S. I. Sidorenko

Formation of CuxAu1−x phases by cold homogenization of Au/Cu nanocrystalline thin films

Summary It is shown, by using depth profiling with a secondary neutral mass spectrometer and structure investigations by XRD and TEM, that at low temperatures, at which the bulk diffusion is frozen, a complete homogenization can take place in the Cu/Au thin film system, which leads to formation of intermetallic phases. Different compounds can be formed depending on the initial thickness ratio. The process starts with grain boundary interdiffusion, which is followed by a formation of reaction layers at the grain boundaries that leads to the motion of the newly formed interfaces perpendicular to the grain boundary plane. Finally, the homogenization finishes when all the pure components have been consumed. The process is asymmetric: It is faster in the Au layer. In Au(25nm)/Cu(50nm) samples the final state is the ordered AuCu3 phase. Decrease of the film thicknesses, as expected, results in the acceleration of the process. It is also illustrated that changing the thickness ratio either a mixture of Cu-rich AuCu and AuCu3 phases (in Au(25nm)/Cu(25nm) sample), or a mixture of disordered Cu- as well as Au-rich solid solutions (in Au(25nm)/Cu(12nm) sample) can be produced. By using a simple model the interface velocity in both the Cu and Au layers were estimated from the linear increase of the average composition and its value is about two orders of magnitude larger in Au (ca. 10−11 m/s) than in Cu (ca. 10−13 m/s).

Corrosion of 2024 alloy after ultrasonic impact cladding with iron

ABSTRACT The iron-containing layers were produced on the 2024 alloy surface using ultrasonic impact treatment (UIT) in the ambient air and argon environment. Multiple high-energy collisions of the pin of Armco-iron by the treated surface induce the iron cladding by means of solid-state welding of Fe dopants and Al substrate. SEM and EDX analysis and microhardness measurements showed a formation of oxide/intermetallic layers, which thickness ranges from 15–20 to 30–35 μm and hardness achieves ∼4 and ∼9 GPa after the argon-UIT and air-UIT processes, respectively. The polarisation tests in 3.5%NaCl medium showed that the layers are characterised by lower corrosion rates and more positive corrosion potentials than those of the original alloy owing to the formation of Alx-Fey intermetallics. The noblest behaviour was registered for the air-UIT-processed 2024 alloy.

Influence of the substrate choice on the L10 phase formation of post-annealed Pt/Fe and Pt/Ag/Fe thin films

Pt/Fe and Pt/Ag/Fe layered films were deposited by DC magnetron sputtering on MgO(001), SrTiO3(001), and Al2O3(0001) single crystalline substrates at room temperature. The films were post-annealed between 623 K and 1173 K for 30 s in flowing N2 atmosphere. The onset of the L10-FePt phase formation in films deposited on MgO(001) and SrTiO3(001) substrates was observed after annealing between 773 and 873 K, while chemical L10 ordering sets in for Pt/Fe bilayers on Al2O3(0001) at lower temperatures accompanied by strong (001)-texture. It is concluded that elastic stress, arising from the difference in thermal expansion coefficients between film and substrate, promotes ordering and texture formation.

Influence of the annealing atmosphere on the structural properties of FePt thin films

FePt thin films with a thickness of 30 nm were deposited by dc magnetron sputtering at room temperature onto SiO2(100 nm)/Si(100) substrates. These films were post-annealed in a temperature range of 500 °C to 900 °C for 30 s in three different atmospheres—N2, Ar, and forming gas (Ar+H2 (3 vol. %)). Irrespective of the annealing atmosphere, the chemically ordered L10 FePt phase has formed after annealing at 500 °C. Higher annealing temperatures in N2 or Ar atmosphere resulted in a strong increase in grain size and surface roughness but also in the appearance of a pronounced (001) texture in the FePt films. However, these films show the presence of iron oxide. In contrast, annealing in forming gas atmosphere suppressed the oxidation process and resulted in a reduced grain size and lower surface roughness. However, no (001)—but a strong (111)—texture was obtained after annealing at 700 °C, which might be related to the reduced unit cell tetragonality and incorporation of hydrogen to the FePt lattice. Thus, t...

Low-temperature formation of the FePt phase in the presence of an intermediate Au layer in Pt /Au /Fe thin films

Pt /Fe and Pt /Au /Fe layered films were deposited at room temperature by dc magnetron sputtering on Al2O3(0 0 0 1) single crystalline substrates and heat treated in vacuum at 330 °C with different durations (up to 62 h). It is shown by secondary neutral mass spectrometry depth profiling and x-ray diffraction that the introduction of an additional Au layer between Pt /Fe layers leads to enhanced intermixing and formation of the partially chemically ordered L10 FePt phase. The underlying diffusion processes can be explained by the grain boundary diffusion induced reaction layer formation mechanism. During the solid state reaction between Pt and Fe, the Au layer moves towards the substrate interface replacing the Fe layer. This was explained by the much faster diffusion of Fe, as compared to Pt, along the grain boundaries in Au. Enhancement of the process and formation of the ordered FePt phase in the presence of the Au intermediate layer were interpreted by the effect of stress accumulation during the grain boundary reactions: the disordered FePt phase formed initially at different Au and Pt grain boundaries can experience appropriate compressive stress along the {1 0 0} directions, which can initiate the formation of the chemically ordered L10 FePt phase.

Investigation of a pulsed magnetron sputtering discharge with a vacuum pentode modulator power supply

Abstract A pulsed magnetron sputtering discharge at different modes of discharge ignition and a large range of duty cycles and pulse rates from single pulses to 50 kHz was investigated. A 2 kV vacuum pentode modulator was used for the generation of current pulses with amplitudes up to 2 A and target power densities up to 145 W / cm 2 . Ignition of a pulsed discharge occurs with some delay, but still at the rise of the voltage pulse, if in the inter-electrode gap either a starting-up discharge with a current of some tens of milliamperes is sustained or if the residual concentration of charged particles after a previous pulse is still high enough. A spike of electron current to the substrate with energies up to 100 eV is generated at the current front of the high-current discharge when the voltage drops to its equilibrium value. These electrons are presumably secondary electrons. The effective cathode secondary emission and gas ionization take place at the current front when the voltage drop at the gap is higher than the equilibrium value. Therefore, the duration of the current front lasts only some microseconds and an excess concentration of charged particles is generated in the gap. During the high-current discharge stage the plasma expands with the velocity of ambipolar diffusion from the near-target region. The ion current to substrate reaches its maximum value after some tens of microseconds. For this reason, the pulse duration should not be lower than 20– 40 μs for ion-assisted deposition. In the afterglow period deionization of the post-discharge plasma takes place. Due to the surplus ion conductivity of the plasma the starting-up discharge is suppressed. With delay in self-restoring the starting-up discharge is some tens of microseconds. This time determines the duration of maximum pauses between the control pulses without the starting-up discharge. Thus, work in the middle-frequency range of pulse rates allows to exclude a starting-up discharge and to obtain the lowest delay for establishing the magnetron discharge at each of the following pulses.

Formation of nanocrystalline structure of TaSi2 films on silicon

The nanocrystalline structure and mechanical properties of TaSi2 films deposited by sputtering of TaSi2 target have been investigated by x-ray diffraction, cross-sectional transmission electron microscopy (TEM), four-point electrical resistance measurement, and cyclic depth-sensitive nanoindentation. The purpose of this work is to study the formation of nanocrystalline structure in TaSi2 films on a silicon substrate. As revealed, a decrease in the deposition rate leads to an increase in the O and C impurity content in the films. Contamination of the film by O and C atoms during a low-rate deposition causes the formation of an amorphous phase in the deposited films. Upon annealing, the amorphous structures crystallize into mixtures of disilicide and a small amount of polysilicide, i.e. TaSi2 and Ta5Si3, respectively. After annealing at 970 K, the formation of a nanocrystalline structure with a grain size about 10 nm takes place in the film produced at a deposition rate of 0.2 nm/sec. The formation of a nanocrystalline structure changes drastically the mechanical properties of the film. The nanohardness and elastic modulus increase significantly, and the film becomes brittle and overstressed. After deposition in the film produced at the 1 nm/sec deposition rate mainly Ta disilicide and the amorphous phase are observed. After annealing, the amorphous phase near the Si substrate coexists with column-shape grains of Ta disilicide of size 150 × 500 nm. The annealed thin film becomes nonuniform in thickness. The nanohardness and elastic modulus increase.

The Effect of Deformation on Structure and Properties of Surface Diffusion Layers Formed in Iron Alloys under Alloying by Nitrogen and Carbon

The influence of preliminary plastic deformation in the range of 5–70 % on the structure formation and mechanical properties of surface layers in iron-based alloys under diffusion alloying by nitrogen and carbon in ammonia and propane-butane gaseous environment at th temperature 853 K during 0.5-6 hours was studied. Surface diffusion layers were investigated by me ans of X-ray diffraction, microhardness and wear resistance tests. It was e st blished that the surface layer of iron alloy after gas saturation by nitrogen and carbon consisted of ε -phase with the hexagonal closed packed crystal structure or θ -phase with the orthorhombic structure isostructural to cementite lattice and the solid solution of nitrogen and carbon in α -phase. The deformation within the range of 25–30 % substantially affects surface diffusion layer structur e, phase and chemical composition and properties. The θ phase was revealed in the layer after 25–30 % deformation and saturation in gas mixture of 90 % ammonia and 10 % propane-butane. Obtained in this way layers show maximum microhardness, wear resistance and thickness. The ε -p ase was formed in the alloy after deformation out of the 25–30 % ranges. The lattice spacing of the α -phase containing nitrogen and carbon decreases non-linearly within the 25–40 % degree of plastic def ormation. We assume that high strengthening of the surface layers results from intera ction of disperse carbonitrides on such crystal lattice defects as dislocations.

Influence of Annealing Environment and Film Thickness on the Phase Formation in the Ti/Si(100) and (Ti +Si)/Si(100) Thin Film Systems

Influence of an annealing environment and film thickness on the phase formation in the Ti(30 nm)/Si(100), [(Ti+Si) 200 nm]/Si(100) thin film systems produced by magnetron sputtering and the Ti(200 nm)/Si(100) thin film system produced by electron-beam sputtering were investigated by X-ray and electron diffraction, Auger electron spectroscopy (AES), secondary ion mass-spectrometry (SIMS) and resistivity measurements. Solid-state reactions in the thin film systems under investigation were caused by diffusion processes during annealing in the different gas environments: under vacuum of 10-4 - 10-7 Pa, flow of nitrogen and hydrogen. It is shown that the decrease of Ti layer thickness from 200 to 30 nm in the Ti/Si(100) film system causes the increase of the transition temperature of the metastable C49 TiSi2 phase to the stable C54 TiSi2 phase up to 1070 K at vacuum annealing. During annealing in the nitrogen flow of the Ti(30 nm)/Si(100) thin film system the C49 TiSi2 is the first crystal phase which is formed at 870 K. For annealings of the [(Ti+Si) 200 nm]/Si(100) thin film system by impulse heating method or for furnace annealings in inert gas atmosphere of N2, Ar, H or higher vacuum (10-5 Pa) the crystallization process has two stages: the first metastable C49 TiSi2 phase is formed at 870 K and then at higher temperatures it is transformed to the stable C54 TiSi2 phase.

Effect of Copper on the Formation of Ordered L10(FePt) Phase in Nanosized Fe50Pt50/Cu/Fe50Pt50 Films on SiO2/Si (001) Substrates

The effect from thickness of an intermediate copper layer in nanosized Fe50Pt50 (15 nm)/Cu (x)/Fe50Pt50 (15 nm) (x = 7.5, 15, and 30 nm) composite films on SiO2 (100 nm)/Si(001) substrates on the diffusion-controlled phase formation processes—transformation of the disordered magnetically soft A1(FePt) phase into the ordered magnetically hard L10(FePt) phase during annealing in vacuum—is studied by physical materials science methods: X-ray diffraction and measurement of magnetic properties. The A1(FePt) phase forms in all films during deposition. Annealing in vacuum in the temperature range 300–900°C is accompanied by thermally activated diffusion processes between the Cu and FePt layers. When thickness of the intermediate Cu layer increases from 7.5 nm up to 15 nm, the onset temperature of A1(FePt) → L10(FePt) phase transformation raises by 100°C, i.e., to 800°C. Simultaneously, the coercivity in films decreases since Cu dissolves in the FePt lattice.