Two contributions to the ratio of the mean secondary electron generation of backscattered electrons to primary electrons at high electron energy

2014 ◽  
Vol 28 (06) ◽  
pp. 1450046 ◽  
Author(s):  
Ai-Gen Xie ◽  
Chen-Yi Zhang ◽  
Kun Zhong
Keyword(s):  
Atomic Number ◽  
Secondary Electron ◽  
High Energy ◽  
Primary Electron ◽  
Experimental Results ◽  
High Electron ◽  
Secondary Electrons ◽  
Backscattered Electrons ◽  
The Mean ◽  
Primary Electrons

Based on the main physical processes of secondary electron emission, experimental results and the characteristics of backscattered electrons (BE), the formula was derived for describing the ratio (β angle ) of the number of secondary electrons excited by the larger average angle of emission BE to the number of secondary electrons excited by the primary electrons of normal incidence. This ratio was compared to the similar ratio β obtained in the case of high energy primary electrons. According to the derived formula for β angle and the two reasons why β > 1, the formula describing the ratio β energy of β to β angle , reflecting the effect that the mean energy of the BE W AV p0 is smaller than the energy of the primary electrons at the surface, was derived. β angle and β energy computed using the experimental results and the deduced formulae for β angle and β energy were analyzed. It is concluded that β angle is not dependent on atomic number z, and that β energy decreases slowly with z. On the basis of the two reasons why β > 1, the definitions of β and β energy and the number of secondary electrons released per primary electron, the formula for β E-energy (the estimated β energy ) was deduced. The β E-energy computed using W AV p0, energy exponent and the formula for β E-energy is in a good agreement with β energy computed using the experimental results and the deduced formula for β energy . Finally, it is concluded that the deduced formulae for β angle and β energy can be used to estimate β angle and β energy , and that the factor that W AV p0 increases slowly with atomic number z leads to the results that β energy decreases slowly with z and β decreases slowly with z.

MAXIMUM SECONDARY ELECTRON YIELDS FROM SEMICONDUCTORS AND INSULATORS

2016 ◽  
Vol 24 (04) ◽  
pp. 1750045 ◽  
Author(s):  
A. G. XIE ◽  
Z. H. LIU ◽  
Y. Q. XIA ◽  
M. M. ZHU
Keyword(s):  
Electron Emission ◽  
Secondary Electron ◽  
Maximum Yield ◽  
Secondary Electron Emission ◽  
High Energy ◽  
Secondary Electrons ◽  
Backscattered Electrons ◽  
Universal Formula ◽  
Yield Formula ◽  
Primary Electrons

Based on the processes and characteristics of secondary electron emission and the formula for the yield due to primary electrons hitting on semiconductors and insulators, the universal formula for maximum yield [Formula: see text] due to primary electrons hitting on semiconductors and insulators was deduced, where [Formula: see text] is the maximum ratio of the number of secondary electrons produced by primary electrons to the number of primary electrons. On the basis of the formulae for primary range in different energy ranges of [Formula: see text], characteristics of secondary electron emission and the deduced universal formula for [Formula: see text], the formulae for [Formula: see text] in different energy ranges of [Formula: see text] were deduced, where [Formula: see text] is the primary incident energy at which secondary electron yields from semiconductors and insulators, [Formula: see text], are maximized to maximum secondary electron yields from semiconductors and insulators, [Formula: see text]; and [Formula: see text] is the maximum ratio of the number of total secondary electrons produced by primary electrons and backscattered electrons to the number of primary electrons. According to the deduced formulae for [Formula: see text], the relationship among [Formula: see text], [Formula: see text] and high-energy back-scattering coefficient [Formula: see text], the formulae for parameters of [Formula: see text] and the experimental data as well as the formulae for [Formula: see text] in different energy ranges of [Formula: see text] as a function of [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] were deduced, where [Formula: see text] and [Formula: see text] are the original electron affinity and the width of forbidden band, respectively. The scattering of [Formula: see text] was analyzed, and calculated [Formula: see text] values were compared with the values measured experimentally. It was concluded that the deduced formulae for [Formula: see text] were found to be universal for [Formula: see text].

Comparison of Amplification and Imaging Behaviours of Several Gases In The Environmental Sem

1997 ◽  
Vol 3 (S2) ◽  
pp. 1195-1196 ◽  
Author(s):  
B.L. Thiel ◽  
A.L. Fletcher ◽  
A.M. Donald
Keyword(s):  
Water Vapour ◽  
Secondary Electron ◽  
High Energy ◽  
Background Signal ◽  
Backscattered Electrons ◽  
Gas Molecules ◽  
Calculated Fraction ◽  
Primary Electrons ◽  
Environmental Sem ◽  
Selection Of

We have investigated the amplification properties of several imaging gases in the Environmental SEM (ESEM) with the intent of forming a set of general guidelines for the selection of gases. In the ElectroScan ESEM, a gas ionisation cascade is used to amplify the secondary electron signals emanating from the specimen surface. The presence of gas in the chamber also gives rise to a pressure dependent background signal derived from ionisation events between gas molecules and high energy primary beam and backscattered electrons. The fraction of secondary electron signal decreases as the pressure is raised. This point is illustrated in figures la and lb which show the calculated fraction of signal contributed by secondary, backscattered, and primary electrons as a function of pressure in helium and water vapour. Helium yields a very pure secondary electron signal over the entire range of pressures shown. Unfortunately, helium does not provide a great deal of signal amplification compared to water vapour (figure 2).

Contrast and Resolution in Scanning Electron Microscopes

1967 ◽  
Vol 25 ◽  
pp. 256-257
Author(s):  
Shizuo Kimoto ◽  
Hiroshi Hashimoto ◽  
Kiyoshi Mase
Keyword(s):  
Secondary Electron ◽  
Primary Electron ◽  
Secondary Electron Image ◽  
Scattered Electron ◽  
Secondary Electrons ◽  
Backscattered Electrons ◽  
Electron Image ◽  
Backscattered Electron ◽  
Electron Microscopes ◽  
Scanning Electron

In scanning electron microscopy, secondary and backscattered electrons play a most important role. When considering these two forms of signal source, it is necessary to treat them separately on the basis of contrast and resolution, since their production processes and energies are different. In practice, the electrons detected by the secondary electron detector consist of secondary electrons excited by a primary electron probe, those excited by backscattered electrons in the specimen and secondary electrons liberated from the specimen's environmental parts during backscattered electron bombardment. Consequently, it is difficult to completely eradicate the effect of backscattered electrons upon the secondary electron image. This paper presents information in regards to the differences in contrast and resolution between the secondary and back- scattered electron image under the condition of optimum secondary/backscattered electron separation. First, it was shown how secondary electron image contrast is affected by secondary electrons liberated by backscattered electrons.

Optimisation of the S.E. Signal to Background Ratio in ESEM

1998 ◽  
Vol 4 (S2) ◽  
pp. 296-297
Author(s):  
T.H. Keller ◽  
B.L. Thiel ◽  
A.M. Donald
Keyword(s):  
Experimental Study ◽  
Secondary Electron ◽  
High Energy ◽  
Background Signal ◽  
Secondary Electrons ◽  
Background Ratio ◽  
Backscattered Electrons ◽  
High Energy Electrons ◽  
Gas Molecules ◽  
Environmental Sem

We have performed a theoretical and experimental study of the signal composition in the Environmental SEM (ESEM) with the intention of forming a set of general guidelines for optimising the signal to background ratio. In the ElectroScan ESEM, a gas ionisation cascade is used to amplify the secondary electron signals emanating from the specimen surface. The presence of gas in the chamber also gives rise to a pressure dependent background signal derived from ionisation events between gas molecules and high energy primary beam and backscattered electrons, as well as secondary electrons generated by the probe skirt.The signal collected by an environmental secondary detector (ESD) (ElectroScan, 1991) or a gaseous secondary detector (GSED) (ElectroScan, 1994) is an amplified signal which is a composite of at least three contributions. These are the amplified currents arising from the ionisation of the gas by high energy electrons from the primary (Ipe) and backscattered electrons (Ihse).

An Improved Mean Atomic Number Background Correction for Quantitative Microanalysis

1996 ◽  
Vol 2 (1) ◽  
pp. 1-7 ◽  
Author(s):  
John J. Donovan ◽  
Tracy N. Tingle
Keyword(s):  
Atomic Number ◽  
Minor Element ◽  
Binary Compound ◽  
Primary Electron ◽  
Background Correction ◽  
X Ray ◽  
The Mean ◽  
Set Up ◽  
X Ray Background ◽  
The Continuum

Quantitative EPMA (electron probe microanalysis) intensity measurements require an accurate correction for the X-ray continuum (or background) created by the Bremsstrahlung effect from the primary electron beam. This X-ray continuum, as measured on a wavelength-dispersive spectrometer at any particular wavelength, is primarily a function of the mean atomic number of the material being analyzed. One can calibrate the dependence of the continuum on mean atomic number by measuring and curve fitting the X-ray intensities at the analytical peak in pure elements, oxides, and binary compound standards that do not contain any of the analyte or any interfering elements and use that calibration to calculate the X-ray background correction. For unknown samples, the mean atomic number is determined from the elemental concentrations calculated by the ZAF or φ(ρz) matrix correction, and the fit regression coefficients are used iteratively to calculate the actual background correction. Over a large range of mean atomic number we find that the dependence of the continuum intensity on mean atomic number is well described by a second-order polynomial fit. In the case of low-energy X-ray lines (<1 to 2 keV), this fit is significantly improved by correcting the X-ray continuum intensities for absorption. For major and most minor element analyses, the improved mean atomic number background correction procedure presented in this paper is accurate and robust for a wide variety of samples. Empirical mean atomic number background data are presented for a typical 10-element silicate and a 15-element sulfide analytical set up that demonstrate the validity of the technique as well as some potential limitations.

Quantitative Microprobe Analysis by Means of Target Current Measurements*

1966 ◽  
Vol 10 ◽  
pp. 447-461 ◽  
Author(s):  
J. W. Colby ◽  
W. N. Wise ◽  
D. K. Conley
Keyword(s):  
Binary Systems ◽  
Secondary Electron ◽  
Surface Condition ◽  
Energy Levels ◽  
Target Material ◽  
High Energy ◽  
Secondary Electrons ◽  
Secondary Electron Yield ◽  
Electron Yield ◽  
Electron Backscatter

AbstractIn the microprobe analyzer, a portion of the high energy electrons impinging on the surface are backscattered from the sample and re-emitted at high energy levels. Low energy (less than 50 eV) or secondary electrons also ate emitted. Both the electron backscatter yield and the secondary electron yield are related to the mean atomic number of the target material and, hence, may be used to provide information about the target composition. Unfortunately, however, the secondary electron yield is very sensitive to the surface condition of the specimen and various instrument parameters. This complicates the otherwise simple linear relationship between sample composition and electron backscatter yield.It is shown that the effects due to secondary electrons can be minimized by biasing the sample, and that good results can be obtained in the analysis of binary systems. The limitations and utility of the method are discussed, and backscatter yields are determined.

Comparison of plasma-density and electron-temperature profiles during the auroral modelling campaign ARIES

1991 ◽  
Vol 69 (8-9) ◽  
pp. 950-958 ◽  
Author(s):  
Joëlle Margot ◽  
A. G. McNamara
Keyword(s):  
Electron Temperature ◽  
Plasma Density ◽  
High Energy ◽  
Primary Electron ◽  
Temperature Profiles ◽  
Height Distribution ◽  
Optical Intensity ◽  
High Energy Electron ◽  
E Region ◽  
Primary Electrons

Plasma-density and electron-temperature profiles were measured during the auroral modelling campaign ARIES. This campaign consisted of two rockets launched in the auroral E region under different geophysical conditions. The plasma-density and electron-temperature behaviours were tentatively related to the energy and intensity of the ionizing primary-electron fluxes. It is concluded that the plasma-density height distribution can be used to estimate the primary-electrons energy. The set of data presented is sufficiently complete to allow, when used together with other types of experiments such as the height distribution of the optical intensity and the high-energy electron spectra, the achievement of the objective of the ARIES multi-instrument campaign, i.e., refinement of the auroral model.

scholarly journals The efficiency of secondary electron emission

1933 ◽  
Vol 139 (838) ◽  
pp. 436-447 ◽  
Keyword(s):  
Velocity Distribution ◽  
Electron Emission ◽  
Secondary Electron ◽  
Secondary Electron Emission ◽  
Inelastic Collisions ◽  
Secondary Beam ◽  
X Rays ◽  
Secondary Electrons ◽  
The Third ◽  
Primary Electrons

The velocity distribution of the secondary electrons produced by bombarding a metallic face with a stream of primary electrons has been a matter of interest ever since the beginning of the study of secondary electron emission. As early as in 1908, Richardson and von Baeyer independently showed that slow moving electrons were copiously reflected from conducting faces. Farnsworth showed that for primary electrons having velocities less than 9 volts, most of the secondary electrons had velocities equal to the primary. As the primary potential was increased, the percentage of the reflected electrons decreased gradually but was appreciable at 110 volts. Davisson and Kunsman obtained reflected electrons even at primary potentials of 1000 and 1500 volts in the cases of some metal faces. At higher potentials we have also the electrons that undergo the Davisson and Germer scattering from the many crystal facets on the bombarded targets. As the potential is increased, the number of electrons with low velocities increases steadily and at large applied potentials, we have a large percentage of these in the secondary beam. These conclusions followed as a result of the work of Farnsworth who studied the distribution of velocities of the secondary electrons by the retarding potential method. He did not actually calculate the energy distribution from his curves but has drawn attention to the above conclusions. A careful investigation of the velocity distribution of the secondary electrons from various conducting faces was made by Rudberg at primary potentials ranging up to about 1000 volts. He adopted a magnetic deflection method similar to the one used in the analysis of the β rays and of the electrons excited by X-rays. The method had indeed been used by previous workers for the study of secondary emission, but Rudberg improved the technique considerably and obtained better focussing conditions. His results suggest that there are three groups of electrons in the secondary beam. The first group contains electrons returning with the same velocity as the primary. In the second group of electrons, we have those which undergo inelastic collisions with the orbital and structure electrons and hence are returned with some loss of energy. Richardson has drawn attention to the well-marked minimum between the two groups in Rudberg’s curves and infers that free electrons are not involved in the collisions. Finally there is the third group which contains the slow secondary electrons. The second and the third groups appear to be definitely connected with each other since they are both predominant at high primary potentials and become negligible at low primary potentials. Richardson suggests that the third group is the result of the excitation accompanying the inelastic collisions.

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