Inelastic scattering of Ne atoms from a LiF(001) surface

Scattering experiments with a ²⁰Ne nozzle beam from a LiF(001) surface in the 〈100〉 azimuth are reported. The (11) and (1̄1̄) Bragg reflections show broad tails due to inelastic scattering. These tails can be attributed by time-of-flight measurements to single phonon scattering on acoustic modes. The inelastic contribution decreases rapidly with increasing energy of the phonons involved.     

Surface Corrugation in Rotational and Diffractive Scattering of O2 from LiF (001)

A quantum dynamic calculation on a five-dimensional O₂/LiF (001) model system is performed using the multi-configuration time-dependent Hartree method. The obtained results show that the mechanism of rotational and diffractive excitation in details: Comparison with the rotational excited state, the initially non-rotational state is seen to favor the inelastic scattering in the rotational excitation process. The surface corrugation can damp the quantum interferences and produce a greater amount of rotational inelastic scattering at the expense of the elastic process in the rotational excitation process. The diffraction process and the average energy transferred into the rotational and diffractive mode are also discussed.     

Translational heating of D(2) molecules thermally desorbed from Si(100) and Ge(100) surfaces

The translational energies of D(2) molecules thermally desorbed from the Si(100) and Ge(100) surfaces under a heating rate of 6 K/s have been measured. In contrast to the previous laser desorption study, results show a considerable translational heating; the observed translational temperature is about 3 times higher than the desorption temperature for both surfaces. This fact indicates that energy barriers for adsorption are present even in the desorption pathway. Detailed balance is applicable to the adsorption and desorption dynamics of hydrogen on the Si(100) surface.     

Inelastic scattering of helium from bulk longitudinal acoustic phonons in LiF(001)

The analysis of some recent time-of-flight spectra reported by Doak for He inelastic scattering from LiF(001) along the 〈110〉 azimuth reveals important contributions from bulk longitudinal acoustic (LA) phonons. The large intensity due to LA phonons compared to that due to Rayleigh waves is shown to be the result of resonance enhancement. The independent determination of the coupling to LA phonons and to Rayleigh waves permits an estimate of the atom-surface, potential softness.     

Inelastic Pion Scattering from 12C at 800 MeV/c

The differential cross section of the inelastic scattering of pion at 800 MeV/c fir the 3^- excited states of ¹²C is calculated by making use of eikonal approximation and the collective coordinate. The calculation indicates that the 3_- state of ¹²C is octupole vibrational state.The results are in agreement with experimental data.     

Cluster Model Analysis of Pion Elastic and Inelastic Scattering from 12C

Angular distributions of differential cross sections for the ¹²C(π ^±, π ^±)¹²C and ¹²C(π ^±, π ^±)¹²C^* reactions at pion kinetic energy ranging from 50 to 260 MeV have been analyzed with the 3α-particle model of ¹²C. The model provides good fits to a wide range of data. Differential cross sections for inelastic transitions to the (2^?+?; 4.44 MeV) and (3^???; 9.64 MeV) states in ¹²C are computed and the deformation lengths δ ₂ and δ ₃ are extracted. It is found that the extracted deformation lengths are sensitive to the nuclear model used and similar to the corresponding values found with other probes and nuclear models.     

Oxidation of heated diamond C(100):H surfaces

This paper extends a previous study (Pehrsson and Mercer, submitted to Surf. Sci.) on unheated, hydrogenated, natural diamond (100) surfaces oxidized with thermally activated oxygen (O^*₂). In this paper, the oxidation is performed at substrate temperatures from T_sub=24 to 670°C. The diamond surface composition and structure were then investigated with high resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), electron loss spectroscopy (ELS) and low energy electron diffraction (LEED).

The oxygen coverage (θ) increased in two stages, as it did during oxidation at T<80°C. However, there are fundamental differences between the oxidation of nominally unheated and heated diamond surfaces. This difference is attributed to simultaneous adsorption and rapid desorption of oxygen species at higher temperatures; the desorption step is much slower without heating. The initial oxidation rates were similar regardless of the substrate temperatures, but the peak coverage (θ) was lower at higher temperatures. For example, θ plateaued at 0.4±0.1 ML at 600°C. The lower saturation coverage is again attributed to oxygen desorption during oxidation. Consistent results were obtained on fully oxidized surfaces, which when heated in vacuum to T_sub=600°C, lost 60% of their adsorbed oxygen. ELS revealed few C=C dimers on the oxidized surfaces, and more graphitization than on unheated surfaces. Oxidation at elevated temperatures also increased the carbonyl to ether ratio, reflecting etching-induced changes in the types of surface sites. The carbonyl and C–H stretch frequencies increased with oxygen dose due to formation of higher oxidation states and/or hydrogen bonding between adjacent groups. The oxygen types did not interconvert when the oxidized surfaces were heated in vacuum. Oxygen desorption generated a much more reactive surface than heating-induced dehydrogenation of the smooth, hydrogenated surface.     

Inelastic changes during the formation of multilayers of C2H6 on Ag(110)

Adsorption of C₂H₆ on Ag(110) has been studied using inelastic He atom scattering. Changes in the inelastic spectrum have been observed for the first time during adsorption up to three monolayers. No changes occurred as a fourth layer was added. The spectrum moves to lesser energy values. The ratio of the energy gain and loss events varies from layer to layer (at constant surface temperature). The (00) peak also reflects some changes in intensity during adsorption.     

Si（100）（2×1）表面光学二次谐波强度随温度的变化关系

通过测量基频光波长为１．０６４μｍ时几个不同掺杂类型和掺杂浓度的Ｓｉ（１００）（２×１）样品表面反射二次谐波强度随温度的变化关系，说明在此波长上二次谐波不是来源于表面耗尽场的影响，而是来源于表面态电子。Ｓｉ（１００）（２×１）表面反射二次谐波强度反比于温度的平方。本文提出了一个简单模型，给出了初步解释。     

Elastic and inelastic scattering of slow positrons from a LiF(100) surface

The intensity profile for the elastic specular reflection of 5–100 eV positrons from a LiF(100) surface (ang1e of incidence 45°) has been measured using a simple time-of-flight spectrometer. The profile exhibits strong maxima below 25 eV and a smaller peak at 57 eV. Positron energy loss spectra have also been measured for a range of incident energies by retarding field analysis of the scattered beam. The mean energy loss appears to increase with increasing incident beam energy. Both the elastic and inelastic results are compared with similar data for slow-electron scattering obtained with the same apparatus.     

Photoelectron diffraction imaging for C2H2 and C2H4 chemisorbed on Si(100) reveals a new bonding configuration

A new adsorption site for adsorbed acetylene on Si(100) is observed by photoelectron imaging based on the holographic principle. The diffraction effects in the carbon 1s angle-resolved photoemission are inverted (including the small-cone method) to obtain an image of the atom's neighboring carbon. The chemisorbed acetylene molecule is bonded to four silicon surface atoms. In contrast to the C2H2 case, the image for adsorbed C2H4 shows it bonded to two Si surface atoms.     

中高能电子被分子的散射总截面与能量关系的研究

讨论了CO和CO2分子被电子散射的总截面与能量及其分子结构常数之间的关系, 证明了在不同的能量区间总截面与能量之间的关系不同, 但是在能量低于1 500 eV时可以利用键长、键角计算电子被分子散射总截面, 计算简便, 结果可靠, 并将CO2的结果与已有的拟合公式、实验数据进行了比较.