Effects of Space Charge on ESEM Gas Amplification

1997 ◽  
Vol 3 (S2) ◽  
pp. 609-610 ◽  
Author(s):  
B.L. Thiel ◽  
M.R. Hussein-Ismail ◽  
A.M. Donald
Keyword(s):  
Electric Field ◽  
Electrostatic Field ◽  
Secondary Electron ◽  
Sample Surface ◽  
Cascade Process ◽  
Secondary Electrons ◽  
Positive Ions ◽  
Space Charges ◽  
Cascade Amplification ◽  
Environmental Sem

We have performed a theoretical investigation of the effects of space charges in the Environmental SEM (ESEM). The ElectroScan ESEM uses an electrostatic field to cause gas cascade amplification of secondary electron signals. Previous theoretical descriptions of the gas cascade process in the ESEM have assumed that distortion of the electric field due to space charges can be neglected. This assumption has now been tested and shown to be valid.In the ElectroScan ESEM, a positively biased detector is located above the sample, creating an electric field on the order of 105 V/m between the detector and sample surface. Secondary electrons leaving the sample are cascaded though the gas, amplifying the signal and creating positive ions. Because the electrons move very quickly through the gas, they do not accumulate in the specimen-to-detector gap. However, the velocity of the positive ions is limited by diffusion.

scholarly journals Time Dependent Study of the Positive ion Current in the Environmental Scanning Electron Microscope (ESEM)

2001 ◽  
Vol 7 (S2) ◽  
pp. 788-789
Author(s):  
S.W. Morgan ◽  
M.R. Phillips
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Sample Surface ◽  
Primary Electron ◽  
Environmental Scanning Electron Microscope ◽  
Environmental Scanning ◽  
Secondary Electrons ◽  
Positive Ions ◽  
Cascade Amplification ◽  
Scanning Electron

The Environmental Scanning Electron Microscope (ESEM) is capable of image generation in a gaseous environment at sample chamber pressures of up to 20 torr. in an ESEM, low energy secondary electrons emitted from a sample surface, by virtue of the primary electron beam, are accelerated towards the positively biased metallic ring (typically +30 to +550V) Gaseous Secondary Electron Detector (GSED). As these electrons accelerate towards the ring they undergo ionizing collisions with gas molecules producing positive ions and additional electrons known as environmental secondary electrons. The environmental electrons further ionize the gas on their way to the ring producing a cascade amplification of the original signal. The amplified signal induced in the ring is used to form an image. The electric field generated between the GSED ring and the grounded stage causes the positive ions produced in the cascade to drift towards the sample, effectively neutralizing negative charge build up on the surface of a non-conducting sample.

Transport of Secondary Electrons Through a Film of Condensed Water; Implications for Imaging Wet Samples

1997 ◽  
Vol 3 (S2) ◽  
pp. 1199-1200
Author(s):  
I. C. Bache ◽  
B. L. Thiel ◽  
N. Stelmashenko ◽  
A. M. Donald
Keyword(s):  
Surface Layer ◽  
Electron Emission ◽  
Secondary Electron ◽  
Secondary Electron Emission ◽  
Water Layer ◽  
Sample Surface ◽  
Secondary Electrons ◽  
Secondary Electron Emission Coefficient ◽  
Condensed Water ◽  
Environmental Sem

We have performed a theoretical and experimental study of the the effect that a surface layer of condensed water has on the emission of secondary electrons from the surface. This is an issue of considerable interest to users of the Environmental SEM (ESEM) when imaging wet samples. Previous work has been performed to investigate the effect of a layer of water on back scattered electrons (BSE), but secondary electron (SE) imaging is more commonly used in ESEM, so an understanding of the interactions of SE with water is important. The aim of this work is to quantify the thickness of water through which imaging is possible, by considering both the interactions of secondary electrons with the water, and the interactions of the water layer with the sample, which may affect the secondary electron emission coefficient, δ.The effects that a surface layer of water may have on electron emission from a sample surface can be split into three regimes.

scholarly journals Ignition and advancement of surface discharges at atmospheric air under positive lightning impulse voltage depending on perpendicular electric stress and solid dielectrics: modelling of the propagating phenomenology

2018 ◽  
Vol 82 (2) ◽  
pp. 20801 ◽  
Author(s):  
Mohammed Adnane Douar ◽  
Abderrahmane Beroual ◽  
Xavier Souche
Keyword(s):  
Electric Field ◽  
Electrostatic Field ◽  
Physical Mechanisms ◽  
Space Charges ◽  
Electric Stress ◽  
Impulse Voltage ◽  
Lightning Impulse ◽  
Surface Discharges ◽  
Solid Dielectrics ◽  
The Relationship

In many high voltage equipment, partial discharges are regarded as one of the most widespread pathology whose ignition conditions and effects are studied by scientists and manufacturers to avoid major failures. Actually, those electrical gaseous phenomena generally occur under several constraints such as the electrostatic field level, the nature of insulating surface being polluted or not, and switching or lightning transients. The present paper discusses physical mechanisms related to the creeping discharges propagation growing over insulators subjected to perpendicular electric field and positive lightning impulse voltage. More precisely, the developed discussion attempts to answer some observations especially noticed for main discharges feature namely (i) the discharges morphology, (ii) their velocity and (iii) the space charges effects on electric field computation. Several factors like (i) the influence of the type of a material’s interface, its electric conductivity, permittivity and discharges mobility, (ii) the relationship between the applied electrostatic field, the space charges, the velocity, the propelling pressure and discharges temperature are among numerous parameters that have been addressed in this study which discusses lightning impulse transients phenomena.

Electrons, Ions and Cathodoluminescence in the Environmental SEM

1998 ◽  
Vol 4 (S2) ◽  
pp. 290-291
Author(s):  
Brendan J. Griffin
Keyword(s):  
Sample Surface ◽  
Operating Conditions ◽  
Contrast Imaging ◽  
Near Surface ◽  
Positive Ions ◽  
The Face ◽  
Neutral Conditions ◽  
Chamber Gas ◽  
Environmental Sem

“Secondary” or ‘low energy’ electron emission in the environmental SEM is a complex summation of surface and near surface interactions of electron and ions, fields developed within the sample and conventional electron-sample interactions. Little is understood about the first two aspects and recent data has illustrated limitations on our understanding of cathodoluminescence. The recently described Charge Contrast Imaging (CCI) has drawn attention to the fact that the role of ions in the environmental SEM have been largely ignored. Generally the positive ions have been regarded to provide charge cancellation at the specimen surface but otherwise to have little effect. This view has persisted in the face of evidence that even without gas amplification effects, charge neutral conditions are obtained at the sample surface with a chamber gas pressure of 0.1 torr2, a pressure far lower than normal operating conditions for the ESEM (1 -2 0 torr).

The interaction of atomic particles with solid surfaces at intermediate energies I. Secondary electron emission

1969 ◽  
Vol 314 (1516) ◽  
pp. 39-51 ◽  
Keyword(s):  
Electron Emission ◽  
Secondary Electron ◽  
Secondary Electron Emission ◽  
Molecular Ions ◽  
Solid Surfaces ◽  
Surface Layers ◽  
Secondary Electrons ◽  
Intermediate Energies ◽  
Positive Ions ◽  
The Individual

The electron emission from a number of metal and carbon targets bombarded by various positive ions is measured by a method employing a magnetic field to separate secondary electrons from scattered ions. Molecular ions are shown to produce emission approximately equal to that which would be produced by the individual atoms independently. Accurate measurements have been made of the energy distribution of secondary electrons. These are close to Gaussian. It is concluded that secondary electron emission is confined to the surface layers of the target atoms since no electrons possess energies close to zero.

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).

Monte Carlo simulations of the ion-cascade process in the ESEM

1996 ◽  
Vol 54 ◽  
pp. 834-835
Author(s):  
B.L. Thiel ◽  
I.C. Bache ◽  
A.L. Fletcher ◽  
P. Meredith ◽  
A.M. Donald
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Cascade Process ◽  
Secondary Electrons ◽  
Monte Carlo Calculations ◽  
Steady State Kinetic ◽  
Electron Cascade ◽  
State Kinetic ◽  
Primary Electrons ◽  
Environmental Sem

Our Monte Carlo simulations and experimental measurements show the Townsend Gas Capacitor (TGC) model to be highly inappropriate for describing the electron cascade process in the Environmental SEM (ESEM). Previous workers have described the signal collected by the Gaseous Secondary Electron Detector (GSED) as having contributions from secondary as well as backscattered and primary electrons, all being amplified by gas cascade. Although these models are qualitatively correct, they require a more sophisticated description of Townsend’s First Ionisation Coefficient, α. Figure 1 illustrates the short-comings of the TGC models when compared to experimentally obtained amplification curves. (Details of the amplification measurements made with various imaging gases will be given elsewhere, along with specifics of the Monte Carlo Calculations.)The major flaw in applying the TGC model to the ESEM stems from the assumption that the secondary electrons and their environmental daughters reach a steady-state kinetic energy distribution en-route to the detector.

Transient Response of Electrostatic Field due to Collision ESD between Spherical Electrodes by using Bare-chip Optical Electric Field Sensor

2020 ◽  
Vol 140 (12) ◽  
pp. 599-600
Author(s):  
Kento Kato ◽  
Ken Kawamata ◽  
Shinobu Ishigami ◽  
Ryuji Osawa ◽  
Takeshi Ishida ◽  
...  
Keyword(s):  
Electric Field ◽  
Transient Response ◽  
Electrostatic Field ◽  
Electric Field Sensor ◽  
Field Sensor

Analysis of Voltage Contrast in Secondary Electron Images Using a High-Energy Electron Spectrometer

2019 ◽  
Author(s):  
Natsuko Asano ◽  
Shunsuke Asahina ◽  
Natasha Erdman
Keyword(s):  
Focused Ion Beam ◽  
Ion Beam ◽  
Sample Surface ◽  
High Energy ◽  
Secondary Electrons ◽  
Analysis Technique ◽  
Quantitative Understanding ◽  
Voltage Contrast ◽  
Acceleration Voltage ◽  
Failure Localization

Abstract Voltage contrast (VC) observation using a scanning electron microscope (SEM) or a focused ion beam (FIB) is a common failure analysis technique for semiconductor devices.[1] The VC information allows understanding of failure localization issues. In general, VC images are acquired using secondary electrons (SEs) from a sample surface at an acceleration voltage of 0.8–2.0 kV in SEM. In this study, we aimed to find an optimized electron energy range for VC acquisition using Auger electron spectroscopy (AES) for quantitative understanding.

Numerical Simulation of Leakage Current on Conductive Insulator Surface

2019 ◽  
Vol 8 (4) ◽  
pp. 9487-9492
Keyword(s):  
Numerical Simulation ◽  
Electric Field ◽  
Leakage Current ◽  
Method Of Lines ◽  
Electron Attachment ◽  
Negative Ions ◽  
Conduction Current ◽  
Insulator Surface ◽  
Finite Difference Approximations ◽  
Positive Ions

The outdoor insulator is commonly exposed to environmental pollution. The presence of water like raindrops and dew on the contaminant surface can lead to surface degradation due to leakage current. However, the physical process of this phenomenon is not well understood. Hence, in this study we develop a mathematical model of leakage current on the outdoor insulator surface using the Nernst Planck theory which accounts for the charge transport between the electrodes (negative and positive electrode) and charge generation mechanism. Meanwhile the electric field obeys Poisson’s equation. Method of Lines technique is used to solve the model numerically in which it converts the PDE into a system of ODEs by Finite Difference Approximations. The numerical simulation compares reasonably well with the experimental conduction current. The findings from the simulation shows that the conduction current is affected by the electric field distribution and charge concentration. The rise of the conduction current is due to the distribution of positive ion while the dominancy of electron attachment with neutral molecule and recombination with positive ions has caused a significant reduction of electron and increment of negative ions.

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