cording to a thermal expansion calculation, there would be no size mismatch between NiSi2and Si lattices at 380°C, which was defined as zero-mismatch temperature. The implantation was conducted with a metal vapor vacuum arc (MEVVA) ion implanter at an extraction voltage of 45 kV. Based on a thermal conduction estimation, a temperature rise of 380°C required the Ni-ion current density to be 35 μA/cm². For the Si(111) wafers, the high conducting NiSi2layers were indeed directly formed after Ni-ion implantation with this specific current density to a normal dose of 2 × 10¹⁷ions/cm²and the resistivity was as low as 9 μΩ cm. For the Si(111) wafers pre-covered with a 10-nm Ni over-layer, the resistivity of the NiSi2layers obtained under the same conditions decreased down to about 6 μΩ cm. The superior electrical property of the NiSi2was thought to be related to its formation temperature, i.e. at a zero-mismatch temperature of 380°C, which resulted in minimizing the stress and stress-induced defects involved in its formation as well as cooling process.

Gao K. Y.;Liu B. X.

Applied Physics A Materials Science and Processing

1999

Epitaxial CoSi2 layers can be synthesized by a single-step technique of high-current Co-ion implantation into Si wafers, without in situ heating or post-annealing, using a metal vapor vacuum arc (MEVVA) ion source. In particular, plain and continuous epitaxial CoSi2 layers with good crystallinity can be obtained on Si(111). Measurements show that increasing the formation temperature and the implantation dose can improve the crystallinity of the layers.

Zhu H. N.;Liu B. X.

Journal of Physics D Applied Physics

1999

Metal Vapor Vacuum Arc (MEVVA) ion implantation was employed to synthesize NiSi2 layers on Si(100) wafers and was conducted at a voltage of 45 kV with various current densities to a fixed dose of 2×10¹⁷ ions/cm², required by the chemical stoichiometry. From a thermal expansion calculation, there would be no size mismatch between NiSi2 and Si lattices at 380°C. A current density of 35 μA/cm² was required, according to an estimation, to heat the wafers to 380°C. Implanting with this selected current density, a unique NiSi2 layer was indeed obtained with a resistivity as low as 14 ± 2 μΩ cm. Furthermore, a temperature dependence of the resistivity was observed and the NiSi2 layers formed at temperatures deviated from the zero-mismatch temperature featured greater resistivities than that of the layer synthesized at 380°C. The experimental results are reported in detail together with a discussion of the observed temperature dependence. © 1999 Elsevier Science B.V. All rights reserved.

Gao K. Y.;Liu B. X.

Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms

1999

High aluminum content intermetallic compound NbAl3 was formed by Nb ion implantation into Al films with a current density of 108 μA cm^-2 using a metal vapor vacuum arc (MEVVA) ion source. When the Nb ion dose was of 3×10¹⁷ ions cm^-2, NbAl3 phase was formed. With increasing the ion dose, the crystallinity of NbAl3 phase was gradually improved. The NbAl3 layer with a thickness of about 1900 angstroms was obtained on the Al surface implanted by Nb ions up to a dose of 8×10¹⁷ cm^-2. The microhardness of the Nb implanted Al films was significantly increased by the NbAl3 phase.

Miao W.;Tao K.;Liu B. X.;Li B.

Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms

2000

Continuous and plain CrSi2 layers were directly formed on Si by high-current Cr ion implantation into Si wafers, which were heated simultaneously by the ion beam itself and maintained at relatively low temperatures down to 150 °C. Interestingly, the CrSi2 layers so obtained were of n-type and their Hall mobility was high as 1085 cm² V^-1s^-1. Scanning electron microscopy and atomic force microscopy analyses were employed to study the morphology of the CrSi2 formed.

Zhu H. N.;Gao K. Y.;Liu B. X.

Journal of Physics D Applied Physics

2000

Continuous and plain n-type CrSi2 semiconductor layers featuring a relatively sharp interface with the underneath Si were synthesized by a single-step metal vapor vacuum arc (MEVVA) ion implantation and the synthesizing process was reproducible. Hall measurements showed that the electrical parameters changed with the formation temperature. At an optimal formation temperature of 260°C, a high room temperature (RT) Hall mobility of 1085 cm² V^-1 s^-1 was obtained. Besides, the bandgap values of 0.7 and 0.84 eV were observed for the CrSi2 layers formed under different experimental conditions. The mechanism responsible for the formation of CrSi2 layers on Si wafers is also discussed.

Zhu H. N.;Liu B. X.

Applied Surface Science

2000

The Al-enriched intermetallic compound DO23-Al3Zr was directly formed by Zr ion implantation into Al films at a current density of 64 μA cm^-2 using a metal vapour vacuum arc (MEVVA) ion source at a dose of 4×10¹⁷ ions cm^-2. With increasing ion dose the crystallinity of the DO23-Al3Zr phase was gradually improved, and at a dose of 5×10¹⁷ ions cm^-2 the DO23-Al3Zr layer was about 100 nm thick. The formed DO23-Al3Zr phase played a significant role in enhancing the hardness as well as the elastic modulus of the Al films.

Miao W.;Tao K.;Li B.;Liu B. X.

Journal of Physics D Applied Physics

2000

Samarium ion implantation was conducted to synthesize Sm-disilicide films on silicon wafers, using a metal vapor vacuum arc ion source and the continuous SmSi2 films were directly obtained with neither external heating during implantation nor post-annealing. Diffraction and surface morphology analysis confirmed the formed Sm-disilicilde films were of a fine crystalline structure under appropriate experimental conditions. Besides, the formation mechanism of the SmSi2 phase is also discussed in terms of the temperature rise caused by ion beam heating and the effect of ion dose on the properties of the SmSi2 films.

Cheng X. Q.;Zhu H. N.;Liu B. X.

Materials Research Society Symposium Proceedings

2001

CrSi2 layers were synthesized on Si wafers by high current pulsed Cr ion implantation into Si wafers with or without a pre-deposited thin Cr overlayer. For the bare Si wafers, at a substrate temperature of 220 °C, the plain and continuous CrSi2 layers were successfully obtained, while at 300 °C, some voids emerged in the formed layers. Interestingly, for the Si wafers with a Cr overlayer, Cr ion implantation induced the growth of surface fractal consisting of the CrSi2 grains. It was found that the fractal dimension was independent of the substrate temperature and increased approaching a value of 2.0 with increasing ion dose.

Zhu H. N.;Liu B. X.

Thin Solid Films

2001

In the equilibrium immiscible Ag-Co system, the total energies of six possible structures for the A 3 B types were calculated as a function of their lattice constant(s) by employing the Vienna ab initio simulation package and the calculation predicted that the D0 19 , L1 2 , L6 0 , and D0 3 structures were relatively stable. The predicted nonequilibrium state was confirmed by the fact that a metastable fcc Ag 3 Co phase was indeed obtained in the Ag-Co multilayers upon ion irradiation at 77 K incorporated with the interfacial free energy and its lattice constant determined by diffraction analysis also matched well with the calculation.

Liu J. B.;Li Z. F.;Zhang J. X.;Liu B. X.;Kresse G.;Hafner J.

Physical Review B Condensed Matter and Materials Physics

2001