纳米ZnO光学性质研究进展

介绍了纳米ZnO常见发光谱的发光机制。在室温光致发光谱(PL)中,一般在380 nm处出现紫外发光,也有报道在357和377 nm处的紫外发光,列举了几种不同的发光解释。对于深能级发光,一般在400～550 nm出现连续的发光带,也有观察到深能级的声子伴线和声子复制现象。在低温光致发光谱的紫外发射中,一般观察到由自由激子发射(FX)、中性施主束缚激子发射(D0X)、施主-受主对跃迁峰(DAP)、中性施主束缚激子对应的双电子卫星峰(TES)以及声子伴线。综述了纳米ZnO的喇曼光谱、透射光谱、电致发光谱(EL)的特征,最后展望了纳米ZnO的光学性能研究前景。     

基于PLD法制备ZnO:Eu3+,Li+薄膜的发光性质研究

采用脉冲激光沉积(PLD)技术在Si(111)衬底上生长了Eu3+、Li+共掺杂的ZnO薄膜。分别对样品进行了X射线衍射(XRD)谱测试和光致发光(PL)谱分析,重点研究了退火处理对样品结构和发射光谱的影响。XRD谱测试表明,样品具有很好的C轴择优取向。PL谱研究表明,当用325nm光激发样品时,样品的发射光谱仅由ZnO基质的紫外发射和蓝光发射组成,并没有发现稀土Eu3+的特征发光峰;样品的蓝光发射源于电子从Zn填隙形成的浅施主能级到Zn空位形成的浅受主能级跃迁;和真空中退火的样品相比,O2中制备的样品的蓝光发射减弱,紫外发光增强。用395nm的光激发时,退火前样品分别在594nm和613nm处存在两个明显的Eu3+特征发光峰,退火后的样品仅发现Eu3+位于594nm的特征发光峰,这表明,退火处理不利于稀土离子的特征发射,但O2中退火的样品ZnO基质红绿波段发射光谱明显增强。     

Cu掺杂ZnO薄膜的结构及发光特性

采用溶胶-凝胶旋涂法在玻璃衬底上制备了不同Cu掺杂量的ZnO薄膜。用显微镜和X射线衍射(XRD)研究了Cu掺杂对ZnO薄膜形貌和微结构的影响。结果表明,制备得到的ZnO薄膜具有应变小和c轴择优取向。室温下测量了样品Zn1-xCuxO的光致发光(PL)谱,发现所有样品的PL谱中均观察到435nm左右的蓝光发光带,发光带强度与Cu的掺杂量有关;当x=0.06时,Zn1-xCuxO薄膜的PL谱中出现了较强的蓝光发射。分析了掺杂量对发光性能的影响,并对样品的发光机制进行了探讨,推断出蓝光峰来源于电子由导带底到锌空位(VZn)能级的跃迁及锌填隙(Zni)能级到价带顶的跃迁,它们可通过改变Cu的掺杂量予以控制。     

900℃空气退火对L-MBE生长的ZnO薄膜发光特性的影响

采用激光分子束外延法在蓝宝石衬底(0001)上生长了高度c轴择优取向的高质量ZnO薄膜,在空气中对生长的薄膜进行900℃退火处理,并对退火前后样品的结晶质量、发光特性采用X射线衍射(XRD)、变温光致发光(PL)研究.退火处理后的ZnO薄膜(0002)面XRDθ-2θ扫描曲线强度明显增强.在光致发光实验中,观测到薄膜分别在3.352,3.309和3.237eV附近有3个明显的近紫外发光峰,分别对应自由激子发射、中性施主或受主束缚激子I9及其声子伴线1Lo.随着温度升高,峰位逐渐向长波方向移动(即所谓"红移"),半高宽(FWHM)逐渐展宽;在发光谱中,来自于晶体缺陷的深能级(DL)区发光强度极小.     

900℃空气退火对L-MBE生长的ZnO薄膜发光特性的影响

采用激光分子束外延法在蓝宝石衬底(0001)上生长了高度c轴择优取向的高质量ZnO薄膜,在空气中对生长的薄膜进行900℃退火处理,并对退火前后样品的结晶质量、发光特性采用X射线衍射(XRD)、变温光致发光(PL)研究.退火处理后的ZnO薄膜(0002)面XRDθ-2θ扫描曲线强度明显增强.在光致发光实验中,观测到薄膜分别在3.352,3.309和3.237eV附近有3个明显的近紫外发光峰,分别对应自由激子发射、中性施主或受主束缚激子I9及其声子伴线1Lo.随着温度升高,峰位逐渐向长波方向移动(即所谓"红移"),半高宽(FWHM)逐渐展宽;在发光谱中,来自于晶体缺陷的深能级(DL)区发光强度极小.     

非掺杂n型氮化镓外延层的光致发光

研究了热处理对非掺杂 n型氮化镓外延层光致发光谱的影响和光谱中各发光带强度与温度之间的关系 .热处理后 ,光谱中的带边峰和黄光峰的强度较热处理前都有明显降低 .黄光峰强度随温度升高的衰减速度要比带边峰慢得多 .由这些实验结果得出结论 :光谱中的带边峰是由自由激子和束缚在一浅施主能级的束缚激子的谱线重合而成 ,这个浅施主能级很有可能是由氮空位产生 ;黄色荧光的机制应为自由电子或施主能级向深受主能级的跃迁 ,并且黄色荧光肯定和氮化镓中的一内部缺陷产生的深受主能级有关 ,该内部缺陷很有可能是镓空位 .     

非掺杂n型氮化镓外延层的光致发光

研究了热处理对非掺杂n型氮化镓外延层光致发光谱的影响和光谱中各发光带强度与温度之间的关系．热处理后,光谱中的带边峰和黄光峰的强度较热处理前都有明显降低．黄光峰强度随温度升高的衰减速度要比带边峰慢得多．由这些实验结果得出结论：光谱中的带边峰是由自由激子和束缚在一浅施主能级的束缚激子的谱线重合而成,这个浅施主能级很有可能是由氮空位产生;黄色荧光的机制应为自由电子或施主能级向深受主能级的跃迁,并且黄色荧光肯定和氮化镓中的一内部缺陷产生的深受主能级有关,该内部缺陷很有可能是镓空位．     

氧压与ZnO薄膜发光特性的关系研究

在不同的环境氧压下用脉冲激光沉积方法在Si(111)衬底上生长了ZnO薄膜,以325 nm He-Cd激光器为激发源获得了薄膜的荧光光谱以研究其发光特性,用X射线衍射仪(XRD)和原子力显微镜(AFM)研究了薄膜的晶体结构和表面形貌,结果表明氧压在20 Pa和50Pa之间制备的ZnO薄膜具有良好的紫外发光特性和较好的晶体质量.分析了ZnO薄膜的发光机理,认为薄膜紫外峰源自自由激子复合发光,绿光峰的发光机制与锌位氧OZn关系密切,氧空位是蓝光发射的重要原因.     

掺锂氧化锌纳米线的光致发光特性

氧化锌（ZnO）是直接宽带隙半导体材料,有高达60meV的激子束缚能,是下一代短波长光电材料的潜在材料。首先制备了优良的多孔氧化铝（Anodic Aluminum Oxide）有序孔洞阵列;以其为模板,采用直流电化学沉积的方法,在其规则排列的孔中沉积得到锌的纳米线;然后将其在高温下氧化,得到氧化锌的纳米线。XRD图显示Li掺杂前后的ZnO纳米线具有较好的晶态结构。对Li掺杂前后的ZnO纳米线进行光学特性测量,结果表明,ZnO纳米线有两个发光峰,分别位于382nm和508nm处;Li掺杂较大地改善了ZnO纳米线的发光性能,本征发光峰移到395nm处,蓝绿发光强度也有了很大程度的提高。     

Ar等离子体处理对GaAs纳米线发光特性的影响

采用Ar等离子体处理GaAs纳米线,通过光致发光测试研究了等离子体偏压功率对GaAs纳米线发光性能的影响。在不同测试温度和不同激发功率密度下,研究了发光光谱各个发光峰的来源和机制。研究结果表明:随着功率增加,GaAs自由激子发光逐渐消失,束缚激子发光强度先减小后增大;当功率增加到200 W时,出现施主-受主对(DAP)发光。通过对比不同样品在283℃下的发光光谱,得到了等离子体处理过程中GaAs纳米线的结构变化:当处理功率较小时,Ar等离子体在消除表面态的同时将空位缺陷引入GaAs中;当处理功率较大时,GaAs的晶体结构遭到破坏,形成施主类型的缺陷,出现DAP发光。     

Si(100)衬底对ZnO纳米线阵列生长方向的控制作用

采用热分解ZnO粉末法,以Au为催化剂,在Si(100)衬底上外延生长了ZnO纳米线阵列。用扫描电子显微镜(SEM)分析表明:ZnO纳米线的直径在100nm左右,长度约3μm,与衬底表面的夹角约为70.5°,纳米线具有四个特定的倾斜方向A,B,C,D。X射线衍射(XRD)图谱上只有ZnO(0002)衍射峰,说明ZnO纳米线沿C轴择优生长。结合Si与ZnO的晶格结构特征,理论研究得出ZnO纳米线与Si基片的晶格匹配关系为:[0001]_(ZnO)∥[114]_(Si),[0001]_(ZnO)∥[■■4]_(Si),[0001]_(ZnO)∥[1■4]_(Si),[0001]_(ZnO)∥[■14]_(Si),失配度为1.54%。得出了Si(100)衬底对ZnO纳米线生长方向具有控制作用的结论。     

Growth and characterization of ZnO nanowires grown on the Si(1 1 1) and Si(1 0 0) substrates: Optical properties and biaxial stress of nanowires

In this paper the effects of silicon substrates with different orientations on the morphological and optical properties as well as biaxial stress of ZnO nanowires were investigated. The ZnO nanowires were grown on Si(1 0 0) and Si(1 1 1) substrates by the vapor–solid (VS) method using a physical vapor deposition reactor. In addition ZnO nanowires were grown on Si(1 1 1) substrate by the vapor–liquid–solid (VLS) method using an Au film as catalyst, which were deposited on Si(1 1 1) substrate using a sputtering method, with the same conditions. Room temperature photoluminescence (PL) spectrum showed a stronger ultraviolet (UV) peak at 381 nm for the nanowires that were grown on Si(1 1 1) by the VS method than those that were grown on Si(1 0 0) with the same green emission (deep-level emission (DLE)) intensities at about 520 nm peak. On the other hand, the PL result of the ZnO nanowires, which were grown by the VLS method, showed the same intensities for the both UV and DLE peaks. Furthermore, the effects of silicon substrate orientation and Au catalyst on biaxial stress of the nanowires were studied by Raman spectrometer. It was discussed that Au catalyst was one of the important factors that could affect the biaxial stress value of the ZnO nanowires that were grown on Si substrates.     

Investigation of luminescence properties of ZnO nanowires at room temperature

The controllable growth processes of ZnO nanowires by evaporation of metal zinc with high purity and its luminescence properties have been investigated in detail. Firstly, the power of ZnO nanowires with high yield and homogeneous dimension was synthesized using the special quartz boat at 600 °C. Then, the oriented ZnO nanowires with about 20 nm diameter were synthesized by using a 90 nm-thick layer of ZnO nanocrystals on the Si substrate as the seed layer. Both fabrication processes are repeatable and no catalysts are necessary. Finally, photoluminescence (PL) spectroscopy for ZnO nanowires using an He-Cd laser line of 325 nm as the excitation source were measured at room temperature and both samples showed a sharp strong ultraviolet (UV) near-band edge emission. However, different UV peak positions (385 nm for ZnO nanowire powder, 377 nm for ZnO nanowire array) can be observed. The size confinement effect for excitons and carriers is proposed to explain the blue shift of the near-band edge emission with decreasing size and the native defects are responsible for the green emission.     

非晶SiO2纳米线的合成及其显微结构和光学性质的研究

本研究以硅片为衬底,热蒸发一氧化硅粉末在较低温度下合成了大量直径均匀的非晶SiO2纳米线.这些纳米线直径分布在15 nm～40 nm之间,长度几十微米.选区电子衍射(SAED)、能谱(EDS)、电子能量损失谱(EELS)分析结果表明这些纳米线为非晶SiO2纳米线.光致发光(PL)谱测试结果显示纳米线在波长550 nm处存在一个较强的PL峰.本文进一步指出了蒸发源SiO粉末的颗粒度和蒸发温度对纳米线生长有强烈的影响.     

Structure study of electrodeposited ZnO nanowires

In this work, we report on the structure study of electrodeposited ZnO nanowires. The samples were mounted as a working electrode and the deposition was performed in a classical three electrodes electrochemical cell. For obtaining ZnO nanowires, the working electrode was a polycarbonate membrane with a random distribution of nanometric pores, gilded one side to ensure electric contact. The morphology and structure characterizations of the different diameters ZnO nanowires were carried out by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The electrons pattern diffraction confirmed the same crystal structure of electrodeposited ZnO nanowires indexed by X-ray diffraction (XRD) on electrodeposited ZnO thin films: hexagonal ZnO phase with cell parameters a=0.32584 nm and c=0.52289 nm. Both TEM investigations and HRTEM images reveal a monocrystalline structure for electrodeposited ZnO nanowires. A roughness of few nanometers on the wire surface was observed. Meanwhile, no preferential growth direction has been obviously detected.     

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．     

Fabrication of Periodic Nanostructure Assemblies by Interfacial Energy Driven Colloidal Lithography

A novel interfacial energy driven colloidal lithography technique to fabricate periodic patterns from solution‐phase is presented and the feasibility and versatility of the technique is demonstrated by fabricating periodically arranged ZnO nanowire ensembles on Si substrates. The pattern fabrication method exploits different interfaces formed by sol–gel derived ZnO seed solution on a hydrophobic Si surface covered by a monolayer of colloidal silica spheres. While the hydrophobic Si surface prevents wetting by the seed solution, the wedge shaped regions surrounding the contact point between the colloidal particles and the Si substrate trap the solution due to interfacial forces. This technique allows fabrication of uniform 2D micropatterns of ZnO seed particles on the Si substrate. A hydrothermal technique is then used to grow well‐defined periodic assemblies of ZnO nanowires. Tunability is demonstrated in the dimensions of the patterns by using silica spheres with different diameters. The experimental data show that the periodic ZnO nanowire assembly suppresses the total reflectivity of bare Si by more than a factor of 2 in the wavelength range 400–1300 nm. Finite‐difference time‐domain simulations of the wavelength‐dependent reflectivity show good qualitative agreement with the experiments. The demonstrated method is also applicable for other materials synthesized by solution chemistry.     

Substrate effect on morphology and photoluminescence from ZnO monopods and bipods

A simple wet chemical bath deposition has been successfully deployed to fabricate zinc oxide (ZnO)nanostructures. For substrate free growth, the nanostructure is spindle like monopods. But when the nanostructures grow on the glass and quartz substrates, they are bipods (two monopods joined together base to base). Variation in the size of the spindles of the monopods and bipods and the particle size was observed due to the strain exists in the thin film due to lattice mismatch at the interface of the thin film and the substrates. The X-ray diffraction (XRD) and selected area diffraction results confirmed the hexagonal unit cell structures of the monopods and bipods. Also the growth rates of various planes are different and the growth is anisotropic. The substrate free grown monopods show visible photoluminescence (PL) at 421 nm. But the emission gets shifted by 3 and 6 nm for ZnO thin film deposited on quartz and glass substrates respectively due to interfacial strain. In case of ZnO on quartz substrate a strong ultra-violet (UV) peak was observed at 386 nm due to band edge transition. These emissions are also accompanied by few weaker emission peaks due to various defect related transition.     

Study of the Piezoelectric Power Generation of ZnO Nanowire Arrays Grown by Different Methods

The piezoelectric power generation from ZnO nanowire arrays grown on different substrates using different methods is investigated. ZnO nanowires were grown on n‐SiC and n‐Si substrates using both the high‐temperature vapor liquid solid (VLS) and the low‐temperature aqueous chemical growth (ACG) methods. A conductive atomic force microscope (AFM) is used in contact mode to deflect the ZnO nanowire arrays. No substrate effect was observed but the growth method, crystal quality, density, length, and diameter (aspect ratio) of the nanowires are found to affect the piezoelectric behavior. During the AFM scanning in contact mode without biasing voltage, the ZnO nanowire arrays grown by the VLS method produced higher and larger output voltage signal of 35 mV compared to those grown by the ACG method, which produce smaller output voltage signal of only 5 mV. The finite element (FE) method was used to investigate the output voltage for different aspect ratio of the ZnO nanowires. From the FE results it was found that the output voltage increases as the aspect ratio increases and starts to decreases above an aspect ratio of 80 for ZnO nanowires.