CdSe电沉积层的组成及形成机理

伏安曲线和现场光电流测定用于研究在钛基体上阴极电沉积形成Cdse薄膜的机理. XPS实验表明, CdSe沉积层的组成与沉积电位、沉积时间和溶液组成有关.在0.1 mol·L~(-1)CdSO_4+4 mmol·L~(-1)H_2SeO_3+0.2 mol·L~(-1) H_2SO_4溶液中, 当电位比-0.50 V正时生成富Se层, 而当电位比-0.70 V还负时生成富Cd层. 在-0.69 V下沉积, 沉积层的Se/Cd计量比接近1.1. 在同一电位下, 若提高H_2Se0_3浓度, 则沉积物中Se的含量增多. 实验结果表明, CdSe电沉积因条件不同遵循两种不同的机理, 据此讨论了克服Se/Cd比大于1的可能措施。     

不同晶型纳米CdS的合成及其光催化活性

以醋酸镉为镉源,硫脲为硫源,采用配合物热分解法,通过改变硫脲/醋酸镉的摩尔配比,合成了具有不同晶型的纳米CdS．当n（S）／n（Cd）=0．5—3时,合成的CdS相分别为立方相（n（S）／n（Cd）=0．5）,立方相和六方相的混相（n（S）／n（Cd）=1．0～1．5）,六方相（n（S）／n（Cd）≥2）．通过XRD,TEM,UV—Vis光谱,IR光谱等对CdS的相组成,形貌,粒径,吸光性能,表面结构等进行了表征．光催化降解罗丹明B的活性结果表明,不同CdS相组成的活性顺序为立方相〉六方相〉混相（立方＋六方）,其中立方CdS相由于有较强的吸附作用、光吸收性能和较小的粒径（10～13nm）,对罗丹明B具有最好的光催化降解活性．     

Thin films of bicontinuous cubic mesostructured silica templated by a nonionic surfactant

Thin films ofbicontinuous cubic mesostructured silica were formed using the nonionic poly(oxyethylene)-alkyl ether surfactant Brij-56 as a structure-directing agent. The synthesis conditions were chosen such that the estimated volume fraction of surfactant in the silica/surfactant films corresponded approximately to the composition at which the bicontinuous cubic phase occurs in the water/surfactant phase diagram. Small-angle X-ray scattering and transmission electron microscopy measurements reveal that the cubic phase corresponds to the Ia3(-)d double-gyroid structure, with some distortion due to anisotropic film shrinkage. The cubic structure grows as faceted domains that are well-oriented with respect to the substrate and often occur in coexistence with a lamellar phase. By adjusting the temperature at which the films are aged, it is possible to create films with 2D hexagonal, cubic, or lamellar structures at a single composition.     

An sp2 and sp3 hybrid nanocrystalline carbon film electrode for anodic stripping voltammetry and its application for electrochemical immunoassay

A hybridized nanocrystalline carbon film electrode consisting of sp(2) and sp(3) bonds was investigated to reveal the reduction properties of Cd(2+) and for application as a highly sensitive and reliable electrochemical immunoassay. Conductive nanocrystalline carbon film consisting of about 60% sp(2) and 40% sp(3) bonds was fabricated using electron cyclotron resonance (ECR) sputtering equipment, and then the Cd(2+) concentrations were measured with an ECR sputtered carbon (ECR nano-carbon) electrode by employing an anodic stripping voltammetry (ASV) technique. The preconcentrated Cd was analyzed with Kelvin probe force microscopy and energy dispersive X-ray spectroscopy while observing the morphology change with an atomic force microscope and a scanning electron microscope. The preconcentrated Cd on the ECR nano-carbon electrode was revealed to be a thin sheet structure, which was significantly different from the Cd on a conventional carbon material that grows with a coralloid structure. The background current during an ASV measurement maintains a low level equivalent to that found with boron-doped diamond because the surface of the ECR nano-carbon is robust and angstrom-level flat. The carbon-electrode performance for ASV was improved by controlling its structure at a nanometer scale without any metal doping or coating. Finally, the ECR nano-carbon was used for biomolecular determination by electrochemical immunoassay with a CdSe nanoparticle label. Electrochemical immunoassay results were successfully obtained with the ECR nano-carbon, and they correlated well with fluorescence results obtained for CdSe nanoparticles.     

Use of the ternary phase diagram of a mixed cationic/glucopyranoside surfactant system to predict mesostructured silica synthesis

Mixed surfactant systems have the potential to impart controlled combinations of functionality and pore structure to mesoporous metal oxides. Here, we combine a functional glucopyranoside surfactant with a cationic surfactant that readily forms liquid crystalline mesophases. The phase diagram for the ternary system CTAB/H(2)O/n-octyl-beta-D-glucopyranoside (C(8)G(1)) at 50 degrees C is measured using polarized optical microscopy. At this temperature, the binary C(8)G(1)/H(2)O system forms disordered micellar solutions up to 72 wt% C(8)G(1), and there is no hexagonal phase. With the addition of CTAB, we identify a large area of hexagonal phase, as well as cubic, lamellar and solid surfactant phases. The ternary phase diagram is used to predict the synthesis of thick mesoporous silica films via a direct liquid crystal templating technique. By changing the relative concentration of mixed surfactants as well as inorganic precursor species, surfactant/silica mesostructured thick films can be synthesized with variable glucopyranoside content, and with 2D hexagonal, cubic and lamellar structures. The domains over which different mesophases are prepared correspond well with those of the ternary phase diagram if the hydrophilic inorganic species is assumed to act as an equivalent volume of water.     

Room temperature ferromagnetism in Mn-doped ZnS nanocrystalline thin films grown by sol–gel dip coating process

Nanocrystalline Zn_1?xMn_xS (x = 0.00, 0.01, 0.02, 0.03, 0.05, and 0.1) thin films having different Mn content were grown by the sol–gel dip coating process. The effect of Mn content on the structural, optical and magnetic properties of Zn_1?xMn_xS nanocrystalline thin films were investigated. X-ray diffraction results showed the presence of single hexagonal phase corresponding to ZnS with a preferred orientation along the ZnS (002) hexagonal plane direction without any detectable secondary phase, suggesting the incorporation of Mn ions into the ZnS lattice. Scanning electron microscope revealed the surface of the nanocrystalline films to be homogeneous and dense and the grains of the film surface were randomly scattered. In ultraviolet–visible measurements, the band gap energy corresponding to the absorption edge estimated were found to be 3.59–3.23 eV depending on the Mn doping ratio. Magnetic measurements showed that a paramagnetic behavior at 5 K and ferromagnetic behavior at 300 K.     

Control of metal-ion composition in the synthesis of ternary II-II'-VI nanoparticles by using a mixed-metal cluster precursor approach

The ternary molecular nanoclusters [Zn(x)Cd(10-x)Se4(SePh)12(PnPr3)4] (x = 1.8, 1 a; x = 2.6, 1 b) were employed as single-source precursors for the synthesis of high-quality hexagonal Zn(x)Cd(1-x)Se nanocrystals. The tellurium clusters [Zn(x)Cd(10-x)Te4(TePh)12(PnPr3)4] (x = 1.8, 2 a; x = 2.6, 2 b) are equally convenient precursors for the synthesis cubic Zn(x)Cd(1-x)E nanoparticles. The thermolysis of the cluster molecules in hexadecylamine provides an efficient system in which the inherent metal-ion stoichiometry of the clusters is retained in the nanocrystalline products, whilst also affording control of particle size within the 2-5 nm range. In all cases, the nanoparticles are monodisperse, and luminescence spectra exhibit emission energies close to the absorption edge. Analysis of the optical spectra and X-ray diffraction patterns of these materials indicates a metal-ion concentration gradient within the structures of the nanocrystals, with Zn(II) ions predominantly located near the surface of the particles.     

巯基乙酸为稳定剂在MWCNTs上原位生长CdSe量子点

以巯基乙酸作为稳定剂在无毒的溶剂中和较低的温度下实现了CdSe量子点在MWCNTs（多壁碳纳米管）上的原位生长,并用TEM、HRTEM、EDS、XRD、XPS和PL等工具对CdSe量子点-MWCNTs异质结（CdSe-MWCNTs）进行了表征.结果表明, CdSe量子点的晶型为立方晶型,平均粒径大约为4 nm, CdSe-MWCNTs也具有一定的荧光性质.     

Formation of Crystalline CdSe Particles from a Single‐Source‐Precursor according to Ostwald's Rule

The formation of crystalline CdSe particles in the thermal degradation of Cd(SePh)₂·TMEDA (TMEDA = tetramethylethylenediamine) as a single‐source‐precursor was investigated by in‐situ powder X‐ray diffraction. It was shown that the primary grains were formed in the cubic zinc blende modification. After an increase in particle size by further annealing a phase transition to the thermodynamically favored hexagonal wurtzite type was detected. This behaviour indicates that, according to Ostwald's rule, the primary grains consist of the less stable polymorph due to the lower activation barrier of its formation. When the volume energy of the particles gets dominant over the surface energy, the metastable form is transformed and the system adopts the modification of lowest energy.     

Surface-enhanced Raman scattering and polarized photoluminescence from catalytically grown CdSe nanobelts and sheets

We have successfully fabricated single-crystalline CdSe nanowires, nanobelts, and sheets by a chemical vapor deposition (CVD) method assisted with laser ablation. The synthesized CdSe nanostructures have hexagonal wurtzite phase as characterized by X-ray diffraction (XRD). CdSe nanobelts can range in length from several tens to a hundred micrometers, in thickness from 40 to 70 nm, and a tapered width which is approximately 3 microm at one end and tapers off to approximately 100 nm at a catalytic gold particle. Both selected area electron diffraction (SAED) and high-resolution transmission electron microscopic (HRTEM) measurements show that the single-crystalline hexagonal belts and sheets grew along the [0.1-1.0] direction with side surface of +/-(0 0 0 1) and top surface of +/-(2 -1 -1 0). While the growth mechanism of nanobelts complies with a combination of vapor-liquid-solid (VLS) and vapor-solid (VS) processes, the formation of sheets is primarily based on the VS mechanism. For comparison, the phonon modes of CdSe nanobelts and bulk powder have been measured by surface-enhanced Raman scattering (SERS) and normal Raman scattering (NRS) spectroscopies with off- and near-resonant excitations. A blue-shift of 2.4 cm(-1) for the longitudinal optical (LO) phonon of CdSe nanobelts, relative to bulk CdSe, is attributed to a lattice contraction in the belt structure, which is confirmed by the XRD measurement. Room-temperature microphotoluminescence (PL) at approximately 1.74 eV from single CdSe nanobelts shows a 3-fold enhancement compared to that from bulk CdSe powder and displays a partial polarization dependence of emission angles.     

NaGdF4:Eu3+/AAO薄膜的制备与表征

采用水热法在多孔阳极氧化铝(AAO)模板上制备了NaGdF<,4>:Eu<'3+>(摩尔分数5.0%)/AAO薄膜,并研究了制备方法、溶液浓度和退火温度对薄膜样品形貌、结构和发光性质的影响.XRD结果表明,在低于500 ℃退火,得到具有NaGdF<,4>六方相结构的NaGdF<,4>:Eu<'3+>/AAO薄膜;而在5...     

Synthesis and characterization of water-soluble CdSe nanoparticles capped by AOT

Water-soluble CdSe nanoparticles were synthesized using AOT (sodium bis(2-ethylehexyl)-sulfosuccinate) as stabilizer, cadmium acetate and Na2SeSO3 as precursors in aqueous phase. The influence of some key factors, such as reaction time, temperature, concentration and molar ratio of precursors on the optical properties of CdSe nanoparticles was systematically investigated through UV-Vis and PL spectra. Powder X-ray diffraction (XRD) was used to characterize the crystalline structure of synthesized CdSe nanoparticles. As-prepared CdSe nanoparticles exhibit an apparent quantum confinement effect and typical hexagonal wurtzite structures. Finally, the optimal experimental conditions were obtained.     

Nature of phase transitions in crystalline and amorphous GeTe-Sb2Te3 phase change materials

The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous Ge(1)Sb(2)Te(4) (GST124) phase change materials as a function of pressure and temperature using high-resolution synchrotron x-ray diffraction in a diamond anvil cell. The phase transformation sequences upon compression, for cubic and hexagonal GST124 phases are found to be: cubic → amorphous → orthorhombic → bcc and hexagonal → orthorhombic → bcc. The Clapeyron slopes for melting of the hexagonal and bcc phases are negative and positive, respectively, resulting in a pressure dependent minimum in the liquidus. When taken together, the phase equilibria relations are consistent with the presence of polyamorphism in this system with the as-deposited amorphous GST phase being the low entropy low-density amorphous phase and the laser melt-quenched and high-pressure amorphized GST being the high entropy high-density amorphous phase. The metastable phase boundary between these two polyamorphic phases is expected to have a negative Clapeyron slope.     

CdO as the archetypical transparent conducting oxide. Systematics of dopant ionic radius and electronic structure effects on charge transport and band structure

A series of yttrium-doped CdO (CYO) thin films have been grown on both amorphous glass and single-crystal MgO(100) substrates at 410 degrees C by metal-organic chemical vapor deposition (MOCVD), and their phase structure, microstructure, electrical, and optical properties have been investigated. XRD data reveal that all as-deposited CYO thin films are phase-pure and polycrystalline, with features assignable to a cubic CdO-type crystal structure. Epitaxial films grown on single-crystal MgO(100) exhibit biaxial, highly textured microstructures. These as-deposited CYO thin films exhibit excellent optical transparency, with an average transmittance of >80% in the visible range. Y doping widens the optical band gap from 2.86 to 3.27 eV via a Burstein-Moss shift. Room temperature thin film conductivities of 8,540 and 17,800 S/cm on glass and MgO(100), respectively, are obtained at an optimum Y doping level of 1.2-1.3%. Finally, electronic band structure calculations are carried out to systematically compare the structural, electronic, and optical properties of the In-, Sc-, and Y-doped CdO systems. Both experimental and theoretical results reveal that dopant ionic radius and electronic structure have a significant influence on the CdO-based TCO crystal and band structure: (1) lattice parameters contract as a function of dopant ionic radii in the order Y (1.09 A) < In (0.94 A) < Sc (0.89 A); (2) the carrier mobilities and doping efficiencies decrease in the order In > Y > Sc; (3) the dopant d state has substantial influence on the position and width of the s-based conduction band, which ultimately determines the intrinsic charge transport characteristics.     

Amphiphilic N-benzoyl-1-amino-1-deoxy-D-glucitol derivatives forming thermotropic lamellar, columnar and different types of cubic mesophases

Novel amphiphilic glucamine derivatives have been synthesized. These are N-benzoyl-1-deoxy1-methylamino-D-glucitols and N-benzoyl-1-amino-1-deoxy-D-glucitols carrying one, two or three aliphatic chains (CnH2n 1O- with n 3, 6 and 12) grafted to the benzamido group. The thermotropic mesophases of these compounds were studied by thermal polarizing optical microscopy and differential scanning calorimetry, and some also by X-ray scattering. Depending on the number and the length of the alkyl chains lamellar, bicontinuous cubic, hexagonal columnar or inverted micellar cubic mesophases were detected by analogy with lyotropic systems. In the contact region between lamellar phases of the single chain amphiphiles and micellar cubic phases of the mesomorphic triple chain compounds, hexagonal columnar phases can be induced. A hexagonal columnar phase was also induced in the contact region between a bicontinuous and a micellar cubic mesophase. The lyotropic liquid crystalline behaviour of the dodecyloxy substituted N-benzoyl-1-deoxy-1-methylamino-D-glucitols was investigated by the solvent penetration method using ethylene glycol as protic solvent. On increasing the solvent content, the double chain compound forms a cubic and a lamellar mesophase and the triple chain compound forms a hexagonal columnar lyomesophase. The dodecyloxy substituted compounds were also investigated with respect to their behaviour as thin films at the air-water interface using a Langmuir film-balance. Different types of pi/Aisotherms were observed whereby the molecular areas at collapse were determined either by the size of the carbohydrate head group (single chain compounds) or by the number of alkyl chains (double and triple chain compound).     

A study of cadmium sulfide nanocrystalline films by grazing incidence X-ray diffraction

Thin cadmium sulfide films were prepared on a monocrystalline-crystal silicon substrate by chemical deposition from aqueous solutions. Grazing incidence X-ray diffraction revealed that the cadmium sulfide films are comprised of nanocrystal particles, with 80% of the particles having a size of 5 ± 1 nm. Some nanocrystals have a wurtzite structure, while others, a sphalerite one. The presence of cubic phase in the films is indicative of a nonequilibrium state of the nanocrystalline films. Thirty minutes after the onset of the formation of cadmium sulfide, the size and crystal structure of the constituent particles of the film become independent of the deposition time—only the film thickness increases. In addition, the initial stage of the formation of the cadmium sulfide film is accompanied by the deposition of cadmium hydroxide Cd(OH)₂.     

Photocatalytic patterning of monolayers for the site-selective deposition of quantum dots onto TiO2 surfaces

A novel photochemical mechanism is reported for the site-selective deposition of quantum dots onto nanocrystalline TiO2 films. The patterning mechanism involves the combination of surfactant-mediated self-assembly and monolayer photolithography. In the self-assembly process, CdS and CdSe quantum dots were attached to TiO2 surfaces through bifunctional mercaptoalkanoic acid (MAA) linkers. MAAs were adsorbed to the TiO2 surface as the deprotonated carboxylates, primarily through monodentate coordination to Ti4+ sites. CdSe quantum dots were bound to the terminal thiol groups of surface-adsorbed MAAs, with a surface adduct formation constant, Kad, of (2.1 +/- 0.7) x 104 M-1. The color and optical density of the quantum dot-functionalized TiO2 films were tunable. Monolayer photopatterning involved the TiO2-catalyzed oxidative degradation of surface-adsorbed mercaptohexadecanoic acid (MHDA). A mechanism is proposed wherein MHDA degradation occurs through both oxidative decarboxylation and the formation of interchain disulfides. These MHDA photodegradation processes regulate the extent to which CdSe quantum dots adsorb onto the TiO2 surface. Illumination through a photomask yielded optically patterned, quantum dot-functionalized TiO2 films that were characterized by scanning electron microscopy and energy-dispersive X-ray analysis.     

电化学沉积CdSe纳晶薄膜的性能及沉积机理

电化学沉积是半导体薄膜制备的一种简便方法,常用于Ⅱ-族化合物半导体薄膜的制备.通过电沉积条件的适当改变可成功地在导电衬底上制备半导体纳晶薄膜^[1].CdSe薄膜作为一种透光性好、导电性好的半导体材料,可进行光学性能和光电性能方面的研究,而半导体纳晶多孔电极的光电化学特性与体材料之间有很大不同.本文采用电化学沉积法制备了CdSe纳晶薄膜并研究了其性能,通过扫描隧道显微镜(STM)形貌分形分析进一步研究其沉积机理.     

Effects of Dissipation on Contact Angle Measurements Using a Dynamic Method

We report studies of the effect of hydrothermal treatment on physical properties such as crystalline phase, size, and morphology of nanosized cadmium sulfide (CdS) particles. CdS precipitates have been synthesized by the reaction of Cd(NO(3))(2) with Na(2)S at room temperature. These CdS precipitates have been hydrothermally treated in the range 120-240 degrees C with variation of the treatment time. The effects of acid catalysts and other additives were also investigated. The particles prepared were characterized by XRD, TEM, and BET methods. With increased hydrothermal treatment temperature and time, crystallization from amorphous to crystalline form, cubic or hexagonal, and an increase of particle size occurred. CdS particles of well-developed hexagonal form were obtained at a hydrothermal treatment temperature of 240 degrees C; the primary hexagonal grain size was on the order of 20-30 nm. The addition of an acid catalyst, HCl, or of Cd(NO(3))(2) into the precipitate sol promoted crystal growth and phase transformation during the hydrothermal treatment, but another additive, Na(2)S, showed the opposite trend. It appears that hydrothermal treatment combined with proper additives could be an effective method for preparation of nanosize crystalline CdS particles. Copyright 2001 Academic Press.     

In situ Raman spectroscopy of H2 interaction with WO3 films

It is well known that WO(3) interacts efficiently with H(2) gas in the presence of noble metals (such as Pd, Pt and Au) at elevated temperatures, changing its optical behaviors; and that its crystallinity plays an important role in these interactions. For the first time, we investigated the in situ Raman spectra changes of WO(3) films of different crystal phases, while incorporating Pd catalysts, at elevated temperatures in the presence of H(2). The Pd/WO(3) films were prepared using RF sputtering and subsequently annealed at 300, 400 and 500 °C in air in order to alter the dominant crystal phase. The films were then characterized using SEM, XRD, XPS, and both UV-VIS and Raman spectroscopy. In order to fundamentally study the process, the measurements were conducted when films were interacting with 1% H(2) in synthetic air at elevated sample temperatures (20, 60, 100 and 140 °C). We suggest that the changes of Raman spectra under such conditions to be mainly a function of the crystal phase, transforming from monoclinic to a mix phase of monoclinic and orthorhombic achieved via increasing the annealing temperature. The as-deposited sample consistently shows similar Raman spectra responses at different operating conditions upon H(2) exposure. However, increasing the annealing temperature to 500 °C tunes the optimum H(2) response operating temperature to 60 °C.