Single Molecular Precursor Research Articles

A new single molecular precursor route to fluorine-doped nanocrystalline tin oxide anodes for lithium batteries

A new single molecular precursor route to fluorine-doped nanocrystalline tin oxide anodes for lithium batteries

Synthesis, structural characterization, photoluminescence and thermal properties of [(Ph3P)2Cu(μ-SeC{O}R)2Cu(PPh3)

A number of neutral unsymmetrical dimers [(Ph3P)2Cu(μ-SeC{O}R)2Cu(PPh3)] (R = C6H5 (1), C6H4-Me-4 (2), C6H4-OMe-4 (3), C6H4-Cl-4 (4), C6H4-F-4 (5) and CH3 (6)) were synthesized in moderate yield, and characterized by analytical and spectroscopic techniques including 31P NMR. Variable temperature 31P NMR experiments appear to indicate that the molecular structure is retained in solution. X-Ray structure determination of 2 and 6 confirmed the molecular geometry of the unsymmetrical dimer. In 2 the two 4-MeO-C6H4CO groups have anti stereochemistry with respect to the Cu2Se2 ring while MeCO groups have syn configuration in 6. A weak C–H⋯OC intramolecular hydrogen bond present between the two selenoacetato ligands appears to dictate the syn geometry in 6. This hydrogen bonding is also responsible for the non-planarity of the Cu2Se2 ring. These compounds are photoemissive in CH2Cl2 solution. Thermogravimetry and pyrolysis experiments in nitrogen atmosphere show that 1–6 are good single source precursors to copper selenide bulk materials. Preliminary experiments show that these compounds are good single source molecular precursors for cubic phase Cu2−xSe nanoparticles with an average size of 75 ± 15 nm.

Group 11 and 13 metal thiocarboxylate compounds as single source molecular precursor for bulk metal sulfide materials and thin films

A number of new Cu(I), Ag(I), Ga(III) and In(III) metal thiocarboxylate compounds have been synthesized and characterized using various methods including X-ray crystallography. Thermal degradation of these compounds resulted in the formation of the corresponding metal sulfide materials. The metal sulfides thus obtained were characterized using XRD and SEM techniques. Solid solutions of the type (Et 3NH)[In 1xGa x(SC{O}Ph) 4] have been used as single source precursors to the corresponding In 2xGa xS 3 materials. In addition, compounds of the type [(Ph 3P)CuM(SC{O}Ph) 4], and [(Ph 3P) 2AgM(SC{O}R) 4] ( M = Ga 3+ and In 3+; R = Me and Ph) have been found to be useful as single source precursors for CuMS 2, AgGaS 2, AgInS 2 and MIn 5S 8 materials and thin films.

Architectural control of magnetic semiconductor nanocrystals.

Shape- and dopant-controlled magnetic semiconductor nanocrystals have been achieved by the thermolysis of nonpyrophoric and less reactive single molecular precursors under a monosurfactant system. Reaction parameters governing both the intrinsic crystalline phase and the growth regime (kinetic vs thermodynamic) are found to be important for the synthesis of various shapes of MnS nanocrystals that include cubes, spheres, 1-dimensional (1-D) monowires, and branched wires (bipods, tripods, and tetrapods). Obtained nanowires exhibit enhanced optical and magnetic properties compared to those of 0-D nanospheres. Proper choice of molecular precursors and kinetically driven low-temperature growth afford dopant controlled 1-D Cd1-xMn(x)S nanorods at high levels (up to approximately 12%) of Mn, which is supported by repeated surface exchange experiments and X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) analyses.

Growth of TiO 2 thin films on Si(1 0 0) and Si(1 1 1) substrates using single molecular precursor by high-vacuum MOCVD and comparison of growth behavior and structural properties

We have deposited titanium dioxide (TiO 2) thin films on Si(1 0 0) and Si(1 1 1) substrates in the temperature range of 500–750°C and in the pressure range of 3.0×10 −7–5.0×10 −5 Torr using a single molecular precursor such as titanium (IV) iso-propoxide (Ti[OCH(CH 3) 2] 4, 97%) by high-vacuum metal-organic chemical vapor deposition method. Highly oriented, stoichiometric TiO 2 thin films with rutile phase were successfully deposited on both Si(1 0 0) and Si(1 1 1) substrates between 650°C and 750°C under a working pressure of 1.0×10 −5 Torr. X-ray diffraction results clearly showed different growth behaviors between Si(1 0 0) and Si(1 1 1) substrates. The main film growth directions are [1 1 0] on Si(1 0 0) and [2 0 0] on Si(1 1 1), respectively. Scanning electron microscope and transmission electron microscope images showed a quite smooth surface with no cracks and sharp interface between film layers, suggesting good adhesion and uniformity in depth. In the case of TiO 2 films, grown under low temperature below 600°C and high pressure above 3.0×10 −5 Torr, transmission electron diffraction pattern showed a mixed structure with spot and ring patterns, resulting in polycrystalline film formation. By increasing the growth temperature to 650°C and decreasing the pressure to 3.0×10 −7 Torr, however, strong spot images with weak ring pattern were observed, indicating that the film crystallinity as well as growth direction was strongly affected by deposition temperature and pressure.

Epitaxial growth of cubic SiC thin films on silicon using single molecular precursors by metalorganic chemical vapor deposition

Heteroepitaxial cubic SiC thin films have been deposited on silicon substrates at temperatures in the range of 750–1000 °C using single molecular precursors by the metalorganic chemical vapor deposition (CVD) method. Single-crystalline, crack-free, stoichiometric cubic SiC films were successfully grown on both Si(001) and Si(111) substrates without surface carbonization at as low as temperature of 920 °C with 1,3-disilabutane, H3Si–CH2–SiH2–CH3, as a liquid single source precursor which contains silicon and carbon in 1:1 ratio. Cubic SiC thin films highly oriented in the [001] direction were also obtained on Si(001) using either a liquid mixture of 1,3,5-trisilapentane (TSP), H3Si–CH2–SiH2–CH2–SiH3, and 2,4,6-trisilaheptane (TSH) at 980 °C or 2,6-dimethyl-2,4,6-trisilaheptane (DMTSH), H3C–SiH(CH3)–CH2–SiH2–CH2–SiH(CH3)–CH3 at 950 °C without carrier gas. These growth temperatures were much lower than conventional CVD growth temperatures, and this is a report of cubic SiC film growth using the single molecular precursors of trisilaalkanes (i.e., DMTSH and TSP+TSH). The as-grown SiC films were characterized by in situ reflection high-energy electron diffraction and by ex situ x-ray diffraction, transmission electron diffraction, scanning electron microscopy, Auger electron spectroscopy, and Rutherford backscattering spectroscopy

Preparation and Characterization of Nanocrystal V2O5

Nanocrystal V2O5 with granular shape and of various sizes was prepared by oxidative pyrolysis of the single molecular precursor, (NH4)5[(VO)6(CO3)4(OH)9]·10H2O, at ≤630°C in a flow of air or oxygen gas. The thermolysis process of the precursor was investigated by TGA/DTGA and DTA in a flow of air. The data of the DTA curve indicate that fine particles of V2O5 are easier to crystallize and have a lower melting point. The IR spectra of various size V2O5 show that the absorption wavenumbers of the bands decreased gradually and the absorption at 494∼518 cm−1 disappeared gradually as the powder sizes decreased, which is attributed to size effect.

A new single molecular precursor route to fluorine-doped nanocrystalline tin oxide anodes for lithium batteries

A fluorine-doped nanocrystalline tin oxide has been prepared by thermolysis of xerosol derived from a single molecular precursor. A fluorine to tin atomic ratio, as high as 0.14, was estimated from the results of elemental analysis. The oxidation state of Sn and conducting properties were determined by Mössbauer spectroscopy and resistivity measurements. According to the electrochemical experiments, a reversible capacity up to ∼800 mAh/g has been achieved.

MOCVD of MgAl 2O 4 thin films using new single molecular precursors: application of β-hydrogen elimination to the growth of heterometallic oxide films

We have deposited the MgAl 2O 4 thin films on Si(1 0 0) substrates in the temperature range of 270∼600°C using newly developed single molecular precursors of Mg[(μ-O t Bu) 2AlMe 2] 2 and Mg[Al(O t Bu) 4] 2 by MOCVD. Polycrystalline, crack-free stoichiometric MgAl 2O 4 thin films were successfully grown on at as low as 400°C. This growth temperature was much lower than that of conventional CVD, and this is the first report of the MgAl 2O 4 growth using Mg[(μ-O t Bu) 2AlMe 2] 2. During film deposition, the vapor pressure of Mg[Al(O t Bu) 4] 2 was decreased due to oligomerization of the precursor itself. When Mg[(μ-O t Bu) 2AlMe 2] 2 was used, however, the vapor transport problem of the precursor was solved by introducing more volatile alkyl group. β-Hydrogen elimination was employed in the growth mechanism. The synthesized precursors and the as-grown films were characterized with NMR, XRD, XPS, RBS, and SEM, and the gas-phase by-products of the CVD reaction were collected and identified by gas chromatography.

Syntheses of semiconductor nanoparticles using single-molecular precursors.

Methods for the preparation of II-VI, III-V, and II-V as well as other compound semiconductor nanoparticles using main group single-molecular precursors have been developed. The work involves the design and synthesis of compounds containing all the elements required within the desired nanoparticulate material. Precursors are tailored to give reproducible, clean decomposition at moderate temperatures, leading to high quality, defect free, mono-dispersed nanoparticles. In this article we cover key aspects of precursor and nanoparticle synthesis. One of the more successful and reproducible series of single-source precursors used, and the one on which we have concentrated our research efforts, is the bis(dialkyldithio-/diseleno-carbamato)cadmium(II)/zinc(II) compounds, M(E(2)CNR(2))(2) (M = Zn or Cd, E = S or Se, and R = alkyl) for the preparation of chalcogenide nanoparticulate materials. Preliminary mechanistic studies suggest that the precursor to nanoparticle deposition route is strongly influenced by the alkyl substituent groups present, and may well determine the phase and quality of the final metal chalcogenide nanoparticles produced. Herein we discuss the synthesis of semiconductor nanoparticles using such single-molecular precursors.

Growth of TiO 2 thin films on Si(100) substrates using single molecular precursors by metal organic chemical vapor deposition

Growth of titanium dioxide (TiO 2) thin films on Si(100) substrates was carried out using a single molecular precursor at deposition temperature in the range of 300–700°C by the metal organic chemical vapor deposition (MOCVD) method. Titanium(IV) isopropoxide, (Ti[OCH(CH 3) 2] 4), was used as a precursor without any carrier gas. Crack-free, anatase type TiO 2 polycrystalline thin films with a stoichiometric ratio of Ti and O were successfully deposited on Si(100) at temperature as low as 500°C. XRD and TED data showed the formation of the highly oriented anatase phase with the [211] direction for the TiO 2 thin films grown on Si(100) at below 500°C, whereas with increasing the deposition temperature to 700°C, the main film growth direction was changed to be [200], suggesting a possibility of epitaxial thin film growth. Two distinct growth behaviors were observed from the Arrhenius plots. Below 500°C, the growth rate of TiO 2 is apparently limited the substrate temperature. The activation energy for TiO 2 film deposition calculated in this region is approximately 77.9 kJ/mol, while that for a film grown above 500°C shows a negative value, indicating a predominant diffusion controlled deposition process. Using Al/TiO 2/p-Si metal-insulator semiconductor (MIS) diode structure, a dielectric constant was also obtained from a capacitance-voltage ( C– V) curve to be 21.

Growth of SiC thin films on graphite for oxidation-protective coating

We have deposited thick SiC thin films on graphite substrates in the temperature range of 700–850 °C using single-molecular precursors by both thermal metal–organic chemical-vapor deposition (MOCVD) and plasma-enhanced MOCVD (PEMOCVD) methods for oxidation-protection wear and tribological coating. Hexamethyldisilane (HMDS), (CH3)3Si–Si(CH3)3, was used as a single-source precursor, and hydrogen and Ar were used as a bubbler and carrier gas. A highly oriented polyerystalline cubic SiC layer in the [111] direction was successfully deposited on graphite at temperatures as low as 800 °C with HMDS by PEMOCVD. For thermal MOCVD, on the other hand, only amorphous SiC layers were obtained at 850 °C. From this study, we confirmed that PEMOCVD was a highly effective process in improving the characteristics of the SiC layers compared to those grown by thermal MOCVD. The mechanical and oxidation-resistant properties have been assessed. The optimum SiC film was obtained at 850 °C and rf power of 200 W. The maximum deposition rate and microhardness are 2 μm/h and 4336 kg/mm2 Hv, respectively. The hardness was strongly influenced by the composition ratio of the SiC protective layers.

One-step synthesis of size tuned zinc selenide quantum dots via a temperature controlled molecular precursor approach

One-step size-controlled synthesis of ZnSe quantum dots is studied and the obtained QDs are luminescent with the emission wavelength varying over a wide range (up to 100 nm) depending on the particle size; the single-molecular precursor is an air-stable bis(phenylselenolato)zinc N,N,N′,N′-tetramethylethylenediamine (TMEDA) complex, which effectively affords different sizes of ZnSe QDs depending on growth temperatures.

Growth of AlN and GaN Thin Films on Si(100) Using New Single Molecular Precursors by MOCVD Method

Thin films of hexagonal AlN and GaN have been deposited on Si(100) substrates by MOCVD in the temperature range of 650 to 850 °C using cyclic diethylaluminium amide (DEAA), bis [diethyl(t-butylamido)aluminium] (DETBAA), cyclic dimethylgallium amide (DMGA), and bis [diethyl(t-butylamido)gallium] (DETBAG), as new single molecular precursors. On Si(100) at temperatures as low as 750 °C, strong preferential growth of hexagonal GaN(0002) thin films were successfully grown from DMGA without carrier gas. In the case of AlN film growth, however, only polycrystalline h-AlN thin films were obtained at temperatures above 750 °C using the precursors of DEAA and DETBAA. The XP spectra of all deposited AlN and GaN films are indistinguishable from that of AlN and GaN powders, and the Auger depth profile confirms that the films are stoichiometric and do not contain an appreciable amount of carbon. This is the first report on the growth of the h-GaN films from the synthesized precursors of DMGA and DETBAG, and we investigated their physical properties by nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and gas chromatography (GC).

Growth of AlN and GaN Thin Films on Si(100) Using New Single Molecular Precursors by MOCVD Method

Growth of AlN and GaN Thin Films on Si(100) Using New Single Molecular Precursors by MOCVD Method

Growth of magnesium oxide thin films using single molecular precursors by metal–organic chemical vapor deposition

Thin films of MgO have been deposited on Si(100) and c-plane sapphire substrates by the metal–organic chemical vapor deposition (MOCVD) method using Mg(tmhd) 2 and Mg(acac) 2 as single molecular precursors and oxygen as carrier gas. We have synthesized the metal–organic precursors used in this study. Strongly [111] oriented polycrystalline MgO films were obtained on both Si(100) and c-plane sapphire substrates using these precursors in the temperature range 500–600°C. The MgO thin films grown on Si(100) at 600°C and on c-plane sapphire at 500°C with Mg(tmhd) 2 are highly oriented in the [111] direction, whereas the MgO film grown on Si(100) at 350°C and then annealed at 520°C has no preferred orientation. In the case of using Mg(acac) 2 as precursor, however, the MgO film deposited on c-plane sapphire surface at a deposition temperature above 500°C was grown with more [110] and [100] dominant orientation relatively rather than [111]. Furthermore, we have also shown that the synthesized precursors Mg(tmhd) 2 and Mg(acac) 2 are suitable precursors for obtaining MgO thin films by MOCVD and the substrate or precursor type and the growth temperature will be important factors influencing either the crystal growth direction or the crystallinity of the films.

Supersonic jet epitaxy of single crystalline cubic SiC thin films on Si substrates from t-Butyldimethylsilane

Cubic SiC thin films have been grown by supersonic jet epitaxy (SJE) using the single molecular precursor t-butyldimethylsilane (TBDMS), (CH 3) 3C–SiH(CH 3) 2. Single crystal cubic SiC thin films were grown on both carburized and uncarburized Si(100) at a temperature of 830°C. Highly oriented cubic SiC(111) thin films were obtained on carburized and uncarburized Si(111) substrates at 830°C. This growth temperature is much lower than conventional CVD growth temperatures. It is believed that this is the first report of SiC growth using t-butyldimethylsilane.

MOCVD of BN and GaN thin films on silicon: new attempt of GaN growth with BN buffer layer

Highly oriented polycrystalline h-BN thin films were deposited on silicon substrates in the temperature range of 600–900°C from the single molecular precursor of borane–triethylamine complex, (C2H5)3N:BH3, by supersonic jet assisted chemical vapor deposition. Hydrogen was used as carrier gas, and additional nitrogen was supplied by either ammonia through a nozzle or nitrogen via a remote microwave plasma. Hexagonal GaN films were also grown on Si(100) with h-BN buffer layers at temperatures between 550 and 750°C with dual supersonic molecular beam sources. Triethylgallium, (C2H5)3Ga, and ammonia, NH3, were used as precursors. Hydrogen was used as seeding gas for the precursors, providing a wide range of possible kinetic energies for the supersonic beams. The h-BN buffer layers and the GaN films were characterized in situ by Auger electron spectroscopy (AES), and ex situ by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and optical transmission. This is the first report of growing the h-BN films on silicon substrates from the single source precursor of borane-triethylamine complex and new attempts of GaN film growth on silicon with BN buffer layer.

Epitaxial Growth of Cubic SiC Films on Si Substrates by High Vacuum Chemical Vapor Deposition Using 1,3‐Disilabutane

Heteroepitaxial cubic SiC films were grown on (001) Si substrates at 900 to 980°C using 1,3‐disilabutane as a single molecular precursor under high vacuum conditions (5.0 to ). A carbonized buffer layer, grown in situ by gas source molecular beam epitaxy (GSMBE) of propane was employed to minimize the effect of lattice mismatch between the Si substrate and the SiC overlayer. The crystalline structure, chemical composition, and thickness of the deposited films were investigated by in situ reflection high‐energy diffraction, x‐ray diffraction, Rutherford back scattering, Auger electron spectroscopy and transmission electron microscopy. The results show that high quality epitaxial 3C‐SiC films with correct stoichiometry can be deposited on Si in this temperature range. The single precursor 1,3‐disilabutane has been found suitable for the epitaxial growth of cubic SiC on (001) Si substrates.

Growth of Cubic SiC Thin Films on Silicon from Single Source Precursors by Supersonic Jet Epitaxy

AbstractCubic SiC thin films have been grown by supersonic jet epitaxy of single molecular precursors on Si(100), Si(111) and Separation by IMplanted OXygen (SIMOX) silicon on insulator (SOI) substrates at temperatures in the range 780 - 1000 °C. Real-time, in situ optical reflectivity was used to monitor the film growth. Films were characterized by ellipsometry, x-ray diffraction (XRD), and transmission electron microscopy (TEM). Monocrystalline, crack-free epitaxial cubic SiC thin films were successfully grown at 830 °C on carbonized Si(111) substrates using supersonic molecular jets of dimethylisopropylsilane, (CH3)2CHSiH(CH3)2, and diethylmethylsilane, (CH3CH2)2SiHCH3. Highly oriented cubic SiC thin films in the [100] direction were obtained on SIMOX(100) at 900 °C with dimethylisopropylsilane and on Si(100) at 1000 °C with diethylmethylsilane. A carbonized Si(100) surface was found to enhance SiC deposition from diethylmethylsilane at a growth temperature of 950 °C.