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DOE OSTI2020

Materials Data on ReSi2 by Materials Project

ReSi2 is Protactinium-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Re is bonded in a distorted q6 geometry to ten equivalent Si atoms. There are two shorter (2.60 Å) and eight longer (2.62 Å) Re–Si bond lengths. Si is bonded in a distorted q6 geometry to five equivalent Re and five equivalent Si atoms. There are four shorter (2.59 Å) and one longer (2.65 Å) Si–Si bond lengths.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Sc3(ReSi2)2 by Materials Project

Sc3(ReSi2)2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are three inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to six Si4- atoms to form a mixture of distorted edge, face, and corner-sharing ScSi6 pentagonal pyramids. There are a spread of Sc–Si bond distances ranging from 2.59–2.84 Å. In the second Sc3+ site, Sc3+ is bonded to six Si4- atoms to form a mixture of edge, face, and corner-sharing ScSi6 pentagonal pyramids. There are a spread of Sc–Si bond distances ranging from 2.79–2.95 Å. In the third Sc3+ site, Sc3+ is bonded in a 8-coordinate geometry to eight Si4- atoms. There are a spread of Sc–Si bond distances ranging from 2.80–3.10 Å. There are two inequivalent Re+3.50+ sites. In the first Re+3.50+ site, Re+3.50+ is bonded in a 6-coordinate geometry to six Si4- atoms. There are a spread of Re–Si bond distances ranging from 2.47–2.72 Å. In the second Re+3.50+ site, Re+3.50+ is bonded in a 5-coordinate geometry to five Si4- atoms. There are a spread of Re–Si bond distances ranging from 2.45–2.57 Å. There are five inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 10-coordinate geometry to six Sc3+, two equivalent Re+3.50+, and two equivalent Si4- atoms. There are one shorter (2.53 Å) and one longer (2.83 Å) Si–Si bond lengths. In the second Si4- site, Si4- is bonded in a 10-coordinate geometry to six Sc3+, two equivalent Re+3.50+, and two equivalent Si4- atoms. In the third Si4- site, Si4- is bonded in a 9-coordinate geometry to four Sc3+, four Re+3.50+, and one Si4- atom. The Si–Si bond length is 2.48 Å. In the fourth Si4- site, Si4- is bonded in a 1-coordinate geometry to four Sc3+, three Re+3.50+, and two Si4- atoms. The Si–Si bond length is 2.49 Å. In the fifth Si4- site, Si4- is bonded in a 5-coordinate geometry to six Sc3+, two equivalent Re+3.50+, and one Si4- atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on ReSi2(PO5)3 by Materials Project

ReSi2(PO5)3 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Re7+ is bonded to six O2- atoms to form distorted ReO6 octahedra that share a cornercorner with one ReO6 octahedra and corners with three PO4 tetrahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Re–O bond distances ranging from 1.72–2.11 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to six O2- atoms to form SiO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.75–1.82 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one SiO4 tetrahedra and corners with three PO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.60–1.64 Å. There are three inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one ReO6 octahedra, corners with two equivalent SiO6 octahedra, and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 29–48°. There are a spread of P–O bond distances ranging from 1.52–1.59 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one ReO6 octahedra, corners with two equivalent SiO6 octahedra, and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 29–46°. There are a spread of P–O bond distances ranging from 1.51–1.58 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one ReO6 octahedra, corners with two equivalent SiO6 octahedra, and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 27–47°. There are a spread of P–O bond distances ranging from 1.52–1.59 Å. There are sixteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two equivalent Re7+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Re7+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Si4+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Re7+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Si4+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Si4+ and one P5+ atom. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to one Si4+ and one P5+ atom. In the ninth O2- site, O2- is bonded in a bent 150 degrees geometry to one Si4+ and one P5+ atom. In the tenth O2- site, O2- is bonded in a single-bond geometry to one Re7+ atom. In the eleventh O2- site, O2- is bonded in a bent 150 degrees geometry to one Re7+ and one P5+ atom. In the twelfth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Si4+ and one P5+ atom. In the thirteenth O2- site, O2- is bonded in a bent 150 degrees geometry to one Si4+ and one P5+ atom. In the fourteenth O2- site, O2- is bonded in a bent 150 degrees geometry to one Si4+ and one P5+ atom. In the fifteenth O2- site, O2- is bonded in a single-bond geometry to one Re7+ atom. In the sixteenth O2- site, O2- is bonded in a bent 150 degrees geometry to one Si4+ and one P5+ atom.

36 MATERIALS SCIENCE↗

NASA NTRS1991

Amorphization and recrystallization of epitaxial ReSi2 films grown on Si(100)

The effects of implantation damage and the chemical species of the implant on structural and electrical properties of epitaxial ReSi2 films on Si(100) implanted with Si-28 or Ar-40 ions, at doses ranging from 10 to the 13th/sq cm to 10 to the 15th/sq cm, were investigated using the backscattering spectrometry, XRD, and the van der Pauw techniques. Results showed that ion implantation produces damage in the film, which increases monotonically with dose; the resistivity of the film decreases monotonically with dose.

Kim, Kun HO↗

NASA NTRS1990

Narrow bandgap semiconducting silicides: Intrinsic infrared detectors on a silicon chip

Work done during the final report period is presented. The main technical objective was to achieve epitaxial growth on silicon of two semiconducting silicides, ReSi2 and CrSi2. ReSi2 thin films were grown on (001) silicon wafers by vacuum evaporation of rhenium onto hot substrates in ultrahigh vacuum. The preferred epitaxial relationship was found to be ReSi2(100)/Si(001) with ReSi2(010) parallel to Si(110). The lattice matching consists of a common unit mesh of 120 A(sup 2) area, and a mismatch of 1.8 percent. Transmission electron microscopy revealed the existence of rotation twins corresponding to two distinct but equivalent azimuthal orientations of the common unit mesh. MeV He(+) backscattering spectrometry revealed a minimum channeling yield of 2 percent for an approximately 1,500 A thick film grown at 650 C. Although the lateral dimension of the twins is on the order of 100 A, there is a very high degree of alignment between the ReSi2(100) and the Si(001) planes. Highly oriented films of CrSi2 were grown on (111) silicon substrates, with the matching crystallographic faces being CrSi2(001)/Si(111). The reflection high-energy electron diffraction (RHEED) patterns of the films consist of sharp streaks, symmetrically arranged. The predominant azimuthal orientation of the films was determined to be CrSi2(210) parallel to Si(110). This highly desirable heteroepitaxial relationship has been obtained previously by others; it may be described with a common unit mesh of 51 A(sup 2) and mismatch of 0.3 percent. RHEED also revealed the presence of limited film regions of a competing azimuthal orientation, CrSi2(110) parallel to Si(110). A channeling effect for MeV He(+) ions was not found for this material. Potential commercial applications of this research may be found in silicon-integrated infrared detector arrays. Optical characterizations showed that semiconducting ReSi2 is a strong absorber of infrared radiation, with the adsorption constant increasing above 2 x 10(exp 4) cm(sup -1) for photon energies above 0.2 eV. CrSi2 is of potential utility for detection at photon energies above approximately 0.3 eV.

Mahan, John E.↗

NASA NTRS1989

Narrow bandgap semiconducting silicides: Intrinsic infrared detectors on a silicon chip

Polycrystalline thin films of CrSi2, LaSi2, and ReSi2 were grown on silicon substrates. Normal incidence optical transmittance and reflectance measurements were made as a function of wavelength. It was demonstrated that LaSi2 is a metallic conductor, but that CrSi2 and ReSi2 are, in fact, narrow bandgap semiconductors. For CrSi2, the complex index of refraction was determined by computer analysis of the optical data. From the imaginary part, the optical absorption coefficient was determined as a function of photon energy. It was shown that CrSi2 possesses an indirect forbidden energy gap of slightly less than 0.31 eV, and yet it is a very strong absorber of light above the absorption edge. On the other hand, the ReSi2 films exhibit an absorption edge in the vicinity of 0.2 eV. Measurements of the thermal activation energy of resistivity for ReSi2 indicate a bandgap of 0.18 eV. It is concluded that the semiconducting silicides merit further investigation for development as new silicon-compatible infrared detector materials.

Mahan, John E.↗