Vapor Deposition Experiments Research Articles

Investigating the Structural, Spectroscopic, and Electrochemical Properties of [Fe{(EPiPr2)2N}2] (E = S, Se) and the Formation of Iron Selenides by Chemical Vapor Deposition

The anionic L = [(EPiPr2)2N]– (E = S, Se) form of the dichalcogenidoimidodiphosphinato‐type ligands containing iPr peripheral groups has been shown previously to afford tetrahedral [MIIL2] complexes (E = S, M = Mn, Co, Ni, Zn; E = Se, M = Co, Ni, Zn). The syntheses of the analogous [FeL2] complexes [E = S (1), Se (2)] were performed in this work through metathesis reactions between FeCl2 and the corresponding KL salts. For both 1 and 2, X‐ray crystallography revealed two distinct molecules in the asymmetric unit. Complexes 1 and 2 are isostructural and exhibit P–E and P–N bond‐length differences compared with those of the free ligands, and these differences are translated into shifts of the corresponding IR bands. Cyclic voltammetry studies showed that the FeII → FeIII oxidation in 2 occurs at a lower potential than that of 1. The zero‐field Mössbauer spectra of the two complexes are quite similar and provide evidence of similar S = 2 electronic structures. The observation of crystallographically distinct FeIIE4 sites for both 1 and 2 is also revealed in the corresponding Mössbauer spectra. Complex 2 was employed as a single‐source precursor in catalyst‐aided chemical vapor deposition experiments, which afforded the iron selenides FeSe and Fe3Se4.

Energetics of reactions in a dielectric barrier discharge with argon carrier gas: IV ethyl lactate

We report dielectric barrier discharge (DBD)‐based atmospheric pressure (AP) plasma enhanced chemical vapor deposition (PECVD) experiments using argon carrier gas and ethyl lactate (EL) as the precursor molecule (“monomer”). As in our preceding research with other monomers, unprecedented precision and reproducibility is again demonstrated, here to create plasma polymerized (PP‐EL) deposits. PP‐EL is thought to be an excellent candidate for bio‐medical applications on account of the non‐toxic nature of resulting PP‐EL deposits. We have shown that a narrow range of energy values absorbed from the plasma, Em, between roughly 21 and 42 eV/molecule, lead to PP‐EL coatings of widely varying structural and physical properties, ones with controlled retention of chemical features of the EL monomer, and a predictable rate of degradation in aqueous media.

Influence of Water on Chemical Vapor Deposition of Ni and Co thin films from ethanol solutions of acetylacetonate precursors.

In chemical vapor deposition experiments with pulsed spray evaporation (PSE-CVD) of liquid solutions of Ni and Co acetylacetonate in ethanol as precursors, the influence of water in the feedstock on the composition and growth kinetics of deposited Ni and Co metal films was systematically studied. Varying the water concentration in the precursor solutions, beneficial as well as detrimental effects of water on the metal film growth, strongly depending on the concentration of water and the β-diketonate in the precursor, were identified. For 2.5 mM Ni(acac)2 precursor solutions, addition of 0.5 vol% water improves growth of a metallic Ni film and reduces carbon contamination, while addition of 1.0 vol% water and more leads to significant oxidation of deposited Ni. By tuning the concentration of both, Ni(acac)2 and water in the precursor solution, the fraction of Ni metal and Ni oxide in the film or the film morphology can be adjusted. In the case of Co(acac)2, even smallest amounts of water promote complete oxidation of the deposited film. All deposited films were analyzed with respect to chemical composition quasi in situ by XPS, their morphology was evaluated after deposition by SEM.

Controlled production of carbon nanofibers over cement clinker via oxidative dehydrogenation of acetylene by intrinsic carbon dioxide

In the course of the production of cement clinker, a high amount of carbon dioxide (CO2) is released, causing an undesirable impact on the environment. The in situ conversion of this CO2 to carbon nanomaterials that can reinforce cement would be a novel approach delivering both on-site CO2 removal and high value-added cement products. The production of carbon nanomaterials over cement clinker via oxidative dehydrogenation of acetylene by CO2 is investigated. Chemical vapor deposition experiments were performed at 450–800°C. Carbon nanofibers (CNFs) were obtained as the major product at 575–725°C. This temperature range strongly relates to the temperatures at which active Fe3+ species in clinker are abundant, indicating that these species are responsible for the reaction. The presence of CO2 can effectively preserve the catalytic domains. As a consequence, with CO2 the CNF diameters increase gradually in the temperature range of 600–700°C and yet the product yield is higher. The characteristics and yield of CNFs strongly depend on the reaction temperature. Thus, fine-tuning this parameter is a simple and practical strategy for controlling the CNF diameter and amount in the CNF/clinker composite material and in turn the mechanical properties of the cement. The proper operating temperature with respect to CNFs with diameters in the order of ten nanometers and the maximum yield is 625°C. By performing additional experiments we later found that approximately 10% of CO2 produced by the cement industry is potentially reduced via the synthesis technique presented in this work.

Incorporation of nitrogen into TiO2 thin films during PVD processes

In this paper we investigate the possibility of incorporating nitrogen into amorphous, photocatalytic TiO2 thin films, prepared at room temperature, during the growth process. The aim is to reduce the bandgap of the UV active thin films. Physical vapor deposition experiments employing a titanium vacuum arc with gas backfill ranging from pure oxygen to pure nitrogen, are carried out. The resulting films are characterized for chemical composition, phase composition, optical properties and hydrophilicity in order to determine a correlation between gas composition and thin film properties. The experimental results point that a visible change in the band structure of the deposited layers is achieved.

Thermally Robust Gold and Silver Iminopyrrolidinates for Chemical Vapor Deposition of Metal Films

Dimeric silver(I) and gold(I) tert-butyl-imino-2,2-dimethylpyrrolidinates were synthesized and characterized by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), single-crystal X-ray diffraction, and chemical vapor deposition (CVD) experiments. The motivation for this work arose from the excellent thermal stability of the previously reported analogous copper(I) compound and included the completion of a series of potential precursors for atomic layer deposition. These compounds are stable in air and soluble in aromatic or chlorinated solvents. In the solid state, TGA and DSC showed these compounds to be thermally stable up to 170 °C and to have good evaporation yields up to 240 °C. Gas phase decomposition temperatures were 140 °C for the silver compound and 300 °C for the gold compound, as determined by CVD experiments, where these compounds decomposed to produce metallic films. Reduction of the metal ions via dehydrogenation of the ligands is proposed as a thermolysis pathway.

Ammonia clathrate hydrates as new solid phases for Titan, Enceladus, and other planetary systems

There is interest in the role of ammonia on Saturn's moons Titan and Enceladus as the presence of water, methane, and ammonia under temperature and pressure conditions of the surface and interior make these moons rich environments for the study of phases formed by these materials. Ammonia is known to form solid hemi-, mono-, and dihydrate crystal phases under conditions consistent with the surface of Titan and Enceladus, but has also been assigned a role as water-ice antifreeze and methane hydrate inhibitor which is thought to contribute to the outgassing of methane clathrate hydrates into these moons' atmospheres. Here we show, through direct synthesis from solution and vapor deposition experiments under conditions consistent with extraterrestrial planetary atmospheres, that ammonia forms clathrate hydrates and participates synergistically in clathrate hydrate formation in the presence of methane gas at low temperatures. The binary structure II tetrahydrofuran + ammonia, structure I ammonia, and binary structure I ammonia + methane clathrate hydrate phases synthesized have been characterized by X-ray diffraction, molecular dynamics simulation, and Raman spectroscopy methods.

Field emission from diamond-coated multiwalled carbon nanotube “teepee” structures

Dense arrays of vertically aligned multiwalled carbon nanotubes (MWCNTs) have been seeded with a nanodiamond suspension in methanol using electrospray deposition. This treatment caused the tips of groups of 20–40 MWCNTs to stick together forming structures resembling “teepees.” Subsequent short chemical vapour deposition experiments using standard diamond-growing conditions allowed the nanodiamond seeds to grow into a thin continuous film, locking the teepee structures into this shape. Field emission tests show that these diamond-coated carbon nanotubes (CNTs) teepees retain the low threshold voltage of the uncoated CNTs but with greatly improved emission stability and lifetime.

Organophosphine/phosphite‐stabilized silver(I) complexes bearing N‐acetylbenzamide ligand: synthesis, characterization and potential application in metal organic chemical vapor deposition

New N‐silver(I) acetylbenzamide complexes of type Ln⋅AgNC9H8O2 (L = PPh3; n = 1, 2a; n = 2, 2b; n = 3, 2c; L = P(OEt)3; n = 1, 2d; n = 2, 2e; n = 3, 2f) were prepared. These complexes were obtained in high yields and characterized by elemental analysis, 1H NMR, 13C{H} NMR, 31P{H} NMR and IR spectroscopy, respectively. The molecular structure of 2b has been determined by X‐ray single‐crystal analysis in which the silver atom is in a distorted tetrahedral geometry and crystallizes as cis–trans. New N‐silver(I) acetylbenzamide complexes have a four‐membered ring, which could influence their chemical and physical properties and modulate volatility. Metal organic chemical vapor deposition experiments were carried out successfully at 400°C and 450°C using 2e as precursor for the deposition of silver films, respectively. The high‐purity silver film obtained at 400°C is dense and homogeneous. Copyright © 2012 John Wiley & Sons, Ltd.

Transient stages during the chemical vapour deposition of silicon carbide from CH3SiCl3/H2: impact on the physicochemical and interfacial properties of the coatings

Transient chemical vapour deposition experiments were produced from MTS/H2 mixtures by varying the deposition temperature or the gas flow rates (QMTS or QH2) versus time. The gas phase, deposition rates and properties of the transient coating (φTr) were investigated and adhesion assessments of SiC/φTr/SiC bilayers were performed by scratch testing. Transient stages resulting from a decrease of QMTS or temperature lead to silicon co-deposition, but do not affect interfacial properties. Transient stages resulting from a decrease of QH2 eventually lead to carbon co-deposition. Thick and continuous carbon interlayers lead to a poor adhesion whereas thin and discontinuous layers do not.

Intercalation of Transition Metals into Stacked Benzene Rings: A Model Study of the Intercalation of Transition Metals into Bilayered Graphene.

Structures of neutral metal-dibenzene complexes, M(C6H6)2 (M = Sc-Zn), are investigated by using Møller-Plesset second order perturbation theory (MP2). The benzene molecules change their conformation and shape upon complexation with the transition metals. We find two types of structures: (i) stacked forms for early transition metal complexes and (ii) distorted forms for late transition metal ones. The benzene molecules and the metal atom are bound together by δ bonds which originate from the interaction of π-MOs and d orbitals. The binding energy shows a maximum for Cr(C6H6)2, which obeys the 18-electron rule. It is noticeable that Mn(C6H6)2, a 19-electron complex, manages to have a stacked structure with an excess electron delocalized. For other late transition metal complexes having more than 19 electrons, the benzene molecules are bent or stray away from each other to reduce the electron density around a metal atom. For the early transition metals, the M(C6H6) complexes are found to be more weakly bound than M(C6H6)2. This is because the M(C6H6) complexes do not have enough electrons to satisfy the 18-electron rule, and so the M(C6H6)2 complexes generally tend to have tighter binding with a shorter benzene-metal length than the M(C6H6) complexes, which is quite unusual. The present results could provide a possible explanation of why on the Ni surface graphene tends to grow in a few layers, while on the Cu surface the weak interaction between the copper surface and graphene allows for the formation of a single layer of graphene, in agreement with chemical vapor deposition experiments.

Pentacene Growth on Fullerene: Simulation of Vapor‐Phase Deposition and Growth of a Pentacene Thin Film on C60 (001) (Adv. Mater. 39/2011)

The formation of the heterojunction between two organic semiconductors, pentacene on top of Buckminster fullerene, is simulated using a virtual vapor deposition experiment. As reported by Luca Muccioli and co-workers, the thin-film growth is characterized by a lying-to-standing collective reorientation of pentacene molecules, corresponding to the onset of crystalline order. The mechanism is coverage dependent and reorientation occurs earlier for the second monolayer.

In-situ observation of 〈110〉 oriented Ge nanowire growth and associated collector droplet behavior

Using in-situ microscopy, we show that germanium nanowires can be grown by a vapor-liquid-solid process in 〈110〉 directions both on Ge(100) and Ge(111) substrates if very low supersaturation in the collector droplet is ensured. This can be provided if thermal evaporation is utilized. Such a behavior is also in agreement with earlier chemical vapor deposition experiments, where 〈110〉 oriented wires were obtained for very small wire diameters only. Our conclusions are supported by in-situ observations of nanowire kinking towards 〈111〉 direction occurring more frequently at higher evaporation rates.

Isostructural copper–zinc mixed metal complexes for single source deposition of Cu–ZnO composite thin films

The mixed metal complex [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Br]·THF (1) and its isostructural analogues ([Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Cl]·THF (2) and [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Cl/Br]·THF (3)) have been prepared by a simple metal ligand assembly method and were characterized by their melting points, elemental analysis, IR spectroscopy, thermogravimetry and single crystal X-ray structures. The compounds are distinguished only by the nature of the halide ions and are made up of the same [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)X]·THF molecular building block with Cu(3)ZnO(4) cubane moieties as the central core in which the four metal ions and four oxygen atoms are joined together in alternate positions of the cuboid. All the complexes crystallize with similar packing and crystallographically related symmetry settings, distinguished mainly by the degree of disorder within the complexes and the ordering of the complexes in the structures. The triclinic cell of (1) emulates the monoclinic cell of (2) and is pseudomerohedrally twinned by a symmetry operation of the monoclinic cell. The molecules in (2) are 1:1 disordered around a crystallographic mirror plane. The structure of the mixed halogen compound (3) in turn is a superstructure of the less symmetric structures of (1) and (2) formed by ordering of the complexes along the longest axis of (3). Aerosol-assisted chemical vapour deposition (AACVD) experiments showed that they are promising precursors to deposit thin films of crystalline Cu/ZnO composites. The surface morphology, microstructure, chemical composition and crystallinity of the resulting Cu/ZnO composite thin films were analysed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX), which suggest that the films are thin, crystalline, uniform, smooth and tightly adherent to the substrates with average crystallite sizes in a range between 40.2 and 80.0 nm. Particle sizes, shapes and film morphology were investigated as a function of precursor and decomposition temperature.

Organophosphine/phosphite stabilized disilver(i) methanedisulphonates: synthesis, solid state structures and their potential use as MOCVD precursors

New disilver(I) methanedisulphonate complexes [CH(2)(SO(3))(2)Ag(2)·L(n)] (L = PPh(3); n=2, 2a; n=3, 2b; n=4, 2c; n=5, 2d; n=6, 2e; L=P(OEt)(3); n=2, 2f; n=4, 2g; n=6, 2h) were prepared by the reaction of [CH(2)(SO(3))(2)Ag(2)], which could be synthesized from methanedisulphonic acid and Ag(2)CO(3) in water, with triphenylphosphine or triethylphosphite in dichloromethane under a nitrogen atmosphere. The solid state structures of three complexes 2c, 2d and 2f were determined by single X-ray structure analysis. Hot-wall metal organic chemical vapor deposition (MOCVD) experiments were carried out at 395 °C, 420 °C and 450 °C using 2g as precursor for the deposition of silver films, respectively. The silver film with high purity obtained at 420 °C is dense and homogeneous, which is composed of many well isolated, granular particulates spreading all over the substrate surface.

Chemical vapour deposition of In2O3 thin films from a tris-guanidinate indium precursor

A new homoleptic sublimable indium(III) guanidinate, (In[(N(i)Pr)(2)CNMe(2)](3) (1), was synthesized from a facile high-yield procedure. Compound 1 crystallized is a P1 space group; a = 10.5989(14) Å, b = 11.0030(15) Å, c = 16.273(2) Å, α = 91.190(2)°, β = 96.561(2)°, γ = 115.555(2)°; R = 3.50%. Thermogravimetric analysis showed 1 to produce elemental indium as a residual mass. Thermolysis in a sealed NMR tube showed carbodiimide and protonated dimethyl amine by (1)H NMR. Chemical vapour deposition experiments above 275 °C with air as the reactant gas showed 1 to readily deposit cubic indium oxide with good transparency.

Phosphite copper(i) trifluoroacetates [((RO)3P)mCuO2CCF3] (m = 1, 2, 3): synthesis, solid state structures and their potential use as CVD precursors

Metal-organics [((RO)(3)P)(m)CuO(2)CCF(3)] (R = CH(3): 11a, m = 1; 11b, m = 2; 11c, m = 3. R = CH(2)CH(3): 12a, m = 1; 12b, m = 2; 12c, m = 3. R = CH(2)CF(3): 13a, m = 1; 13b, m = 2; 13c, m = 3) are either accessible by the reaction of [((RO)(3)P)(m)CuCl] (R = CH(3): 5a, m = 1; 5b, m = 2; 5c, m = 3. R = CH(2)CH(3): 6a, m = 1; 6b, m = 2; 6c, m = 3) with [KO(2)CCF(3)] (7), or treatment of [Cu(2)O] (8) with HO(2)CCF(3) (9) and P(OR)(3) (2, R = CH(3); 3, R = CH(2)CH(3); 4, R = CH(2)CF(3)). (31)P{(1)H} NMR spectra [((CH(3)O)(3)P)(m)CuO(2)CCF(3)] (m = 1, 1.5, 2, 2.5, 3, 3.5, and 4) have been studied at 25 and -80 °C showing phosphite ligand exchange in solution. The molecular structures of 11a and 13a-13c in the solid state are reported. Complexes 11a and 13a are tetramers featuring μ-η(2)(1κO:2κO')- and μ(3)-η(2)(1κO:2κO':3κO')-(11a) or μ(3)-η(2)(1κO:2κO':3κO')-bonded O(2)CCF(3) ligands (13a) with the Cu(I) ions being part of CuPO(2) and CuPO(3) units (11a), while in 13a solely a CuPO(3) moiety is present. Skeletal isomerism of 11a vs. 13a is discussed. Compound 13b is dimeric ({CuP(2)O(2)}(2)) with pseudo-tetrahedral Cu environments and μ-η(2)(1κO:2κO')O(2)CCF(3) functionalities. In monomeric 13c the O(2)CCF(3) ligand is η(1)(κO)-bonded to a tetra-coordinated Cu(i) ion. The thermal solid state properties of 11, 12 and 13 were studied by Thermo Gravimetry (TG). These complexes decompose by phosphite elimination, decarboxylation and dealkylation. Hot-wall Chemical Vapour Deposition (CVD) experiments were carried out at 380 °C using 11c as precursor for the deposition of copper onto pieces of TiN-coated oxidized silicon substrates. Copper layers of high purity were obtained with grain sizes between 200-1200 nm.

Synthesis, Characterization, and Mass Transport Properties of a Self-Generating Single-Source Magnesium Precursor for MOCVD of MgF2Films

The diglyme [CH3O(CH2CH2O)2CH3] adduct of the magnesium bis-hexafluoroacetyl-acetonato [Mg(hfa)2·2H2O·2diglyme] has been synthesized in a single-step reaction. It has been characterized by elemental analyses, IR spectroscopy, and 1H and 13C NMR. Single-crystal X-ray diffraction studies provide evidence of a mononuclear hexa-coordinated complex with an octahedral structure for the Mg(hfa)2·2H2O moiety and diglyme coordinated in the outer sphere (triclinic system, space group= P1̅; a = 8.952(3) Å, b = 9.036(3) Å, c = 11.98(1) Å, α = 110.44(5)°, β = 108.64(4)°, γ = 97.06(3)°, Z = 1). The “thermal robustness” and mass transport properties of the adduct have been investigated by thermogravimetric analysis and chemical vapor deposition experiments. Thermal analysis data revealed high volatility and good thermal stability with a residue left lower than 1%. The Mg(hfa)2·2H2O·2diglyme has been successfully applied to the low-pressure metal-organic chemical vapor deposition (MOCVD) of MgF2 films. The good quality of the deposited films indicates that the adduct is a very attractive single-source precursor for deposition of MgF2 films.

Multivariable study on homoepitaxial diamond growth using isotopically enriched carbon-13 gas mixtures

We report our observations on the homoepitaxial diamond growth by microwave plasma chemical vapor deposition (MPCVD) experiments on Type Ib diamond substrates conducted by varying three independent variables. In a feed gas mixture of H2, N2, O2, and 13CH4, the amount of nitrogen was varied in the range of 0 to 4000 ppm, the amount of methane was varied from 2% CH4/H2 to 6% CH4/H2, and the substrate temperature was varied in the range of 850 to 1200 °C. We used isotopically enriched carbon-13 methane gas as the source of carbon in the plasma to clearly distinguish the grown diamond layer from the underlying substrate using Raman spectroscopy. The x-ray rocking curve measurements confirmed the homoepitaxial nature of the deposited layers with a slight increase in the full width at half-maximum for sample grown with the highest nitrogen content in the plasma. Optical and atomic force microscopy revealed dramatic changes in surface morphology with variation in each parameter. The nitrogen incorporation in carbon-13 diamond layers was monitored through photoluminescence spectroscopy of nitrogen–vacancy complexes. A twentyfold increase in diamond growth rate was clearly achieved in this multivariable study.

Vanadium selenoether and selenolate complexes, potential single-source precursors for CVD of VSe2thin films

Reactions of VCl4 with one mol equiv. of L–L (L–L = MeSe(CH2)2SeMe, MeSe(CH2)3SeMe, nBuSe(CH2)2SenBu) in anhydrous CH2Cl2 solution at room temperature give [VCl4(L–L)] as very moisture-sensitive dark purple solids. Using VCl4 and excess selenoether in gently refluxing CH2Cl2 leads to reduction to [VCl3(L–L)] (L–L as above and o-C6H4(CH2SeMe)2), while VCl4 reacts with excess SeMe2 at room temperature to give [VCl3(SeMe2)2]. All new complexes were characterised by microanalysis, IR and UV/visible spectroscopy and magnetic measurements. Reaction of [(Cp)2VCl2] with two mol equiv. of LiSetBu in anhydrous thf gives the VIV selenolate complex [(Cp)2V(SetBu)2] as a very moisture-sensitive brown solid. The new complexes have been investigated as possible reagents for deposition of vanadium selenide. While low pressure chemical vapour deposition (LPCVD) experiments showed that the diselenoether complexes were not sufficiently volatile for VSe2 deposition, [VCl3(SeMe2)2] gives very thin deposits of VSe2. LPCVD studies on [(Cp)2V(SetBu)2] at 600 °C produce thicker black films of VSe2. In all cases EDX measurements show that the films are Se deficient.