Secondary electron emission of sputtered alumina films

Secondary electron emission yieldδ was measured for thin films of alumina prepared byrf sputtering technique. Single pulse method was used along with 4-gridleed optics system to determineδ. Maximum value of 4·3 was obtained at primary energy of 350 eV. The Dionne’s theory was used to analyse the results and the emission probability escape depth and absorption coefficient of secondaries were also estimated. Fairly good correlation is observed between experimental and theoretical values ofδ for beam energies upto 1 keV.     

Secondary electron emission from thin carbon films

For the purpose of investigating how secondary electrons are produced in carbon, the correlation between energy-loss events and secondary electrons was studied experimentally by using the coincidence method. If a secondary electron is detected in coincidence with an electron transmitted through a thin film which has lost an amount of energy E, then the process causing this energy loss results in the production of secondary electrons. We established the existence of these coincidences and have taken inelastic and coincidence spectra for films of different thickness. We found that in carbon secondary electrons are predominantly produced as a result of energy losses of about 20 eV, with an efficiency of about 5%. The escape depth of secondary electrons was also estimated to be approximately 30 Å.     

Secondary electron yield enhancement by MgO capping layers

The yield of secondary electrons emitted from an epitaxial three monolayer (3 ML) NiO(1 0 0)/Ag(1 0 0) film excited by soft X-ray linearly polarized synchrotron radiation at the Ni L_2,3 absorption threshold has been measured for different values of the thickness of a MgO(1 0 0) capping layer. Compared with the as grown 3 ML NiO(1 0 0)/Ag(1 0 0) film, we observe a significant enhancement by about a factor 1.2 of the secondary electron emission for the capped 8 ML MgO(1 0 0)/3 ML NiO(1 0 0)/Ag(1 0 0) sample. A further substantial yield enhancement by a factor 1.6 with respect to the uncapped NiO sample is observed after deposition of an additional 8 ML MgO(1 0 0) film, for a total capping layer thickness of 16 ML. The observed secondary electron yield enhancement is discussed in terms of modified electronic structure, surface work function changes, and characteristic electron propagation lengths.     

Secondary electron emission from highly charged carbon grains

Surfaces in contact with a plasma can influence its characteristics and, on the other hand, the impact of plasma particles can change surface properties of materials immersed in a plasma. Carbon is often present in plasma systems either as a building material or a product of technological processes, thus its behavior is an important factor of these applications. The paper deals with investigations of secondary emission of 1–6 μm spherical grains from amorphous carbon under the electric field of the order of 10⁸ V/m. We have found that the secondary emission yield increases with the electric field at the sample surface nearly linearly and does not depend on the grain diameter. Long-lasting (hours) electron irradiation of the sample surface leads to a significant decrease of the yield that was attributed to the removal of an absorbed layer from the grain surface. This conclusion is supported by the fact that a similar effect was achieved after several minutes of simultaneous electron and ion treatments.     

Secondary electron emission control in X-ray photoelectron spectroscopy

Secondary electron emission (SEE) is a major player in surface charging during X-ray photoelectron spectroscopy (XPS); its characteristics and applicability as a current source for electrical measurements are studied. We employ sample biasing and a top retarding grid to control the photoelectron current, and further compare their I–V characteristics with direct spectroscopy of the secondary electrons. Using silica-coated gold substrates, the effect of sample work function on the emitted secondary electrons is shown and fine control over the surface potential gradients, in the range of 10–100 meV, is achieved. XPS-based chemically resolved electrical measurements (CREM) can thus be extended to the positive current regime.     

Secondary electron yield measurements of carbon covered multilayer optics

Carbon contamination on extreme ultraviolet (EUV) optics has been observed in EUV lithography. In this paper, we performed in situ monitoring of the build-up and removal of carbon contamination on Mo/Si EUV multilayers by measuring the secondary electron yield as a function of primary electron energy. An electron beam with an energy of 2 keV was used to simulate the EUV radiation induced carbon contamination. For a clean EUV multilayer, the maximum secondary electron yield is about 1.5 electrons per primary electron at a primary electron energy of 467 eV. The maximum yield reduced to about 1.05 at a primary electron energy of 322 eV when the surface was covered by a non-uniform carbon layer with a maximum thickness of 7.7 nm. By analyzing the change in the maximum secondary electron yield with the final carbon layer thickness, the limit of detection was estimated to be less than 0.1 nm.     

Secondary electron emission from thin self-supporting films of silver

The paper deals with the measurement of secondary electron emission and the scattering of primary electrons on thin self-supporting films of Ag. The measured values of the practical range agree with the older results obtained by Kanter. New results are those concerning the maximum depth from which the primaries are scattered back to the front surface and the maximum range of secondaries, which has been found to be about 300 å.     

The diamond surface: II. Secondary electron emission

The total secondary electron emission spectrum from diamond has been examined, and details of the Auger spectra, characteristic loss spectra and K-level ionisation loss spectra have been presented. These features from the clean diamond surface were contrasted to those from graphite and amorphous-carbon. The fine structure in the carbon Auger spectra were compared with the line shape calculated using the band structure model, and the chemical sensitivity of the Auger spectra was demonstrated. A high energy Auger satellite peak in the diamond spectrum was ascribed to the Auger transition occurring from a doubly ionised carbon atom. This result was substantiated by the observation of loss peaks associated with the singly ionised level. The characteristic energy losses were assigned to interband transitions and plasma losses, and have been compared to optical data where possible.     

Secondary electron emission spectroscopy of solid and liquid high-density polyethylene

Kinetic energy spectra of secondary electrons emitted from liquid and solid high-density polyethylene owing to low-energy electron impacts are measured as a function of temperature. It is found that the spectral features associated with high density-of-states parts of the conduction band smear out with increasing temperature, and disappear completely above the melting point. The smearing out of the conduction band structure is explained as a result of breakdown of the inter-molecular and/or the intra-molecular symmetry induced by thermal excitations of the molecular vibrations.     

A secondary electron emission correction for quantitative auger yield measurements

The Auger electron yield from the de-excitation of L_2,3 core holes of Cu is determined, in the approximation of isotropic emission, from the integral of the characteristic (elastic) Auger emission. The characteristic emission function is obtained from the secondary electron spectrum in two steps: First, the cascade background at a given Auger line is characterized accurately by the method of cascade linearization and subtracted. In the second step the resulting line is debroadened by an approximation to deconvolution debroadening. The concept of modulation stability is introduced as a criterion for credibility of the results of this analysis.     

Secondary emission from small dust grains at high electron energies

A previous model for secondary electron emission from small grains is modified to calculate yields for micron sized grains, both spherical and cylindrical, when the primary electrons constitute a high energy parallel beam. It is found that, in general, the secondary electron yield is significantly higher than for the case of normal incidence. Moreover, the equilibrium potentials of the grain are always positive due to this enhanced secondary emission. These results are compared with experimental data recently available for micron sized glass particles, and equilibrium potentials, calculated based on the model presented here, and are found to be in reasonably good agreement with their measured potentials     

Secondary electron emission data of cesiated oxygen free high conductivity copper

Because of its relevance for negative hydrogen ion sources, the change in secondary electron emission with the adsorption of Cs on Cu was studied. Properly prepared disks of oxygen free high conductivity (OFHC) copper yielded a maximum secondary electron emission δ_max=1.54±3%. The deposition of ≈0.5 monolayer of Cs resulted in δ_max=3.40±3%.     

Secondary electron yield from stainless steel surface coated with titanium nitride

The experiment on measurement of secondary electron yield from surface of a stainless steel Kh189 sample covered with titanium nitride is performed at stand “Recuperator”. This work is related to known problem of electron clouds formation in a vacuum chamber by a propagating charge particle beam. An original method of secondary electron yield measurement was developed in this experiment. The obtained results allow one to estimate efficiency of coating nitride titanium.     

Secondary electron emission and the detection of the vacuum level in ESCA

Samples irradiated in an ESCA spectrometer emit and receive intense electron fluxes due to secondary emission. Charging and surface potential of non conducting sample is mainly determined by these electron fluxes. The measurement of the secondary electron emission energy distribution (SEED) allows the determination of the sample vacuum level and in particular its work function in the case of conducting samples. Criteria to check the correctness of (SEED) measurements are presented.     

Axial emission profiles and apparent secondary electron yield in abnormal glow discharges in argon

This paper reports investigations of argon glow discharges established between flat disk electrodes, at pressure × electrode separation values between 45 Pa cm and 150 Pa cm. Parallel to the experimental studies the discharge is also described by a self-consistent hybrid model. The model uses as input data the measured electrical characteristics, this way making it possible to determine the apparent secondary electron emission coefficient. The model is verified through comparison of the measured and calculated spatial profiles of light emission, which are in good agreement for a wide range of conditions in the abnormal glow mode. Additionally, we investigate the dependence of the field reversal position on the discharge conditions and test the usual assumption that the position of the peak of emission closely coincides with the cathode fall - negative glow boundary. Received 21 May 2002 Published online 24 September 2002     

Energy-resolved analysis of ferroelectric electron emission from TGS using emission electron microscopy

Ferroelectric electron emission arises when the spontaneous polarization of a ferroelectric is switched due to the application of an electric field. In order to study the origin of emission and the related emission mechanism, space-resolved emission electron microscopy has been employed. The integral energy distribution of the emitted electrons from triglycine-sulfate surfaces has been investigated using a cylindrical sector analyzer and an imaging retarding field analyzer. Space-resolved emission photography and energy distribution measurements were obtained, revealing the effect of ferroelectric switching on the electric field distribution and hence on the emission process. Evidence of secondary electron emission from the metal electrodes has been found.     

Secondary scintillation yield from GEM and THGEM gaseous electron multipliers for direct dark matter search

The search for alternatives to PMTs as photosensors in optical TPCs for rare event detection has significantly increased in the last few years. In particular, in view of the next generation large volume detectors, the use of photosensors with lower natural radioactivity, such as large area APDs or GM-APDs, with the additional possibility of sparse surface coverage, triggered the intense study of secondary scintillation production in micropattern electron multipliers, such as GEMs and THGEMs, as alternatives to the commonly used uniform electric field region between two parallel meshes. The much higher scintillation output obtained from the electron avalanches in such microstructures presents an advantage in those situations. The accurate knowledge of the amount of such scintillation is important for correct detector simulation and optimization. It will also serve as a benchmark for software tools developed and/or under development for the calculation of the amount of such scintillation.     

Electron yield per ion charge-state correction for an ion collector with unsuppressed secondary electron emission

The electron yield per ion charge-state γ/q was measured for emission of electrons from clean polycrystalline gold induced due to impact of Ta ^q+ (11≤q≤41) ions with kinetic energy per chargeE _i/q from 15 keV/q to 150 keV/q. The dependence of γ on angle of incidence was analyzed with use of relation γ(ϑ)=γ₀ cos^−f ϑ. The fitting of experimental data gives a range of γ₀/q from 1 to 1.75 for Ta¹³⁺ and from 1.5 to 1.73 for Ta³⁹⁺. The dependence of γ₀/q onq andE _i is discussed with respect to measurement of ion currents emitted from laser-produced plasmas with an ion collector with unsuppressed secondary electron emission. This work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, U.S. Department of Energy, and by grant A1010819 from the Grant Agency of the Academy of Sciences of the Czech Republic.     

Visualization of field induced ferroelectric electron emission from TGS using emission electron microscopy

Field induced electron emission from triglycinesulfate (TGS) has been investigated using parallel imaging electron emission microscopy (EEM). The emission phenomenon has been induced by applying an ac electrical field up to 2 kV/mm to a single crystal of approximately 0.1 mm thickness. Emission patterns have been observed as a function of the applied field amplitude and of the crystal temperature. At voltages below the coercive field, no emission is visible. When approaching the Curie temperature, emission gradually disappears. This indicates an electron emission mechanism relying on the existence of a switchable ferroelectric phase. The information content of the images is discussed, an interpretation is given on the basis of existing theories. PACS 68.37.-d; 77; 77.80.Fm; 77.80.-e