The formation of excited states of sputtered yttrium atoms

Optical spectra of ion-photon emission of atoms sputtered by bombarding the yttrium target surface with 40-keV Xe⁺ ions are studied experimentally. It is found that the levels corresponding to transitions from the 4d shell are excited more efficiently in the sputtering process. Possible new mechanisms for the excitation of atomic levels in the sputtering of a solid are considered.     

The measurement of energy parameters for atoms sputtered in excited states

Ti I lines from excited Ti atoms sputtered from Ti and a variety of Ti compounds by 55 keV Ar⁺ bombardment have been studied and the intensity decay, as a function of distance, has been measured in front of the target surface for normal incidence bombardment. These decay curves have been analyzed using the model of Dzioba et al. The model has been examined with respect to its internal consistency in the predictions for integral and differential yield measurements using several Ti I and an Al I line. Although care must be taken in defining an adequate slit size for each particular decay curve, the integral and differential measurements infer consistent E1 values. These values have been generally found to increase with the excitation energy of the Ti I level studied, and to decrease with surface (or bulk) contamination of O, N, C and B. Selected characteristics of photon emission are discussed in relation to the E1 values obtained.     

Comments on the physical significance of E1 values for excited sputtered atoms

Measurements of parameters associated with the emitted photons from a number of elements have indicated that the kinetic energies of sputtered excited atoms may be of the order of 10²–10³ eV. A recent result of Yu et al. [Phys. Rev. Letters 48 (1982) 427] is in contradiction to those results. We argue that the high energy values reported are the result of cascade repopulation of the upper level of the observed transition, distorting the experimental observations. Cascade corrections could reduce the energy values to the order of 10 eV, similar to the most probable energy of secondary ions.     

Experimental investigation of the energy distribution of sputtered excited target atoms bombarded by medium-energy ions

In this paper we experimentally investigate the parameter dependence of a model energy distribution of excited potassium atoms, knocked out by bombarding a KCl monocrystal with normally incident Ar⁺ ions, on the ion energy and the partial oxygen pressure in the chamber. On the basis of the obtained results a model of the energy distribution is proposed that corresponds to the kinetic formation mechanism for the excited atoms during the sputtering of the target.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 9–12, March, 1985.     

Optogalvanic spectroscopy of sputtered atoms

Optogalvanic Spectroscopy (OGS) is finding wide ranging applications in atomic structure studies, laser wavelength calibration, intensity and frequency stabilization of lasers and analytical chemistry. Sputtered atoms produced in a hollow cathode lamp by the bombardment of a rare gas discharge is a convenient source for optogalvanic spectroscopy work. Here, we discuss the sputtered ion/atom optogalvanic spectroscopy applications to low resolution atomic spectroscopy, laser wavelength calibration, studies of radioactive samples available in limited quantities, studies of atoms in highly excited states and Rydberg atoms and high resolution laser spectroscopy. For the sake of completeness, we list other applications of OGS without going into details.     

Depth of origin of sputtered atoms

Estimates are given for the distribution of the depth of origin of sputtered atoms in the low-fluence limit, as well as the corresponding distribution of atoms sputtered into a given energy interval. The former distribution is well described by an exponential profile, with the characteristic depth being consistent with previous results. The latter distribution is characterized by an energy-dependent depth scale and a shape that varies from exponential at low sputtered-atom energies to inverse-power form at higher energies.     

Anisotropic angular distribution of sputtered atoms

The sputtering yield angular distributions have been calculated on the basis of the ion energy dependence of total sputtering yields for Ni and Mo targets bombarded by low-energy Hg⁺ ions. The calculated curves show excellent agreement with the corresponding Wehner's experimental results of sputtering yield angular distributions. This fact clearly demonstrates the intrinsic relation between the ion energy dependence of total sputtering yields and the sputtering yield angular distribution. This intrinsic relation had been ignored in Yamamura's papers [Yamamura, Y. (1982). Theory of sputtering and comparison to experimental data, Nucl. Instr. and Meth., 194, 515–522; Yamamura, Y. (1981). Contribution of anisotropic velocity distribution of recoil atoms to sputtering yields and angular distributions of sputtered atoms, Rad. Eff., 55, 49–55.] due to some obvious mistakes.     

Deexcitation of sputtered metastable aluminum atoms

An experimental system was set up incorporating pulsed ion beam sputtering, two Nd:YAG pumped dye lasers and an imaging time-of-flight (TOF) analysis system. The system was used to perform state-selective analyses of neutral atoms sputtered from surfaces using resonant one-color and two-color ionization schemes. We have measured, for the first time, TOF mass spectra of Al atoms sputtered into the ground state and first excited state (with an excitation energy of 0.014 eV) from single crystals of Ni₃Al and NiAl. The population ratio of the first excited state to the ground state in the sputtered flux was estimated to be 0.91 for Ni₃Al and 0.95 for NiAl, respectively. This indicates that the magnitude of the excitation energy plays an important role even in the deexcitation rate of sputtered metastable state atoms with an open outer shell.     

Model of ionization of atoms sputtered from solids

A new microscopical quantum-mechanical model of ionization of sputtered particles is described which takes into account electron excitations due to the atomic motions in the substrate. The substrate is represented by a simple atomic, metal-like, chain. Numerical calculations yield ionization probabilities R⁺ which have magnitudes close to the experimental values and have realistic velocity dependence. The function of R⁺ versus the sputtered atom ionization energy can be well approximated by the Maxwell-Boltzmann law with an effective temperature of about 3500 K.     

Charge exchange features of excited sputtered particle production

Abstract

The results are presented which have been obtained by studying the angular dependence of photon and ion emission and the spatial energy distribution of excited silicon ions produced under ion bombardment of monocrystalline and amorphized silicon surface. The experimental data are discussed which have been obtained mostly by the coincidence method. The theoretical concepts making it possible to account for the observed behavioural features are also discussed.     

The energy distributions of atoms sputtered from HfC

The energy spectra of Hf and C atoms sputtered from an HfC target with a 6 keV Xe⁺ beam have been measured. It was found that the target constituents of widely different masses were sputtered with energy distributions of the same form. The results are compared with the collision cascade theory for compound targets.     

Long-range interactions of excited hydrogen atoms

Accurate calculations are reported of the first and second-order long-range interactions of a hydrogen atom in its ground state and a hydrogen atom in the excited 2s, 2p, 3s, 3p and 3d states. The connections with the spectroscopic states of molecular hydrogen are established. First-order mixing occurs for the n = 3 states and the form of the long-range interaction is complicated.     

Reactions of excited atoms and molecules with atoms and molecules

Penning electron distributions arising from the ionization of Na and K by He (1s 2s ^1,3 S)-metastables in thermal collisions, as well as the absolute cross section for Penning ionization of Na by He (2³ S) and relative cross sections for ionization of Na and K by He(2¹ S) and He(2³ S) are measured. It is shown that under fairly general conditions the well depth ε* of the interaction potential between the metastable and the target particle can be obtained directly from the measured electron distributions. ε*-values are reported for the moleules He(1s 2s ^1,3 S)-Na(² S), K(² S) (^2,2Ω), and for He(1s 2s ^1,3 S)-Hg(¹ S)(^1,3Ω). These latter values are obtained from previously published measurements and are to be considered preliminary. Further, additional evidence is given, that Penning ionization with metastables is an electron exchange process.     

Reactions of excited atoms and molecules with atoms and molecules

From a He-beam excited by electron impact we eliminated the He(2¹ S) component to better than 0.5% by irradiating light from a He discharge. The quenching process ishv(2¹ P→2¹ S)+He(2¹ S)→He(2¹ P)→He(1¹ S +hv) (2¹ P 1)¹ S. By measuring the ions produced in collisions of the He-metastables with various target gases in a mass spectrometer, singlet to triplet Penning-cross section ratios were obtained. These ratios are without exception close to one, which is taken as evidence for the previously proposed electron exchange mechanism of the Penning ionization. In the case that more ions are produced in the collision of He (2¹ S) and He(2³ S) with a target gas, separate relative production cross sections are obtained for the two metastables. For the rare gases the measurements are performed at two temperatures of the He-beam, 320 and 90 °K. It is found that the cross section ratio of associative — to Penning ionization increases considerably as the temperature is decreased for both, He(2¹ S) and He(2³ S), the effect being much more pronounced for He(2¹ S). The results of this work are found to confirm conclusions drawn from measured energy distributions of the electrons ejected in the Penning process.