一步溶液法制备ZnO亚微米晶体棒及其发光性能

用硝酸锌(Zn(NO₃)₂·4H2O)或醋酸锌(Zn(CH₃COO)₂·2H2O)分别与六亚甲基四胺((CH₂)₆N₄)以等浓度0.005mol/L配制成两种反应溶液,通过化学溶液法在玻璃衬底上生长出ZnO六角型亚微米棒(长5~8μm,直径300~700nm)。测量了样品的XRD和扫描电镜像。经XRD分析,所得样品均为纤锌矿的ZnO六角型晶体。扫描电镜(SEM)像表明,生长时间为3h或5h时,样品为细长条的棒状结构,长径比超过10:1;生长48h后的ZnO亚微米棒的一端被腐蚀成一定深度的ZnO亚微米管。用负离子配位四面体生长模型分析了ZnO亚微米棒的生长机理。ZnO亚微米棒退火前后的光致发光谱表明,退火处理后的发射谱中的紫外峰消失,而红色发光峰红移并且增强(峰值由630nm左右移到710nm),同时它的激发光谱中的室温激子激发峰也增强。     

Al和Sb共掺对ZnO有序阵列薄膜的结构和光学性能的影响

采用水热合成法在预先生长的ZnO种子层的玻璃衬底上制备出Al和Sb共掺ZnO纳米棒有序阵列薄膜. 通过X射线衍射、扫描电镜、透射电镜和选区电子衍射分析表明:所制备的薄膜由垂直于ZnO种子层的纳米棒组成, 呈单晶六角纤锌矿ZnO结构, 且沿[001]方向择优生长, 纳米棒的平均直径和长度分别为27.8 nm和1.02 μm. Al和Sb共掺ZnO纳米棒有序阵列薄膜的拉曼散射分析表明:相对于未掺杂ZnO薄膜的拉曼振动峰(580 cm^-1), Al和Sb共掺ZnO阵列薄膜的E₁(LO)振动模式存在拉曼位移. 当Al和Sb的掺杂量为3.0at%,4.0at%,5.0at%,6.0at%时, Al和Sb共掺ZnO阵列薄膜的拉曼振动峰的位移量分别为3,10,14,12 cm^-1. E₁ (LO) 振动模式位移是由Al和Sb掺杂ZnO产生的缺陷引起的. 室温光致发光结果表明:掺杂Al和Sb后, ZnO薄膜在545 nm处的发光强度减小,在414 nm处的发光强度增加. 这是由于掺杂Al和Sb后, ZnO薄膜中Zn_i缺陷增加, O_i缺陷减少引起的. 关键词： Al和Sb共掺ZnO薄膜 纳米棒有序阵列 结构表征 拉曼散射     

MOCVD方法生长ZnO微米柱的结构与光学性质

通过X射线衍射、扫描电子显微镜和变温光致发光光谱对MOCVD方法生长在蓝宝石衬底上的ZnO微米柱材料的结构及发光特性进行了表征.X射线衍射结果表明,ZnO具有良好的c轴择优取向,扫描电子显微镜图中可观察出ZnO微米在呈六角结构生长,半径约为0.5～1.5μm.样品的发光光谱通过He-Cd激光器的325nm线激发,从光谱中发现低温(81K)下出现极强的与激子相关的带边发光峰,温度升高到360K时与自由激子相关的紫外发射峰仍然是清晰可见.     

In掺杂的ZnO纳米棒的共振Raman光谱研究

本文报道In掺杂ZnO纳米棒的成功制备和对其结构以及光荧光性能的详尽研究。在室温条件下ZnO的共振拉曼谱线容易受到很强的荧光干扰, 甚至导致共振拉曼谱线完全被湮没。微量In掺杂入ZnO纳米棒中, 调控紫外发光峰由378 nm(纯ZnO)红移至397 nm; 另外, 在制备过程中引入过量的氧, 在样品中产生大量缺陷, 降低了ZnO的紫外近带边发光峰强度。这两方面导致在室温下可清楚的观察到In掺杂ZnO纳米棒的6阶LO拉曼峰。     

微纳跨尺度ZnO结构的紫外发射机理研究

利用气相输运的方法在Si(100)衬底上生长了ZnO的微纳跨尺度结构.扫描电镜照片可以明显地看到样品表面为椎顶六角微米柱-纳米棒的复合结构.样品在室温下的光致发光谱出现了很强的紫外发射峰,没有观察到与杂质或缺陷相关的深能级发射,表明样品有很好的光学质量.通过详细的研究样品的紫外发射谱与温度(83—307K)的依赖关系,发现在室温下样品的近带边发射包含两个部分,分别与自由激子发射和自由载流子到施主(受主)的跃迁(FB跃迁)相关,这个施主(受主)束缚态的离化能为124.6meV. 关键词： ZnO微纳跨尺度结构 光致发光谱 自由载流子到施主(受主)的跃迁 自由激子发射     

ZnO纳米棒的低温溶液法制备、光电特性研究及其在有机/无机复合电致发光中的应用

利用水热法制备了垂直于衬底的定向生长的ZnO纳米棒,利用扫描电子显微镜及光致发光的方法对其形貌及光学特性进行了表征,利用场发射性能测试装置对ZnO纳米棒的场发射性能进行了测试.结果表明:利用水热法在较低的温度(95 ℃) 下生长了具有较好形貌和结构的ZnO纳米棒,并表现出了较好的场发射特性,当电流密度为1 μA/cm²时,开启电场是2.8 V/μm,当电场为6.4 V/μm时,电流密度可以达到0.67 mA/cm²,场增强因子为3360.稳定性测试表明,在5 h内,4.5 V/μm的电场下,其波动不超过25%.将制备的ZnO纳米棒应用到有机/无机电致发光中,其中ZnO纳米棒为电子传输层,m-MTDATA(4,4',4″-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine) 为空穴传输层,得到了ZnO的342 nm的紫外电致发光,此发光较ZnO纳米棒光致发光的紫外发射有约40 nm的蓝移. 关键词： ZnO纳米棒 场发射 水热法 有机/无机复合电致发光     

制备一维可控形貌的ZnO微米棒

用化学溶液法以醋酸锌和六亚甲基四胺为原料在玻璃衬底上生长出不同形貌的亚微米和微米ZnO棒。探讨了反应液的酸碱度和反应液浓度对生成的ZnO棒形貌的影响，并分析了其生长机制。通过控制一定的酸碱度和溶液浓度，可以得到规则的六角ZnO棒状阵列。这种规则的六角棒沿着[002]方向生长。测量了样品的XRD，扫描电镜像(SEM)，并对其发光性能进行了测量分析。其中规则六角ZnO棒的光致发光光谱中有一很强的峰值650nm红色宽谱带和一峰值约387nm的激子发光峰。激子发光峰加宽，实际上是自由激子的发光峰(380nm)和Zni的发光峰(430nm)的叠加。而红色发光峰可能是Vo2+中的电子和价带中的空穴辐射复合所致。     

ZnO亚微米和微米棒的晶体生长及发光性质

用硝酸锌Zn(NO3 )2·4H2O和六亚甲基四胺 (CH2 )6N4,通过化学溶液法在玻璃衬底上生长出ZnO六角形亚微米和微米棒(长 5~6μm,直径 0. 8 ~5μm)。生长时间达两天后,ZnO棒呈中空六角形微米管。测量了样品的X射线衍射(XRD)谱,扫描电镜像和喇曼光谱。ZnO微米棒的光致发光为橙红色宽谱带发射(峰值 630nm, 半峰全宽 250nm), 其激发光谱除带间本征激发(短于 370nm)外,还有很强的在导带底附近的室温激子激发峰(峰值 387nm,半峰全宽 30nm)。而阴极射线发光有两个发射峰,橙色宽谱带强峰 (峰值580nm,半峰全宽约为140nm)是缺陷发光峰,近紫外窄谱带弱峰(峰值 395nm,半峰全宽约为 20nm)是激子发光峰。     

石墨烯对ZnO微米棒光学特性的影响

采用化学气相沉积(CVD)方法制备了具有良好结晶质量和(002)择优取向的ZnO微米棒。在此基础上,选取单根ZnO微米棒,将其部分搁置于单层石墨烯表面。光致发光(PL)谱结果表明,石墨烯不仅增强了ZnO微米棒的紫外发光强度,同时也对光场在ZnO微米棒中的分布有很大的限域作用。分析认为这是由于石墨烯的表面等离子效应引起了ZnO微米棒与石墨烯之间的光-物质相互作用导致的。在拉曼(Raman)光谱中,石墨烯对ZnO微米棒的E2(L)声子振动模和E2(H)声子振动模的强度具有明显的减弱效应,这进一步证明二者之间存在光子的传输和电荷的转移,从而导致其晶格振动受到抑制。     

高质量ZnO微米棒的制备及其光学性质

利用水热法制备ZnO微米棒。醋酸镁[Mg(CH3COO)2.4H2O]、醋酸锌[Zn(CH3COO)2.2H2O]和六次甲基四胺(C6H12N4)以一定比例配置成反应溶液,把反应溶液加热到90℃,反应时间为24h,能够在硅衬底上生长高质量的ZnO微米棒。用扫描电镜(SEM)和X射线衍射仪对ZnO微米棒的晶体结构和表面形貌进行了分析,结果表明,样品为细长条棒状结构,呈现六方纤锌矿结构,长径比可达10∶1,并且在[002]方向择优生长。在样品中并未发现镁离子,它有可能扮演着催化剂的角色。对ZnO微米棒的光致发光性能进行测量,由PL光谱分析可知,样品在384nm处有一个紫外发光峰,半峰全宽为13nm,紫外发光峰强度比可见发光峰强度大的多,样品的质量较好。     

Shuttle-like ZnO nano/microrods: Facile synthesis, optical characterization and high formaldehyde sensing properties

Shuttle-like ZnO nano/microrods were successfully synthesized via a low temperature (80 °C), “green” (without any organic solvent or surfactant) and simple hydrothermal process in the solution of zinc chloride and ammonia water. X-ray diffraction and Raman spectroscopy indicated that the ZnO nano/microrods are a well-crystallized hexagonal wurtzite structure. Yet photoluminescence analysis showed that abundant intrinsic defects (52.97% electron donor defects and 45.49% electron acceptor defects) exist on the surface of ZnO crystals. Gas sensors based on the shuttle-like ZnO nano/microrods exhibited high sensitivity, rapid response-recovery and good selectivity to formaldehyde in the range of 10-1000 ppm at an optimum operating temperature of 400 °C. Through applying linear fitting to the plot of sensitivity versus formaldehyde concentration in logarithmic forms, the chemisorbed oxygen species on the ZnO surface were found to be O²⁻ (highly active among O₂, O₂⁻ and O⁻ species). Notably, formaldehyde can be easily distinguished from acetaldehyde with a selectivity of about 3. The high formaldehyde sensitivity is mainly attributed to the synergistic effect of abundant electron donor defects (52.97%) and highly active oxidants (surface adsorbed O²⁻ species) co-existed on the surfaces of ZnO.     

Characterization and optical property of ZnO nano-, submicro- and microrods synthesized by hydrothermal method on a large-scale

In the present paper, well-dispersed ZnO nano-, submicro- and microrods with hexagonal structure were synthesized by a simple low temperature hydrothermal process from zinc nitrate hexahydrate without using any additional surfactant, organic solvent or catalytic agent. The phase and structural analysis were carried out by X-ray diffraction (XRD), the morphological analysis was carried out by field emission scanning electron microscopy (FESEM) and the optical property was characterized by room-temperature photoluminescence (PL) spectroscopy. The results revealed the high crystal quality of ZnO powder with hexagonal (wurtzite-type) crystal structure and the formation of well-dispersed ZnO nano-, submicro- and microrods with diameters of about 50, 200 and 500 nm, and lengths of 300 nm, 1 μm and 2 μm, respectively, on a large-scale just using the different temperatures. Room-temperature PL spectrum from the ZnO nanorods reveals a strong UV emission peak at about 360 nm and no green emission band at ∼530 nm. The strong UV photoluminescence indicates the good crystallization quality of the ZnO nanorods. Room-temperature PL spectra from the ZnO submicro- and microrods reveal a weak UV emission peak at ∼400 nm and a very strong visible green emission at 530 nm, that is ascribed to the transition between V_oZn_i and valence band.     

Template-free hydrothermal synthesis of ZnO microrods for gas sensor application

Zinc oxide microrods with controlled diameter were prepared without the addition of template and additive by a simple hydrothermal route only using Zn(CH₃COO)₂·2H₂O as a precursor. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron diffraction (ED). The crystal structure of prepared ZnO microrods is hexagonal phase polycrystalline with zincite structure. With the increase of the precursor concentration from 0.05 M to 0.6 M, the diameter of the ZnO microrods increased from 1 μm to 5 μm. A localized oriented attachment mechanism was prepared to account for the formation of ZnO microrods. The gas-sensing performance experiments indicated that the prepared ZnO microrods exhibited highly sensitive, selective gas-sensing properties, and good stability to acetone vapor. The response and recovery time of ZnO-based gas sensor to 100 ppm acetone vapor are 12 s and 18 s, respectively. The mechanism of the ZnO-based sensor was investigated.     

Fabrication and characterization of ZnO micro and nanostructures prepared by thermal evaporation

A simple method of thermal evaporation to fabricate micro and nanostructures of zinc oxide was presented. ZnO micro and nanostructures, prepared under different quantity of O₂, were characterized by techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and analytical transmission electron Microscope. The SEM images indicated that the products prepared under the condition of sufficient O₂ were needle-like microrods and the samples synthesized under the condition of deficient O₂ were nanorods and nanowires with very high aspect ratio. The results of XRD and Raman shifts revealed that the ZnO micro and nanostructures synthesized under different quantity of O₂ were both single crystalline with the hexagonal wurtzite structure. The HRTEM images indicated that the ZnO nanowire prepared under the condition of deficient O₂ was single crystalline and grown along the direction of [0 0 1]. Photoluminescence measurement was carried out and it showed that the spectra of ZnO micro and nanostructures prepared under different quantity of O₂ exhibited similar emission features. In addition, the growth mechanism of ZnO micro and nanostructures was preliminarily discussed.     

Structural, optical and magnetic properties of Cr doped ZnO microrods prepared by spray pyrolysis method

A series of Cr-doped ZnO micro-rod arrays were fabricated by a spray pyrolysis method. X-ray diffraction patterns of the samples showed that the undoped and Cr-doped ZnO microrods exhibit hexagonal crystal structure. Surface morphology analysis of the samples has revealed that pure ZnO sample has a hexagonal microrod morphology. From X-ray photoelectron spectroscopy studies, the Cr 2p3/2 binding energy is found to be 577.3 eV indicating that the electron binding energy of the Cr in ZnO is almost the same as the binding energy of Cr³⁺ states in Cr₂O₃. The optical band gap E_g decreases slightly from 3.26 to 3.15 eV with the increase of actual Cr molar fraction from x = 0.00 to 0.046 in ZnO. Photoluminescence studies at 10 K show that the incorporation of chromium leads to a relative increase of deep level band intensity. It was also observed that Cr doped samples clearly showed ferromagnetic behavior; however, 2.5 at.% Cr doped ZnO showed remnant magnetization higher than that of 1.1 at.% and 4.6 at.% Cr doped samples, while 4.6 at.% Cr doped ZnO samples had a coercive field higher than the other dopings.     

Luminescence anisotropy of ZnO microrods

The local features of light emission from ZnO microrods were studied: it is revealed that ZnO luminescence spectra are significantly influenced by the crystal morphology. It is shown that the near and edge ultraviolet emission occurs primarily from the top (0001) planes of ZnO microrods; while the defect related visible emission was found to occur dominantly from the side facets. The room temperature cathodoluminescence analysis revealed that visible emission consists of a few overlapping peaks, arising due to recombination on common points and surface defects (Zn_i, V_o, V_o⁰/V_o^?*_, V_o^** and surface defects.). While at low temperature, only the luminescence due to neutral donor bound exciton (D⁰X) emission is observed. The data obtained suggest that the light emission spectra of ZnO material of diverse morphology cannot be directly compared, although some common spectral features are present.     

Excitation wavelength dependent photoluminescence intensity of six faceted prismatic ZnO microrods

This article presents the investigation on the large-scale synthesis of ZnO microrods with a simple low temperature hydrothermal method without using surfactants, organic solvents, or catalytic reagents. The synthesized ZnO powder is characterized with different techniques. The X-ray diffraction study reveals the excellent crystal quality of the ZnO product possessing the hexagonal (wurtzite-type) crystal structure. The scanning electron microscope observation confirms the formation of six faceted prismatic hexagonal ZnO microrods with the aspect ratio of 10. It also reveals that the ZnO microrods grow along the (0 0 0 1) direction and finally emerge with a sharp tip because of the existence of polar faces. The UV–vis spectrum shows a sharp absorption peak centered at 370 nm, which is in a good agreement with the equivalent bulk band gap value. The strong UV absorption peak implies the excellent crystal quality of the synthesized ZnO microrods. Room temperature photoluminescence spectroscopic study of the ZnO microrods with different excitation wavelengths reveals a strong band edge emission peak centered at 398 nm and a defect related visible blue emission peak at 460 nm. The decrease in photoluminescence intensity with negligible red shift in peak position is observed with increasing excitation wavelength.     

Fabrication and photoluminescence of P doped ZnO nanobelts by thermal evaporation method

Uniform and flat single crystal ZnO:P nanobelts (NBs) were fabricated on Si (1 0 0) substrates by the thermal evaporation method. The growth process, free-catalyst self-assembly vapor-solid (V-S) mechanism, was described and investigated deeply in terms of thermodynamics and kinetics. Then, the photoluminescence (PL) properties of ZnO NBs were studied in a temperature range from 10 to 270 K. At 10 K the recombination of acceptor-bound exciton (A⁰X) was predominant in the PL spectrum, and was attributed to the transition of P_Zn−2V_Zn complex bound exciton. The active energy of A⁰X and acceptor binding energy were calculated to be 17.2 and 172 meV, respectively. The calculated acceptor binding energy of P doped ZnO nanostructure is in good agreement with that of P doped ZnO film.     

Structural and optical properties of ZnO and Al-doped ZnO microrods obtained by spray pyrolysis method using different solvents

ZnO and Al-doped ZnO microrods were obtained by spray pyrolysis method using different solvents such as methanol and propanol. The effect of the type of solvent in the starting solution on the structural, morphological and optical properties of the samples was investigated. X-ray diffraction patterns showed that the undoped and Al-doped ZnO microrods exhibited hexagonal crystal structure with a preferred orientation along (0 0 2) direction. Surface morphology of the samples obtained by scanning electron microscopy revealed that undoped and Al-doped ZnO microrods grew as quasi-aligned hexagonal shaped microrods with diameters varying between 0.7 and 1.3 μm irrespective of solvents used. Optical studies indicated that microrods had a low transmittance (≅30%) and the band gap increased from 3.24 to 3.26 eV upon Al doping. Photoluminescence measurements indicated the existence of two emission bands in the spectra: one sharp ultraviolet luminescence at ∼383 nm and one broad visible emission ranging from 420 to 580 nm.