MIDAS) at ASU has efficient collection of secondary electrons using a 'parallelizer' and full sample preparation system[5]. Here we report in-situ deposition and annealing studies on the Ge/Si(100) epitaxial system, and the observation of surface steps on vicinal Si(100) using b-SEI under UHV conditions in MIDAS.Epitaxial crystal growth has previously been studied using SEM and SAM based experiments [4]. The influence of surface defects such as steps on epitaxial growth requires study with high spatial resolution, which we report for the Ge/Si(100) system. Ge grows on Si(100) in the Stranski-Krastonov growth mode wherein it forms pseudomorphic layers for the first 3-4 ML (critical thickness) and beyond which it clusters into islands[6]. In the present experiment, Ge was deposited onto clean Si(100) substrates misoriented 1° and 5° toward <110>. This was done using a mini MBE Knudsen cell at base pressure ~ 5×10-11 mbar and at typical rates of 0.1ML/min (1ML =0.14nm). Depositions just above the critical thickness were done for substrates kept at room temperature, 375°C and 525°C. The R T deposits were annealed at 375°C and 525°C for various times. Detailed studies were done of the initial stages of clustering into very fine (∼1nm) Ge islands and their subsequent coarsening and facetting with longer anneals. From the particle size distributions as a function of time and temperature, useful film growth parameters have been obtained. Fig. 1 shows a b-SE image of Ge island size distribution for a R T deposit and anneal at 525°C. Fig.2(a) shows the distribution for a deposition at 375°C and Fig.2(b) shows at a higher magnification a large facetted island of Ge. Fig.3 shows a distribution of very fine islands from a 525°C deposition. A strong contrast is obtained from these islands which are at most a few ML thick and mottled structure can be seen in the background between the islands, especially in Fig.2(a) and Fig.3.

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