A new charge-correction method in X-ray photoelectron spectroscopy

The 2p_{$\text{3}\text{2}$} binding energy (242.3 eV) of Ar implanted in insulating materials is available to correct for charging shifts. Argon ions hav materials SiO₂ and soda glass. In each case the charging shift for Ar 2p_{$\text{3}\text{2}$} electrons agrees exactly with those for core-level elec The charge-corrected binding energies of the insulating materials permit the identification of atomic chemical states. Ion-induced reduction of the ins investigations.     

Structure relations in the x-ray photoelectron spectra of three chromium compounds

The chemical shift in electron binding energy, magnetic splitting of electron shells, and structures in the valence band are examined for chromium in the 3 + and 6 + oxidation states.The splitting of the Cr 3s energy level is associated with the appearance of a sharp Cr 3d line in the valence band. The relative chemical shift in the Cr 2p_{$\text{3}\text{2}$} line between Cr₂O₃ and K₂Cr₂O₇ is verified in the mixed compound KCr₃O₈ which contains both types of Cr ions, and the structure of this compound is verified by the X-ray photoelectron spectra. The spin-orbit intensity ratio of the 2p doublet of Cr⁶⁺ is 3, instead of the theoretical value of 2, and the spin-orbit splitting is less than for Cr³⁺. In the 3p level of Cr the relative chemical shift is 3.5 eV whereas for the 2p_{$\text{3}\text{2}$} level the shift is only 2.4 eV. The differences in chemical shift and intensity ratio can not be explained.     

X-ray photoelectron spectroscopic study of the physical adsorption of xenon and the chemisorption of oxygen on tungsten (111)

X-ray photoelectron spectroscopy (ESCA) has been used to study the physical adsorption of Xe and the chemisorption of oxygen by W (111). An ultrahigh vacuum ESCA spectrometer has been modified such that thermal desorption behavior from the W (111) crystal can be directly compared with ESCA spectra of the adsorbed species. In addition, since the work function of a W (111) crystal covered with one monolayer of Xe is accurately known from previous work, the binding energy of the $\text{Xe}\text{(3}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}$ adsorbate level can be accurately compared to the gaseous $\text{Xe}\text{(3}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}$ level.When Xe is physisorbed to 1 monolayer the $\text{Xe}\text{(3}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}$ level exhibits a binding energy (relative to the vacuum level) which is 2.1 eV below that found for Xe (g). At lower Xe coverages the shift becomes monotonically greater, approaching 2.6 eV at a Xe coverage of 0.05. This 0.5 eV shift downward is accompanied by an increase of only 0.05 eV in adsorption energy as coverage decreases, and may be partially caused by the presence of ~ 10–20 % of extraneous adsorption sites other than W (111) which adsorb Xe with higher adsorption energy. The adsorption energy of Xe may also be increased by coadsorption of oxygen and the $\text{Xe}\text{(3}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}$ binding energy exhibits a corresponding shift downward as adsorbed oxygen coverage is increased to θ_o = 0.5. Electronic relaxation processes affecting the final state are dominant factors in determining the magnitude of the chemical shift upon adsorption, in agreement with the predictions of Shirley. The magnitude of the relaxation effect seems to be very sensitive to small changes in Xe adsorption energy. Similar effects have been seen for chemisorption of CO.The adsorption of O₂ at 120 K by W (111) yields a single broad O(1s) peak whose line-width decreases with increasing coverage. The final spectra at θ_o = 1 monolayer are very similar to those obtained at temperatures of 300 K or above on polycrystalline tungsten.     

A study of the (00) LEED beam intensity at normal incidence from CdS(0001), Cu(001), Cu(111), and Ni(111)

A Faraday cage apparatus is used for the measurement of the (00) LEED beam intensity, I₍₀₀₎, and the total secondary emission coefficient, δ(E_k), for angles of incidence from 0° ± 2° to 8° ± 2°, with an energy resolution of ± 0.037 of the incident beam energy, in the energy range 1 to 200 eV. The data are normalized and expressed as a fraction of the incident beam intensity. The basic principle of operation is the separation of the incident and specularly diffracted beams in a uniform magnetic field. Monolayer, or in-plane, resonances associated with the emergence of nonspecular beams, as well as beam threshold minima, are observed in I₍₀₀₎ at normal incidence from clean CdS(0001), Cu(111), and Ni(111). Some major differences are observed in the I₍₀₀₎ profiles for the clean (111) surfaces of nickel and copper. All secondary Bragg peaks, except the 2$\text{2}\text{3}$ order, have greater intensities for Ni(111) in the energy range 50–150 eV, thus indicating that the atomic scattering cross-section for electrons in this energy range is larger for nickel than for copper. For the (111) surface of nickel, the (11) resonance is missing, but the (10) resonance and all $\text{1}\text{3}$ order secondary Bragg peaks between the second and fifth orders are observed. For Cu(111) both the (10) and (11) resonances are observed, but the $\text{1}\text{3}$, $\text{2}\text{3}$, 1$\text{2}\text{3}$, and 3$\text{1}\text{3}$ order secondary Bragg peaks are missing in this energy range. These data indicate that multiple scattering with evanescent intermediate waves, or “shadowing”, is predominate on the (111) surfaces on nickel and copper for energies above 30 eV, and that below 30 eV multiple scattering with propagating intermediate waves is predominate on Cu(111). Correlation of the (00) beam intensity profiles from clean Ni(111) at 0°, 2°, and 6° with the intensity profiles of the (10). (1&#x0304;0), and (11) non-specular beams is nearly one-to-one from 30 eV to 100 eV, thus supporting the dynamical theories of LEED in which peaks in the (00) beam are expected to occur at nearly the same energies as peaks in the non-specular beams.     

X-rays from antiprotonic helium in helium gas

X-ray transitions to the 4F, 3D, and 2P atomic levels of p?He have been observed with antiprotons stopped in He gas at 4 and 1.1 atm NT. The population by radiative transitions of the 3D level in gas Y_M(4atm) = (28±14)% and Y_M(1.1 atm) = (43±22)% exceeds by more than one order of magnitude that measured in liquid He. The annihilation width of the 3D level Γ^a_3D = 2.8±1.0 × 10^?3eV is determined from the ratio between the numbers of X-rays feeding and depopulating the 3D level. The strong-interaction shift of the 2P level ε(2P) = ?14±6 eV is obtained by inputting the $\text{p}\text{He}$ experimental X-ray yields into a cascade calculation, the results of which are in good agreement with well-established data from muonic, pionic, and kaonic helium.     

Site-selective adsorption of xenon on a stepped Ru(0001) surface

The adsorption of xenon has been studied with UV photoemission (UPS), flash desorption (TDS) and work function measurements on differently conditioned Ru(0001) surfaces at 100 K and at pressures up to 3 × 10^?5 Torr. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) served to ascertain the surface perfectness. On a perfect Ru(0001) surface only one Xe adsorption state is observed, which is characterized by$\text{Xe}\text{5}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$,$\text{1}\text{2}$ electron binding energies of 5.40 and 6.65 eV, an adsorption energy of E_ad≈ 5 kcal/mole and dipole moment of μ'_T ≈ 0.25 D. On a stepped-kinked Ru(0001) surface, the terrace-width, the step-height and step-orientation of which are well characterized with LEED, however, two coexisting xenon adsorption states are distinguishable by an unprecedented separation in$\text{Xe}\text{5}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$,$\text{1}\text{2}$ electron binding energies of 800 meV, by their different UPS intensities and line shapes, by their difference in adsorption energy ofΔE_ad ≈ 3 kcal/mole and finally by their strongly deviating dipole moments of μ_S = 1.0 D and μ_T = 0.34 D. The two xenon states (which are also observed on a slightly sputtered surface) are identified as corresponding to xenon atoms being adsorbed at step and terrace sites, respectively. Their relative concentrations as deduced from the UPS intensities quantitatively correlate with the abundance of step and terrace sites of the ideal TLK surface structure model as derived from LEED. Furthermore, ledge-sites and kink-sites are distinguishable via E_ad. The E_ad heterogeneity on the stepped-kinked Ru(0001) surface is interpreted in terms of different coordination and/or different charge-transfer-bonding at the various surface sites. The enormous increase in Xe 5p electron binding energy of 0.8 eV for Xe atoms at step sites is interpreted as a pure surface dipole potential shift. —The observed effects suggest selective xenon adsorption as a tool for local surface structure determination.     

Superradiation from non-ideal plasmas in electric field

An effect of external static electric field on emission of radiation from non-ideal plasmas of erosion focus has been experimentally observed. An order-of-magnitude increase in radiation intensity for spectral interval hv = 40 ? 350 eV with electric field increasing up to 10³V/cm has been found for plasmas with $\text{ξ}\text{Z}\text{?1}$, where ξ is the number of electrons in Debye sphere, Z = 2 ? 3 is the stage of ionization. The energy emitted has been several times higher than the black body energy for the same spectral interval at maximum electric field achieved. The effect vanishes at $\text{ξ}\text{Z}\text{?10}$.     

Room temperature adsorption and growth of Ga and In on cleaved Si(111)

Low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and photoemission yield spectroscopy (PYS) measurements have been performed on a set of ultrahigh vacuum cleaved Si(111) surfaces with different bulk dopings as a function of Ga or In coverage θ. The metal layers are obtained by evaporation on the unheated substrate and θ varies from zero to several monolayers (ML). First, the 2×1 reconstruction of the clean substrate is replaced by a $\text{3}\text{×}\text{3}$ R30° structure at $\text{1}\text{3}$ ML, meanwhile the dangling bond peak at 0.6 eV below the valence band edge E_vs is replaced by a peak at 0.1 eV for Ga or 0.3 eV for In, below E_vs. At the same time, the ionization energy decreases by 0.4 eV (Ga) or 0.6 eV (In), while the Fermi level pinning position gets closer to the valence band edge by about 0.1eV. Upon increasing θ, new LEED structures develop and the electronic properties keep on changing slightly before metallic islands start to grow beyond θ ～1 ML.     

Quantum size effect in electron transmission through Cu and Ag films on W(110)

The transmission coefficient of very low energy electrons ( ? 10 eV) normally incident on (111) epitaxial films of Cu and Ag on W(110) is modulated by interference between scattering from the vacuum/metal and metal/metal interfaces. Comparison with calculations of free-electron scattering from a one-dimensional potential model, in which grading of the metal/metal interface is represented by a smoothing of the potential step, indicates that this interface is abrupt within approximately one layer spacing. We obtain a value of 11.0 (8.0) ± 1.0 eV for the inner potential of Cu (Ag) and mean free path lengths of $\text{39 ± 8}\text{A}\text{?}$ at an energy of 7.0 eV relative to the Fermi energy and $\text{29 ± 11}\text{A}\text{?}$ at 9.0 eV for Cu, and $\text{25 ± 10}\text{A}\text{?}$ at 7.5 eV for Ag. Work function values are obtained by the field emission retarding potential technique. We investigate the effects of the surface potential barrier, inelastic scattering and surface roughness, and evaluate the validity of the one-dimensional model presented.     

High resolution proton scattering from 42Ca

Differential cross sections were measured for ⁴²Ca(p, p) at four angles between E_p = 1.2 and 3.0 MeV, with an overall energy resolution of 325 eV. Spins, parities and proton widths were extracted for 170 resonances. Two analogue states were identified and spectroscopic factors determined. The nearest neighbor spacing distributions were analyzed. Proton strength functions were determined for $\text{1}\text{2}$⁺, $\text{1}\text{2}$^? and $\text{3}\text{2}$^? resonances.     

Delayed onset of 4d photoemission relative to the giant 4d photoabsorption of La

For the giant 4d photoabsorption of La, both the total photoabsorption spectrum and the N_4.5-derived Auger emission intensity spectrum increase significantly above hν ? 112 eV, with spectral peaks at hν = 118 and 119 eV, respectively. However, the predominant 4d photoemission partial cross section shows a delayed onset of ～ 4 eV, with a peak at hν = 121 eV, while the 5s, 5p, and 5d partial cross sections all show a strong resonant enhancement at lower energies, with spectral peaks at hν = 116.6 eV. These results are compared with a recent many-body calculation for Ce. The photon energy dependence of the La 4d_{$\text{5}\text{2}$}/4d_{$\text{3}\text{2}$} photo-emission branching ratio is consistent with a “final-state model.”     

Subject index

Field-emission energy distributions from the (100) facet of Ge exhibit a double peak. Comparison of the measured distributions with theory shows that the lower energy peak arises from valence band emission while the higher energy peak represents emission from a band of surface states overlapping the valence band. The field-emission energy distribution from the surface states is a maximum at 0.18 eV above the valence band edge. The surface of the emitter is found to be 4kT degenerate n-type with an applied field of $\text{3 × 10}{}^7\text{V}\text{cm}$. This implies 6.3 × 10¹² surface states/cm² at the center of the clean, annealed (100) facet. The effect of the applied field is to broaden the surface state distribution. The degree of broadening can be accounted for by the Stark effect. Adsorption of contamination from the vacuum system ambient or geometric alteration of the surface from the annealed end form reduces the number of surface states.     

Looking at DIC through an l-window

The energy spectra and angular distributions observed in deep inelastic collisions (DIC) between heavy ions are usually ascribed to statistical fluctuations caused by the large excitation energies involved. We give arguments that fluctuations due to qiiantal effects may also be important and derive an expression for the double differential cross section $\text{d}{}^2\text{σ}\text{dθdQ}$ (θ is the scattering angle, Q the energy loss) which contains only these latter fluctuations. The typical features observed are reproduced by the theory which, apart from an overall normalization factor, contains just one parameter.     

High-resolution photoemission study of adatom bonding effects: Cl (√2 × √2) R 45° on Cu (100)

We have investigated photoemission from an ordered $\text{(}\text{2}\text{×}\text{2}\text{) R 45°}$ Cl-overlayer on Cu (100) at good angular (Δθ ? 1°) and energy (ΔE = 100 meV) resolution. We observe two prominent adsorbate- induced features at 1.95 eV (FWHM ≈ 100 meV) and 5.4 eV (0.65 eV) below E_F. By determination of their angular momentum character, their spatial orientation and their energy dispersion, they are identified as “antibonding” and “bonding” resonances, respectively. Significant modification of the Cu d-band emission is observed and interpreted in terms of substrate orbitals which are involved in bonding.     

Electrical conduction and 1ƒ noise in Li-DOPED MnO

Electrical resistivity, thermoelectric power and current noise were measured on Li-doped MnO single crystals in the temperature range from 300 to 1000 K. Below 700 K the crystals are p-type and the activation energy of the resistivity is 0.75 eV. Around 700 K the activation energy changes from 0.75 to 1.25 eV owing to a change from p- to n-type conduction. The depth of the Li acceptor is found to be 0.65 eV. From resistivity and thermoelectric power data it is concluded that the bandgap in first approximation can be written as E_s(T) = E_o ? γT between 750 and 1000 K, with E_o = 1.9 eV and γ = 6 × 10^?4 eV/K. The current noise spectra show $\text{1}\text{?}$ noise. The magnitude of the $\text{1}\text{?}$ noise is strongly temperature dependent. From the noise data it is deduced that E_o = 2.2 eV and γ = 10^?3 eV/K in the temperature range 430–700 K.     

Intersections of quasi-energy levels in the relativistic theory of multiply charged ions

The relativistic generalization of the quasi-energy method is given with the help of which the influence of an alternating electric field on the energy levels (2 $\text{1}\text{2}$ 0), (2 $\text{1}\text{2}$ 1) of multiply charged H-like ions is investigated. Intersections are found of quasi-energy levels in external fields with frequencies ω₀ ? ΔE_L and definite values of the field amplitude.     

Angular distributions of auger electron emission: Clean and gas-adsorbed polycrystalline Ni surfaces

The excitation angle (β) and emission angle (θ) dependences of the Ni M₂,₃VV (61 eV) and Ni L₃VV (850 eV) Auger emissions from clean polycrystalline Ni surfaces, and the S L₂, ₃ M₂, ₃M₂, ₃ (150 eV) Auger emission from S-adsorbed poly-Ni surfaces have been investigated. In the case of Ni (61 eV) and S Auger emissions, the β-dependence shows the $\text{1}\text{cos β}$ distribution, while a significant deviation from $\text{1}\text{cos β}$ is observed for Ni (850 eV) Auger emission. The cosθ distribution and the intermediate between isotropic and cosθ distributions are observed for Ni (61 eV), and for Ni (850 eV) and S Auger emissions, respectively. Those results have been found to be in fairly good agreement with the calculations based on the simple continuum model without consideration of the diffraction effect and the inherent anisotropic emission.     

Optical spectroscopy of surfaces: Reflectance studies of chemisorption

A high precision technique has been used to study the small changes in near-normal incidence reflectance R caused by chemisorption of gases on an atomically clean metal surface maintained in ultrahigh vacuum. Examples are given for O₂, CO, and H₂ on Mo(100) in the photon energy range 1.9 <?ω < 4.8eV. The relative reflectance change $\text{ΔR}\text{R}$ is negative and reaches as much as 1%. Structure that appears in ΔR(e), where e=exposure (pressure × time), is attributed to different binding configurations of the adatoms as observed, e.g., in LEED experiments. The dependence of $\text{ΔR}\text{R}$ on ?ω suggests the presence of adsorbate-induced surface states within a few eV of the Fermi energy. Possible approaches to determining the dielectric function of the surface region from the data are discussed.     

The input mobility of an infinite circular cylindrical elastic shell filled with fluid

The force input mobility of an infinite elastic circular cylindrical shell filled with fluid is derived by using the spectral equations of motion. Mobilities are evaluated and their physical interpretations are discussed for a steel shell of thickness $\text{h}\text{a}\text{= 0·05}$ filled with water and vibrating in the n = 0, 1 and 2 circumferential modes. The results are subsequently used to analyze the related situations of wave transmission through a radial ring constraint and the far field vibrational energy distributions between the contained fluid and the shell wall for line and point driving forces.     

Energies of Cu1+ ions sputtered from Cu by very low energy (50 eV < E < 1 keV) Inert gas ions

He⁺, Ne⁺ and Ar⁺ ions with energies E₁ between 50 and 1000 eV were used to bombard a polycrystalline Cu target at an angle of 45°. The energies, E₂, of the Cu₁⁺ ions sputtered at 90° to the primary beam were investigated using a UHV magnetic sector mass spectrometer. The maxima of the energy distributions as measured by the instrument, were at values of E₂ of about 4 eV (±1 eV), nearly independent of e₁ and primary ion mass. Plots of log N(E₂) versus log E₂ displayed limited linear portions over which the functional dependence of N(E₂) is proportional to E₂^?0.5. Plots of the average secondary ion energy, ē₂, versus the energy transferred by the primary ion to a Cu atom in a direct collision $\text{([}\text{4m}{}_1\text{m}{}_2\text{(m}{}_1\text{+ m}{}_2\text{)}{}^2\text{]E}{}_1\text{)}$, indicate that ē₂ increases linearly with transfer energy up to a transferred energy of about 200 eV, independent of primary ion mass. Above about 200 eV transferred energy, ē₂ asymptotically approaches values which depend upon primary ion mass. At transferred energies below about 200 eV, the collision kinematics in the fust few collisions appears to dominate the emission process.