Cuprous oxide (Cu2O) nanowires were grown by a simple, catalyst-free thermal oxidation method starting from a copper foil substrate. Wire growth was performed at different conditions by varying oxygen partial pressure and heating temperature, and produced structural defects such as stacking faults and twin structures of grown nanowires were characterized by transmission electron microscopy. A moderate oxygen partial pressure ~5% with a relatively high temperature at 500 oC is found to be an optimal condition for growing high-quality Cu2O nanowires, while either lowering temperature or enhancing O2 partial pressure can yield higher density of planar defects. In order to further investigate optical properties of grown nanowires, photoluminescence measurements were also performed and correlated with structural characterization results, indicating that increase of structural defects such as stacking faults and twins tended to enhance broad defect-related emissions and suppress the exciton emissions near Cu2O band-edge.
Large-scale CuO nanowires are commonly synthesized by the thermal oxidation method. However, the growth mechanism remains controversial between diffusion growth mechanism and vapor-solid (VS) growth mechanism. In this study, we investigated the morphology and atomic structure of the CuO nanowires by electron microscopes to clarify the growth mechanism. We found that they were grown with the annealing ambient during the cooling process and there were screw dislocations in the nanowires. These features indicate that the VS growth mechanism is applicable to explain the growth of the CuO nanowires…
Incorporation of Bi into GaAs-(Ga,Al)As-Ga(As,Bi) core-shell nanowires grown by molecular beam epitaxy is studied with transmission electron microscopy. Nanowires are grown on GaAs(111)B substrates with Au-droplet assisted mode. Bi-doped shells are grown at low temperature (300 °C) with a close to stoichiometric Ga/As flux ratio. At low Bi fluxes, the Ga(As,Bi) shells are smooth, with Bi completely incorporated into the shells. Higher Bi fluxes (Bi/As flux ratio ~ 4%) led to partial segregation of Bi as droplets on the nanowires sidewalls, preferentially located at the nanowire segments with w…
Comprehensive investigation on the correlation of growth, structural and optical properties of GaN nanowires grown on Si(111) substrates by plasma assisted molecular beam epitaxy technique
Moire based strain analysis in wurtzite GaAs -- rock-salt (Pb,Sn)Te core-shell nanowires grown by molecular beam epitaxy
Institute of Physics, Polish Academy of Sciences(波兰科学院物理研究所);Faculty of Physics, University of Warsaw(华沙大学物理学院);Ensemble3 Centre of Excellence(Ensemble3卓越中心);International Research Center MagTop, Institute of Physics, Polish Academy of Sciences(波兰科学院物理研究所国际研究中心MagTop)
We analyse the morphological, structural and luminescence properties of self-assembled ZnO nanowires grown by chemical vapour transport on Si(001). The examination of nanowire ensembles by scanning electron microscopy reveals that a non-negligible fraction of nanowires merge together forming coalesced aggregates during growth. We show that the coalescence degree can be unambiguously quantified by a statistical analysis of the cross-sectional shape of the nanowires. The examination of the structural properties by X-ray diffraction evidences that the nanowires crystallize in the wurtzite phase, …
Selective area growth (SAG) of nanowires and networks promise a route toward scalable electronics, photonics and quantum devices based on III-V semiconductor materials. The potential of high-mobility SAG nanowires however is not yet fully realized, since interfacial roughness, misfit dislocations at the nanowire/substrate interface and non-uniform composition due to material intermixing all scatter electrons. Here, we explore SAG of highly lattice-mismatched InAs nanowires on insulating GaAs(001) substrates and address these key challenges. Atomically smooth nanowire/substrate interfaces are a…
Hexagonal group IV materials like silicon and germanium are expected to display remarkable optoelectronic properties for future development of photonic technologies. However, the fabrication of hexagonal group IV semiconductors within the vapour-liquid-solid method has been obtained using gold as a catalyst thus far. In this letter, we show the synthesis of hexagonal Ge on self-assisted GaAs nanowires using molecular beam epitaxy. With an accurate tuning of the Ga and As molecular beam flux we selected the crystal phase, cubic or hexagonal, of the GaAs NWs during the growth. A 500 nm-long hexa…
Direct evidence of enhanced Ga interdiffusion in InAs vertically aligned free-standing nanowires
我们提出了直接的证据,增强Ga相互扩散的InAs独立的纳米线生长在中等温度下的分子束外延GaAs(111)B。扫描电子显微镜以及共面和掠入射几何形状的X射线衍射测量表明,名义上生长的InAs纳米线实际上是由In $_{0.86}$ Ga $_{0.14}$ As制成的。与典型的气-液-固生长不同,这些纳米线是通过扩散诱导生长结合来自衬底材料的强相互扩散形成的。基于实验结果,一个简单的纳米线生长模型占镓互扩散。该生长模型可普遍应用于III-V族纳米线的分子束异质外延。
The accurate control of the crystal phase in III-V semiconductor nanowires (NWs) is an important milestone for device applications. In this work, we present a method to select and maintain the wurtzite (WZ) crystal phase in self-assisted NWs. By choosing a specific regime where the NW growth process is a self-regulated system, the main experimental parameter to select the zinc-blende (ZB) or WZ phase is the V/III flux ratio. The latter can be monitored by changing the As flux, and drives the system toward a stationary regime when the wetting angle of the Ga droplet falls in a target interval, …
GaN nanowires grown by molecular beam epitaxy generally suffer from dominant nonradiative recombination, which is believed to originate from point defects. To suppress the formation of these defects, we explore the synthesis of GaN nanowires at temperatures up to 915 $°C$ enabled by the use of thermally stable TiN$_x$/Al$_2$O$_3$ substrates. These samples exhibit indeed bound exciton decay times approaching those measured for state-of-the-art bulk GaN. However, the decay time is not correlated with the growth temperature, but rather with the nanowire diameter. The inverse dependence of the dec…
N-type doping of GaAs nanowires has proven to be difficult because the amphoteric character of silicon impurities is enhanced by the nanowire growth mechanism and growth conditions. The controllable growth of n-type GaAs nanowires with carrier density as high as 1020 electron/cm3 by self-assisted molecular beam epitaxy using Te donors is demonstrated here. Carrier density and electron mobility of highly doped nanowires are extracted through a combination of transport measurement and Kelvin probe force microscopy analysis in single-wire field-effect devices. Low-temperature photoluminescence is…
Significant enhancement of hole mobility in [110] silicon nanowires compared to electrons and bulk silicon
利用sp 3d 5s * 紧束缚能带结构和电子和空穴的波函数,我们证明了在[110]生长的硅纳米线(SiNWs)中声学声子限制的空穴迁移率大于电子迁移率。所考虑的SiNW的室温声学限制的空穴迁移率可以高达2500 cm 2/Vs,这是几乎三倍大于体声学限制的硅空穴迁移率。结果还表明,[110]生长的硅纳米线的电子和空穴迁移率超过了类似直径的[100]硅纳米线,空穴迁移率相差近两个数量级。由于小直径的硅纳米线主要沿[110]方向生长,结果强烈表明这些硅纳米线可能在未来的电子学中有用。我们的研究结果也与最近的实验测量硅纳米线的流动性。
Spatially-resolved luminescence and crystal structure of single core-shell nanowires measured in the as-grown geometry
我们报道了单个的、生长态的核-多壳GaAs/In $_{0.15}$ Ga $_{0.85}$ As/GaAs/AlAs/GaAs纳米线的结构和光学性质之间的直接相关性。通过分子束外延在预先图案化的Si(111)衬底上制造,在一排良好分离的成核位置上,可以在生长的几何形状中访问单个纳米线。通过同步辐射纳米探针X射线衍射技术监测轴向111布拉格反射,揭示了沿纳米线生长轴的多型体分布。对于相同的纳米线,空间分辨的发射特性,通过阴极发光高光谱线扫描在扫描电子显微镜。相关的两个测量,我们揭示了一个蓝移的壳量子阱发射能量结合的发射强度增加的片段表现出的混合结构的交替纤锌矿和锌的堆叠相比,纯晶体多型体。这种混合结构的存在下,独立地证实了横截面透射电子显微镜。