Imaging bulk insulators with secondary electrons in an UHV STEM

1991 ◽  
Vol 49 ◽  
pp. 662-663
Author(s):  
J. Liu ◽  
G. G. Hembree ◽  
J. A. Venable
Keyword(s):  
Electron Beam ◽  
Surface Potential ◽  
Coming Out ◽  
Electron Spectroscopy ◽  
High Spatial Resolution ◽  
Target Material ◽  
Incident Beam ◽  
Secondary Electrons ◽  
Resolution Electron ◽  
Electron Imaging

When an insulator is bombarded by electrons a surface potential will build up if the total number of electrons entering the sample is not equal to that coming out. This potential can be positive or negative depending on the energy of the incident electrons and the target material. The effects of charging will limit, or at least perturb, the use of electron beam techniques for examining the surface properties of insulators. Various methods have been developed to avoid insulator charging. However none of these methods can be applied to high spatial resolution electron beam studies of clean insulator surfaces. At the electron beam energies typically used in STEM instruments the surface of bulk insulators will always acquire a negative potential. Secondary electron imaging (SEI) and Auger electron spectroscopy (AES) would be possible if the surface potential were stable under electron beam illumination and was small compared with the incident beam potential.

High spatial resolution surface potential measurements using secondary electrons

1980 ◽  
Vol 93 (2-3) ◽  
pp. A100-A101
Author(s):  
A.P. Janssen ◽  
P. Akhter ◽  
C.J. Harland ◽  
J.A. Venables
Keyword(s):  
Spatial Resolution ◽  
Surface Potential ◽  
High Spatial Resolution ◽  
Secondary Electrons ◽  
Surface Potential Measurements

The Observation Of Mg)-Al Interface By Hrem and Microdiffraction

1985 ◽  
Vol 43 ◽  
pp. 240-241
Author(s):  
S.Y. Zhang ◽  
J.M. Cowley
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
High Resolution ◽  
Materials Science ◽  
Incident Beam ◽  
High Resolution Electron Microscopy ◽  
Interface Structure ◽  
Resolution Electron ◽  
Powerful Means ◽  
Interface Structures

The combination of high resolution electron microscopy (HREM) and nanodiffraction techniques provided a powerful means for characterizing many of the interface structures which are of fundamental importance in materials science. In this work the interface structure between magnesium oxide and aluminum has been examined by HREM (with JEM-200CX) and nanodiffraction (with HB-5). The interfaces were formed by evaporating Al on freshly prepared cubic MgO smoke crystals under various vacuum conditions, at 10 -4, 10-5 10-6 and 10-7 torr. The Al layers on the MgO (001) surface are about 100Å thick. TEM observations were performed with the incident beam along the MgO [100] direction so that the interface could be revealed clearly. The nanodiffraction patterns were obtained with the electron beam of 15Å diameter parallel to the interface.

High spatial resolution surface potential measurements using secondary electrons

1980 ◽  
Vol 93 (2-3) ◽  
pp. 453-470 ◽  
Author(s):  
A.P. Janssen ◽  
P. Akhter ◽  
C.J. Harland ◽  
J.A. Venables
Keyword(s):  
Spatial Resolution ◽  
Surface Potential ◽  
High Spatial Resolution ◽  
Secondary Electrons ◽  
Surface Potential Measurements

Comparison of Channeling Contrast between Ion and Electron Images

2013 ◽  
Vol 19 (2) ◽  
pp. 344-349 ◽  
Author(s):  
L.A. Giannuzzi ◽  
J.R. Michael
Keyword(s):  
Electron Beam ◽  
Critical Angle ◽  
Incident Beam ◽  
Secondary Electrons ◽  
Crystalline Materials ◽  
Multiple Images ◽  
Electron Channeling ◽  
Backscattered Electrons ◽  
Ion Channeling ◽  
Primary Contribution

AbstractIon channeling contrast (iCC) and electron channeling contrast (eCC) are caused by variation in signal resulting from changes in the angle of the incident beam and the crystal lattice with respect to the target. iCC is directly influenced by the incident ion range in crystalline materials. The ion range is larger for low-index crystal orientated grains, resulting in the emission of fewer secondary electrons at the surface yielding a lower signal. Ions are stopped closer to the surface for off-axis grains, resulting in the emission of many secondary electrons yielding a higher signal. Conversely, backscattered electrons (BSEs) are the primary contribution to eCC. BSEs are diffracted or channeled to form an electron channeling pattern (ECP). The BSE emission of the ECP peaks when the electron beam is normal to the surface of an on-axis grain, and therefore a bright signal is observed. Thus, iCC and eCC images yield inverse contrast behavior for on-axis oriented grains. Since there is a critical angle associated with particle channeling, accurately determining grain boundary locations require the acquisition of multiple images obtained at different tilt conditions.

Proposed Scheme for a Directional Low-Loss Detector

1976 ◽  
Vol 34 ◽  
pp. 514-515
Author(s):  
Oliver C. Wells
Keyword(s):  
Electron Beam ◽  
Beam Energy ◽  
Secondary Electron ◽  
Incident Beam ◽  
Low Loss ◽  
Secondary Electrons ◽  
Glancing Angle ◽  
Electron Detection ◽  
Incident Beam Energy ◽  
Input Aperture

The conventional low-loss electron detector (1,2) is shown in Fig. 1. The electron beam strikes the specimen with a glancing angle of typically between 30° and 45°. The input grid G1 is held at +200V. The filter grid G2 is held at +200V to collect secondary electrons or at -19.8kV for low-loss work with an incident beam energy of 20keV. The scintillator is held at +10kV for secondary electron detection or at -10kV for low-loss work. Comparison pairs of micrographs are obtained by recording one image in each mode. The signalto- noise ratio is approximately the same in each case.We are proposing to replace the single scintillator/light-pipe/photomultiplier system with a pair of such assemblies separated by a partition, such that an input electron will reach one or other of the scintillators, depending on which part of the input aperture it enters. The video waveform will be obtained using a sum-or-difference unit connected to the two photomultipliers.

Remarks on the application of backscattered electron imaging (BEI) to the scanning electron microscopy (SEM) of biological structures

1983 ◽  
Vol 41 ◽  
pp. 484-487
Author(s):  
Etienne de Harven
Keyword(s):  
High Resolution ◽  
Incident Beam ◽  
Spot Size ◽  
Primary Electron ◽  
Critical Point Drying ◽  
Cell Shapes ◽  
High Resolution Images ◽  
Backscattered Electron ◽  
Electron Imaging ◽  
Scanning Electron

Biological ultrastructures have been extensively studied with the scanning electron microscope (SEM) for the past 12 years mainly because this instrument offers accurate and reproducible high resolution images of cell shapes, provided the cells are dried in ways which will spare them the damage which would be caused by air drying. This can be achieved by several techniques among which the critical point drying technique of T. Anderson has been, by far, the most reproducibly successful. Many biologists, however, have been interpreting SEM micrographs in terms of an exclusive secondary electron imaging (SEI) process in which the resolution is primarily limited by the spot size of the primary incident beam. in fact, this is not the case since it appears that high resolution, even on uncoated samples, is probably compromised by the emission of secondary electrons of much more complex origin.When an incident primary electron beam interacts with the surface of most biological samples, a large percentage of the electrons penetrate below the surface of the exposed cells.

Analysis of Contrast Reversal in SEM Images

1972 ◽  
Vol 30 ◽  
pp. 398-399
Author(s):  
M. D. Coutts ◽  
E. R. Levin
Keyword(s):  
Incident Beam ◽  
Normal Incidence ◽  
Beam Current ◽  
Secondary Emission ◽  
Image Contrast ◽  
Sem Images ◽  
Secondary Electrons ◽  
Image Position

On tilting samples in an SEM, the image contrast between two elements, x and y often decreases to zero at θε, which we call the no-contrast angle. At angles above θε the contrast is reversed, θ being the angle between the specimen normal and the incident beam. The available contrast between two elements, x and y, in the SEM can be defined as,(1)where ix and iy are the total number of reflected and secondary electrons, leaving x and y respectively. It can easily be shown that for the element x,(2)where ib is the beam current, isp the specimen absorbed current, δo the secondary emission at normal incidence, k is a constant, and m the reflected electron coefficient.

Voltage-center COMA-free alignment for high-resolution Electron Microscopy

1994 ◽  
Vol 52 ◽  
pp. 410-411
Author(s):  
K. Ishizuka ◽  
K. Shirota
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Incident Beam ◽  
Chromatic Aberration ◽  
High Resolution Electron Microscopy ◽  
Beam Deflection ◽  
Objective Lens ◽  
Main Magnetic Field ◽  
Beam Direction ◽  
Resolution Electron

In a conventional alignment for high-resolution electron microscopy, the specimen point imaged at the viewing-screen center is made dispersion-free against a voltage fluctuation by adjusting the incident beam direction using the beam deflector. For high-resolution works the voltage-center alignment is important, since this alignment reduces the chromatic aberration. On the other hand, the coma-free alignment is also indispensable for high-resolution electron microscopy. This is because even a small misalignment of the incident beam direction induces wave aberrations and affects the appearance of high resolution electron micrographs. Some alignment procedures which cancel out the coma by changing the incident beam direction have been proposed. Most recently, the effect of a three-fold astigmatism on the coma-free alignment has been revealed, and new algorithms of coma-free alignment have been proposed.However, the voltage-center and the coma-free alignments as well as the current-center alignment in general do not coincide to each other because of beam deflection due to a leakage field within the objective lens, even if the main magnetic-field of the objective lens is rotationally symmetric. Since all the proposed procedures for the coma-free alignment also use the same beam deflector above the objective lens that is used for the voltage-center alignment, the coma-free alignment is only attained at the sacrifice of the voltage-center alignment.

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