ZnO纳米颗粒受激发射的时间分辨特性

在飞秒脉冲激光激发下,观察到了均匀沉积法获得的ZnO纳米颗粒的受激辐射现象,并从频域和时域两方面研究了ZnO纳米多晶的室温激射特性。氧化锌纳米颗粒中出现激子-激子散射导致的激射阈值为7.2 GW·cm-2,激射模式类似于F-P谐振腔模式,时域谱则表现为寿命曲线中出现快速衰减成分。与荧光的时间衰减曲线不同,P带时间衰减具有对称结构,高斯拟合结果只有几个ps,接近条纹相机的时间分辨率极限。研究ZnO纳米颗粒的受激发射与激光特性对揭示ZnO晶体的内部结构和激子激发态的性质、激光产生的机理等有重要意义。     

磁控溅射制备ZnO薄膜的受激发射特性的研究

用射频磁控反应溅射法在二氧化硅衬底上制备ZnO薄膜。得到了在不同温度下ZnO薄膜的吸收与光致发光。观测到了纵光学波 (LO)声子吸收峰与自由激子吸收峰 ;室温 (30 0K)下 ,PL谱中仅有自由激子发光峰。这些结果证实了ZnO薄膜具有较高的质量。探讨了变温ZnO薄膜的发光特性。研究了ZnO薄膜的受激发射特性。     

ZnCdTe-ZnTe多量子阱的光泵受激发射

本文报导了ZnCdTe-ZnTe多量子阱的受激发射机理.阈值时(J_th)受激发射峰相对于激子吸收峰的能量差(19meV)与激子束缚能接近.激发光强度在3J_th～4.8J_th之间变化时,该能量差随激发光强度的变化规律与激子-激子散射过程的理论结果符合得很好,从而把该材料在上述激发光强内的受激发射机理归结为激子-激子散射过程.     

纳米结构ZnO晶体薄膜室温紫外激光发射

文章综述了纳米结构的氧化锌半导体薄膜在室温下自由激子的自发辐射以及由自由激子引起的受激发射的特性，阐述了在不同激发密度下室温紫外受激发射的机理．纳米结构氧化锌半导体薄膜是用激光分子束外延(L-MBE)技术生长在蓝宝石衬底上的．薄膜由密集而规则排列的纳米尺度的六角柱组成．这些纳米六角柱起着限制激子运动的作用，激子的量子尺寸效应，使激子的跃迁振子强度大幅度增强．同时六角柱之间的晶面组成了一个天然的激光谐振腔．室温下用三倍频的YAG脉冲激光激发，可从这些纳米结构的氧化锌薄膜中观测到很强的紫外激光发射．研究发现，在中等激发密度下，紫外受激发射是由于激子与激子间碰撞而引起的辐射复合．在高密度激发条件下，由于激子趋于离化，紫外受激发射主要由电子-空穴等离子体的辐射复合引起．由于纳米结构中激子的跃迁振子增强效应，在室温下测量到的光学增益高达320cm^-1，这比在同样条件下测量到的块状氧化锌晶体的光学增益要高一个量级以上．与传统的电子-空穴等离子体激光辐射相比，激子引起的受激发射可在较低的激发密度条件下实现．这在实际应用上很有价值．     

ZnCdTe-ZnTe多量子阱的光泵受激发射

本文报导了ＺｎＣｄＴｅ－ＺｎＴｅ多量子阱的受激发射机理．阈值时（Ｊｔｈ）受激发射峰相对于激子吸收峰的能量差（１９ｍｅＶ）与激子束缚能接近．激发光强度在３Ｊｔｈ～４．８Ｊｔｈ之间变化时，该能量差随激发光强度的变化规律与激子—激子散射过程的理论结果符合得很好，从而把该材料在上述激发光强内的受激发射机理归结为激子－激子散射过程     

ZnO薄膜受激发射特性的研究

氧化锌薄膜因其大的激子结合能和强的光发射、激光阈值低和能在高温下工作等优点而成为制备短波长激光、发光二极管等光电子器件的有希望材料。采用激光分子束外延 (L MBE)方法制备了ZnO薄膜。在室温下 ,测量了样品的吸收光谱 ,以及不同光泵浦强度下的发射光谱。从光谱图中可以看出该材料有很好的质量。研究了ZnO薄膜的受激发射特性及机理 ;测量了发射光强与泵浦光强之间的关系 ;比较了较高激发密度下的受激发射、自发发射和激光脉冲的时间特性 ,这些都证实了该发射是受激发射。     

高质量纳米ZnO薄膜的光致发光特性研究

报道了利用低压-金属有机物化学气相沉积技术生长纳米ZnS薄膜，然后，将ZnS薄膜在氧气中于800℃温度下进行热氧化制备高质量纳米ZnO薄膜.x射线衍射结果表明，纳米ZnO薄膜具有六角纤锌矿多晶结构.室温下观察到一束强的紫外(3.26 eV) 光致发光和很弱的深能级发射.根据激子峰的半高宽度与温度的关系确定了激子-纵向光学声子（LO）的耦合强度（ГLO）.由于量子限域效应使ГLO减少较多. 关键词： 光致发光 热氧化 激子 纳米ZnO薄膜     

高性能ZnO纳米块体材料的制备及其拉曼光谱学特征

利用六面顶高压设备制备了高密度、低脆性、纳米级的ZnO块体材料，用MDI/JADE5 X射线衍射仪(Cu靶)和XL30S-FEG场发射扫描电子显微镜对高压样品的相组成、晶粒尺寸及微观形貌进行了表征.利用E55+FRA106/5傅里叶变换激光拉曼光谱仪通过ZnO块体样品位于50—500cm^-1之内的拉曼光谱, 研究了极性半导体纳米材料的拉曼光谱学特征.发现在极性半导体ZnO纳米块体材料中，没有出现明显的尺寸限制效应. 关键词： ZnO纳米块体 拉曼光谱 尺寸限制效应     

纳米微晶结构ZnO及其紫外激光

本文介绍了近年来研制Ⅱ Ⅵ族半导体激光器的一个新的途径———ZnO的纳米微晶结构。它分为两大类别 :即六角柱形蜂巢状结构和粉末状颗粒结构。都已在近紫外波段实现了室温下光泵激发的受激发射。它将是继Ⅱ Ⅵ族硒化物和Ⅲ Ⅴ族氮化物之后的新型半导体激光器材料。     

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     

Decay dynamics of ultraviolet photoluminescence in ZnO nanocrystals

Time resolved photoluminescence (PL) measurements at low temperature are performed on colloidal ZnO nanocrystals dispersed in t-butanol. Considering the particle size dependence of the decay times we conclude that the luminescence is composed of two trap related emissions one of which undergoes lifetime shortening due to a non-radiative process. Initial fast shift of the spectrum within 30 ps is observed and it is interpreted as a fast hole cooling just after the excitation.     

Room temperature ferromagnetic pure ZnO

Pure ZnO films were prepared by pulsed laser deposition on oxidized Si substrates under different oxygen pressure and substrate temperature. Clear room temperature ferromagnetism has been observed in the ZnO film prepared under high vacuum and room temperature. The observation of anomalous Hall effect confirms the intrinsic nature of the ferromagnetism. The photoluminescence and X-ray photoelectron spectroscopy spectra show the high concentration of oxygen vacancies in the ferromagnetic ZnO film. Our results clearly demonstrate the ferromagnetic contribution of the oxygen vacancies mediated by the spin polarized electrons hopping between discrete states in pure ZnO.     

Room temperature magnetism of Fe doped CdS nanocrystals

Undoped and Fe doped CdS nanocrystals with Fe content of 2–5 at% of average crystallite size 1.2–2 nm have been obtained using chemical co-precipitation method with 2-mercaptoethonal as capping agent at 80 °C. X-ray diffraction (XRD) results showed that the undoped CdS nanocrystals were in mixed phase of cubic and hexagonal, where as the doped CdS nanocrystals were in hexagonal phase. Room-temperature ferromagnetism has been observed in Fe-doped CdS nanocrystals. Magnetic studies indicated diamagnetism in undoped, ferromagnetism in lightly doped (2 and 3 at%) and paramagnetism in samples of higher Fe content (4 and 5 at%). The substitutional incorporation of Fe³⁺ ion in Cd²⁺ sites was reflected in structural and electron paramagnetic resonance (EPR) measurements. Isolated as well as interacting Fe³⁺ ions are observed in EPR.     

Synthesis and ultraviolet emission of aligned ZnO rod-on-rod nanostructures

Aligned ZnO rod-on-rod nanostructures were synthesized on silicon substrate via a simple thermal evaporation process at low temperature without catalysts. Pictures taken with the use of the scanning electron microscope demonstrate that the well-ordered ZnO rod-on-rod nanostructures grow on the Si substrate, and the single nanostructure consists of two parts. Transmission electron microscopy image and the selected area electron diffraction pattern indicate that the single-crystal nanorod grows along [0001] direction. The X-ray diffraction pattern proves that the samples have good crystal quality. The detailed nanorod growth mechanism is proposed and discussed. The room-temperature photoluminescence (PL) spectrum shows the dominant ultraviolet emission, which indicates their potential application in ultraviolet optoelectronic devices. The temperature-dependent PL spectra reveal that the strong ultraviolet emission should originate from the longitudinal optical phonon replicas of free exciton.     

Enhanced ultraviolet photoresponse based on ZnO nanocrystals/Pt bilayer nanostructure

The development of solution strategies for Zinc oxide(Zn O) quantum dots provides a pathway to utilizing Zn O nanocrystal thin films in optoelectronic devices.In this work,quasi-spherical Zn O quantum dots with a diameter of 5 nm are synthesized by using ethanol as a solvent.Zn O nanocrystal thin film is obtained by spin-coating Zn O quantum dots on a Au interdigital electrode(IDE)/Al2O3 substrate and annealing at different temperatures in order to yield the optimal photosensitive on/off ratio of Zn O.For further enhancing the responsivity,ion sputtering is utilized to deposit Pt nanoparticles on the surface of Zn O nanocrystal thin film,the responsivity of the Zn O/Pt bilayer nanostructure increases from 0.07 A/W to 54 A/W,showing that the metal/inorganic nanocrystal bilayer nanostructure can be used to improve the performance of optoelectronic devices.The excellent properties of Zn O/Pt bilayer nanostructure have important applications in future electronic and optoelectronic devices.     

Room temperature ferromagnetism in Ni-doped ZnO films

Zn_1−xNi_xO (x = 0.02, 0.03, 0.04, 0.05, 0.07) films were prepared using magnetron sputtering. X-ray diffraction indicates that all samples have a wurtzite structure with c-axis orientation. X-ray photoelectron spectroscopy results reveal that the Ni ion is in a +2 charge state in these films. Magnetization measurements indicate that all samples have room temperature ferromagnetism. In order to elucidate the origin of the ferromagnetism, Zn_0.97Ni_0.03O films were grown under different atmospheric ratios of argon to oxygen. The results show that as the fraction of oxygen in the atmosphere decreases, both the saturation magnetization and the number of oxygen vacancies increase, confirming that the ferromagnetism is correlated with the oxygen vacancy level.     

Room temperature magnetic properties of ZnO nanostructured films

The ZnO nanorod array films have been epitaxially deposited on indium tin oxide (ITO) glass along 〈0001〉 direction. It is found that the film is grown in a two-step process including nanoparticle film nucleation and oriented rod growth. The as-prepared ZnO film shows a dominant diamagnetic signal and a weak ferromagnetic signal at room temperature. The room temperature ferromagnetism deteriorated by annealing in air or N₂. The photoluminescent spectra revealed that the intensity of ZnO defect band decreases after annealing. Thus, the decreased ferromagnetism is likely to have resulted from the decrease of oxygen vacancies and defects in the as-prepared film. Moreover, ZnO deposited at various times showed that defects located at or near the interface between the substrate and the film play a major role in ferromagnetism. It suggests that ferromagnetism can be tuned by changing the defects in ZnO.     

Peculiarities of electron field emission from ZnO nanocrystals and nanostructured films

ZnO microcrystals and nanocrystals were grown on silicon substrates by condensation from vapour phase. Nanostructured ZnO films were deposited by plasma enhanced metal organic chemical vapour deposition (PEMOCVD). The parameters of field emission, namely form-factor β and work function , were calculated for ZnO structures by the help of the Fowler–Nordheim equation. The work functions from ZnO nanostructured films were evaluated by a comparison method. The density of emission current from ZnO nanostructures reaches 0.6 mA/cm² at electric force F=2.110⁵ V/cm. During repeatable measurements β changes from 5.810⁴ to 2.310⁶ cm⁻¹, indicating improvement of field emission. Obtained values of work functions were 3.7±0.37 eV and 2.9–3.2 eV for ZnO nanostructures and ZnO films respectively.     

Room temperature fabrication of silicon nanocrystals by pulsed laser deposition

Reaction of 10 nm gold nanoparticles (AuNPs) with a thiol-functionalized bipyridine copper(II) complex, Cu[(N-(6-mercaptohexyl)-2,2′-bipyridinyl-5-carboxamide)]Cl₂ (3), and (1-mercaptohex-6-yl)tri(ethylene glycol) (5) in different ratios resulted in mixed monolayer modified NPs with varying surface coverage of capping agent. The copper complex modified NPs were used for surface plasmon resonance (SPR) promoted homogeneous catalysis applied to the hydrolysis of the nerve agent methyl parathion (MeP) at pH 8.0. Low power green laser (532 nm) irradiation of solutions of modified AuNPs with MeP resulted in significant increase in the rate of phosphate ester hydrolysis which could not be attributed to a thermal process. Ratios of initial rates (laser/dark) at high substrate concentrations of MeP as a function of copper catalyst coverage were determined. A possible mechanism for catalytic enhancement involving dissociation of catalytically inactive hydroxy-bridged Cu(II) dimer is discussed.