Fabrication and characterization of dual-band organic/inorganic photodetector for optoelectronic applications

In this work, the optoelectronic performance of organic/inorganic heterojunction photodiode based on alpha-sexithiophene (α-6T/n-Si) is introduced. A thin film of α-6T was deposited on the n-type silicon substrate by a thermal evaporation technique. The topographical properties of the α-6T thin film grown on the n-Si substrate were investigated using a field emission scanning electron microscope (FESEM) technique. A network of nanocrystalline needles over the film surface was observed which give rise to an improvement in the electric charge transport. The optical properties of the prepared thin film were investigated using a spectrophotometric technique. The high absorption of α-6T in UV and visible region suggested the ability of this architecture for UV and visible light detection. The I-V characteristics of the fabricated photodiode were investigated in dark and under different illumination intensities and different wavelengths. The present architecture showed a good response to halogen lamb light, where the estimated values of rising and falling time at 160 mW/cm² were about 400 ms and 450 ms, respectively. The results show the possibility of using Au/α-6T/n-Si/Al structure as a photodetector for a wide range of the solar spectrum (UV–Visible).     

Room temperature weak ferromagnetism and magnetoconductance in functional CuO film

The granular CuO films are deposited on n-Si (1 0 0) and sapphire substrates using sol-gel route. Small microstrain leads to ∼5 times larger grain sizes (200-300 nm) and ∼2.5 times larger film thickness (∼0.57 μm) for sapphire than n-Si substrate, which are confirmed by X-ray diffraction and Atomic Force Microscopy. A diode-like current-voltage characteristics are observed for film deposited on n-Si substrate, which is absent for sapphire substrate. Typical manifestation of ferromagnetic character is observed for CuO films, which are strongly influenced by the substrates. Magnetic anisotropy is larger for sapphire substrate than n-Si substrate. At room temperature considerably large magnetoconductance ∼21% and soft ferromagnetic character of CuO film on n-Si substrate are attractive for functional applications.     

Hydrothermal synthesis and ferromagnetism of CuO nanosheets

Large quantity of CuO nanosheets was synthesized through hydrothermal method. The samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and superconducting quantum interference device. The results showed that the as prepared samples are monoclinic phase CuO with width of about 500 nm, length of about 1000 nm and thickness of 40-50 nm. Magnetic measurements revealed ferromagnetism was existed in the CuO nanosheets. The ferromagnetism could be attributed to the uncompensated spins on the surface of the nanosheets.     

n型硅微尖场发射电子能谱的模拟计算

结合金属的场发射电子能谱,模拟计算了场渗透对n型半导体硅微尖的场发射能谱的影响,并与n型硅微尖的场发射能谱实验结果进行了比较,讨论了模拟计算误差的来源。计算结果表明电场渗透现象导致硅的场发射能谱向低能方向偏移,表面电场越高,能谱的偏移量越大,其偏移程度可超过1eV。导致硅微尖的场发射能谱偏移的主要因素是半导体的场渗透现象。     

The influence of electronic transport across interface junction between Si substrate and the root of ZnO micro-prism on field emission performance

ZnO micro-prisms are prepared on the p-type and n-type Si substrates, separately. The $I$--$V$ curves analysed by AFM show that the interface junctions between the ZnO micro-prisms and the p-type substrate and between the ZnO micro-prisms and the n-type Si substrate exhibit p--n junction behaviour and ohmic contact behaviour, respectively. The formation of the p--n heterojunction and ohmic contact is ascribed to the intrinsic n-type conduction of ZnO material. Better field emission performance (lower onset voltage and larger emission current) is observed from an individual ZnO micro-prism grown on the n-type Si substrate. It is suggested that the n-Si/n-ZnO interfacial ohmic contact benefits the electron emission; while the p-Si/n-ZnO interface heterojunction deteriorates the electron emission.     

Hybrid solar cells with conducting polymers and vertically aligned silicon nanowire arrays: The effect of silicon conductivity

Organic/inorganic hybrid solar cells, based on vertically aligned n-type silicon nanowires (n-Si NWs) and p-type conducting polymers (PEDOT:PSS), were investigated as a function of Si conductivity. The n-Si NWs were easily prepared from the n-Si wafer by employing a silver nanodot-mediated micro-electrochemical redox reaction. This investigation shows that the photocurrent-to-voltage characteristics of the n-Si NW/PEDOT:PSS cells clearly exhibit a stable rectifying diode behavior. The increase in current density and fill factor using high conductive silicon is attributed to an improved charge transport towards the electrodes achieved by lowering the device's series resistance. Our results also show that the surface area of the nanowire that can form heterojunction domains significantly influences the device performance.     

Heterojunctions of TiO2 nanoparticle film and c-Si with different Fermi level positions

The photovoltaic properties of heterojunctions of titanium dioxide (TiO₂) nanoparticle films with single crystal silicon (c-Si) substrates with different Fermi level (E _f) positions were studied. The TiO₂ nanoparticles of rutile and anatase structures were studied without any sintering process. To clarify the photovoltaic properties, the characteristics of the heterojunction solar cells of TiO₂ nanoparticle films with p-Si and n-Si substrates were investigated, where several Si substrates with different resistivities were used. The I–V characteristics of p-Si/TiO₂ heterojunction showed the rectifying behavior and photovoltaic effect. The n-Si/TiO₂ heterojunction also showed good rectifying characteristics; however, the conversion efficiency was extremely lower than that of p-Si/TiO₂ heterojunction. The conversion efficiencies of various Si/TiO₂ (rutile) heterojunction solar cells against the Fermi level E _f of c-Si showed the maximum in the p-doped region. The photovoltaic properties of the Si/TiO₂ heterojunction also depended on the crystal structure of TiO₂, and the conversion efficiency of anatase is higher than that of rutile, which was attributed to the higher carrier mobility of anatase.     

Nanoplate-like CuO: hydrothermal synthesis,characterization, and electrochemical properties

Plate-like nanocrystalline CuO was synthesized via the hydrothermal process using copper nitrate trihydrate as inorganic precursor and 1,3-diaminoprapane which acts as a structure-directing template. The morphology, the structure, the crystallinity and the composition were studied through x-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). It was found that the hydrothermal reaction time had a marked effect on the morphology and particularly, on the particle size and the nature of the resulting products. The optical properties of the as-synthesized CuO nanoplatelets were studied by UV-visible diffuse reflectance spectra (DRS) and the values of the band were found to be 1.93 eV. Electrochemical measurements have revealed a reversible redox behavior with a doping/de-doping process corresponding to reversible cation intercalation/de-intercalation. This process is easier for the smaller sized Li⁺ cation compared to the larger Na⁺ cation and to the largest K⁺ cation.     

Cross-sectional characterization of cupric oxide nanowires grown by thermal oxidation of copper foils

CuO nanowires have been synthesized by heating a Cu foil in an ambient condition. The diameters of nanowires can be controlled by changing the annealing temperature. The morphology, composition, and structure were analyzed by using X-ray diffraction (XRD) and scanning electron microscope (SEM). To investigate the detailed layering structure of the substrates after oxidation, the cross-sectional analysis was also performed by using field emission-SEM and energy dispersive X-ray spectroscopy (EDX). The EDX measurements indicated that the CuO nanowires were grown on the CuO/Cu₂O layer, which was formed on the surface of Cu foil.     

Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection

A simple sonochemical route was developed for the preparation of gold nanoparticles/boron nitride sheets (AuNPs/BNS) nanocomposites without using reducing or stabilizing agents. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and UV–vis absorption spectra were used to characterize the structure and morphology of the nanocomposites. The experimental results showed that AuNPs with approximately 20 nm were uniformly attached onto the BNS surface. It was found that the AuNPs/BNS nanocomposites exhibited good catalytic activity for the reduction of H₂O₂. The modified electrochemical sensor showed a linear range from 0.04 to 50 mM with a detection limit of 8.3 μM at a signal-to-noise ratio of 3. The findings provide a low-cost approach to the production of stable aqueous dispersions of nanoparticles/BNS nanocomposites.     

Organic photodetectors: Role of multiple donor–acceptor interfaces

We have fabricated photodetectors based on electron–accepting and electron-donating organic materials. Multiple heterojunctions between the donor and acceptor layers were introduced. The thickness of the donor and acceptor materials was controlled in the molecular scale. By keeping the total thickness of the devices the same, we have studied the performance of the photodetectors as a function of the number of such molecular-level interfaces. The results showed that the number of donor–acceptor interfaces enhanced exciton dissociation but, at the same time, hindered charge transport by introducing energy barriers. We have shown that a trade-off between the two effects existed at an optimum number of donor–acceptor interfaces, where the device showed better photodetector performance.     

CuO薄膜的制备及其光伏特性

通过反应磁控溅射在n型硅和玻璃衬底上制备了p型CuO薄膜.使用X射线衍射仪和紫外-可见光-近红外光度计研究了p型CuO薄膜的结构和光学特性,得出其平均晶粒尺寸和光学带隙分别为8nm和1.36eV.通过研究其电压-电流关系确定了在p型CuO薄膜和n型硅衬底之间形成了p-n结.在AM 1.5光照条件下p-CuO/n-Si电池的开路电压为0.33V,短路电流密度为6.27mA/cm2,填充因数和能量转化效率分别为0.2和0.41%.     

Fabrication and characterization of thermal evaporated n-Si/ p-ZnTe thin film heterojunction diodes

The paper reports the fabrication and detailed electrical characterization of thermal evaporated n-Si/p-ZnTe thin film heterojunction diodes. The heterojunction diodes were prepared by depositing ZnTe films on n-Si substrates. The conduction mechanism, barrier height, space charge density and width of the depletion region were determined by I–V and C–V characteristics of the heterojunction diodes. The bandgap and activation energies of n-Si and p-ZnTe were also determined and a theoretical band diagram of n-Si/p-ZnTe heterojunction was drawn based on Anderson's model.     

Microwave-assisted synthesis of flower-like and leaf-like CuO nanostructures via room-temperature ionic liquids

Flower-like and leaf-like cupric oxide (CuO) single-crystal nanostructures have been successfully synthesized using ionic liquid 1-octyl-3-methylimidazolium trifluoroacetate ([Omim]TA) under the microwave-assisted approach. By controlling the concentration of [Omim]TA and reaction temperature, shape transformation of CuO nanostructures could be achieved in a short period of time. The results indicate that ionic liquid [Omim]TA plays an important role in the formation of different morphologies of CuO crystals. The crystal structure and morphology of products were characterized by X-ray powder diffraction (XRD), infrared spectrum (IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED). A possible mechanism for CuO nanostructure was proposed. In addition, UV-vis spectroscopy was employed to estimate the band gap energies of CuO crystals.     

The effect of external electric field on mass attenuation coefficients of some semiconductor

In this study, we measured the mass attenuation coefficient of n-type GaAs, p-type GaAs, n-type Si and Au/n-Si/n⁺Si/Al samples with and without external electric field. Samples were set in perpendicular direction to the 100?mCi ²⁴¹Am radioactive source and counts were made with a NaI(Tl) detector. It was observed that when an external electric field was applied onto the samples, mass attenuation coefficients were increased. Results showed that this study is consistent with previous studies.     

Green synthesis and characterization of gold nanoparticles using extract of anti-tumor potent Crocus sativus

In the present study, we have explored anti-tumor potent Crocus sativus (saffron) as a reducing agent for one pot size controlled green synthesis of gold nanoparticles (AuNps) at ambient conditions. The nanoparticles were characterized using UV–vis, scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and FTIR analysis. The prepared AuNPs showed surface Plasmon resonance centered at 549 nm with average particle size of 15±5 nm. Stable, spherical and triangular crystalline AuNPs with well-defined dimensions were synthesized using anti-tumor potent Crocus sativus (saffron). Crystalline nature of the nanoparticles is confirmed from the HR-TEM, SAED and SEM images, and XRD patterns. From the FTIR spectra it is found that the biomolecules are responsible for capping in gold nanoparticles.     

pH-Dependent Single-Step Rapid Synthesis of CuO Nanoparticles and Their Optical Behavior

This paper reports the pH-dependent growth of copper oxide (CuO) nanoparticles by wet chemical precipitation method using pH value of the samples as the only variable parameter. The phase purity, morphology, optical behavior, and elemental analysis of synthesized nanoparticles are shown to be critically dependent on the pH of the samples. Scanning electron microscope (SEM) results shows that a higher pH results well-defined CuO nanoflakes. X-ray powder diffraction (XRD) results disclosed that the growth of pure CuO with monoclinic structure at higher pH 8, whereas mixed phase was formed at lower pH 7. The average crystallite size of samples prepared at pH 8 to 10 was varying from 23.36 to 25.78 nm. The infrared spectroscopy showed that the O–H stretching peaks become narrow with an increase in the pH value. Optical results revealed the existence of the sharp absorption edges with precise excitonic features and photoluminescence bands both located at visible and near infrared spectral region attributed to the excellent optical behavior and narrow size distribution of particles. The additional near infrared band in photoluminescence spectrum located at 860 nm is attributed the defect-related luminescence. The growth mechanism of CuO nanostructures was discussed in the light of our findings.     

Growth of bicrystal CuO microsheets from aqueous solution

This Letter reports on a simple wet chemical approach to synthesize bicrystal cupric oxide (CuO) microsheets. The field-emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) show those microsheets typically present the uniform foldout-like shape. The portrait length of our products was in the range of 20–30 μm, and several micrometers of width. Electron diffraction studies implied that each CuO microsheet was a twin crystal.     

Magnetic and field emission properties of straw-like CuO nanostructures

This paper reports CuO straw-like nanostructures (nanostraws) synthesized on copper foil substrate through a simple solution method at room-temperature without using any template. The microstructure and morphological of CuO nanostraws were investigated by the X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM), revealing that the straw-like nanostructures were exhibited the nanocrystalline nature with monoclinic structure and monodispersed in large quantity. The possible growth mechanism for the formation of CuO nanostraws products was discussed in detail. In addition magnetic properties and field emission properties of as-obtained products were also investigated.     

Increased spectral sensitivity of Si photodetector by surface plasmon effect of Ag nanowires

Highly-sensitive Si photodetectors were prepared by using Ag nanowires (AgNWs). A transparent indium-tin-oxide (ITO) coating was coated on a Si substrate followed by spin-coating of AgNWs-containing solution. AgNWs having average length of 5–20 μm with a diameter of about 40–60 nm were observed in FESEM images. The haze effect of AgNWs was totally avoided because of the optimum value of diameter. The transmittance of above 85% was shown by AgNWs over a broad spectral range due to surface plasmon resonance effect. The AgNW-coated device showed an excellent rectifying ratio of 288. Under light illumination, AgNWs-coated device exhibited a significant photoresponse ratio of 5373. This advanced feature of AgNWs-templated method would be applied in broadband wavelength photodetection devices.