The effect of the concentration and oxidation state of Sn on the structural and electrical properties of indium tin oxide nanowires

High quality single-crystalline indium tin oxide (ITO) nanowires with controlled Sn contents of up to 32.5 at.% were successfully synthesized via a thermal metal co-evaporation method, based on a vapor-liquid-solid growth mode, at a substrate temperature of as low as 540?°C. The high solubility of Sn in the nanowires was explained with the existence of Sn(2+) ions along with Sn(4+) ions: the coexistence of Sn(2+) and Sn(4+) ions facilitated their high substitutional incorporation into the In(2)O(3) lattice by relaxing structural and electrical disturbances due to the differences in ionic radii and electrical charges between Sn and In(3+) ions. It was revealed that, while the lattice parameter of the ITO nanowires had a minimum value at a Sn content of 6.3 at.%, the electrical resistivity had a minimum value of about 10(-3) Ω cm at a Sn content of 14 at.%. These structural and electrical behaviors were explained by variation in the relative and total amounts of the two species, Sn(2+) and Sn(4+).     

Low-temperature synthesis of indium tin oxide nanowires as the transparent electrodes for organic light emitting devices

Low-temperature growth of indium tin oxide (ITO) nanowires (NWs) was obtained on catalyst-free amorphous glass substrates at 250?°C by Nd:YAG pulsed-laser deposition. These ITO NWs have branching morphology as grown in Ar ambient. As suggested by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), our ITO NWs have the tendency to grow vertically outward from the substrate surface, with the (400) plane parallel to the longitudinal axis of the nanowires. These NWs are low in electrical resistivity (1.6×10?? Ω cm) and high in visible transmittance (~90–96%), and were tested as the electrode for organic light emitting devices (OLEDs). An enhanced current density of ~30 mA cm?2 was detected at bias voltages of ~19–21 V with uniform and bright emission. We found that the Hall mobility of these NWs is 2.2–2.7 times higher than that of ITO film, which can be explained by the reduction of Coulomb scattering loss. These results suggested that ITO nanowires are promising for applications in optoelectronic devices including OLED, touch screen displays, and photovoltaic solar cells.     

Enhanced photoluminescence in Au-embedded ITO nanowires

Gold (Au)-embedded indium tin oxide (ITO) nanowires were synthesized by thermal evaporation of a mixture of In(2)O(3,) SnO(2) and graphite powders on Si (100) substrates coated with Au thin films followed by annealing. At the initial stages of annealing, Au formed a continuous linear core located along the long axis of each ITO nanowire. The morphology of the Au core changed from a continuous line to a discrete line, and then to a droplet-like chain, finally evolving into a peapod in which crystalline Au nanoparticles were encapsulated in crystalline ITO with increasing annealing temperature. The ITO nanowires with the Au core showed an emission band at ~380 nm in the ultraviolet region. The ultraviolet emission intensity increased rapidly with increasing annealing temperature. The intensity of emission from the Au-peapod ITO nanowires (annealed at 750 °C) was approximately 20 times higher than that of the emission from the Au-core/ITO-shell ITO nanowires with a continuous linear shaped-Au core (annealed at 550 °C). This ultraintense ultraviolet emission might have originated mainly from the enhanced crystalline quality of the annealed ITO nanowires.     

Preparation and electrical properties of electrospun tin-doped indium oxide nanowires

Well-aligned tin-doped indium (ITO) nanowires have been prepared using the electrospinning process. The Sn doping mechanism and microstructure have been characterized by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Devices for I-V measurement and field-effect transistors (FETs) were assembled using ITO nanowires with top contact configurations. The effect of Sn doping on the electrical conductivity was significant in that it enhanced the conductance by over 10(7) times, up to ～1?S?cm(-1) for ITO nanowires with an Sn content of 17.5 at.%. The nanowire FETs were operated in the depletion mode with an electron mobility of up to 0.45?cm(2)?V(-1)?s(-1) and an on/off ratio of 10(3).     

ZnO nanowires hydrothermally grown on PET polymer substrates and their characteristics

Zinc oxide nanowires (ZnO NWs) were successfully synthesized on the ITO/PET polymer substrates by a hydrothermal method. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy investigations were carried out to characterize the crystallinity, surface morphologies, and orientations of these NWs, respectively. The influence of NW surface morphologies on the optical and electrical properties of ZnO NWs was studied. The hydrothermally grown ZnO NWs with direct band gap of 3.21 eV emitted ultraviolet photoluminescence of 406 nm at room temperature. Field emission measurements revealed that the threshold electric fields (Eth, current density of 1 mA/cm2) of ZnO NWs/ITO/PET and ZnO NWs/ZnO/ITO/PET are 1.6 and 2.2 V/microm with the enhancement factors, beta values, of 3275 and 4502, respectively. Furthermore, the field emission performance of ZnO NWs deposited on the ITO/PET substrate can be enhanced by illumination with Eth of 1.3 V/microm and displays a maximum emission current density of 18 mA/cm2. The ZnO NWs successfully grown on polymer substrate with high transmittance, low threshold electric field, and high emission current density may be applied to a flexible field emission display in the future.     

Ti-doped indium tin oxide thin films for transparent field-effect transistors: control of charge-carrier density and crystalline structure

Indium tin oxide (ITO) films are representative transparent conducting oxide media for organic light-emitting diodes, liquid crystal displays, and solar cell applications. Extending the utility of ITO films from passive electrodes to active channel layers in transparent field-effect transistors (FETs), however, has been largely limited because of the materials' high carrier density (>1 × 10(20) cm(-3)), wide band gap, and polycrystalline structure. Here, we demonstrate that control over the cation composition in ITO-based oxide films via solid doping of titanium (Ti) can optimize the carrier concentration and suppress film crystallization. On 120 nm thick SiO(2)/Mo (200 nm)/glass substrates, transparent n-type FETs prepared with 4 at % Ti-doped ITO films and fabricated via the cosputtering of ITO and TiO(2) exhibited high electron mobilities of 13.4 cm(2) V(-1) s(-1), a low subthreshold gate swing of 0.25 V decade(-1), and a high I(on/)I(off) ratio of >1 × 10(8).     

High-performance transparent conducting oxide nanowires

We report the growth and characterization of single-crystalline Sn-doped In2O3 (ITO) and Mo-doped In2O3 (IMO) nanowires. Epitaxial growth of vertically aligned ITO nanowire arrays was achieved on ITO/yttria-stabilized zirconia (YSZ) substrates. Optical transmittance and electrical transport measurements show that these nanowires are high-performance transparent metallic conductors with transmittance of approximately 85% in the visible range, resistivities as low as 6.29 x 10(-5) Omega x cm and failure-current densities as high as 3.1 x 10(7) A/cm2. Such nanowires will be suitable in a wide range of applications including organic light-emitting devices, solar cells, and field emitters. In addition, we demonstrate the growth of branched nanowire structures in which semiconducting In2O3 nanowire arrays with variable densities were grown epitaxially on metallic ITO nanowire backbones.     

聚(2-甲氧基-5-十二烷氧基)对苯乙炔/ZnO纳米线混合膜的光伏特性

采用脱氯化氢的方法合成了聚(2-甲氧基-5-十二烷氧基)对苯乙炔(PMODOPV)。利用热蒸发法在铜基片上制备氧化锌纳米线,以此为负极直接旋涂聚合物溶液,制备结构为氧化铟锡(ITO)/聚乙撑二氧噻吩-聚(苯乙烯磺酸盐)(PEDOT∶PSS)/PMODOPV/ZnO/Cu的光伏器件。考察了器件的光伏特性以及纳米线的加入对光伏器件的影响。研究发现,加入ZnO纳米线制备的器件具有高的开路电压和短路电流,在标准AM1.5太阳光模拟灯照射下(1000W/cm2),器件的短路电流达到了5.37×10-3A/cm2,开路电压达到了1.01V,功率转换效率相应地达到了1.37%,其中功率转换效率与没有掺杂氧化锌纳米线的PMODOPV器件相比有明显提高。文中在氧化锌纳米线上旋涂PMODOPV获得活性层,从其膜表面的SEM图中可以看出,氧化锌纳米线类似网状的交织在聚合物的膜层中,纳米线与聚合物实现了微观尺度的结合。     

Sn-doped hematite nanostructures for photoelectrochemical water splitting

We report on the synthesis and characterization of Sn-doped hematite nanowires and nanocorals as well as their implementation as photoanodes for photoelectrochemical water splitting. The hematite nanowires were prepared on a fluorine-doped tin oxide (FTO) substrate by a hydrothermal method, followed by high temperature sintering in air to incorporate Sn, diffused from the FTO substrate, as a dopant. Sn-doped hematite nanocorals were prepared by the same method, by adding tin(IV) chloride as the Sn precursor. X-ray photoelectron spectroscopy analysis confirms Sn(4+) substitution at Fe(3+) sites in hematite, and Sn-dopant levels increase with sintering temperature. Sn dopant serves as an electron donor and increases the carrier density of hematite nanostructures. The hematite nanowires sintered at 800 °C yielded a pronounced photocurrent density of 1.24 mA/cm(2) at 1.23 V vs RHE, which is the highest value observed for hematite nanowires. In comparison to nanowires, Sn-doped hematite nanocorals exhibit smaller feature sizes and increased surface areas. Significantly, they showed a remarkable photocurrent density of 1.86 mA/cm(2) at 1.23 V vs RHE, which is approximately 1.5 times higher than that of the nanowires. Ultrafast spectroscopy studies revealed that there is significant electron-hole recombination within the first few picoseconds, while Sn doping and the change of surface morphology have no major effect on the ultrafast dynamics of the charge carriers on the picosecond time scales. The enhanced photoactivity in Sn-doped hematite nanostructures should be due to the improved electrical conductivity and increased surface area.     

Sn-catalyzed synthesis of SnO2 nanowires and their optoelectronic characteristics

We report the rational synthesis of one-dimensional SnO(2) nanowires (SnO(2)NWs) via a Sn-catalyzed vapor-liquid-solid (VLS) growth mechanism, in which Sn nanoparticles can direct the oriented growth of SnO(2)NWs at high temperature. I-V measurement of a field effect transistor made of individual SnO(2)NWs exhibits typical n-type semiconducting characteristics with an electron mobility and concentration of 14.36?cm(2)?V( - 1)?s( - 1) and 1.145 × 10(17)?cm( - 3), respectively. The SnO(2)NW-based photodetector shows a high sensitivity to UV light radiation, and a fast light response speed of millisecond rise time/fall time with excellent stability and reproducibility, whereas it is nearly blind to illumination with wavelengths in the visible range. Detailed reasons to account for the detection selectivity and rapid response speed are proposed. The generality of the above results suggests that our SnO(2)NW photodetectors have potential application in nanoscaled optoelectronic devices.     

在线紫外辐照辅助沉积柔性ITO薄膜的研究

显示技术正朝着柔性化、超薄化方向发展,低温制备柔性ITO薄膜已经成为一大趋势.本文在射频磁控溅射过程中,引入在线紫外辐照,室温条件下在有机衬底上制备柔性ITO薄膜的工艺,其最低方块电阻为5Ω,电阻率为2.5×10 -4Ω·cm,透光率为92%,远远优于未采用紫外辐照制备的柔性ITO薄膜.我们用四探针测试仪、分光光度计、原子力显微镜、X射线衍射仪等测试仪器,对未采用和采用在线紫外辐照制备的薄膜进行测试,分析探讨了紫外线辐照对薄膜的光电性能、表面形貌和生长取向的影响.研究结果表明:在紫外线的照射下,ITO薄膜表面形貌得到改善,晶界缺陷减少,生长更均匀,致密度更好,在降低薄膜电阻率的同时,提高了薄膜在可见光区的透射率,在紫外辐照下,ITO薄膜更趋于〈222〉的择优取向,且平均晶粒尺寸变大,结晶度提高,宏观表现为薄膜的电阻率降低.     

Fluorine-doped tin oxide films grown by pulsed direct current magnetron sputtering with an Sn target

Fluorine-doped tin oxide (FTO) films have been deposited by pulsed DC magnetron sputtering with an Sn target. Various ratios of CF4/O2 gas were injected to enhance the optical and electrical properties of the films. The extinction coefficient was lower than 1.5×10(-3) in the range from 400 to 800?nm when the CF4O2 ratio was 0.375. The resistivity of fluorine-doped SnO2 films (1.63×10(-3)?Ω?cm) deposited at 300?°C was 27.9 times smaller than that of undoped SnO2 (4.55×10(-2)?Ω?cm). Finally, an FTO film was consecutively deposited for protecting the oxidation of indium tin oxide films. The resistivity of the double-layered film was 2.68×10(-4)?Ω?cm, which increased by less than 39% at a 450?°C annealing temperature for 1?h in air.     

Auger recombination in III-nitride nanowires and its effect on nanowire light-emitting diode characteristics

We have measured the Auger recombination coefficients in defect-free InGaN nanowires (NW) and InGaN/GaN dot-in-nanowire (DNW) samples grown on (001) silicon by plasma-assisted molecular beam epitaxy. The nanowires have a density of ～1 × 10(11) cm(-2) and exhibit photoluminescence emission peak at λ ～ 500 nm. The Auger coefficients as a function of excitation power have been derived from excitation dependent and time-resolved photoluminescence measurements over a wide range of optical excitation power density. The values of C(0), defined as the Auger coefficient at low excitation, are 6.1 × 10(-32) and 4.1 × 10(-33) cm(6)·s(-1) in the NW and DNW samples, respectively, which are in reasonably good agreement with theoretical predictions for InGaN alloy semiconductors. Light-emitting diodes made with the NW and DNW samples exhibit no efficiency droop up to an injection current density of 400 A/cm(2).     

ZnO-Sn:ZnO core-shell nanowires and ZnO-Zn2SnO4 comb-like nanocomposites

Novel single-crystalline ZnO-Sn:ZnO (SZO) core-shell nanowires and ZnO-Zn2SnO4 (ZTO) comb-like nanocomposites were synthesized by thermal chemical vapor deposition at a low temperature of 650 degrees C. Scanning electron microscopy and transmission electron microscopy show the diameters and lengths of the core-shell nanowires are in ranges of 25-60 nm and 300-500 nm, respectively. The atomic ratios of Sn to (Zn + Sn) in the central and shell parts of the nanowire are 0.4 at.% and 6.1 at.%, respectively. The ZnO-ZTO comb-like nanocomposites possess ZnO nanocombs with ZTO nano-layers deposited on both sides of them. The ZnO branches and ZTO layers are single-crystalline wurtzite and spinel structures growing along the [0002] and [111] directions, respectively. Room-temperature cathodoluminescence measurements show the nanocomposites exhibit strong ultraviolet (UV) emissions at 300, 384 nm, and a broad green emission. The novel luminescence shows promising singularity for opto-electronic applications.     

Preparation of indium-tin oxide (ITO) aciculae by a novel concentration-precipitation and post-calcination method

Indium-tin oxide (ITO) aciculae were prepared by adding tin into indium hydroxide aciculae, which were synthesized by a concentration-precipitation method, and subsequent calcining. X-ray powder diffraction (XRD) indicated that indium hydroxide aciculae were partially crystallized and ITO aciculae were a well-crystallized solid solution, and both of them had a cubic structure. Using scanning electron microscope (SEM), it was found that the cross-sectional diameters of most of ITO aciculae were in the range of 2 to 9 μm, and the aspect ratios of about 95% of aciculae were more than 6. Energy dispersion spectrometer (EDS) and phenylfluorone spectrophotometry analysis were used to measure Sn content of ITO aciculae, and it was revealed that the Sn content of the surface layer was higher than that of the bulk. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) showed that the intensive dehydration of In(OH)₃ took place in the temperature rage of 260–280 °C and the formation of ITO solid solution started at temperature higher than 280 °C. According to the results of XRD, TGA–DTA and N content analysis, indium-containing nitrates or nitrites maybe existed in indium hydroxide aciculae. The specific resistance of the pellet formed by pressing ITO aciculae at a pressure of 10 MPa was measured by a four-probe method at room temperature, and it was as low as 1.2×10⁻² Ω cm.     

Enhanced ionic conductivity of AgI nanowires/AAO composites fabricated by a simple approach

AgI nanowires/anodic aluminum oxide (AgI NWs/AAO) composites have been fabricated by a simple approach, which involves the thermal melting of AgI powders on the surface of the AAO membrane, followed by the infiltration of the molten AgI inside the nanochannels. As-prepared AgI nanowires have corrugated outer surfaces and are polycrystalline according to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. X-ray diffraction (XRD) shows that a considerable amount of 7H polytype AgI exists in the composites, which is supposed to arise from the interfacial interactions between the embedded AgI and the alumina. AC conductivity measurements for the AgI nanowires/AAO composites exhibit a notable conductivity enhancement by three orders of magnitude at room temperature compared with that of pristine bulk AgI. Furthermore, a large conductivity hysteresis and abnormal conductivity transitions were observed in the temperature-dependent conductivity measurements, from which an ionic conductivity as high as 8.0 × 10(2)?Ω(-1)?cm(-1) was obtained at around 70?°C upon cooling. The differential scanning calorimetry (DSC) result demonstrates a similar phase transition behavior as that found in the AC conductivity measurements. The enhanced ionic conductivity, as well as the abnormal phase transitions, can be explained in terms of the existence of the highly conducting 7H polytype AgI and the formation of well-defined conduction paths in the composites.     

Si基有机光电探测器低阻欧姆电极制作

在Si单晶表面真空沉积有机半导体材料苝四甲酸二酐(PTCDA)可形成有机/无机异质结。利用铟锡氧化物(ITO)沉积在PTCD表面作为光的入射窗口,在其表面溅射Al/Ni接触电极,在氢气保护气氛中经350℃,3分钟合金化,其比接触电阻ρs达5.2×10-5.cm2。利用α台阶仪,原子力显微镜,紫外可见分光光度计及x射线衍射仪,对其形成良好低阻欧姆电极的工艺条件及表面和界面进行了分析讨论。     

Electric conductivity-tunable transparent flexible nanowire-filled polymer composites: orientation control of nanowires in a magnetic field

Cobalt compound nanowires were dispersed in a transparent nonconductive polymer film by merely stirring, and the film's transparency and electrical conductivity were examined. This composite film is a unique system in which the average length of the nanowires exceeds the film's thickness. Even in such a system, a percolation threshold existed for the electric conductivity in the direction of the film thickness, and the value was 0.18 vol%. The electric conductivity value changed from ～1 × 10(-12) S/cm to ～1 × 10(-3) S/cm when the volume fraction exceeded the threshold. The electric conductivity apparently followed the percolation model until the volume fraction of the nanowires was about 0.45 vol %. The visible light transmission and electric conductivity of the composite film of about 1 vol % nanowires were 92% and 5 × 10(-3) S/cm, respectively. Moreover, the electric conductivity in the direction parallel to the film surface did not depend on the amount of the dispersed nanowires, and its value was about 1 × 10(-14) S/cm. Even in a weak magnetic field of about 100 mT, the nanowires were aligned in a vertical and parallel direction to the film surface, and the electric conductivity of each aligned composite film was 2.0 × 10(-2) S/cm and 2.1 × 10(-12) S/cm. The relation between the average wire length and the electric conductivity was examined, and the effect of the magnetic alignment on that relation was also examined.     

Large-scale, hot-filament-assisted synthesis of tungsten oxide and related transition metal oxide nanowires

A scalable and versatile method for the large-scale synthesis of tungsten trioxide nanowires and their arrays on a variety of substrates, including amorphous quartz and fluorinated tin oxide, is reported. The synthesis involves the chemical-vapor transport of metal oxide vapor-phase species using air or oxygen flow over hot filaments onto substrates kept at a distance. The results show that the density of the nanowires can be varied from 10(6)-10(10) cm(-2) by varying the substrate temperature. The diameter of the nanowires ranges from 100-20 nm. The results also show that variations in oxygen flow and substrate temperature affect the nanowire morphology from straight to bundled to branched nanowires. A thermodynamic model is proposed to show that the condensation of WO(2) species primarily accounts for the nucleation and subsequent growth of the nanowires, which supports the hypothesis that the nucleation of nanowires occurs through condensation of suboxide WO(2) vapor-phase species. This is in contrast to the expected WO(3) vapor-phase species condensation into WO(3) solid phase for nanoparticle formation. The as-synthesized nanowires are shown to form stable dispersions compared to nanoparticles in various organic and inorganic solvents.     

衬底温度对Sn掺杂ZnO薄膜结构、电学和光学性能的影响

采用射频磁控溅射技术在石英衬底上制备了掺杂浓度为0.5％(原子分数)的ZnO∶Sn(TZO)薄膜,研究了不同衬底温度下薄膜的结构、形貌、电学和光学的性能.研究发现,TZO薄膜沿着C轴择优生长,在400℃时结晶度最好,最低电阻率为2.619×10-2Ω·cm,在可见光范围内具有较好的透光率.