Vapor Phase Deposition Method Research Articles

The Discovery of Plasmon Resonance in Germanide Nanowires Grown on Cu Foil

Free-standing and single-crystalline Cu3Ge nanowires (NWs) were synthesized by a vapor-phase deposition method on the Cu foil. The NWs are grown along the [010] direction via a vapor–solid mechanism. The localized surface plasmon resonance of individual NWs on a Si substrate is investigated using the dark-field scattering spectroscopy. The resonance peak wavelength for NWs with different diameters is observed, which ranges from 500 to 550 nm. This study proves the existence and provides an insight for understanding the LSPR property of free-standing Cu3Ge NWs.

Detection of volatile organic compounds using flexible gas sensing devices based on tungsten oxide nanostructures functionalized with Au and Pt nanoparticles

Flexible gas sensor devices are fabricated and optimized by integrating directly, via a single-step vapor-phase deposition method, highly crystalline tungsten oxide nanostructures functionalized with either gold or platinum nanoparticles. Gas tests of these devices show significant improvements with respect to flexible gas sensors based on non-functionalized structures, including greater responses to various volatile organic compounds (ethanol, acetone, methanol and toluene) and better selectivity towards ethanol and methanol, as demonstrate results for the sensors based on platinum-functionalized structures. The method presented here, which includes the fabrication of the whole flexible gas sensing device and the integration of functional nanostructures without the use of transfer methods, provides a simpler, faster and inexpensive method for the fabrication of highly functional flexible microsystems for gas sensing.

Formation of ripples in atomically thin MoS2 and local strain engineering of electrostatic properties

Ripple is a common deformation in two-dimensional materials due to localized strain, which is expected to greatly influence the physical properties. The effects of the ripple deformation in the MoS2 layer on their physics, however, are rarely addressed experimentally. We here grow atomically thin MoS2 nanostructures by employing a vapor phase deposition method without any catalyst and observed the ripples in MoS2 nanostructures. The MoS2 ripples exhibit quasi-periodical ripple structures in the MoS2 surface. The heights of the ripples vary from several angstroms to tens of nanometers and the wavelength is in the range of several hundred nanometers. The growth mechanism of rippled MoS2 nanostructures is elucidated. We have also simultaneously investigated the electrostatic properties of MoS2 ripples by using Kelvin probe force microscopy, which shows inhomogeneous surface potential and charge distributions for MoS2 ripple nanostructures with different local strains.

Synthesis, characterization of WS2 nanostructures by vapor phase deposition

Ultrathin two-dimensional WS2 nanostructures with various morphologies have been prepared on SiO2/Si (300 nm) and sapphire substrates by vapor phase deposition method. Simultaneously, tungsten nanostructures have also been obtained during the growth process. The nanostructures and morphologies of as-prepared products were systematically characterized by employing atomic force microscopy, Raman spectroscopy as well as scanning electron spectroscopy. The electrostatic properties of WS2 nanostructures were investigated exhibiting uniform surface potential and charge distributions. We have also detected the photoluminescence properties of WS2 nanostructures, which are dependent on the thickness and nanostructures of synthesized WS2. These results suggest that the optoelectronic properties of WS2 nanostructures can be effectively tuned by quantum confinement effect and nanostructures.

Revealing the Preferred Interlayer Orientations and Stackings of Two‐Dimensional Bilayer Gallium Selenide Crystals

Characterizing and controlling the interlayer orientations and stacking orders of two-dimensional (2D) bilayer crystals and van der Waals (vdW) heterostructures is crucial to optimize their electrical and optoelectronic properties. The four polymorphs of layered gallium selenide (GaSe) crystals that result from different layer stackings provide an ideal platform to study the stacking configurations in 2D bilayer crystals. Through a controllable vapor-phase deposition method, bilayer GaSe crystals were selectively grown and their two preferred 0° or 60° interlayer rotations were investigated. The commensurate stacking configurations (AA' and AB stacking) in as-grown bilayer GaSe crystals are clearly observed at the atomic scale, and the Ga-terminated edge structure was identified using scanning transmission electron microscopy. Theoretical analysis reveals that the energies of the interlayer coupling are responsible for the preferred orientations among the bilayer GaSe crystals.

Effect of Crystalline Quality on Magnetic Properties of Mn-Doped ZnO Nanowires

Mn-doped ZnO nanowires are synthesized by a vapor phase deposition method in air and in a vacuum, respectively. X-ray diffraction results show that all the diffraction peaks correspond to the hexagonal wurtzite structure. X-ray absorption fine structure spectra suggest that a single Mn2+-containing phase exists and Mn2+ions occupy Zn2+ ions in the ZnO lattice. Photoluminescence spectra show that many defects exist in the doped nanowires as the samples grown in air, and the crystalline quality decreases with the increase of Mn. These samples exhibit obvious room-temperature ferromagnetic characteristics, and the magnetization increases with the increase of Mn. The sample with higher crystal quality grown in a vacuum exhibits the paramagnetic behavior at room temperature. As the as-grown samples are annealed, the crystalline quality improves, while the magnetization of the samples grown under the air condition translates from room-temperature ferromagnetism to the paramagnetism behavior. The above results indicate that the magnetic property of the Mn-doped ZnO nanowires can be controlled by the crystalline quality.

A comparative study of size-dependent magnetoresistance and Hall resistance of Sb2Te3 nanoflakes

Single crystal Sb2Te3 topological insulator nanoflakes with the thickness of 25nm and 456nm were synthesized via vapor phase deposition method. The Hall resistance and magnetoresistance of the nanoflakes have been measured at temperatures 2K and 300K in the fields up to 9T. The magnetoresistance and Hall resistance of the nanoflakes demonstrate significant differences, so that despite ordinary magnetoresistance and Hall effect obtained for 25nm sample 450nm nanoflake demonstrates unusual magnetoresistance and nonlinear Hall resistance. The sense of curvature of both Rxx(B) and Rxy(B) dependences is inversed at high temperature. The experimental data have been analyzed in the frame of a multichannel transport model. The difference in the behavior is attributed to the existence of the charge carriers with high and low mobility, as well as to their relative contribution (which varies depending on the temperature) to the magneto-transport of the nanoflakes.

Photoresponse properties of large-area MoS2 atomic layer synthesized by vapor phase deposition

Photoresponse properties of a large area MoS2 atomic layer synthesized by vapor phase deposition method without any catalyst are studied. Scanning electron microscopy, atomic force microscopy, Raman spectrum, and photoluminescence spectrum characterizations confirm that the two-dimensional microstructures of MoS2 atomic layer are of high quality. Photoelectrical results indicate that the as-prepared MoS2 devices have an excellent sensitivity and a good reproducibility as a photodetector, which is proposed to be ascribed to the potential-assisted charge separation mechanism.

Magnetotransport properties of Sb2Te3 nanoflake

Magnetotransport properties of a single crystal Sb2Te3 topological insulator nanoflake with the thickness of 25nm, synthesized via a vapor phase deposition method, are studied. The mobility and number of carriers are obtained through the Hall resistance measurement data. The magnetoresistance shows pronounced weak antilocalization effect. Temperature dependence of the phase coherence length confirms the 2D nature of the observed weak antilocalization effect. The fluctuations in the magnetoresistance are attributed to the combined contribution of the universal conductance fluctuation and the Shubnikov de Haas oscillations of the 2D electron gas. The Shubnikov de Haas oscillations reveal two well defined frequencies ascribed to states with spin-up and spin-down polarizations. The Rashba parameter and the energy gap between the two spin polarized subbands have been obtained and were equal to δ=0.75×10−11eVm and ΔE=2.4meV correspondingly.

Controlled vapor phase growth of single crystalline, two-dimensional GaSe crystals with high photoresponse.

Compared with their bulk counterparts, atomically thin two-dimensional (2D) crystals exhibit new physical properties, and have the potential to enable next-generation electronic and optoelectronic devices. However, controlled synthesis of large uniform monolayer and multi-layer 2D crystals is still challenging. Here, we report the controlled synthesis of 2D GaSe crystals on SiO2/Si substrates using a vapor phase deposition method. For the first time, uniform, large (up to ~60 μm in lateral size), single-crystalline, triangular monolayer GaSe crystals were obtained and their structure and orientation were characterized from atomic scale to micrometer scale. The size, density, shape, thickness, and uniformity of the 2D GaSe crystals were shown to be controllable by growth duration, growth region, growth temperature, and argon carrier gas flow rate. The theoretical modeling of the electronic structure and Raman spectroscopy demonstrate a direct-to-indirect bandgap transition and progressive confinement-induced bandgap shifts for 2D GaSe crystals. The 2D GaSe crystals show p-type semiconductor characteristics and high photoresponsivity (~1.7 A/W under white light illumination) comparable to exfoliated GaSe nanosheets. These 2D GaSe crystals are potentially useful for next-generation electronic and optoelectronic devices such as photodetectors and field-effect transistors.

ZnO nanowires modified with Au nanoparticles for nonenzymatic amperometric sensing of glucose

ZnO nanowires (NWs) synthesized using the vapor-phase deposition method on an Au electrode substrate with and without Au nanoparticle (NP) modification are applied for glucose detection. A significant enhancement of glucose sensitivity is obtained with Au NP modification. The Au NPs/ZnO NWs/Au electrode has peak currents gradually increasing from 41.2 to 155.5 μA, and the ZnO NWs/Au electrode has peak currents increasing from 23.6 to 82.2 μA with glucose concentration (5, 10, 15, 20, and 25 mM) in cyclic voltammograms. Moreover, chronoamperometry results indicate that the response current of the Au NPs/ZnO NWs/Au electrode reached 140 μA in 18 mM glucose in 0.1M NaOH, whereas that of the ZnO NWs/Au electrode was only around 74 μA in 31.5 mM glucose.

Synthesis, characterization and electrostatic properties of WS2 nanostructures

We report the direct growth of atomically thin WS2 nanoplates and nanofilms on the SiO2/Si (300 nm) substrate by vapor phase deposition method without any catalyst. The WS2 nanostructures were systematically characterized by optical microscopy, scanning electron microscopy, Raman microscopy and atomic force microscopy. We found that growth time and growth temperature play important roles in the morphology of WS2 nanostructures. Moreover, by using Kelvin probe force microscopy, we found that the WS2 nanoplates exhibit uniform surface and charge distributions less than 10 mV fluctuations. Our results may apply to the study of other transition metal dichalcogenides by vapor phase deposition method.

Comparative study of solution–phase and vapor–phase deposition of aminosilanes on silicon dioxide surfaces

The uniformity of aminosilane layers typically used for the modification of hydroxyl bearing surfaces such as silicon dioxide is critical for a wide variety of applications, including biosensors. However, in spite of many studies that have been undertaken on surface silanization, there remains a paucity of easy-to-implement deposition methods reproducibly yielding smooth aminosilane monolayers. In this study, solution- and vapor-phase deposition methods for three aminoalkoxysilanes differing in the number of reactive groups (3-aminopropyl triethoxysilane (APTES), 3-aminopropyl methyl diethoxysilane (APMDES) and 3-aminopropyl dimethyl ethoxysilane (APDMES)) were assessed with the aim of identifying methods that yield highly uniform and reproducible silane layers that are resistant to minor procedural variations. Silane film quality was characterized based on measured thickness, hydrophilicity and surface roughness. Additionally, hydrolytic stability of the films was assessed via these thickness and contact angle values following desorption in water. We found that two simple solution-phase methods, an aqueous deposition of APTES and a toluene based deposition of APDMES, yielded high quality silane layers that exhibit comparable characteristics to those deposited via vapor-phase methods.

High carrier mobility of CoPc wires based field-effect transistors using bi-layer gate dielectric

Polyvinyl alcohol (PVA) and anodized Al2O3 layers were used as bi-layer gate for the fabrication of cobalt phthalocyanine (CoPc) wire base field-effect transistors (OFETs). CoPc wires were grown on SiO2 surfaces by organic vapor phase deposition method. These devices exhibit a field-effect carrier mobility (μEF) value of 1.11 cm2/Vs. The high carrier mobility for CoPc molecules is attributed to the better capacitive coupling between the channel of CoPc wires and the gate through organic-inorganic dielectric layer. Our measurements also demonstrated the way to determine the thicknesses of the dielectric layers for a better process condition of OFETs.

Spiral growth of topological insulator Sb2Te3 nanoplates

Sb2Te3 nanoplates synthesized by vapor phase deposition method have been systemically investigated employing atomic force microscopy, which exhibit regular spiral structures on the surface. The height of spiral steps is determined to be 1 nm corresponding to one quintuple layer, with an inter-step separation ranging from 500 nm to 1 μm. Growth mechanism of spiral structures on the Sb2Te3 nanoplate surface is elucidated, which can be applied to other layered materials with van der Waals epitaxy growth. The electrostatic properties of Sb2Te3 nanoplates with spiral structures are also simultaneously characterized.

Electrodeposited three-dimensional Ni–Si nanocable arrays as high performance anodes for lithium ion batteries

A configuration of three-dimensional Ni-Si nanocable array anodes is proposed to overcome the severe volume change problem of Si during the charging-discharging process. In the fabrication process, a simple and low cost electrodeposition is employed to deposit Si instead of the common expansive vapor phase deposition methods. The optimum composite nanocable array electrode achieves a high specific capacity ~1900 mA h g(-1) at 0.05 C. After 100 cycles at 0.5 C, 88% of the initial capacity (~1300 mA h g(-1)) remains, suggesting its good capacity retention ability. The high performance of the composite nanocable electrode is attributed to its excellent adhesion of the active material on the three-dimensional current collector and short ionic/electronic transport pathways during cycling.

Electrical Properties of Polycrystalline α-HgI2 Detector

Potentially low cost and large-area polycrystalline mercuric iodide (α-HgI2) is one of the preferred materials for the fabrication of room temperature X-ray and gamma-ray detectors. In this paper, polycrystalline α-HgI2 films have been grown through combining vertical deposition method with hot wall vapor phase deposition (HWPVD) method. X-ray diffraction (XRD), scan electron microscopes (SEM) and Raman spectrum were used to characterization the HgI2 films obtained, and I-V characteristics was also tested. Using the polycrystalline α-HgI2 films, we get the detector. According to the detector, on the one hand, a dark current test is made by using KEITHL EY 485 picoammeter; on the other hand, the Agilent 4294A precision impedance analyzer is taken to test the characteristic curve of its capacitor frequency.

Fermi level shift in topological insulator–silicon heterostructures

Ultrathin high-quality Bi2Te3 and Bi2Se3 topological insulator nanoplates are prepared on n-type and p-type silicon (111) substrates via vapor phase deposition method forming topological insulator–silicon heterostructures. The quantitative results obtained by Kelvin probe force microscopy indicate that the work function and Fermi level of both Bi2Te3 and Bi2Se3 nanoplates depend on the substrates, which are ascribed to the charge exchange that exists at the interface between nanoplates and silicon substrates with different doping. Our results provide an effective strategy to tune electronic properties of TI nanostructures through topological insulator–silicon heterostructures.

Tribological investigations of perfluoroalkylsilanes monolayers deposited on titanium surface

Therefore the present work reports a systematic study of titanium modification by fluoroalkylsilanes and surface characterization from the tribological point of view. The vapor phase deposition method was used to modify titanium surfaces by fluoroalkylsilanes and the influence of the used modifier on the tribological properties is presented. The modification procedure efficiency, surface structure and morphology were characterized by secondary ion mass spectrometry, infrared spectroscopy and atomic force microscopy.The effectiveness of modification of the titanium surface was monitored by the measurement of the wetting contact angle and the surface free energy. The increase of surface hydrophobicity was observed upon the modification by increasing the wetting contact angle and reducing the surface free energy. The tribological performance of various perfluoroalkylsilanes films on the titanium surface was investigated in mili- and nano-newton load ranges. Dependence of the adhesive force and coefficient of friction values obtained in nano- and micro-scale on fluoroalkyl chain length was observed.Nano- and micro-tribological measurements show that titanium modified by fluoroalkylsilanes has lower adhesion and coefficient of friction than unmodified one. The investigation also indicates a decrease of the friction coefficient with increasing fluoric alkyl chain length. It was found that the titanium modified by fluoroalkylsilanes with longer alkyl chains is a prime candidate for practical use as a lubricant in biomedical and electronic applications.

Investigation of the structure of fluoroalkylsilanes deposited on alumina surface

This paper presents investigation of the structure of fluoroalkylsilanes on alumina surface by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), Fourier transform infrared (FT-IR) spectroscopy and atomic force microscopy (AFM).The fluoroalkylsilanes were prepared on alumina surface using the vapor phase deposition (VPD) method. XPS and ToF-SIMS measurements confirm the presence of fluoroalkylsilanes on the alumina surface. AFM was used to compare the frictional behavior of samples after modifying the alumina surface by fluoroalkylsilanes. Nanotribological studies of fluoroalkylsilanes films with different head groups on the alumina surface include, besides frictional studies, also adhesive forces investigations.It is shown that surface modification of alumina by fluoroalkylsilanes decreases coefficient of friction and adhesive forces values by more than 50% compared to unmodified alumina. In comparison to a non-modified alumina surface all tested silanes, particularly compounds with three reactive atoms in the head group, cause a decrease in the friction coefficients in nanofriction tests. The same effect was also observed for adhesion measurements. It was found that the alumina modified by trifunctional fluoroalkylsilanes have a higher degree of hydrophobicity, lower adhesion, and lower coefficient of friction than the monofunctional fluoroalkylsilanes covered alumina surface.