Polymorphism and phase transitions in TlS

The conditions for synthesis and the range of existence of the monoclinic TlS modification in the Tl-S system have been determined by means of differential thermal, X-ray diffraction, and microstructural analyses. It was shown that the monoclinic phase is a structural analogue of TlGaSe₂. Possible variants of formation of structural sheets and the nature of phase transitions in the monoclinic TlS modification are discussed.     

Improper ferromagnetic phase transitions in crystals

A complete set of possible improper phase transitions leading to polarization and magnetization of crystals is found from tensor bases of representations of the black-and-white point group of crystal symmetry by using the multiplication table of irreducible representations. The dependences of the secondary order parameter on the primary order parameter are presented for different classes of the symmetry group.     

Phase transitions and orientational order in thin oxygen films

The structure of condensed oxygen films has been studied by the transmission electron diffraction method. Specimens were prepared directly in situ by depositing 99.99% pure gas on amorphous carbon and polycrystalline Al substrates. Measurements were made in the temperature range between 5 K and the sublimation point. It was established that the as-grown oxygen films had a short-lived α′ structure, which was transformed into an α-phase or a β modification depending on the temperature range. The temperature behavior of the structural characteristics of oxygen deposits has been investigated. An unusual character of the α–β transition was manifested in the appearance of α′ reflections on the diffraction pattern during the transformation. A few possible mechanisms of the transition are discussed in the paper. The influence of quenching conditions on crystals’ growth has also been investigated. The new conditions for the formation of a magnetically distorted α′-phase were established. An unknown phase of solid oxygen was observed in samples deposited under certain conditions. One of its possible origins is an altered orientational arrangement of molecules in closely packed layers. The conditions required for the disordered phase of solid oxygen to form have been determined. Amorphous oxygen was also observed as a result of rapid cooling of crystalline samples.     

Laser-induced phase transitions in PbI2

Pure crystals of PbI₂ have been grown using zone-refining system. The structural phase transition 12 R → 2 H has been observed when exposed to ruby laser light. The results have been explained on the basis of structural considerations of PbI₂ and compared with the earlier existing findings in literature.     

Electron beam induced surface modification of amorphous Sb2Se3 thin film

The change in the surface morphology of amorphous Sb₂Se₃ thin films during the electron beam irradiation has been studied mainly by atomic force microscopy (AFM). Electron beam at accelerating voltages 30 kV is focused onto the surface of the specimens of 100-μm thickness, and then the surface morphology of each specimen has been observed by AFM in air. The modification of the film surface includes lateral and vertical resizing which is typically in the micrometer and sub-micrometer range. Protrusions above the surface as high as 90 nm are observed at 180 pA electron beam current, whilst trenches as deep as 97 nm are observed at 800 pA electron beam current (total thickness of thin film is 100 nm). The dependence of patterns characteristics on irradiation parameters such as exposure time and beam current has also been studied. Physical mechanisms for trench and mound formation are proposed.     

Aluminum induced formation of SiGe alloy in Ge/Si/Al thin film structure

In this work, a study of aluminum induced crystallization (AIC) of thin film germanium/silicon/aluminum (Ge/Si/Al) structure on oxidized silicon is presented. The Ge/Si/Al trilayer structure was prepared in three consecutive thin film deposition processes. The AIC was performed in nitrogen at 500 °C within time duration between 1 and 9 h. The progress of crystallization was monitored by optical microscopy, Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS). It was found that in Ge/Si/Al structure the AIC can lead to formation of SiGe alloy at temperature of 500 °C. This presents an alternative low-temperature formation method of SiGe which is suitable for integration with the conventional Si technology in electronic device fabrication.     

Stability and phase changes in thin layers of rare-earth metals/iron and other binary compounds

The structure, thermal stability and phase transformations in thin Gd–Fe films have been studied. The films were obtained by means of thermal evaporation in vacuum. At room temperature of substrates (T_s) amorphous films were formed, at T_s = 300–500 K – amorphous–crystal condensates, and at T_s > 500K – polycrystalline films. The crystal structure of condensates was determined at various temperatures and crystallization of amorphous films was found to have a heterogeneous character. During crystallization of Gd₂Fe₁₇ amorphous films, formation of two phases, viz. Gd₆Fe₂₃ and a-Fe was observed. In the films obtained at substrates temperature > 500K, the presence of three phases was established: a hexagonal phase Gd₂Fe₁₇ of the Th₂Ni₁₇-type structure, a rhombohedral phase Gd₂Fe₁₇ of the Th₂Zn₁₇-type structure and a hexagonal phase GdFe₅ of the CaCu₅-type structure. GdFe₂ films had a face-centered cubic structure, expected in bulk GdFe₂.     

Structural phase transitions in heteroepitaxial ferroelectric films

The changes in the structural—deformational characteristics occurring during the phase transitions in the crystal lattice of epitaxially grown thin (Ba,Sr)TiO₃ films on the (001) cleavage of MgO crystals have been studied. It is shown that microdeformations along the surface normal of the wall of a c-domain film increase with the temperature and attain maximum values in the vicinity of the phase transition. No decrease in the dimensions of the coherent-scattering regions was observed. The comparison of the deformation of the “average” lattice and microdeformations led to the assumption that the transition from the paraelectric to the ferroelectric phase is accompanied by the dislocation-induced formation of a dipole-glass-type intermediate phase at the temperatures exceeding that of the phase transition.     

Temperature dependence of lattice parameters of SBN single crystals in the vicinity of their structural phase transitions

Changes of lattice parameters of Sr_xBa_1‒xNb₂O₆ (0.35 < x < 0.72) solid solution single crystals were measured as a function of temperature. The X‐ray Bond’ method was used to carry out very precise measurements of the lattice parameters. Fine correlations between values of the lattice parameter and the Sr concentration in the solid solution of Sr_xBa_1‒xNb₂O₆ single crystals are found. A conventional analysis of lattice parameter data in terms of spontaneous strain and strain/order parameter coupling shows that a normal structural phase transition does occur. While the ferroelectric system (SBN26) displays a nearly tricritical behavior, β ≈ 0.20, the relaxor one (SBN61) complies with the two‐dimensional Ising‐model‐like criticality, β ≈ 0.17.     

Pseudosymmetry and ferroelectric phase transitions in the KTP structure type

The characteristic pseudosymmetry observed in the crystal structures of KTiOPO₄-type ferroelectrics have been analyzed. The low-symmetry phases of all the crystals under consideration are characterized by a pronounced pseudosymmetry. The transition temperature monotonically decreases with an increase of the pseudosymmetry parameter of the crystal structure of the ferroelectric phase. The approach suggested to evaluate the transition temperature is more precise and universal than the Abrahams-Jamieson-Kurtz criterion.     

Ferroelastic phase transitions in fluorides with cryolite and elpasolite structures

The ferroelastic phase transitions are investigated in several series of fluoride crystals belonging to the elpasolite and cryolite families (space group \(Fm\bar 3m\)) with the general formula A₂BB′ F₆. The influence of the size and shape of cations and anions on the entropy and the mechanism of structural distortions is discussed.     

Electrical transport mechanism in boron nitride thin film

Both dc and ac transport characteristics of plasma enhanced chemical vapor deposited (PECVD) boron nitride (BN) thin film was investigated by dc current vs. dc voltage measurement at different temperatures and admittance vs. gate voltage at various frequencies/temperatures, respectively. MIM ≡ metal (Al)-insulator (BN)-metal (Al) or MIS ≡ metal (Al)-BN-semiconductor (p-Silicon) test devices were conventionally produced. Both conductivity anisotropy and dc/ac detailed transport mechanism were analyzed within the frame of a turbostratic structure (t-BN), interfacing the substrate by a thin amorphous layer (a-BN). This defective BN film has been justified by both infrared (IR) analysis and indirectly by the resulting electrical transport behavior. Transport and its variations as a function of temperature/frequency are in agreement with a hopping mechanism across Gauss-like energy distributed localized deep traps.     

Capture of adatoms by clusters in thin film deposition

The adatom diffusion and capture by clusters are considered as a random-walk problem. The method of solution is developed. Green's function for a square substrate lattice is obtained. This permits one to give a general solution for a steady-state adatom distribution around clusters and for Halpern's arrival probability. This solution is applicable for calculating capture numbers of some small capture centres. An interpolation formula for the capture number, as dependent on the perimeter length of the capture centre, is proposed for λ a. The adatoms fluxes to the 10 and 11 steps on the surface are calculated. The fluxes are anistropic but the anisotropy disappears with λ/a → ∞. The applicability of the steady-state approach is discussed. It is shown that this approximation is valid for low adatom density. The adatom fluxes to monatomic and diatomic immobile clusters are calculated under conditions when these clusters cannot be treated as capture centres. The conservation equations for these clusters are formulated whereby two different configurations of three-atomic clusters are taken into account.     

Identification of the dynamics of plasma‐induced damage in a CuInSe2 thin film by fractal processing

A planar ionization system for rapid visualization and recording the resistance inhomogeneity and photoconductivity distribution in a chalcopyrite‐type semiconductor (CuInSe₂) copper‐indium‐diselenide film is studied. A part of the discharge energy is transferred to the electrodes of the system by the bombardment of the electrode surface due to an electron‐ion flow. This process leads to the sputtering mechanism of the electrode surface material. It is shown that the plasma‐induced damage (PID) in a CuInSe₂ thin film was primarily due to the effectiveness of sputtering and physico‐chemical interactions in the discharge gap during the transition from Townsend to the glow type. At the same time a nondestructive method is suggested for the analysis of the dynamics of PID in the CuInSe₂ thin film by fractal processing in the planar ionization system. Some properties of the device have been evaluated, such as a relative change of the resistance inhomogeneity is determined by a relative change of discharge light emission (DLE) intensity when a current is passed through an ionization cell. For the quantitative analysis of the change in the dynamic feature of PID of CuInSe₂ thin films, fractal dimension analysis was used following the records of the DLE intensity. The quality of the film was analyzed using both the profile and spatial distributed DLE intensities data showing the surface inhomogeneity and damage in the thin film as function of time. Thus, by using fractal concept, the order of the surface damage and the quality of the CuInSe₂ as function of time can be assessed exactly and the size and location of the surface inhomogeneities in thin film to be ascertained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The characteristics of solid phase crystallized (SPC) polycrystalline silicon thin film transistors employing amorphous silicon process

We investigated the electrical properties of polycrystalline silicon (poly-Si) thin film transistors (TFTs) employing field-enhanced solid phase crystallization (FESPC). An n+ amorphous silicon (n+ a-Si) layer was deposited to improve the contact resistance between the active Si and source/drain (S/D) metal instead of ion doping. By using C–V measurement method, we could explain the diffused phosphorous ions (P+ ions) on the channel surface caused a negatively shifted threshold voltage (V_TH) of ?7.81 V at a drain bias of 0.1 V, and stretched out a subthreshold swing (S) of 1.698 V/dec. This process was almost compatible with the widely used hydrogenated amorphous silicon (a-Si:H) TFT fabrication process and also offers a better uniformity when compared to the conventional laser-crystallized poly-Si TFT process because of non-laser crystallization.     

Light harvesting architectures for electron beam evaporated solid phase crystallized Si thin film solar cells: Statistical and periodic approaches

The fabrication of light trapping architectures for electron beam (e-beam) evaporated polycrystalline Si thin film solar cells is investigated based on tailored self-organized light scattering silica nanospheres and 2 dimensional periodic nanoimprinted structures on glass. A microscopic analysis reveals a unique correlation between the microstructure of high-rate e-beam evaporated Si and the substrate topography. These features provide the basis for the design of nanostructured Si that complies with its distinctive growth characteristics. A layer of self-organized nanospheres embedded in a sol–gel matrix and an anti-reflection coating is found to be an e-beam compatible light trapping approach for poly-Si solar cells, contributing to an increase of 50% in current collection. We developed a preparation process for arrays of equidistant free-standing Si crystals with remarkable optical absorption characteristics based on a nanoimprinted glass substrate by selectively etching e-beam evaporated Si. This periodic approach opens design possibilities for effective three-dimensional architectures for advanced photon management.     

DSC characterisation of various phase transitions in mesomorphic benzylidene anilines

To analyse the order of the phase transitions in a number of mesomorphic benzylidene anilines, the DSC (Differential Scanning Calorimetry) method proposed by NAVARD and HAUDIN is used. This method involves the measurement of the ratio (N) of the DSC peak heights H₂/H₁ for a given transition, performed with two different heating rates (T₂/T₁). N is a function of the ratio r₂/r₁(= R) and the magnitude of N provides a simple way to characterize the order of a phase transition.     

Ferroelectric phase transitions in KNO3 embedded into porous glasses

This paper presents the results of dielectric and dilatometric measurements of porous glasses filled with KNO₃ from water solution and from the melt. It was shown that ferroelectric phase transition is observed during the cooling process only in KNO₃ nanocrystals introduced into the porous matrix. The phase diagram of transition temperatures versus average values of pore dimensions was obtained. The phenomenological model describing the phase transition and size effects in KNO₃ crystals is proposed.     

Study of phase transitions and the incommensurate phase in ACBX 4 crystals by the Monte Carlo method

The statistical model of successive phase transitions in the family of crystals described by the general formula ACBX ₄ has been studied. It is assumed that tetrahedral BX ₄ groups in the disordered tetragonal phase can be located in four equally probable equilibrium positions. Five representatives with different sequences of phase transitions in this family of crystals are considered. The effective equilibrium constants of interactions between tetrahedral groups are calculated within the framework of the electrostatic model. The corresponding phase diagrams and the thermodynamic characteristics of the phase transitions are studied by the Monte Carlo method. The experimental data provided the establishment of the sequence of phase transitions in Rb₂ZnCl₄ and K₂SeO₄ crystals with the formation of an intermediate incommensurate phase. The character of the structure modulation in this phase is established. The calculated thermodynamic characteristics of the phase transitions agree quite well with the experimental data for all the crystals under consideration.