Anisotropy of secondary ion emission from a Ni4Mo single crystal

The azimuthal and polar angle distribution of Ni⁺ and Mo⁺ ions emitted from an ordered Ni⁴ Mo single crystal irradiated with 10-keV Ar⁺ ions was studied. Different azimuthal distributions for Ni⁺ and Mo⁺ ions emitted from the (001) Ni₄Mo face were detected; emission maxima were observed in 〈 011 〉 and 〈 001 〉 directions for Ni⁺ and Mo⁺ ions, respectively. It was shown that polar distributions of nickel’s secondary ions vary with its energy. The observed systematic features were explained by correlated collisions in the upper layers of a Ni₄Mo single crystal.     

Plasmonic secondary electron emission from alkali metals

One of the authors (Gornyi) has demonstrated earlier the possibility of plasmonic secondary electron emission (PSEE). Here electrons striking a solid substance excite in it plasmons, which then break up and in turn excite electrons. These electrons, upon being emitted into vacuum, form clusters of secondary electrons with definite energy levels. When energy-loss spectra of electrons are compared with energy spectra of secondary electrons and with work-function curves for secondary electrons, all of them plotted for lithium, sodium, and potassium, then the occurrence of the PSEE phenomenon in these metals can be established. The PSEE explains the peaks along the energy spectra and the work-function curves for secondary electrons. These peaks were not understood before.     

Theoretical results on electron emission from copper surfaces

Some results of calculations on the angular distribution of electrons emitted from the (100) and (110) surfaces of Cu are presented. The emphasis is on final state effects in describing (i) emission from sources located in dilute overlayers and (ii) at lattice sites in the bulk. For the case of a dilute overlayer a strong similarity is observed in the results obtained for single and for multiple scattering by the bulk.     

Ion bombardment induced amorphous layers on single crystal stainless steel-a combined rutherford backscattering and transmission electron microscopy study

Abstract

Decomposition reactions of NaClO₃, KClO₃, and KIO₄ induced by 3 keV Ar⁺ ions and 1254 eV X-rays are investigated by X-ray photoelectron spectroscopy (XPS). The reactions lead to the formation of binary halides with preferential losses of oxygen. The decomposition pattern, monitored at the various stages of reaction, indicates almost direct changeover to the final products with only a few intermediate species formed. Product abundancies are compared for the ion, X-ray, and electron induced reactions and discussed in relation to the various radiation induced reaction mechanisms.     

Ion irradiation induced nano pattern formation on TiO2 single crystal

Nanodots have been fabricated on rutile TiO₂(1 1 0) single crystals using Ar ion beam. Ion beam sputtering creates oxygen vacancies, leading to a 45 nm thick Ti rich layer, on the surface. Post-sputtering, rutile TiO₂ also exhibits a decrease in the inter planar separation along [1 1 0] direction. Additionally, blueshift in the E_g Raman mode, representing the vibrations of oxygen atoms along c-axis, is also observed. Both these results suggest the development of a compressive stress along c-axis upon sputtering. Enhancement in intensity of A_1g Raman mode also indicates modification in TiO vibrational influence.     

NMR at single crystal surfaces

15 sites on 1 cm². To overcome this for the important class of alkali adsorbates on metals and semiconductors, two methods are presented. Common to both is the preparation of a highly nuclear spin-polarized atomic beam of ⁶Li in the one case and ⁸Li in the other. The latter isotope is radioactive and undergoes a β-decay with a half-life of 0.84 s. Li adsorbed on the close-packed Ru(001) surface is investigated. The longitudinal relaxation time, T₁, is the main observable and is used to deduce the local electronic density of states [LDOS(E_F,r=0)] and Li diffusion barriers. The second experiment uses ⁶Li as an adsorbate, also studied on Ru(001). The nuclear polarization is measured by beam foil spectroscopy. A novel particle detected (photon counting) Fourier transform NMR technique is demonstrated. This is done by observing the time-dependent flux of circularly polarized light emitted behind the foil after a 90° pulse has been employed at the surface. Electric field gradients and transverse relaxation times, T₂, are thus determined. A large difference between T₁ and T₂ is traced to the dimensionality of the system. Received: 21 March 1997/Accepted: 12 August 1997     

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     

Evidence for electron emission stimulated desorption from negative electron affinity GaAs surfaces

While desorption from surfaces caused by impinging electrons (electron stimulated desorption) is a well-established effect, electrons to be emitted also may give rise to desorption from an emitting surface (electron-emission stimulated desorption). Evidence for this effect is derived from data on the degradation of electron emission from negative electron affinity GaAs surfaces. The time dependence of the degradation is calculated, and agreement with the observed linear time dependence is found. Using the experimental degradation ata, the desorption cross section for the electron-emission stimulated desorption is obtained as 2 × 10^?25 cm².     

Theory of secondary electron emission

The fine structure in angle-resolved secondary electron spectra is shown to be related to the total reflectivity in low-energy electron diffraction (LEED). Theoretical results for tungsten are compared with experimental data. For non-normal emission, spin-orbit coupling is predicted to produce spin polarization of the emitted electrons.     

Kinetics of electron emission from the TGS ferroelectric crystal

A study is reported on the behavior in time of the electron emission current density from a triglycine sulfate ferroelectric crystal measured at fixed temperatures. This relation is shown to have an exponential nature. The characteristic emission relaxation time depends on temperature and decreases as one approaches the phase-transition point. The magnitude of the relaxation time and its temperature dependence can be accounted for both within a mechanism in which the emission decay is associated with the emptying of surface electron states, and in terms of the Maxwellian relaxation process.     

Deformation enhanced photoemission from oriented aluminum single crystal surfaces

Plastic-deformation-enhanced UV photoemission from oriented single crystal surfaces of aluminum has been studied. Clean single crystals of aluminum oriented in [111] direction were flexurally fatigued under UHV conditions and for the first time photoelectron energy distribution curves were obtained as a function of fatigue life using the Hel (21.2 eV) and the HeII (40.8 eV) photon lines. The integrated photocurrent was measured as a function of fatigue life using the photon lines from helium and argon sources. A progressive decrease in work function was observed as the specimen was subjected to increasing number of fatigue cycles. At a strain amplitude of ±0.2%, a drop of 0.2 eV in the work function occurred after 3000 fatigue cycles. Further, significant changes in aluminum valence band emission as a result of fatigue have been observed along with the formation of slip-steps on the surface of the aluminum specimen as seen under the scanning electron microscope. This alteration in the surface microgeometry caused by fatigue is believed to be responsible for the observed changes in the work function and the electronic band structure. The change in the total integrated photoyield caused by fatigue is thus determined by work function and valence band changes.     

固体金属二次电子发射的Monte-Carlo模拟

二次电子的发射在生产实践中有着广泛的应用,但其相关测量结果受实验环境和实验仪器的影响很大．在实验中难以精确测量．所以本文建立了一个包含二次电子激发、在固体内部传输和最后逸出固体表面的二次电子系统模型．采用Monte-Carlo的模拟方法仿真二次电子运动轨迹,定量分析二次电子的发射系数和能谱分布．并探讨它们与一次电子的入射角度和入射能量的关系．仿真结果表明：本文建立的二次电子系统模型能较好地反映实际情况．通过该模型仿真,可以定量得到二次电子发射系数和能谱分布与一次电子的入射能量和入射角度的关系．     

Ultraviolet photon induced secondary electron emission from TiO2: Theory and experiment

A theory of ultraviolet photon induced secondary electron emission has been developed which takes into account both the space and energy dependence of electron sources as well as multiple scattering. Ultraviolet photoemission experiments on single crystal surfaces of TiO₂ show that the secondary electron distribution is quite sensitive to the work function of the surface and has distinctive structure. The theory reproduces these features in terms of properties of the empty conduction band states.     

The perturbation theory of diffraction effects in secondary electron emission on the crystal surface

An explicit expression, based on the Born approximation, has been obtained for the density distribution of ～1 keV primary electrons inside a single crystal. The crystal is considered as made up of atomic layers perpendicular to the crystal surface. The primary electron density at the center of each layer, integrated over the depth of emergency, is assumed to be responsible for effects of secondary electron emission. The azimuthai density dependencies calculated with allowance for all the diffracted waves demonstrates a strong localization at small azimuthai angles. This effect is treated to be of a waveguide nature.     

Computer simulation of fast recoil ejection from single crystal surfaces

The computer simulation program MARLOWE is used to analyze the most probable surface recoil processes leading to ejection of atoms from (001) gold surfaces subsequent to the irradiation with 20 keV argon atoms. The occurence of two-and threedimensional mechanisms resulting from high-energy recoils involving one and two atomic layers is discussed for atoms ejected in a direction parallel to the plane of incidence. Generally, a close correspondence is found between the mechanisms involved and the features in the energy distributions. The occurence of direct and deflected recoils is confirmed, as well as mechanisms involving the generation of displacements in the two first atomic layers. The dependence of these mechanisms on the conditions of incidence and the ejection direction is investigated. It is suggested that three-dimensional effects, although dominating, mainly contribute to the background in the energy distributions. The intensities in the features in the energy distributions were found to be strongly influenced by shadowing; affecting both the one-and two-layer processes. The influence of thermal vibrations, surface defects and impurities is briefly examined.     

Space-charge limitation of secondary electron emission

The paper deals with the calculation of the potential minimum due to the emission of true secondary electrons from a plane electrode. The results together with the corresponding limitation of the emission current are given in the form of graphs because an analytical solution of the problem is impossible.