Improvement of visible light photocatalytic activity over graphene oxide/CuInS2/ZnO nanocomposite synthesized by hydrothermal method

In this study, graphene oxide/CuInS₂/ZnO as a new photocatalyst with light absorption properties in the visible region were successfully synthesized via hydrothermal route. The UV–vis absorption spectra of the catalyst suggested that the graphene oxide/CuInS₂/ZnO is active under visible light. It was evaluated the photocatalytic activities of graphene oxide/CuInS₂/ZnO on the degradation of Rhodamine B under visible light irradiation and was found that the graphene oxide/CuInS₂/ZnO obtained exhibit photocatalytic activity higher than single ZnO and CuInS₂/ZnO. Presence of graphene oxide with high specific surface area and great conductivity make it as a good support for CuInS₂/ZnO and improves removal efficiency for degradation of Rhodamine B.     

Composite structure of ZnO films coated with reduced graphene oxide: structural,electrical and electrochemical properties

ZnO films coated with reduced graphene oxide (RGO-ZnO) were prepared by a simple chemical approach.The graphene oxide (GO) films transferred onto ZnO films by spin coating were reduced to RGO films by two steps (exposed to hydrazine vapor for 12 h and annealed at 600 ℃).The crystal structures,electrical and photoluminescence properties of RGO-ZnO films on quartz substrates were systematically studied.The SEM images illustrated that RGO layers have successfully been coated on the ZnO films very tightly.The PL properties of RGO-ZnO were studied.PL spectra show two sharp peaks at 390 nm and a broad visible emission around 490 nm.The resistivity of RGO-ZnO films was measured by a Hall measurement system,RGO as nanofiller considerably decrease the resistivity of ZnO films.An electrode was fabricated,using RGO-ZnO films deposited on Si substrate as active materials,for super capacitor application.By comparison of different results,we conclude that the RGO-ZnO composite material couples possess the properties of super capacitor.     

Exploring the Origin of the Temperature‐Dependent Behavior of PbS Nanocrystal Thin Films and Solar Cells

Temperature‐dependent studies of the electrical and optical properties of cross‐linked PbS nanocrystal (NC) solar cells can provide deeper insight into their working mechanisms. It is demonstrated that the overall effect of temperature on the device efficiency originates from the temperature dependence of the open‐circuit voltage and the short‐circuit current, while the fill factor remains approximately constant. Extensive modeling provides signs of band‐like transport in the inhomogeneously coupled NC active layer and shows that the charge transport is dominated by diffusion. Moreover, via low temperature absorption and photoluminescence (PL) measurements, it is shown that the optical properties of PbS thin films before and after benzenedithiol (BDT) treatment exhibit very distinct behavior. After BDT treatment, both the optical density (OD) and PL are shifted to lower energies, indicating the occurrence of electronic wave function overlap between adjacent NCs. Decrease of the temperature leads to additional red‐shift of the OD and PL spectra, which is explained by the well‐known temperature dependence of the PbS NCs' bandgap. Moreover, BDT treated PbS NCs show unusual properties, such as decrease of the PL signal and broadening of the spectra at low temperatures. These features can be attributed to the partial relaxation of the quantum confinement and the opening of new radiative and nonradiative pathways for recombination at lower temperatures due to the presence of trap states.     

PLD法制备ZnO薄膜的退火特性和蓝光机制研究

通过脉冲激光沉积(PLD)方法,在O2中和100～500℃衬底温度下,用粉末靶在Si(111)衬底上制备了ZnO薄膜,在300℃温度下生长的薄膜在400～800℃温度和N2氛围中进行了退火处理,用X射线衍射(XRD)谱、原子力显微镜(AFM)和光致发光(PL)谱表征薄膜的结构和光学特性。XRD谱显示,在生长温度300℃时获得较好的复晶薄膜,在退火温度700℃时获得最好的六方结构的结晶薄膜;AFM显示,在此退火条件下,薄膜表面平整、晶粒均匀;PL谱结果显示,在700℃退火时有最好的光学特性。     

Synthesis of Highly Luminescent SnO2 Nanocrystals: Analysis of their Defect‐Related Photoluminescence Using Polyoxometalates as Quenchers

Colloidal semiconductor nanocrystals (NCs), called quantum dots (QDs), have been intensively studied because of their excellent photoluminescence (PL) quantum yields. However, commercial QDs such as CdSe and InP contain toxic or expensive rare elements, limiting their sustainable use. This study focuses on nontoxic, stable, and cheap tin oxides, and synthesized luminescent SnO₂ NCs of ≈2 nm in size by a heating‐up method. Tin precursors and diols in a high‐boiling point solvent with oleylamine as the surfactant are heated at 240 °C. SnO₂ NCs show defect‐related photoluminescence at 400–460 nm by excitation at 370 nm, achieving a high quantum yield of more than 60%. The PL intensity is stable even when the NCs are stored in atmospheric air at room temperature for over 1 year. The defect‐related emissions of the SnO₂ NCs are studied using polyoxometalates (POMs) as the PL quencher. POMs efficiently quench the PL emissions by extracting excited electrons from the conduction band and shallow surface defects. The results reveal that PL emissions from SnO₂ NCs are associated with radiative charge recombination via shallow defect levels on the surface and in the bulk, demonstrating the effectiveness of the PL quenching technique using POMs in studying the PL emission mechanism in QDs.     

Facile method for the preparation of high-performance photodetectors with a GQDs/perovskite bilayer heterostructure

A high-performance nitrogen doped graphene quantum dots (GQDs)/all-inorganic (CsPbBr₃) perovskite nanocrystals (NCs) heterostructure photodetector was fabricated on a quartz substrate, using the low cost spin coating technique followed by hot plate annealing. The GQDs/CsPbBr₃ NCs heterostructure photodetector exhibits a high overall performance with a photoresponsivity of 0.24 AW⁻¹, on/off ratio of 7.2 × 10⁴, and specific detectivity of up to 2.5 × 10¹² Jones. The on/off ratio of the hybrid device was improved by almost ten orders of magnitude, and the photoresponsivity was enhanced almost three times compared to the single layer perovskite NCs photodetector. The performance enhancement of the hybrid device was due to its highly efficient carrier separation at the GQDs/CsPbBr₃ NCs interface. This results from the coupling of the GQDs layer, which efficiently extracts and transports the photogenerated carriers, with the CsPbBr₃ NCs layer, which has a large absorption coefficient and high quantum efficiency. The interfacial charge transfer from the CsPbBr₃ NCs to the GQDs layer was demonstrated by the quenching in the photoluminescence (PL) spectra, and the fast-average decay time in the time-resolved photoluminescence (Trpl) spectra of the hybrid photodetector. Moreover, the performance-enhancement mechanism of the hybrid GQDs/CsPbBr₃ photodetector was elucidated by analyzing the band alignment of the GQDs and CsPbBr₃ under laser illumination.     

Bandgap Engineering in OH‐Functionalized Silicon Nanocrystals: Interplay between Surface Functionalization and Quantum Confinement

In this work, a systematic first‐principles study of the quasi‐band structure of silicon nanocrystals (Si‐NCs) is provided, focusing on bandgap engineering by combining quantum confinement of the electronic states with OH surface‐functionalization. A mapping between the bandgap, Si‐NC diameter, and the degree of hydroxide coverage is provided, which can be used as a guideline for bandgap engineering. Complementary to first‐principles calculations, the photoluminescence (PL) wavelength of Si‐NCs in the quantum‐confinement regime is measured with well‐defined diameters between 1 and 4 nm. The Si‐NCs are prepared by means of a microplasma technique, which allows a surfactant‐free engineering of the Si‐NCs surface with OH groups. The microplasma treatment technique allows us to gradually change the degree of OH coverage, enabling us, in turn, to gradually shift the emitted light in the PL spectra by up to 100 nm to longer wavelengths. The first‐principles calculations are consistent with the experimentally observed dependence of the wavelengths on the OH coverage and show that the PL redshift is determined by the charge transfer between the Si‐NC and the functional groups, while on the other hand surface strain plays only a minor part.     

退火对用PLD法制备ZnO薄膜的发光影响

用脉冲激光沉积(PLD)方法在Si(111)和蓝宝石衬底上制备的氧化锌薄膜,在不同的退火温度和不同的退火氛围中进行了退火处理.退火温度及退火氛围对ZnO薄膜的结构和发光特性的影响用X射线衍射(XRD)谱和光致发光谱进行了表征.实验结果表明,随着退火温度的提高,ZnO薄膜的压应力减小,并向张应力转化.在不同的退火温度退火...     

One-pot synthesis of ZnO/reduced graphene oxide nanocomposite for supercapacitor applications

ZnO/reduced graphene oxide (RGO) nanocomposite films were prepared by the sol–gel deposition method using a combination of zinc acetate and graphite. The solution derived composite films were extensively characterized using high resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–visible spectroscopy, photoluminescence emission measurements, and four probe measurements. It was found that a highly transparent film with low resistivity could be obtained with the addition of a small amount of RGO into the deposition precursor. The results also showed that the sintering temperature reduces the resistivity and transparency of the films. XRD measurements revealed that films sintered >500 °C exhibit additional peaks, and suggest nucleation of different phases of the films. As a demonstration, the ZnO/RGO composite was integrated into a supercapacitor, and the resulting energy storage performance was tested.     

Study on the fluorescence quenching of ZnO by graphene oxide

Zinc oxide (ZnO) microrod arrays were synthesized on Si substrate by a vapor phase transport (VPT) method in a tube furnace. The obtained ZnO microrods are characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The photoluminescence (PL) measurement indicates that the ZnO microrods have a strong ultraviolet (UV) emission centered at ~391 nm and a defect-related emission centered at ~530 nm. After the microrods were coated with graphene oxide (GO), the PL intensity of the hybrid microstructure is quenched compared with that of the bare one at the same excitation condition, and the PL intensity changes with the concentration of the GO. The fluorescence quenching mechanism is also discussed in this work.     

利用P-MBE在Si(111)衬底上生长氧化锌薄膜及其光学性质的研究

在Si(111)衬底上利用等离子体辅助分子束外延(P-MBE)生长氧化锌(ZnO)薄膜,研究了在不同衬底生长温度下(350～750℃)制备的ZnO薄膜的结构和光学性质．随着衬底温度的升高,样品的X射线及光致发光的半高宽度都是先变小后变大,衬底温度为550℃样品的结构及光学性质都比较好,这表明550℃为在Si(111)衬底上生长ZnO薄膜的最佳衬底温度;同时,我们还通过550℃样品的变温光致发光谱(81～300K)研究了ZnO薄膜室温紫外发光峰的来源,证明其来源于自由激子发射．     

The Effect of Substrate Material and Postannealing on the Photoluminescence and Piezo Properties of DC-Sputtered ZnO

Abstact Zinc oxide (ZnO) thin films were deposited on various substrates by DC sputtering deposition. Thermal annealing was performed at up to 1,200°C in N₂ for 30 min. The effect was investigated using x-ray diffraction (XRD), photoluminescence (PL) spectra, scanning electron microscopy (SEM), and piezoresponse force microscopy (PFM). The influence on PL response depends both on substrate material and annealing temperature. The PFM images reveal that the ZnO films have inversion domains. While annealing improves the piezoresponse, the inversion domains still persist. The cross-sectional analysis of the inversion domains shows domain boundary widths of approximately 1.5 nm. (Received ...; accepted ...)     

脉冲激光沉积法制备氧化锌薄膜

ZnO是一种新型的Ⅱ-Ⅵ族半导体材料,具有优良的晶格、光学和电学性能,其显著的特点是在紫外波段存在受激发射。利用脉冲激光沉积法(PLD)在氧气氛中烧蚀锌靶制备了纳米晶氧化锌薄膜,衬底为石英玻璃,晶粒尺寸约为28-35 nm。X射线衍射(XRD)结果和光致发光(PL)光谱的测量表明,当衬底温度在100-250℃范围内时,所获得的ZnO薄膜具有c轴的择优取向,所有样品的强紫外发射中心均在378-385 nm范围内,深能级发射中心约518-558 nm,衬底温度为200℃时,得到了单一的紫外光发射(没有深能级发光)。这归因于其较高的结晶质量。     

Simultaneous Reduction and Surface Functionalization of Graphene Oxide by Mussel‐Inspired Chemistry

This study presents a method of simultaneous reduction and surface functionalization of graphene oxide by a one‐step poly(norepinephrine) functionalization. The pH‐induced aqueous functionalization of graphene oxide by poly(norepinephrine), a catecholamine polymer inspired by the robust adhesion of marine mussels, chemically reduced and functionalized graphene oxide. Moreover, the polymerized norepinephrine (pNor) layer provided multifunctionality on the reduced graphene oxide that includes surface‐initiated polymerization and spontaneous metallic nanoparticle formation. This facile surface modification strategy can be a useful platform for graphene‐based nano‐composites.     

Preparation‐Condition Dependence of Hybrid SiO2‐Coated CdTe Nanocrystals with Intense and Tunable Photoluminescence

When aqueously prepared CdTe nanocrystals (NCs) are coated with a SiO₂ shell containing Cd ions and a sulfur source, they show a drastic increase in photoluminescence (PL) efficiency with a significant red shift and spectral narrowing after reflux. This is ascribed to the creation of a hybrid structure characterized by the formation of CdS‐like clusters in the vicinity of the NCs in the SiO₂ shell. Since these clusters are close to the NCs, their effective size increases to reduce the quantum size effect. The dependences of the PL properties on the preparation conditions are systematically investigated. The PL efficiency increases from 28% to 80% in the best case with a red shift of 80 nm. The PL behaviors differ from those of normal CdTe NCs and include less temperature quenching and longer PL lifetime. The SiO₂ coating enables bioconjugation with IgG without deterioration of PL efficiency, making hybrid NCs amenable for bioapplication.     

氢化对ZnO发光性质的影响

通过低温光致发光(PL)谱研究氢化对ZnO发光性质的影响.氢通过一个直流等离子体发生装置引入到ZnO晶体.研究发现氢的引入影响了束缚激子的相对发光强度,特别是氢化以后I4峰(3.363eV)的强度增加.与未氢化样品相比较,氢化样品显示出不同的温度依赖PL谱.在4.2K温度下,测量了氢化样品表面以下不同深度处的PL谱.研究发现I4峰的强度和I4峰与I8峰强度比随深度变化而变化,说明了在引入的氢和浅施主之间的直接联系.一般而言,氢化会增强带边发射并钝化绿光发射.     

Optical and thermal properties of precursor-controlled graphene–zinc nanocomposites

Graphene, a monolayer two dimensional carbon sheet can be utilized as a support to anchor functional nanomaterials to form novel nanocomposites for a variety of potential applications. We present an approach for the in situ preparation of graphene–zinc oxide nanocomposites through a reflux process in which either zinc acetate or zinc chloride can serve as precursors. The synthesized samples were characterized by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray analysis, ultraviolet–visible spectroscopy and thermogravimetry analysis (TGA–DSC) for structural, optical and thermal properties. It has been found that nanocomposites comprise of zinc oxide (ZnO) nanostructures deposited on graphene sheets, and the choice of zinc precursor has a deterministic influence on the morphology, structure and properties of the graphene–ZnO nanocomposites. In addition, the novel structure of zinc acetate based nanocomposite has induced improved absorption and thermal stability of the graphene/ZnO nanocomposite as compared to zinc chloride based nanocomposite and would be promising for future applications in nanotechnology.     

退火过程对c轴择优取向的ZnO薄膜的光学性质的影响

利用溶胶凝胶法在石英衬底上采用旋涂法制备出ZnO薄膜,通过X射线衍射仪发现不同的退火温度对ZnO薄膜的择优取向有很大影响;通过紫外可见分光光度计和室温发光谱可以看出,制备的薄膜有很好的光学透过性和很强的紫外发光特性,而不同的退火温度对其光学性质有很大的影响。实验发现采用此种方法在650℃左右退火是一个合适的退火温度,结构特性和光学性质都相对较好;采用热分析方法可知ZnO将在375℃左右从非晶转向结晶状态,因而在常规ZnO薄膜制备方法中增加一步500oC的热处理将有助于提高ZnO薄膜的结晶质量。     

Properties of Indium-Doped ZnO Films Prepared in an Oxygen-Rich Plasma

Indium-doped zinc oxide (ZnO:In) films were prepared in an Ar:O₂ plasma by reactive magnetron sputtering. The x-ray diffraction (XRD) patterns presented the crystal structures of ZnO:In films, while transmission spectra and photoluminescence (PL) spectra showed the changed band gap and the visible emission from defects, as compared to the PL spectra of undoped ZnO films. It was concluded that the increase of substrate temperature enhanced the crystal quality of ZnO:In films; the incorporation of In made the c-axis constant of the samples larger than that of undoped ZnO films; the blue emission was due to the transition from an unknown donor level by indium doping to the valance band; and the orange-green emission originated from acceptor defects (O_Zn) formed in the O-rich plasma. Meanwhile, the current- voltage characteristics and persistent photoconductivity phenomenon also could be explained by the increased acceptor defects (O_Zn) that formed when the substrate temperature was increased.     

Formation of Cu<Subscript>2</Subscript>O and ZnO Crystal Layers by Magnetron Assisted Sputtering and Their Optical Characterization

Copper (I) oxide and zinc oxide films are formed on silicon and glassy quartz substrates by magnetron assisted sputtering. The thickness of the films is tens and hundreds of nanometers. The films are grown at different substrate temperatures and different oxygen pressures in the working chamber. The film samples are studied by the X-ray diffraction technique, scanning electron microscopy, and optical methods. It is established that an increase in the substrate temperature yields a change in the surface morphology of copper (I) oxide films towards the formation of well-pronounced crystallites. The reflectance and Raman spectra suggest that the quality of such films is close to that of bulk Cu₂O crystals produced by the oxidation of copper. As concerns ZnO films, an increase in the substrate temperature and an increase in the partial oxygen pressure make it possible to produce films, for which a sharp exciton structure is observed in the reflectance spectra and the emission of excitons bound at donors is observed in the luminescence spectra.