Di(2-pyridyl)ketone stabilized titanium dioxide nanoparticles for the room temperature processed electron transporting layer in organic photovoltaics

Monodisperse TiO₂ nanoparticles are obtained through hydrolysis of titanium butoxide in the presence of di(2-pyridyl)ketone (DPK) and para-toluenesulfonic acid. The DPK ligand stabilized the surface of the TiO₂ nanoparticle through complexation with TiO₂. DPK stabilized TiO₂ (TNP-DPK) can be dispersed without aggregation in alcoholic solutions at concentrations higher than 1 M. The synthesized particles have 4–5 nm size and spherical shape at amorphous phase. The atomic force microscope image reveals that only 0.1 wt% of TNP-DPK solution can form a conformal and dense film on top of the active layer. The TNP-DPK solution is used for an electron transporting layer (ETL) in organic photovoltaics (OPV) that utilizing poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th) as a photoactive layer. The power conversion efficiency of the OPV is significantly improved from 7.18% to 9.08% by inserting the TNP-DPK layer between photoactive layer and Al electrode. Based on the internal quantum efficiency and transient photo voltage experiments, the TNP-DPK layer is found to improve the charge collection efficiency and reduce the charge recombination at the active layer/electrode interface. These results clearly show that the solution processed TNP-DPK layer can play a role as an efficient ETL in OPVs.     

Plasma-enhanced chemical vapour deposition of fluorinated silicon dioxide films using novel alkylsilanes

Deposition processes and film properties of plasma-enhanced chemical vapour deposition (PECVD) films derived from fluoroalkylsilanes are described. The fluorinated silicon dioxide (FSG) films have lower dielectric constants (3.3–3.7) than non-fluorinated silicon dioxide films (>4). With similar dielectric strengths, the reduced capacitance obtained with FSG films makes them useful as intermetal dielectrics (IMDs). The films are characterised using Fourier transform infrared spectroscopy, Auger electron spectroscopy, ellipsometry and capacitance-voltage measurements. Characterisation of the changes in FSG upon exposure to ambient conditions and a method for stabilising the films are presented     

Interfacial modifying layer-driven high-performance organic thin-film transistors and their nitrogen dioxide gas sensors

Organic thin-film transistors (OTFTs) based on bottom-gate bottom-contact configuration were fabricated by inserting two kinds of modifying layers at the interface of source/drain electrode and organic semiconductor, while nitrogen dioxide (NO₂) sensing capability was also evaluated based on the obtained OTFTs. Compared to OTFT without interfacial layer, the field-effect mobility (μ) was enhanced from 0.018 cm²/Vs to 0.15 cm²/Vs by incorporating with MoO_x interfacial layer. Moreover, when exposed to 30 ppm NO₂, the saturation current and μ of OTFT with MoO_x interfacial layer increase 22.7% and 26.7%, respectively, while in original OTFT, the values are only 3.0% and 3.7%, respectively. The mechanism of performance improvement of OTFT sensor was systematically studied by focusing on the interface of source/drain electrode and organic semiconductor. The reduced contact resistance leads to higher μ, meanwhile, pentacene morphology modulation on MoO_x contributes to better diffusion of NO₂ molecules. As a result, higher μ and more diffused gas molecules enhance the gas sensing property of the transistor.     

The deposition of nanocrystalline TiO2 thin film on silicon using Sol-Gel technique and its characterization

TiO₂ thin films were deposited using Sol-Gel spin coating technique using titanium isoperoxide as the Titania precursor. The films were characterized using X-ray diffraction, capacitance voltage measurement and Raman characterization technique. The XRD and Raman spectra indicate the presence of anatase TiO₂ phase in the film. The grain size as calculated using the Scherrer’s formula was found to be 30, 66 and 59 nm for TiO₂(0 0 4), TiO₂(2 0 0) and TiO₂(2 1 1), respectively. The grain size was found to increase after annealing at 800 °C. The dielectric constant as calculated using capacitance voltage measurement was found to be 25. The refractive index of the film was 2.34.     

Sensing behavior and mechanism of titanium dioxide-based MOS hydrogen sensor

A Pd/TiO₂/Si MOS sensor (Pdtisin sensor) is proposed for the detection of hydrogen gas. The sensor is fabricated on a p-type 1 1 1 silicon wafer having resistivity of 3–6 Ω cm. The thickness of TiO₂ in this structure is about 600 nm. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of the device is observed on the exposure of hydrogen gas at room temperature. The mechanism of hydrogen sensing of titanium dioxide-based MOS sensor (MOS capacitor) has been investigated by evaluating the change in flat-band voltage (V_FB) and fixed surface state density of the device in presence of hydrogen gas. The device exhibits very large parallel shift in C–V as well in G–V characteristics. The possible mechanism on Pd/TiO₂ and TiO₂/Si surface in presence of hydrogen gas has been proposed. The response and recovery time of the device is also measured at room temperature.     

Photoelectrocatalytic degradation of p-hydroxybenzoic acid at the surface of a titanium/titanium dioxide nanotube array electrode using electrochemical monitoring

In this study, the titanium/titanium dioxide nanotube array (Ti/TiO₂-NTA) electrode was prepared with anodic oxidation of Ti foil electrode. The morphology of Ti/TiO₂-NTA electrode was evaluated with scanning electron microscopy images. The results showed that the inner diameter of nanotubes is below of 100 nm. The electrochemical behavior of the as-prepared Ti/TiO₂-NTA electrode was studied using the cyclic voltammetry. In addition, a significant photoelectrochemical behavior of the p-hydroxybenzoic acid (p-HBA) was observed on the Ti/TiO₂ electrode using the hydrodynamic photoamperometry experiments. Then, the photoelectrocatalytic (PEC) degradation of the p-HBA was performed by this electrode, and compared with photocatalytic (PC), electrooxidation (EC), and direct photolysis by ultra-violet ray. It was found from mechanistic studies that the rate constant for the PEC process of Ti/TiO₂-NTA electrode was higher than other degradation processes. The p-HBA concentration monitoring was carried out with the differential pulse voltammetry. Finally, the effects of the solution pH, applied potential, and the p-HBA concentration on the degradation efficiencies were studied and the results showed that the optimum pH for the photoelectrocatalytic degradation was equal to 7.00. The optimum potential and the optimum concentration were about 0.5 V (vs. Ag|AgCl|KCl (3M) as reference electrode) and 0.129 mM in the studied ranges, respectively.     

掺杂Ce4+对溶胶-凝胶法制备二氧化钛薄膜的结构和光催化特性的影响

采用溶胶-凝胶浸渍提拉法分别在氧化硅和石英衬底上制备了Ce4+掺杂的二氧化钛(TiO2)薄膜,在800℃的退火温度下保温30 min.采用X射线衍射仪(XRD)、扫描电镜(SEM)及紫外-可见分光光度计,对TiO2薄膜的结构和光催化性能进行了详细分析,并且进行了对甲基橙的降解实验.研究结果表明:掺杂后的薄膜由锐钛矿向金红石的相转变温度升高.随着掺杂浓度的升高,薄膜经历了由颗粒粒度分明转变到薄膜形成好、未出现明显颗粒的过程,且Ce4+掺杂摩尔百分数为10％的薄膜形成较好.随着Ce4+掺杂浓度升高,TiO2薄膜的光吸收峰先红移再蓝移,紫外区吸收范围先增大后降低.掺杂后薄膜对甲基橙降解率均得到提高,而掺杂10％降解率最大.     

Nanocrystalline TiO2 Photocatalytic Membranes with a Hierarchical Mesoporous Multilayer Structure: Synthesis,Characterization, and Multifunction

A novel sol–gel dip‐coating process to fabricate nanocrystalline TiO₂ photocatalytic membranes with a robust hierarchical mesoporous multilayer and improved performance has been studied. Various titania sols containing poly(oxyethylenesorbitan monooleate) (Tween 80) surfactant as a pore‐directing agent to tailor‐design the porous structure of TiO₂ materials at different molar ratios of Tween 80/isopropyl alcohol/acetic acid/titanium tetraisopropoxide = R:45:6:1 have been synthesized. The sols are dip‐coated on top of a homemade porous alumina substrate to fabricate TiO₂/Al₂O₃ composite membranes, dried, and calcined, and this procedure is repeated with varying sols in succession. The resulting asymmetric mesoporous TiO₂ membrane with a thickness of 0.9 μm exhibits a hierarchical change in pore diameter from 2–6, through 3–8, to 5–11 nm from the top to the bottom layer. Moreover, the corresponding porosity is incremented from 46.2, through 56.7, to 69.3 %. Compared to a repeated‐coating process using a single sol, the hierarchical multilayer process improves water permeability significantly without sacrificing the organic retention and photocatalytic activity of the TiO₂ membranes. The prepared TiO₂ photocatalytic membrane has great potential in developing highly efficient water treatment and reuse systems, for example, decomposition of organic pollutants, inactivation of pathogenic microorganisms, physical separation of contaminants, and self‐antifouling action because of its multifunctional capability.     

Precursor-dependent structural and electrical characteristics of atomic layer deposited films: Case study on titanium oxide

Thin (10–20 nm) TiO₂ films were atomic layer deposited from TiCl₄, Ti(OC₂H₅)₄, H₂O and H₂O₂ in the substrate temperature range 125–350 °C. The structure, chemical composition and electrical properties were correlated to the process temperature and nature of precursors, whereas the effect of precursors on conduction mechanisms was considerable only in the films grown at 125 °C, otherwise controlled by oxide-electrode interfaces. The use of chloride resulted in films with highest permittivity while the use of hydrogen peroxide resulted in lowest permittivity but also in lowest leakage. The post-deposition (pre-metallization) annealing resulted in densification and (re)crystallization of TiO₂ layer but also in thickening of low-permittivity interface layers.     

Interface control and photovoltaic properties of n-type silicon/metal junction by organic dye

The electronic parameters and photovoltaic properties of the Au/methylene blue/n-Si diodes were investigated by current-voltage and capacitance-conductance-frequency techniques. The diode exhibits a non-ideal behavior due the series resistance, organic layer and oxide layer. The barrier height (1.04 eV) of the Au/methylene blue/n-Si is higher than that of Au/n-Si Schottky diode (0.83 eV) due to an excess barrier formed by organic layer. The interface state density of the diode was determined using a conductance technique and was found to be 3.25 × 10¹² eV⁻¹ cm⁻². The diode shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 0.23 V and short-circuit current I_sc of 20.8 μA under 100 mW/cm². It is evaluated that Au/methylene blue/n-Si is an organic-on-inorganic photodiode with the obtained electronic parameters and methylene blue organic dye controls the interface and electrical properties of conventional metal/n-type silicon junction.     

改性纳米二氧化钛修饰长周期光纤光栅的折射率传感特性

为进一步提高长周期光纤光栅(LPFG)的折射率灵敏度,制作了改性纳米二氧化钛粒子(TiO2)修饰LPFG的传感器.利用TiO2表面水解后产生的羟基与聚丙烯酸上的羧基结合实现对其表面进行改性,通过共价键结合方式将改性后纳米TiO2粒子固定在光栅表面构成TiO2-LPFG传感器.实验研究了该传感器对折射率和温度响应特性.结...     

Synthesis of silicon dioxide film using high-concentration ozone and evaluation of the film quality

We investigated the ozone oxidation characteristics on a hydrogen-terminated Si substrate. A high-concentration ozone gas generator with an ozone condensation unit was specially designed and assembled for this study. During the oxidation by ozone with the concentration of 25 vol.% in the temperature range from 340°C to 625°C at 8 Torr (1.1 kPa), the formed oxide film thickness increased with oxidation time in accordance with the parabolic law, which suggests a diffusion-controlled step, while the oxidation by pure oxygen attained saturated states within 3 min of initiating oxidation. The activation energy for parabolic constants in the ozone oxidation was determined to be 0.52 eV. This value is much smaller than the activation energy for dry oxidation with oxygen, while it is almost the same as that in the plasma oxidation with the mixture of rare gas and oxygen. Moreover, the quality of the ozone oxidation film was evaluated by estimating the amount of suboxides (Si³⁺+Si²⁺+Si⁺) using x-ray photoelectron spectroscopy (XPS) analysis and the compressive stress using Fourier transform infrared (FT-IR) spectroscopic analysis. Both results showed that the quality of film subjected to ozone oxidation at 500°C is equal or superior to that of the film subjected to pyrogenic oxidation at 750°C in spite of the faster oxidation rate, and thus, the significant advantages of ozone oxidation at low oxidation temperatures could be confirmed.     

Inside Front Cover: Nanocrystalline TiO2 Photocatalytic Membranes with a Hierarchical Mesoporous Multilayer Structure: Synthesis,Characterization, and Multifunction (Adv. Funct. Mater. 8/2006)

The inside cover shows a hierarchical, mesoporous, multilayer TiO2 photocatalytic membrane synthesized via a novel sol–gel dip‐coating process employing surfactant templates reported by Dionysiou and co‐workers on p. 1067. The resulting asymmetric mesoporous TiO2 membrane supported onto a porous Al2O3 substrate exhibited hierarchical changes in pore diameter and materials porosity from the top to the bottom layer. The TiO2 membrane has multiple simultaneous functions, including photocatalysis, disinfection, separation, and anti‐biofouling. A novel sol–gel dip‐coating process to fabricate nanocrystalline TiO₂ photocatalytic membranes with a robust hierarchical mesoporous multilayer and improved performance has been studied. Various titania sols containing poly(oxyethylenesorbitan monooleate) (Tween 80) surfactant as a pore‐directing agent to tailor‐design the porous structure of TiO₂ materials at different molar ratios of Tween 80/isopropyl alcohol/acetic acid/titanium tetraisopropoxide = R:45:6:1 have been synthesized. The sols are dip‐coated on top of a homemade porous alumina substrate to fabricate TiO₂/Al₂O₃ composite membranes, dried, and calcined, and this procedure is repeated with varying sols in succession. The resulting asymmetric mesoporous TiO₂ membrane with a thickness of 0.9 μm exhibits a hierarchical change in pore diameter from 2–6, through 3–8, to 5–11 nm from the top to the bottom layer. Moreover, the corresponding porosity is incremented from 46.2, through 56.7, to 69.3 %. Compared to a repeated‐coating process using a single sol, the hierarchical multilayer process improves water permeability significantly without sacrificing the organic retention and photocatalytic activity of the TiO₂ membranes. The prepared TiO₂ photocatalytic membrane has great potential in developing highly efficient water treatment and reuse systems, for example, decomposition of organic pollutants, inactivation of pathogenic microorganisms, physical separation of contaminants, and self‐antifouling action because of its multifunctional capability.     

Structural characterization of DC magnetron-sputtered TiO2 thin films using XRD and Raman scattering studies

Titanium dioxide films have been deposited using DC magnetron sputtering technique onto well-cleaned p-silicon substrates at an oxygen partial pressure of 7×10^–5 mbar and at a sputtering pressure (Ar+O₂) of 1×10^–3 mbar. The deposited films were calcinated at 673 and 773 K. The composition of the films as analyzed using Auger electron spectroscopy reveals the stoichiometry with an O and Ti ratio 2.08. The influence of post-deposition annealing at 673 and 773 K on the structural properties of the titanium dioxide thin films have been studied using XRD and Raman scattering. The structure of the films deposited at the ambient was found to be amorphous and the films annealed at temperature 673 K and above were crystalline with anatase structure. The lattice constants, grain size, microstrain and the dislocation density of the film are calculated and correlated with annealing temperature. The Raman scattering study was performed on the as-deposited and annealed samples and the existence of Raman active modes A_1g, B_1g and E_g corresponding to the Raman shifts are studied and reported. The improvement of crystallinity of the TiO₂ films was also studied using Raman scattering studies.     

Photocatalytic degradation of RhB and TNT and photocatalytic water splitting with CZTS microparticles

Cu₂ZnSnS₄ (CZTS) is a main candidate material for solar energy conversion through both photovoltaics and photocatalysis based on environmentally friendly elements and with a direct band gap of 1.5 eV. We report the synthesis of quasi Cu₂ZnSnS₄ microparticles with unprecedented narrow size distributions. The structural, morphological and core level analysis has been carried out by XRD, SEM and XPS techniques. These microparticles have shown excellent photocatalytic activity toward degradation of Rhodamine B dye (RhB) and TNT under visible light. The extent of mineralization has been analyzed by COD and TOC values. Photocatalytic water splitting for H₂ generation has also been reported.     

Photocatalyst Cr-doped titanium oxide nanoparticles: Fabrication,characterization, and investigation of the effect of doping on methyl orange dye degradation

The Cr/TiO₂ nanoparticles were synthesized via sol–gel technique by using tetraisopropylorthotitanate (TIPOT) and chromium nitrate (Cr(NO₃)₃·9H₂O) as precursors. The framework substitution of Cr into TiO₂ nanoparticles was evaluated by X-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive X-ray microanalysis (SEM-EDX), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) techniques. XRD results showed that pure TiO₂ and Cr/TiO₂ nanoparticles own anatase phase with some rutile phase. SEM and TEM images confirmed the successful doping of Cr³⁺ ions into TiO₂ structure. The result of photocatalytic degradation of methyl orange (MO) demonstrated that appropriate Cr³⁺ doping can greatly enhance photocatalytic activity of TiO₂, which was attributed to the "red-shift" in ultraviolet–visible light (UV–vis) absorption spectra of TiO₂ nanoparticles while doped with Cr³⁺ ions and also to the improved transfer efficiency of photogenerated electrons and holes caused by incorporation of Cr³⁺ ions. The optimal Cr³⁺ concentration to obtain the highest photocatalytic activity was 5% mol. The relatively high photocatalytic activity of Cr/TiO₂ nanoparticles, suggests that it may have a promising future for water and wastewater purifications.     

Photoluminescent and photocatalytic properties of bismuth doped strontium aluminates blended with titanium dioxide

Bismuth co-doped long persistent phosphor (LPP) powders were obtained by a combustion synthesis technique followed by a post-annealing under carbon atmosphere. Bismuth content was varied from 1.0 to 15.0 mol%. X-ray diffraction analysis revealed that the powders show mainly a mixture of three phases: the SrAl₂O_4, the SrAl₁₄O₂₅ and the Sr₂Al₆O₁₁ crystalline phases. Photocatalyst composites were obtained by wet mixing of TiO₂ anatase and LPP powders followed by annealing in air at 450 °C. Photoluminescence measured spectra under 380 nm excitation show a tunable emission from green (510 nm) to greenish-blue (463 nm) in which peak wavelength localization is related to the Bi content. Photoluminescence intensity decreases as Bi content increases. Degradation of methylene blue solutions, irradiated by UV light (254 nm), was monitored by the decrease of its 650 nm absorption peak in regular periods. The best photocatalytic activity is observed when in the composite blend a 2.0 mol% of Bi content was used, and complete methylene degradation is reached after 210 min. These photocatalyst composite powders are potential candidates to clean-up wastewater applications, and might be potential candidates for photocatalytic hydrogen generation in aqueous solutions.     

CO2激光诱导条件下的金属沉积层的微观分析

为了研究低功率CO2激光诱导条件下,从水性溶液中诱导金属沉积机理,利用动态力显微镜分析了金属Ag过程中的晶粒分布以及晶体生长概貌;利用电子探针研究了金属沉积层在环氧树脂表面的横向和纵向沉积现象;利用X射线衍射方法研究了Ag-Cu沉积层中的Cu晶体生长过程中晶格常数的变化。结果表明,Ag晶粒在基材表面的沉积规律、生长分布与工艺参量以及激光模式有密切关系;金属微粒在环氧树脂表面的横向沉积,直接影响金属层的宽度,而其纵向沉积直接决定金属层的厚度;同Cu相比,Ag-Cu层也在(111),(200),(220)3个晶面衍射强度较大,但点阵常数α有微小变化,说明在沉积过程中有少量的杂质原子渗透到Cu金属层。     

Increasing bondability and bonding strength of gold stud bumps onto copper pads with a deposited titanium barrier layer

A flip-chip assembly is an attractive scheme for use in high performance and miniaturized microelectronics packaging. Wafer bumping is essential before chips can be flip-bonded to a substrate. Wafer bumping can be used for mechanical-single point stud bump bonding (SBB), and is based on conventional thermosonic wire bonding. This work proposes depositing a titanium barrier layer between the copper film and the silver bonding layer to achieve perfect bondability and sufficiently strong thermosonic bonding between a stud bump and the copper pad.A titanium layer was deposited on the copper pads to prevent copper atoms from out-diffusing during thermosonic stud bump bonding. A silver film was then deposited on the surface of the titanium film as a bonding layer to increase the bondability and bonding strength for stud bumps onto copper pads. The integration of the silver bonding layer with a diffusion barrier layer of titanium on the copper pads yielded 100% bondability between the stud bump and pads. The strength of bonding between the gold bumps on the copper pads significantly exceeds the minimum average values in JEDEC specifications. The diffusion barrier layer of titanium effectively prevents copper atoms from out-diffusing to the silver bonding layer surface during thermosonic bonding, which fact can be interpreted with reference to the experimental results of energy dispersive spectrometry (EDS) and analyses of Auger depth profiles. This diffusion barrier layer of titanium efficiently provides perfect bondability and sufficiently strong bonding between a stud bump and copper pads with a silver bonding layer.     

Two-step fabrication of thin film encapsulation using laser assisted chemical vapor deposition and laser assisted plasma enhanced chemical vapor deposition for long-lifetime organic light emitting diodes

A thin film encapsulation layer was fabricated through two-sequential chemical vapor deposition processes for organic light emitting diodes (OLEDs). The fabrication process consists of laser assisted chemical vapor deposition (LACVD) for the first silicon nitride layer and laser assisted plasma enhanced chemical vapor deposition (LAPECVD) for the second silicon nitride layer. While SiN_x thin films fabricated by LAPECVD exhibits remarkable encapsulation characteristics, OLEDs underneath the encapsulation layer risk being damaged during the plasma generation process. In order to prevent damage from the plasma, LACVD was completed prior to the LAPECVD as a buffer layer so that the laser during LACVD did not damage the devices because there was no direct irradiation to the surface. This two-step thin film encapsulation was performed sequentially in one chamber, which reduced the process steps and increased fabrication time. The encapsulation was demonstrated on green phosphorescent OLEDs with I–V-L measurements and a lifetime test. The two-step encapsulation process alleviated the damage on the devices by 19.5% in external quantum efficiency compared to the single layer fabricated by plasma enhanced chemical vapor deposition. The lifetime was increased 3.59 times compared to the device without encapsulation. The composition of the SiNx thin films was analyzed through Fourier-transform infrared spectroscopy (FTIR). While the atomic bond in the layer fabricated by LACVD was too weak to be used in encapsulation, the layer fabricated by the two-step encapsulation did not reveal a Si–O bonding peak but did show a Si–N peak with strong atomic bonding.