Showing papers in "Physica Status Solidi (a) in 1994"

Spectroscopy of a new laser garnet Lu3Sc2Ga3O12:Nd3+. Intensity luminescence characteristics, stimulated emission, and full set of squared reduced‐matrix elements |〈‖U(t)‖〉|2 for Nd3+ ions

Abstract: A new laser crystal Lu3Sc2Ga3O12:Nd3+ with ordered garnet structure is developed. Its stimulated emission at 1.0622 μm wavelength (4F3/2 4I11/2 generating channel) with laser-diode and Xe-flashlamp pumping at room temperature is excited. For prospecting spectroscopic and laser investigations with Nd3+ -ion doped crystals the detailed calculations of the full set of squared reduced-matrix elements for all 4f3 intermanifold J J′ transitions with maximal energy till about 67000 cm−1 are performed.

Network Modification of DLC Coatings to Adjust a Defined Surface Energy

Abstract: In addition to the well-known properties of diamond-like-carbon (DLC) coatings, the surface tension is a new criterion to characterize this kind of thin films. To influence the surface tension of DLC coatings, their structure is modified by the incorporation of different elements like fluorine or silicon into the matrix of the amorphous network. Furthermore, the surface tension can be strongly influenced by the deposition parameter. With the appropriate reactive gas and process parameter it is possible to adjust separately the polar and the dispersive components of the surface tension. Using fluorinated hydrocarbons an almost PTFE-like coating with a surface tension of 22 mN/m is realized. Since halogenous monomers are very controversial it is desirable to find other reactive gases for modifying the surface tension on the basis of amorphous hydrocarbon layers. First investigations with silicon containing monomers point out the possibility to prepare hard coatings with a surface tension also comparable to PTFE but with a much better microhardness of about 15 GPa instead of 6 GPa for fluorinated thin films or 0.3 GPa for PTFE, respectively. To calculate the surface tension of plasma polymerized thin films, the applicability of contact angle measurements (sessile-drop method) is investigated first by comparing different approaches for the adhesion energy and evaluation methods, respectively.

Formalism for the evaluation of strongly non-linear surface stress fields by X-ray diffraction performed in the scattering vector mode

Abstract: A formalism is proposed for the evaluation of residual stress fields in polycrystalline materials which vary significantly within the penetration depth τ of the X-rays. It is shown that the penetration depth may be varied independently of the angle Ψ by rotating the sample around the scattering vector gΨΨ which is parallel to the normal of the reflecting lattice planes Nh. Therefore, it becomes possible to separate individual components of the stress tensor from the fundamental equation of X-ray stress analysis and to evaluate the gradients σij(τ) without any assumption in form of an analytical expression to describe the depth profiles. Es wird ein Formalismus fur die Ermittlung von Eigenspannungsfeldern in polykristallinen Werkstoffen vorgeschlagen, die deutliche Anderungen innerhalb der Eindringtiefe τ der Rontgenstrahlung aufweisen. Es wird gezeigt, das sich die Eindringtiefe unabhangig vom Winkel Ψ variieren last, wenn man die Probe um den Streuvektor gΨΨ dreht, der parallel zur Normalen Nth der beugenden Netzebenen liegt. Damit wird es moglich, einzelne Komponenten des Spannungstensors aus der Grundgleichung der rontgenographischen Spannungsermittlung abzutrennen und die Gradienten σij(τ) ohne Annahmen in Form eines analytischen Ansatzes zur Beschreibung der Tiefenprofile zu ermitteln.

Stress induced modifications in ferroelectric films

Abstract: Stresses in rf sputtered polycrystalline BaTiO3 thin films, deposited at 300 to 700°C and at pressures from 0.1 to 100 Pa, on both Si and sapphire single crystals, are investigated. From the measured total stress values at room temperature, both the intrinsic stresses in the film and biaxial modulus of the film, Ef/(1–νf), are calculated. At lower deposition temperatures and pressures compressive intrinsic stresses are obtained, whereas at high deposition temperatures and pressures intrinsic stresses are tensile in nature. The biaxial modulus value approaches the single crystal value for films deposited at low pressures and decreases significantly with increasing deposition pressure. BaTiO3 films with high compressive stresses (≧ 400 MPa) show higher refractive indices, higher extinction coefficients, and lower optical band gaps compared to those for films with low compressive stresses (≈ 40 MPa). Furthermore, Curie point and coercive fields are increased, while remanant polarization decreases with increasing compressive stress. In addition, films in a state of high compression show a broad peak in the dielectric constant versus temperature curve which indicates a diffuse transition from ferroelectric to paraelectric state. By a judicious choice of deposition conditions, BaTiO3 films having low intrinsic stresses and properties close to those of single crystals are obtained. For example, some of the properties of BaTiO3 films deposited at 650°C and at 2 Pa pressure on silicon substrate are: n = 2.37 at 700 nm, Eg = 3.13 eV, Pr = 15.9 μC/cm2, Ec = 10.2kV/cm, Cure point 129°C, and σi = −47 MPa.

Thin Film Nanoprocessing by Laser/STM Combination

Abstract: A new technique of laser direct writing of nanoscale structures is proposed. The technique is based on a local intensity enhancement of optical radiation near a tip of a scanning tunneling microscope and allows to overcome the fundamental spot limitation (about a half of the wavelength λ) of the conventional lens-focused beams. In the first experimental results unconventional tips of silver are used in order to increase the effect. By using a laser with λ = 800 nm features of 10 to 40 nm in diameter are reversibly written on the surface of gold films. Theoretical possibilities and mechanisms of the near-field enhancement of optical radiation by very small conductive objects are briefly summarized. [Russian Text Ignored].

Hardness and elastic moduli of Bi2−xPbxCa2Sr2Cu3Oy superconductors

Abstract: X-ray diffraction, de resistivity, and microhardness studies of Bi2−xPbxCa2Sr2Cu3Oy Superconductors with x = 0 to 0.4 are performed. The first two studies evidence the formation and improvement of the 2223 phase with the rise in Pb concentration up to 0.3, and later a reduction. The variation of microhardness with load P is analysed for each Bi2−xPbxCa2Sr2Cu3Oy SuperconductorsBi2−xPbxCa2Sr2Cu3Oy Superconductors with x = 0 to 0.4. Experimental results of the diagonal length of the indenter impression, d, corresponding to each load P is fitted with the relation P = A1d + A2d2 and the constants A1 and A2 are determined for each sample. Both A1 and A2 are found to have an anomalous variation with Pb concentration attaining, at x = 0.3 a minimum and a maximum, respectively. Young's modulus and yield strength of each sample are determined using the constant A2 and their values are maximum for the sample with x = 0.3. Moreover, the constant A1 is negative for the sample with x = 0.3 and positive for the rest of the samples. These results are explained on the basis of low and high Tc phases, surface energy, and bulk hardness.

Structural, optical, and electrical properties of cadmium oxide films deposited by spray pyrolysis

Abstract: Transparent conducting cadmium oxide films are prepared by the spray pyrolytic technique. The dependence of structural, optical, and electrical properties on the film thickness is investigated. X-ray diffraction studies confirm the polycrystallinity of the films and the films show preferential orientation along the (200) plane. The crystallite size and the dislocation density are also determined from the above patterns. The films show about 70% transmittance in the wavelength range 750 to 850 nm and the values of band gap and refractive index are in the order 2.35 to 2.50 eV and 1.95 to 2.65, respectively. Hall measurements indicate that the films are n-type, having carrier concentration ≈ 1026 m−3 and mobility (17.5 to 19) × 10−4m2/Vs.

Analysis of charging and discharging currents in polyethyleneterephthalate

Abstract: Charging and discharging currents in polyethyleneterephthalate samples for different polarization times, temperatures, and fields and for different measuring intervals are measured. Special attention is paid to external measuring circuit. The current obeys a Curie-von Schweidler law only for short times. The charging current changes its shape if the polarization time is long or the polarization field is high, depending on the product time × field. The discharging current is strongly dependent on the external resistance used in measuring circuit. Three characteristic parts are observed. The first part fits well with a Debye relaxation function. The second part seems to be a straight line and the slope is dependent on measuring resistance and the charge existing in the sample. As the resistance is higher, the slope is higher. The third part, reported for the first time in this paper, represents the current that is released from the sample for a long time and sometimes is considered as a parasitic current. If the external resistance is big enough, this current can lead to increases of the voltage on the sample. The slope of the discharge current is dependent on the charge contained in the sample. On a mesure les courants de chargement et de dechargement pour differents temps, champs et temperatures de polarization et pour differents intervales de mesure. Les courants satisfont la lois de Curie-von Schweidler seulement pour de petites intervales du temps de mesure. Le courant de chargement change sa forme si le temps de polarisation est long ou si l'intensite du champ electrique de polarisation est assez grande. Il depend du produit champ × temps. On a obtenu trois zones characteristiques pour le courant de dechargement comme une fonction de temps. La premiere zone est bien approximee par une fonction de relaxation du type Debye. La deuxieme est lineaire dont sa pente depend de la resistance externe de mesure. Si la resistance croǐt, la pente croǐt aussi. La troisieme zone qu'on met en evidence pour la premiere fois dans ce travail, represente un courant qui est longuement elibere par l'echantillon. Si la resistance externe est grande ce courant peut provoquer la croissance de la tension sur l'echantillon. La forme du courant de dechargement depend de la charge accumulee dans l'echantillon.

The influence of iodine on the electrical properties of lead phthalocyanine (PbPC) interdigital planar gas sensors

Abstract: The electrical behaviour of AuPbPcAu planar gas sensors is studied as a function of exposure to I2–air mixture. The changes in the I–U characteristics of PbPc thin films on exposure to iodine and after subsequent annealing in vacuum at various temperatures are investigated. It is found that iodine generates acceptor levels within the PbPc energy band gap. The dark current in the devices is studied as a function of temperature and film thickness at a constant bias voltage. The effects of iodine exposure on the film surface and bulk conductivity are identified. The response time and operating conditions for PbPc thin film iodine gas sensors are also reported.

Auger Depth Profile Analysis of Deeply Buried Interfaces

Abstract: The requirements to be met for achieving good depth resolution for Auger depth profiling of thin layers buried by a thick (more than 100 nm) overlayer are discussed, assuming that one uses rotated specimens and glancing angle of incidence. It is shown that the glancing angle of incidence is necessary to avoid the defect accumulation, while for reducing the atomic mixing low ion energy is to be used. Depth profiling results of various multilayer systems are discussed. The dependences of the depth resolution on ion energy and angle of incidence show a trend similar to those resulted by the TRIM code, but the absolute values of the calculated and measured depth resolutions are strongly different.

A fast X-ray method to determine Ge content and relaxation of partly relaxed Si1-xGex layers on silicon substrates

Abstract: A fast X-ray method is presented to determine the Ge content and the relaxation of partly relaxed SiGe layers on Si substrates using a conventional powder diffractometer. The lattice parameters of the layer parallel and normal to the (001) substrate surface are obtained by a usual ω-2θ scan with symmetrical 004 reflection and an ω scan in asymmetrical reflection to measure the relative misorientation between inclined net planes of substrate and layer. The accuracy of this method is checked at a sample with pseudomorphic SiGe layer and its application is demonstrated at three partly relaxed samples with medium Ge content. Es wird eine rontgenographische Methode unter Verwendung eines konventionellen Pulverdiffraktometers vorgestellt, mit der eine schnelle Bestimmung des Ge-Gehalts und der Relaxation von teilweise relaxierten SiGe-Schichten auf Si-Substrat vorgenommen werden kann. Die Gitterparameter der Schicht parallel und senkrecht zur (001)-Substratoberflache werden erhalten durch einen ublichen ω-2θ-Scan mit symmetrischer 004-Reflexion bzw. einem ω-Scan in asymmetrischer Reflexion, wodurch die relative Fehlorientierung zwischen den geneigten Netzebenen von Substrat und Schicht gemessen wird. Die Uberprufung der Genauigkeit der Methode erfolgt an einer Probe mit pseudomorpher SiGe-Schicht, und ihre Anwendung wird an drei teilweise relaxierten Proben mit mittlerem Ge-Gehalt demonstriert.

Acentric disordered Nd3+:La3Ga5SiO14 crystal. A broadband luminescence material with high thermal conductivity to generate picosecond laser pulses

Abstract: The disordered acentric Nd3+ : La3Ga5SiO14 crystal with trigonal Ca3Ga2Ge4O14 structure is tested in an actively and passively mode-locked laser system, which generates stable single pulses of 5.8 ps duration at pulse energy 250 μJ and wavelength λ = 1067 nm (4F3/2 4I11/2 laser channel). The pulse repetition rate can be increased to above 10 Hz. The disordered laser crystal delivers comparable output energy with higher stability compared with phosphate laser Nd3+ :glass. Some important physical properties of La3Ga5SiO14 are considered.

Study of ac susceptibility on the lafe13-xsix system

Abstract: The LaFe13-xSix system is studied by X-ray diffraction and ac susceptibility measurements between 77 and 300 K. With the increase of the Si content x, a structural transition from cubic NaZn13-type structure to tetragonal Ce2Ni17Si9-type structure and three kinds of magnetic behavior are observed. At low x-values (1.4 less-than-or-equal-to x less-than-or-equal-to 2.4), a disordered cubic NaZn13-type structure occurs, and the ac susceptibility versus temperature curves exhibit a ferromagnetic behavior. For 2.6 less-than-or-equal-to x less-than-or-equal-to 3.0, a structural transition from cubic to tetragonal is found, the ac susceptibility is characterized by a ferromagnetic behavior with a lambda-shaped cusp, corresponding to the partially ordered occupation of Fe and Si atoms. Finally, for 3.2 less-than-or-equal-to x less-than-or-equal-to 5.0, an ordered tetragonal structure with paramagnetic behavior appears

Recording hardness testing. Problems of measurement at small indentation depths

Abstract: The characterization of the mechanical properties of surface layers produced by coating or other processing demands the measurement of the hardness at very low indentation dephts. The exact position of the zero point of the depth scale and possible tip faults, respectively, influence the reliability of the results in this region. Therefore, the elimination of such artefacts is necessary to determine the real behaviour of the material. A procedure is proposed which allows the determination of the zero point by extrapolation for two types of hardness tester, load step type, as well as closed loop type ones. Additionally an exact estimation of the standard deviation is given. A criterion allows to investigate the influence of indenter tip faults. Nominally homogeneous materials (glass, copper, polymer) show unambiguously the existence of a depth depending hardness, the so-called “indentation size effect” (ISE), as a characteristic property of the material. One must conclude that an exact analysis of the ISE for penetration depths smaller than 40 times the digit distance of the sensor system is only possible by an increase of its sensitivity. Die Charakterisierung der mechanischen Eigenschaften von Oberflachen nach Beschichtung oder nach Bearbeitung erfordert Messungen der Harte bei sehr geringen Eindringtiefen. Die genaue Position des Nullpunktes der Eindringtiefenskala bzw. mogliche Indenterspitzenfehler beeinflussen die Zuverlassig-keit der Ergebnisse in diesem Bereich. Deshalb mussen solche Fehlerquellen unbedingt eliminiert werden, um das reale Materialverhalten zu ermitteln. Es wird ein Verfahren vorgeschlagen, das die Bestimmung des Nullpunktes durch Extrapolation fur zwei Geratetypen, die unter Gewichtsbelastung bzw. im geschlossenen Kraftkreis arbeiten, erlaubt. Zusatzlich wird eine exakte Abschatzung der Standardabweichungen angegeben. Ein Kriterium ermoglicht, den Einflus des Indentenrspitzenfehlers zu untersuchen. Nominell homogene Materialien (Glas, Kupfer, Polymere) zeigen eindeutig die Existenz einer tiefenabhangigen Harte, den sogenannten “indentation size effect” (ISE), als eine charakteristische Materialeigenschaft. Es ist zu schlusfolgern, das eine exakte Analyse dieses ISE fur Eindringtiefen, die kleiner als das 40fache des digitalisierten Meswerteabstandes des Sensor-Systems sind, nur durch eine Vergroserung von dessen Mesempfindlichkeit zu erreichen ist.

Step formation on the ion-bombarded Ag(100) surface studied by LEED and Monte Carlo simulations†

Abstract: The development of the morphology of an Ag(100) single-crystal surface bombarded with 600 eV Ar+ ions at 170 K and at room temperature is studied by spot profile analysis of LEED. A temperature-dependent saturation of the step density is observed and a distinct smoothing of the surface after bombardment occurs already at room temperature. Under out-of-phase condition the LEED spots show a fourfold shape that differs in orientation at both temperatures. Monte Carlo simulations of the atom removal including thermal surface diffusion reveal at 170 K the formation of 〈100〉 and 〈110〉 step edges with equal probability, whereas at room temperature rearrangement processes at the steps lead to the preferential formation of the close-packed 〈110〉 edges. The intensity distribution under out-of-phase condition calculated from the Monte Carlo snap shots exhibits the same temperature dependence of the spot shapes as observed experimentally. The interlayer mass transport occurring during annealing at room temperature is found to be based on jumps running downward the 〈100〉 step edges. Mittels LEED-Reflexprofilanalyse wird die Morphologieentwicklung der Ag(100)-Oberflache nach dem Beschus mit 600 eV Ar+ -Ionen bei 170 K und Raumtemperatur untersucht. Es werden eine temperaturabhangige Sattigung der Stufendichte sowie bei Raumtemperatur eine deutliche Ausheilung der Oberflachenschaden nach dem Beschus beobachtet. Die LEED-Reflexe zeigen bei Gegenphase-Bedingung eine vierzahlige Gestalt, deren Orientierung von der Substrattemperatur abhangt. Monte-Carlo-Simulationen zur Atomabtragung unter Einbeziehung thermisch aktivierter Oberflachendiffusion belegen bei 170 K die gleichberechtigte Bildung von 〈100〉- und 〈110〉-orientierten Stufenkanten, wahrend bei Raumtemperatur Prozesse an den Stufenkanten zur bevorzugten Ausbildung der dichtgepackten 〈110〉-Kanten fuhren. Die von den simulierten Oberflachenmorphologien berechneten Intensitatsverteilungen bei Gegenphase-Bedingung weisen dieselbe Temperaturabhangigkeit der Reflexgestalt auf, wie sie im LEED-Experiment beobachtet wurde. Der wahrend der Ausheilung bei Raumtemperatur auftretende Massentransport zwischen den Schichten erfolgt uber die 〈100〉-Stufenkanten.

Fundamental optical absorption edge and compositional disorder in γ1‐(GaxIn1−x)2Se3 single crystals

Abstract: Results are given of an investigation of the absorption processes at the absorption edge of the ternary system (GaxIn1−x)2Se3 in the In-rich region. In E ∥ c polarization, the absorption coefficient for all investigated concentrations exhibits an exponential dependence on photon energy following Urbach's rule. The analysis of the results confirms that the absorption processes in the absorption edge of γ1-(GaxIn1−x)2Se3 are governed by a superposition of at least two different mechanisms, one related to the crystal phonons and the other resulting from structural and compositional disorder. The latter mechanism seems to be fundamental, influencing the absorption processes equivalently in amorphous and monocrystal states. In both E ∥ c and E ⊥ c polarization an apparent dependence of absorption coefficient on sample thicknesses at constant photon energy is observed. The effect is assigned to a subsurface damage introduced by mechanical polishing.

Reversible Radiation Effects in Vitreous As2S3. II. Mechanism of Structural Transformations

Abstract: Reversible γ-induced structural transformations in vitreous As2S3 are studied using ESR and differential IR Fourier-spectroscopy techniques. It is shown that the investigated low-temperature (T < 100 K) as well as high-temperature (T ≈ 300 K) radiation-structural transformations are associated with chemical bond breaking and switching.

Synthesis of Li2B4O7:Cu phosphor

Abstract: Li2B4O7 is a low-Z, tissue-equivalent material and several phosphors based on this material are proposed for use in dosimetry of ionizing radiations using thermoluminescence. The synthesis of this phosphor using boric acid is a bit tricky as the stoichiometry and the crystallinity of the product depend on several factors. A new synthesis using solid state diffusion is used. The characterization of Li2B4O7: Cu phosphor thus prepared, using XRD, thermoluminescence, and PL techniques is described. It is also shown that the crystalline Li2B4O7: Cu containing monovalent Cu has good TL sensitivity, while glassy Li2B4O7 and divalent Cu are detrimental for TL.

Differential load feed analysis: An energy-related alternative to the interpretation of hardness indentation measurements

Abstract: The presented new theoretical approach to the interpretation of hardness indentation measurements is based on an energy-related consideration of the deformation principles in solid state materials under the action of a penetrating indenter. The equations developed therefrom are directly comparable to the first derivative of the experimentally recorded indentation load with respect to the indentation depth. They permit the calculation of specific energies of the different deformation processes. A direct correlation to the conventional hardness conception is derived for the specific energy of isotropic volume densification. The efficiency of the new approach is examined by extensive experimental data of bulk materials as well as coating–substrate composites. The results are shown to demonstrate the correct charge of the energy-related data interpretation. The obtained specific energies permit the quantification of adhesion between substrates and coatings as well as of the extension of specific deformation ranges under the action of the indenter. The results are shown to be in agreement with conventional characterization methods.

The kinetics of strain relaxation in lattice-mismatched semiconductor layers

Abstract: A scheme is proposed within which the elements of dislocation propagation, interaction, nucleation, and multiplication may be combined to yield a model of strain relaxation in lattice-mismatched semiconductor layers. Interaction between perpendicular dislocations is considered more fully than previously, and criteria that determine whether a propagating threading dislocation will be blocked because of such an interaction are incorporated into the kinetic model. These criteria are developed in detail using the full half-space stresses of a dislocation, and then an approximation is presented that allows the results yielded by these criteria to be reproduced almost exactly, using formulae of great simplicity. Theoretical consideration of the nucleation and multiplication processes is found to be more difficult, but elementary treatments are presented that allow the kinetic model to be tested against experiment with reasonable results. Various problems inherent in the modelling of strain relaxation are highlighted and discussed.

Influence of Ba content on the magnetic after‐effect spectra in barium ferrites

Abstract: The magnetic after-effect (MAE) spectra of barium ferrites (BaO · nFe2O3) of various compositions, 5 < n < 123, are carefully investigated in the temperature range 4.4 K < T < 460 K. Increasing Ba content causes drastic alterations of the typical, magnete-specific MAE mechanisms: (i) gradual suppression of the Verwey transition at Tv ≤ 125 K; (ii) deterioration of electron tunnelling and hopping in the low-temperature range below Tv; (iii) appearance of interstitial-type relaxations at 170 and 240 K and modifications of vacancy-induced after-effects at 300 and 360 K. Die magnetischen Nachwirkungsspektren von Bariumferriten (BaO · nFe2O3) unterschiedlicher Zusamensetzung, 5 < n < 123, werden im Temperaturbereich 4.4 K < T < 460 K eingehend untersucht. Zunehmender Ba-Gehalt verursacht auffallige Veranderungen der fur Magntit charakteristischen Nachwirkungsmechanismen: (i) Unterdruckung des Verwey-Ubergangs bei Tv ≤ 125 K; (ii) Behinderung der elektronischen Tunnel- und “Hopping”-Prozesse im Tieftemperaturbereich unterhalb Tv; (iii) Auftreten neuer, durch Zwischengitteratome verursachter Relaxationen bei 170 und 240 K, sowie Beeinflussung der durch Leerstellen induzierten Prozesse bei 300 und 360 K.

Chemically deposited n-CdO thin films for solar cell applications

Abstract: In the present note we report the preparation and characterization of large area n-type conducting CdO films for the first time by a low cost technique, viz. the chemical bath deposition. (orig.)

Electron transport in 2‐t‐butyl‐9,10‐N,N′‐dicyanoanthraquinonediimine

Abstract: Electron mobilities are measured in vapor deposited layers of 2-t-butyl-9,10-N,N′-dicyanoanthraquinonediimine (DCAQ). The results are described within the framework of a formalism based on disorder, due to Bassler and coworkers. According to the formalism, charge transport occurs by hopping through a maniforld of localized states with superimposed positional disorder. The key parameters of the formation are Σ, the energy width of the hopping site manifold and Σ, a parameter that describes the degree of positional disorder. For DCAQ, σ = 0.101 eV and σ = 2.0. The experimental results are interpreted to show that the energy width of the hopping site manifold is mainly determined by dipole moments associated with the cyanoimine functionalities of the DCAQ molecule while the degree of positional disorder is attributed to packing constraints. A comparison is made between DCAQ and literature results recently reported for hole transport in a number of vapor deposited donor compounds.

Structural characteristics of HDPE/CaCO3 polymer composites probed by positron annihilation

Abstract: The results of positron lifetime measurements as a function of volume fraction Φv of CaCO3 particles on the high density polyethylene/CaCO3 (HDPE/CaCO3) polymer composites with and without addition of a coupling agent are presented. It is observed that, first, positronium (Ps) is formed and annihilates in the free-volume hole of HDPE and the free-volume concentration decreases with increasing Φv; second, the positron lifetime τ2 and its intensity I2 are strongly affected by the structure of the interface layer between CaCO3 particle and HDPE matrix. An interesting correlation between positron parameters and the tensile strength of the composites is found.

Crystal structure and phase transition in the perovskite-type layer molecular composite NH3(CH2)4NH3PbCl4

Abstract: The crystal structure of NH3(CH2)4NH3PbCl4 at room temperature (RT phase) is determined by X-ray diffraction. The structural arrangement is of two-dimensional type, with ammonium alkylene chains located in between corner-sharing PbCl6 octahedra layers. The connection between the inorganic and organic parts of the structure is assumed by hydrogen bonds of N–H…Cl type. The crystallographic data are: monoclinic, space group P21/c, Z = 4, a = 0.7944(2) nm, b = 0.7772(5) nm, c = 1.9761(8) nm, β = 94.84(3)°. The organic chain is not centrosymmetrical and shows a left-hand conformation at one extremity. The presence of a phase transition is evidenced at T = 323.8 K by calorimetric and diffraction methods. The crystallographic data of the high-temperature phase (HT form) are obtained from single and powder crystal investigations: monoclinic, space group P21/a, Z = 2, a = 0.7963(5) nm, b = 0.7735(6) nm, c = 1.1011(1) nm, β = 102.22(9)°. La structure cristalline de la phase stable a la temperature ambiante (RT phase) de NH3(CH2)4NH3PbCl4 est determinee par diffraction des rayons X. L'arrangement est de type bidimensionnel avec des couches alternees de plans mineraux constitues d'octaedres PbCl6 lies par leurs sommets equatoriaux et de phases organiques constituees de molecules NH3–(CH2)4–NH3. La liaison entre les deux parties inorganique et organique de la structure est assuree par des liaisons hydrogene de type N–H … Cl. Les donnees cristallographiques de la phase sont: monoclinique, Z = 4, a = 0,7944(2) nm, b = 0,7772(5) nm, c = 1,9761(8) nm, β = 94,84(3)°, groupe P21/c. La chaǐne organique est assymetrique et presente une conformation gauche a l'une de ses extremites. Une transition de phase est mise en evidence a T = 323,8 K par methodes calorimetrique et diffractometrique. Les donnees cristallographiques de la phase haute temperature (HT phase) sont determinees a partir des experiences sur poudre et sur monocristaux: monoclinique, Z = 2, a = 0,7963(5) nm, b = 0,7735(6) nm, c = 1,1011(1) nm, β = 102,22(9)°, groupe P21/a.

Growth Conditions, Optical and Dielectric Properties of Yttrium Oxide Thin Films

Abstract: Thin Y2O3 films are grown by reactive synthesis, their optical and dielectric properties (electric resistivity, dielectric losses and permittivity, electric strength, and refractive index) are measured. Their dependence upon deposition parameters (deposition rate and reactive gas pressure) is investigated. Comparison of experimental data with those obtained by film growth modelling by the Monte-Carlo method suggests an insignificant influence of diffusion jumps and long-range order on the formation of Y2O3 films at low deposition temperature (300 to 400 K). The perspectives of Y2O3 films as dielectric layers in integrated circuits and high refractive layers for laser mirrors are shown.