共查询到20条相似文献,搜索用时 15 毫秒
1.
László Óvári 《Applied Surface Science》2006,252(24):8624-8629
Rhodium clusters were prepared by evaporation on a nearly stoichiometric TiO2(1 1 0) surface. The growth of metal nanoparticles, as a function of rhodium coverage, could be followed by monitoring the Rh 3d5/2 XP peak position and by low energy ion scattering spectroscopy (LEIS). The substrate temperature in the 160-300 K regime during evaporation significantly influences the cluster size, leading to smaller crystallites at low temperature. Annealing the surface results in the agglomeration of rhodium, which commenced at lower temperature for smaller clusters. At high temperatures (∼900 K) encapsulation of rhodium also occurred. 相似文献
2.
InAs quantum dots (QDs) were grown by molecular beam epitaxy in the Stranski-Krastanow growth mode. The samples were placed between two undoped GaAs slices and annealed in nitrogen ambient at different temperature. Effect of annealing temperature on the evolution of QDs morphology is investigated by the AFM. This behavior can be attributed to the mechanisms of QDs ripening, intermixing and segregation in the annealing process. A number of QDs have evoluted into the uniform distribution quantum rings (QRs) when the sample was annealed at the temperature of 800 °C. The results indicated that high density and uniform QRs can be obtained by the post-growth technique. 相似文献
3.
利用非平衡格林函数方法研究了由半无限长扶手椅型和锯齿型边界石墨纳米带连接而成的L型石墨纳米结的热输运性质.结果表明,L型石墨纳米结的热导依赖于L型石墨纳米结的夹角和石墨纳米带的宽度.在L型石墨纳米结的夹角从30°增加到90°再增加到150°过程中,其热导显著增大.夹角为90°的L型石墨纳米结的热导随着扶手椅型纳米带宽度增加时,在低温区热导随着宽度的增大而降低,在高温区热导随宽度的增大而升高.对于夹角为150°的L型石墨纳米结,其热导无论是在低温区还是在高温区都随着锯齿型纳米带宽度的增加而降低.利用声子透射谱对这些热输运现象进行了合理的解释.研究结果阐明了不同L型石墨纳米结中的热输运机理,为设计基于石墨纳米结的热输运器件提供了重要的物理模型和理论依据.
关键词:
石墨纳米结
热输运
热导 相似文献
4.
Dot array and line patterns of multi-walled carbon nanotubes (MWCNTs) were successfully grown by laser-induced chemical vapor deposition (LCVD) on a transparent substrate at room temperature. In the proposed technique, a Nd:YVO4 laser with a wavelength of 532 nm irradiates the backside of multiple catalyst layers (Ni/Al/Cr) through a transparent substrate to induce a local temperature rise, thereby allowing the direct writing of dense dot and line patterns of MWCNTs below 10 μm in size to be produced with uniform density on the controlled positions. In this LCVD method, a multiple-catalyst-layer with a Cr thermal layer is the central component for enabling the growth of dense MWCNTs with good spatial resolution. 相似文献
5.
Chang Zhao Y.H. Chen C.X. Cui B. Xu L.K. Yu W. Lei J. Sun Z.G. Wang 《Solid State Communications》2006,137(11):630-633
We report the growth of well-ordered InAs QD chains by molecular beam epitaxy system. In order to analyze and extend the results of our experiment, a detailed kinetic Monte Carlo simulation is developed to investigate the effects of different growth conditions to the selective growth of InAs quantum dots (QDs). We find that growth temperature plays a more important role than growth rate in the spatial ordering of the QDs. We also investigate the effect of periodic stress on the shape of QDs in simulation. The simulation results are in good qualitative agreement with our experiment. 相似文献
6.
Quasi-horizontal GaN nanowire array network has been grown on Au-film-coated MgO substrates via a sublimation sandwich technique. These GaN nanowire arrays principally grew along two directions which were perpendicular to each other and nearly parallel to the substrate, forming a regular network. The formation of the nanowire network was a hetero-epitaxial vapor-liquid-solid (VLS) process assisted by Au catalysts and was dependent on the substrates. Transmission electron microscopy revealed that the nanowires were single-crystalline wurtzite GaN. Raman scattering spectrum of the nanowire network presented some new features. 相似文献
7.
Self-assembled InGaN quantum dots (QDs) were grown on GaN templates by metalorganic chemical vapor deposition. 2D–3D growth
mode transition through Stranski–Krastanov mode was observed via atomic force microscopy. The critical thickness for In0.67Ga0.33N QDs was determined to be four monolayers. The effects of growth temperature, deposition thickness, and V/III ratio on QD
formation were examined. The capping of InGaN QDs with GaN was analyzed. Optimized InGaN quantum dots emitted in green spectra
at room temperature. 相似文献
8.
A numerical simulation of the two-temperature model has been performed for Au, Ag, Cu and Al. Based on findings in the numerical simulation, an analytical model for the ablation rates in the high fluence regime is proposed. Furthermore, it is shown that a temperature-dependent electron-lattice coupling must be introduced to have qualitative agreement with the logarithmic growth in the low fluence regime. For aluminum, experimental ablation rates with varying fluence is presented and compared with the numerical simulation. 相似文献
9.
Heng Pan Nipun Misra Seung H. Ko Costas P. Grigoropoulos Nate Miller Eugene E. Haller Oscar Dubon 《Applied Physics A: Materials Science & Processing》2009,94(1):111-115
Nanoparticle solutions are considered promising for realizing low cost printable high performance flexible electronics. In
this letter, excimer laser annealing (ELA) was employed to induce melting of solution-deposited ZnO nanoparticles and form
electrically conductive porous films. The properties of the films were characterized by scanning electron microscopy, high-resolution
transmission electron microscopy, DC conductance, and photoluminescence measurements. Thin-film field-effect transistors have
been fabricated by ELA without the use of conventional vacuum or any high temperature thermal annealing processes. The transistors
show n-type accumulation mode behavior with mobility greater than 0.1 cm2/V s and current on/off ratios of more than 104. Optimization and control of the laser processing parameters minimized thermal impact on the substrate. This technique can
be beneficial in the fabrication of metal oxide based electronics on heat sensitive flexible plastic substrates using low-cost,
large-area solution processing combined with direct printing techniques. 相似文献
10.
Guangbi Yuan Xiaohua Liu Weidong He Dunwei Wang 《Applied Physics A: Materials Science & Processing》2009,96(2):399-402
The yield of Ge nanowires (NWs) synthesized using the vapor–liquid–solid (VLS) method was discovered to be highly sensitive
to the rate of precursor feeding. When other parameters were fixed, fast filling of precursors yielded nearly 100% Ge NWs
with regard to the growth seeds. By contrast, slow feeding produced nearly no or very low yield of Ge NWs. The dramatic difference
was attributed to a layer of Ge coating on the surface of growth seeds. The coating formed at relatively low precursor pressures
as a result of the imbalance in the VLS process. The results shed new light on the VLS mechanism in general.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
11.
Nanoscale effects in focused ion beam processing 总被引:3,自引:0,他引:3
Focused ion beams with diameters of 8 to 50 nm are used for material processing in the nanoscale regime. In this paper, effects
of the ion beam–solid interaction determining the formation of small structures by ion-beam sputtering and chemically assisted
material deposition and etching are investigated. In the case of decreasing feature size, angle-dependent sputtering, a non-constant
sputter rate, and scattered ions play an important role. The impact on side-wall angle, aspect ratio, and shape of the bottom
of the etched structures is discussed. In beam tail regions, these effects will be especially pronounced, leading to material
swelling instead of material removal. Ion beam assisted etching and deposition will face additional effects. For small structures,
gas depletion becomes a significant drawback. The impact on gas depletion and the competition with sputtering are discussed.
Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003
RID="*"
ID="*"Corresponding author. Fax: +49-9131/761360, E-mail: frey@iis-b.fhg.de 相似文献
12.
J. F. Zhou Z. Chen L. B. He C. H. Xu L. Yang M. Han G. H. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):283-286
InSb nanostructures have been synthesized by the use of
gas aggregation process. Nanoparticles with different shapes are obtained by
controlling the growth and deposition temperature of the InSb nanoclusters.
Triangular nanocrystals are commonly observed when the clusters are
extracted from the condensation chamber of the source and deposited on the
room temperature substrate at high vacuum. When the deposition is performed
inside the condensation chamber at high temperature near the melting point
of bulk InSb, nanoparticles formed on the substrate surface show several
kinds of 3-dimensional morphologies, such as triangular or rectangular
prisms, as well as hexagonal tablets. Keeping the same conditions for the
cluster source operation and deposition, after long time growth, nanorods
with hexagonal and quadrangular cross sections are formed through
vapor-liquid-solid (VLS) process. The origin of the difference on the
morphologies and shapes of the nanostructures is attributed to the
anisotropic growth of InSb, which is temperature dependent. 相似文献
13.
A chemical reaction for the preparation of B-C-N compounds by using carbon tetrachloride (CC14), boron tribromide (BBr3), lithium nitride (Li3N) and sodium as reactants has been carried out at the temperature of 400℃. Measurements of FTIR, XRD, TEM and EELS show that two kinds of compounds have been formed in the prepared sample. One is hollow sphere-like C-N with an amorphous, structure; the other is piece-like polycrystalline B-C-N with the hexagonal structure. Their determined compositions are close to C3N and BC2N, respectively. 相似文献
14.
采用化学气相沉积系统制备ZnO纳米线,以覆盖一层约5nm厚的Ag薄膜的单晶Si(001)为衬底,纳米线的生长遵循气-液-固(VLS)机理。对得到的样品采用X射线衍射(XRD)和扫描电镜(SEM)进行晶体结构和形貌的表征。XRD结果表明衬底温度在600~700℃时生长的ZnO纳米线具有六方结构和统一的取向。通过扫描电子显微镜分析,比较了生长温度对纳米线直径和长度的影响。实验表明我们可以通过催化剂和温度来实现ZnO纳米线生长的可控。与传统的VLS生长方式不同的是在我们制备的ZnO纳米线顶端并没有看到催化剂颗粒,表明纳米线的生长方式是底部生长,我们对其生长机理进行了研究。 相似文献
15.
Epitaxial La1−xSrxMnO3 (LSMO) films were prepared by excimer laser-assisted metal organic deposition (ELAMOD) at a low temperature using ArF, KrF, and XeCl excimer lasers. Cross-section transmission electron microscopy (XTEM) observations confirmed the epitaxial growth and homogeneity of the LSMO film on a SrTiO3 (STO) substrate, which was prepared using ArF, KrF, and XeCl excimer lasers. It was found that uniform epitaxial films could be grown at 500 °C by laser irradiation. When an XeCl laser was used, an epitaxial film was formed on the STO substrate at a fluence range from 80 to 140 mJ/cm2 of the laser fluence for the epitaxial growth of LSMO film on STO substrate was changed. When the LaAlO3 (LAO) substrate was used, an epitaxial film was only obtained by ArF laser irradiation, and no epitaxial film was obtained using the KrF and XeCl lasers. When the back of the amorphous LSMO film on an LAO substrate was irradiated using a KrF laser, no epitaxial film formed. Based on the effect of the wavelength and substrate material on the epitaxial growth, formation of the epitaxial film would be found to be photo thermal reaction and photochemical reaction. The maximum temperature coefficient of resistance (TCR) of the epitaxial La0.8Sr0.2MnO3 film on an STO substrate grown using an XeCl laser is 4.0%/K at 275 K. XeCl lasers that deliver stabilized pulse energies can be used to prepare LSMO films with good a TCR. 相似文献
16.
Recent experiments by Ross and co-workers proved the possibility of a mononuclear regime with heterogeneous nucleation as well as jerky growth in the vapor–liquid–solid (VLS) process for silicon nanowires. In this work, a theoretical model is presented which incorporates the effects of (i) a mononuclear regime with layer by layer growth, (i) heterogeneous nucleation of each new layer at the edge of a Au–Si droplet, (iii) drop of supersaturation after each successful nucleation and respective fast layer growth, (iv) time-dependent nucleation barrier during each new waiting period and (v) correlation between subsequent waiting periods (non-Markovian sequence of waiting periods). 相似文献
17.
A. Lunk P. Bachem P. Scheible L. Ulrich 《Applied Physics A: Materials Science & Processing》2001,72(5):557-564
The development of in situ diagnostics of the most important species and reactions in the plasma and/or on the surface during
thin-film growth is one of the current topics in plasma-enhanced vapor deposition. In situ thin film diagnostic methods which
could be used in plasma processing are restricted due to the presence of electrons and ions. The advantages and disadvantages
of different applicable methods will be discussed. The spectroscopic in situ control of boron nitride film growth is presented
as an example of surface modification in low-temperature, low-pressure plasma processing. The growth of cubic and hexagonal
boron nitride is observed by polarized infrared reflection spectroscopy in absorption and ellipsometric configurations as
well as by single-wavelength ellipsometry in the visible spectral range. Modeling of the experimental results gives detailed
information on growth conditions and internal stress of the films.
Received: 8 August 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001 相似文献
18.
A. Aierken T. Hakkarainen M. Sopanen J. Riikonen J. Sormunen M. Mattila H. Lipsanen 《Applied Surface Science》2008,254(7):2072-2076
Formation of self-assembled InAs 3D islands on GaAs (1 1 0) substrate by metal organic vapor phase epitaxy has been investigated. Relatively uniform InAs islands with an average areal density of 109 cm−2are formed at 400 ° C using a thin InGaAs strain reducing (SR) layer. No island formation is observed without the SR layer. Island growth on GaAs (1 1 0) is found to require a significantly lower growth temperature compared to the more conventional growth on GaAs (1 0 0) substrates. In addition, the island height is observed to depend only weakly on the growth temperature and to be almost independent of the V/III ratio and growth rate. Low-temperature photoluminescence at 1.22 eV is obtained from the overgrown islands. 相似文献
19.
Chaoyi Yan Tao Zhang Pooi See Lee 《Applied Physics A: Materials Science & Processing》2009,94(4):763-766
Silica nanowires were synthesized through a self-supplied vapor–liquid–solid (VLS) mechanism. Unlike randomly entangled nanowires
on the substrate, highly ordered nanowire arrays have been successfully fabricated using a sandwich-like configuration to
define and enhance the local gas-flow. As-synthesized nanowires were characterized to be amorphous silicon dioxide with Au
as catalysts. The role of the sandwich-like structure and the effect of gas-flow on the alignment of silica nanowires are
demonstrated. 相似文献
20.
A route towards optimisation of uniformity and density of InAs/(InGaAs)/GaAs quantum dots grown by metal organic vapor phase epitaxy (MOVPE) through successive variations of the growth parameters is reported. It is demonstrated that a key parameter in obtaining a high density of quantum dots is the V/III ratio, a fact which was shown to be valid when either AsH3 (arsine) or tertiary-butyl-arsine (TBA) were used as group V precursors. Once the optimum V/III ratio was found, the size distribution was further improved by adjusting the nominal thickness of deposited InAs material, resulting in an optimum thickness of 1.8 monolayers of InAs in our case. The number of coalesced dots was minimised by adjusting the growth interruption time to approximately 30 s. Further, the uniformity was improved by increasing the growth temperature from 485 °C to 520 °C. By combining these optimised parameters, i.e. a growth temperature of 520 °C, 1.8 monolayers InAs thickness, 30 s growth stop time and TBA as group V precursor, a full-width-half-maximum (FWHM) of the low temperature luminescence band of 40 meV was achieved, indicating a narrow dot size distribution. 相似文献