Analysis of current–voltage and capacitance–voltage characteristics of perylene-monoimide/n-Si Schottky contacts

The electrical and interface state properties of Au/perylene-monoimide (PMI)/n-Si Schottky barrier diode have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements at room temperature. A good rectifying behavior was seen from the I–V characteristics. The series resistance (R_s) values were determined from I–V and C–V characteristics and were found to be 160 Ω and 53 Ω, respectively. The barrier height (Φ_b) of Au/PMI/n-Si Schottky diode was found to be 0.694 eV (I–V) and 0.826 eV (C–V). The ideality factor (n) was obtained to be 4.27 from the forward bias I–V characteristics. The energy distribution of interface state density (N_ss) of the PMI-based structure was determined, and the energy values of N_ss were found in the range from E_c ? 0.508 eV to E_c ? 0.569 eV with the exponential growth from midgap toward the bottom of the conduction band. The values of the N_ss without R_s are 2.11 × 10¹² eV^?1 cm^?2 at E_c ? 0.508 eV and 2.00 × 10¹² eV^?1 cm^?2 at E_c ? 0.569 eV. Based on the above results, it is clear that modification of the interfacial potential barrier for metal/n-Si structures has been achieved using a thin interlayer of the perylene-monomide.     

Stereochemical studies of oligomers XXIX. Reinvestigation of the structure of N-m-tolyl phthalimide

C₁₅H₁₁NO₂, Mr 237.3, monoclinic, space groupC _c, a=8.539(2),b=19.865(4),c=7.599(2)?,β=111.44(2)°,V=1199.8 ?³,Z=4,D _c=1.31 gcm⁻³,λ(CuKα)=1.5418 ?,μ=6.74cm⁻¹,F(000)=496, room temperature. The structure was solved by direct methods with SHELX-86 and refined down to agreement valueR=0.046 for 1117 reflections above 2σ(I). The angle between the plane of the phthalimide group, which shows a little bent [1.2(2)°] between its two rings, and the tolyl group is 56.1(1)°. The packing of the molecules is stabilized by van der Waal’s forces only. Part XXVIII: Bocelli and Rizzoli (1990)     

Effect of annealing on the electronic parameters of Au/poly(ethylmethacrylate)/n-InP Schottky diode with organic interlayer

A thin poly(ethylmethacrylate) (PEMA) layer is deposited on n-InP as an interlayer for electronic modification of Au/n-InP Schottky structure. The electrical properties of Au/PEMA/n-InP Schottky diode have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements at different annealing temperatures. Experimental results show that Au/PEMA/n-InP structure exhibit a good rectifying behavior. An effective barrier height as high as 0.83 eV (I–V) and 1.09 eV (C–V) is achieved for the Au/PEMA/n-InP Schottky structure after annealing at 150 °C compared to the as-deposited and annealed at 100 and 200 °C. Modified Norde's functions and Cheung method are also employed to calculate the barrier height, series resistance and ideality factors. Results show that the barrier height increases upon annealing at 150 °C and then slightly decreases after annealing at 200 °C. The PEMA layer increases the effective barrier height of the structure as this layer creates a physical barrier between the Au metal and the n-InP. Terman's method is used to determine the interface state density and it is found to be 5.141 × 10¹² and 4.660 × 10¹² cm^?2 eV^?1 for the as-deposited and 200 °C annealed Au/PEMA/n-InP Schottky diodes. Finally, it is observed that the Schottky diode parameters change with increasing annealing temperature.     

Field dependence of a.c. Electroluminescence in ZnS: Mn,Cu, Cl film panels

Electroluminescent (EL) film panels of ZnS: Mn, Cu, Cl operated by a.c. electric field are studied at room temperature. The emission spectrum consists of a single peak at 590 nm. The EL emittance B varies with frequency f of the applied a.c. electric field as B = B_s ? B_m exp ? f/f_c where B_s, B_m and f_c are constants. This equation indicates that B approaches a saturation value B_s when f?f_c and a linear relation between B and f when f?f_c. At a fixed frequency f, B is found to depend on the applied voltage V as B = A exp [-G/F + V^{$\text{1}\text{2}$})] where A, G and F are constants. This formula is valid at all stages of the operating life of the film panel.     

An influence of deposition temperature on structural,optical and electrical properties of sprayed ZnO thin films of identical thickness

Nanocrystalline ZnO thin films were deposited at different temperatures (T_s = 325 °C–500 °C) by intermittent spray pyrolysis technique. The thickness (300 ± 10 nm) independent effect of T_s on physical properties was explored. X-Ray diffraction analysis revealed the growth of wurtzite type polycrystalline ZnO films with dominant c-axis orientation along [002] direction. The crystallite size increased (31 nm–60 nm) and optical band-gap energy decreased (3.272 eV–3.242 eV) due to rise in T_s. Scanning electron microscopic analysis of films deposited at 450 °C confirmed uniform growth of vertically aligned ZnO nanorods. The films deposited at higher T_s demonstrated increased hydrophobic behavior. These films exhibited high transmittance (>91%), low dark resistivity (～10^?2 Ω-cm), superior figure of merit (～10^?3 Ω^?1) and low sheet resistance (～10² Ω/□). The charge carrier concentration (η -/cm³) and mobility (μ – cm²V^?1s^?1) are primarily governed by crystallinity, grain boundary passivation and oxygen desorption effects.     

Specific resistivity of dislocations and vacancies for super-pure aluminium at 4.2 K determined in-situ and post-recovery deformation and correlated to flow stress

ABSTRACT

The evolution of dislocations during shape-change of metal forms results from microstructural shear mechanism that is essential to enhance ductility. However, at room temperatures for face-centred cubic metals, this evolution results in the generation of vacancies that tend to form nano-voids, the growth of which leads to ductile failure. The correlated occurrence of dislocations and vacancies may be differentiated using the change of resistivity with plastic strain at 4.2?K, because resistivity is very sensitive to single vacancies compared to the formation of stacking faulted defects and dislocations. In order to assess the microstructure, the specific resistivity of these defect species was measured at 4.2?K, whereby thermal recovery processes are non-existent. The resistivity per dislocation line-length per volume was determined to be 1.87?×?10^?25?Ωm³ for super-pure aluminium. The change in resistivity directly correlated to the shear flow stress squared. Vacancy-like defects formed during plastic flow were correlated to the recoverable resistivity after 298?K anneal and the derived volume fraction (C_V) from mechanical data. The magnitude could be expressed as 12.9?×?10^?9?Ωm per C_V in % or as 1.21?×?10^?25?Ωm³ in terms of line-length of vacancies per volume. The choice of representation depends on the presumed vacancy distribution. However, the recoverable flow stress upon 298?K anneal only appear to be proportional to √ C_V at low strains; that is, at high strains the generated vacancies had transformed to defects that give rise to a small decrease in resistivity but a more notable increase in the flow stress. The possible mechanisms for this transformation are discussed.     

Investigation of piezoelectric properties of crystals using surface excitation of ultrasonic waves and some results for ferroelectric triglycine sulphate

The surface excitation of ultrasonic waves as a new method of investigation of piezoelectric properties of materials is suggested and experimental results specified to theZ-direction of a single crystal of triglycine sulphate (TGS) are reported. It has been found that the piezoelectric stress constant e₂₃ of TGS depends on temperatureθ as:e ₂₃=K ₂₃(θ_c?θ)^?1 whereK ₂₃=(31±0.5) As m^?2 deg andθ _c=49.6°C. The influence of an externally applied d.c. electric field has been studied in order to account for a residual excitation of ultrasonic waves in TGS at temperatures above the Curie point.     

A new molecular C60 complex with bis(methylenedithio)tetrathiafulvalene (BMDT-TTF): Synthesis, crystal structure, and properties

A new molecular C₆₀ complex of the composition (BMDT-TTF) · C₆₀ · 2CS₂ (I) with the bis(methylenedithio)tetrathiafulvalene (BMDT-TTF) organic donor is synthesized. The molecular and crystal structures of this complex are determined by x-ray diffraction. The (BMDT-TTF) · C₆₀ · 2CS₂ (I) compound crystallizes in a monoclinic crystal system. The main crystal data are as follows: a=13.550(5) Å, b=9.964(7) Å, c=17.125(8) Å, β=99.52(4)°, V=2280(2) ų, M=1229.45, and space group P2₁/m. Crystals of I have a layered structure: layers consisting of C₆₀ molecules alternate with layers composed of BMDT-TTF and CS₂ molecules. It is found that, in complex I, the donor and C₆₀ molecules are linked through the shortest contacts, which leads to a change in the molecular geometry of BMDT-TTF. The donor molecules in a crystal layer are characterized by the shortest S...S contacts. The IR data indicate the electroneutrality of the fullerene molecule. The electrical conductivity of (BMDT-TTF) · C₆₀ · 2CS₂ single crystals is measured using the four-point probe method at room temperature: σ_RT=2×10^?5 Ω^?1 cm^?1.     

Structure and d.c. conductivity of amorphous Si1−xSnx alloys

Amorphous Si_1?xSn_x alloys have been prepared by vapor deposition at a pressure of about 10^?8 Torr on substrates maintained at 77 K. Density measurements and electron diffraction show that Sn atoms are substituted for Si in a random continuous network. The d.c. resistivity of samples of stabilized structure is correctly described by the variable range hopping formula. Structural changes are revealed by the variation of the resistivity at 77 K of samples annealed from 77 K to the crystallization temperature.     

Electrical transport measurements in a quasi-onedimensional semiconductor ZrS3

We have used the technique of chemical vapour transport to prepare needle shaped single crystal of ZrS₃. Results of the measurements of d.c. resistivity. Hall coefficient and thermoelectric power of the temperature range 100–500 K are reported. All the samples exhibited semiconducting behaviour with a room temperature resistivity of about 15 Ω-cm and an activation energy of 0.20±0.02 eV. Room temperature thermoelectric power is -850 μVK^?1 and the dominant carriers are electrons. The thermoelectric power varies as (1/T), a behaviour associated with a typical semiconductor. Mobility at low temperatures is limited by ionized impurity scattering and is given by μ₁ = 6.5 × 10^?2T^3/2 cm²V^7-1 sec^?1. At high temperatures, phonon scattering is dominant and the mobility is given by μ₂ = 1.35 × 10⁺⁵T^?32 cm²V^?1 sec^?1.     

Properties of single vacancies and of divacancies in copper

The electrical resistivity change at high temperatures due to vacancies was determined as a function of temperature. From the data E^F_1V=1.00 eV, E^B_2V=0.45 eV and about C^tot_V=4 × 10^-4 at the melting point results.     

Polymorphic phase transition and thermal stability in squaric acid (H2C4O4)

Phase transformations in squaric acid (H₂C₄O₄) have been investigated by thermogravimetry and differential scanning calorimetry with different heating rates β. The mass loss in TG apparently begins at onset temperatures T_di=245±5 °C (β=5 °C min^?1), 262±5 °C (β=10 °C min^?1), and 275±5 °C (β=20 °C min^?1). A polymorphic phase transition was recognized as a weak endothermic peak in DSC around 101 °C (T_c⁺). Further heating with β=10 °C min^?1 in DSC revealed deviation of the baseline around 310 °C (T_i), and a large unusual exothermic peak around 355 °C (T_p), which are interpreted as an onset and a peak temperature of thermal decomposition, respectively. The activation energy of the thermal decomposition was obtained by employing relevant models. Thermal decomposition was recognized as a carbonization process, resulting in amorphous carbon.     

Pressure dependence of superconductivity in the pseudo-one-dimensional compound Tl2Mo6Se6

Measurements of the temperature and pressure dependences of the resistivity of the pseudo-one-dimensional ternary compound Tl₂Mo₆Se₆ are presented. We find that the conductivity parallel to the highly conducting c-axis is enhanced by pressure and the superconducting transition temperature T_c is suppressed by pressure at a rate $\text{?T}{}_{\mathrm{c}}\text{?P}\text{=?7.6×10}{}^{\mathrm{?5}}$ kbar^?1. These results are discussed in relation to the current models of transport in one-dimensional conductors.     

Phase transitions in N—n-propylpyridinium-TCNQ2 and N—n-butylpyridinium-TCNQn at high pressures

The electrical resistivity of N-n-propylpyridinium-TCNQ₂ (NPPy-TCNQ₂) and N-n-butylpyridinium-TCNQ_n (NBPy-TCNQ_n) has been measured as a function of temperature and pressure. Phase transitions in these salts have been studied at high pressures. The transition temperature (T_c) in NPPy-TCNQ₂ at atmospheric pressure increased with increasing pressure at the rate of dT_c/dP = + 12.0 degkbar^?1. The value of volume change calculated from the Clapeylon-Clausius relation was + 4.4 cm³ mol^?1. The electrical resistivity along the a- and c-axis increased with increasing pressure below 7 kbar. This anomalous electrical behaviour is closely related to the crystal structure of NPPy-TCNQ₂. The resistivity dropped sharply at about 11 kbar. This abrupt change may be due to a new pressure induced phase transition.The T_c of the NBPy-TCNQ_n increased remarkably with increasing pressure up to 0.7 kbar, above which the phase transition disappeared. The phase transitions of N-n-alkyl-substituted pyridinium TCNQ salts depend strongly on the nature of cations.     

Superconductivity in the graphite-potassium intercalation compound C8K

Superconducting properties of pseudo-single crystals of C₈K were investigated by low frequency a.c. magnetic susceptibility and electrical resistivity measurements. The measured values of T_c were between 128 and 198 mK for 13 samples. Measurements of the superconducting transition in a magnetic field revealed a remarkable anisotropy, such that if θ is defined as the angle between the applied magnetic field and the layer plane, type II superconductivity was observed for 0° ≦ ∣ θ ∣ ? 25° and type I superconductivity for 25° ? ∣ θ ∣≦ 90°. The angular dependences of H_c2 and H_c3 were fairly well-explained by the effective mass model.     

Br NQR relaxation of the mixed-valence compound (NH4)4SbIIISbVBr12

⁸¹Br NQR measurements of the mixed-valence compound (NH₄)₄Sb^III Sb^VBr₁₂, which has Sb^VBr₆ ^? and Sb^IIIBr₆ ^3? octahedra in different oxidation states in the tetragonal pseudo-K₂PtCl₆ structure, were carried out by pulse method in the temperature range between 80 and 300 K. The phase transition temperature of T _c = 212 K was redetermined. The T ₁ values are quite different between Sb^VBr₆ ^? and Sb^IIIBr₆ ^3? octahedra. For all resonance lines T ₁ minima were observed at T _c. The T ₁ behavior at T _c was explained by a softening of the rotary lattice mode around a principal axis of each octahedron along the c axis of the crystal. The distinctive feature in the temperature dependence of both ⁸¹Br NQR frequencies and T ₁ values for each anion indicates that the static rotation may occur for Sb^VBr₆ ^? but not for Sb^IIIBr₆ ^3? at T _c in the low temperature phase.     

Electrical measurements of the electron irradiation induced E- and H-traps in GaAs under hydrostatic pressure

The change of resistivity of the 2.3 MeV-electron-irradiated bulk n- and p-GaAs have been measured at hydrostatic pressure up to 5 kbar at RT. Corrections for the changes in free electron and hole mobilities with pressure have been neglected. The resistivity changes are explained by a dependence on pressure of the ionisation energy of the radiation-induced E- and H-traps. The results indicate that most from these radiation- induced levels moves away from the conduction-band edge (γ_c-point) at a rate approximately (0.8?1.0)γ_G, here γ_G=11.6×10^?6 eV bar^?1 is the energy gap pressure coefficient for GaAs at RT. The high changes in ionization energies of E2 to E5-traps upon pressure are to be compared with the lower changes in ionization energies found for the deep-lying impurity levels. In accordance with the theoretical investigation it was suggested that most of the investigated radiation-induced levels in GaAs are t₂-states of Ga- and As-vacancies.     

TSC study of electric dipole relaxations in chlorapatite

Electric dipole relaxations in chlorapatite, Ca₅(PO₄)₃Cl, have been studied with the fractional polarization mode of the thermally stimulated currents (TSC) method. Fifty-one of the fifty-seven sets of data obtained in the range 10–443°K fell naturally into four groups yielding compensation temperatures T_C of T_C1, = 202°C, T_C2: = 202°C, T_C3 = 420°C and T_C4= 644°C, with estimated error < 10°C, and characteristic relaxation times τ_C of τ_C1 = 1.3 × 10^?7s, τ_C2 = 3.2 × 10^?6s, τ_C3 = 8.8 × 10^?5s and τ_C4 = 2.3 × 10^?4s. Atomic-scale physical models involving Cl^? ion motion are offered for the 202°C compensation at the temperature of the reported monoclinic-to-hexagonal phase transition and for the 420°C compensation, at which temperature the Cl^? ions individually are thought to have enough thermal energy to maintain the hexagonal form dynamically.     

Syntheses and structure characterization of inorganic/organic coordination polymers: Ag(dpa), Co(O3PH)(4,4′-bpy)(H2O), Zn(O3PH)(4,4′-bpy)0.5 and Mn[O2PH(C6H5)]2(4,4′-bpy) (dpa=2,2′-dipyridylamine; 4,4′-bpy=4,4′-bipyridine)

Four novel coordination polymers: Ag(dpa) I, Co(O₃PH)(4,4′-bpy)(H₂O) II, Zn(O₃PH)(4,4′-bpy)_0.5 III and Mn[O₂PH(C₆H₅)]₂(4,4′-bpy) IV (dpa=2,2′-dipyridylamine; 4,4′-bpy=4,4′-bipyridine), were synthesized by microwave heating and characterized by X-ray crystallography. I crystallizes in monoclinic space group P21/n with a=11.576(2) Å, b=5.585(2) Å, c=15.243(4) Å, β=109.00(2)°, V=931.8(3) ų. II crystallizes in monoclinic Cc space group with a=22.477(7) Å, b=5.280(1) Å, c=10.404(4) Å, β=96.08(3)°, V=1227.8(7) ų. III crystallizes in monoclinic P21/c space group with a=9.758(2) Å, b=7.449(3) Å, c=10.277(2) Å, β=100.02(2)°, V=735.6(4) ų. IV crystallizes in monoclinic space group P2/c with a=10.174(1) Å, b=11.817(3) Å, c=18.784(4) Å, β=102.14(1)°, V=2207.8(8) ų. I consists of linear metal–metal chains wrapped by dpa ligands. II and III consist of two-dimensional M^II(O₃PH) inorganic sheets cross-linked by 4,4′-bpy ligands, while IV is formed by Mn[O₂PH(C₆H₅)]₂ sheets cross-linked by 4,4′-bpy ligands. I exhibits two-step thermal decomposition at ~200 and ~250°C, resulting in the reduction of Ag⁺ to Ag metal. II loses its coordination water at ~100°C, leaving vacant coordination sites at Co²⁺ ions, while the original framework remains intact. The removal of 4,4′-bpy in II–IV occurs at elevated temperatures above 250, 200 and 400°C respectively.     

Capacity fading reason of LiNi0.5Mn1.5O4 with commercial electrolyte

The cycling performances of LiNi_0.5Mn_1.5O₄ (LNMO) were investigated and the reasons of capacity fading were discussed. The results show that LNMO can deliver about 115 mAh?g^?1 at 1C at different temperatures; however, it retains only 61.57 % of its initial capacity after 130th cycles at 60 °C, which is much lower than 94.46 % of LNMO at 25 °C, and the cycling performance at 1C is better than that at 0.5C. The reason of capacity fading of LNMO at 60 °C is mainly due to the lower decomposition voltage of 4.3 V with commercial electrolyte and the larger decomposition current, of which the electrolyte decomposes and interacts with active materials to lead to the larger irreversible capacity loss. While the worse cycling performance at low rate is attributed to the longer interaction time between the electrolyte with the decomposition voltage of 4.5 V and the active materials.