O<Subscript>2</Subscript> photodesorption from a Ag<Subscript>8</Subscript>O<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack> cluster

The decay path of an Ag₈(O₂)^- cluster photoexcited by a 3.1 eV photon is elucidated using time-resolved photoelectron spectroscopy. Photoabsorption results in the formation of an excited state giving rise to a peak in the photoelectron spectra with well-resolved vibrational finestructure. With a lifetime of about 100 fs this bound state decays into an anti-bonding state which dissociates into O₂ and Ag₈^- on a timescale of 10 ps. In the photoelectron spectra, this corresponds to a broad maximum shifting gradually towards higher binding energy while the O₂ and Ag₈^- separate. Finally, the spectrum of bare Ag₈^- appears. This process is unique to small clusters, because on metal surfaces excited state lifetimes are too short to allow for direct dissociation.     

Mixed spin- and spin- Ising models with random nearest-neighbour interactions

Using the effective field theory with correlations, we study mixed spin?3/2 and spin?1/2 Ising models with random bonds and crystal-field interactions on the honeycomb lattice. The nearest-neighbour couplings J_ij are taken as random variables with distribution P(J_ij) = pδ(J_ij ? J)+(1 ? p)δ(J_ij ? αJ), where J > 0 and |α| ≤ 1. In a certain range of negative values of α, the phase diagrams exhibit re-entrant behaviour. In detail, we investigate separately two kinds of disorder: Bond dilution (α = 0) and random ±J interactions (α = ?1). In both cases, the influence of the an-isotropy on the phase diagrams shows some new outstanding features.     

Electrical switching studies on As<Subscript>40</Subscript>Te<Subscript>60-x</Subscript>Se<Subscript>x</Subscript> and As<Subscript>35</Subscript>Te<Subscript>65-x</Subscript>Se<Subscript>x</Subscript> glasses

The I–V characteristics of bulk As₄₀Te_60-xSe_x and As₃₅Te_65-xSe_x glasses have been studied with a current sweep of 0–18 mA-0, over a wide range of compositions (4≤x≤22). All the glasses studied showed a threshold electrical switching behaviour. The number of switching cycles withstood by the samples has been found to depend on the ON-state current. It is seen that the switching voltages increase with increase in selenium content. Further, the switching voltages are found to be almost independent of the thickness of the sample (d), in the range 0.18–0.3 mm. Also, the switching voltages and the number of switching cycles withstood by the samples are found to decrease with temperature. Received: 6 November 2002 / Accepted: 8 November 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +91-80/360-0135, E-mail: sasokan@isu.iisc.ernet.in     

Neutron scattering study of combustion-synthesized Ce<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>

Powder neutron diffraction and Hi-Q neutron diffraction data have been recorded and analysed in order to obtain the local and long range order of Cu in Cudoped CeO₂ with three doping levels of Cu. Rietveld method and MCGR techniques of data analysis for the two types of data reveal that the Cu ion is in the 2+ oxidation state and has a vacancy in its first coordination shell. These deductions from the data analysis fit well with the mechanism of catalysis we propose.     

<Emphasis Type="Italic">B</Emphasis><Stack><Subscript>s</Subscript><Superscript>0</Superscript></Stack> physics at LHCb

The LHCb experiment is in preparation, to be ready for the start of the LHC. The physics which will be performed by LHCb is reviewed, focussing on what can be learnt fromB _s ⁰ mesons.     

Solar-blind MSM-photodetectors based on Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>N heterostructures

Solar-blind MSM photodetectors based on the AlGaN heterostructures have been fabricated and investigated. The influence of material properties on device parameters is discussed. Effect of different buffer layers on the detector performances has been examined. Detectors exhibit low dark currents and high sensitivity within the range of 250–290 nm. Effect of optical excitation energy on GaN-based MSM-detector performance is analyzed and discussed. At high excitation level the detector speed of response is limited by the field screening caused by the space-charge of the holes. The impulse response of GaN-based MSM-detector is compared favorably with GaAs MSM-device.     

Superconductivity in Ti-doped iron-arsenide compound Sr<Subscript>4</Subscript>Cr<Subscript>0.8</Subscript>Ti<Subscript>1.2</Subscript>O<Subscript>6</Subscript>Fe<Subscript>2</Subscript>As<Subscript>2</Subscript>

Superconductivity was achieved in Ti-doped iron-arsenide compound Sr₄Cr_0.8Ti_1.2O₆Fe₂As₂ (abbreviated as Cr-FeAs-42622). The X-ray diffraction measurement shows that this material has a layered structure with the space group of P4/nmm, and with the lattice constants a = b = 3.9003 Å and c = 15.8376 Å. Clear diamagnetic signals in ac susceptibility data and zero-resistance in resistivity data were detected at about 6 K, confirming the occurrence of bulk superconductivity. Meanwhile we observed a superconducting transition in the resistive data with the onset transition temperature at 29.2 K, which may be induced by the nonuniform distribution of the Cr/Ti content in the FeAs-42622 phase.     

Magnetic and transport properties of monocrystalline<Emphasis Type="Italic">Fe</Emphasis><Subscript>3</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>4</Subscript>

A monocrystal ofFe ₃ O ₄ is characterized by resistance, magnetoresistance and magnetic measurements in a temperature range from 4.2 K to 350 K and magnetic field-cycling from −9 T to 9 T. The resistance measurements revealed a metal-insulator Verwey transition (VT) atT _v =123.76 K with activation energy E=92.5 meV at T >T _v and temperature-substitute for the activation energy below the VT,T ₀=E/k _B ≈3800 K within 70 K–110K. The magnetotransport results independently verified the VT at 123.70 K, with discontinuous change in the magnetic moment ΔM≈0.21 ΔM≈0.21μ _B and resistance hysteresis, dependent on the magnetic field in a narrow temperature range of 0.4° around theT _v . The magnetic characterization established self consistentlyT _v as ≈123.67 K, the jump in the magnetization at the VT≈0.25μ _B and confirmed, that the magnetocrystalline anisotropy is the main microscopic mechanism responsible for the magnetization of the monocrystal (88%) with additional natural and imposed defects contributing as 12%.     

Static and dynamic properties of KCN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cl<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>

An extended three-body force shell model (ETSM) has been applied to investigate the static and dynamic properties of KCN _x Cl_1−x for the compositionx = 0.56 and 1.0 at 300 K. The phonon dispersion curves computed by us are compared with the single crystal neutron diffraction data. The unusual features of these curves are the upward curvature seen in some of the acoustic branches. This is a result ofK-dependent softening of the phonon due to translation-rotation coupling. The transverse acoustic branch is more soft near the zone centre.     

GaSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript><Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solutions

The most probable parameters of the pure, doped, and mixed GaSe_1−xS_x (x ≤ 0.4) crystals (solid solutions) are presented together with the results of investigations of their crystal structure and defects, optical and mechanical properties, and damage thresholds. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 35–40, June, 2007.     

Photophysics of C<Subscript>60</Subscript> and C<Subscript><Emphasis Type="Bold">60</Emphasis></Subscript><Superscript><Emphasis Type="Bold">-</Emphasis></Superscript> in faujasite zeolites

While the intercalation of C₆₀ and the formation of C ₆₀ ^- in the supercages of NaX and NaY are confirmed by using ¹²⁹Xe NMR and ESR, the photophysical properties of C₆₀ and C ₆₀ ^- are characterized by monitoring transient reflectance spectra and kinetics, fluorescence kinetics, and diffuse reflectance spectra. C ₆₀ ^- is considerably more abundant in NaY than in NaX. This difference is explained in terms of polarity difference between two zeolites. Both C₆₀ and C ₆₀ ^- have remarkably elongated excited-state lifetimes due to their collision-free environment in zeolitic nanocavities although C ₆₀ ^- has much shorter lifetimes than C₆₀. C ₆₀ ^- , in particular, shows intense absorption and emission due to its reduced symmetry in zeolites. Received 13 July 2001 and Received in final form 8 October 2001     

Spin-wave resonances in Eu<Subscript>0.8</Subscript>Ce<Subscript>0.2</Subscript>Mn<Subscript>2</Subscript>O<Subscript>5</Subscript> and EuMn<Subscript>2</Subscript>O<Subscript>5</Subscript> multiferroics

Spin-wave resonances have been observed in superlattices arising due to the phase separation and self-organization of charge carriers in Eu_0.8Ce_0.2Mn₂O₅ single crystals. The resonances are found within the 5–80 K temperature range at frequencies close to 30 GHz. Similar resonances with intensities about an order of magnitude lower are also observed in EuMn₂O₅. The latter suggests the existence of charge transfer processes between the manganese ions of different valences in EuMn₂O₅.     

Impedance analysis of Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> ferroelectric ceramic

AC impedance spectroscopy technique has been used to study electrical properties of Bi_3.25La_0.75Ti₃O₁₂ (BLT) ceramic. Complex impedance plots were fitted with three depressed semicircles, which are attributed to crystalline layer, plate boundary and grain boundary and all three were found to comprise of universal capacitance nature [C = C0w ⁿ⁻¹]. Grain boundary resistance and capacitance evaluated from complex impedance plots have larger values than that of plate boundary and crystalline layer. The activation energies (E _a) for DC-conductance in grain boundary, plate boundary and crystalline layer are 0.68 eV, 0.89 eV and 0.89 eV, respectively. Relaxation activation energies calculated from impedance plots showed similar values, 0.81 eV and 0.80 eV for crystalline layer and plate boundary, respectively. These activation energy values are found to be consistent with the E _a value of oxygen vacancies in perovskite materials. A mechanism is offered to explain the generation of oxygen vacancies in BLT ceramic and its role in temperature dependence of DC-conductance study.      

溶胶-凝胶法制备BaGd1-xEuxB9O16红色磷光粉的发光

采用溶胶-凝胶法制备出BaGd_1-xEu_xB₉O₁₆红色磷光粉,对过程的物料配比、前驱体处理和晶化温度等制备条件进行了讨论。结果表明,样品在850 ℃下开始晶化,900 ℃时就能够获得较好的晶化产物,结合不同晶化温度下的发光强度比较确定,晶化温度为950 ℃时,BaGd_1-xEu_xB₉O₁₆磷光粉具有较高的结晶状态和发光强度。当Eu浓度x=0.9时具有最大的发光强度;初始原料配比硼酸须按计量过量15%。所得荧光粉的激发光谱峰值为264,394,465,534 nm等,分别归属于Eu-O电荷迁移带及Eu³⁺的⁷F₀-⁵L₆、⁷F₀-⁵D₂和⁷F₀-⁵D₁跃迁,发射光谱呈Eu³⁺的特征红光,最强的发射峰位于614 nm,归属于⁵D₀-⁷F₂跃迁。进一步研究表明该磷光粉中存在着Gd³⁺对Eu³⁺的能量传递。     

Inelastic neutron scattering in Zr<Subscript>2</Subscript>NiH<Subscript>1.9</Subscript> and Zr<Subscript>2</Subscript>NiH<Subscript>4.6</Subscript>

In this paper we report the results obtained from inelastic neutron scattering measurements on Zr₂NiH_1.9 and Zr₂NiH_4.6 using triple-axis spectrometer at Dhruva reactor, Trombay. The spectrum up to 35 meV represents largely the lattice modes of Zr and Ni atoms. The vibrational frequencies of hydrogen atoms are expected predominantly at higher energies. The phonon spectra from 35–180 meV were recorded using a Be filter as analyser. In order to analyse the observed neutron spectra, we assume a set of Ein-stein modes due to the hydrogen atoms which are delta functions in energy. These delta functions are broadened by the resolution of the instrument. The vibrational frequencies obtained from the fitting of the observed phonon spectra have been assigned to various tetrahedral sites in both the compounds.     

Effects of PEDOT:PSS and crystal violet interface layers on current-voltage performance of Schottky barrier diodes as a function of temperature and variation of diode capacitance with frequency

In this study, diode applications of Crystal Violet (CV) and PEDOT materials were studied. The Ni/p-Si/Al, Ni/CV/p-Si/Al and Ni/PEDOT:PSS/CV/p-Si/Al diodes were fabricated. The I–V (current-voltage) characteristics of all diodes were analyzed at room temperature, it was determined that the PEDOT:PSS and CV materials improved the basic diode parameters. Also, I–V characteristics of Ni/PEDOT:PSS/CV/p-Si/Al of diode were investigated for different temperature values. It has been determined that the basic diode parameters are strongly dependent on temperature. It was determined that while the barrier height (Φ_b) increased with increasing temperature, the ideality factor (n) and the series resistance (R_s) values decreased. Using temperature-dependent measurements, it was determined that the potential barrier and ideality factor values at the contact interface has a double Gaussian distribution. In addition, C–V (capacitance-voltage) measurements of these diodes were analyzed depending on the frequency. It was found that the diode capacitance decreased with increasing frequency.     

吴茱萸内酯的NMR研究

从吴茱萸Evodia Rutaecarpa (Juss.) Benth.中分离得到并鉴定了化合物吴茱萸内酯, 我们应用二维核磁技术首次对化合物吴茱萸内酯的核磁信号进行了准确归属, 并纠正了文献中部分氢信号归属的错误。     

Special magnetic phenomena in heavily doped La<Subscript>0.7−<Emphasis Type="Italic">x</Emphasis></Subscript>Dy<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> system

The magnetism in heavily Dy doped La_0.7−x Dy _x Sr_0.3MnO₃ (0.40⩽x⩽0.70) system is studied in this paper. The M-T relation seems to be complicated with the increase of x. For sample with x = 0.40, AFM behavior exists at T⩽T _N and M-T curves under zero field cooling (ZFC) and field cooling (FC) exhibit typical behavior of spincluster glass state above T _N. For the sample with x = 0.50, the M-T curve under ZFC exhibits a valley at a low temperature while the M-T curve under FC exhibits the negative magnetization below T _N. For samples with x = 0.60, 0.70, their ZFC M-T curves are similar to that of x = 0.50, but the FC M-T curves do not exhibit negative values any more. All the peculiar phenomena above are well explained by Néel double-lattice model combined with M-H relation at typical temperatures. The molecular field theory fits well the negative magnetization for x = 0.50. Supported by the State Key Project of Fundamental Research of China (Grant No. 2007CB925001), the State Key Development Program for Basic Research of China (Grant No. 001CB610604), the Natural Science Foundation of Anhui Higher Education Institutions of China (Grant Nos. 2006KJ266B and ZD2007003-1), Anhui Key Laboratory of Spin Electron and Nanomaterials (Cultivating Base)     

Site occupancy of Fe in ternary Ni<Subscript>75−</Subscript><Emphasis Type="Italic">x</Emphasis>Fe<Subscript>x+y</Subscript>Al<Subscript>25−</Subscript><Emphasis Type="Italic">y</Emphasis>alloys

The results of a detailed structural and magnetic study clearly indicate that regardless of the thermal history of the samples, Fe has a strong preference for the Ni sites in Ni-poor (nonstoichiometric) Ni₇₅Al₂₅ alloys. Fe substitution has a profound effect on the nature of magnetism in Ni₂₅Al₂₅ Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India.