Ion secondary electron emission from Al2O3 and MgO films

Coefficients of ion induced secondary electron emission (ISEE) γ from thin films of Al₂O₃ and MgO have been measured for argon ions in the energy range between 0–3 keV. Dionne's equation for secondary electron emission, which consists of production and emission terms has been modified to explain the kinetic emission of ISEE. The production term for ion induced secondary electrons has been separately formulated, taking account of the energy loss of primary ions, while the process of emission is considered to remain the same as in SEE. The escape depth λ_S and emission probability B were obtained from the SEE data and were used, along the range value of incident ions, to calculate the emission term in ISEE. The modified form of the equation was used to evaluate theoretically expected ISEE yield energy curves. Fairly good correlation is observed in theoretical and experimental curves which supports the validity of the proposed theoretical model.     

反冲原子对低速离子轰击Si表面时电子发射产额的影响

在兰州重离子加速器国家实验室电子回旋共振离子源高电荷态原子物理实验平台上,用低能(0.75keV/u≤EP/MP≤10.5keV/u,即3.8×105m/s≤vP≤1.42×106m/s)He2+,O2+和Ne2+离子束正入射到自清洁Si表面时二次电子发射产额的实验结果.结果表明电子发射产额γ近似正比于入射离子动能EP/MP.在相同动能下,γ(O)γ(Ne)γ(He),对于原子序数ZP比较大的O2+和Ne2+离子,ZP大者反而γ小,这与较高入射能量时的结果截然不同.通过计算不同入射能量下入射离子的阻止能损S,发现反冲原子对激发二次电子的作用随入射离子能量的降低显著增大,这正是导致在较低能量范围内二次电子发射产额与较高入射能量时存在差异的主要原因.     

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.     

Infrared emission from surfaces under low-energy electron impact

The infrared photon emission from metal surfaces stimulated by the impact of low-energy electrons of kinetic energies between 0–10 eV has been measured. The results are presented as isochromat spectra from clean Ag and Na surfaces under different temperatures. Some IR emission features have been associated tentatively with inverse photoemission processes.     

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.     

多晶体二次电子的角度分布

 根据二次电子发射的主要物理过程,推导了内二次电子到达多晶表面并逸出的几率的角度分布、斜射入多晶的高能原电子产生的二次电子的角度分布和由背散射电子产生的二次电子的角度分布。同时,推导了高能原电子轰击多晶产生的二次电子的角度分布公式,该公式表明多晶的二次电子遵循余弦分布,且与原电子的入射角无关。分析结果表明: 在内二次电子最大逸出深度范围内,如果由射入多晶的原电子和背散射电子产生的内二次电子数是常数, 则多晶的二次电子的角度分布遵循余弦分布;如果由射入多晶的原电子和背散射电子产生的内二次电子数越来越少,则多晶的二次电子发射角度分布随出射角减少得比出射角的余弦值更慢;如果由射入多晶的原电子和背散射电子产生的内二次电子越来越多,则多晶的二次电子发射角度分布随出射角减少得比出射角的余弦值更快。     

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.     

多晶体二次电子的角度分布

根据二次电子发射的主要物理过程,推导了内二次电子到达多晶表面并逸出的几率的角度分布、斜射入多晶的高能原电子产生的二次电子的角度分布和由背散射电子产生的二次电子的角度分布。同时,推导了高能原电子轰击多晶产生的二次电子的角度分布公式,该公式表明多晶的二次电子遵循余弦分布,且与原电子的入射角无关。分析结果表明: 在内二次电子最大逸出深度范围内,如果由射入多晶的原电子和背散射电子产生的内二次电子数是常数, 则多晶的二次电子的角度分布遵循余弦分布;如果由射入多晶的原电子和背散射电子产生的内二次电子数越来越少,则多晶的二次电子发射角度分布随出射角减少得比出射角的余弦值更慢;如果由射入多晶的原电子和背散射电子产生的内二次电子越来越多,则多晶的二次电子发射角度分布随出射角减少得比出射角的余弦值更快。     

Thermal desorption of metals from tungsten single crystal surfaces

After a short review of the experimental methods used to determine desorption energies E and frequencies v the assumptions underlying the theoretical analysis of the experimental data are discussed. Then recent experimental results on the flash desorption of Cu, Ag and Au from clean, well characterized W {110} and {100} surfaces are presented and analysed in detail, in particular with respect to the coverage dependence. The results obtained this way clearly reveal the limitations of previous analysis methods and of the experimental technique per se (such as structure and phase changes below and in the temperature region in which desorption occurs). Furthermore the need for more theoretical work to understand the large changes of v and E with coverage and the so-called “compensation effect”, i.e. the relation between In v and E, becomes evident.     

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.     

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.