热氧化法制备ZnO纳米棒及其结构表征

在无催化剂条件下,采用热蒸发Zn源,以N2为载气体,在SiO2衬底上反应沉积制备出单晶氧化锌纳米棒。XRD研究表明纳米棒为结晶完好的纤锌矿结构,并且为非定向生长,非定向生长的氧化锌纳米棒减弱了棒之间的屏蔽效应,表现出较好的场发射效果,为未来场发射电子器件的实际应用提供了可靠依据。     

Ge/Si复合纳米结构电荷存储特性的模拟研究

这一研究工作模拟计算了 Ge/ Si复合纳米结构 MOSFET存储器的擦写和存储时间特性。结果表明 ,Ge/ Si复合纳米结构存储器在低压下即可实现 μs和 ns量级编程。与 Si纳米结构存储器相比 ,由于 Ge/ Si复合势阱的作用 ,器件的电荷保留时间提高了 3～ 5个量级 ,有效地解决了快速擦写编程与长久存储之间的矛盾 ,使器件的性能得到明显改善。     

衬底退火温度对ZnO纳米结构形貌和发光特性的影响

利用热蒸发Zn粉的方法,在Au/掺铝氧化锌(AZO) /石英衬底上生长ZnO纳米结构。为了研究不同 温度退火后的衬底对生长的ZnO纳米结构的影响,Au/AZO/石英衬底在生长纳米结构前分别在 300、500和700℃真空下退火。Au/AZO/石英衬底的表面形貌用原子力显微镜(AFM)观测 。ZnO纳米结构的微结构、形貌和 光学性能分别用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和荧光光 谱仪进行测量。结果表明,在未退火和300 ℃ 退火衬底上生长了大量的ZnO纳米棒,而在500℃退火衬底上沉积了大量ZnO纳米颗粒。单晶结构 的纳米棒的平均直径分别约50nm,其 生长机制为蒸气-液体-固体(VLS)生长机制。荧光光谱显示所有的样品 都存在紫外发光峰和深能级发射带,随着退火温度的升高,生长的纳米结构的紫外发光峰相 对强度增强,而深能级发射强度减弱。     

CdSe/SiO_2异质复杂纳米结构的可控制备

复杂纳米结构至今依然是材料领域研究的前沿。采用简单的气相合成法,通过反应温度选择和初始反应物配方设计,实现了复杂形貌CdSe/SiO2异质纳米结构的可控制备,在直径为100nm左右的一维纳米棒端部成功嫁接了直径约400nm的碗状SiO2纳米空心球。通过XRD,FESEM,HRTEM,EDS和SAED等手段分析试样的形貌、成分和晶体学特征。XRD测试表明,生成产物是CdSe和SiO2的复合材料;EDS分析进一步确认一维纳米棒和碗状空心球的化学成分分别为CdSe和SiO2;HRTEM和SAED测试表明,CdSe纳米棒是沿[0002]方向生长的单晶结构,SiO2纳米空心球为非晶结构。这种新奇的异质纳米结构可以作为未来纳米靶向药物的载体材料。     

ZnO纳米晶须的形态控制及其结构表征

采用激光分子束外延法先在Si(111)衬底上制备Zn薄膜,在不同的氧气体积流量和生长温度下,用热蒸发法在镀有Zn薄膜的Si(111)衬底上制备了不同形貌的ZnO纳米晶须。分别用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)对样品的成分、微结构和形貌进行了表征。Zn薄膜在高温下被氧化,并为晶体生长提供均匀的成核点,有利于形成一定大小和数量的ZnO晶核。研究结果表明,氧气体积流量和生长温度对ZnO纳米晶须的形貌有一定的影响。     

四脚针状ZnO纳米结构的制备及表征

采用以Zn粉、C粉为原料,采用热蒸发法,在没有任何载气和700℃下制备了四脚针状ZnO纳米结构。C粉起到了催化剂的作用但产物却不存在催化剂去除的问题,同时C粉氧化生成的CO/CO2还起到了载气的作用。扫描电镜(SEM)表明,四脚针状ZnO具有很细的尖端,直径为50 nm。X射线衍射(XRD)、微区拉曼图谱的特征峰表明,四脚针状ZnO是高纯的六角纤锌矿结构。光致发光(PL)谱在403 nm附近有微弱的紫光发射峰,而在510 nm附近出现了很强的绿光发射峰。     

Si基 ZnO纳米壁网格结构紫外探测器的制备

利用等离子体辅助分子束外延设备在Si（111）衬底上在没有任何催化剂情况下,得到了ZnO纳米壁的网状结构。这些ZnO纳米壁网格结构是c轴择优取向的。纳米结构的厚度为10到20纳米,高度大约为50纳米,这种纳米结构被制成平面的金属-半导体-金属结构的光导型紫外探测器件。这种探测器具有高响应,宽范围的特点。波长从360纳米减小到250纳米的过程中,器件的响应度无明显下降。在5V的偏压下,暗电流小于6μA。ZnO 纳米结构探测器响应峰值出现在360纳米处,其数值为15 A/W。探测器的紫外可见抑制比在2个量级以上。     

SiO_2/NiO复合纳米颗粒的制备及表征

提出了共溶胶双水解的方法来制备SiO_2基复合纳米材料,并用氧化镍作为复合对象来制备SiO_2/NiO复合纳米颗粒。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能量色散谱(EDS)和透射电子显微镜(TEM)等方法对复合纳米颗粒的形貌和结构进行了表征。测试结果表明:该方法成功制备出了SiO_2/NiO复合纳米颗粒。该复合纳米颗粒是由SiO_2与NiO两种物质构成的,其中SiO_2小球是非晶结构的,粒径为200～300 nm;NiO纳米颗粒是多晶结构的,直径在20 nm左右。每个SiO_2小球上复合的NiO纳米颗粒数目并不均一,但是复合纳米颗粒分散性比较好,几乎没有团聚现象产生。最后,对这种制备方法的合成机理进行了初步的解释。     

Zn/ZnO纳米电缆的制备及电子显微分析

利用X射线衍射仪(XRD)、X射线能谱仪(EDS)、扫描电子显微镜(SEM)以及透射电子显微镜(TEM)等实验手段对热蒸发ZnO粉末产物的形貌、组成成分、两种相的取向关系以及微观结构进行了表征。结果表明：实验所得到的制备产物由Zn／ZnO纳米电缆组成,电缆的直径在50-200nm之间而长度可达几百微米。电缆由单质Zn组成的芯和由ZnO组成的外壳组成。两相具有两种比较固定的取向关系[11 2^-0]zn／／[11 2^-0]ZnO。和[0001]Zn／／[0001]ZnO。     

Growth and characterization of GaAs films deposited on Ge/Si composite substrates by metalorganic chemical vapor deposition

We report the results of studies which have been made on heteroepitaxial layers of GaAs and AlGaAs grown by metalorganic chemical vapor deposition on composite substrates that consist of four different types of heteroepitaxial layered structures of Ge and Ge-Si grown by molecular beam epitaxy on (100)-oriented Si substrates. It is found that of the four structures studied, the preferred composite substrate is a single layer of Ge ∼1 μm thick grown directly on a Si buffer layer. The double-crystal X-ray rocking curves of 2 μm thick GaAs films grown on such substrates have FWHM values as small as 168 arc sec. Transmission electron micrographs of these Ge/Si composite substrates has shown that the number of dislocations in the Ge heteroepitaxial layer can be greatly reduced by an anneal at about 750° C for 30 min which is simultaneously carried out during the growth of the GaAs layer. The quality of the GaAs layers grown on these composite substrates can be greatly improved by the use of a five-period GaAs-GaAsP strained-layer superlattice (SLS). Using the results of these studies, low-threshold optically pumped AlGaAs-GaAs DH laser structures have been grown by MOCVD on MBE Ge/Si composite substrates.     

Thermal evaporation of Ge on Si for near infrared detectors: Material and device characterization

Using a low-temperature process, we thermally evaporated Ge thin films on Si substrates and investigated both structural and electrical properties of samples grown at various temperatures. The characterization included X-ray diffraction, atomic force microscopy and Hall measurements and aimed at determining a suitable temperature range in terms of crystal quality and transport properties. Finally, we employed Ge films on Si to fabricate near infrared photodiodes and test them in terms of dark current and responsivity.     

Growth of Si and Ge nanostructures on Si substrates using ultrathin SiO/sub 2/ technology

Using scanning reflection electron microscopy and a high-temperature scanning tunneling microscopy (STM), we study the growth processes of Si and Ge nanostructures on Si substrates covered with ultrathin SiO/sub 2/ films. Si windows are formed in the ultrathin SiO/sub 2/ films by irradiating focused electron beams used for SREM or field emission electron beams from STM tips before or during heating samples. Ge nanoislands are grown only at the Si window positions by depositing Ge on the samples and by subsequent annealing of them. Moreover, Ge nanoislands about 7 nm in size and ultrahigh density (>10/sup 12//cm/sup 2/) are grown on the ultrathin SiO/sub 2/ films. These nanoislands can be manipulated by STM when they are separated from Si substrates by the ultrathin SiO/sub 2/ films. Si, Ge, Ge/Si and Si/Ge/Si nanoislands can also be grown on the Si windows by selective growth using Si/sub 2/H/sub 6/ and GeH/sub 4/ gases. These nanoislands are found to be stable on the Si windows during high-temperature annealing. These results indicate that ultrathin SiO/sub 2/ technology is useful for growing Si and Ge nanostructures on given areas.     

Si基外延Ge薄膜及退火对其特性的影响研究

采用超高真空化学气相沉积(UHV-CVD)系统,用低温Ge缓冲层技术在Si衬底上外延了张应变Ge薄膜.扫描电镜(TEM)图表明Si基外延Ge薄膜拥有低的位错密度,原子力显微镜(AFM)测试Ge层表面粗糙度仅为1.2 nm.对Si基外延Ge薄膜进行了不同温度下的退火,并用双晶X射线衍射(DCXRD)曲线和Raman谱进行...     

Ge/Si量子点的生长研究进展

要有效应用SK模式生长的Ge量子点,必须实现Ge量子点的位置可控并且进一步缩小Ge量子点的尺寸.阐释了这方面的研究进展,特别对图形衬底生长Ge量子点,利用Si表面的自组织性在错切割的邻晶面衬底上生长有序Ge岛,表面杂质诱导成岛这三个方面的进展加以介绍分析.     

Evolution of ZnO nanostructures on silicon substrate by vapor-solid mechanism: Structural and optical properties

ZnO nanostructures with different morphologies and sizes were synthesized on silicon substrate simply by the thermal evaporation of high-purity metallic zinc powder in the presence of oxygen without the use of any catalyst or additives. It was observed that the substrate temperature and the distance of the substrate from the source material play a critical role to determine the morphologies and sizes of the deposited structures. Scanning electron microscopic observations revealed that different types of nano- and microstructures, such as ZnO pyramid-shaped nanotowers, nanowires attached with the sheet-like structures, nanorods, microcages, and microtubes were obtained at different temperature zones with specific distances of the substrate from the source material. High-resolution transmission electron microscopy and x-ray diffraction studies confirm that the deposited products are single crystalline with wurtzite hexagonal structures. The room-temperature photoluminescence spectra of all the deposited structures displayed a strong near-band-edge emission with negligible green emission.     

Modification of quantum dots in Ge/Si nanostructures by pulsed laser irradiation

The goal of this study was the development of a method for the modification of a quantum dot (QD) structure in Ge/Si nanostructures by pulsed laser irradiation. The Ge_xSi_1?x QD structures were analyzed using data furnished by Raman spectroscopy. Frequency-dependent admittance measurements were used to study the energy spectrum of holes in the Ge/Si heterostructures with Ge_xSi_1?x QDs before and after the laser treatment. The obtained experimental data show that laser treatment makes it possible to reduce the sheet density of QDs, modify their composition, and increase the average size. The most important result is that the QD parameters become more uniform after the treatment with nanosecond laser pulses. In a sample with ODs of 8-nm average lateral size (six monolayers of Ge), the scatter of energy levels in the QD array is reduced by half after the treatment with 10 laser pulses.