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This paper attempts to elucidate the relationship between bottom-up inductive and top-down deductive approaches to the calculation of electron-impact ionization cross sections for atoms. Specifically, the ionization cross sections for atomic hydrogen and helium derived from the various approaches are compared in detail.

We describe improvements to the fast-beam apparatus that has been used extensively for electron-impact ionization cross section measurements for atoms, molecules, and free radicals in our group for the past 15 years. A high-intensity, dispenser-type electron emitter capable of producing an electron beam of more than 2 mA at electron energies above 50 eV is used instead of a conventional indirectly heated, oxide-coated electron source. We also replaced the channel electron multiplier by a position-sensitive, triple multi-channel plate ion detector. Experiments using well-established ionization cross sections in conjunction with extensive ion trajectory simulations were carried out to verify the performance of the modified fast-neutral-beam apparatus. This apparatus was subsequently employed in the measurement of absolute partial cross sections for the formation of various singly charged positive ions produced by electron impact on SiCl3 for impact energies from threshold to 200 eV. A comparison with calculations and with the previously reported ionization cross section for SiCl4, SiCl2, and SiCl is also made.

We report calculations of the cross-sections for electron impact detachment of the diatomic anions B 2 − , O 2 − , BO − , and CN − using the DM formalism. The calculations use ‘ionic’ weighting factors to adequately represent the ionic character of the target and in each case a Mulliken population analysis of the anion and the neutral molecule was carried out in an effort to localize the ‘extra’ electron in the anion compared to the neutral molecule. When compared with available experimental data, the calculated DM cross-sections were found to exceed the measured data by factors ranging from 1.6 to 5.5.

We report results of the calculation of electron-impact ionization cross-sections for atoms with atomic numbers Z in the intermediate range of Z -values (20 Z Z -values in this range (which contains many atoms of practical importance), there are some experimentally determined ionization cross-sections, but there has only been a single systematic theoretical study from 30 years ago, which was based on the Born approximation. The Born approximation tends to yield cross-sections which show an “overestimation” in the energy regime of the cross-section maximum compared to experimental data. The DM approach, on the other hand, has adequately reproduced the region of the cross-section maximum for many low- Z atoms as well as for the heavier rare gases. In the present case of atoms with Z -values from 20 to 56, the DM calculation typically shows a cross-section maximum lower than that predicted from the Born approximation by 25–50%, except for Xe, Ni, Cd, and Pd. The Born approximation and the DM formalism yield cross-sections that converge at higher impact energies.

We report results of the calculation of electron-impact ionization cross section for the lanthanide atoms Ce through Lu, which are collectively referred to as the (4f) transition-metals, using the Deutsch-Mark (DM) formalism. The lanthanides are characterized by an unfilled (5d) sub-shell and a partially filled (4f) sub-shell. The strong correlation of the open (4f) sub-shell with the (5d) sub-shell and the considerable uncertainty in the binding energies of the electrons in the (4f), (5s), (5p), (5d), and (6s) sub-shells as well as in their energetic ordering are shown to affect the choice of parameters that are required for the cross section calculations in the DM model as inferred from a comparison between the calculated DM cross sections and available experimental cross section data.

Absolute cross sections for electron impact dissociative excitation and ionization of CD+ leading to the formation of ionic products ( D+, C+, C2+ and C3+) are reported in the energy range from their respective thresholds to 2.5 keV. Around the maximum, cross sections are found to be ( 10.5 +/- 1.0) x 10(-17) cm(2), ( 20.6 +/- 3.5) x 10(-17) cm(2), ( 1.20 +/- 0.11) x 10(-17) cm(2) and ( 8.2 +/- 1.5) x 10(-20) cm(2) for D+, C+, C2+ and C3+, respectively. In the very low- energy region, dissociative excitation leading to the C+ formation dominates over the D+ one. The cross section for dissociative ionization ( C+ + D+ formation) is found to be ( 6.9 +/- 1.3) x 10(-17) cm(2) around 105 eV and the corresponding threshold energy is ( 22.1 +/- 0.5) eV. The animated crossedbeams method is used and the analysis of ionic product velocity distributions allows the determination of the kinetic energy release distributions. They are seen to extend from 0 to 15 eV both for C+ and for D+, and up to 40 eV both for C2+ and for C3+. For singly charged products, the comparison of the present energy thresholds and kinetic energy release with published data allows the identification of states contributing to the observed processes. In particular, contributions from primary ions formed in the a(3)Pi metastable state are perceptible. At fixed electron energy, the cross sections for the various ionization channels are seen to reduce exponentially with the potential energy of each dissociated ion pair. Anisotropies are estimated to be in the range 8 +/- 2% for both C+ and D+. The total CD+ single ionization cross section calculated by application of the Deutsch - Mark formalism is found to be in good agreement with experimental results.

Absolute cross sections for electron impact ionization of CO+ leading to the formation of doubly and triply charged products (CO2+, C2+ and O2+, C3+ and O3+) are reported in the energy range from their respective thresholds to 2500 eV. Around the maximum, cross section values are found to be ( 13.36 +/- 0.56) x 10(-18) cm(2), ( 5.58 +/- 0.55) x 10(-18) cm(2) and (1.37 +/- 0.14) x 10(-18) cm(2) for CO2+, C2+ and O2+, respectively, and (28.3 +/- 7.0) x 10(-21) cm(2) and (2.4 +/- 0.7) x 10(-21) cm(2) for C3+ and O3+, respectively. The analysis of ionic product velocity distributions, obtained by means of a crossed electron-ion beam set-up, allows the determination of the kinetic energy release distributions. They are seen to extend from 0 to 50 eV both for C2+ and O2+. The mean kinetic energy releases for C3+ and O3+ are found to be 33 +/- 5 eV and 39 +/- 9 eV, respectively. The cross sections are seen to depend exponentially on the potential energy of each dissociated ion pair. The total single CO+ ionization cross section calculated by application of the Deutsch-Mark ( DM) formalism is found to be in good agreement with the experimental results.

Recent experiments (Nagesha and MacAdam 2003 Phys. Rev. Lett. 91 113202) determined electron-impact ionization cross sections for 11 selected Na(ns) and Na(nd) Rydberg states (with the principal quantum number n in the range of 35–51), which exceeded predictions based on the well-known Vriens–Smeets (VS) fitting formula by more than an order of magnitude. This motivated us to extend the semi-classical Deutsch–Mark (DM) formalism to the calculation of ionization cross sections of these Na Rydberg states. The results show that the calculated DM ionization cross sections also lie below the experimentally determined cross sections by factors ranging from 15 to about 40. This indicates either that the ionization of these Rydberg atoms involves some new aspects or mechanisms that are not adequately described by models based on low-n data, or that the very difficult experiments suffered from a systematic error in the absolute calibration process that remained unrecognized.

We used the semi-classical Deutsch-Mark (DM) formalism to calculate absolute electron-impact ionization cross sections of excited Ne atoms from threshold to 1000 eV. Excited states of Ne where the outermost valence electron is excited to states with principal quantum numbers up to n = 7 and orbital angular momentum quantum numbers up to l = 2 have been considered and systematic trends in the calculated cross section data are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present a comprehensive comparison between the results of the recently revised DM formula, which now exhibits the quantum mechanically correct high-energy behavior, and measured atomic ionization cross sections for selected atoms covering a wide range of targets of different electronic structure as well as elements along columns of the periodic table. Specifically, we selected the following elements (listed in order of increasing atomic number Z): Na, Si, S, Cl, K, Ca, Fe, Ga, Br, In, Cs, Hg, Bi, and U. The main objective of this study is to compare the results of the revised DM formula for these elements in both the low- and high-energy regime with available experimental data and to extend the formalism to targets with higher atomic number Z, where contributions to the ionization cross section from f-electrons have to be considered. In cases, where several, sometimes conflicting experimental data sets have been reported, an attempt is made to provide guidance as to the reliability of various measured cross sections. In addition, we also calculated ionization cross sections for the technically important species Cr, Mn, and W, for which no experimental data are available.

We report absolute partial cross sections for the formation of selected positive and negative ions resulting from electron interactions with uracil. Absolute calibration of the measured partial cross sections for the formation of the three most intense positive ions, the parent C4H4N2O+2 ion and the C3H3NO+ and OCN+ fragment ions, was achieved by normalization of the total single uracil ionization cross section (obtained as the sum of all measured partial single ionization cross sections) to a calculated cross section based on the semi-classical Deutsch–Mark formalism at 100 eV. Subsequently, we used the OCN+ cross section in conjunction with the known sensitivity ratio for positive and negative ion detection in our apparatus (obtained from the well-known cross sections for SF+4 and SF−4 formation from SF6) to determine the dissociative attachment cross section for OCN− formation from uracil. This cross section was found to be roughly an order of magnitude smaller, about 5 × 10−22 m2 at 6.5 eV, compared to our previously reported preliminary value. We attribute this discrepancy to the difficult determination of the uracil target density in the earlier work. Using a reliably calculated cross section for normalization purposes avoids this complication.

We extended our previously developed semi-empirical method for the calculation of cross section functions (absolute value and energy dependence) for the electron-impact ionization of the neutral fullerenes C60 and C70, of the ionized fullerenes C60z+ (z=1–3), and of multiple ionization processes of the negatively charged fullerenes Cm− (m=60, 70, and 84) to the fragmentation and dissociative ionization of neutral and ionized C60 and C70. Measured cross sections for these processes were found to display a sharp peak in the cross section function at low impact energies which was attributed to a plasmon excitation at these energies [Phys. Rev. Lett. 85 (2000) 3604], whereas the high-energy shape of the cross sections exhibited the well-known energy dependence of a direct ionization process. The introduction of a “decay factor” in our model allowed us to separate the two contributions and we found in all cases that the plasmon contribution to the cross section exhibits a very similar shape.

The semiclassical Deutsch-Mark (DM) formalism was used to calculate absolute cross sections for the electron-impact ionization of excited argon atoms from threshold to 1000 eV. Excited states of Ar where the outermost valence electron is excited to states with principal quantum numbers up to n = 7 and orbital angular momentum quantum numbers up to l = 2 have been considered. Systematic trends in the calculated cross section data are discussed. © 2004 Elsevier B.V. All rights reserved.

A microphysical description of the charging of dust grains in a plasma is presented. The model which is based on plasma-wall interaction processes predicts the dependence of the grain charge on the particle radius and on the particle temperature better than the commonly used assumptions of a spherical capacitor. The results of the model are compared with measurements of the particle charge which were performed in different discharge configurations. (C) 2004 Elsevier B.V. All rights reserved.

The research effort in the area of dusty plasmas initially aimed at avoiding particle formation and controlling the contamination level in industrial reactors. Nowadays, dusty plasmas have grown into a vast field and new applications of plasma-processed dust particles are emerging. There is demand for particles with special properties, and for particle-seeded composite materials. Low-pressure plasmas offer a unique possibility of confinement, control and fine tailoring of particle properties. The interaction between plasma and injected micro-disperse powder particles can also be used as a diagnostic tool for the study of plasma surface processes. Examples for determining the electric field in front of electrodes and for determining the particle charge are given as well as for obtaining information on the energy fluxes in the plasma.

We measured absolute partial and total cross sections for the electron ionization of hexafluoroethane (C 2 F 6 ) from threshold to 900 eV using a time-of-flight mass spectrometer (TOF-MS), which can be operated in a linear and in a reflection mode. Measurements were also made for tetrafluoromethane (CF 4 ), which is perhaps the most thoroughly investigated complex polyatomic molecule in terms of ionization cross sections, in an effort to demonstrate the reliable performance of our apparatus. Our measurements for both CF 4 and C 2 F 6 are compared with other available experimental data and with calculated cross sections.

We report calculated total single ionization cross-sections for the three molecules—CFH3, CF3Br, and CF3I using the Deutsch–Mark (DM) formalism. In the case of CF3H, our calculated cross-sections are in good agreement with the BEB calculation of Kim et al. and with the recent measurement of Iga et al., but disagree with earlier experimental data. Our calculated cross-sections for CF3Br and CF3I are in good agreement with recent experiments, which reported measured data for these two molecules for the first time.

We report the first application of the semi-classical Deutsch-Mark formalism to the calculation of the absolute electron-impact ionization cross section of simple molecular ions. Our calculated cross sections for the electron-impact ionization of CO2+ and N-2(+) are compared with recently published (as well as with unpublished) experimental data for these molecular ions. The level of agreement between the experimentally determined and the calculated cross section is satisfactory, in particular in view of the added complications in the experimental determination of ionization cross sections of molecular ions.

We used the Deutsch-Mark (DM) formalism to calculate atomic K-shell electron impact ionization cross sections for the elements Fe, Co, Mn, Ti, Zn, Nb, and Mo. The calculated K-shell ionization cross sections are compared with recently measured K-shell ionization cross sections. Good to satisfactory agreement was found for all atoms with the exception of Ti. Moreover, when compared to other available K-shell ionization cross sections for these atoms, calculated using other theoretical methods and semiempirical formulae, the predictions of the DM formalism achieve a level of agreement with experimental data that is as good or better than the predictions from the other methods.

The research effort in the area of dusty plasmas initially aimed at avoiding particle formation and controlling the contamination level in industrial reactors. Nowadays, dusty plasmas have grown into a vast field and new applications of plasma-processed dust particles are emerging. There is demand for particles with special properties, and for particle-seeded composite materials. Low-pressure plasmas offer a unique possibility of confinement, control and fine tailoring of particle properties. The role of plasma technology in treatment and surface modification of powder grains is reviewed and illustrated with examples. The interaction between plasma and injected micro-disperse powder particles can also be used as a diagnostic tool for the study of plasma surface processes.

We used the Deutsch-Mark (DM) formalism to calculate atomic K-shell ionization cross sections for the elements chromium (Cr), nickel (Ni), copper (Cu), scandium (Sc) and vanadium (V). The calculated K-shell ionization cross sections were compared with recently measured K-shell ionization cross sections and good to satisfactory agreement has been found for all five elements. Moreover, when compared with other available calculated K-shell ionization cross sections for these five atoms using a variety of theoretical methods and semi-empirical formulae, the predictions of the DM formalism achieve a level of agreement with experimental data that is as good as, or sometimes better than, the predictions from the other methods.

In this review experimental techniques developed in the past years in our laboratory concerning (i) the measurement of partial electron impact ionization cross sections, (ii) the determination of kinetic energy release distributions for fragment ions produced by spontaneous and electron-induced dissociations of molecular ions and (iii) the derivation of appearance energies for parent and fragment ions will be summarized and results will be given for the propane molecule as an example relevant for plasma applications.

The Deutsch-Mark (DM) formalism has been used to calculate absolute electron impact ionization cross sections for the technologically relevant molecules NO2, BF3, BCl3, HX (X = F, Cl, Br, J), Br2, J2, WF6, GeHx (x = 1–4), TMS (tetramethylsilane), HMDSO (hexamethyldisiloxane), and TEOS (tetraethoxysilane). Our calculations are compared with experimental data, where available, and with calculated cross sections based on the Binary-Encounter-Bethe (BEB) method of Kim and Rudd. In some cases, comparisons are also made with predictions from the modified additivity rule (MAR).

Radiative efficiency of emission of resonance radiation from a dc glow discharge plasma is derived experimentally from spatial density profiles of atoms in resonant states. Density profiles are determined by tunable diode laser absorption spectroscopy. Resonance radiation transport is considered both by Lawler and Curry's analytical formula (Lawler J E and Curry J J 1998 J. Phys. D: Appl. Phys. 31 3225) and by Monte Carlo simulations. Radial dependences of the escape factor are studied. Power loss by resonance radiation is found to be about 50% of electrical power input. The impact of resonance radiation on similarity laws in discharge physics is discussed.

A summary is given of different elementary processes influencing the thermal balance and energetic conditions of substrate surfaces during plasma processing. The discussed mechanisms include heat radiation, kinetic and potential energy of charged particles and neutrals as well as enthalpy of involved chemical surface reactions. The energy and momentum of particles originating from the plasma or electrodes, respectively, influence via energy flux density (energetic aspect) and substrate temperature (thermal aspect) the surface properties of the treated substrates. The various contributions to the energy balance are given in a modular mathematical framework form and examples for an estimation of heat fluxes and numerical values of relevant coefficients for energy transfer, etc. are given. For a few examples as titanium film deposition by hollow cathode arc evaporation, silicon etching in CF4 glow discharge, plasma cleaning of contaminated metal surfaces, and magnetron sputtering of aluminum the energetic balance of substrates during plasma processing will be presented. Furthermore, the influence of the resulting substrate temperature on characteristic quantities as etching or deposition rates, layer density, microstructure, etc. will be illustrated for some examples, too.

Radiative efficiency of resonance line emission of a dc glow discharge plasma is derived from experimentally determined profiles of atoms in resonant states. Spatial density profiles were determined by diode laser atomic absorption spectroscopy and laser induced fluorescence. Absorption measurements were used for absolute calibration. The influence of the shape of spatial density profiles was considered. Investigations show that power dissipation by resonance radiation transport remains nearly constant for the currents investigated (i = 1 ... 20 mA). Total power loss due to resonance radiation was found to be about 25% of electrical power input.

Much emphasis has been devoted recently to the experimental determination of absolute electron-impact ionization cross sections of molecules and radicals because of the importance of these cross sections in many applications (e.g. as input parameters to modeling codes for various purposes). Supporting theoretical calculations have been lagging behind to some extent. Because of the inherent complexity of such calculations, simplistic additivity rules and semiempirical methods have often been used in place of more rigorous calculation schemes, particularly in applications where a larger number of cross section data were needed with reasonable precision. Although these methods have often proved to be quite successful as descriptive tools (i.e. reproducing existing experimental ionization cross sections reasonably well), their ability to calculate cross sections for species for which no experimental data are available (predictive capabilities) tend to be limited or questionable. This topical review describes recent progress in the development of more rigorous approaches for the calculation of absolute electron-impact molecular ionization cross sections. The main emphasis will be on the application of the semiclassical Deutsch–Mark (DM) formalism, which was originally developed for the calculation of atomic ionization cross sections, to molecular targets, and on the binary–encounter–Bethe (BEB) method of Kim and Rudd. The latter is a simpler version of the more rigorous binary–encounter–dipole (BED) theory, which was also first developed for the calculation of atomic ionization cross sections, and based on the methods developed by Khare and co-workers. Extensive comparisons between available experimental cross sections and the predictions of these theoretical models will be made for 31 molecules and free radicals (H 2 , N 2 , O 2 , S 2 , C 2 , C 3 , O 3 , H 2 O, NH 3 , CO 2 , CH 4 , CH 3 , CH 2 , CH, CF 4 , CF 3 , CF 2 , CF, NF 3 , NF 2 , NF, SiF 3 , SiF 2 , SiF, TiCl 4 , C 2 H 2 , C 2 H 6 , C 6 H 6 , SiF 6 , C 2 F 6 , CH 3 OH).

We measured absolute cross sections for the electron-impact ionization and dissociative ionization of the C2F5 free radical from threshold to 200 eV using the fast-neutral-beam technique. The electron-impact ionization of C2F5 is dominated by two channels, the formation of the CF3+ fragment ion which has the largest partial ionization cross section with a value of 3.5 × 10-16 cm2 at 70 eV and the formation of the C2F5+ parent ion with a cross section of 1.3 × 10-16 cm2 at 70 eV. Both partial cross sections have error margins of about ±15%. All other partial ionization cross sections have maximum cross section values of less than 0.1 × 10-16 cm2. The total single C2F5 ionization cross sections at 70 eV (derived from the two measured partial ionization cross sections and an estimate for the sum of the cross sections for all weaker, unobserved ionization processes) was found to be about 5 × 10-16 cm2. A comparison of the measured total single-ionization cross sections with a calculated cross section, using a modified additivity rule, shows good agreement up to an electron energy of 50 eV, but poor agreement at higher impact energies. This behaviour is somewhat similar to that observed for the CFx (x = 1-3) free radicals, but it is very different from the excellent agreement between the calculated and measured total single-ionization cross sections that was observed for the stable molecules CF4 and C2F6.

The semiclassical Deutsch-Mark (DM) formalism was used in a series of calculations of cross sections for the formation of Bem+ (m = 1–4), Bm+ (m = 1–5), Cm+ (m = 1–6), and Om+ (m = 1–8) ions by electron impact on the neutral atoms. Our calculated cross sections are compared with available experimental and other theoretical data and systematic trends in the data are highlighted. We also calculated a set of ionization rate coefficients on the basis of the calculated cross sections and Maxwell-Boltzmann electron energy distributions. In many applications, particularly applications relating to fusion plasmas, rate coefficients are more desirable than ionization cross sections.

The semiclassical Deutsch-Mark (DM) formalism was used to calculate absolute cross sections for the electron-impact ionization of metastable atoms such as metastable rare-gas atoms and metastable mercury and cadmium atoms from threshold to 200 eV. Systematic trends in the calculated cross section data are discussed and a comparison is made with available experimental data and with other calculations. Specifically, we calculated separately the contributions to the ionization cross sections arising from the removal of the single excited electron in the outermost subshell and the removal of the lower-lying inner-shell electrons.

The semi-empirical Deutsch-Mark (DM) formula was used to calculate cross sections for the formation of Nm + (m = 2-7) and Arm + (m = 2-18) ions by electron impact on the neutral atoms. Our calculated cross sections for these multiple ionization processes are compared with available experimental and other theoretical data and systematic trends in the data are highlighted.

We employed the fast-neutral-beam technique in a measurement of the absolute partial cross section for the formation of ions following controlled electron-impact ionization of the fullerene from threshold to 200 eV. Our measurement is the first report of an absolute measurement of this cross section which does not employ any normalization procedure and which does not rely on the use of controversial vapour pressure versus temperature data for to determine the number density in the ion source. All quantities that determine the ionization cross section were measured directly in our apparatus. We found a peak value for the parent ionization cross section of in the energy range between 70 and 80 eV. This value is in very good agreement (to within 5%) with the cross section reported earlier by Matt et al (1996 J. Chem. Phys. 105 1880) who employed a novel normalization procedure. Our cross section is significantly lower than the cross sections reported by several other investigators who relied on vapour pressure data in their absolute calibration.

We studied the electron impact ionization of hexamethyldisiloxane (HMDSO), Si2O(CH3)6, which is widely used in plasma-enhanced polymerization applications. Appearance energies and absolute partial cross sections for the formation of fragment ions with relative intensities >1% of the most abundant ion, the Si2O(CH3)5+ fragment ion, were measured in a high resolution double focusing sector field mass spectrometer with a modified ion extraction stage for electron energies from threshold to 100 eV. Dissociative ionization was found to be the dominant process. The main ionization channel removes a complete methyl group to produce the fragment ion Si2O(CH3)5+ with a cross section of 1.7 × 10−15 cm2 at 70 eV. The stoichiometric and isotope composition of the various fragment ions was determined by using the high resolution (m/Δm = 40,000) of the mass spectrometer used in these studies. The methyl ion is formed with considerable excess kinetic energy, whereas all other fragment ions are formed with essentially no excess energy. The experimental total single ionization cross section of HMDSO (2.2 × 10−15 cm2 at 70 eV impact energy) is in good agreement with the result of a semiempirical calculation (2.1 × 10−15 cm2 at the same energy).

During dc oxygen plasma cleaning of hydocarbon-containing light lubricants deposited on aluminum the energy fluxes towards the substrates have been determined by temperature measurements. The contributions to the total energy influx are due to exothermic combustion reactions of the petroleum-like lubricants by the plasma generated oxygen atoms and due to kinetic ion energy transfer. By variation of the discharge mode and substrate voltage the effect of the two contributions could be separated. In the anomalous glow discharge mode, where the ion energy influx was of importance, the treated substrates were at cathode potential (− 500 to − 1200 V) and vice versa, in the hollow cathode discharge mode the substrates were at floating potential where only the chemical component contributes to substrate heating. A comparison of the measurements with calculations based on simple model assumptions is given.

We derived a model describing the radial distribution of the ion and electron densities and the radial electric field strength in the positive column of a glow discharge. The set of equations related to the plasma consists of the equations for particle and momentum conservation for the ions and electrons and the Poisson-equation. In a novel approach, the necessary boundary conditions in our model result from a system of balance equations for the charge carriers on the insulated wall surrounding the positive column.

The semiclassical Deutsch - Mark (DM) formalism for the calculation of absolute cross sections for the single ionization of atoms has been extended to the calculation of cross sections for the multiple ionization of ground state atoms (degree of ionization m > 3). Comparisons are presented with the predictions of two recently published semi-empirical methods and with available experimental data for some selected targets. The DM formalism is conceptually straightforward to apply; the semi-empirically determined parameters can easily be related to physical quantities and the formalism has already been successfully applied to the single ionization of atoms, ions, molecules, radicals and clusters, as well as to the double and triple ionization of atoms. In those cases where predictions from all three methods and experimental data are available, we find that, with very few exceptions, our method yields a level of agreement with the experimental data which is comparable to or better than the predictions from the other two methods.

Ultracold atoms in optical lattices are an important platform for quantum information science, lending itself naturally to quantum simulation of many-body physics and providing a possible path towards a scalable quantum computer. To realize its full potential, atoms at individual lattice sites must be accessible to quantum control and measurement. This challenge has so far been met with a combination of high-resolution microscopes and resonance addressing that have enabled both site-resolved imaging and spin-flips. Here we show that methods borrowed from the field of inhomogeneous control can greatly increase the performance of resonance addressing in optical lattices, allowing us to target arbitrary single-qubit gates on desired sites, with minimal crosstalk to neighboring sites and greatly improved robustness against uncertainty in the lattice position. We further demonstrate the simultaneous implementation of different gates at adjacent sites with a single global control waveform. Coherence is verified through two-pulse Ramsey interrogation, and randomized benchmarking is used to measure an average gate fidelity of ~95%. Our control-based approach to reduce crosstalk and increase robustness is broadly applicable in optical lattices irrespective of geometry, and may be useful also on other platforms for quantum information processing, such as ion traps and nitrogen-vacancy centers in diamond., Comment: Originally submitted version. Longer version with some substantive edits to appear in Nature Communications

We observe coherently enhanced reflection (Bragg scattering) of a near resonant laser beam from cesium atoms ordered by a periodic array of optical potential wells known as an optical lattice. The reflected light is enhanced by a factor of $\ensuremath{\sim}{10}^{5}$ over scattering from a disordered atomic sample. We measure the magnitude of the reflectivity and its detuning dependence as functions of the density and the degree of localization of the atoms. The change in lattice constant due to the frequency-dependent effective index of refraction seen by the lattice light field is observed.

The concentration of metastable atoms can significantly be influenced by changing the gas temperature [1]. Starting from a set of balance equations, consisting of the balance equation for the electrons, the balance equation for excited atoms and the current balance equation the impedance behaviour is calculated in dependence on the gas temperature. Based on a theoretical description of the discharge plasma a nonlinear equivalent circuit representing the behaviour of the positive column at higher gas-temperatures (250 K – 500 K) is developed. The circuit posseses only positive parameters for the reactances which can be calculated by means of the elementary processes occuring in the discharge plasma. Experimental investigations of the static current/voltage characteristic and the impedance behaviour support the proposed circuit model.

Measurements of the total and selected partial cross sections for the electron impact ionization of cyclopentadienyltrimethylplatinium (C 5 H 5 )Pt(CH 3 ) 3 [CpPtMe 3 ], bismethylcydopentadienylruthenium (CH 3 C 5 H 4 ) 2 Ru [(MeCp) 2 Ru], and bismethylcyclopentadienylferrum (CH 3 C 5 H 4 ) 2 Fe [(MeCp) 2 Fe] in the energy range from threshold up to 90 eV are presented. A double focussing mass spectrometer with an improved ion extraction system to avoid the discrimination of fragment ions with excess energy was used. The following values for the total single ionization cross sections σ at an impact energy of 70eV and for the ionization energies (EI) were determined : σ = (13.7 ± 2.5) 10 -16 cm 2 , EI = 7.6 ± 0.5 eV [CpPtMe 3 ], σ = (23.2 ± 4.2) x 10 -16 cm 2 , EI = 7.5 ± 0.5 eV [(MeCp) 2 Ru], σ = (20.2 ± 3.6) x 10 -16 cm 2 , EI = 8.1 ± 0.5 eV [(MeCp) 2 Fe]. The results are compared with known mass spectra of the Pt- and Fe-compound. Schemes for the fragmentation and ion formation processes in the ion source are discussed. The fragment ion composition as a function of the ion source temperature was investigated. The production rate of pure metal ions is small. The measured total single ionization cross sections when compared with calculations using two additivity rules were found to be lower than the calculated values.

Our investigations have been motivated by former works of MICHEL and ACHTERBERG [1]. They described thc important influence of the external circuit elements and connected therewith the mechanism of feedback (BARKHAUSEN k.υ ≥ 1). The properties of external and self-excited moving striations (thrcshold current, fundamental frequency) are strongly influenced by the feedback. This paper demonstrates the differences occuring either a voltage or a current source in the external circuit is used in order to perturb the discharge and to realize different degrees of feedback by changing the external resistor R ext. of the discharge. It is shown the impact on the fields of existence of self excited striations in a non driven discharge. Furthermore our investigations yield differences in the width of ARNOL'D tongues [2] of periods one and two in the perturbed discharge depending on a varied degree of feedback. Last not least its influence on the behaviour of quasiperiodic and chaotic states is demonstrated. The investigations permit first information concerning the sensivitity of one parameter variation (feedback controll by external resistor) which might be used e.g. for a stabilization of unstable periodic orbits (controlling chaos).

The semi-empirical Deutsch-Mark (DM) formalism for the calculation of absolute cross sections for the single ionization of atoms has been extended to the calculation of cross sections for the double and triple ionization of ground state atoms. Detailed comparisons are made with available experimental data from threshold to 200 eV. In general, we find good agreement between the present calculations and the available experimental data. On that basis, we feel confident that the present formalism can be applied to predict double and triple ionization cross sections for those atoms, for which no experimental data are currently available, with an accuracy in the 30- 50% range for impact energies where direct ionization processes dominate and where contributions from tightly bound inner shells can be neglected. This level of precision should be sufficient for modelling purposes and many other practical applications. 1 Introduction The ionization of an atom in its ground state by electron impact is one of the most important fundamental collisional interactions in. atomic physics. Ionization processes play an important role in many applications including discharges and plasmas, gas lasers, planetary, cometary and stellar atmospheres, and radiation chemistry [

The recently developed semiempirical DM-approach for the calculation of electron impact single ionization cross sections is applied here to the ionization of the rare gases (Ne, Ar, Kr and Xe) via ejection of an outer s-shell electron. The results obtained are compared with previous experimental and theoretical s-shell ionization cross section functions.

We study the quantum phases of a three-color Hubbard model that arises in the dynamics of the p-band orbitals of spinless fermions in an optical lattice. Strong, color-dependent interactions are induced by an optical Feshbach resonance. Starting from the microscopic scattering properties of ultracold atoms, we derive the orbital exchange constants at 1/3 filling on the cubic optical lattice. Using this, we compute the phase diagram in a Gutzwiller ansatz. We find novel phases with 'axial orbital order' in which pz and px + ipy (or px - ipy) orbitals alternate., 4+epsilon pages, 3 figures. Similar to version published in PRA(R)

Investigations in a periodically driven neon glow discharge show that the occurrence of bestabilities can lead to chaotic states. These states are caused by wave phenomena. Characterizing this behaviour by means of the autocorrelation and the crosscorrelation function without the knowledge of the power spectra can imply false interpretations. These are due to the different dissipation of the fluctuations synchronous with the phase-shifted excitation. It is demonstrated that much information obtained from a large set of data is needed for a reliable evaluation of the dynamics of chaotic states.

In this paper a development of a nonlinear equivalent circuit of the column plasma in the oscillating regime with two inertial factors is demonstrated. The model is based on a theoretical description of the plasma by means of the balance equations of electrons and of metastable atoms. The circuit can be compared to the nonlinear equivalent circuit for a neon gas discharge in a homogeneous regime which we introduced in a previous paper. Both circuits posses only positive parameters of the reactances which can be calculated on the basis of elementary processes occurring in the discharge plasma.

The behaviour of gas discharges can be modelled by equivalent circuits built on the basis of a theoretical description of the plasma. This paper introduces a method to develop a nonlinear equivalent circuit directly by means of the balance equations of the column plasma and by the help of the knowledge obtained from the design of the linear equivalent circuit. The linear network theory was used for the derivation. The circuit found in this way is similar to a derived linear equivalent circuit of the column plasma with two inertial factors (delayed effects) for a neon gas discharge described in previous papers.

We study the use of an optical Feshbach resonance to modify the $p$-wave interaction between ultracold polarized $^{171}\mathrm{Yb}$ spin-$1/2$ fermions. A laser exciting two colliding atoms to the ${}^{1}{S}_{0}+{}^{3}{P}_{1}$ channel can be detuned near a purely-long-range excited molecular bound state. Such an exotic molecule has an inner turning point far from the chemical binding region, and thus, three-body recombination in the Feshbach resonance will be highly suppressed in contrast to that typically seen in a ground-state $p$-wave magnetic Feshbach resonance. We calculate the excited molecular bound-state spectrum using a multichannel integration of the Schr\"odinger equation, including an external perturbation by a magnetic field. From the multichannel wave functions, we calculate the Feshbach resonance properties, including the modification of the elastic $p$-wave scattering volume and inelastic spontaneous scattering rate. The use of magnetic fields and selection rules for polarized light yields a highly controllable system. We apply this control to propose a toy model for three-color superfluidity in an optical lattice for spin-polarized $^{171}\mathrm{Yb}$, where the three colors correspond to the three spatial orbitals of the first excited $p$ band. We calculate the conditions under which tunneling and on-site interactions are comparable, at which point quantum critical behavior is possible.

Measurements of the impedance behaviour of the positive column of a glow discharge are falsified by parasitic capacities. A model, which respects these capacities, was developed and tested by computer simulations and experimental data. Using this model it is possible to correct the influence of parasitic capacities on experimental measured impedance curves. The efficiency of this method is demonstrated on some measurements in a neon discharge.