Effect of secondary electrons on the yield of electron-stimulated desorption of neutral atoms under differently localized core-level excitations in a substrate

Electron stimulated desorption (ESD) of neutral atomic Cs from graphene on Ir has been studied for two cases: when Cs intercalation does present and when it does not take place. Two peaks have been found at desorbed atom energy distribution: high-energy (HE) at the energy of 0.36 eV and low-energy (LE) one at the energy of 0.13 eV. HE peak has been observed for both cases, we attribute it with excitation of 2s carbon core level. LE peak was observed only when intercalation does not take place; we attribute it with excitation of 4f and 5p core levels of Ir. A model is put forward to describe atomic Cs ESD; we proposed that graphene on Ir acts as dielectric in the processes discussed above.

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Specimen Collection Effect in Scanning Electron Microscopy Images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095492 ◽

1972 ◽

Vol 30 ◽

pp. 448-449

Author(s):

J. Temple Black ◽

Jose Guerrero

Keyword(s):

Surface Morphology ◽

Secondary Electron Emission ◽

Secondary Electrons ◽

Charge Effects ◽

Material Density ◽

Specimen Collection ◽

The Subject ◽

Curved Paths ◽

Subject Material ◽

Microscopy Images

In the SEM, contrast in the image is the result of variations in the volume secondary electron emission and backscatter emission which reaches the detector and serves to intensity modulate the signal for the CRT's. This emission is a function of the accelerating potential, material density, chemistry, crystallography, local charge effects, surface morphology and especially the angle of the incident electron beam with the particular surface site. Aside from the influence of object inclination, the surface morphology is the most important feature In producing contrast. “Specimen collection“ is the name given the shielding of the collector by adjacent parts of the specimen, producing much image contrast. This type of contrast can occur for both secondary and backscatter electrons even though the secondary electrons take curved paths to the detector-collector.Figure 1 demonstrates, in a unique and striking fashion, the specimen collection effect. The subject material here is Armco Iron, 99.85% purity, which was spark machined.

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Analysis of Contrast Reversal in SEM Images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010009525x ◽

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.

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Imaging and diffraction modes in Scanning Transmission Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100144814 ◽

1986 ◽

Vol 44 ◽

pp. 684-687

Author(s):

J. M. Cowley ◽

R. Glaisher ◽

J. A. Lin ◽

H.-J. Ou

Keyword(s):

Scanning Transmission Electron Microscopy ◽

High Efficiency ◽

Fiber Optic ◽

Image Intensifier ◽

Detector System ◽

Detector Plane ◽

Secondary Electrons ◽

Transmission Electron ◽

Scanning Transmission ◽

Special Detector

Some of the most important applications of STEM depend on the variety of imaging and diffraction made possible by the versatility of the detector system and the serial nature, of the image acquisition. A special detector system, previously described, has been added to our STEM instrument to allow us to take full advantage of this versatility. In this, the diffraction pattern in the detector plane may be formed on either of two phosphor screens, one with P47 (very fast) phosphor and the other with P20 (high efficiency) phosphor. The light from the phosphor is conveyed through a fiber-optic rod to an image intensifier and TV system and may be photographed, recorded on videotape, or stored digitally on a frame store. The P47 screen has a hole through it to allow electrons to enter a Gatan EELS spectrometer. Recently a modified SEM detector has been added so that high resolution (10Å) imaging with secondary electrons may be used in conjunction with other modes.

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Imaging magnetic microstructure with SEMPA

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010015099x ◽

1993 ◽

Vol 51 ◽

pp. 1032-1033

Author(s):

M. H. Kelley ◽

J. Unguris ◽

R. J. Celotta ◽

D. T. Pierce

Keyword(s):

Electron Microscopy ◽

Thin Films ◽

Scanning Electron Microscopy ◽

Sandwich Structure ◽

Magnetic Coupling ◽

Polarization Analysis ◽

Secondary Electrons ◽

Magnetic Microstructure ◽

Escape Depth ◽

Scanning Electron

By measuring the spin polarization of secondary electrons generated in a scanning electron microscope, scanning electron microscopy with polarization analysis (SEMPA) can directly image the magnitude and direction of a material’s magnetization. Because the escape depth of the secondaries is only on the order of 1 nm, SEMPA is especially well-suited for investigating the magnetization of ultra-thin films and surfaces. We have exploited this feature of SEMPA to study the magnetic microstrcture and magnetic coupling in ferromagnetic multilayers where the layers may only be a few atomic layers thick. For example, we have measured the magnetic coupling in Fe/Cr/Fe(100) and Fe/Ag/Fe(100) trilayers and have found that the coupling oscillates between ferromagnetic and antiferromagnetic as a function of the Cr or Ag spacer thickness.The SEMPA apparatus has been described in detail elsewhere. The sample consisted of a magnetic sandwich structure with a wedge-shaped interlayer as shown in Fig. 1.

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Electron-beam damage of oxides at high current densities

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100155141 ◽

1989 ◽

Vol 47 ◽

pp. 634-635

Author(s):

M. R. McCartney ◽

J. K. Weiss ◽

David J. Smith

Keyword(s):

Electron Beam ◽

Electron Microscope ◽

Current Density ◽

Transition Metal Oxides ◽

Time Resolved ◽

Rapid Acquisition ◽

Resolution Electron ◽

Current Densities ◽

Electron Stimulated Desorption ◽

Channel Analyzer

It is well-known that electron-beam irradiation within the electron microscope can induce a variety of surface reactions. In the particular case of maximally-valent transition-metal oxides (TMO), which are susceptible to electron-stimulated desorption (ESD) of oxygen, it is apparent that the final reduced product depends, amongst other things, upon the ionicity of the original oxide, the energy and current density of the incident electrons, and the residual microscope vacuum. For example, when TMO are irradiated in a high-resolution electron microscope (HREM) at current densities of 5-50 A/cm2, epitaxial layers of the monoxide phase are found. In contrast, when these oxides are exposed to the extreme current density probe of an EM equipped with a field emission gun (FEG), the irradiated area has been reported to develop either holes or regions almost completely depleted of oxygen. ’ In this paper, we describe the responses of three TMO (WO3, V2O5 and TiO2) when irradiated by the focussed probe of a Philips 400ST FEG TEM, also equipped with a Gatan 666 Parallel Electron Energy Loss Spectrometer (P-EELS). The multi-channel analyzer of the spectrometer was modified to take advantage of the extremely rapid acquisition capabilities of the P-EELS to obtain time-resolved spectra of the oxides during the irradiation period. After irradiation, the specimens were immediately removed to a JEM-4000EX HREM for imaging of the damaged regions.

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