J. De Wachter

COMPREHENSIVE RUTHERFORD BACKSCATTERING AND CHANNELING STUDY OF ION-BEAM-SYNTHESIZED ERSI1.7 LAYERS

Heteroepitaxial ErSi1.7 layers with excellent crystallinity (χmin of Er is 1.5%) have been prepared by high‐dose 90 keV Er implantation into a Si(111) substrate using channeled implantation. Such an ErSi1.7/Si system offers a rare opportunity to study comprehensively the structure, orientation, and strain using Rutherford backscattering spectrometry and channeling analysis. We found that the minimum yield and width of the [0001] dip of the Er atoms are quite different from that of the Si atoms in the silicide layer. It is confirmed that the azimuthal orientation of the hexagonal ErSi1.7 layer to the cubic Si substrate is ErSi1.7 [0001] ∥ Si[111] and ErSi1.7 {1120} ∥ Si {110}, and that the epilayer is compressively strained. Besides, by using the angular scan and image scan, we reveal that the dips of the {1010} family are missing for the Si atoms in the epilayer but do exist for the Er atoms in the same epilayer. The reason for this drastic difference is explained by the separate {1010} planes and the ...

Growth and properties of ion beam synthesized Si/CoxNi1−xSi2/Si(111) structures

Heteroepitaxial CoxNi1−xSi2 layers with good crystalline quality (χmin=3.5%) have been formed by ion beam synthesis. For a sample with x=0.66, we found that this ternary silicide layer contains 11% type B and 89% type A orientation. The transmission electron microscopy investigation reveals that the type B component is mainly located at the interfaces and with a thickness of only a few monolayers. X‐ray diffraction studies of the sample show that the strain of the type B component is smaller than that of the type A and is probably the reason for such a unique distribution of the type B component in the epilayer. Rutherford backscattering‐channeling, Auger electron spectroscopy, transmission electron microscopy, and x‐ray diffraction have been used in this study.

Unusually large substitutional fraction for Fr implanted in Fe observed by emission channelling

Abstract An emission channelling study has been performed on α-emitting Fr implants in Fe. The implantation dose was kept below 10 11 atoms cm 2 to assure single cascade conditions. Low dose was possible as the experiment was done on line, and data was recorded with a position sensitive detector. The study revealed 45% of francium in substitutional sites at room temperature and 57% in substitutional sites at 120 K. No evidence for vacancy trapping was found, suggesting a small trapping radius for Fr in Fe.

Implantation temperature dependent distribution of NiSi2 formed by ion beam synthesis in silicon

The formation and distribution of NiSi2 in (111) silicon by Ni‐ion implantation with a fluence of 1.1×1017 cm−2 and an energy of 90 keV is studied as a function of the temperature during implantation. For temperatures below 200 °C, a buried layer of NiSi2 precipitates is formed. Increasing the temperature gradually from 200 to 350 °C leads first to the formation of a double buried NiSi2 layer which with increasing temperature evolves into an epitaxial NiSi2 surface layer. A tentative model to explain for the observed anomalous behavior is presented.

Structural characterization of thin epitaxial Fe films

Thin Fe films grown on MgO by molecular beam epitaxy are analyzed by X-ray diffraction (XRD), Rutherford backscattering and channeling spectrometry (RBS-C). This extensive characterization of a simple system as single Fe films allows us to do a detailed structural characterization, which can be used as a yardstick in the interpretation of Fe layers in more complex structures as, e.g., multilayers. The atomic force microscopy (AFM), X-ray diffraction and Rutherford backscattering and channeling spectrometry results demonstrate the films smoothness, mosaic structure, and epitaxial quality, respectively. Simulations of both X-ray diffraction, by the Suprex routine, and Rutherford backscattering spectrometry results, by the RUMP simulation code, show that the experimentally determined structural parameters by different techniques match each other. Moreover, by using the measured thickness, mosaic spread and oxidation as input parameters in Monte Carlo simulations of ion channeling scans, a good agreement with the experimental dips was obtained as well.

Structural characterization of ion‐beam synthesized NiSi2 layers

NiSi2(111) and NiSi2(100) layers with good crystalline quality have been formed by ion‐beam synthesis. An unusual Ni atom distribution showing two completely separated layers during a single implantation step has been observed by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). The orientation, strain, and stiffness of the NiSi2 layers have been studied by RBS/channeling, x‐ray diffraction, and TEM. The results show that the continuous NiSi2 layers have type‐A orientation with a parallel elastic strain larger than the theoretical value of 0.46% for pseudomorphic growth. The perpendicular strain of the NiSi2(111) layers is apparently smaller than that of NiSi2(100) layers, indicating a higher stiffness in the 〈111〉 direction.

Channeled ion beam synthesis: a new technique for forming high-quality rare-earth silicides

Abstract High dose 166Er or 160Gd implantations are used to form rare-earth (RE) silicides in Si. After implanting 0.8−2.0 × 1017 at./cm2 with 90 keV into Si(111) substrates kept at ∼ 450 to 530°C, we found that using conventional non-channeled implantation (tilted over 7°), it is impossible to form a continuous RESi1.7 layer. On the contrary, using channeled implantation, a continuous epitaxial ErSi1.7 layer with very good crystalline quality can be synthesized; a lowest χmin value of 1.5% for a surface ErSi1.7 layer is obtained. This different behaviour is explained using a model based on the difference in implantation depth, defect density and sputtering yield between random and channeled implantation, and the results are compared with Monte Carlo simulations. Such a high-quality RESi1.7/Si system offers a rare opportunity to study the structure, orientation and strain comprehensively using Rutherford backscattering and channeling spectrometry, X-ray diffraction and TEM. We found that the azimuthal orientation of the hexagonal RESi1.7 layer to the cubic Si substrate is RESi1.7[0001]/t|Si[111] and RESi1.7{11 2 0}/t|Si{110}. It is further observed that the ErSi1.7 epilayer is compre strained and quasi-pseudomorphic. In the case of GdSi1.7, the most difficult rare-earth silicide to form, and enhanced stabilization of the hexagonal over the orthorhombic phase is observed.

Structure determination of very thin epitaxial layers of metastable body centered cubic Co with ion channeling

The structure of a 20 A thin Co layer embedded between Fe layers grown with molecular beam epitaxy on MgO is determined with ion beam channeling. From the position and the ratio of the widths of the angular yield profiles for different crystallographic directions, we show that Co is forced in the metastable body centered cubic structure. The presence of tetragonal distortion in the Co layer is observed.

Simultaneous synthesis of well-separated buried and surface silicides using a single ion implantation step

An unusual Ni distribution with two completely separated buried and surface silicide layers has been observed after Ni ion implantation in Si(111) kept at a temperature of 300 °C, with a dose of 1.1×1017/cm2 and at a fixed energy of 90 keV. RBS/channeling, AES, and cross‐sectional TEM have been used to study this phenomenon as a function of the substrate temperature and Co co‐implantation. A model is presented, based on the diffusion of the transition metal, the defect annealing during the implantation, and the gettering power of the surface and the end of range defects.

Mössbauer spectroscopy investigation of body centered cubic Co in Co/Fe superlattices prepared with MBE

A new spectrum component is observed in Mössbauer spectra of thin body centered cubic Co layers prepared in Fe/Co superlattices doped with57Co. It is characterized by a large magnetic hyperfine field (31.2 T) and an isomer shift nearly equal to that of α-Fe. The decrease of the isomer shift in bcc Co with respect to hcp Co is consistent with smaller s to d charge transfer in bcc Co as compared to hcp Co. The cubic structure of the CoFe superlattices is evidenced with X-ray diffraction and ion-channeling measurements. The Fe/Co interface is investigated with conversion electron Mössbauer spectroscopy. It is shown that the interface alloy thickness is about six monolayers for growth temperatures up to 450 K and that increasing alloying occurs for higher growth temperatures.