E. Szilágyi

Theoretical approximations for depth resolution calculations in IBA methods

Abstract One of the most important parameters in depth profiling using ion beam analysis (IBA) is depth resolution. Theoretical approximations are presented that lead to relatively fast calculations for the following contributions: energy and angular spread of the beam; geometric spread caused by finite beam size and detectors solid angle; energy straggling and multiple scattering in the sample; effect of the absorber foil; energy resolution of the detection method and resonance width in resonance methods. Multilayered multi-elemental targets are also considered and the different contributions are composed statistically by a method that takes into account the peculiar shapes of the corresponding probability densities. A computer code, DEPTH, successfully demonstrated the speed and reliability of the calculations.

Energy spread in ion beam analysis

Abstract In ion beam analysis (IBA) the depth profiles are extracted from the experimentally determined energy profiles. The spectra, however, are subject to finite energy resolution of both extrinsic and intrinsic origin. Calculation of those effects such as instrumental beam, geometry and detection-related energy and angular spreads as well as energy straggling, multiple scattering and Doppler effects in the sample itself is not trivial, especially since it involves treatment of non-independent random processes. A proper account for energy spread is vital in IBA not only for correct extraction of elemental and isotopic depth profiles from the measured spectra, but already prior to data acquisition, in optimising experimental conditions to reach the required depth resolution at a certain depth. After a short review of the literature on the different energy spread contributions experimental examples are given from resonance, RBS, elastic BS and ERDA practice in which an account for energy spread contributions is essential. Some further examples illustrate extraction of structural information (roughness, pore size, etc.) from elaborated depth resolution calculation for such layer structures.

Accurate determination of Quantity of Material in thin films by Rutherford backscattering spectrometry

Ion beam analysis (IBA) is a cluster of techniques including Rutherford and non-Rutherford backscattering spectrometry and particle-induced X-ray emission (PIXE). Recently, the ability to treat multiple IBA techniques (including PIXE) self-consistently has been demonstrated. The utility of IBA for accurately depth profiling thin films is critically reviewed. As an important example of IBA, three laboratories have independently measured a silicon sample implanted with a fluence of nominally 5 × 10(15) As/cm(2) at an unprecedented absolute accuracy. Using 1.5 MeV (4)He(+) Rutherford backscattering spectrometry (RBS), each lab has demonstrated a combined standard uncertainty around 1% (coverage factor k = 1) traceable to an Sb-implanted certified reference material through the silicon electronic stopping power. The uncertainty budget shows that this accuracy is dominated by the knowledge of the electronic stopping, but that special care must also be taken to accurately determine the electronic gain of the detection system and other parameters. This RBS method is quite general and can be used routinely to accurately validate ion implanter charge collection systems, to certify SIMS standards, and for other applications. The generality of application of such methods in IBA is emphasized: if RBS and PIXE data are analysed self-consistently then the resulting depth profile inherits the accuracy and depth resolution of RBS and the sensitivity and elemental discrimination of PIXE.

Optimization of the depth resolution in elastic recoil detection

Abstract Elastic recoil detection (ERD) by 1H(4He,4He)1H reaction is a fast, nondestructive method for depth profiling of hydrogen isotopes. The paper presents an experimental and theoretical study of the depth resolution under different conditions. A depth resolution of 10 nm can be achieved.

Theoretical calculation of the depth resolution of IBA methods

Abstract One of the most important parameters in depth profiling via ion beam analysis (IBA) is the depth resolution. Unfortunately its approximations in the literature are not general and theoretically well based. To fill this gap and help our decisions when selecting the suitable IBA method, a relatively fast and accurate algorithm was developed and implemented in a PC-code called DEPTH. The code takes into account the following effects: (1) energy and angular spread of the beam, (2) geometrical spread caused by the finite beam spot and detector solid angle, (3) straggling and multiple scattering in the sample, (4) the width of the resonance (in resonance methods), (5) absorber foil (if any) and (6) energy resolution of detection method. The energy distribution contributions coming from multiple scattering are taken into account with their statistical dependence and non-Gaussian shape. The effect of the absorber foil is approximated with its transfer function.

Oxidation of SiC investigated by ellipsometry and Rutherford backscattering spectrometry

Oxidation of SiC was performed in Ar–O2 mixture of atmospheric pressure at 1100 °C and compared with that of Si. The partial pressure of O2 varied from 100 to 1000 mbar, while the oxidation time ranged from 0.5 to 45 h. The thickness of the oxide films was determined by spectroscopic ellipsometry and Rutherford backscattering spectrometry. The time and the pressure dependence of the oxidation kinetics of SiC are well described by the modified Deal–Grove model. In the diffusion-limited region, even for the faster case, the oxidation kinetics of the C-terminated face of SiC is not clearly limited by oxygen indiffusion, as for pure silicon. To interpret the ellipsometry spectra, two models of possible structure were used. In the case of the one-layer model, for layer thicknesses above 30 nm, the refractive index of the oxide layers is identical to that of thermally oxidized Si, and it increases rapidly with decreasing thickness below about 15 nm. This increase is significantly larger for C-terminated than fo...

Theoretical approximation of energy distribution of elastically recoiled hydrogen atoms

Abstract One of the most important characteristics in depth profiling using ion beam analysis (IBA) is energy (or depth) resolution. A computer code, DEPTH, was developed to calculate the above values for different IBA methods. In this paper it will be shown that DEPTH can calculate accurately also the shape of the energy distribution of the detected ions. Examples will be given for the elastic recoil detection analysis (ERDA) performed at reflection geometry. This is one of the most complicated cases, since here multiple scattering effects are also significant because of the applied glancing incidence and detection angles. To investigate these effects experimentally samples containing thin double layers of Al, Cu, Ag and Au separated by interfacial hydrogenated amorphous carbon films were prepared and measured by ERDA using He ions.

Hydrogen depth resolution in multilayer metal structures, comparison of elastic recoil detection and resonant nuclear reaction method

Abstract Four different metals: Al, Cu, Ag and Au have been used to produce four special multilayer samples to study the depth resolution of hydrogen. The layer structure of each sample was analysed using 2 MeV He Rutherford backscattering spectrometry, 4.5 MeV He elastic recoil detection (ERD) and 30 MeV F6+ HIERD. Moreover the hydrogen distribution was analysed in all samples using H( 15 N, αγ)12C nuclear reaction analysis (NRA) with resonance at 6.385 MeV. The results show that the best depth resolution and sensitivity for hydrogen detection are offered by resonance NRA. The He ERD shows good depth resolution only for the near surface hydrogen. In this technique the depth resolution is rapidly reduced with depth due to multiple scattering effects. The 30 MeV F6+ HIERD demonstrated similar hydrogen depth resolution to He ERD for low mass metals and HIERD resolution is substantially better for heavy metals and deep layers.

On the limitations introduced by energy spread in elastic recoil detection analysis

Abstract Improvements in experimental techniques have led to monolayer depth resolution in heavy ion elastic recoil detection analysis (HI-ERDA). Evaluation of the spectra, however, is not trivial. The spectra, using even the best experimental set-up, are subject to finite energy resolution of both extrinsic and intrinsic origin. A proper account for energy spread is necessary to extract the correct depth profile from the measured spectra. With calculation of the correct energy (or depth) resolution of a given method, one can decide in advance whether or not the method will resolve details of interest in the depth profile. To achieve the best depth resolution, it is also possible to find optimum parameters for the experiments. The limitations introduced by the energy spread effects are discussed. An example for simulation is shown for high energy resolution HI-ERDA measurements. Satisfactory agreement between the simulated and the measured HI-ERDA spectra taken by 60 MeV 127 I 23+ ions on highly oriented pyrolythic graphite (HOPG) sample is found, in spite of the non-equilibrium charge state of the recoils and the difference in the stopping powers caused by the given charge state of the incident ion and the recoil, which are not taken into account. To achieve more precise data evaluation these effects should be included in simulation codes, or all the subspectra corresponding to different recoils charge states should be measured and summed.

Tailoring Fe∕Ag superparamagnetic composites by multilayer deposition

Fe∕Ag granular multilayers were examined by magnetization and Mossbauer spectroscopy measurements. Very-thin (0.2 nm) discontinuous Fe layers show superparamagnetic properties that can be tailored by the thickness of both the magnetic and the spacer layers. Novel heterostructures, superparamagnetic and ferromagnetic layers stacked in different sequences, were prepared and the specific contribution of the ferromagnetic layers to the low-field magnetic susceptibility was identified.