Shubnikov-de Haas oscillations in a new dual-layered quasi-two-dimensional organic metal (BETS)4CoBr4(C6H4Cl2)

The interlayer and intralayer resistances and Shubnikov-de Haas oscillations in a new dual-layered quasi-two-dimensional organic metal (BETS)₄CoBr₄(C₆H₄Cl₂) with a periodically varying structure of cation layers have been studied. It has been shown that the interlayer resistivity corresponds to an incoherent or weakly incoherent transport regime. The oscillations of the magnetoresistance have been described by a model of a chain of coherent magnetic breakdown orbits taking into account the quantum interference effect. The behavior of the interlayer transport, as well as quantum oscillations, is in good agreement with the theoretical calculations of the band structure.     

Hydrostatic-Pressure-Induced Reentrance of the Metallic State in the κ-(ET)2Hg(SCN)2Cl Quasi-Two-Dimensional Organic Conductor

On cooling below 30 K, the κ-(ET)₂Hg(SCN)₂Cl quasi-two-dimensional organic metal, which is in the quantum spin liquid state at liquid helium temperatures, undergoes a transition to the Mott insulator state. The application of a hydrostatic pressure p = 0.7 kbar stabilizes the metallic state and makes it possible to study the behavior of the interlayer magnetoresistance at liquid helium temperatures. The field dependence of the magnetoresistance exhibits an unlimited power-law growth, which indicates that the polaron mechanism contributes to the interlayer transport. The spectrum of observed magnetoresistance oscillations corresponds to the Fermi surfaces characteristic of conducting layers with the κ-type structure.

     

Effect of pressure on the interlayer transport and the electronic structure in the organic quasi-two-dimensional bilayer metal θ-(BETS)<Subscript>4</Subscript>HgBr<Subscript>4</Subscript>(C<Subscript>6</Subscript>H<Subscript>5</Subscript>Cl)

The behavior of the interlayer resistance and the magnetoresistance in the organic quasi-twodimensional bilayer metal θ-(BETS)₄HgBr₄(C₆H₅Cl) is studied at normal pressure and a hydrostatic pressure of 10 kbar. The interlayer transport under atmospheric pressure is found to occur in an incoherent mode. The applied pressure does not change the electronic structure of the conducting layers and causes a transition to a weakly coherent mode at low temperatures.     

Interlayer transport of electron in bilayer graphene with phonon-induced lattice distortion in the presence of biased potential

The interlayer transport of electron in bilayer graphene influenced by phonon in the presence of biased potential is investigated using the tight-binding approach. The in-plane optical mode E_2g and out-of-plane optical mode B_1g associated with the applied biased potential are considered to compute and discuss the interlayer transport probability of an electron initially localized on the bottom layer at the Dirac point in the Brillouin zone. Without the biased potential, the interlayer transport probability is equal to 0.5 regardless of the phonon displacement except for a few special cases. Applying a biased potential to the layers, we find that in different phonon mode the function of the transport probability with respect to applied biased potential and phonon displacement is complex and various, but on the whole the transport probability decreases with the increase in the absolute value of the applied biased potential. These phenomena are discussed in detail in this paper.     

Transport critical-current and voltage-current characteristics of Bi(2223) silver-clamped thick films

The transport critical current properties of Bi(2223) silver-clamped thick films are studied by the measurement of its dependence on magnetic field and temperature close to T _c. It is found that the transport critical current follows a power law J _c(1–T/T _c)^3/2 for the sample with J _c>2.0×10⁴ A/cm² (77K, zero field) and that J _c(H) is basically reversible for increasing and decreasing magnetic field. After the transport current exceeds the critical current, the voltage-current (V-I) characteristics show a flux-creep-like behaviour until they smoothly join the flux-flow state. From the measurement of V-I curves, the pinning property of the sample may be estimated using the flux-creep mode. The flux-flow resistance is found to have a nonlinear magnetic field dependence.     

Study on characteristics of a double-conductible channel organic thin-films transistor with an ultra-thin hole-blocking layer

The properties of top-contact organic thin-film transistors (TC-OTFTs) using ultra-thin 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP) as a hole-blocking interlayer have been improved significantly and a BCP interlayer was inserted into the middle of the pentacene active layer. This paper obtains a fire-new transport mode of an OTFT device with double-conductible channels. The accumulation and transfer of the hole carriers are limited by the BCP interlayer in the vertical region of the channel. A huge amount of carriers is located not only at the interface between pentacene and the gate insulator, but also at the two interfaces of pentacene/BCP interlayer and pentacene/gate insulator, respectively. The results suggest that the BCP interlayer may be useful to adjust the hole accumulation and transfer, and can increase the hole mobility and output current of OTFTs. The TC-OTFTs with a BCP interlayer at V_DS=-20~V showed excellent hole mobility μ_FE and threshold voltage V_TH of 0.58~cm²/(V\cdots) and --4.6~V, respectively.     

Structural and magnetic phase transitions in (Chloroanilinium)2CuX4 (X = Cl, Br)

Successive structural phase transitions of (4-ClC₆H₄NH₃)₂CuCl₄, which occur in a very narrow temperature range were reinvestigated by Fourier transform nuclear quadrupole resonance (FT NQR) measurements. The phase transitions at 275.5 and 277.0 K were confirmed. The effect of the deuteration of the ammonium end on these transitions was studied. The³⁵Cl NQR frequencies of organic cation were observed to decrease by about 4 kHz and the phase transition temperatures to decrease by about 2 K by the deuteration, suggesting that the ?NH₃ ⁺ … Cl hydrogen bond is weakened by the deuteration. The magnetic phase transition temperature of 8.6 K showed no remarkable change within experimental error by the deuteration. It was found that the magnetically ordered state is broken by the radio-frequency magnetic field of about 15–35 Oe usually employed in pulsed NQR. However, in the deuterated compound (4-ClC₆H₄ND₃)₂CuCl₄, the ordered state was found to be stabler for the usual radiofrequency power. By combining with the NQR data of (4-ClC₆H₄NH₃)₂CuBr₄ and (3,5-Cl₂C₆H₃NH₃)₂CuCl₄, the possibility is discussed of tuning the interlayer interaction between the organic cation layer and the inorganic complex anion layer by the halogen substitution in the organic cation as well as by the halogen replacement in the inorganic complex anion.     

The IR and Raman spectra of Tb0.2Dy0.9Gd0.9(MoO4)3

The IR and Raman spectra of the ternary molybdate Tb_0.2Dy_0.9Gd_0.9(MoO₄)₃ have been recorded and analysed on the basis of the vibrations of MoO²⁻₄ ions. The splitting of the non-degenerate Mo—O symmetric stretching mode due to the vibrational interaction between neighbouring ions is observed. The large splitting observed for the v₃(F₂) mode is probably due to the large number of MoO²⁻₄ ions and strong interlayer coupling present in the unit cell.     

Magnetic and electric properties of (Fe,Co)/(Si,Ge) multilayers

We review selected results concerning the interlayer exchange coupling in Fe/Si _x Fe_1−x , Fe/Ge and Co/Si layered structures. Among the ferromagnet/semiconductor systems, Fe/Si structures are the most popular owing to their strong antiferromagnetic interlayer coupling. We show that such interaction depends not only on semiconducting sublayer thickness, but also on deposition techniques and on the chemical composition of the sublayer as well. In similar heterostructures e.g. Fe/Ge, antiferromagnetic coupling was observed only in ion-beam deposited trilayers at low temperatures. In contrast, in Fe/Ge multilayers deposited by sputtering, no such coupling was found. However, when the Ge is partially substituted by Si, antiferromagnetic interlayer coupling appears. For Co/Si multilayers, we observed a very weak exchange coupling and its oscillatory behavior. The growth of Co on Si occurs in an island growth mode. The evolution of magnetic loop shapes can be successfully explained by the interplay between interlayer coupling and anisotropy terms.     

STRUCTURE, MAGNETIC PROPERTIES AND GIANT MAGNETORESISTANCE OF YMn6Sn6-xGax (x=0-0.6) COMPOUNDS

Structure, magnetic and transport properties of YMn₆Sn_6-xGa_x (0≤x≤0.6) compounds with a HfFe₆Ge₆-type structure were investigated. It was found that the Ga substitution leads to a contraction of the unit-cell volume. A transition from an antiferromagnetic to a ferromagnetic (or ferrimagnetic) state can be observed for samples (0.1≤x≤0.2) with increasing temperature. The antiferro-ferromagnetic transition for samples with x≤0.2 can also be induced by an external field. The required field is very low, and decreases with increasing Ga concentration. More Ga concentration (x≥0.3) leads to the samples being ferromagnetic in the whole temperature range below the Curie temperature. The Ga substitution weakens the interlayer magnetic coupling between the Mn spins. Corresponding to the metamagnetic transition, a magnetoresistance as large as 32% under a field of 5 T was observed at 5 K for the sample with x=0.2.     

Electric and magnetic properties of the perovskites Ba2(FeMo)O x (5.88 ≤ x 6.01)

The purpose of this work is to establish the relation between the magnetic, electric, and magnetotransport properties and the oxygen nonstoichiometry of the compounds Ba₂(FeMo)O _x (5.88 ≤ x ≤ 6.01). The investigations established the behavior of the magnetization, resistance, and magnetoresistance of samples in this series. It is shown that the behavior of the magnetization can be described by assuming that the iron ions become divalent (Fe³⁺→ Fe²⁺) as a result of the reduction of the samples and the molybdenum ions become hexavalent (Mo⁵⁺ → Mo₆₊) as a result the oxidation of the samples. It is established that there are two contributions to the magnetoresistance which arise as result of magnetic ordering of the intragranular interlayer and intergranular transfer of spin-polarized charge carriers. It is inferred that electric transport in samples of this series is determined by percolation processes between granules with metallic conductivity separated by a dielectric interlayers.     

Role of buried ultra thin interlayer silicide on the growth of Ni film on Si(100) substrate

The presence of a buried, ultra-thin amorphous interlayer in the interface of room temperature deposited Ni film with a crystalline Si(100) substrate has been observed using cross sectional transmission electron microscopy (XTEM). The electron density of the interlayer silicide is found to be 2.02 e/?³ by specular X-ray reflectivity (XRR) measurements. X-ray diffraction (XRD) is used to investigate the growth of deposited Ni film on the buried ultra-thin silicide layer. The Ni film is found to be highly textured in an Ni(111) plane. The enthalpy of formation of the Ni/Si system is calculated using Miedema’s model to explain the role of amorphous interlayer silicide on the growth of textured Ni film. The local temperature of the interlayer silicide is calculated using enthalpy of formation and the average heat capacity of Ni and Si. The local temperature is around 1042 K if the interlayer compound is Ni₃Si and the local temperature is 1389 K if the interlayer compound is Ni₂Si. The surface mobility of the further deposited Ni atoms is enhanced due to the local temperature rise of the amorphous interlayer and produced highly textured Ni film. Received: 2 March 2000 / Accepted: 28 March 2000 / Published online: 11 May 2000     

Shubnikov-de Haas oscillations spectrum of the strongly correlated quasi-2D organic metal (ET)8[Hg4Cl12(C6H5Br)2] under pressure

Pressure dependence of the Shubnikov-de Haas (SdH) oscillations spectra of the quasi-two dimensional organic metal (ET)₈[ Hg₄Cl₁₂(C₆H₅Br)₂] have been studied up to 1.1 GPa in pulsed magnetic fields of up to 54 T. According to band structure calculations, its Fermi surface can be regarded as a network of compensated orbits. The SdH spectra exhibit many Fourier components typical of such a network, most of them being forbidden in the framework of the semiclassical model. Their amplitude remains large in all the pressure range studied which likely rules out chemical potential oscillation as a dominant contribution to their origin, in agreement with recent calculations relevant to compensated Fermi liquids. In addition to a strong decrease of the magnetic breakdown field and effective masses, the latter being likely due to a reduction of the strength of electron correlations, a sizeable increase of the scattering rate is observed as the applied pressure increases. This latter point, which is at variance with data of most charge transfer salts is discussed in connection with pressure-induced features of the temperature dependence of the zero-field interlayer resistance.     

Raman spectroscopic study of the mineral finnemanite Pb5(As3+O3)3Cl

The arsenite mineral finnemanite Pb₅(As³⁺ O₃)₃Cl has been studied by Raman spectroscopy. The most intense Raman band at 871 cm⁻¹ is assigned to the ν₁(AsO₃)³⁻ symmetric stretching vibration. Three Raman bands at 898, 908 and 947 cm⁻¹ are assigned to the ν₃(AsO₃)³⁻ antisymmetric stretching vibration. The observation of multiple antisymmetric stretching vibrations suggest that the (AsO₃)³⁻ units are not equivalent in the molecular structure of finnemanite. Two Raman bands at 383 and 399 cm⁻¹are assigned to the ν₂(AsO₃)³⁻ bending modes. Density functional theory enabled calculation of the position of AsO₃²⁻ symmetric stretching mode at 839 cm⁻¹, the antisymmetric stretching mode at 813 cm⁻¹ and the deformation mode at 449 cm⁻¹. Raman bands are observed at 115, 145, 162, 176, 192, 216 and 234 cm⁻¹ as well. The two most intense bands are observed at 176 and 192 cm⁻¹. These bands are assigned to PbCl stretching vibrations and result from transverse/longitudinal splitting. The bands at 145 and 162 cm⁻¹ may be assigned to Cl Pb Cl bending modes. Copyright © 2009 John Wiley & Sons, Ltd.     

Intermediate temperature solid oxide fuel cell using (La,Sr)(Co,Fe)O3-based cathodes

Anode-supported SOFCs involving LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ)-based cathodes are fabricated utilizing GDC interlayer on 8YSZ electrolyte for intermediate temperatures. The GDC interlayer between the LSCF cathode and YSZ electrolyte is used to prevent formation of insulating phases such as SrZrO₃ or La₂Zr₂O₇. The cell performance with the GDC interlayer was ten times better than the one without GDC at operating temperature of 750 °C. However, the observed power density (370 mW/cm²) was lower than the value reported in the literature. This can be attributed to an imperfect GDC interlayer in the present study. The GDC interlayer was porous and non-uniform, so that adverse interfacial reactions could not be completely prevented. The chemical incompatibility at the interface was evaluated by SEM and EPMA, which explains the dependence of cell performance on sintering temperatures of the GDC interlayer.     

Magnetic susceptibility of the compound (CH2)10(NH3)2FeCl4

The magnetic susceptibility of the compound (CH₂)₁₀(NH₃)₂FeCl₄ is measured in the temperature range from liquid nitrogen temperature up to room temperature. The effect of thermal and magnetic history on the data obtained is also discussed. It is shown that the compound is antiferromagnetic with a Néel temperature of 93 K but it appears that the antiferromagnetic intra-layer exchange interaction co-exists with a weak ferromagnetic interlayer interaction.     

Improving efficiency of organic light-emitting devices by optimizing the LiF interlayer in the hole transport layer

The efficiency of organic light-emitting devices (OLEDs) based on N,N'-bis(1-naphthyl)-N,N'-diphenyl-N,1'-biphenyl-4,4'-diamine (NPB) (the hole transport layer) and tris(8-hydroxyquinoline) aluminum (Alq₃) (both emission and electron transport layers) is improved remarkably by inserting a LiF interlayer into the hole transport layer. This thin LiF interlayer can effectively influence electrical performance and significantly improve the current efficiency of the device. A device with an optimum LiF layer thickness at the optimum position in NPB exhibits a maximum current efficiency of 5.96 cd/A at 215.79 mA/cm², which is about 86% higher than that of an ordinary device (without a LiF interlayer, 3.2 cd/A). An explanation can be put forward that LiF in the NPB layer can block holes and balance the recombination of holes and electrons. The results may provide some valuable references for improving OLED current efficiency.     

Features of the dissipative electron transport near the boundary in the system Al(N)-In(S)

The temperature behavior of the coherent electron transport that arises in the presence of Andreev reflections is studied near the boundary of a hybrid system consisting of aluminum (N) and indium (S). The qualitative change of the temperature behavior upon changes in the electron mean free path l _el as a result of the elastic deformation of the sample is observed for the first time on the same sample, at probes mounted in the normal region at fixed distances and from the boundary. As the temperature is lowered, the measured effective resistance decreases for l _el ? L _{1, 2} and increases in a certain temperature region in which l _el ～ L _{1, 2}. It is shown that phenomena of this kind correspond to quantum-interference features in the scattering of coherent electronic and Andreev hole excitations on elastic centers.     

Multilayer relaxation of the Mg(0001) surface

We have Investigated the interplanar relaxation of the clean (0001)-(1 × 1) surface of magnesium at 100 K using a dynamical LEED I-V analysis. In contrast to almost all other metal surfaces, an expansion has been observed for the first interlayer spacing of this clean surface. Using an extended database, the results indicate that the first three interlayer spacings are relaxed from the bulk value by Δd₁₂ = +1.9 ± 0.3%, Δd₂₃ = +0.8 ± 0.4%, and Δd₃₄ = −0.4 ± 0.5%. A comparison of this observed multi relaxation with experimental and theoretical results for similar free-electron closepacked metal surfaces, e.g. Al(111), suggests that a surface expansion is a normal property of high electron density simple metals.     

Long-term stability of Bi(2223) and Dy(123) superconducting tapes in the direct current circuit

The stability of critical parameters T _c and I _c of commercial high-temperature superconducting wires upon long-term passage of transport current (about 0.7I _c) in liquid nitrogen (77 K) is studied. Voltage-current characteristics U(I), as well as the critical current and critical temperature, are investigated for the case of Bi(2223) hermetic multifilament wires and Dy(123) superconducting tapes covered by a thin Ag layer. In the former case, a considerable decrease in the critical current (by ～30%) and swelling of the wires after passage of the current for 323 h are observed. The same is true for a reference sample, which does not experience the action of current and stays in liquid nitrogen for 700 h. The decrease in the critical current in the Bi(2223) sample is likely to be associated with penetration of a liquid coolant into the composite conductor: evaporating and expanding as a result of heating, it severely deforms the material. The Dy(123) sample grown epitaxially demonstrates high stability of the critical current after it has experienced the action of current for 400 h and been kept in liquid nitrogen for 1000 h.