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Dynamic friction, wear volumes and wear morphology have been studied for sliding wear in polysilicon in ambient air at μN normal loads using on-chip micron-scale test specimens. With increasing number of wear cycles, the friction coefficients show two distinct types of behavior: (i) an increase by a factor of two and a half to a steady-state regime after peaking at three times the initial value of about 0.10 ± 0.04, with no failure after millions of cycles; (ii) an increase by a factor larger than three followed by failure after ∼105 cycles. Additionally, the average nano-scale wear coefficient sharply increased in the first ∼105 cycles up to about 10−4 and then decayed by an order of magnitude over the course of several million cycles. For both modes of behavior, abrasive wear is the governing mechanism, the difference being attributed to variations in the local surface morphology (and wear debris) between the sliding surfaces. The oxidation of worn polysilicon surfaces only affects the friction coefficient after periods of inactivity (>30 min).

Besides the well-known resistance switching originating from the amorphous-crystalline phase-change in GeSbTe thin films, we demonstrate another switching mechanism named ‘polarity-dependent resistance (PDR) switching’. The electrical resistance of the film switches between a low- and high-state when the polarity of the applied electric field is reversed. This switching is not connected to the phase-change, as it only occurs in the crystalline phase of the film, but connected to the solid-state electrolytic behavior i.e. high ionic conductivity of (Sb-rich) GeSbTe under an electric field. I-V characteristics of nonoptimized capacitor-like prototype cells of various dimensions clearly exhibited the switching behavior when sweeping the voltage between +1 V and -1 V (starting point: 0 V). The switching was demonstrated also with voltage pulses of amplitudes down to 1 V and pulse widths down to 1 microsecond for several hundred of cycles with resistance contrasts up to 150 % between the resistance states. Conductive atomic force microscopy (CAFM) was used to examine PDR switching at nanoscales in tip-written crystalline marks, where the switching occurred for less than 1.5 V with more than three orders of resistance contrasts. Our experiments demonstrated a novel and technologically important switching mechanism, which consumes less power than the usual phase-change switching and provide opportunity to bring together the two resistance switching types (phase-change and PDR) in a single system to extend the applicability of GeSbTe materials.

This paper addresses the crystallization of amorphous Sb3.6Te films (40 nm thick) and 5 at.% Ge containing Sb3.6Te films (10, 20 and 40 nm thick) as studied using in-situ annealing in a Transmission Electron Microscope (TEM). These materials show growth-dominated crystallization, in contrast to Ge2Sb2Te5 that shows nucleation-dominated crystallization. Particularly the crystal-growth velocity in these systems is measured as a function of temperature from which the activation energy for growth can be derived. The strong effect of the 5 at.% Ge addition on the total crystallization behavior is revealed: Ge increases the crystallization temperature (from 95 to 150 °C), increases the activation energy for growth (from 1.58 to 2.37 eV), increases the nucleation rate and decreases the growth anisotropy.

With a well-controlled laser melt injection (LMI) process, for the first time the feasibility is demonstrated to produce SiC particles (SiCp) reinforced Ti6Al4V functionally graded materials (FGMs). SiCp are injected just behind the laser beam into the extended part of the laser melt pool that is formed at relatively high beam scanning velocities. The process allows for the minimization of the decomposition reaction between SiCp and Ti6Al4V melt, and also leads to FGMs of SiCp/Ti6Al4V instead of a homogeneous composite layer on Ti6Al4V substrates. An injection model is designed based on the temperature/viscosity field of the laser pool for a deeper understanding the mechanism of formation of the FGMs with LMI. The model is based on finite element calculations of the temperature field in the melt pool, physical considerations of the LMI process and it is supported by experimental observations. Three types of reaction layers are observed around SiCp, namely a thin monocrystalline TiC layer, a cellular polycrystalline TiC layer and a thick mixed layer of TiC with Ti5Si3. Among them, only the monocrystalline TiC layer exhibits particular orientation relationships to the SiCp lattice, i.e. (111)TiC//(0001)SiC and TiC//SiC or (111)TiC // (1012)SiC and TiC//SiC. These two kinds of TiC reaction layers act as a barrier against the interfacial reaction and its swift formation during rapid cooling hinders the dissolution of SiCp in the Ti-melt.