Temperature,roughness and depth resolution in ion sputter profiles

The depth resolutions of evaporated silver layers on polished polycrystalline copper substrates are studied at various temperatures during argon ion sputtemg with AES. A detailed analysis of the profile shape at the interface reveals the nature of contributions to the terms governing interface resolution. The profiles are all accurately described by an error function leading edge followed by an exponential trailing edge. The characteristic of the trailing edge is governed by the development of roughness which depends on the depth, z, sputtered as z^0.875. The roughness is reduced at elevated temperatures by the action of surface diffusion such that the maximum reduction occurs at the highest temperature and the lowest sputtering rate. The characteristic of the leading edge is composed of three terms added in quadrature, (i) defect-enhanced diffusion of copper into the silver film, (ii) roughness as above, and (iii) a constant term due to film nucleation. In the present samples the increased interdiffusion at elevated temperatures and low sputtering rates largely offsets the improvements in topography so that, overall, the depth resolution appears to be a very weak function of temperature. However, in other systems where interdiffusion is small, the resolution could be greatly enhanced.     

Electronic structure of adsorbed alkali atoms for comparison with UPS data

We have generalised our earlier work calculating the induced density of states in alkali chemisorption to include the valence np level in addition to the s level. This allows the theory to take account of the possibility of sp hybridization. Hybridization is said to be weak is the sp level separation ΔE_sP exceeds twice the width of the s or p_z resonance. In the converse case hybridization is strong and the induced density of states no longer reflects distinguishable s and p_z resonances. We argue that ΔE_sP for the chemisorbed alkali exceeds considerably that for the free alkali atom. In the case of Na on r_s = 2 jellium (considered typical of the smaller alkali on r_s = 2?3 substrates) hybridization is strong for the atomic value of ΔE_sp but weak when a somewhat larger value is taken, making the conclusions a little indefinite. For Cs on Cu(111), we find a clear situation of weak hybridization with the atomic ΔE_sP and a fortiori with a more realistic value. There should thus be a well defined 6s resonance in this system. Our estimate of the width of the 6s resonance is in good agreement with photoemission data.     

Isotopenanalyse an niederenergetischen Teilchen der Elemente Bor,Kohlenstoff, Stickstoff und Sauerstoff aus der kosmischen Strahlung in Plastik-Detektoren

In eight cellulose nitrate sheets of a plastic detector stack flown in 1968 from Ft. Churchill in 1.8 g/cm² floating altitude stopping heavy cosmic ray particles of about 100 MeV/Nuc were measured. In 0.2 m² of the 1.6 m² large stack 30 boron, 190 carbon, 83 nitrogen and 263 oxygen particles were analysed. A resolution of ΔZ=±0.1 charge units and ΔM=±0.7 mass units was obtained. Using oxygen particles for a calibration at¹⁶O the mean values of the mass distributions of the other elements are: 10.79±0.17 for boron, 12.22±0.08 for carbon, 14.61±0.12 for nitrogen.     

Analysis of C60 and Cs sputtering ions for depth profiling gold/silicon and GaAs multilayer samples by time of flight secondary ion mass spectrometry

Time of flight secondary ion mass spectrometry (ToF-SIMS) depth profiles of several inorganic layered samples using Cs⁺ and C₆₀⁺ primary sputtering ions of different energies are compared to evaluate sputter yield and depth resolution. A gold/silicon model system is employed to study interfaces between metals and semiconductors, and multilayers of AlGaAs, Al, and InAs in GaAs are analyzed to explore the ability of C₆₀⁺ to analyze semiconductor interfaces in GaAs. Roughness measurements are reported to differentiate between different factors affecting depth resolution. The best depth resolution from all samples analyzed is achieved using 1 keV Cs⁺. However, C₆₀⁺ sputtering has advantages for analyzing conductor/insulator interfaces because of its high sputter yield, and for analyzing deeper heterolayers in GaAs due to lower sputter-induced roughness.     

The elliptical dimension of space-time atmospheric stratification of passive admixtures using lidar data

State-of-the-art airborne lidar data of passive scalars have shown that the spatial stratification of the atmosphere is scaling: the vertical extent (Δz) of structures is typically ≈Δx^H_z where Δx is the horizontal extent and H_z is a stratification exponent. Assuming horizontal isotropy, the volumes of the structures therefore vary as ΔxΔxΔx^H_z=Δx^D_s where the “elliptical dimension” D_s characterizes the rate at which the volumes of typical non-intermittent structures vary with scale. Work on vertical cross-sections has shown that 2+H_z=2.55±0.02 (close to the theoretical prediction 23/9).In this paper we extend these (x, z) analyses to (z, t). In the absence of overall advection, the lifetime Δt of a structure of size Δx varies as Δx^H_t with H_t=2/3 so that the overall space-time dimension is D_st=29/9=3.22…. However, horizontal and vertical advection lead to new exponents: we argue that the temporal stratification exponent H_t≈1 or ≈0.7 depending on the relative importance of horizontal versus vertical advection velocities. We empirically test these space-time predictions using vertical-time (z, t) cross-sections using passive scalar surrogates (aerosol backscatter ratios from lidar) at ∼3 m resolution in the vertical, 0.5-30 s in time and spanning 3-4 orders of magnitude in scale as well as new analyses of vertical (x, z) cross-sections (spanning over 3 orders of magnitude in both x, z directions). In order to test the theory for density fluctuations at arbitrary displacements in (Δz, Δt) and (Δx, Δz) spaces, we developed and applied a new Anisotropic Scaling Analysis Technique (ASAT) based on nonlinear coordinate transformations. Applying this and other analyses to data spanning more than 3 orders of magnitude of space-time scales we determined the anisotropic scaling of space-time finding the empirical value D_st=3.13±0.16. The analyses also show that both cirrus clouds and aerosols had very similar space-time scaling properties. We point out that this model is compatible with (nonlinear) “turbulence” waves, hence potentially explaining the observed atmospheric structures.     

Investigation on z-scan experiment by use of partially coherent beams

Z-Scan experiment using partially coherent beams is investigated theoretically. We derive the expression for the cross-spectral density of the Gaussian Schell-model (GSM) beam passing through the nonlinear thin sample. Then the influences of the aperture radius and the spatial degree of coherence on the z-scan curves are analyzed. We find that transmittance difference ΔT_p-v between the peak and valley in z-scan curves decreases gradually with the increment of the aperture radius, which is similar to the case of the fully coherent beams. It is also shown that ΔT_p-v is getting bigger with the increment of the spatial degree of coherence α₀, and when α₀ is larger than a certain value, ΔT_p-v becomes almost unchanged. The results show that the z-scan experiment with partially coherent beams may provide a feasible method for measuring the spatial degree of coherence.     

Low-energy electron-induced reactions in thin films of glucose and N-acetyl-glucosamine

Reactions induced in thin films of α-d-glucose and N-acetylglucosamine by low-energy electron exposure at incident electron energies (E₀) between 5 eV and 15 eV have been investigated by high-resolution electron energy loss spectroscopy (HREELS). The reactions of α-d-glucose upon electron exposure were also studied in the presence of molecular oxygen. Electron exposure leads to characteristic changes of the vibrational spectra indicating that OH groups are lost with the formation of CC double bonds taking place preferentially above the ionisation threshold of the investigated molecules. At lower E₀, OH groups are equally decomposed suggesting that dissociative electron attachment contributes to the reactions but formation of double bonds is not observed. The results show that different reaction channels are effective depending on E₀ and that the outcome of electron-driven chemistry in saccharides may be controlled by changing from the subionisation regime to E₀ above the ionisation threshold. Generally, low-energy electron exposure in the absence of O₂ produces a material with lower oxygen content, i.e. leads to a reduction of the saccharide. In the case of N-acetylglucosamine, removal of the amide group from the sugar is also important at subionisation energies. In contrast, as shown for α-d-glucose, low-energy electron exposure in the presence of O₂ leads to oxidation of the sugar even at cryogenic temperature.     

The nature of anharmonicity and anomalous piezoelectric properties of ferroelectric SbSBr crystal

The contribution of soft mode at Sb atom's sites, to the temperature dependences of Sb atom's equilibrium position's difference Δz(T) has been studied theoretically, when SbSBr crystal is deformed along a(x), b(y) and c(z)-axis in paraelectric phase and is deformed along c(z)-axis in ferroelectric phase. The largest change of Δz₃₃(T) occurs in the ferroelectric phase near the phase transition temperature in the range from 16 K to 21 K. The temperature dependence of Sb atom's equilibrium position's displacements Δz₃₃ is very similar to the temperature dependence of experimental piezoelectric modulus, when SbSBr crystal is deformed in the direction of c(z)-axis in ferroelectric phase.     

Yield oscillations of inelastic processes under channeling conditions at angles greater than the critical angle

A quantum-mechanical analysis of the angular dependence of the yield of inelastic processes in thin crystals under planar-channeling conditions reveals strong intensity oscillations at a given depth for incidence angles ψ > ψ_c. The dependence of the period of these oscillations on the distance z from the surface of incidence is investigated, and pronounced oscillations of the yield versus z are shown to occur simultaneously at fixed ψ.     

Influence of oxygen on the formation of cubic boron nitride by r.f. magnetron sputtering

Formation of cubic boron nitride by r.f. magnetron sputtering has been studied with O₂ addition to the common working gas Ar/N₂. The chemical and the phase composition were determined with Auger electron spectroscopy sputter depth profiling and Fourier transform infrared spectroscopy. The result shows that oxygen hinders the formation of cBN in sufficient nitrogen-supply, but facilitates the growth of cBN in insufficient nitrogen-supply. With insufficient nitrogen-supply, there exists an optimal oxygen-supply in the working gas that promoted the establishment of the stoichiometric condition in the growing film. O-concentration in the film increases with oxygen-supply in the working gas. cBN forms only when the oxygen concentration is below 5% and c_N/c_B (ratio of concentration of nitrogen atoms and boron atoms) is 1 in the film.     

On the chemical sputtering of oxygen-exposed molybdenum

The sputtering of oxygen-exposed molybdenum was studied by means of mass analysis of emitted neutral and charged particles. The irradiation was performed with 8 keV Ar⁺ ions at temperatures of 25° and 485°C. It was found that the enhanced sputtering yield at elevated temperature during oxygen exposure is due to beam-induced desorption of MoO₂ and cascade sputtering of MoO. At this temperature considerable oxygen incorporation also takes place owing to recoil mixing and diffusion.EURATOM Association     

A model calculation of the auger depth profile at a sharp interface of two homogeneous substances and its comparison with the experimental depth profile of an aluminium oxide — aluminium interface

A heuristic model theory for the detectable concentration as a function of sputter depth z is formulated, using a convolution of the original concentration distribution with a gaussian sputter response function. Afterwards the gaussian width σ is set to be proportional to the sputter depth z to obtain an integral relation between the original and the detectable concentration distribution. This integral relation is then applied to a sharp interface of two substances of constant concentration and the theoretical Auger depth profile is calculated. This calculation is compared with the experimental Auger depth profile of an aluminium oxide — aluminium interface. The theoretical Auger depth profile is fitted by using a least squares fit with the parameters R (sputter rate) and the proportionality factor k and compared to the experimental curve. For all three observed Auger peaks, oxidized aluminium (53 eV), non-oxidized aluminium (68 eV) and oxygen (505 eV), the fitting is excellent. The parameter R is for all three signals the same only k slightly differs.     

Correlation between processing and properties of TiOxNy thin films sputter deposited by the reactive gas pulsing technique

Titanium oxynitride thin films were deposited by d.c. reactive magnetron sputtering from titanium metallic target and from oxygen and nitrogen as reactive gases. The nitrogen mass flow rate was maintained constant whereas that of the oxygen was pulsed during the deposition. A constant pulsing period was used and the introduction time of the oxygen was systematically changed from 0 to 100% of the period time. The reactive gas pulsing technique allowed to prepare TiO_xN_y films with various metalloid concentrations (0≤x≤2.0 and 0≤y≤1.0) and led to changes of the crystallographic structure from f.c.c. TiN to tetragonal TiO₂. The variations of the metalloid content in the films result in changes in the electrical and optical properties and the reverse evolution of the oxygen and nitrogen content correlates with the transition from metallic to semiconducting behavior. The sputtering conditions were investigated taking into account the poisoning phenomena of the surface of the target from real time measurements of the target potential and from the reactive atmosphere, followed by mass spectrometry. Such diagnostics allowed to understand and to control better the advantageous role of the reactive gas pulsing technique and conducted to close relationships between the process parameters and the film properties.     

Depth profiling using C60 SIMS—Deposition and topography development during bombardment of silicon

A C₆₀⁺ primary ion source has been coupled to an ion microscope secondary ion mass spectrometry (SIMS) instrument to examine sputtering of silicon with an emphasis on possible application of C₆₀⁺ depth profiling for high depth resolution SIMS analysis of silicon semiconductor materials. Unexpectedly, C₆₀⁺ SIMS depth profiling of silicon was found to be complicated by the deposition of an amorphous carbon layer which buries the silicon substrate. Sputtering of the silicon was observed only at the highest accessible beam energies (14.5 keV impact) or by using oxygen backfilling. C₆₀⁺ SIMS depth profiling of As delta-doped test samples at 14.5 keV demonstrated a substantial (factor of 5) degradation in depth resolution compared to Cs⁺ SIMS depth profiling. This degradation is thought to result from the formation of an unusual platelet-like grain structure on the SIMS crater bottoms. Other unusual topographical features were also observed on silicon substrates after high primary ion dose C₆₀⁺ bombardment.     

Comment on “Evaluation of concentration-depth profiles by sputtering in SIMS and AES” by S. Hofmann

The statistics of the sputtering process, which has been used to explain sputterbroadening effect due to surface roughness, has been treated with conditional probabilities. This results in the relationship, , instead of derived by S. Hofmann [Appl. Phys.9, 59 (1976)], where δz,z, and are the depth resolution, sputtered depth and sputtering yield, respectively.     

Improvement of depth resolution in XPS analysis of fluorinated layer using C60 ion sputtering

Depth profile of C₆₀ ion-used X-ray photoelectron spectroscopy (XPS) was studied on fluorinated organic layers with different thicknesses. We found that the depth resolution decreased, the sputtering rate went down and the surface turned rough as the layer thickness increased. This is because carbon-rich layer was formed on the surface by cross-linking reaction of the polymer and/or accumulation of degraded C₆₀ through continuous sputtering. Surprisingly, the high sputtering rate drastically improved the resolution of the analysis. The rate over 48.7 nm/min did not show any deterioration on the depth resolution, the sputtering rate and surface smoothness.     

高阻隔铝塑膜辉光放电发射光谱深度谱测量参数的优化

脉冲-射频辉光放电发射光谱(GDOES)深度剖析是一种基于辉光放电原理的原子光谱技术,广泛应用于薄膜材料与功能多层膜结构中成分随深度分布的表征.该技术具有真空度要求低,灵敏度高,溅射速率快等优点.同时脉冲-射频电源所采用的瞬间高功率模式可使得氩离子周期性轰击样品表面,避免了由于热量积累所导致的熔融或碳化,因此脉冲-射频...     

Cluster SIMS using metal cluster complex ions

Metal cluster complexes are chemically synthesized organometallic compounds, which have a wide range of chemical compositions with high molecular weight. Using a metal cluster complex ion source, sputtering characteristics of silicon bombarded with normally incident Ir₄(CO)₇⁺ ions were investigated. Experimental results showed that the sputtering yield at 10 keV was 36, which is higher than that with Ar⁺ ions by a factor of 24. In addition, secondary ion mass spectrometry (SIMS) of boron-delta-doped silicon samples and organic films of poly(methyl methacrylate) (PMMA) was performed. Compared with conventional O₂⁺ ion beams, Ir₄(CO)₇⁺ ion beams improved depth resolution by a factor of 2.5 at the same irradiation conditions; the highest depth resolution of 0.9 nm was obtained at 5 keV, 45° with oxygen flooding of 1.3 × 10⁻⁴ Pa. Furthermore, it was confirmed that Ir₄(CO)₇⁺ ion beams significantly enhanced secondary ion intensity in high-mass region.     

SIMS depth profiling of Pd/B4C, Ni/C, and Cr/Sc multilayer metal structures using registration of cluster secondary ions: The problem of depth resolution enhancement

The possibility of minimizing matrix effects during the SIMS depth profiling of multilayer metal structures is investigated, based on the use of cluster secondary ions that include a combination of the element to be analyzed and sputtering cesium or oxygen ions. For Pd/B₄C, Ni/C, and Cr/Sc structures, the use of cluster secondary ions enabled us to substantially enhance depth resolution up to 1–2 nm.