CARRIER PHOTOGENERATION IN POLY（N-VINYL-CARBAZOLE）-BASED PHOTOCONDUCTIVE THIN-FILM DEVICES

In this paper, photoexcitation processes in the bilayer devices based on inorganic materials and poly（N-vinylcarbazole） （PVK） were investigated. In order to clarify the roles of inorganic materials in photoconductive properties of bilayer devices, TiO2 and ZnS were chosen to combine with PVK. A model for generation of photocurrent （Iph） in single layer device of PVK was obtained. It is deduced that the recombination rate constant （Pcomb） and the ionization rate constant （y） ofexcitons should be considered as the most important factors for Iph. For inorganic materials （TiO2 or ZnS）/PVK bilayer devices, in reverse bias of-4 V, the photocurrent of 115 mA/cm^2 in the TiO2/PVK device was observed, but the photocurrent in the ZnS/PVK device was only 10 mA/cma under the illumination light of 340 nm and the light intensity of 14.2 mW/cm^2. The weaker photocurrent is attributed to the absorption of ZnS within UV region and the energy offset at the interface between PVK and ZnS, which impedes the transport of charge carriers.     

Surface Conductivity of DR1-Functionalized Organic-Inorganic Sol-Gel Materials

In recent years, in looking for an important photorefractive application, several studies on electro-optic and photoconductive sol-gel responses have been done. A very important effort has been addressed to establish the appropriate induced-orientation procedure, in order to get the highest electro-optic coefficient. In this way a very high coefficient of 48 pm/V at 831 nm in sol-gel has been already found. Similarly, the importance of the non-linear chromophore concentration into the material electro-optic behavior has been studied. However, the influence of the orientation procedure and the chromophore concentration over the photoconductive response has not been performed. In this work we study the vacuum-surface-charge-transport under and without illumination after poling times of 10, 30 and 120 min on DR1-functionalized sol-gel thin films of 1.3 m in thickness with a suitable concentration of DR1. We include the measures before poling for other chromophore concentrations. We found the largest density of photocurrent at 633 nm for a poling time of 30 min. We also measured the order parameter in order to follow the Corona induced orientation evolution as function of time for each case. The saturation found into this parameter and into the photoconduction show the existence of an optimal poling time.     

PHOTOCONDUCTIVE PROPERTIES OF PVK:Alq3 BLEND FILMS STUDIED BY STEADY-STATE AND TIME-RESOLVED TRANSIENT PHOTOCURRENT SPECTRA

The carrier transport properties of the blends of the hole transport material poly(N-vinylcarbazole) (PVK) and the electron transport material tris (8-hydroxyquinolinolato) aluminumⅢ(Alq_3) are investigated at room temperature using steady-state and time-resolved transient photocurrent measurements as a function of doping concentration of Alq_3.Due to lower LUMO and higher HOMO energy level of Alq_3 than those of PVK,Alq_3 molecules may act as carrier trap states in PVK films at low concentration.However...     

Carbon nanotube-containing photorefractive polymer composites operating at telecommunication wavelengths

The field dependences of photocurrent, the two-beam coupling gain coefficient, and the grating formation time constant in polymer composites made from polyvinylcarbazole (PVK) and single-wall carbon nanotubes (SWNTs) were measured under the conditions of one-photon SWNT excitation with continuous laser radiation at a wavelength of 1550 nm. Carbon nanotubes are responsible for optical electronic absorption up to ～2000 nm in this composite. The dependence of the quantum efficiency of generation of mobile charge carriers on the electric field E ₀ as determined from the photocurrent coincides with the curves calculated via the Onsager equation expanded to the (E ₀)⁴ term, at a quantum yield of thermalized electron-hole pairs of η₀ = 0.07 and a charge separation distance in the pair of r ₀ = 9.8 Å. An analysis of the photorefractive characteristics showed that the admixture of fullerene C₆₀ in an amount of 3 wt % to the PVK composite with 0.26 wt % SWNT leads to a twofold increase in the beam-coupling gain coefficient. In the PVK-matrix composite containing 0.26 wt % SWNT and 3 wt % C₆₀, the beam-coupling gain coefficient Γ of a 1550-nm laser beam and the net gain Γ-α are 32 and ～27 cm^?1, respectively, at a constant field of E ₀ = 140 V/μm.     

Ferroelectric and Pyroelectric Properties of Highly (111)-oriented Nanocrystalline Pb(Zr0:95Ti0:05)O3 Thin Films

"Lead zirconate titanate Pb(Zr0:95Ti0:05)O3 (PZT95/5) antiferroelectric thin films with 300 nm thickness were grown on Pt/Ti/SiO2/Si substrates by a sol-gel method with rapid thermal annealing processing. The X-ray diffraction results showed that the highly (111)-oriented pervoskite PZT95/5 thin films were grown on Pt/Ti/SiO2/Si substrates when annealed at 600-700 oC. Electrical measurements were conducted on PZT95/5 films in metal-ferroelectric-metal capacitor configuration. The PZT95/5 thin films annealed at 600-700 oC showed well-saturated hysteresis loops at an applied voltage of 20 V. At 1 kHz, the dielectric constant and dielectric loss of the films were 519 and 0.028, 677 and 0.029, 987 and 0.025, respectively for the thin films annealed at 600, 650, and 700 oC. The average remanent polarization (Pr) and the coercive electric field (Ec) obtained from the P-E hysteresis loops, were 19.1 1C/cm2 and 135.6 kV/cm, 29.31C/cm2 and 88.57 kV/cm, 45.3 1C/cm2 and 102.1 kV/cm, respectively for PZT95/5 thin films annealed at 600, 650 and 700 oC for 10 min in the oxygen atmosphere. This showed a good ferroelectricity of the prepared PZT95/5 films on Pt/Ti/SiO2/Si substrates by the simple sol-gel processing. The pyroelectric coeocient (p) of antiferroelectric PZT95/5 films was measured by a dynamic technique. At room temperature, the p values of the antiferroelectric PZT95/5 films at 1 kHz were 274, 238, and 212 1C/m2K."     

TiO_2/SiO_2纳米薄膜的光催化活性和亲水性

通过 sol-gel工艺在钠钙玻璃表面制备了均匀透明的 TiO2/SiO2复合纳米薄膜 .实验结果表明 : 当 SiO2添加量较高时 , TiO2/SiO2复合纳米薄膜的光催化活性明显降低 ;当 SiO2添加量较低时 ,TiO2/SiO2复合薄膜的光催化活性无明显变化 .在 TiO2薄膜中添加 SiO2,可以抑制薄膜中 TiO2晶粒的长大 ,同时薄膜表面的羟基含量增加 , 水在复合薄膜表面的润湿角下降 , 亲水能力增强 .当 SiO2含量为 10％－ 20％（摩尔分数）时获得了润湿角为 0°的超亲水性薄膜 .     

Photoconductive UV Detectors Based on ZnO Films Prepared by Sol-Gel Method

Highly c-axis oriented ZnO thin films were deposited on single crystal Si (111) substrates by sol-gel method. The photoconductive UV detectors based on ZnO thin films, being a metal-semiconductor-metal (MSM) structure with interdigital (IDT) configuration, were fabricated by using Au as contact metal. The characteristics of dark and photocurrent of the UV detector, the UV photoresponse of the detector were investigated. The linear current-voltage (I-V) characteristics under both forward and reverse bias exhibit ohmic metal-semiconductor contacts. Under illumination using monochromatic light with a wavelength of 365 nm, photo-generated current arrived at 44.89 μ A at a bias of 6 V. The detector exhibits an evident wide-range spectral responsivity and shows a trend similar to that in photoluminescence (PL) spectrum. PL spectrum of detector exhibits two peaks, one is the near band edge emission, and another is the deep-level emission in the visible region.     

富勒烯掺杂有机光电导材料的光电导性

富勒烯掺杂有机光电导材料的光电导性徐铸德，陈万喜，冷拥军，许小平，李文铸（浙江大学化学系，物理系，杭州，３１００２７）汪茫（浙江大学高分子科学与工程学系）关键词富勒烯，光化学，光物理，光电导体光电导材料在现代静电成像领域中有极广泛的应用，近年来，有机...     

石墨炔修饰的ZnO薄膜紫外探测器

制备了石墨炔修饰的金属-半导体-金属结构的ZnO紫外探测器,研究了不同旋涂次数的石墨炔修饰对探测器性能的影响。实验结果表明,石墨炔修饰的探测器比未修饰器件的光电流提高4倍,暗电流降低2个数量级,同时探测器的响应度和探测率也明显提高,其中旋涂2次的石墨炔修饰的器件特性为最优。在10 V偏压下,旋涂2次的石墨炔修饰的探测器响应度高达1759 A·W⁻¹,探测率高达4.23× 10¹⁵ Jones,这是迄今为止报导过的溶胶-凝胶法制备的ZnO紫外探测器的最高值。经过对探测器各项性能的测试分析可知,石墨炔修饰的ZnO探测器性能的提高归因于石墨炔良好的空穴传输特性。暗环境下ZnO与石墨炔界面处形成p-n结,使探测器的暗电流大幅降低;光照条件下光生空穴在石墨炔中聚集,减少了电子空穴对的复合,有效提高了器件的光电流。由于石墨炔修饰减少了ZnO表面的氧分子吸附和解吸附过程,器件的响应速度也明显加快。     

Enhanced diffraction efficiency in a photorefractive liquid crystal cell with poly(9-vinylcarbazole)-infiltrated mesoporous TiO2 layers

The photorefractive effect of a layer-structured liquid crystal cell was significantly enhanced when a C60-doped poly(9-vinylcarbazole) (PVK)/TiO2 nanocomposite was used in two photoconductive layers. The C60-doped PVK/TiO2 nanocomposite film was prepared by infiltrating C60-doped PVK into a highly ordered mesoporous TiO2 layer. The addition of the TiO2 layer to the C60-doped PVK layer increased the first-order Raman-Nath diffraction efficiency from 24% to 42.9%. This enhancement of diffraction efficiency is attributed to a blocking effect of charge recombination in the composite layer. The electron transfer from the PVK layer into the TiO2 layer would decrease the recombination of photogenerated charges in the PVK layer, while charges in the PVK layer could participate in the formation of a space-charge field.     

Photoelectric and photorefractive properties of polyvinylcarbazole composites with graphene in the visible spectral range

The photoelectric and photorefractive characteristics of polyvinylcarbazole (PVK) composites with 0.15 wt % graphene at a wavelength of 532 nm have been measured. The dependence of the quantum efficiency of generation of mobile charge carriers as determined from the photocurrent is well approximated by the Onsager equation calculated accurate to E ₀ ³ for the quantum yield of thermalized electron-hole pairs of φ₀ = 1 and their initial separation radius of r ₀ = 10.9 Å. The long-wavelength edge of optical absorption for PVK lies at 365 nm. Thus, the photogeneration of mobile carriers during illumination of the composite at 532 nm is due to photoexcitation of graphene. The measurement of the photorefractive properties has revealed that the two-beam coupling gain coefficient is Γ = 50 cm^?1 at E ₀ = 150 V/μm and equal intensities of incident beams. It has been found that at E ₀ = 83.3 V/μm, the two-beam coupling gain coefficient increases from 8 to 14 cm^?1 as the ratio of incident beam intensities I ₁(0)/I ₂(0) increases from 1 to 2.4.     

Synthesis and characterization of ordered and disordered polycrystalline La(2)NiMnO(6) thin films by sol-gel

Polycrystalline La(2)NiMnO(6) thin films are prepared on Pt/Ti/SiO(2)/Si substrates by the sol-gel method. Through controlling the processing parameters, the cation ordering can be tuned. The disordered and ordered thin films exhibit distinct differences for crystal structures as well as properties. The crystal structure at room temperature characterized by X-ray diffraction and Raman spectra is suggested to be monoclinic (P2(1)/n) and orthorhombic (Pbnm) for the ordered and disordered thin films, respectively. The ferromagnetic-paramagnetic transition is 263 K and 60 K for the ordered and disordered samples respectively, whereas the saturation magnetic moment at 5 K is 4.9 μ(B) fu(-1) (fu = formula unit) and 0.9 μ(B) fu(-1). The dielectric constant as well as magnetodielectric effect is higher for the ordered La(2)NiMnO(6) thin films. The magnetodielectric effect for the ordered thin film is dominantly contributed to the intrinsic coupling of electric dipole ordering and fluctuations and magnetic ordering and fluctuations, while it is mainly contributed to Maxwell-Wagner (M-W) effects for the disordered thin film. The successful achievements of ordered and disordered polycrystalline La(2)NiMnO(6) thin films will provide an effective route to fabricate double-perovskite polycrystalline thin films by the sol-gel method.     

有机光导液晶光阀(透射式)及其性能的研究

本文报道用聚乙烯咔唑-2,4,7三硝基芴酮电荷转移复合物作光导层,与向列型及胆甾向列型混合液晶组成的夹心池结构制成的扭曲场效应、相变存储效应及动态存储效应三种直流透射式光阀及其性能的研究结果。制得的光阀均有明显开关效应。此外,还详细研究了扭曲场效应液晶光阀的阈值电压、对比度及上升时间与写入光功率的依赖关系。用白光写入,He-Ne激光读出,在扭曲场效应光阀上可实现非相干光-相干光转换,得到图象。用MTF法测得的光阀分辨率为34lps/mm。     

Photo- and electroluminescence in thin films of covalently bonded azomethin-zinc/SiO2 hybrid materials

We report the design and chemical synthesis of covalently bonded azomethin-zinc/SiO(2) hybrid transparent thin films with photoluminescent and electroluminescent emissions in condensed solid state by a sol-gel approach.     

聚乙烯咔唑/杂多阴离子杂化LB膜的制备、结构与光电性质

首次选用聚乙烯咔唑（PVK）、二十二烷酸（BA）与杂多阴离子用LB技术制备 了五种有机/无机杂化LB膜，PVK/BA/HPC（HPC = Na_5(PZ(H_2O)Mo_(11)O_(39)]· 5H_2O, Z = Mn, Co, Cu, Zn, Ni）。用原子力显微镜（AFM），UV-vis，小角X射 线衍射（LAXRD），表面光电压谱（SPS），荧光光谱等对LB膜的结构与性质进行了 表征。结果表明：它们在空气/水界面有好的成膜性能，崩溃压为22 ～27 mN/m， 杂多阴离子作为一个单层夹在PVK和BA双层之间。PVK/BA/HPC LB膜的光致发光具有 PVK激基缔合物的特征荧光，其光电压谱有较强的光电响应。     

Vapor-phase synthesis of mesoporous SiO2-P2O5 thin films

Mesoporous SiO2-P2O5 films were synthesized from the vapor phase onto a silicon substrate. First, a precursor solution of cetyltrimethylammonium bromide (C16TAB), H3PO4, ethanol, and water was deposited on a silicon substrate by a spin-coating method. Then, the C16TAB-H3PO4 composite film was treated with tetraethoxysilane (TEOS) vapor at 90-180 degrees C for 2.5 h. The H3PO4-C16TAB composite formed a hexagonal structure on the silicon substrate before vapor treatment. The TEOS molecules penetrated into the film without a phase transition. The periodic mesostructure of the SiO2-P2O5 films was retained after calcination. The calcined films showed a high proton conductivity of about 0.55 S/cm at room temperature. The molar ratio of P/Si in the SiO2-P2O5 film was as high as 0.43, a level that was not attained by a premixing sol-gel method. The high phosphate group content and the ordered periodic mesostructure contributed to the high proton conductivity.     

Properties of chlorine-doped poly(N-vinylcarbazole) thin films

Thin films of poly(N-vinylcarbazole) (PVK) have been obtained by thermal evaporation under vacuum. The chain length of the polymer is shortened by this deposition technique, which induces a strong reactivity between chlorine and the PVK films. After chlorine doping, there is complex salt formation as shown by electron spin resonance spectroscopy (ESR) and X-ray photoelectron spectroscopy (XPS). However, the major part of the chlorine has reacted with PVK. The thermal evaporation induces amorphization of the PVK, while chlorine doping induces polymer degradation with NH₄Cl formation. Because of this degradation the carriers detected by ESR are strongly localized on carbazole radicals, thereby explaining the small increase in the conductivity of PVK films even after chlorine doping.     

Sb掺杂纳米TiO2光催化剂的晶体结构与光催化性能

Nanoscale Sb doped titanium dioxide thin films photocatalyst (Ti1-xSbO2) were obtained from dip-coating sol-gel method. The influence of dopant Sb density on the crystal structure and the phase transformation of the thin films were characterized by X-ray diffraction (XRD) and Raman spectra. The results of XRD showed that as-prepared films were not only in anatase state but also in brookite. The crystalline size was estimated to be around 13.3-20 nm. Raman spectra indicated there coexisted other phases and a transformation from brookite to anatase in the samples doped with 0.2% Sb. After doping a proper amount of Sb, the crystallization rate and the content of the anatase Ti1?xSbO2 in the thin films was clearly enhanced because Sb replaced part of the Ti of TiO2 in the thin films. The anode current density (photocurrent density) and the first order reaction speed constant (k) of thin films doped with 0.2% Sb reached 42.49 1A/cm2 and 0.171 h/cm2 under 254 nm UV illumination, respectively, which is about 11 times and 2 times that of the non-doped TiO2 anode prepared by the same method respectively.     

Spectroscopic and electrical properties of SiO2 films prepared by simple and cost effective sol-gel process

Amorphous SiO2 thin films were prepared on glass and silicon substrates by cost effective sol-gel method. Tetra ethyl ortho silicate (TEOS) was used as the precursor material, ethanol as solvent and concentrated HCl as a catalyst. The films were characterized at different annealing temperatures. The optical transmittance was slightly increased with increase of annealing temperature. The refractive index was found to be 1.484 at 550 nm. The formation of SiO2 film was analyzed from FT-IR spectra. The MOS capacitors were designed using silicon (100) substrates. The current-voltage (I-V), capacitance-voltage (C-V) and dissipation-voltage (D-V) measurements were taken for all the annealed films deposited on Si (100). The variation of current density, resistivity and dielectric constant of SiO2 films with different annealing temperatures was investigated and discussed for its usage in applications like MOS capacitor. The results revealed the decrease of dielectric constant and increase of resistivity of SiO2 films with increasing annealing temperature.     

Optical, electrical and dielectric properties of TiO2-SiO2 films prepared by a cost effective sol-gel process

Titanium dioxide (TiO(2)) and silicon dioxide (SiO(2)) thin films and their mixed films were synthesized by the sol-gel spin coating method using titanium tetra isopropoxide (TTIP) and tetra ethyl ortho silicate (TEOS) as the precursor materials for TiO(2) and SiO(2) respectively. The pure and composite films of TiO(2) and SiO(2) were deposited on glass and silicon substrates. The optical properties were studied for different compositions of TiO(2) and SiO(2) sols and the refractive index and optical band gap energies were estimated. MOS capacitors were fabricated using TiO(2) films on p-silicon (100) substrates. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated for the films annealed at 200°C for their possible use in optoelectronic applications.