Fabrication of graphene with CuO islands by chemical vapor deposition

Graphene prepared on Cu foil by chemical vapor deposition was studied as a function of post growth cooling conditions. CuO islands embedded in the graphene film were discovered and studied by scanning electron microscopy, atomic force microscopy, and X-ray photoemission spectroscopy. It is shown that nanostructured holes can be formed within a graphene film by reduction using hydrogen cooling immediately after film growth. We also observe the formation of symmetrical oxide islands in these holes. This study provides an easy way to fabricate a graphene + CuO composite, and the method may be extended to other graphene based structures.     

Magic carbon clusters in the chemical vapor deposition growth of graphene

Ground-state structures of supported C clusters, C(N) (N = 16, ..., 26), on four selected transition metal surfaces [Rh(111), Ru(0001), Ni(111), and Cu(111)] are systematically explored by ab initio calculations. It is found that the core-shell structured C(21), which is a fraction of C(60) possessing three isolated pentagons and C(3v) symmetry, is a very stable magic cluster on all these metal surfaces. Comparison with experimental scanning tunneling microscopy images, dI/dV curves, and cluster heights proves that C(21) is the experimentally observed dominating C precursor in graphene chemical vapor deposition (CVD) growth. The exceptional stability of the C(21) cluster is attributed to its high symmetry, core-shell geometry, and strong binding between edge C atoms and the metal surfaces. Besides, the high barrier of two C(21) clusters' dimerization explains its temperature-dependent behavior in graphene CVD growth.     

Crystalline orientation of the InN films prepared by atmospheric pressure halide chemical vapor deposition

The structural analysis of the hexagonal InN film prepared on a Si(100) substrate by the AP-HCVD technique using InCl₃ and NH₃ as starting materials were carried out by the X-ray pole figure analysis. The deposited films consist of the hexagonal InN pillar crystals. It was found that the pillar crystals, which have random rotation around the 100 axis, were grown at an angle of 70–90° to the substrate.     

Low temperature growth of highly nitrogen-doped single crystal graphene arrays by chemical vapor deposition

The ability to dope graphene is highly important for modulating electrical properties of graphene. However, the current route for the synthesis of N-doped graphene by chemical vapor deposition (CVD) method mainly involves high growth temperature using ammonia gas or solid reagent melamine as nitrogen sources, leading to graphene with low doping level, polycrystalline nature, high defect density and low carrier mobility. Here, we demonstrate a self-assembly approach that allows the synthesis of single-layer, single crystal and highly nitrogen-doped graphene domain arrays by self-organization of pyridine molecules on Cu surface at temperature as low as 300 °C. These N-doped graphene domains have a dominated geometric structure of tetragonal-shape, reflecting the single crystal nature confirmed by electron-diffraction measurements. The electrical measurements of these graphene domains showed their high carrier mobility, high doping level, and reliable N-doped behavior in both air and vacuum.     

Characterization of iron catalysts prepared by chemical vapor deposition on nonzeolitic supports

Chemical vapor deposition (CVD) of FeCl3 has been used to deposit Fe3+ ions on the surface of sulfated zirconia (SZ) and silica-alumina (SA). Upon exposure to FeCl3 vapor most Br?nsted acid sites and silanol groups are replaced by Fe, as evidenced by IR. With SZ the concentration of the acid sites and thus the retention of Fe increase with the sulfate loading up to approximately 45% of a monolayer, followed by an abrupt decrease at higher loadings. This indicates condensation of sulfate groups to polysulfates, which is in line with a lower number of Br?nsted sites per sulfate. Release of HCl due to the reaction of Br?nsted sites with FeCl3 peaks at 85 degrees C for SZ but only at 345 degrees C for SA. After replacing Cl- by OH- and calcining, the materials were tested as De-NOx catalysts and characterized by temperature-programmed reduction (TPR) with H2 or CO. Mononuclear and dinuclear oxo-ions of Fe coexist with Fe oxide particles in calcined Fe/SA, resulting in a low selectivity for NOx reduction. During reduction of Fe/SA up to 800 degrees C, a significant fraction of the Fe forms a chemical compound with SA, possibly an aluminate. In Fe/SZ the Fe dramatically increases the reducibility of the sulfate groups, from 57% partial reduction to SO2 in the absence of Fe, to 90% deep reduction to S2- ions in its presence. Formation of Fe sulfide is indicated by the enhanced sulfur retention upon reduction. Fe/SZ is active for NOx reduction with isobutane. Catalysts with low Fe content that are prepared by controlled sublimation are superior to those prepared by impregnation. At 450 degrees C and GHSV = 30,000 h(-1), 65% of NOx is reduced to N2 in excess O2.     

Morphology engineering and etching of graphene domain by low-pressure chemical vapor deposition

Controlled growth of single-crystal high-quality ‘track-and-field ground’ shaped graphene domains and the morphological evolution from hexagonal to hexagram graphene domain even square and circular graphene domain has been achieved by low-pressure CVD on solid copper substrate, thereby demonstrating that the shape of the graphene grains can potentially be precisely tuned by optimizing growth parameters. The etching reaction of graphene has also been studied, and results show that a low flow rate of hydrogen (99.999%) is favorable to form hexagonal structure for the etching reaction of graphene due to the exist of oxygen or oxidizing impurities in hydrogen gas commonly used. Controlled growth and etching reaction of graphene determine the final shape of graphene domains and all these efforts contribute to the study of size and morphology and the growth mechanism of graphene domains.     

Large-area graphene single crystals grown by low-pressure chemical vapor deposition of methane on copper

Graphene single crystals with dimensions of up to 0.5 mm on a side were grown by low-pressure chemical vapor deposition in copper-foil enclosures using methane as a precursor. Low-energy electron microscopy analysis showed that the large graphene domains had a single crystallographic orientation, with an occasional domain having two orientations. Raman spectroscopy revealed the graphene single crystals to be uniform monolayers with a low D-band intensity. The electron mobility of graphene films extracted from field-effect transistor measurements was found to be higher than 4000 cm(2) V(-1) s(-1) at room temperature.     

Seedless growth of free-standing copper nanowires by chemical vapor deposition

Free-standing copper nanowires were synthesized by a chemical vapor deposition process at low substrate temperatures using Cu(etac)[P(OEt)3]2 as a precursor. The process requires neither templates nor catalysts to produce copper nanowires of 70-100 nm in diameter, which exhibited high purity and crystallinity with [111] orientation. The grain structures of the films deposited from a series of Cu(I) alkyl 3-oxobutanoate complexes indicated that the high precursor stability was responsible for the columnar growth of the grains, which was evolved to the nanowires eventually.     

A catalytic chemical vapor deposition synthesis of double-walled carbon nanotubes over metal catalysts supported on a mesoporous material

Double-walled carbon nanotubes (DWNTs) have been synthesized by catalytic chemical vapor deposition (CCVD) over supported metal catalysts decomposed from Fe(CH₃COO)₂ and Co(CH₃COO)₂ on mesoporous silica. Bundles of tubes with relatively high percentage of DWNTs, in areas where tubular layered structures could be clearly resolved, have been observed by transmission electron microscopy (TEM). In other areas, crystal-like alignment of very uniform DWNTs was observed for the first time, suggesting that mesoporous silica might play a templating role in guiding the initial nanotube growth. In addition, compatible with nano-electronics research, bridging of catalytic islands by DWNTs has also been demonstrated.     

A general atmospheric pressure chemical vapor deposition synthesis and crystallographic study of transition-metal sulfide one-dimensional nanostructures

A series of transition-metal sulfide one-dimensional (1D) nanostructures have been synthesized by means of a general atmospheric pressure, chemical vapor deposition (APCVD) strategy. Vapour-liquid-solid (VLS) and vapour-solid (VS) mechanisms, along with the results of SEM and TEM observations, were used to explain the formation of these nanostructures. The regularity of the growth in the direction of the hexagonal nanowire is explored; we find that it prefers to grow along (1 0 0), (1 1 0), or (0 0 x) directions owing to particular crystal structures. The adopted synthetic route was expected to provide abundant useful 1D building blocks for the research of mesoscopic physics and fabrication of nanoscale devices.     

Synthesis and characterization of silicon nanowires on mesophase carbon microbead substrates by chemical vapor deposition

Silicon nanowires (SiNWs) have been fabricated by chemical vapor deposition at ambient pressure using SiCl(4) as a silicon source and mesophase carbon microbead powder as a substrate without any templates and/or metal catalysts. The SiNWs have a crystalline core with a very thin amorphous SiO(x) sheath. The obtained SiNWs are homogeneous with average diameters below 50 nm and lengths up to micrometers. Temperature and time effects on the growth of SiNWs were systematically studied. Higher reaction temperatures and longer reaction times resulted in larger diameters and higher yields of SiNWs. SiNWs with a better crystallinity can be obtained at higher temperatures and longer reaction times. The obtained SiNWs were characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy.     

Dendrimer-assisted low-temperature growth of carbon nanotubes by plasma-enhanced chemical vapor deposition

Using a shielded growth approach and N2-annealed, nearly monodispersed Fe2O3 nanoparticles synthesized by interdendritic stabilization of Fe3+ species within fourth-generation poly(amidoamine) dendrimers, carbon nanotubes and nanofibers were successfully grown at low substrate temperatures (200-400 degrees C) by microwave plasma-enhanced chemical vapor deposition.     

Preferential growth of single-walled carbon nanotubes on silica spheres by chemical vapor deposition

The preferential growth of single-walled carbon nanotubes (SWNTs) on silica spheres with various diameters was realized for the first time by chemical vapor deposition (CVD) of methane. SWNTs tend to wrap the silica spheres to form a new superstructure of uniform SWNT nanoclaws when the diameters of the silica spheres are larger than 400 nm. The SWNTs obtained on silica spheres have highly graphitic tubular walls as characterized by Raman spectroscopy and HRTEM. This is a new method to obtain tunable uniform elastic deformation of SWNTs, which may act as the model for the study about the effect of delocalized bending on the properties of SWNTs. In addition, the combination of SWNTs with monodispersed silica spheres could conveniently integrate SWNTs into photonic crystals.     

On-wafer thermomechanical characterization of a thin film polyimide formed by vapor deposition polymerization for through-silicon via applications: Comparison to plasma-enhanced chemical vapor deposition SiO2

Thin-film polyimides were prepared by solvent-less vapor deposition polymerization (VDP) from pyromellitic dianhydride and 4,4′-oxydianiline at 200 °C for liner dielectric formation of vertical interconnects called through-silicon vias (TSVs) used in three-dimensionally stacked integrated circuit (3DICs). FTIR, synchrotron XPS, and TDS were employed for determining the imidization ratio, and in addition, the mechanical properties, coefficient of thermal expansion and Young's modulus, of the VDP polyimide were characterized on Si wafers. The VDP polyimide exhibited extremely high conformality, beyond 75%, toward high-aspect-ratio deep Si holes, compared with conventional SiO₂ prepared by plasma-enhanced chemical vapor deposition. The adhesion between the VDP polyimide and Si wafer was enhanced by an Al-chelate promotor. Remarkably, the VDP polyimide TSV liner dielectrics showed much less thermomechanical stresses applied to the Si surrounding the TSVs than the plasma-chemical vapor deposition SiO₂. The small keep-out zone is expected for scaling down highly reliable 3DICs for the upcoming real artificial intelligence society.     

Crystal quality,electrical and optical properties of single crystal pyrite films prepared by chemical vapor deposition under atmospheric pressure

Crystal quality, electrical and optical properties of single crystal thin films of pyrite prepared by means of chemical vapor deposition under atmospheric pressure (AP-CVD) using FeCl₃ and CH₃CSNH₂ as starting materials have been studied by various analytical method. X-ray diffraction and pole figure measurements showed that the as-grown films are single crystal. It was found that the quality of the pyrite films grown on a Si(100) substrate is significantly dependent upon the ratio of CH₃CSNH₂:FeCl₃ used as source materials. Electrical conductivity and Hall mobility increases as the CH₃CSNH₂:FeCl₃ ratio is increased, while carrier concentration decreases. This is explained in term of the formation of sulphur vacancies. A decrease of the CH₃CSNH₂:FeCl₃ ratio causes the increase of sulphur defects in the pyrite film. This also increases the number of electrons being trapped by the defects, while their mobility is reduced because of the electron being scattering at the vacancies. Strong absorption occurs in the photon energy range higher than 1 eV, and then reaches plateau with an absorption coefficient of about $5\times {10}^4{\text{cm}}^{-1}$ at $E>2\text{eV}$.     

Low-temperature growth of single-walled carbon nanotubes by water plasma chemical vapor deposition

Preferential growth of pure single-walled carbon nanotubes (SWNTs) over multi-walled carbon nanotubes (MWNTs) was demonstrated at low temperature by water plasma chemical vapor deposition. Water plasma lowered the growth temperature down to 450 degrees C, and the grown nanotubes were single-walled without carbonaceous impurities and MWNTs. The preferential growth of pure SWNTs over MWNTs was proven with micro-Raman spectroscopy, high-resolution transmission electron microscopy, and electrical characterization of the grown nanotube networks.     

Bulk synthesis of large diameter semiconducting single-walled carbon nanotubes by oxygen-assisted floating catalyst chemical vapor deposition

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a mean diameter of 1.6 nm were synthesized on a large scale by using oxygen-assisted floating catalyst chemical vapor deposition. The oxygen introduced can selectively etch metallic SWCNTs in situ, while the sulfur growth promoter functions in promoting the growth of SWCNTs with a large diameter. The electronic properties of the SWCNTs were characterized by laser Raman spectroscopy, absorption spectroscopy, and field effect transistor measurements. It was found that the content of s-SWCNTs in the samples was highly sensitive to the amount of oxygen introduced. Under optimum synthesis conditions, enriched s-SWCNTs can be obtained in milligram quantities per batch.     

Enhancing the pyrolysis of scrap rubber for carbon nanotubes/graphene production via chemical vapor deposition

Carbon nanostructures are considered nowadays as very important materials for both fundamental research and industrial applications because of their well-defined morphologies, which leads to excellent performance in various fields. This study presents the preparation of carbon nanostructures starting from cheap source represented by scrap rubber after pursuing optimized pyrolysis of scrap rubber at 500^oC as deduced from thermal gravimetric analysis (TGA). The resulting cracked hydrocarbons from pyrolysis were collected over a well-designed Fe-Ni-Cu/MgO as catalyst via chemical vapor deposition (CVD), in which a growth temperature of 750^oC was undertaken for 60 min. A further attempt was elaborated where the scrap rubber was exposed to thermal aging at 90^oC for 14 days prior to CVD of its pyrolysis products in order to enhance the cracking process and increase the yield of the lighter hydrocarbons produced which leads to formation of well-defined carbon nanostructures. Characterizations on the produced carbon nanostructures were achieved using transmission electron microscopy (TEM) and Raman spectroscopy. The adsorption of methylene blue on the carbon nanostructures was also studied. The characterizations confirmed that the morphology of the resulting carbon nanostructures derived from scrap rubber without prior thermal aging composed of graphene sheets wrapping carbon nanotubes (CNTs-A). After thermal aging of scrap rubber prior to pyrolysis and CVD, the produced carbon nanostructures composed principally of CNTs (CNTs-B) in a well-defined form in higher yield. The Langmuir model appeared to be best-fitting the adsorption of MB on both samples. High monolayer adsorption capacity of 95 mg MB/g was accomplished in case of CNTs-A versus 60 mg MB/g in case of CNTs-B, respectively. Ultraviolet-Visible (UV-Vis.) spectroscopic study revealed that the presence of MB molecules on the surface of CNTs may enhance the electronic properties of the prepared samples.     

Magnetic property and structural study of nickel supported on reduced graphene oxide prepared by chemical vapor deposition

Nickel supported on reduced graphene oxide was synthesized by chemical vapor deposition technique. The crystal structure and magnetic properties of the prepared sample were studied by means of Raman spectrometry, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectrometry (ICP-OES), and vibrating sample magnetometry (VSM). The result of Raman spectroscopy revealed the structure of few-layer graphene as the support for Ni nanoparticles. XP spectrum confirmed the presence of metallic Ni on the a few-layer graphene surface. TE micrograph showed that the nickel nanoparticles were sphere shaped and the mean particle size is about 20 nm deposited on the reduced graphene oxide. The magnetic study showed the ferromagnetic behavior of 3.2 wt% nickel over reduced graphene oxide at room temperature.     

Synthesis of helical and straight carbon nanofibers by chemical vapor deposition using alkali chloride catalysts

Microchimica Acta - Carbon nanofibers were synthesized by chemical vapor deposition using alkali chloride catalysts at a temperature range from 500 to 700 °C. Depending on the...