Action Of Compression Plasma Flows Research Articles

Structure and phase transformation of iron surface layer treated by compression nitrogen plasma flows

Investigation on a surface structure of iron modified by the action of compression plasma flows and determination of element and phase composition was carried out using X-ray diffraction analysis, Auger-electron spectroscopy, optical microscopy and scanning electron microscopy, along with studies on mechanical properties of the material. As a result, a layered structure of total depth up to 60 μm with nitrogen concentration up to 20 at.% develops at a sample surface. The final structure of near-surface area in the processed iron was shown to be formed from the ε-domain due to eutectoid decomposition on cooling, whereas an increase in both hardness and wear resistance results from dispergation of phase components.

Materials surface modification using quasi-stationary plasma accelerators

Quasi-stationary plasma accelerators of a new generation were studied for the capability to modify surface properties of materials widely applied in engineering (carbon steels) and in microelectronics (silicon). The action of high-energy plasma flow was shown to result in hardening the samples from carbon steels, the depth (∼0.1–0.3 mm) and microhardness (more than 10 000 MPa) of the modified surface layer being sufficient for practical purposes. Exposure of silicon wafer to medium-power compression plasma flow results in the formation of periodic sub-micron spatial structures on its surface. The main factors ensuring efficient modification of various materials under the compression plasma flow action are shown to be the rapid heating of surface due to kinetic energy thermalization of compression plasma flow during its deceleration, keeping temperature and pressure at necessary levels until the completion of physico-chemical transformations in the surface layer, and the fast crystallization of the molten layer in the presence of magnetic fields induced by the currents ‘swept-away’ from the discharge device with the compression flow.

Creation of silicon submicron structures by compression plasma flow action

Oriented submicron cylindrical structures obtained in a single pulse treatment of silicon monocrystal by compression plasma flow are described. The nitrogen plasma flow generated by magnetoplasma compressor is used for modification of Si (1 1 1) monocrystal surface. The speed of plasma flow was up to 40 km/s depending on input energy and gas used and its pressure. The electron density and temperature within the region of plasma flow maximal compression was up to 2×10 17 cm −3 and 20,000 K, respectively. Silicon samples placed perpendicular to the flow were exposed to a single 100 μs plasma pulse driven by the discharge current of 70 kA. Typical dimensions of cylindrical structures formed at the crystal surface are 0.1–2 μm in diameter and up to 200 μm in length. The influence of external magnetic field on the dimensions of the cylindrical structures was also investigated. The large diameter cylindrical structures have been noticed to exhibit the hollow features. The catalyst was not used in the process of silicon surface modification.

The effect of dense compression plasma flow on silicon surface morphology

The dense compression plasma flow action on silicon surface layers is investigated. Samples of monocrystalline silicon of (111) and (100) orientations were subjected to plasma flow processings. Values of energy absorbed by the silicon surface range from 5 to 25 J per pulse, the latter corresponding to the flow power density range 0.5·10 5–3·10 5 W/cm 2. Microreliefs of sample surfaces and slices were recorded by means of high-resolution scanning microscopy. The action of the compression plasma flow on the sample results in the melting and subsequent modification of silicon material down to the depth of 6 μm. Micrographs of surface layers clearly show regular cylindrical structures that are the first of their kind ever observed. Cylindrical fragments measure 50–100 μm in length and 0.7–1.5 μm in diameter. These fragments are located on the surface of the sample at intervals of 1–2 μm with a surface density of (2–6)·10 6 cm −2. Possible mechanisms of cylindrical periodic structure formation are discussed. The roles of Rayleigh–Taylor instability, Kelvin–Helmholtz instability and Benard instability in transformations of molten surface layers are considered. It may be inferred that structural-phase changes in the state of silicon surface are related to the fast crystallization of molten layer accompanied by the development of various instabilities in the presence of an induced magnetic field.