TEM Investigations of the Influence of Strain Rate and Mode of Deformation on the Substructure of an Fe-Ni-C alloy

The influence of strain rate and mode of deformation on the substructure of a Fe-Ni-C alloy was estimated by TEM. The softening processes during hot deformation appear as dynamic recovery and dynamic recrystallization. – The dynamic recrystallization is favoured by increased strain rate and one-dimensional state of stress.     

Thermally stimulated relaxation of misfit strains in Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>x</Subscript>/Si(100) heterostructures with different buffer layers

The regularities of the defect formation in Si_1−x Ge_x/Si heterostructures (x = 0.15 and 0.30), consisting of a low-temperature Si buffer layer and a SiGe solid solution, during their growth and subsequent annealings at temperatures 550–650°C are investigated by the methods of optical and transmission electron microscopy and X-ray diffraction. It is shown that the misfit-strain relaxation by plastic deformation under the conditions studied occurs most intensively in heterostructures with low-temperature SiGe buffer layers. The maximum degree of misfit-strain relaxation (no higher than 45%) is observed in the heterostructures with x = 0.30 after annealing at 650°C. The results obtained are explained by the effect of the nature and concentration of dislocation-nucleation centers, existing in low-temperature buffer layers, on the characteristics of the formation of a dislocation structure in the heterostructures under consideration.     

Specific features of the formation of terrace-step nanostructures on the (0001) surface of sapphire crystals

The terrace-step structures on atomically smooth vicinal surfaces of sapphire crystals subjected to thermal annealing after mechanical and chemical treatments have been investigated by atomic-force microscopy. The influence of the vicinal angles and conditions of thermal treatment (including annealings in air and vacuum) of sapphire plates on the metric parameters of terrace-step structures has been analyzed. It is shown that steps with a height from monoatomic (0.22 nm) to 3 nm or more can be formed on the sapphire surface by changing the vicinal angle and thermal-treatment conditions. The results are interpreted in terms of the minimum surface energy and surface diffusion processes.     

Low-temperature anomalies in the plastic response of crystalline materials

The non-uniform, wavy, temperature-dependence of the yield-stress and of the rate of logarithmic creep frequently observed in metals, alloys and non-metallic crystalline solids at low temperature, is shown to be largely a consequence of the progressive inhibition of dynamic recovery processes as T → 0 K. Plastic deformation becomes increasingly localised, resulting in high stress-concentrations. On allowing for this increase in the usual equations of the deformation kineties, the anomalies are very well accounted for.     

Erholung und Rekristallisation des stabilen Austenits bei der Verformung durch Walzen

For the explanation of the processes which take place during a high-temperature thermomechanical treatment (HTTT) in the stable austenite hardness, grain structure and dislocation structure of a Fe 24Ni 0,5C alloy are examined in dependence of the degree and temperature of rolling deformation (ϵ = 13 to 52%; T_v = 830 and 1150°C). The observed structures can be represented by a recovery-recrystallization-diagram, that describes the influence of technological parameters on the recovery and the recrystallization of stable austenite.     

Transformation of defect layer and zinc implant profile in silicon during thermal annealing

The transformation of the structure of a radiation-damaged silicon layer and profiles of implanted dopant Zn during thermal annealings has been investigated. The analysis was performed by Rutherford back-scattering spectroscopy, secondary-ion mass spectrometry, and high-resolution X-ray diffraction. It is established that the surface region of radiation-induced point defects (Frenkel pairs) 78 nm thick is formed in the implanted samples. A heat treatment at 400°C leads to the annealing of interstitial point defects and reduces the damaged-layer thickness to 56 nm. This layer may contain vacancy clusters or clusters of zinc-vacancy complexes. The segregation of implanted dopant Zn is observed near the maximum of its depth distribution. Annealing at 700°C leads to the almost complete recovery of the damaged layer. Two concentration peaks were formed in the sample, i.e., one near the substrate surface and the other near the peak of distribution of radiation-induced point defects. During the ion implantation of zinc and at subsequent stages of thermal annealing, zinc precipitated in the form of zinc silicide (of the ZnSiO₃ type).     

In-situ HVEM Observations of Dislocation Processes during High Temperature Deformation of Silicon Crystals

The characteristics in the plastic deformation of silicon crystals are first reviewed. Such characteristics have been interpreted quantitatively on the basis of some models on the velocity and the multiplication of dislocations during deformation. The results of the in-situ observations of silicon crystals deformed at elevated temperatures in a HVEM are presented. The slowness and the smoothness in the dislocation motion, the dynamic pile-up as a general mode of the collective motion of dislocations, the formation processes of multiplication centers of dislocations observed during the deformation all support the validity of the models adopted. Dislocation dipoles and Lomer-Cottrell sessiles are observed not to act as strong obstacles which play important roles in the work hardening of the crystals.     

Possibilities for In-situ Observation of Basic Deformation Processes and of Other Dynamic Processes

The purposes of this paper are to discuss the possibilities of HVEM in-situ observation for deriving meaningful results on basic deformation processes by illustrating some examples which have been obtained so far and to assess the capabilities of this method to investigate crystal deformation as well as other dynamic processes. First, the experimental procedures developed by our group in Nagoya to study the dynamic behaviour of dislocations are introduced. Research subjects which have been studied effectively by this method so far are illustrated. The lower safety limit of specimen thickness for deriving information typical of bulk materials, the effects of size and free surfaces of a specimen and the effects of electron irradiation etc. are to be discussed to assess the validity of in situ observation of dislocation behaviours. Some prospects on new applications and extensions of in-situ HVEM for physical and materials research are to be presented, including possibilities for in-situ observation of other subjects such as diffusion, environmental effects, interface reaction, chemical reaction, defect formation during growing or processing of semi-conductors, surface treatment and micro fabrication by electron beam etc.     

Plastic fragmentation in crystals of diamond-like hexagonal BN-and SiC-phases

The processes of plastic macro-and microchanges in the shape of 2H-BN and 6H-SiC crystals during their deformation under high pressures (7.7 GPa) and temperatures (1200–1600°C) have been studied by transmission electron microscopy. It is established that deformation in crystals with a high density of basal stacking faults is induced by the rotations in the individual regions of the crystals. The shape changes are associated with rotation, tilt, bending, and displacement of the crystal regions of various dimensions. The localized crystallographic shears along the pyramidal \(\{ 10\bar 12\} \) planes and the rotations about the [0001] axis are revealed. It is shown that all the above processes result in crystal fragmentation.     

Interface and material characterization of thin Al2O3 layers deposited by ALD using TMA/H2O

Thin Al₂O₃ layers were grown by atomic layer deposition using trimethylaluminum (TMA) and water as precursors on 1.2 nm thermal SiO₂ and HF cleaned Si surfaces. The stoichiometry and the contamination (H, OH and C) of as-deposited and N₂ annealed thick Al₂O₃ layers were characterized by secondary ion mass spectrometry (SIMS), elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). We show a perturbed region (≈5 nm thick) at the Al₂O₃/Si interface by XPS and Auger electron spectrometry (AES). Post-deposition annealings induced important interface oxidation, Si atoms injection and SiO₂/Al₂O₃ mixture whereas the initial interface was abrupt. Silicon oxidation before Al₂O₃ growth highly limits interfacial oxidation and improves interfacial quality. We proposed that OH groups may play a key role to explain silicon oxidation during post-deposition annealings in inert ambience with low oxygen contamination levels.     

Thermo-mechanical load capacity and deformation onset of silicon wafers during the high-temperature process

The plastic deformations occurring during technological high-temperature treatment of silicon wafers are discussed and are simulated experimentally by means of static loading. From the results obtained a critical stress-time product is derived which can be used for a quantitative estimate of the maximum permissible load of the wafer during heating and cooling treatments in technological processes.     

Evolution of Structure in Deformed Single Crystals of fcc Metals at Heating

The paper deals with conditions resulting in formation of dislocation structures of different types as well as with the change of these structures at subsequent heating which ends in the recrystallization center formation and growth. The measurements were carried out on single crystals of fcc metals. The principal experimental technique was electron microscopy including the annealing of deformed foils directly in the column of electron microscope with accelerating voltage 150 and 1000 kv. Special attention is given to research of the initial stage of recovery in dislocation structures during annealing — the dislocation recovery as the most universal mechanism occurring at any type of structure even when polygonization and recrystallization are hampered. Studies of initial recrystallization stages were mainly carried out while annealing the deformed single crystals of copper. A high degree of local lattice curvature is shown to be a necessary condition for nucleation, and mechanism of the nucleus formation in regions of a high local curvature differs according to the type of the dislocation structure formed during deformation.     

Optical Properties and Microdefects in CaMoO<Subscript>4</Subscript> Single Crystals

Optical inhomogeneities of calcium molybdate crystals in the initial state and after isothermal annealings have been investigated. The value of anomalous birefringence of the samples has been estimated by Mallard’s method; it is shown that annealing reduces this value. Scattering centers have been observed by the Tyndall method. Microscopy has revealed inclusions 2–10 μm in size in all samples. They can’t be attributed to the crucible material inclusions. Light-scattering indicatrices are plotted based on scattering spectroscopy data. Sizes of the scattering centers are estimated.     

Interface modification of ultrathin SiO2/Si(0 0 1) by nitric oxide treatments: a comparative electron paramagnetic resonance and nuclear reaction analysis study

In this work, we investigate by nuclear reaction analysis (NRA), electron paramagnetic resonance (EPR) spectroscopy and atomic force microscopy (AFM) the NO-induced modifications of the physical properties of oxide layers of thickness <3 nm, obtained by rapid thermal oxidation (RTO) of Si in O₂ or O₂/O₃ mixture. We show that for both types of oxides, the N incorporation kinetics are faster than in the case of thick oxides (>20 nm), and typical concentration of 2×10¹⁵ cm⁻² can be achieved. The N profiles varies with oxide type. In both cases, the interface defect concentration is reduced after furnace NO treatments by up to a factor of six. Our study reveals that this reduction is not only the consequence of the N incorporation but that the thermal relaxation of the nitrided layer also plays a major role. To investigate this effect, we performed He annealings which change the thermal budget of the dielectric layer. We show that the He annealings of the NO treated layers delays the re-oxidation process further and changes the chemical composition of the nitrided oxide layer. By AFM, we show that the NO treatment does not form a continuous nitrided layer but forms islands at the interface.     

Thermally activated deformation of Alpha Zirconium

The effect of temperature on the yield stress of polycrystalline α-zirconium has been examined at temperatures between 77 and 900 K. A strong temperature dependence of the yield stress (interrupted in the temperature ranges 300 to 400 K and 500 to 700 K where the yield stress is independent of temperature) indicates the occurence of the thermally activated processes during deformation. The activation volume at the onset of deformation has been determined as a function of temperature in the range 77 to 523 K.     

Sintering as a result of defect structure

Experimental results are presented and conceptions are developed for the qualitative understanding of the fast densification which is frequently observed in the shrinkage stage during the sintering of disperse one-component compacts. They are based on a dislocation multiplication in the powder particle contact regions which is temporarily connected with the contact growth. Thus, a defect structure state is developed due to which it seems possible that the powder particles as a whole move into the pore space through alternating sliding and deformation processes and get densely packed.     

Effect of Fast Electron Irradiation and Annealing on the Luminescence in GaAs(Zn) crystals. Irradiation-induced 1.26 and 1.39 eV Emission Bands

The effect of 2.2 MeV electron irradiation and subsequent annealings on the photoluminescence in zinc-doped p-type GaAs crystals is studied and analyzed. Rather strong emission bands peaked at hv_m (77 K) near 1.26 eV (induced by electron irradiation) and 1.39 eV (induced by annealing of irradiated crystals) are observed. Evidence is presented that the 1.26 and 1.39 eV emission bands occur due to radiative electronic transitions in As_iZn_Ga and V_AsZn_Ga pairs induced by irradiation and annealing of irradiated crystals, accordingly. The observed variations in the intensities of the 1.26 and 1.39 eV emission bands upon irradiation and subsequent annealings of GaAs(Zn) crystals are explained in terms of irradiation and annealing-induced variations in the amount of 1.26 and 1.39 eV radiative centres resulting from: a) the effective interaction of mobile radiation-induced defects in the arsenic sublattice with zinc atoms leading to the formation of As_iZn_Ga and V_AsZn_Ga pairs; b) the thermal dissociation of As_iZn_Ga and V_AsZn_Ga pairs on individual components.     

Kinetics of strain relaxation in metallic glasses

Torque relaxation and strain recovery measurements under linear heating for three Fe-, Ni- and Co-based metallic glasses are presented. Torque relaxation is determined by the pre-annealing temperature, T_a: at T < T_a, the degree of relaxation is small and high-rate torque relaxation starts near T_a. Analogously, high-rate strain recovery starts near the temperature of preliminary homogeneous deformation. The temperatures where high-rate stress relaxation and strain recovery begins are calculated in the framework of an activation energy spectrum model and are consistent with experiment. A homogeneous-flow model is developed which qualitatively explains macroscopically reversible behaviour as a result of directed irreversible microscopic relaxation events with distributed activation energies.     

Point defects and dichroism in langasite and langatate crystals

The hypotheses about the nature of color centers in langasite family crystals that are discussed in the literature are analyzed. Optical transmission spectra in the wavelength range of 200–800 nm are recorded for langasite and langatate crystals grown in atmospheres of argon and argon mixed with oxygen in different concentrations, both in the initial state and after isothermal annealings at 1000°C in nitrogen, in air, or in vacuum. Dichroism is observed in langasite and langatate crystals, and spectral dependences of the degrees of dichroism are plotted.     

A crowdion mechanism of crystal twinning

The processes of plastic deformation of crystals via mechanical twinning are considered. Models of nucleation and motion of twin boundaries leading to formation of twin interlayers are proposed. These models are based on the crowdion mechanism of deformation in crystals and are considered by an example of close-packed structures. Good agreement between the predictions of the models proposed and the experimental results for crystals deformed by a concentrated load is demonstrated.