Order-disorder phase transition in CoPd thin films

The thin films of a CoPd alloy in the equiatomic composition region are prepared by condensation at different substrate temperatures. The substrate temperature is varied from the liquid nitrogen temperature to +280°C. At low substrate temperatures, the crystal structure of the condensed films is the single-crystal blocks of the hexagonal close-packed (hcp) phase. As the substrate temperature is further increased, the domains characterized in the initial state by the microdiffraction patterns in the form of a diffuse halo appear in the films, and these domains have a clear-cut boundary with the regions indicated by point reflections in the electron diffraction patterns. At substrate temperatures from +150 to 160°C, the CoPd alloy films in the equiatomic composition region are fully amorphous. The given state is a polymorphic transformation of the martensitic type. It arises in the martensitic transformation of the low-temperature hcp phase to the high-temperature fcc phase.     

Structure of heterogeneous states in nanocrystalline CoPd films

Thin films of equiatomic alloy CoPd have been produced by condensation at high substrate temperatures. The films obtained are characterized by microdiffraction patterns in the form of diffuse halo in the initial state. This is polymorphic martensitic transient state, formed during martensitic transformation of the low-temperature hcp phase to the high-temperature fcc phase. The metastable crystal structures arising in these alloy films are identified.     

Structure of heterogeneous states and magnetic properties of CoPd nanocrystalline films

Thin films of a CoPd equiatomic alloy have been obtained by condensation at a high substrate temperature. In their initial states, they are characterized by a microdiffraction pattern in the form of a diffuse halo. This state is a polymorphic martensite-type transformation, which occurs for the martensite transition from the low-temperature hexagonal close-packed phase to the high-temperature face-centered cubic one. Crystalline metastable structures formed in films of this alloy have been identified, and their magnetic characteristics have been determined.     

Transformation behavior of Ni-Mn-Ga/Si(100) thin film composites with different film thicknesses

A series of Ni_51.4Mn_28.3Ga_20.3/Si(100) thin film composites with different film thicknesses varying from 0.1 to 5 μm have been prepared by magnetron sputtering and subsequently annealed. X-ray powder diffraction patterns of the films show the features associated with the lattice-modulated martensitic phase and/or cubic austenite at room temperature. 220-fiber texture was confirmed by the X-rays measurements made at 150 °C. While the Curie temperature is almost film thickness independent, the martensitic transformation temperature shows a strong descended dependence in the submicron range. The substrate curvature measurements demonstrate that the forward and reverse martensitic transformation in the films is accompanied by the reversible relaxation and accumulation of residual stress, originally created by the thermal treatment due to the difference in thermal expansion of the film and substrate. The values of residual stresses measured by both substrate curvature and X-rays diffraction methods at constant temperatures are found to be dependent on the film thickness. This behavior appears in correlation with the thickness dependence of the transformation temperature.     

Development of conductive transparent indium tin oxide (ITO) thin films deposited by direct current (DC) magnetron sputtering for photon-STM applications

Highly conductive and transparent indium tin oxide (ITO) thin films, each with a thickness of 100 nm, were deposited on glass and Si(100) by direct current (DC) magnetron sputtering under an argon (Ar) atmosphere using an ITO target composed of 95% indium oxide and 5% tin oxide for photon-STM use. X-ray diffraction, STM observations, resistivity and transmission measurements were carried out to study the formation of the films at substrate temperatures between 40 and 400 °C and the effects of thermal annealing in air between 200 and 400 °C for between1 and 5 h. The film properties were highly dependent on deposition conditions and on post-deposition film treatment. The films deposited under an Ar atmosphere pressure of ∼1.7×10^-3 Torr by DC power sputtering (100 W) at substrate temperatures between 40 and 400 °C exhibited resistivities in the range 3.0–5.7×10^-5 Ω m and transmissions in the range 71–79%. After deposition and annealing in air at 300 °C for 1 h, the films showed resistivities in the range 2.9–4.0×10^-5 Ω m and transmissions in the range 78–81%. Resistivity and transmission measurements showed that in order to improve conductive and transparent properties, 2 h annealing in air at 300 °C was necessary. X-ray diffraction data supported the experimental measurements of resistivity and transmission on the studies of annealing time. The surface roughness and film uniformity improve with increasing substrate temperature. STM observations found the ITO films deposited at a substrate temperature of 325 °C, and up to 400 °C, had domains with crystalline structures. After deposition and annealing in air at 300 °C for 1 h the films still exhibited similar domains. However, after deposition at substrate temperatures from 40 °C to 300 °C, and annealing in air at 300 °C for 1 h, the films were shown to be amorphous. More importantly, the STM studies found that the ITO film surfaces were most likely to break after deposition at a substrate temperature of 325 °C and annealing in air at 300 °C for 2 or 3 h. Such findings give some inspiration to us in interpreting the effects of annealing on the improvement of conductive and transparent properties and on the transition of phases. In addition, correlations between the conductive/transparent properties and the phase transition, the annealing time and the phase transition, and the conductive/transparent properties and the annealing time have been investigated. Received: 10 July 2000 / Accepted: 27 October 2000 / Published online: 9 February 2001     

Ferromagnetic resonance in Ni-Mn-Ga thin films and thin-film tubes

We report on FMR experiments performed for the first time on thin Ni-Mn-Ga films clamped to the mica substrates and then fully released from them. The aim is to evaluate the role of magnetoelastic coupling in stressed Ni-Mn-Ga Heusler alloy films that undergo martensitic transformation. The experimental results show that the difference in the effective magnetization 4π(M_eff ^tubes-M_eff ^films) is negligible in the austenite phase and it increases to about 1–1.5 kG at temperatures well below the martensitic transformation. The data suggests that magnetoelastic coupling in the martensite phase of Ni-Mn-Ga thin films is typical of normal thin magnetic films with magnetostriction of about 50 ppm.     

Phase transformation of Ni/Si thin films induced by nanoindentation and annealing

Thin Ni/Si films are prepared by depositing a Ni layer with a thickness of 100 nm on a Si (100) substrate. The as-deposited thin-film specimens are indented to a maximum depth of 500 nm using a nanoindentation technique and are then annealed at temperatures of 200°C, 300°C, 500°C and 800°C for 2 min. The microstructural changes and phases induced in the various specimens are observed using transmission electron microscopy (TEM) and micro-Raman scattering spectroscopy (RSS). Based on the load-displacement data obtained in the nanoindentation tests, the hardness and Young’s modulus of the as-deposited specimens are found to be 13 GPa and 177 GPa, respectively. The microstructural observations reveal that the nanoindentation process prompts the transformation of the indentation-affected zone of the silicon substrate from a diamond cubic structure to a mixed structure comprising amorphous phase and metastable Si III and Si XII phases. Following annealing at temperatures of 200∼500°C, the indented zone contains either a mixture of amorphous phase and Si III and Si XII phases, or Si III and Si XII phases only, depending on the annealing temperature. In addition, the annealing process prompts the formation of nickel silicide phases at the Ni/Si interface or within the indentation zone. The composition of these phases depends on the annealing temperature. Specifically, Ni₂Si is formed at a temperature of 200°C, NiSi is formed at a temperature of 300°C and 500°C, and NiSi₂ is formed at 800°C.     

Thickness dependent phase transformation of magnetron-sputtered Ni–Mn–Sn ferromagnetic shape memory alloy thin films

In this study, the influence of film thickness on the first-order martensite–austenite phase transformation of Ni–Mn–Sn ferromagnetic shape memory alloy thin films has been systematically investigated. Different thicknesses of the Ni–Mn–Sn films (from ~100 to 2,500 nm) were deposited by DC magnetron sputtering on Si (100) substrates at 550 °C. X-ray analysis reveals that all the films exhibit austenitic phase with the L2₁ cubic crystal structure at room temperature. The grain size and crystallization extent increase with the increase in film thickness, but the films with thickness above ~1,400 nm show structural deterioration due to the formation of MnSn₂ and Ni₃Sn₄ precipitates. The improvement in the crystallinity of the film with thickness is attributed to the decrease in film–substrate interfacial strain resulting in preferred oriented growth of the films. Temperature-dependent magnetization measurements as well as electrical measurements demonstrate the complete absence of phase transformation for the film of thickness of ~120 nm. For thickness greater than 400 nm, film exhibits the structural transformation, and it occurs at higher temperature with better hysteresis as film thickness is increased up to ~1,400 nm, after which degradation of phase transformation phenomenon is observed. This degradation is attributed to the disorders present in the films at higher thicknesses. Film with thickness ~1,400 nm possesses the highest magnetization with the smallest thermal hysteresis among all the films and therefore best suited for the actuators based on first-order structural phase transformation. Nanoindentation measurements reveal that the higher values of hardness and elastic modulus of about 5.5 and 215.0 GPa obtained in film of 1,014 nm thickness can considerably improve the ductility of ferromagnetic shape memory alloys (FSMA) and their applicability for MEMS applications. The exchange bias phenomenon is also found to be present in the films of thickness 1014, 1412, and 2022 nm exhibiting prominent martensitic transformation. Film of thickness 2,022 nm exhibits maximum exchange bias of ~50 Oe and higher exchange bias blocking temperature of 70 K as compared to other films.     

Effect of ordering on the volume change and the shape memory effect in a Fe3Pt alloy during martensitic transformation

The effect of heat treatment on the volume effect ΔV/V and the shape recovery during the martensitic transformation in a Fe-24 at % Pt alloy is studied. An increase in the annealing time from 0 to 300 min at 650°C is found to decrease ΔV/V gradually from 1.26% for the quenched state to 0.987% for τ = 300 min. The characteristic temperatures of the martensitic transformation decrease and the transformation hysteresis passes through a minimum. The shape memory effect in heat-treated samples reaches 100% after gT = 40 min.     

Calculation of the phase diagram of the TiZr alloy and investigation of the tendency toward separation of the ω phase

The electronic, structural, and thermodynamic properties of the TiZr equiatomic alloy have been calculated in terms of the electron density functional theory and Debye-Grüneisen model. The calculated lattice parameters a and c/a agree well with experimental data for the α, ω, and β phases. It has been shown that the ω phase is stable at atmospheric pressure and low temperatures, and it remains energetically more favorable up to T = 600 K. In the temperature range 600 K < T < 900 K, the α phase becomes stable, and above 900 K, the β phase of the TiZr alloy is stable. The phase diagram constructed in this study agrees qualitatively with the available experimental data. A tendency toward separation of the TiZr equiatomic alloy in the ω phase has been analyzed. It has been demonstrated that, in the ground state, the TiZr equiatomic alloy in the ω phase exhibits a tendency toward ordering rather than toward phase separation.     

Behavior of the nickel-titanium alloys with the shape memory effect under conditions of shock wave loading

The behavior of the Ti_51.1Ni_48.9 and Ti_49.4Ni_50.6 alloys with shape memory effects has been studied under submicrosecond shock wave loading in the temperature range from −80 to 160°C, which includes both the regions of the stable state of the specimens in the austenite and martensite phases and the regions of thermoelastic martensitic transformations. The grain size of the studied alloys varies from initial values 15–30 to 0.05–0.30 μm. The dependences of the dynamic elastic limit on the temperature and on the elemental composition are similar to the dependences of the yield stress of these alloys under low strain rate loading. The rarefaction shock wave formation as a consequence of the pseudoelastic behavior of the alloy during a reversible martensitic transformation has been revealed. A decrease in the grain size leads to an increase in the dynamic elastic limit and decreases the temperatures of martensitic transformations.     

On the simultaneous measurement of the energy and arrival time of a photon

The simultaneous measurement of the energy and arrival time of a single-photon packet, as well as the experimental implementation of such a measurement with the use of a parametric transformation upward in the energy (up conversion), is proposed. Original Russian Text ? S.N. Molotkov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 12, pp. 901–906.     

Optical control of the anisotropy of the orientation of molecules in a liquid

The control of the anisotropy of the orientation of molecules in pure 1,2-dichlorobenzene, C₆H₄Cl₂ at room temperature is demonstrated experimentally. To accomplish the optical control, the medium is exposed to non-resonant excitation with two successive linearly polarized laser pulses with a duration of 60 fs. The state of transient anisotropy is probed with the third pulse by detecting the ultrafast optical Kerr effect via optical heterodyne detection and synchronous demodulation. It is shown that variations in the two parameters, the delay time between two pump pulses, and the angle between the polarization directions of the pump pulses ensure the control of the anisotropy of the orientation of molecules in the subpicosecond region. Original Russian Text ? V.G. Nikiforov, G.M. Safiullin, A.G. Shmelev, A.V. Leont’ev, V.S. Lobkov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 10, pp. 757–761.     

Ni53.2Mn22.6Ga24.2单晶的两步热弹性马氏体相变及其应力应变特性

对具有两步完全热弹性的Ni_53.2Mn_22.6Ga_24.2单晶的物性采用多种测量手段进行了表征,特别研究了不同温度下的应力-应变特性.研究表明,热诱发的中间马氏体相变应变远大于马氏体相变应变.在较低的形变温度下,沿单晶母相［001］方向的压应力诱发的是两步马氏体相变,材料表现出赝弹性;在较高的形变温度下,只能观察到一步马氏体相变,材料展现出完全超弹性特性.此外,利用热力学理论分别计算了诱发马氏体相变和中间马氏体相变的临界应力与形变温度的关系,与实验测量得到的结果相符. 关键词： 马氏体相变 形状记忆效应 应变 超弹性     

Internal friction due to negative stiffness in the indium–thallium martensitic phase transformation

Internal friction and dynamic shear modulus in an indium–21?at.% thallium alloy were measured as functions of frequency and cooling rate using broadband viscoelastic spectroscopy during the martensitic transformation which occurs in this material occurs around 50°C. Microstructural evolution of martensitic bands was captured using time-lapse optical microscopy. The amplitude of damping peaks due to the temperature-induced transformation in the polycrystalline alloy was found to exceed those reported by others for single crystals of similar alloy compositions, in contrast to the usual reduction in damping in polycrystals. The high temperature portion of the damping peak occurs before martensitic bands are observed; therefore this portion cannot be due to interfacial motion. Constrained negative stiffness of the grains can account for this damping, as well as for amplification of internal friction peaks in these polycrystals and for sigmoid-shaped anomalies in the shear modulus at high cooling rates. Surface features associated with a previously unreported pre-martensitic phenomenon are seen at temperatures above martensite-start.     

Evolution of phase transformations after multiple steps of marforming in Ti-rich Ni-Ti SMA

The phase transformations associated with Shape Memory Effect (SME) can be one step, B19' (martensite) ↔ B2 (austenite), or two/multiple steps which include the intermediate R phase, depending on the thermal and thermomechanical history of the alloy. The transformation temperatures are generally observed above room temperature in Ti-rich Ni-Ti alloys, while those observed in Ni-rich alloys occur below room temperature. The goal of the present work is to investigate the phase transformations evolution in Ti-Rich Ni-Ti SMA (Ni-51 at % Ti) when subjected to two distinct thermal treatments (500°C for 30 minutes in air and 800°C for 300 minutes in vacuum) and subsequently multiple steps of marforming thermomechanical treatments intercalated with thermal treatments (500°C for 30 minutes in air) and subsequent four distinct final thermal treatments (400, 450, 500 or 600°C for 30 minutes in air). Further, the stability of phase transformations in the initial ten thermal cycles of these thermomechanically treated samples is also studied. Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) were used to identify the transformation temperatures and the phases that are present after the thermomechanical treatments.     

Microstructural evolution and martensitic transformation mechanisms during solidification processes of liquid metal Pb

The microstructural evolution and the martensitic transformation (bcc–hcp and bcc–fcc) mechanisms during the solidification process of liquid metal Pb were studied by molecular dynamics simulation. Results indicate that, with the decrease of temperature, the system undergoes two phase transitions: from the liquid state into a metastable bcc phase first and then from the bcc phase into a coexisting crystal structure of hcp and fcc phases. Moreover, the complicated martensitic transformation processes are clearly observed by cluster type index method (CTIM) and the tracing method. The two transformation mechanisms are very analogous at the atomic level; the essential difference between them is that, in the bcc–hcp transformation, two adjacent layers shift in opposite directions, whereas in the bcc–fcc transformation, the top layer and bottom layer shift in opposite directions relative to the middle layer. The specific mechanisms for the bcc–hcp and bcc–fcc transformations are confirmed to correspond to the revised Burgers mechanism and Bain mechanism, respectively.     

Cold brittleness and fracture of metals with various crystal lattices: Dislocation mechanisms

The dislocation mechanisms of formation of the ductile–brittle transition temperature and the low-temperature brittle fracture of metals (single crystals, polycrystals) with various crystal lattices (bcc, fcc, hcp) are considered. The conditions of appearance of cold shortness and intracrystalline crack propagation (brittle fracture) are determined. These conditions can be met in bcc and some hcp metals and cannot be met in fcc and many hcp metals. The nondestructive internal friction (at 100 kHz) method is used to determine the temperature ranges of cold shortness (ductile–brittle transition temperatures) in bcc metals (ferritic–martensitic EK-181 steel, V–4Ti–4Cr alloy), which depend on their structure–phase state and strength (yield strength).     

Martensitic transformation in melt-spun Ni-Mn-Ga ribbons

Off-stoichiometric Ni-Mn-Ga alloys, with various chemical compositions, were produced by melt-spinning technique. Transformation behavior was studied by means of differential scanning calorimetery (DSC). Ribbons and bulks reveal reversible martensitic transformation which occurs, dependently on chemical composition, in the range of temperatures: between 100°C and -150°C. Transmission electron microscope and X-ray diffractometer were used for structure examination. Dependently on chemical composition five-layered (10 M) or seven-layered (14 M) martensite was observed, whereas the parent phase shows the B2 structure. Due to high cooling rate realized in melt-spinning technique some amount of amorphous phase was found. For all ribbons magnetization was measured versus change of temperature as well as magnetic field. Due to relatively high density of dislocations lower value of magnetization were obtained.     

Formation,structure, and magnetic changes at annealing of films deposited by laser sputtering of Ni and Pd

The electron microscopy investigations of Pd, Ni, and Ni-Pd alloy films are carried out. The films were produced by laser sputtering of one- and two-element targets. It is shown that, in the case of alternate deposition of nickel and palladium, polycrystalline films with a metastable hcp lattice are formed. The hcp lattice parameters increase monotonically with increasing palladium content in the film. As a result of the annealing, Ni and Ni-Pd alloy films acquire an equilibrium fcc structure. A positive deviation from Vegard’s law occurs for the dependence of the lattice parameter of the solid solution on the Pd concentration. The as-prepared Ni and Ni-Pd alloy films with the hcp structure are characterized by the absence of a magnetic moment. The transition into the ferromagnetic state occurs after annealing, and hysteresis is observed upon magnetization reversal.