Precursors For Chemical Vapor Deposition Research Articles

Coexistence of Van Hove singularities and pseudomagnetic fields in modulated graphene bilayer

The stacking and bending of graphene are trivial but extremely powerful agents of control over graphene’s manifold physics. By changing the twist angle, one can drive the system over a plethora of exotic states via strong electron correlation, thanks to the moiré superlattice potentials, while the periodic or triaxial strains induce discretization of the band structure into Landau levels without the need for an external magnetic field. We fabricated a hybrid system comprising both the stacking and bending tuning knobs. We have grown the graphene monolayers by chemical vapor deposition, using 12C and 13C precursors, which enabled us to individually address the layers through Raman spectroscopy mapping. We achieved the long-range spatial modulation by sculpturing the top layer (13C) over uniform magnetic nanoparticles (NPs) deposited on the bottom layer (12C). An atomic force microscopy study revealed that the top layer tends to relax into pyramidal corrugations with C3 axial symmetry at the position of the NPs, which have been widely reported as a source of large pseudomagnetic fields (PMFs) in graphene monolayers. The modulated graphene bilayer (MGBL) also contains a few micrometer large domains, with the twist angle ∼10°, which were identified via extreme enhancement of the Raman intensity of the G-mode due to formation of van Hove singularities (VHSs). We thereby conclude that the twist-induced VHSs coexist with the PMFs generated in the strained pyramidal objects without mutual disturbance. The graphene bilayer modulated with magnetic NPs is a non-trivial hybrid system that accommodates features of twist-induced VHSs and PMFs in environs of giant classical spins.

Facile one-step synthesis of N-doped carbon nanotubes/N-doped carbon nanofibers hierarchical composites by chemical vapor deposition

The composites consisting of nitrogen-doped carbon nanotubes (N-CNTs) and nitrogen-doped carbon nanofibers (N-CNFs) were fabricated using a mixture of nickel foam (template) and imidazole (solid precursor) in a facile one-step chemical vapor deposition (CVD) process. The morphology and microstructure of the N-doped carbon nanotubes/N-doped carbon nanofibers hierarchical composites (N-CNTs/N-CNFs) were determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectra, and X-ray photoelectron spectroscopy. The results indicated that the sample manifests regular hierarchical composites, great graphitization, and nitrogen doping. Furthermore, a probable growth mechanism is presented to analyze the composites.

Synthesis, characterization, and thermal properties of novel silicon 1,1,3,3‐tetramethylguanidinate derivatives and use as single‐source chemical vapor deposition precursors

AbstractA series of chemical vapor deposition (CVD) precursors have been synthesized by a single‐step reaction of 1,1,3,3‐tetramethylguanidine and a variety of silicon chlorides. The structures of the 1,1,3,3‐tetramethylguanidinate‐based compounds were verified by 1H NMR, 13C NMR, XPS, EI‐MS, and elemental analysis. The thermal stability, transport behavior, and vapor pressures of these compounds were evaluated by simultaneous thermal analyses (STA). These compounds are highly stable and those in liquid form are very volatile. Silicon carbonitride (SiCN) thin films were prepared by using bis (tetramethylguanidine)‐dimethyl‐silane as the precursor in helicon wave plasma chemical vapor deposition (HWP‐CVD). The properties of the films were investigated by SEM, AFM, and XPS. The results showed that the films have good uniformities, low friction coefficient, and high hardness, enabling the films for fabrication of semiconductor devices.

Exploring 1-butanol as a potential liquid precursor for graphene synthesis via chemical vapour deposition and enhanced catalyzed growth methodology

In this study, 1-butanol (C4H9OH) was used as a potential precursor for atmospheric pressure chemical vapour deposition grown graphene. While graphene were obtainable at moderate to high precursor flow rate, they were of double to multilayer as evident from Raman and ultra-violet visible spectroscopy. Here, a simple yet novel growth procedure was implemented to obtain monolayer graphene at much lower precursor flow rate. The procedure utilized additional copper which enable a richer flux of carbonaceous radicals to be produced through catalytic decomposition, leading to high-quality monolayer graphene to be grown on copper substrate. This type of graphene was characterized with Raman of two excitation sources, and the results were consistent with each other. It was found that it exhibited highest I2D/IG intensity ratio (~ 4.85), largest average crystallite size (La, ~ 188 nm), and smallest defect level among other samples. Due to the latter, it possessed lowest sheet resistance compared with other samples (~ 7.75 kΩ/sq). Lastly, the graphene samples were characterized using x-ray photoelectron spectroscopy, where the deconvoluted spectra reveal sub-components of sp2 and sp3 states of carbon, which could provide insights on the reaction mechanics about the transformation of butanol to graphene.

Extraordinary synergetic effect of precursors in laser CVD deposition of SiBCN films

Herein, we report on the synergetic effect of simultaneously using of hexamethyldisilane (HMDS) and trimethylamine borane (TMAB) as precursors for a high-rate laser chemical vapor deposition of SiBCN films. The major components of obtained films were successfully controlled by deposition temperature from B4C to graphene and β-SiC. In addition, B4C and graphene/β-SiC films were synthesized from TMAB and HMDS, respectively. The growth rate of SiBCN films was extremely high (up to 1620 μm/h) in contrast to 18 μm/h and 415 μm/h for graphene/β-SiC and B4C films, respectively. Thermodynamic modeling demonstrated that reactions between nitrogen- and silicon-containing gas species during double-source CVD process could be the possible reason of synergism and growth rate increasing. A mechanical study demonstrated very high hardness (up to 43 ± 7 GPa) and wear resistivity of the SiBCN films. The reported results reveal a significant potential of precursor synergism for the design of new materials with enhanced properties.

Structural and Dynamic Properties of Gallium Alkoxides.

A comparison of chlorido-gallium functionalized alkoxides as precursors for aerosol-assisted chemical vapor deposition (AACVD) was carried out. Variable-temperature (VT)-NMR studies were used to probe the fluxional behavior of these alkoxides in solution, and hence their utility as precursors. The synthesis involved the initial isolation of the dimer [GaCl(NMe2)2]2 via a salt metathesis route from GaCl3 and 2 equiv of LiNMe2. This dimer was then reacted with 4 equiv of HOCH2CH2CH2NEt2, resulting in the formation of Ga[μ-(OCH2CH2CH2NEt2)2GaCl2]3 (1). Mass spectrometry and VT-NMR confirmed the oligomeric structure of 1. Tuning of the ligand properties, namely, the chain length and substituents on N, resulted in formation of the monomers [GaCl(OR)2] (R = CH2CH2NEt2, (2); CH2CH2CH2NMe2, (3)). VT-NMR studies, supported by density functional theory calculations, confirmed that the ligands in both 2 and 3 possess a hemilabile coordination to the gallium center, owing to either a shorter carbon backbone (2) or less steric hindrance (3). Both 2 and 3 were selected for use as precursors for AACVD: deposition at 450 °C gave thin films of amorphous Ga2O3, which were subsequently annealed at 1000 °C to afford crystalline Ga2O3 material. The films were fully characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV–visible spectroscopy, and energy dispersive X-ray analysis.

Imidazol-2-ylidene stabilized tetrahedral cobalt carbonyl complexes: A computational and structural database study

A combined crystallographic database and computational chemistry analyses of tetrahedral cobalt (Co) carbonyl (CO) complexes bearing substituted imidazol-2-ylidene (Im) ligands were studied. These group of compounds are potential catalysts in the hydroformylation of alkenes as well as effective precursors for both chemical vapour deposition and atomic layer deposition in integrated circuit manufacture. A substructure search revealed seventeen (17) crystal structures in the Cambridge Structural Database (CSD). Generally, there was a positive correlation between the Im-Co bond length and the Co–CO bond length implying that a strong Im-CO bonding interaction could give rise to a more stable carbonyl complex. The gas phase structures of these complexes were further studied computationally at the BP86 level of the density functional theory. The def2-TZVPP basis set was used for cobalt with 6-31G (d,p) for all other atoms. It was observed that the Co–CO bond length increased with increase in bulkiness of alkyl substituents at the ortho positions of the Im ligands. Subsequent natural bond orbital (NBO) and chemical reactivity parameter analyses revealed that the chemical softness, electronic chemical potential and the ease of ionization also increased with increase in bulkiness of the alkyl substituents. This property has useful applications in catalytic systems and for the design of precursors in integrated circuit manufacture.

Synthesis and characterization of mist chemical vapor deposited aluminum titanium oxide films

Aluminum titanium oxide (Al1–xTixOy, an alloy of Al2O3 and TiO2), an attractive high-κ dielectric material, was synthesized by mist chemical vapor deposition, utilizing Al2O3 and TiO2 precursors. X-ray diffraction investigations revealed that the Al1–xTixOy (0 < x < 0.72) films deposited at 400 °C have an amorphous-phase structure. It was found that the bandgap of the Al1–xTixOy films decreases with increasing Ti composition. Moreover, the obtained refractive index, mass density and bandgap of Al2O3 and TiO2 films are all comparable to those reported for high-quality Al2O3 and TiO2 films deposited by atomic layer deposition.

Liquid polycarbosilane as a potential chemical liquid vapour deposition precursor for SiC

Abstract A low-viscous liquid polycarbosilane (LPCS) is being proposed as a silicon carbide (SiC) precursor for chemical liquid vapour deposition (CLVD) process. The LPCS was characterized by Gel permeation chromatography (GPC), Fourier transformation infrared (FT-IR) spectroscopy, Nuclear magnetic resonance (NMR) spectroscopy, GC-MS and Thermogravimetric analysis (TGA). Spectroscopic investigations together with Gas chromatography Mass spectrum (GC-MS) indicated that the synthesized LPCS is a mixture of cyclic/linear silanes and carbosilanes. TGA showed the complete evaporation of the LPCS below 250 °C, a suitable property for application as a CLVD precursor. Ceramic conversion of LPCS at different temperatures (900 °C, 1100 °C and 1300 °C) under argon, indicated the formation of nano-sized crystallites of β-SiC at 1300 °C.

Chemical vapor deposition of monolayer-thin WS2 crystals from the WF6 and H2S precursors at low deposition temperature.

Monolayer-thin WS2 with (0002) texture grows by chemical vapor deposition (CVD) from gas-phase precursors WF6 and H2S at a deposition temperature of 450 °C on 300 mm Si wafers covered with an amorphous Al2O3 starting surface. We investigate the growth and nucleation mechanism during the CVD process by analyzing the morphology of the WS2 crystals. The CVD process consists of two distinct growth regimes. During (i) the initial growth regime, a fast and self-limiting reaction of the CVD precursors with the Al2O3 starting surface forms predominantly monolayer-thin WS2 crystals and AlF3 crystals that completely cover the starting surface. During (ii) the steady-state growth regime, a much slower, anisotropic reaction on the bottom, first WS2 layer proceeds with the next WS2 layer growing preferentially in the lateral dimensions. We propose that the precursor adsorption reaction rate strongly diminishes when the precursors have no more access to the Al2O3 surface as soon as the WS2 layer completely covers the Al2O3 surface and that the WS2 crystal basal planes and AlF3 crystals have a low reactivity for WF6 adsorption at 450 °C. Nonetheless, a second layer of WS2 starts to form before the first WS2 layer completely covers the starting surface, albeit the surface coverage of the second layer is low (<20%, after 25 min of CVD reaction). During the steady-state growth regime, predominantly the WS2 crystals in the second monolayer continue to grow in lateral dimensions up to ∼40 nm. These crystals reach larger lateral dimensions compared to the crystals in the bottom, first layer due to low reactivity for WF6 adsorption on the WS2 basal plane compared to Al2O3. Presumably, they grow laterally by precursor species that adsorb on and diffuse across the WS2 surface, before being incorporated at the more reactive edges of the WS2 crystals in the second layer. Such a process proceeds slowly with only up to 40% surface coverage of the second WS2 layer after 150 min of CVD reaction. The CVD reaction is mediated by the starting surface: WF6 precursor preferentially adsorbs on Al2O3, whereas adsorption is not observed on SiO2. Nevertheless, WS2 grows on SiO2 in close proximity to Al2O3 in 90 nm pitch Al2O3/SiO2 line patterns. Hence, functionalization of the starting surface (e.g., SiO2 with Al2O3) can provide opportunities to grow monolayer-thin WS2 crystals at predetermined locations by selective, lateral growth with tunable crystal size, even at low deposition temperatures.

Methylamines as Nitrogen Precursors in Chemical Vapor Deposition of Gallium Nitride

Chemical vapor deposition (CVD) is one of the most important techniques for depositing thin films of the group 13 nitrides (13-Ns), AIN, GaN, InN, and their alloys, for electronic device applicatio ...

Thermochemical study of new volatile palladium(II) and copper(II) β-ketohydrazonates for CVD application

The volatile palladium(II) and copper(II) {O,N}-coordinated bis-chelate complexes of a new type, Pd(dmht)2 and Cu(dmht)2, where dmht = 1,1,1-trifluoro-2-(2,2-dimethylhydrazone)pentan-4-onato, were synthesized, purified and identified by elemental analysis, IR and NMR spectroscopy and mass spectrometry. The thermal behavior of the complexes in the condensed phase was studied by TG-DTA and DSC methods. The temperature dependences of saturated vapor pressure were measured for Pd(dmht)2 and Cu(dmht)2 in the temperature ranges ΔT = (343–388) K (flow method) and ΔT = (321–390) K (flow and Knudsen effusion method), respectively. The ketohydrazonate complexes characterized by close enthalpy and entropy of melting and sublimation processes and the highest volatility among the related compounds. The new complexes were successfully used as precursors for metal-organic chemical vapor deposition of mono- and bimetallic thin films onto Si (100) substrates at the reducing atmosphere.

Spontaneous Nucleation and Growth of Graphene Flakes on Copper Foil in the Absence of External Carbon Precursor in Chemical Vapor Deposition

In this work, we uncover a mechanism initiating spontaneous nucleation of graphene flakes on copper foil during the annealing phase of chemical vapor deposition (CVD) process. We demonstrate that the carbon in the bulk of copper foil is the source of nucleation. Although carbon solubility in a pure copper bulk is very low, excess carbon can be embedded inside the copper foil during the foil production process. Using time-of-flight secondary ion mass spectrometry, we measured the distribution profile of carbon atoms inside the copper foils and its variation by thermal annealing. We also studied the role of hydrogen in the segregation of carbon from the bulk to the surface of copper during annealing by scanning electron microscopy and Raman analysis. We found that carbon atoms diffuse out from the copper foil and accumulate on its surface during annealing in the presence of hydrogen. Consequently, graphene crystals can be nucleated and grown while “any external” carbon precursor was entirely avoided. To our knowledge, this is the first time that such growth has been demonstrated to take place. We believe that this finding brings a new insight into the initial nucleation of graphene in the CVD process and helps to achieve reproducible growth recipes.

Syntheses and Structures of Zinc(tmeda)bis(aryltellurolato) and its Facile Chalcogenospecific Ligand Exchange Reactivity

Anaerobic treatment of Zn(tmeda)Br2, where tmeda denotes N,N,N′,N′‐tetramethylethylenediamine, with a solution of Na(TeAr), sodium aryltellurolate, in ethanol in a 1:2 stoichiometry led to the formation of highly air sensitive Zn(tmeda)(TeAr)2 (1–3), while a 1:1 stoichiometry afforded Zn(tmeda)Br(TeAr) (4). Crystallography revealed all complexes to be monomeric with four coordinate central zinc atoms bound to tmeda and two TeAr, or a TeAr and a Br ligand. Upon mixing two symmetrically substituted Zn(tmeda)(TeAr)2 complexes in solution, 125Te NMR revealed a facile ligand exchange providing Zn(tmeda)(TeAr)(TeAr′). In addition, Zn(tmeda)(TeAr)(TeAr′) complexes form on mixing symmetric Zn(tmeda)(TeAr)2 complexes and (TeAr′)2. The lability of the zinc complexes was put to advantage in ligand‐substitution reactions wherein treatment of SnCl4 with Zn(tmeda)(TeAr)2 affords Sn(TeAr)4 in excellent yields without the concurrent formation of the redox product (TeAr)2. The apparent lability of the Zn–Te bond prevented the volatilization of 1–3 for their use as chemical vapor deposition precursors for the fabrication of ZnTe thin films. On heating, to volatize the complexes, the complexes decompose to cubic ZnTe and TeAr2 sublimes from the samples. Thermal gravimetric analysis indicates the loss of tmeda followed by the loss of TeAr2.

MOLECULAR STRUCTURE AND VIBRATION SPECTRA OF PIVALIC ACID

The metal carboxylates such as metal pivalates (salts of the pivalic acid (CH3)3CCOOH) attract a great interest as most promising precursors for chemical vapor deposition (CVD) technology. The possibility to use these substances in the CVD technology is specified by their good thermal stability and high volatility. For modeling of chemical reactions with metal pivalates in the gas-phase and the data on molecular structure will be very useful, in particularly information about effect of central metal ion to geometry of pivalic ligands. In the frame of this task the structures of metal pivalate molecules and pivalic acid (H(piv)) in a gas phase should be finding. The aim of present work is theoretical investigation of the geometry and IR-spectrum of H(piv) using density functional theory (DFT) methods. All calculations were performed using the Gaussian 03 program. The optimization of geometry and quadratic force field calculations were carried out using DFT functionals B3LYP, PBE, PBE0 and BP86 with correlation-consistent triple-ζ valence cc-pVTZ basis sets for O, C, and H. Appropriate assignment of vibrational modes was carried out by the potential energy distribution (PED) analysis among internal coordinates using the SHRINK program. According to DFT computations, the H(piv) molecule has an equilibrium structure of Cs symmetry with Гvib=26A'+19A''. The theoretical and experimental IR-spectra are satisfactorily agreed. The comparison of the ten intensities of highest bands in spectra allowed determining linear correlation between peaks position in experimental and modeling IR-spectra. It should be note the complicated composition of vibrational modes.

Volatile Heteroligand Complexes of Copper(II): New Precursors for Chemical Vapor Deposition of Copper Films

Two heteroligand ketoiminate–diketonate complexes of copper(II), CuL(hfa) (1), L = pentane-2-imino-4-onato, CH3COCHCNHCH 3 – , and CuL′(hfa) (2), L′ = 2,2,6,6-tetramethyl-3-iminoheptane-5-onato, C(CH3)3COCHCNHC(CH)–, were studied as precursors for chemical vapor deposition of copper films. The flow method was employed to measure the temperature dependences of a saturated vapor pressure of these compounds, the thermodynamic parameters of evaporation–sublimation were calculated, and the volatilities of these compounds and thermal behaviors in the condensed and gaseous phases were compared. The copper films were compared, and it was shown that comparatively high growth rates are reached when (2) is used to obtain copper films in hydrogen.

Constructing Highly Uniform Onion-Ring-like Graphitic Carbon Nitride for Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution.

The introduction of microstructure to the metal-free graphitic carbon nitride (g-C3N4) photocatalyst holds promise in enhancing its catalytic performance. However, producing such microstructured g-C3N4 remains technically challenging due to a complicated synthetic process and high cost. In this study, we develop a facile and in-air chemical vapor deposition (CVD) method that produces onion-ring-like g-C3N4 microstructures in a simple, reliable, and economical manner. This method involves the use of randomly packed 350 nm SiO2 microspheres as a hard template and melamine as a CVD precursor for the deposition of a thin layer of g-C3N4 in the narrow space between the SiO2 microspheres. After dissolution of the microsphere template, the resultant g-C3N4 exhibits uniquely uniform onion-ring-like microstructures. Unlike previously reported g-C3N4 powder morphologies that show various degrees of agglomeration and irregularity, the onion-ring-like g-C3N4 is highly dispersed and uniform. The calculated band gap for onion-ring-like g-C3N4 is 2.58 eV, which is significantly narrower than that of bulk g-C3N4 at 2.70 eV. Experimental characterization and testing suggest that, in comparison with bulk g-C3N4, onion-ring-like g-C3N4 facilitates charge separation, extends the lifetime of photoinduced carriers, exhibits 5-fold higher photocatalytic hydrogen evolution, and shows great potential for photocatalytic applications.

Thermodynamic Analysis of the Behavior of Trimethyl Borate as a Precursor for Chemical Vapor Deposition of Boron-Containing Films

The chemical vapor deposition (CVD) of boron-containing films involving the trimethyl borate precursor has been modeled in the ranges of pressures 0.03 ≤ Р, Torr ≤ 760 and temperatures 300 ≤ Т, K ≤ 2000. The CVD diagram of this system was found to feature existence fields of the following phase complexes: В + В4С, В4С + В2О3, С + В2О3 + В4С, С + В2О3, С + В2О3 + НВО2, С + НВО2, С + В4С, and a В4С phase.

Heterocyclic lead(II) thioureato complexes as single-source precursors for the aerosol assisted chemical vapour deposition of PbS thin films

Abstract The lead N’-benzoylthioureato complexes of N-morpholine (1) and N-pyrrolidine (2) were synthesized and characterized by elemental analysis, Fourier Transform Infra-Red (FT-IR) spectroscopy, proton nuclear magnetic resonance (1H nmr) and thermogravimetric analyses (TGA). The X-ray single crystal structure of complex (1) was determined. The compounds were both used as single source precursors to deposit PbS films on glass substrates at 350, 400 and 450 °C using aerosol assisted chemical vapour deposition (AACVD) The surface morphology of PbS films were determined by scanning electron microscopy (SEM), the crystalline phases established by powder X-ray diffraction (p-XRD) analyses and composition by energy dispersive X-ray spectroscopy (EDX). The particle sizes were found to range between 82 and 85 nm from complex (1) and 70–105 nm for (2) The PbS films were studied by Near Infra-red (NIR) UV–Vis spectroscopy, band gap ranging from 1.46 to 1.55 eV were observed.

Synthesis of two aminosilanes as CVD precursors of SiCxNy films: Tuning film composition by Molecular Structures

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