The core-level photoexcitation and photoionization of SF6 were studied in the vicinity of the resonances below and above the S 2p threshold. The decay channels of the S 2p→6a1g discrete excitation were characterized, with decay leading mostly to valence-shell satellites. The S 2p continuum data show an oscillatory asymmetry parameter β(S 2p) near threshold that is virtually identical to β(Si 2p) in SiF4. It also resembles—but differs from—theoretical curves for β(S 2p) in atomic sulfur and in SF6. Data at the feature assigned as an eg shape resonance indicate strong multielectron properties for this state, because a resonance in the S 2p satellite is observed at the same photon energy as the main-line resonance. We propose a unified model which generally includes configuration interaction both in the continuum-state manifold and between discrete doubly excited states and the continua, to explain this unexpected satellite behavior. Finally, the S(L2,3VV) Auger electron asymmetry parameter shows no significant deviation from zero near the t2g and eg shape resonances.

A temporally sensitive ionization scheme is used in conjunction with a position-sensitive detector to measure simultaneously energy- and angle-resolved distributions of sputtered neutral atoms. We report results for 5-keVAr+ ion-bombarded Rh{111} single-crystal surfaces, both clean and with a p(2×2) overlayer of oxygen atoms. The angular distributions and their variation with ejection kinetic energy are shown to give information about simple collision sequences that produce directionally preferential atom ejection. The changes that occur in the ejection distributions upon O atom adsorption suggest that O atoms occupy the ‘‘expected’’ sites, the sites that would be occupied by Rh atoms in a new monolayer.

The trajectories of neutral particles ejected from surfaces bombarded by keV projectiles have been precisely determined. The neutrals are detected with high efficiency by selective postionization of the desorbed atoms by laser initiated multiphoton resonance excitation. By employing a pulsed beam of primary Ar+ ions, the velocity of the desorbed atoms may be selected by appropriate timing between this pulse and the pulse of ionizing laser radiation. These ions are then imaged to a position-sensitive detector for angle determination. Under present conditions we can detect neutrals whose kinetic energies vary from 0.2–50 eV into a total enclosed angle of over 100° using a total dose of <1012 incident Ar+ ions/cm2. Results are illustrated for polycrystalline Rh, Rh{111}, and Rh{111} covered with adsorbed oxygen. The measurements also illustrate a number of difficiencies of theoretical treatments of the particle/solid interaction problem.

Angle-resolved energy distributions and energy-resolved angle distributions for atoms desorbed from polycrystalline In and Rh foils bombarded by 5-keV Ar + ions are reported. It is possible to record these data under low dose conditions using multiphoton resonance ionization detection for the neutrals after they have left the target. The results show that angle or energy integrated data agree reasonably well with energy transport theories, an observation confirmed by many previous workers. The energy-resolved angle distributions for both In and Rh, however, exhibit a near cos θ distribution for low energy particles and a near cos 2 θ distribution for the higher energy particles. The angle-resolved energy distributions also exhibit a shift in the peak position to lower values as θ is increased from 0 to 75°. Neither effects are predicted by theory. The results are discussed in terms of the anisotropy of the momentum distribution which apparently exists inside the solid during the evolution of the collison cascade.

The design and application of a detector is described, which is capable of simultaneously measuring energy and angular distributions of neutral particles desorbed from surfaces. Specific applications to ion bombardment studies are presented. The detector utilizes the state selectivity, sensitivity, and pulsed characteristics of multiphoton resonance ionization as a time-of-flight sensitive postionization technique. A microchannel-plate element allows position-sensitive detection of the laser-ionized particles. Sample data are presented for ground-state Rh atoms desorbed from clean, ion-bombarded Rh foil and Rh(111) surfaces.

Measurements of energy- and angle-resolved distributions of neutral atoms desorbed from ion-bombarded single crystals are obtained using a novel multiphoton resonance ionization scheme. Experimental results are compared successfully to molecular dynamics calculations of the ion/solid collision event. This comparison suggests that the distributions from Rh{111} are sensitive to the crystal structure of the top atomic layer. Calculated distributions match experimental ones when oxygen atoms are assumed to adsorb in 3-fold hollow (c-site) bonding configurations.

It is clear from the scope of this symposium that major advances have been achieved in our ability to detect and characterize the uncharged species that desorb from ion bombarded surfaces. The use of plasma sources and lasers have been particularly useful in enhancing the sensitivity of detection over the traditional weight-loss methods. In this paper, we describe the use of multi-photon resonance excitation as a post-ionization technique for detecting desorbed neutrals with high sensitivity and selectivity. The discussion will focus on where this approach is most likely to be successful and where it should probably not be utilized. Examples of present applications will be cited,with a special emphasis on the use of laser techniques to determine the energy and angle distributions of particles emitted from single crystals.

Velocity distributions of In atoms in their ground ($^{2}P_{\frac{1}{2}}$) and excited ($^{2}P_{\frac{3}{2}}$) states ejected from In foils by bombardment with 5-keV ${\mathrm{Ar}}^{+}$ ions are measured with a multiphoton resonance-ionization technique. We show for the first time that the $^{2}P_{\frac{3}{2}}$ level is not significantly populated during sputtering and that the only path for population of this state is via laser-induced photodissociation of ${\mathrm{In}}_{2}$ during the detection process. A new deexcitation model for sputtered excited neutral atoms is proposed which is based on the electronic localization of the fine-structure orbital.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation P. H. Kobrin, J. P. Baxter, N. Winograd; Summary Abstract: Angle‐resolved studies of neutrals desorbed from single crystals by ion bombardment. J. Vac. Sci. Technol. A 1 May 1985; 3 (3): 1596–1597. https://doi.org/10.1116/1.573141 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAVS: Science & Technology of Materials Interfaces and ProcessingJournal of Vacuum Science & Technology A Search Advanced Search |Citation Search

The partial cross section, the satellite branching ratio, and the angular-distribution asymmetry parameter for simultaneous photoionization and excitation to the n=2 states of the ${\mathrm{He}}^{+}$ ion have been measured in the 67.5--90-eV photon-energy range. In the nonresonance regions (67.5 eV\ensuremath{\le}h\ensuremath{\nu}\ensuremath{\le}69.5 eV and 75 eV \ensuremath{\le}h\ensuremath{\nu}\ensuremath{\le}90 eV), the asymmetry-parameter values have been used to infer the ratio of the 2p cross section to the 2s cross section. These results indicate that the ${\mathrm{He}}^{+}$(n=2) satellite is predominantly 2p near threshold, in agreement with the experimental and most of the theoretical results reported to date. In the region below the ${\mathrm{He}}^{+}$(n=3) threshold (69.5 eV\ensuremath{\le}h\ensuremath{\nu}\ensuremath{\le}73.0 eV), the effects of a series of autoionizing Rydberg levels on the n=2 cross section, branching ratio, and asymmetry parameter have been measured, this being the first detailed measurement of the angular distribution of a satellite over an autoionization resonance. In addition, qualitative information concerning the total cross section and the 1s partial cross section has been obtained for the first member of this series (3s3p), disagreeing with previous experimental and theoretical results for the total cross section, but in agreement with recent photoemission measurements of the 1s cross section. The present results suggest that the qualitative shapes of the total and 1s cross sections over the 3s3p resonance are similar to the profile of the n=2 cross section for this resonance. To illustrate quantitative methods for the interpretation of autoionization phenomena, the derivation from the resonance data of several parameters defining the autoionization process is described.

Recently, we have demonstrated the selective ionization of atoms sputtered from solids by Multiphoton Resonance Ionization (MPRI) [1,2]. Three salient features of MPRI coupled to ion beam methods make it attractive as an analytical tool. First, the technique can be applied to all elements but He and Ne. Next, MPRI can be made selective to a single element by appropriate choice of the excitation wavelength, eliminating the need for a high resolution mass spectrometer. Both ground and excited state atoms can be examined. Finally, MPRI is extremely sensitive, i.e., with adequate photon fluxes every atom in the laser beam can be ionized [3]. As a consequence of this high sensitivity, the flux of ejected neutral species can be monitored under low dose bombardment conditions. Thus, MPRI of sputtered neutrals should be applicable to problems of structural and chemical analysis, as well as trace level determinations.

A summary is presented of typical gas-phase photoemission studies based on synchrotron radiation in the 50-5000 eV range, using beam lines at the Stanford Synchrotron Radiation Laboratory. Three topics are addressed: atomic inner-shell photoelectron cross sections and asymmetries, correlation peaks in rare gases, and core-level shape resonances in molecules. Photoelectron cross-section a(nZ) and asymmetry-parameter a(n0 studies in mercury vapor at photon energies up to 270 eV (up to 600 eV for a4f) extend coverage of these parameters to n<5 and 5<3. Comparison with Dirac-Slater and relativistic random-phase approximation calculations reveals systematic discrepancies. For example, distinct Cooper minima in a(n iZ,) are observed but not predicted, while predicted a(n9) values are typically too high. Correlation satellites have been studied for the K shells of helium (hv = 68-90 eV), neon (hv = 870-960 eV) and argon (hv = 3200-3320 eV). In helium the n=2 satellite peak was shown to have mainly 2p character at threshold, and its asymmetry was measured through the autoionizing resonance region. Tentative evidence was obtained that the neon satellites are less intense near threshold than in the high-energy limit, and that their intensities stay constant or decrease with increasing energy near threshold. A new satellite was observed in argon at 24.6 eV which appears to increase in intensity with energy. Molecular core-level shape resonances were observed for the first time by photoemission, yielding a(hv) and a(hv) for core levels from 180 eV binding energy (S 2p in SF6 and OCS) through C is in CO, CO2 and CF4, N ls in N2 and NO, and 0 is in CO and CO2 to 2490 eV (S ls in SF6). Several conclusions can be drawn about the photoelectron and Auger cross sections and asymmetry parameters.

The relative intensities of $K$-shell photoelectron satellites near their respective thresholds in Ne and Ar have been measured using synchrotron radiation. The Ne satellites were found to be 25-40% smaller than in the high-energy limit. The $2p\ensuremath{\rightarrow}3s$ "conjugate shakeup" state of ${\mathrm{Ne}}^{+}$ was not observed, in contrast to predictions of many-body perturbation theory. The asymmetry parameter of the neon Auger group was found to be equal to zero at the $1s\ensuremath{\rightarrow}3p$ resonance at 867 eV. This result may indicate that the $3p$ Rydberg electron is essentially decoupled from the core in the Auger decay process. In argon, a $K$-shell satellite was observed at 24.6(3) eV with 6% intensity relative to the main line, confirming a theoretical prediction by Dyall. Tentative evidence was obtained that this branching ratio increases with energy in the first 90 eV above threshold.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolids analysis using energetic ion bombardment and multiphoton resonance ionization with time-of-flight detectionFred M. Kimock, James P. Baxter, David L. Pappas, Paul H. Korbin, and Nicholas. WinogradCite this: Anal. Chem. 1984, 56, 14, 2782–2791Publication Date (Print):December 1, 1984Publication History Published online1 May 2002Published inissue 1 December 1984https://pubs.acs.org/doi/10.1021/ac00278a034https://doi.org/10.1021/ac00278a034research-articleACS PublicationsRequest reuse permissionsArticle Views73Altmetric-Citations79LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

The first gas-phase photoelectron measurements near the nitrogen K edges of N2 and NO are reported. Shape-resonance behavior is exhibited in the cross sections for both N 1s photoemission and N KVV Auger emission. The measured cross sections agree well with absorption and electron-energy-loss results, and with Stieltjes–Tchebycheff moment-theory calculations (for N2) except for a small energy shift. The measured asymmetry parameters for N 1s photoemission also exhibit changes in the shape-resonance region, but not as pronounced as those predicted by the multiple-scattering method (MSM). Comparison of all of the results with the MSM calculations indicates that the shape-resonance effects predicted by the MSM are higher in energy, and are narrower and more intense than those actually observed.

Cross sections and angular-distribution asymmetry parameters were measured directly for C(KVV) Auger electrons and C 1s photoelectrons from CO, CO2, CF4, and OCS, O(KVV) Auger electrons and O 1s photoelectrons from CO and CO2, and S(LVV) Auger electrons and S 2p photoelectrons from OCS using synchrotron radiation. The measurements were made in the photon-energy ranges 270–350, 545–680, and 160–190 eV, respectively. Shape resonances were observed in all of these molecular systems. The cross-section results are compared with previous experimental data obtained by electron energy-loss measurements, electron–ion coincidence results, and photoabsorption studies. The asymmetry-parameter results are the first of their kind for these molecular core levels. The present results are compared with available theoretical predictions obtained from Stieltjes–Tchebycheff imaging techniques, Hartree-Fock static-exchange calculations, and the multiple-scattering method.

The partial cross-sections and photoelectron angular distributions for several lines in atomic Mn have been measured at photon energies between 50 and 72eV. The intensities of the 3d correlation satellites at 24–26 eV binding energy behave similarly to the mainline intensity near the 3p → 3d giant resonance, but show an enhancement near the 3p threshold which is not present for the main line. A configuration-interaction analysis is applied to help identify the origins of the satellites. The 3p/3d branching ratio from 55–72eV and the shape of the 3d cross section in the resonance region are in good agreement with many-body perturbation-theory calculations.

The first photoemission measurements of the I $4d$ and I " $4p$ " subshells in methyl iodide are presented. Cross sections and angular-distribution asymmetry parameters were measured from threshold to 300 eV photon energy for the I $4d$ level (to 440 eV for the asymmetry parameter), and from 175 to 300 eV for the I " $4p$ " level. The I $4d$ results exhibited atomiclike behavior throughout this energy range, mimicking the behavior of the Xe $4d$ subshell. Theoretical calculations for the Xe $4d$ subshell agree very well with the I $4d$ asymmetry-parameter results, indicating that the I $4d$ subshell is localized on the iodine atom in ${\mathrm{CH}}_{3}$I. Nearer to threshold, the spin-orbit final states, ${4d}_{\frac{5}{2}}$ and ${4d}_{\frac{3}{2}}$, were resolved and exhibited nonstatistical intensity ratios mainly due to a kinetic energy effect. The I " $4p$ " asymmetry-parameter results were found to be essentially identical to the asymmetry-parameter results for the I $4d$ subshell at the same photon energies, suggesting strong interchannel coupling. This result is discussed with respect to collective effects in the iodine $N$ shell.