Effects of annealing temperature on morphologies and optical properties of ZnO nanostructures

The effects of annealing temperature on the morphologies and optical properties of ZnO nanostructures synthesized by sol–gel method were investigated in detail. The SEM results showed that uniform ZnO nanorods formed at 900 C. The PL results showed an ultraviolet emission peak and a relatively broad visible light emission peak for all ZnO nanostructures sintered at different temperature. The increase of the crystal size and decrease of tensile stress resulted in the UV emission peak shifted from 386 to 389 nm when annealing temperature rose from 850 to 1000 C. The growth mechanism of the ZnO nanorods is discussed.     

The structure and properties of the Si nanostructures on an HOPG surface

The morphology, electronic structure, and optical properties of self-assembled silicon nanostructures grown on the surface of Highly Oriented Pyrolytic Graphite (HOPG) by molecular beam epitaxy were studied by ultra high vacuum (UHV) scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in situ, and by Raman spectroscopy ex situ. At coverages of less than 1 monolayer (ML), the formation of monolayered silicon nanoislands with an atomic structure similar to that of graphene was observed.     

The influence of annealing temperature on the structure,morphologies and optical properties of ZnO nanoparticles

ZnO nanoparticles (NPs) have been successfully synthesized by the simple solution method at low temperature. The effects of annealing temperature on the structure and optical properties of ZnO NPs were investigated in detail by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) spectroscopy and photoluminescence (PL) measurements. As the annealing temperature was increased above 180 ^°C the particles morphology evolved from spherical to hexagonal shape, indicating that the average particle size increased from 11 nm to 87 nm. The UV-vis and PL spectra showed a red-shift from 3.62 to 3.33 eV when the annealing temperature was increased.     

A crystallographic orientation transition and early stage growth characteristics of thin Bi films on HOPG

We report on the growth of ultra-thin bismuth films on the basal plane of highly ordered pyrolitic graphite (HOPG) substrates. Scanning electron microscopy and atomic force microscopy have been used to characterize the morphology, and the crystallographic orientation was obtained using electron back scatter diffraction. Low coverage films are comprised of islands with a striped surface morphology, and show the orientation relationship with preferred in-plane orientations . With increasing film thickness, we identify an unusual orientation transformation to the commonly found Bi{0 0 0 1} (trigonal) orientation.     

Formation of Gallium-induced nanostructures on single crystal HOPG surface

The room temperature growth of gallium atoms on the highly oriented pyrolytic graphite (HOPG) surface has been performed. The gallium atoms were deposited by thermal evaporation method in an ultra high vacuum system at a base pressure 5 × 10⁻¹⁰ torr. The X-ray photo electron spectroscopy (XPS) studies had been performed to confirm the presence of gallium atoms on HOPG surface. Scanning tunneling spectroscopy (STM) technique was employed to study the surface morphology of the clean HOPG surface and gallium covered HOPG surfaces which recognize the formation of gallium induced nanostructures. The deconvoluted XPS core level spectra of C (1s) and Ga (3d) demonstrate the possible interaction between substrate and the adsorbate atoms. The STM analysis revealed that the gallium deposition on HOPG led to significant change in the surface morphology. It was observed that the Ga atoms adsorbed as layer structure on HOPG surface for low coverage while quasi one-dimensional chain like nanostructure (1 ± 0.2 nm) has been formed for higher Ga coverage. The nanostructured surfaces induced by Ga deposition are found to be stable and could be used as a template for the growth of metallic nanostructures.     

Controlled growth and field emission of vertically aligned AlN nanostructures with different morphologies

The controllable growth of three different morphologies of AlN nanostructures (nanorod, nanotip and nanocrater) arrays are successfully realized by using chemical vapour deposition (CVD) technology. All three nanostructures are of single crystal h-AlN with a growth orientation of [001]. Their growth is attributed to the vapour-liquid-solid (VLS) mechanism. To investigate the factors affecting field emission (FE) properties of AlN nanostructures, we compare their FE behaviours in several aspects. Experimental results show that AlN nanocrater arrays possess the best FE properties, such as a threshold field of 7.2~V/μm and an emission current fluctuation lower than 4%. Moreover, the three AlN nanostructures all have good field emission properties compared with a number of other excellent cathode nanomaterials, which suggests that they are future promising FE nanomaterials.     

Effect of substrate temperature on the growth and luminescence properties of ZnO nanostructures

ZnO nanowires, nanorods and nanoribbons have been prepared by heating a mixture of ZnO/graphite powders using the thermal evaporation and vapor transport on Si(1 0 0) substrates without any catalyst. The nanostructures are grown as a function of substrate temperature ranging from 900 to 1300 K. These nanostructures are of the size 100–300 nm in diameter or width and several tens of micrometers in length. We studied the influence of the substrate temperature on the luminescent properties of these nanostructures. We observed a strong relationship between the substrate temperature and the green emission band in ZnO, i.e., the photoluminescence study revealed that the green emission peak of the ZnO nanostructures is suppressed relative to the band edge emission when the substrate temperature is decreased from 1300 to 900 K.     

Si growth effects on the formation of Er silicide nanostructures

In this work, an ultra-high vacuum scanning tunneling microscopy has been utilized to study the effects of Si atoms to the formation and growth evolution of Er silicide nanostructures. Si evaporation is performed on the vicinal Si(0 0 1) surface as well as Er growth under different growth conditions: growth procedure, annealing temperature and duration time. The experimental results show that the Si evaporation performed at a high temperature plays a key role on the growth of Er silicide nanostructures. The deposited Si atoms become a significant source of the Si reactant and mainly affect the early growth stage of the nanostructures. It is also shown that Er atom is possibly another diffusing species during the growth of Er silicide nanostructures on the Si(0 0 1) surface.     

Effect of substrate temperature on the growth of pulsed-laser deposited ZnO nanostructures

We report on the growth of highly c-axis-oriented ZnO nanostructures by pulsed laser deposition technique without using any catalyst. The full-width-at-half-maximum of (002) peak decreased with an increase in substrate temperature. However, a dip at 150 °C is attributed to the contribution from both the small- and large-size particles. FE-SEM images show that the increase in substrate temperature results in the formation of larger particles. Photoluminescence emission is observed both from near band edge as well as defect-related states for all the nanostructures. The presence of E ₂(low) and E ₂(high) Raman mode intensity and respective increase in the intensity with substrate temperature indicates better crystallinity. Both PL and Raman spectra indicate that A ₁(LO) mode may arise due to the defect related to interstitial zinc.     

Growth and morphologies of one- and three-dimensional MgO nanostructures

A variety of MgO nanostructures have been fabricated by a direct gas reaction route using Mg as starting material. The evaporation of Mg combined with a mixed oxygen/argon gas provided the constituents for the MgO nanostructure growth. They were characterized by scanning electron microscopy (SEM), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). SEM observations revealed several MgO morphologies including one-dimensional nanowires, three-dimensional cube-shaped entities and rope-like nanowires. HRTEM and SAED results indicate that they were single-crystalline face-centered cubic MgO. PACS 81.10.Bk; 79.60.Jv     

XPS study of annealing induced effects on surface and interface electronic properties of Si/Ge nanostructures

The present study is focused on the influence of vacuum thermal treatment on surface/interface electronic properties of Si/Ge multilayer structures (MLS) characterized using X-ray photoelectron spectroscopy (XPS) technique. Desired [Si(5 nm)/Ge(5 nm)]_×10 MLS were prepared using electron beam evaporation technique under ultra high vacuum (UHV) conditions. The core-level XPS spectra of as-deposited as well as multilayer samples annealed at different temperatures such as 100 °C, 150 °C and 200 °C for 1 h show substantial reduction in Ge 2p peak integrated intensity, whereas peak intensity of Si 2p remains almost constant. The complete interdiffusion took place after annealing the sample at 200 °C for 5 h as confirmed from depth profiling of annealed MLS. The asymmetric behaviour in intensity patterns of Si and Ge with annealing was attributed to faster interdiffusion of Si into Ge layer. However, another set of experiments on these MLS annealed at 500 °C suggests that interdiffusion can also be studied by annealing the system at higher temperature for relatively shorter time duration.     

ZnO nanostructures with different morphologies and their field emission properties

Zinc oxide (ZnO) products with the morphologies of balls, nunchakus and belts have been synthesized from aqueous solutions by adjusting the reagent concentration and reaction time. The X-ray diffraction (XRD) peaks of the products were indexed to ZnO materials, but exhibited different relative intensities for the (0 0 2) diffraction peak. Field emission (FE) measurements showed that the turn-on and threshold field for the ZnO nanonunchakus were 3.01 ± 0.005 and 5.47 ± 0.005, 3.71 ± 0.005 and 6.43 ± 0.005 V/μm, respectively, for the ZnO nanobelts, revealing that the products have comparable FE properties with those of the reported ZnO nanowires and carbon nanotubes (CNTs).     

Effect of synthesis route on the morphologies of silver nanostructures by galvanic displacement reaction

The present study is concerned with the preparation of Ag nanostructures by reduction of AgNO₃ with zinc foil by galvanic displacement reaction. The results confirm that the synthesis route has a direct influence on the morphologies of Ag nanostructures. In addition, the effect of synthesis conditions, including the concentration of AgNO₃ aqueous solutions and reaction time, are investigated. X-ray diffraction (XRD), filed emission scanning electron microscope (SEM) and UV-vis spectra are used to characterize the obtained products. A reasonable formation process of Ag nanostructures is proposed based on the characterization results.     

Ultra-long multicolor belts and unique morphologies of tin-doped zinc oxide nanostructures

We demonstrate the synthesis, characterization and application of pure and tin (Sn) doped zinc oxide (ZnO) nanostructures with unique optical properties. Pencil-shaped nanorods were synthesized using a mixture of pure ZnO and carbon as starting material. The growth mechanism of these nanorods is discussed in detail. Sn-doped ultra-long belt-shape ZnO structures show many different colors in a single belt under fluorescent light in an optical microscope. These different colors are attributed to the presence of different defects in the ZnO lattice. X-ray diffraction and UV–VIS spectroscopy results are in good agreement with each other. A major application for these belts is likely to be in a single-particle sensor. A single belt based UV sensor is also fabricated and the results suggest that these photoconducting belts can serve as highly sensitive UV-light detectors.     

Morphology evolution of hierarchical ZnO nanostructures modulated by supersaturation and growth temperature

Three kinds of ZnO hierarchical structures, nanocombs with tube- and needle-shaped teeth and hierarchical nanorod arrays, were successfully synthesized through the chemical vapor deposition method. Combining the experimental parameters, the microcosmic growing conditions (growth temperature and supersaturation) along the flux was discussed at length, and, based on the conclusions, three reasonable growth processes were proposed. The results and discussions were beneficial to further realize the relation between the growing behavior of the nanomaterial and microcosmic conditions, and the hierarchical nanostructures obtained were also expected to have potential applications as functional blocks in future nanodevices. Furthermore, the study of photoluminescence further indicated that the physical properties were strongly dependent on the crystal structure.      

Fascinating morphologies of lead tungstate nanostructures by chimie douce approach

Lead tungstate occurs in nature as tetragonal stolzite of scheelite (CaWO₄) type and monoclinic raspite. In this work, we report, the typical growth of snowflake-like tetragonal stolzite and bamboo-leaf-like monoclinic raspite nanocrystals of PbWO₄ via a simple aqueous precipitation method and a polyol (polyethylene glycol-200) mediated precipitation method at room temperature (27 °C). The synthesised PbWO₄ nanocrystals were characterised by XRD, SEM, EDAX and TGA–DTA. The UV-Vis absorption and photoluminescence studies of PbWO₄ nanocrystals in the two morphologies were performed. The nuclei of PbWO₄ nanocrystals in aqueous medium self-assemble in a tetragonal manner to form the snowflake-like crystals. In polyol medium, PbWO₄ nuclei preferentially grow by oriented attachment process to form the bamboo-leaf-like morphology. The specific morphology of the regularly assembled PbWO₄ nanocrystals in the two phases finds applications in nanoelectronics and photonics. Compared to other well-known scintillators, PbWO₄ is most attractive for high-energy physics applications, because of its high density, short decay time and high irradiation damage resistance.     

The influence of annealing temperature on the morphology of graphene islands

We report on temperature-programmed growth of graphene islands on Ru(0001) at annealing temperatures of 700°C,800°C,and 900°C.The sizes of the islands each show a nonlinear increase with the annealing temperature.In 700°C and 800°C annealings,the islands have nearly the same sizes and their ascending edges are embedded in the upper steps of the ruthenium substrate,which is in accordance with the etching growth mode.In 900°C annealing,the islands are much larger and of lower quality,which represents the early stage of Smoluchowski ripening.A longer time annealing at 900°C brings the islands to final equilibrium with an ordered moir’e pattern.Our work provides new details about graphene early growth stages that could facilitate the better control of such a growth to obtain graphene with ideal size and high quality.     

Controlled synthesis and characterization of layered manganese oxide nanostructures with different morphologies

Layered manganese oxide nanostructures with different morphologies, such as nanowire bundles, cotton agglomerates, and platelikes were successfully fabricated by a simple and template-free hydrothermal method based on a reaction of KMnO₄ and KOH solutions with different concentrations. The obtained nanowire bundles were assembled by nanowires with diameters of 10 to 200 nm and lengths up to 5–10 μm. The cotton agglomerates were composed of manganese oxide layers with a thickness of about 10 nm. Both the concentration of KOH solutions and the reaction temperature played an important role in the formation of layered manganese oxide nanostructures with different morphologies. XRD, SEM, TEM, HRTEM, SAED, TG-DTA, and chemical analysis were employed to characterize these materials. On the basis of the experimental results, a possible formation mechanism of layered manganese oxide nanostructures with different morphologies was presented. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Time-resolved two-photon photoemission spectroscopy of HOPG and Ag nanoparticles on HOPG

Received: 6 November 1998     

Influence of the temperature and duration of the annealing on the lattice structure and growth of the Mg-Al spinel layer

In this paper, MgO film is successfully grown on polycrystalline and monocrystalline alumina substrates using sol-gel method, and polycrystalline and monocrystalline Mg-Al spinels are fabricated by solid state reaction, respectively. The influence of annealing temperature and time on the lattice structure and growth of the formed Mg-Al spinel layer has been investigated. It is indicated that the annealing temperature and time on the as-synthesized polycrystalline Mg-Al spinel has more significant influence than that of single crystal Mg-Al spinel. The thickness of the Mg-Al spinel layer increases with the annealing temperature, both for polycrystalline and for monocrystalline alumina substrates. And the significantly intercrystalline diffusion of Mg²⁺ ions and Al³⁺ ions results in a quicker growth velocity of the Mg-Al spinel layer than that of intracrystalline diffusion.