Electron Escape Depth Research Articles

Secondary electron emission and photoelectric emission with account of excited electrons’ moving backward emission surface

From existing old photoelectric emission PEE and secondary electron emission SEE models and the process that 50 % excited electrons are treated as as those moving backward emission surface, this study develops new SEE model for negative electron affinity semiconductor NEAS with large lSEE and new PEE model, respectively; lSEE denotes mean escape depth of secondary electrons. From our investigations of PEE from metals and NEAS with large lPEE and SEE from NEAS with large lSEE, it can be concluded that the new SEE model for NEAS with large lSEE and new PEE model developed here are correct; lPEE denotes mean escape depth of photo-emitted electrons. The theories of SEE from insulators with 120 Å≤ lSEE ≤ 1.0 × 104 Å are also developed and discussed.

Sub-Nanometer Depth Profiling of Native Metal Oxide Layers Within Single Fixed-Angle X-Ray Photoelectron Spectra.

Many metals form nanometer-thin self-passivating oxide layers upon exposure to the atmosphere, which affects a wide range of interfacial properties and shapes the way how metals interact with their environment. Such native oxide layers are commonly analyzed by X-ray photoelectron spectroscopy (XPS), which provides a depth-resolved chemical state and compositional analysis either by ion etching or modeling of the electron escape depths. The latter is commonly used to calculate the average thickness of a native oxide layer. However, the measurement of concentration profiles at the oxide-metal interface remains challenging. Here, a simple and accessible approach for the depth profiling of ultrathin oxide layers within single fixed-angle XPS spectra is proposed. Instead of using only one peak in the spectrum, as is usually the case, all peaks within the energy range of a standard lab device are utilized, thus resembling energy-resolved XPS without the need for a synchrotron. New models that allow the calculation of depth-resolved concentration profiles at the oxide-metal interface are derived and tested, which are also valid for angular- and energy-resolved XPS. The proposed method not only improves the accuracy of earlier approaches but also paves the way for a more holistic understanding of the XPS spectrum.

Expressions of electron escape probability and photo-emission from metals

The expressions of electron escape probability of several kinds of metal emitters are determined and proved correct here, respectively. From the determined expression of electron escape probability, existing formulas, characteristics of photo-emission PE and experimental data, the formulas for several parameters of PE from metals near threshold frequency γ0 and farther away γ0 were deduced and proved correct, respectively. The Cγ calculated here were analyzed, it concludes that the calculated Cγ are correct, Cγ is the probability that one electron of the conduction band of a given metal absorbs one given frequency photon. Based on the universal formula for λ of photo-emitted electrons undergoing PE from metals near γ0 and corresponding parameters, several special formulas for λ of photo-emitted electrons undergoing PE from Au and Ni near γ0 were obtained, respectively; λ is the mean escape depth of photo-emitted electrons from metals.

Removing gas-phase features in near ambient pressure partial Auger-Meitner electron yield oxygen K-edge NEXAFS spectra

With the advent of ambient pressure X-ray excited electron spectroscopy, near-edge X-ray absorption fine structure spectroscopy is widely used to investigate the hydrogen-bonding environment in aqueous solutions, ice, and adsorbed water. When Auger-Meitner electrons are detected, the method becomes inherently surface-sensitive because of the limited escape depth of electrons. In such X-ray absorption experiments with aqueous samples, gas-phase water is inevitably present. It impacts the acquired spectra in two ways: (1) Absorption along the X-ray path upstream of the sample reduces the photon flux reaching the condensed phase. (2) Spectra originating from gas-phase water in front of the analyzer contribute to the recorded spectra. Here, we develop and discuss a procedure to disentangle the gas-phase and condensed-phase contribution in the acquired spectra. A novel approach to quantify and remove the gas-phase contribution allows receiving condensed-phase near-edge X-ray absorption fine structure spectra at high water vapor pressure free of gas-phase artifacts.

Secondary electron emission and photoemission from a negative electron affinity semiconductor with large mean escape depth of excited electrons

The formulae for parameters of a negative electron affinity semiconductor (NEAS) with large mean escape depth of secondary electrons λ (NEASLD) are deduced. The methods for obtaining parameters such as λ, B, E pom and the maximum δ and δ at 100.0 keV ≥ E po ≥ 1.0 keV of a NEASLD with the deduced formulae are presented (B is the probability that an internal secondary electron escapes into the vacuum upon reaching the emission surface of the emitter, δ is the secondary electron yield, E po is the incident energy of primary electrons and E pom is the E po corresponding to the maximum δ). The parameters obtained here are analyzed, and it can be concluded that several parameters of NEASLDs obtained by the methods presented here agree with those obtained by other authors. The relation between the secondary electron emission and photoemission from a NEAS with large mean escape depth of excited electrons is investigated, and it is concluded that the presented method of obtaining λ is more accurate than that of obtaining the corresponding parameter for a NEAS with large λ ph (λ ph being the mean escape depth of photoelectrons), and that the presented method of calculating B at E po > 10.0 keV is more widely applicable for obtaining the corresponding parameters for a NEAS with large λ ph.

Secondary Electron Emission and Photoemission from Negative Electron Affinity Semiconductor with Large Mean Escape Depth of Excited Electrons

Secondary Electron Emission and Photoemission from Negative Electron Affinity Semiconductor with Large Mean Escape Depth of Excited Electrons

Secondary Electron Emission and Photoemission from Negative Electron Affinity Semiconductor With Large Mean Escape Depth of Excited Electrons

Secondary Electron Emission and Photoemission from Negative Electron Affinity Semiconductor With Large Mean Escape Depth of Excited Electrons

Secondary Electron Emission and Photoemission from Negative Electronaffinity Semiconductor with Large Mean Escape Depth of Excited Electrons

Secondary Electron Emission and Photoemission from Negative Electronaffinity Semiconductor with Large Mean Escape Depth of Excited Electrons

Secondary electron emission from insulators and negative electron affinity semiconductors

Based on expression of primary range R and the R at Epo ≥ 10.0 keV and L at Epo ≥ 1.0 keV calculated by ESTAR program [1], the method of obtaining formula for R at Epo ≥ 1.0 keV is presented; where Epo is incident energy of primary electron, and L is the energy loss of primary electron per unit path length at the incident surface of the materials. Based on the obtained formula for R, experimental δ, relationships among parameters of δ and the processes and characteristics of secondary electron emission SEE, the universal formula for δ is deduced and the method of calculating δ at Epo ≥ 1.0 keV of insulators and negative electron affinity NEA semiconductors is presented and experimentally proved, where δ is secondary electron yield. The methods of calculating mean escape depth of secondary electrons 1/α and B of insulators and NEA semiconductors are presented, respectively; where B is the probability that an internal secondary electron escapes into vacuum upon reaching the surface of emitter. From the relationships among parameters of SEE and the comparison between the values of 1/α and B obtained in this study and those obtained in former work, it concludes that the methods of calculating 1/α and B are correct.

Electron-lattice and electron–electron interactions and Debye temperature studied by temperature dependence of secondary electron emission from insulators

The formulas for temperature dependence of λ(χreal, Eg, T), λ(χreal, Eg, T)p, ẟ and σ of insulators with less impurities were deduced and proved to be true; λ(χreal, Eg, T) is the mean escape depth of secondary electrons emitted from insulators with efficient electron affinity χreal and band gap Eg at Kelvin temperature T, λ(χreal, Eg, T)p is the λ(χreal, Eg, T) due to electron-lattice scatterring in insulators, ẟ is secondary electron yield, σ is total ẟ. Analyses of data and the deduced formulas indicate that the temperature dependence of ẟ and σ of insulators with less impurities increase with the increasing [λ(χreal, Eg, T)/λ(χreal, Eg, T)p], and that λ(χreal, Eg, T), λ(χreal, Eg, T)p, ẟ and σ of insulators with less impurities decrease nearly linearly with increasing T in the range T > ΘD but decrease nonlinearly with increasing T in the range mΘD < T < ΘD, ΘD is Debye temperature, m of a given insulator is a constant which is < 0.4. The method of obtaining λ(χreal, Eg, T)Mee and corresponding χreal by secondary electron emission (SEE) was presented, λ(χreal, Eg, T)Mee is the λ(χreal, Eg, T) due to electron–electron scatterring in insulator. It concludes that the method presented here to obtain special formula for λ(χreal, Eg, T)p and corresponding χreal is a good method to research electron-lattice interaction by SEE, and that the method presented here to obtain values of λ(χreal, Eg)Mee and corresponding χreal is a good method to research electron–electron interaction by SEE. According to the values of ΘD, experimental σ, characteristics of temperature dependence of ẟ and σ and deduced formulas, it concludes that the method presented here to determine ΘD by SEE is a better method to determine ΘD of insulator with less impurities.

Secondary electron emission properties of double-layer B-doped diamond films

B-doped double-layer diamond films were prepared by microwave plasma chemical vapor deposition. The effects of different B-doping concentrations on the crystal quality, surface morphology, surface composition and the conductivity, secondary electron emission performance of the films were investigated. It is found that the increased conductivity with increased B-doping is beneficial for secondary electron emission. However, the degraded crystal quality of diamond, increased surface sp2 carbon and the segregation of B element at surface due to increased B-doping could degrade the secondary electron emission performance of the film. So it can be considered as a competition between improved vertical conductance that tends to increase secondary electron escape depth and finally degrading surface properties as a function of B-doping. The double-layer film with a light B-doping concentration has good crystal quality and enough conductivity, which helps to obtain the best secondary electron emission performance.

Thermal Analysis of Photoelectron Emission (PE) and X-ray Photoelectron Spectroscopy (XPS) Data for Iron Surfaces Scratched in Air, Water, and Liquid Organics

Little is known about the temperature dependence of electron transfer occurring at real metal surfaces. For iron surfaces scratched in seven environments, we report Arrhenius activation energies obtained from the data of photoelectron emission (PE) and X-ray photoelectron spectroscopy (XPS). The environments were air, benzene, cyclohexane, water, methanol, ethanol, and acetone. PE was measured using a modified Geiger counter during repeated temperature scans in the 25–339 °C range under 210-nm-wavelength light irradiation and during light wavelength scans in the range 300 to 200 nm at 25, 200, and 339 °C. The standard XPS measurement of Fe 2p, Fe 3p, O 1s, and C 1s spectra was conducted after wavelength scan. The total number of electrons counted in the XPS measurement of the core spectra, which was called XPS intensity, strongly depended on the environments. The PE quantum yields during the temperature scan increased with temperature, and its activation energies (ΔEaUp1) strongly depended on the environment, being in the range of 0.212 to 0.035 eV. The electron photoemission probability (αA) obtained from the PE during the wavelength scan increased with temperature, and its activation energies (ΔEαA) were almost independent of the environments, being in the range of 0.113–0.074 eV. The environment dependence of the PE behavior obtained from temperature and wavelength scans was closely related to that of the XPS characteristics, in particular, the XPS intensities of O 1s and the O2− component of the O 1s spectrum, the acid–base interaction between the environment molecule and Fe–OH, and the growth of non-stoichiometric FexO. Furthermore, the origin of the αA was attributed to the escape depth of hot electrons across the overlayer.

Study of secondary electron emission from semiconductors induced by electrons from 20 eV to 800 eV and surface state of semiconductors

Based on processes and characteristics of secondary electron emission (SEE), experimental data and the relations among parameters of secondary electron yield from semiconductors δ, the formula for δ in the range of 20 eV ≤ Epo ≤ 800 eV of semiconductors with Epom ≤ 800 eV as a function of Epo, Epom, atomic number Z and maximum δ (δm) was deduced and proved experimentally, where Epo and Epom are incident energy of primary electron and the Epo of δm, respectively. From the existing formula and the relation among Z, mean escape depth of secondary electrons emitted from semiconductors and primary range R at Epom deduced in this study, the formula for R in the range of 150 eV ≤ Epo ≤ 800 eV in monocrystalline semiconductors with Epom ≤ 800 eV, χ ≥ 0.6 eV and Eg ≥ 0.6 eV was successfully deduced, where χ is original electron affinity, Eg is the width of forbidden band. The method of calculating B(χreal, Eg) of semiconductor with Epom ≤ 800 eV, χreal ≥ 0.5 eV and Eg ≥ 0.6 eV and that of calculating B of semiconductor with Epom ≤ 800 eV were presented, respectively; Where B is the probability that an internal secondary electron escapes into vacuum upon reaching the surface of semiconductor, and the B(χreal, Eg) is the B relative to semiconductor with Eg and real electron affinity χreal. It can be concluded that the two methods are correct. From the analysis of calculated B, experimental Epom and relations among parameters of SEE, it can be concluded that this paper can research the surface state of semiconductor with Epom ≤ 800 eV by SEE.

Electronic and Optical Properties of GaAlAs/GaAs Thin Films

It has been shown that the formation of GaAlAs nanofilms on a GaAs surface leads to an increase in the emission coefficient of true secondary electrons and in the quantum yield of photoelectrons, which can be accounted for by the difference of the escape depth of true secondary electrons for GaAs and GaAlAs.

A study of secondary electron emission from semiconductors and insulators

No rude approximations were made in the course of deducing formula for B(χ, Eg) as a function of parameters of secondary electron emission SEE; where B(χ, Eg) is the probability that an internal secondary electron escapes into vacuum upon reaching the surface of semiconductors and insulators SI with width of forbidden band Eg and original electron affinity χ. It can be concluded that the formula for B(χ, Eg) as a function of parameters of SEE can be used to calculate B(χ, Eg). The B(χ, Eg) calculated with the formula for B(χ, Eg) as a function of parameters of SEE and characteristics of B(χ, Eg) and SEE from SI were studied, the formula for B(χ, Eg) of SI with Eg≥0.6 eV and χ≥0.5 eV as a function of χ and Eg was determined. It concludes that the determined formula can be used to calculate B(χ, Eg) of SI with Eg≥0.6 eV and χ≥0.5 eV. The processes and characteristics of SEE from SI, energy loss of primary electron and parameters of SEE were studied, the formulae for δm(Epom, χreal, Eg) in the general case and 1/α(χreal, Eg) of SI with Eg≥0.6 eV and χ≥0.5 eV were deduced and experimentally proved, respectively; where δm(Epom, χreal, Eg) is the maximum secondary electron yield δm of SI with Eg and χreal, Epom is primary incident energy corresponding to δm, χreal is real electron affinity,1/α(χreal, Eg) is mean escape depth of secondary electrons emitted from SI with Eg and χreal.

Calculation of CsI photocathode spectral response in 10-100 keV X-ray energy region

CsI photocathode is widely applied to high energy X-ray detection. And the spectral response is an important character of CsI photocathode. In this paper, the interaction process of high energy X-ray with CsI is analyzed and the spectral response of CsI photocathode is calculated in a 10-100 keV range. The influences of Compton scattering, X-ray fluorescence radiation and Auger emission on the spectral response are analyzed in accordance with the physical process of high energy X-ray interaction with CsI photocathode. These influences prove to be negligible in comparison with photo-ionization influence. Thus only the photoelectric transition is taken into account in calculation. According to the analyses of the processes of the photoelectron creation, transition and escaping, the formula for CsI spectral response is deduced as a function of secondary electron mean escape depth and photocathode thickness. The formula of secondary electron mean escape depth is then deduced as a function of X-ray energy. These formulae indicate that the mean escape depth of the secondary electrons increases markedly with the rise of X-ray energy and has a remarkable influence on the CsI spectral response. The spectral responses for different CsI thickness values are then calculated in a range of 10-100 keV. The results show that 1000 nm CsI has the best response under 20 keV, while 10000 nm CsI has a higher response over 60 keV. Then the calculation data are compared with experimental data of Hara's and Khan's hard X-ray streak camera measurements. These data agree well with each other and prove that our calculation of CsI spectral response for high energy X-ray is reliable. The spectral responses to CsI thickness for 17.5 keV and 60 keV are also calculated and shown in figures. These calculation data match experimental data of Frumkin and Monte-Carlo simulation data of Gibrekhterman. The measurement error of Frumkin's experiment and the uncertainty of the secondary electron mean escape depth are considered to be the reasons for the deviations of calculation and experimental data. The figures of spectral responses to CsI thickness also reveal the optimal thickness values of CsI for different X-ray photon energies. It is shown that 1 m is the optimal thickness for 17.5 keV X-ray detection, and 10 m is optimal for 60 keV. Finally the spectral response of CsI photocathode in a 10-100 keV range is calculated and the formulae prove to be reliable. According to these formulae and calculations, the optimal thickness of CsI photocathode can thus be given for designing and optimizing the high energy X-ray imaging detectors.

Sealed-off helium-filled proportional counter for the conversion electron Mössbauer spectroscopy

Conversion electron Mossbauer spectroscopy (CEMS) is a surface-sensitive technique because of the shallowness of the escape depth of conversion electrons. The proportional counter with the sample built-in is usually used for CEMS with a flow of He mixed with a quenching gas. This flow-type proportional counter with a mixed gas, however, is not suited to high-temperature measurements. For high-temperature operation, we fabricated a sealed-off proportional counter operated above 850 K for CEMS, which is filled with pure He at a pressure of 1–8 × 104 Pa. The distribution of the output pulse voltage revealed an inflection point suggesting that two multiplication mechanisms are operative. The multiplication factor of the proportional counter was estimated to be about 104–105. By means of the fabricated proportional counter, we investigated the magnetic phase transition of Fe3O4, whose Curie temperature is 858 K. We successfully observed the ferromagnetic-paramagnetic phase transition without the reduction of the sample.

Formulae for maximum yield and mean escape depth of secondary electrons emitted from metals

Based on the characteristics of secondary electron emission, the former formulae for the maximum yield of metals [Formula: see text] and primary range in the energy range of [Formula: see text] eV, relation [Formula: see text] among secondary electron escape probability [Formula: see text], average energy required to produce an internal secondary electron [Formula: see text], [Formula: see text], primary energy of [Formula: see text] ([Formula: see text] and parameter [Formula: see text] was deduced. On the basis of [Formula: see text] and the former formula for [Formula: see text], relation [Formula: see text] among mean escape depth of secondary electrons emitted from metals [Formula: see text], atomic number [Formula: see text], back-scattering coefficient [Formula: see text], material density [Formula: see text], [Formula: see text], atomic weight [Formula: see text] and [Formula: see text] was deduced. According to the deduced [Formula: see text], the formula for the ratio of [Formula: see text] to [Formula: see text] and experimental ratio of [Formula: see text] to [Formula: see text], relation [Formula: see text] among [Formula: see text], original work function [Formula: see text] and [Formula: see text] were empirically obtained. According to the characteristics of metal surface, [Formula: see text], [Formula: see text] and [Formula: see text], the formula for [Formula: see text] as a function of [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] and that for [Formula: see text] as a function of [Formula: see text], [Formula: see text] and [Formula: see text] were deduced, respectively. The influences of surface change on [Formula: see text] and [Formula: see text] were analyzed. Calculated [Formula: see text] and [Formula: see text] were compared with the corresponding experimental ones. It was concluded that the deduced formulae for [Formula: see text] and [Formula: see text] can be used to estimate [Formula: see text] and [Formula: see text], respectively.

Depth resolution and preferential sputtering in depth profiling of sharp interfaces

The influence of preferential sputtering on depth resolution of sputter depth profiles is studied for different sputtering rates of the two components at an A/B interface. Surface concentration and intensity depth profiles on both the sputtering time scale (as measured) and the depth scale are obtained by calculations with an extended Mixing-Roughness-Information depth (MRI)-model. The results show a clear difference for the two extreme cases (a) preponderant roughness and (b) preponderant atomic mixing. In case (a), the interface width on the time scale (Δt(16–84%)) increases with preferential sputtering if the faster sputtering component is on top of the slower sputtering component, but the true resolution on the depth scale (Δz(16–84%)) stays constant. In case (b), the interface width on the time scale stays constant but the true resolution on the depth scale varies with preferential sputtering. For similar order of magnitude of the atomic mixing and the roughness parameters, a transition state between the two extremes is obtained. While the normalized intensity profile of SIMS represents that of the surface concentration, an additional broadening effect is encountered in XPS or AES by the influence of the mean electron escape depth which may even cause an additional matrix effect at the interface.

Electronic structure of buried LaNiO3 layers in (111)-oriented LaNiO3/LaMnO3 superlattices probed by soft x-ray ARPES

Taking advantage of the large electron escape depth of soft x-ray angle resolved photoemission spectroscopy, we report electronic structure measurements of (111)-oriented [LaNiO3/LaMnO3] superlattices and LaNiO3 epitaxial films. For thin films, we observe a 3D Fermi surface with an electron pocket at the Brillouin zone center and hole pockets at the zone vertices. Superlattices with thick nickelate layers present a similar electronic structure. However, as the thickness of the LaNiO3 is reduced, the superlattices become insulating. These heterostructures do not show a marked redistribution of spectral weight in momentum space but exhibit a pseudogap of ≈50 meV.