The calculation of electronic parameters of an Ag/chitin/n-Si Schottky barrier diode

We have formed polymeric organic compound chitin film on n-Si substrate by adding a solution of polymeric compound chitin in N,N-dimethylacetamide and lithium chloride on top of an n-Si substrate and then evaporating solvent. It has been seen that the chitin/n-Si contact has demonstrated clearly rectifying behavior and the reverse curves exhibit a weak bias voltage dependence by the current–voltage (I–V) curves studied at room temperature. The barrier height and ideality factor values of 0.959 eV and 1.553, respectively, for this structure have been obtained from the forward bias I–V characteristics. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitin/n-Si substrate in the energy range from (E_c − 0.897) to (E_c − 0.574) eV have been determined from the I–V characteristics. The interface state density, N_ss, ranges from 5.965 × 10¹² cm⁻² eV⁻¹ in (E_c − 0.897) eV to 1.706 × 10¹³ cm⁻² eV⁻¹ in (E_c − 0.574) eV and has an exponential rise with bias this energy range.     

The effect of a novel organic compound chiral macrocyclic tetraamide-I interfacial layer on the calculation of electrical characteristics of an Al/tetraamide-I/p-Si contact

The Al/tetraamide-I/p-Si Schottky barrier diode (SBD) has been prepared by adding a solution of a novel nonpolymeric organic compound chiral macrocylic tetraamide-I in chloroform on top of a p-Si substrate and then evaporating the solvent. It has been seen that the forward-bias current–voltage (I–V) characteristics of Al/tetraamide-I/p-Si SBD with a barrier height value of 0.75 eV and an ideality factor value of 1.77 showed rectifying behaviour. The energy distribution of the interface state density determined from I–V characteristics increases exponentially with bias from 5.81 × 10¹² cm⁻² eV⁻¹ at (0.59-E_v) eV to 1.02 × 10¹³ cm⁻² eV⁻¹ at (0.40-E_v) eV. It has showed that space charge limited current (SCLC) and trap charge limited current (TCLC) are the dominant transport mechanisms at large forward-bias voltages.     

Modification of electrical properties of the Au/1,1′ dimethyl ferrocenecarboxylate/n-Si Schottky diode

The electrical and interface state density properties of the Au/1,1′ dimethyl ferrocenecarboxylate (DMFC)/n-Si structure have been investigated by current–voltage, capacitance–voltage and conductance–frequency methods. The Au/DMFC/n-Si structure exhibits a rectifying behavior with a non-ideal I–V behavior with an ideality factor greater than unity. The ideality factor and barrier height of the Au/DMFC/n-Si Schottky diode is lower than that of Au/n-Si Schottky diode. The interface state density of the diode was determined from G/ω–f plots and was of order of 5.61 × 10¹² eV^?1 cm^?2. It is evaluated that the electrical properties of Au/n-Si diode is controlled using 1′ dimethyl ferrocenecarboxylate organic layer and in turn, Au/DMFC/n-Si structure gives new electronic parameters.     

Controlling of silicon–insulator–metal junction by organic semiconductor polymer thin film

Electrical and photovoltaic properties of a metal–semiconductor–insulator–polymer–metal diode were investigated. The n-Si/SiO₂/MEH-PPV/Al diode shows a rectifying behavior with the rectification ratio of 2.22 × 10⁵ at ±5 V and exhibits a non-ideal behavior due to the series resistance and oxide-organic layers. The organic semiconductor makes a contribution to the I–V characteristics of the diode and the trap-charge limited space charge and space charge limited current mechanisms were observed for the diode. The current–voltage characteristics of the n-Si/SiO₂/MEH-PPV/Al diode under different illumination intensities give an open circuit voltage (V_oc) along with a short circuit current (I_sc). This suggests that the n-Si/SiO₂/MEH-PPV/Al diode is a photovoltaic device with V_oc = 0.456 V and J_sc = 7.89 × 10^?8 A/cm² values under 100 mW/cm² illumination intensity. The photoconductivity mechanism of the diode is controlled by monomolecular recombination. The interface state density D_it values with time constant τ_it of the diode under dark and illumination conditions were found to be 2.53 × 10¹⁰ eV^?1 cm^?2 with 5.09 × 10^?5 s and 2.50 × 10¹⁰ eV^?1 cm^?2 with 8.27 × 10^?5 s, respectively. The obtained results indicate that the n-Si/SiO₂/MEH-PPV/Al diode is a photo-sensitive diode.     

Improved mobility of the copper phthalocyanine thin-film transistor

Copper phthalocyanine (CuPc) organic thin-film transistor (OTFT) was fabricated by thermal evaporation deposition on p-SiO₂ dielectric layer. Organic thin-film transistors used in large display areas need the enhancement of transistor performances by increasing the I_on/I_off ratio and the mobility. The output and transfer characteristics of CuPc-OTFT having source/drain interdigitated-finger geometry were investigated. The mobility, I_on/I_off ratio and inverse sub-threshold slope for the CuPc-OTFT were found to be 5.32 × 10^?3 cm² V^?1 s^?1, 1.94 × 10⁴ and 2.5 V/decade, respectively. The interface state density of the transistor was found to be 3.73 × 10¹¹ eV^?1 cm^?2 using the conductance-frequency method. The CuPc film indicated a homogeneous surface having 3.878 nm small roughness values as observed by atomic force microscope (AFM) measurements. The obtained results indicate that we have improved a CuPc-OTFT transistor with high mobility without being of any substrate treatment.     

Photo and gas sensitivity of thin Cu-phthalocyanine films studied by spectroscopy of unoccupied electron states

Thin films of Cu-phthalocyanine were thermally deposited in UHV on pyrolytic graphite, n-Si(1 0 0), SiO₂/n-Si, and SiO₂/p-Si substrates. Atomic composition of the films was tested by Auger electron spectroscopy. Evolution of surface potential and density of electron states located 0–25 eV above vacuum level were monitored during the film deposition by means of total current electron spectroscopy (TCS). The resulting spectra of the 2–3 nm thick CuPc films on the different substrates were however identical. Admission of 10⁻⁵ Pa O₂ and NO₂ resulted in a reversible decrease and increase of the film surface potential, respectively. A new peak in the TCS appeared and the spectrum was attenuated on the admission of the gases. These changes were attributed to the interaction between the film and the gas molecules adsorbed. The changes were reversible on the gas evacuation. White light illumination reduced (increased) surface potential of the Cu-phthalocyanine film on SiO₂/n-Si (SiO₂/p-Si) substrate. The gas sensitivity is attributed to the processes at the gas/CuPc film interface, while the photovoltaic properties are attributed to the processes at the CuPc film/substrate interface.     

Extraction of electronic parameters of organic diode fabricated with NIR absorbing functional manganase phthalocyanine organic semiconductor

The semiconducting and metal/organic semiconductor properties of the newly synthesized NIR absorbing α-substituted manganase phthalocyanine bearing functional 2,3-dihydroxypropylthio moieties {M[Pc(S–CH₃CH₂(OH)CH₂(OH))]₄X}(M = Mn^III) have been investigated by electrical conductivity–temperature, optical absorption and current–voltage characteristics methods. The electrical conductivity increases with the temperature, suggesting that the peripheral α-substituted-functional manganase phthalocyanine is an organic semiconductor. The optical band gap and trap energy values were determined and were found to be 2.98 eV and 1.95 eV, respectively. The ITO/MnPc/Al diode shows a rectifying behavior due to the formation of MnPc/Al interface with a rectification ratio of 29.4 at ±2 V. The series resistance R_s and ideality factor n values were found to be 102.6 kΩ and 8.89, respectively. The interface state density for the diode was of order of 2.73 × 10¹¹ eV^?1 cm^?2 with the interface time constant of 1.93 × 10^?5.It is evaluated that newly synthesized α-substituted manganase phthalocyanine bearing functional 2,3-dihydroxypropylthio moieties is an organic semiconductor and can be used in electronic device applications as an organic diode.     

Electrosynthesis of polyaniline films on titanium by pulse potentiostatic method

Polyaniline (PANI) was synthesized on titanium electrode from aqueous solution containing 0.3 mol L⁻¹ aniline and 1 mol L⁻¹ HNO₃ by pulse potentiostatic method. The chronoamperogram during polymerization process of aniline was recorded. The effects of the synthesis parameters, such as anodic pulse duration (t_a), cathodic pulse duration (t_c), lower limit potential (E_c) and upper limit potential (E_a), on the morphology and electroactivity of the PANI films were investigated by scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM results present that flake, mica-like, quasi-fibrous and nano-fibrous PANI film could be synthesized with various polymerization parameters. Under the following conditions, t_a = 0.8 s, t_c = 0.1 s, E_c = 0 V and E_a = 1.0 V, high quality nano-fibrous PANI film with the best electroactivity was obtained. The CV results show that the PANI films with different morphologies, which were prepared under the same anodic polymerization charge, have obvious different characteristics. This means that the PANI films with different morphologies have different electrochemical activity.     

Laser doping of chromium as a double acceptor in silicon carbide with reduced crystalline damage and nearly all dopants in activated state

Chromium, a p-type dopant, has been incorporated into silicon carbide by laser doping. Secondary ion mass spectrometric data revealed enhanced solid solubility (2.29 × 10¹⁹ cm⁻³ in 6H–SiC and 1.42 × 19¹⁹ cm⁻³ in 4H–SiC), exceeding the equilibrium limit (3 × 10¹⁷ cm⁻³ in 6H–SiC above 2500 °C). The roughness, surface chemistry and crystalline integrity of the doped sample were examined by optical interferometry, energy dispersive X-ray spectrometry and transmission electron microscopy, respectively, and showed no crystalline disorder due to laser heating. Deep-level transient spectroscopy confirmed Cr as a deep-level acceptor with activation energies E_v + 0.80 eV in 4H–SiC and E_v + 0.45 eV in 6H–SiC. The Hall effect measurements showed that the hole concentration (1.942 × 10¹⁹ cm⁻³) is almost twice the average Cr concentration (1 × 10¹⁹ cm⁻³), confirming that almost all of the Cr atoms were completely activated to the double acceptor state by the laser-doping process without requiring any additional annealing step.     

Thermal expansion of the W5Si3 and T2 phases of the W–Si–B system investigated by high-temperature X-ray diffraction

The coefficients of thermal expansion (CTE) of the W₅Si₃ and T₂ phases of the W–Si–B system were determined using high-temperature X-ray diffraction in the 298–1273 K temperature interval. Alloys with nominal compositions 62.5W37.5Si (at%) and 58W21Si21B (at%) were prepared from high-purity materials through arc melting followed by heat treatment at 2073 K for 12 h under argon atmosphere. The highly different thermal expansion coefficients of W₅Si₃ along the a (5.0 × 10⁻⁶ K⁻¹) and c (16.3 × 10⁻⁶ K⁻¹) axes lead to a high thermal expansion anisotropy (α_c/α_a ≅ 3.3). On the other hand, the T₂-phase exhibits similar thermal expansion coefficients along the a (6.9 × 10⁻⁶ K⁻¹) and c (7.6 × 10⁻⁶ K⁻¹) axes, indicating a behavior close to isotropic (α_c/α_a ≅ 1.1).     

Electronic structure evolution of neutral and dicationic states of conjugated polymers with their band gap

The electronic structures of neutral and dicationic states of 8 conjugated oligomers were studied at UB3LYP/6-31G* level as models of conjugated polymers with different band gaps (E_g). The evolution of the electronic structure for polymers with experimental E_g ranging from 3.0 to 0.0 eV has been investigated for both neutral and dicationic species. For polymers with E_g > 1.1 eV the ground state of neutral oligomers was found to be a closed shell singlet (S0) while the dicationic state was a polaron pair open shell singlet (OSS) state. For polymers with lower E_g, OSS becomes the ground state for both dicationic and neutral states. The energy difference between OSS and S0 state increases with closure of E_g for neutral oligomers. However, in dications the S0–OSS energy difference becomes less than 1 kcal/mol for the low band gap polymers. Both, the charge distribution and the bond length alternation pattern suggest that bipolaronic state and not polaron pair state dominates in dications of the low band gap polymers (E_g < 1.1 eV).     

Photovoltaic properties of poly(terthiophene) doped with light-harvesting dyes and photocurrent generation mechanism

A range of commercially available anionic dyes were successfully incorporated as dopants during the electrodeposition of poly(terthiophene) (P(TTh)). Photovoltaic testing revealed that the best photoelectrochemical cell (PEC) was based on P(TTh) doped with Sulforhodamine B, which showed short-circuit-current (I_sc) = 178 μA cm⁻², open-circuit-voltage (V_oc) = 318 mV, fill-factor (FF) = 29.6% and power-conversion-efficiency (PCE) = 0.0334% under white light illumination intensity of 500 W m⁻². Photocurrent action spectroscopy of the PECs based on dye-doped P(TTh)s prepared here, and of the PECs prepared in a previous study, showed that only a cationic dye directly contributed to photocurrent, while anionic dyes did not. It is proposed that these observations are due to attractive or repulsive electrostatic interactions between dyes and the electron acceptor I₃⁻ at the polymer/electrolyte interface.     

Effect of hydrogen on internal friction and elastic modulus in titanium alloys

The effect of hydrogen on the variation with temperature of internal friction (Q^?I) and elastic modulus (E) of a number of Ti-based alloys has been studied in the Hz and kHz frequency ranges. A relaxation peak of internal friction with a high degree of relaxation (Q^?I_max ～ 10^?1) and with a ΔE effect is observed in all hydrogen-doped samples at T ～ 600 K at ～1 kHz, and at T ～ 500 K at ～1 Hz. Such a peak is not present in samples without hydrogen. The activation energy W and the frequency factor v₀ of the observed relaxation are determined to be W ～ 1.55 eV, v₀ ～ 10¹⁷ s^?1. It is shown that the observed effects are connected with the mechanism of grain boundary relaxation, as the introduction of hydrogen into titanium alloys leads to the formation of fine-grained structures.     

Photovoltaic devices based on polythiophenes and substituted polythiophenes

In recent years there has been considerable interest in the fabrication of photovoltaic devices using polymeric and organic materials. This paper presents work carried out using a range of polythiophenes, including some substituted with porphyrin moieties as light harvesters. Homopolymers and copolymers were investigated for their performance in photovoltaic devices, and the use of both solid polymer electrolyte and liquid electrolyte was examined. Both photoelectrochemical cells and Schottky devices were investigated. The best photoelectrochemical cell was fabricated using polyterthiophene which had V_oc=139 mV, I_sc=123.4 μA cm⁻², fill factor=0.38, and energy conversion efficiency=0.02% at a halogen lamp intensity of 317 W m⁻². The Schottky device gave a V_oc=0.5 V and I_sc of 0.98 μA cm⁻² at a halogen lamp intensity of 500 W m⁻².     

Grain size effects on contact resistance of top-contact pentacene TFTs

Multiple top-contact OTFTs with various channel lengths (L_c) were successfully scaled-down to the L_c of 1.8 μm by using the membrane shadow mask and the interface between the evaporated Au and pentacene was analyzed based on the channel resistance method. For large grain pentacene (S-80) deposited at 80 °C, the parasitic resistance (R_p) at V_GS = −20 V has 1.8 ± 0.2 kΩ cm, whereas for small grain pentacene (S-20) deposited at 20 °C has 4.2 ± 0.2 kΩ cm, which means that R_p depends on the grain size of pentacene. The grain size and grain boundary trap density for pentacene can be possibly origins to determine R_p, which is critically correlated with bulk transport in pentacene. The grain boundary trap density (N_t) for S-80 and S-20 was extracted as (5.6 ± 0.5) × 10¹¹ and (1.2 ± 0.3) × 10¹² cm⁻² from the Levinson plots, respectively. In addition, activation energy of R_p for S-80 is in the range from 42 to 48 meV, whereas for S-20 is from 72 to 108 meV.     

Low-temperature specific heat of the superconductor Mo3Sb7

The low-temperature specific heat of a superconductor Mo₃Sb₇ with T_c = 2.2 ± 0.05 K has been measured in magnetic fields up to 5 T. In the normal state, the electronic specific heat coefficient γ_n, and the Debye temperature Θ_D are found to be 34.5(2) mJ mol⁻¹ K⁻² and 283(5) K, respectively. The enhanced γ_n value is interpreted as due to a narrow Mo-4d band pinned at the Fermi level. The electronic specific heat in the superconducting state can be analyzed in terms a phenomenological two BCS-like gap model with the gap widths 2Δ₁/k_BT_c = 4.0 and 2Δ₂/k_BT_c = 2.5, and relative weights of the molar electronic heat coefficients γ₁/γ_n = 0.7 and γ₂/γ_n = 0.3. Some characteristic thermodynamic parameters for the studied superconductor, like the specific heat jump at T_c, ΔC(T_c)/γ_nT_c, the electron–phonon coupling constant, λ_e−ph, the upper H_c2 and thermodynamic critical H_c0 fields, the penetration depth λ, coherence length ξ and the Ginzburg–Landau parameter κ are evaluated. The estimated values of parameters such as 2Δ₀/k_BT_c, ΔC(T_c)/γ_nT_c, N(E_F) and λ_e−ph suggest that Mo₃Sb₇ belongs to an intermediate-coupling regime. The electronic band structure calculations indicate that the density of states near the Fermi level is formed mainly by the Mo-4d orbitals and that there is no overlap between the Mo-4d and Sb-sp orbitals.     

Synthesis,crystal structure and electrical conductivity of [bmim][Ni(dmit)2]3 (bmim = 1-butyl-3-methylimidazolium,dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

A new complex [bmim][Ni(dmit)₂]₃ has been prepared, and its crystal structure and electrical conductivity where determined and measured. Crystallographic parameters for C₂₆H₁₅N₂S₃₀Ni₃: triclinic system; space group: P-1; a=12.760(3), b=19.441(4), c=11.670(2) Å; α=102.00(3), β=117.10(3), γ=95.06(3)°; Z=2, R=0.0579 (I>2σ(I)). The conductivity of this salt at room temperature is 1.7×10⁻² S cm⁻¹ and it shows semiconduction in the temperature range of 110–290 K.     

Controlling of electrical characteristics of Al/p-Si Schottky diode by tris(8-hydroxyquinolinato) aluminum organic film

We study how tris(8-hydroxyquinolinato) aluminum organic semiconductor layer at p-silicon/Al interface can affect electrical transport across this interface. Al/Alq3/p-Si device shows a good rectifying behavior with an ideality factor value of 1.95. The barrier height values obtained from I–V and Norde method were found to be 0.84 and 0.82 eV, respectively. This indicates that the barrier height obtained from Norde method is lower than that of barrier height value obtained from I–V due to the series resistance effect. The modification of the interfacial potential barrier for Al/p-Si diode was achieved using an interlayer of the Alq3 organic semiconductor and this is ascribed to the fact that the Alq3 interlayer increases the effective barrier height, because of the interface dipole induced by passivation of the organic layer. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance and interface state density values. The series resistance of the diode was changed from 9 kΩ to 1 kΩ with increasing frequency. The distribution profile of R_s–V gives a peak at low frequencies in the depletion region and disappears with increasing frequency.     

A transmission electron microscopy study of the A-site disordered perovskite Na0.5Bi0.5TiO3

A transmission electron microscopy study of Na_0.5Bi_0.5TiO₃ (NBT) crystals shows two types of ferroelectric domains characterized by interface boundaries lying in the {1 1 0}_C and {1 0 0}_C planes. A one-dimensional {1 0 0}_C modulated texture is also observed locally. The electron diffraction study reveals the presence of (0 0 1)_T tetragonal platelets a few cells thick within the R3c matrix. They develop within the three basal {1 0 0}_C planes of the prototype phase and represent relics of the high-temperature tetragonal phase. The loss of symmetry compared to the average structure of NBT can thus clearly be attributed to the existence of these tetragonal platelets. The {1 0 0}_C modulated texture corresponds to a modulation of strain induced by the coexistence of two types of octahedra tilting systems: a⁻a⁻a⁻ for the rhombohedral matrix and a⁰a⁰c⁺ for the tetragonal platelets. These (0 0 1)_T platelets indirectly intervene in the relaxation process classically encountered at about 230 °C, in marked contrast to the behaviour of Pb(Mg_1/3Nb_2/3)O₃.     

Mg–Ni–Gd–Ag bulk metallic glass with improved glass-forming ability and mechanical properties

The improvement of glass-forming ability (GFA) and mechanical properties by using Ag to substitute Mg in the Mg–Ni–Gd bulk metallic glass (BMG) were studied. The Mg₆₉Ni₁₅Gd₁₀Ag₆ bulk metallic glass (BMG) could be cast into glassy rod up to 7 mm. The activation energies of Mg₆₉Ni₁₅Gd₁₀Ag₆ metallic glass were calculated by the Kissinger’s method to be E_g = 2.24 eV, E_x = 1.65 eV, E_p1 = 1.36 eV, E_p2 = 1.59 eV, E_p3 = 1.26 eV and E_p4 = 1.99 eV. The compressive fracture strength and the plastic strain of Mg₆₉Ni₁₅Gd₁₀Ag₆ BMG reached 846 MPa and 0.37% respectively.