Tiefenverteilung der Anregung charakteristischer Röntgenstrahlung in Kupfer durch 12 bis 30 keV-Elektronen

The depth distribution of characteristic X-ray production in copper by 12 to 30 keV electrons has been measured with a zink tracer. The results are examined in terms of characteristic distribution parameters which show a potential law energy dependence. Reduction of the depth data and the electron energies by means of electron range and excitation energy, respectively, allows comparison with experimental and theoretical results of other authors on various target-tracer-combinations. Although a general energy dependence is found for the majority of the reduced characteristic parameters the accuracy of the data is not satisfying. Some of the measured distributions obviously contain large systematical errors.     

Charge saturation and neutral substitutions in halomethanes and their group 14 analogues

A computational analysis of the charge distribution in halomethanes and their heavy analogues (MH(4-n)X(n): M = C, Si, Ge, Sn, Pb; X = F, Cl, Br, I) as a function of n uncovers a previously unidentified saturation limit for fluorides when M ≠ C. We examine the electron densities obtained at the CCSD, MP2(full), B3PW91, and HF levels of theory for 80 molecules for four different basis sets. A previously observed substituent independent charge at F in fluoromethanes is shown to be a move toward saturation that is restricted by the low polarizability of C. This limitation fades into irrelevance for the more polarizable M central atoms such that a genuine F saturation is realized in those cases. A conceptual model leads to a function of the form [q(M(n')) - q(M(n))] = a[χ(A') - χ(A)] + b that links the electronegativities (χ) of incoming and leaving atoms (e.g., A' = X and A = H for the halogenation of MH(4-n)X(n)) and the associated charge shift at M. We show that the phenomenon in which the charge at the central atom, q(M), is itself independent of n (e.g., at carbon in CH(4-n)Br(n)) is best described as an "M-neutral substitution"--not saturation. Implications of the observed X saturation and M-neutral substitutions for larger organic and inorganic halogenated molecules and polymeric materials are identified.     

Deriving the mean primary-particle diameter and related quantities from the size distribution and the gravimetric mass of spark generated nanoparticles

Spark generated carbon and iridium nanoparticles were characterised by their electrical-mobility diameter D and by the mass of particulate matter collected in parallel on filter. The particles exhibited slightly skewed lognormal size distributions with mean mobility diameters between 18 and 74 nm. The masses calculated from the measured distributions under the assumption that the particles were spherical (diameter D) and of bulk mass density turned out to be much higher than the gravimetric mass, by factors between 8 and as high as 340. This very pronounced difference initiated a search for an improved relation between particle size and mass. Data analysis suggested that the mass increases linearly with increasing D. Hence the measured distributions were evaluated under the assumption that the spark generated matter was composed of spherical primary nanoparticles of mean diameter d, aggregated in the form of chains of joint length βD, with β>1. Using reasonable values of β between 2 and 4, the mean diameter of carbon primary particles turned out to be 10±1.8 nm, in excellent agreement with size data recently obtained by transmission electron microscopy (TEM). The primary iridium particles were found to be distinctly smaller, with diameters between 3.5±0.6 nm and 5.4±0.9 nm. The comparatively small uncertainty is due to the fact that the primary-particle diameter is proportional to the square root of β. The calculated volume specific surface areas range between 500 and 1700 m²/cm³. These numbers are close to the ‘active’ surface areas previously measured by the BET method. The good agreement with TEM and BET data suggests that the novel approach of nanoparticle characterisation is meaningful. Accordingly, the number concentrations of all individual primary particles rather than the concentrations measured by the mobility analyser should be␣considered the correct dose metric in studies on animal exposure to spark generated nanoparticles. The␣evaluated data imply that the numbers quoted in the literature must be enlarged by factors ranging between about 10 and a maximum as high as 80. An erratum to this article can be found at     

Secondary-ion emission from silicon bombarded with atomic and molecular noble-gas ions

The emission of Si⁺ from a clean silicon surface has been studied for bombardment with various atomic and molecular noble gas ions at energies between 1.5 and 30 keV. It was found that the degree of ionization of Si⁺ depends strongly (l?inearly) on the projectile energy but only weakly on the projectile mass. These results suggest that the degree of ionization is heavily affected by the (dynamic) perturbation of the bulk properties of the bombarded area which increases with increasing nuclear energy deposition.     

The use of secondary ion mass spectrometry for studies of oxygen adsorption and oxidation

Thin oxide layers on silicon and tantalum as well as oxygen saturated silicon surfaces have been investigated by means of SIMS. Sputter depth profiling was achieved using a raster scanned 2 keV argon ion beam. The results clearly indicate that oxygen adsorption does not lead to on oxide-like structure. Moreover it is found that air-grown room temperature oxides on silicon are depleted of oxygen as compared to the composition of thick silicon dioxides. The results are discussed with reference to recently reported SIMS studies on oxygen covered surfaces.     

Messung der Energieverlustspektren von Aluminium- und Silberfolien mit hoher Auflösung

The energy loss spectra of polycrystalline aluminium and silver foils have been measured with high resolution. For the plasmon energy of aluminium 14.97 eV is obtained. The half width of the plasmon peak is 0.60 eV corresponding to a relaxation time τ=1.1×10^?15 sec in fair agreement with optical data. In silver films of certain thicknesses the surface plasmon peak and the plasmon peak can be separated in the energy loss spectrum. The values of the energy losses are 3.64 and 3.78 eV respectively.     

Comparison of profile tailing in SIMS analyses of various impurities in silicon using nitrogen,oxygen, and neon ion beams at near-normal incidence

We have performed a systematic SIMS study into the effect of (i) the chemical nature and (ii) the energy of the primary ions on the decay length which characterizes the exponential fall-off of impurity sputter profiles. The samples consisted of low resistivity, p-type Si covered with thin metallic overlayers. Bombardment was carried out at 2° off normal. Aspect (i) was investigated for tracers of Cu and Ga using N ₂ ⁺ , O ₂ ⁺ , and Ne⁺ primary ions at an energy of 5 keV/atom. The effect of the beam energy, aspect (ii), was studied for eight different tracer species and N ₂ ⁺ primary ions at energies between 2 and 5 keV/atom. In the case of Ga, was found to be shorter with N ₂ ⁺ or O ₂ ⁺ primary ions (=7.0 and 7.5 nm, respectively) than with Ne⁺ (=12 nm). This effect is attributed to beam induced formation of Si₃N₄ or SiO₂ layers, whereby the effective width of the internal distribution of intermixed Ga impurities in the Si subsystem is reduced significantly. In contrast to Ga, the decay length for Cu is smallest under bombardment with Ne⁺ (=16 nm), quite large with N ₂ ⁺ (26 nm) and extremely large with O ₂ ⁺ (2.2 m). Segregation of Cu atoms at the Si₃N₄/Si and the SiO₂/Si interface, respectively, is responsible for this depressed impurity removal rate. Within experimental accuracy the observed variation of the decay length with N ₂ ⁺ energy E [keV/atom] can be written in the form =kE ^p, where k and p are element specific parameters which range from k=1.2 nm for Pb to 10 nm for Cu and from p=0.6 for Cu and Ag to 1.0 for Pb. The results are discussed with reference to conceivable shapes of the distribution of intermixed impurity atoms.On leave from NTT Applied Electronics Laboratories, 3-9-11, Midori-cho, Musashino-shi, Tokyo 180, Japan     

Quantitative analysis of W-C:H coatings by EPMA,RBS (ERD) and SIMS

Several analytical techniques have been used to characterize homogeneous films of tungsten-containing hydrogenated carbon (W-C: H), deposited on Si with a film thickness of 1–1.5 m. Electron probe microanalysis (EPMA) enables one to determine the major components W (3–43 at %) and C, impurities (< 2 at %) of Ar and O, and the mass thickness (300–1800 g/cm²) of the films. The agreement between the results of EPMA and the data (W-content, mass thickness) provided by Rutherford backscattering spectrometry (RBS) is 5–10% relative. Quantitative analysis of hydrogen in W-C:H films (1–16 at %) is carried out by the technique of elastic recoil detection (ERD). A suitable scheme for the determination of H in W-C: H films by SIMS is proposed, based on monitoring the intensity ratio of HCs⁺/CCs⁺ secondary ions.     

Time-of-flight secondary ion mass spectrometry of matrix-diluted oligo- and polypeptides bombarded with slow and fast projectiles: Positive and negative matrix and analyte ion yields, background signals, and sample aging

Human angiotensin II, chain B of bovine insulin, and porcine insulin were determined by time-of-flight secondary ion mass spectrometry under impact of approximately 25 keV Xe+ and SF5+ ion beams and approximately 100 MeV 252Cf fission fragments. Matrix-embedded samples, dissolved in a large surplus of alpha-cyano-4-hydroxycinnamic acid, were prepared by nebulizer spray deposition, neat samples by the droplet technique. It is shown that the status of the sample can be assessed by evaluating the matrix-specific features of the mass spectra. The beneficial effect of matrix isolation was small for angiotensin but large for the insulin samples, which did not show parent peaks from neat material. Negative ion yields under SF5+ impact were up to a factor of 50 higher than with Xe+. For positive secondary ions, the enhancement was much smaller. The mass spectra produced by slow ion beams or fast fission fragments were qualitatively similar. Quantitative differences include the following: with fast projectiles the yields were about 10-30 times higher than with slow ions, but similar for negative ion emission under SF5+ bombardment; the analyte-to-matrix yield ratios were higher with slow ions and up to 250 times higher than the molar analyte concentration; for analyte ions the peak-to-background ratios were higher using slow projectiles; the fraction of carbon-rich collisionally formed molecular ions was much higher with fast projectiles. Sample aging in vacuum for up to five weeks strongly reduced the yield of protonated analyte molecules ejected by slow ion impact, but not of deprotonated species. Hence protonation seems to correlate with sample "wetness" or the presence of volatile proton-donating additives.     

Model calculation of ion collection in the presence of sputtering

This paper presents a zero order approximation of ion collection during sputtering. Neglecting diffusion, range shortening and knock-on effects and assuming a constant sputtering yield general analytical results are developed which allow a comparison with experimental data. The accumulation of implantation profiles and the build-up of surface concentrations and collected quantities are described in detail for Gaussian range distributions. A thorough discussion of available experimental results indicates that the model is suitable for a variety of projectile-target combinations, in particular for medium mass noble gas atoms collected in high melting point targets. Application to sputtering experiments presents further evidence of a strong fluence dependence of the silicon sputtering yield. Some comments are devoted to recently reported analytical and numerical treatments of ion collection during sputtering.