H. D. Li

Growth of the fractal patterns in Ni-Zr thin films during ion-solid interaction

An experimental study of the growth of fractal patterns during ion beam‐solid interaction in the Ni‐Zr alloy system is reported. The observed fractal patterns in the alloy films feature both isotropic and anisotropic characters depending on their growth surroundings. The fractal dimension of the isotropic fractal patterns is determined to be 1.4±0.1. The possible growth mechanism of the observed patterns is discussed.

Structural correlation in tantalum nitride formation by direct nitrogen implantation

Abstract Tantalum targets were implanted with 80 keV nitrogen ions at doses from 5 × 10 16 to 5 × 10 17 N cm −2 at room temperature. X-ray analyses of the implanted layers show a correlation between the types of nitrides formed and the implantation dosage. As the nitrogen content increases nitrogen-rich nitrides start forming. Ta 2 N first forms at the lower implantation level; at higher doses TaN starts forming. Possible shearing mechanisms responsible for nitride formation are proposed.

Amorphous RE-TR magnetic alloys formed by ion mixing*

Rare earth-transition metal (RE-TR) alloys are well known for their excellent magnetic properties, especially in the amorphous state. In recent years, some RE-TR alloys have been used as the recording matrix of the magneto-optical disk, in which only very thin film is required. Ion mixing is a suitable method for producing amorphous alloy films and this study was undertaken to investigate the possibility of ion mixing as an alternative way to produce such kind of magnetic alloy films. Various binary, ternary and even quadrunary combinations among RE (Gd, Tb, Nd) and TR (Fe, Cc) metals were studied by 300 keV Xe ion mixing of multilayered samples at LN 2 or room temperature. Generally speaking, amorphous alloys were formed after adequate dose irradiation, while metastable crystalline phases were observed at relatively low dose mixing stages. Ten amorphous RE-TR alloys were obtained and their Kerr rotating angles, i.e. the changing of the polarized angle between the incident and reflected laser beams interacting with the alloy surface, were measured by a He-Ne laser with a wavelength of 632.8 nm. It was found that the Kerr rotating angles of the ion mixed films were comparable or even superior to those of the alloys manufactured by sputtering technique, e.g. a Kerr angle of 48′35″ was observed for a Tb-Fe film so obtained. Experimental results of ion induced amorphous phase formation as well as the magnetic properties of the ion mixed films are reported and discussed.

Simulations on radiation damage initiated by O(1) PKA in YBa2Cu3O7

Radiation damage processes initiated by O(1) PKA of the Cu-O chain in the orthorhombic YBa2Cu3O7 were studied by molecular dynamics simulations. A special anisotropy of the displacement threshold energy (Ed) of the O(1) PKA was found. The average Ed in the basal (001) plane was only 4.2 eV. This value is much lower than that in other planes, for example Ed (100) is 18.8 eV. For a damaging event of 0.5 keV O(1) PKA in the basal (001) plane, atomic configurations belonging to a Frank dislocation with a (c6) [001] Burgers vector were observed.

Magnetic Co/Al multilayers prepared by planar magnetron sputtering

Structures and magnetic properties of Co/Al multilayers prepared by means of planar magnetron sputtering were investigated. We compare the results with those of the previously reported films fabricated by electron‐beam deposition. It is found that remarkable differences exist between the films synthesized by the two methods. For example, the sputtered multilayers show a transition from in‐plane to out‐of‐plane magnetization at a crossover thickness of Co layer from 14 to 7 A. For samples with tCo ≤ 6 A, the Co layers were discontinuous. Formation of the CoAl compound in the samples has not been observed.

Formation of silver trinitride by nitrogen implantation

The formation of AgN3 phase, for the first time, by high-dose nitrogen implantation (2*1018 N cm-2) was confirmed by electron diffraction pattern as well as by the ESCA analysis. A slight shift of the Ag3d3/2 line (373.9 eV) was observed in the ESCA spectrum, indicating that a weak bonding among the Ag and N atoms had formed. The complexity of the orthorhombic structure and the fragility of the bonding are probably the very reasons why the AgN3 phase was difficult to form. However, high-dose implantation can help the kinetics and hence induce the formation of the AgN3 phase in the implanted layer.

Fractal growth at dendrite tips in an ion-irradiated thin solid film

SummaryExperimental observations of fractal growth at dendrite tips during crystalline-to-amorphous phase transition in an ion-irradiated Mo65Ni35 thin film are reported. It was found that the observed anisotropic fractal patterns were of a DLA type but not exactly self-similar. The possible mechanism of this exception to the ordinary parabolic tip growth of the dendrites is discussed.