Precursors For Chemical Vapor Deposition Research Articles

Vanadium and Manganese Carbonyls as Precursors in Electron-Induced and Thermal Deposition Processes.

The material composition and electrical properties of nanostructures obtained from focused electron beam-induced deposition (FEBID) using manganese and vanadium carbonyl precursors have been investigated. The composition of the FEBID deposits has been compared with thin films derived by the thermal decomposition of the same precursors in chemical vapor deposition (CVD). FEBID of V(CO)6 gives access to a material with a V/C ratio of 0.63–0.86, while in CVD a lower carbon content with V/C ratios of 1.1–1.3 is obtained. Microstructural characterization reveals for V-based materials derived from both deposition techniques crystallites of a cubic phase that can be associated with VC1−xOx. In addition, the electrical transport measurements of direct-write VC1−xOx show moderate resistivity values of 0.8–1.2 × 103 µΩ·cm, a negligible influence of contact resistances and signatures of a granular metal in the temperature-dependent conductivity. Mn-based deposits obtained from Mn2(CO)10 contain ~40 at% Mn for FEBID and a slightly higher metal percentage for CVD. Exclusively insulating material has been observed in FEBID deposits as deduced from electrical conductivity measurements. In addition, strong tendencies for postgrowth oxidation have to be considered.

Synthesis of Aminosilane Chemical Vapor Deposition Precursors and Polycarbosilazanes through Manganese-Catalyzed Si–N Dehydrocoupling

Synthesis of Aminosilane Chemical Vapor Deposition Precursors and Polycarbosilazanes through Manganese-Catalyzed Si–N Dehydrocoupling

Uniform growth of MoS2 films using ultra-low MoO3 precursor in one-step heating chemical vapor deposition

In chemical vapor deposition (CVD), homogeneous molybdenum vapor concentration is important in synthesizing uniform thickness and large coverage of two-dimensional molybdenum disulfide (2D-MoS2) films. Here, we synthesize few-layer MoS2 films with uniform thickness and adequate coverage over 50 mm2 size area using ultra-low molybdenum trioxide (MoO3) precursor placed directly under a face-down silicon dioxide/silicon (SiO2/Si) substrate in one-step heating CVD. The precursor mass is controlled by dispersing MoO3 powder in ethanol (C2H5OH) and varying the volume of MoO3/C2H5OH solution coated on SiO2/Si substrates into 10, 20 and 25 µL. Field emission scanning electron microscopy images reveal that 20 µL MoO3/C2H5OH solution produces ∼93% area coverage of 2D-MoS2 films. The average Raman spectra show the typical presence of MoS2 peaks around 378.8 cm−1 and 404 cm−1 referring to the E12g and A1g modes, respectively. The difference between the two Raman modes for all samples is ∼25 cm−1, indicating few-layer MoS2 films. The thickness of MoS2 films is estimated at around 2.8 ± 0.44 nm and 3.2 ± 0.43 nm (∼6 layers) using atomic force microscopy analysis. These findings suggest that ultra-low MoO3 precursor is useful to produce uniform thickness and high coverage few-layer MoS2 films using one-step heating CVD.

Plan-view TEM observation of a single-domain κ-Ga2O3 thin film grown on ε-GaFeO3 substrate using GaCl3 precursor by mist chemical vapor deposition

We demonstrated the growth of a single-domain κ-Ga2O3 thin film on ε-GaFeO3 by using an organic-free compound as a precursor for mist chemical vapor deposition. X-ray diffraction analysis revealed that an 86 nm thick κ-Ga2O3 thin film was grown almost coherently with slight lattice relaxation. The surface morphology of the κ-Ga2O3 thin film exhibited a step-terrace structure without island growth. Furthermore, plan-view TEM observations revealed that the κ-Ga2O3 thin film grown on ε-GaFeO3 had a single domain, whereas the previously reported κ-Ga2O3 thin film grown on AlN template had a domain structure.

Nickel Silicide Catalyst from Photovoltaic Waste for the Methanation Reaction

A technology designed for recycling photovoltaic (PV) cells at the end of their life was successfully used for the preparation of a nickel silicide catalyst. PV cells were mixed with magnesium scrap to produce magnesium silicide (Mg2Si), with almost total conversion under optimized conditions (400 °C, 5 Pa, 25 min), in a constructed semi-open tubular reactor. Subsequently, magnesium silicide was hydrolyzed by 25% phosphoric acid to produce a mixture of silicon hydrides, which were utilized as chemical vapor deposition (CVD) precursors for the preparation of a nickel silicide catalyst. The activity and stability of the prepared catalyst was repeatedly tested for methanation reactions. It was verified that the nickel silicide catalyst showed an approximately 20% higher activity for the methanation reactions compared to the commonly used nickel catalyst.

Thermodynamics of germanium chemical vapor deposition via germane and digermane

Chemical vapor deposition is notoriously a challenging chemical process. Growth rates are stated either under mass-transfer control or under kinetic control at lower temperature. But a few drastic assumptions enable a radical simplification of the reaction mechanism. And both growth regimes are unified with Sedgwick’s simplified thermodynamic model. Linear functions of temperature akin to Gibbs free energy of reaction are mined out of germanium deposition experiments. Two growth mechanisms are identified, one with ΔHro = 83.4 kcal/mol (Ge–H bond) and a second one with ΔHro = 104.2 kcal/mol (H – H bond). The contribution of higher order germane is also discerned in germane thermal decomposition. The square root coupling of growth rates to input flows is neatly demonstrated with thermodynamics. Finally, chemical vapor deposition growth rate vs. precursor partial pressure plot fingerprints a hydrogen Langmuir adsorption isotherm. The adsorption isotherm reveals a thermodynamic contribution beneath a mass-transfer control.

Low-Pressure CVD of GeE (E = Te, Se, S) Thin Films from Alkylgermanium Chalcogenolate Precursors and Effect of Deposition Temperature on the Thermoelectric Performance of GeTe.

The homologous series [GenBu3(EnBu)] (E = Te, Se, S; (1), (3) and (4)) and [GenBu2(TenBu)2] (2) have been synthesized as mobile oils in excellent yield (72-93%) and evaluated as single-source precursors for the low-pressure chemical vapor deposition (LPCVD) of GeE thin films on silica. Compositional and structural characterizations of the deposits have been performed by grazing-incidence X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, and Raman spectroscopy, confirming the phase purity and stoichiometry. Electrical characterization via variable-temperature Hall effect measurements is also reported. Given the strong interest in GeTe and its alloys for thermoelectric applications, variable-temperature Seebeck data were also investigated for a series of p-type GeTe films. The data show that it is possible to tune the thermoelectric response through intrinsic Ge vacancy regulation by varying the deposition temperature, with the highest power factor (40 μW/K2cm@629 K) and effective ZT values observed for the films deposited at higher temperatures.

New Volatile Perfluorinated Amidine-Carboxylate Copper(II) Complexes as Promising Precursors in CVD and FEBID Methods.

In the present study, we have synthesised and characterised newly copper(II) complexes with the general formula [Cu2(NH2(NH=)CC2F5)2(µ–O2CRF)4], where RF = CF3, C2F5, C3F7, C4F9. Infrared spectroscopy, mass spectrometry with electron ionisation (EI MS), and density-functional theory (DFT) calculations were used to confirm compounds’ composition and structure. The volatility of the compounds was studied using thermal analysis (TGA), EI MS mass spectrometry, variable temperature infrared spectroscopy (VT IR), and sublimation experiments. Research has revealed that these compounds are the source of metal carriers in the gas phase. The thermal decomposition mechanism over reduced pressure was proposed. TGA studies demonstrated that copper transfer to the gaseous phase occurs even at atmospheric pressure. Two selected complexes [Cu2(NH2(NH=)CC2F5)2(µ–O2CC2F5)4] and [Cu2(NH2(NH=)CC2F5)2(µ–O2CC3F7)4] were successful used as chemical vapour deposition precursors. Copper films were deposited with an evaporation temperature of 393 K and 453 K, respectively, and a decomposition temperature in the range of 573–633 K without the use of hydrogen. The microscopic observations made to investigate the interaction of the [Cu2(NH2(NH=)CC2F5)2(µ–O2CC2F5)4] with the electron beam showed that the ligands are completely lost under transmission electron microscopy analysis conditions (200 keV), and the final product is copper(II) fluoride. In contrast, the beam energy in scanning electron microscopy (20 keV) was insufficient to break all coordination bonds. It was shown that the Cu-O bond is more sensitive to the electron beam than the Cu-N bond.

Improved route to a diphenoxide-based precursor for chemical vapour deposition of parylene AF-4.

In this work, we present the synthesis of an alternative precursor for chemical vapour deposition of parylene AF-4 to the widely used standard, octafluoro[2.2]paracyclophane. The standard precursor suffers from uncertainties in its supply chain and its synthesis is of low yield. A comparison between different reaction parameters and solvents is drawn by means of thermal, laboratory-scale and microwave-assisted reactions and quantitative nuclear magnetic resonance (qNMR) studies.

The Early Steps of Molecule-to-Material Conversion in Chemical Vapor Deposition (CVD): A Case Study.

Transition metal complexes with β-diketonate and diamine ligands are valuable precursors for chemical vapor deposition (CVD) of metal oxide nanomaterials, but the metal-ligand bond dissociation mechanism on the growth surface is not yet clarified in detail. We address this question by density functional theory (DFT) and ab initio molecular dynamics (AIMD) in combination with the Blue Moon (BM) statistical sampling approach. AIMD simulations of the Zn β-diketonate-diamine complex Zn(hfa)2TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine), an amenable precursor for the CVD of ZnO nanosystems, show that rolling diffusion of this precursor at 500 K on a hydroxylated silica slab leads to an octahedral-to-square pyramidal rearrangement of its molecular geometry. The free energy profile of the octahedral-to-square pyramidal conversion indicates that the process barrier (5.8 kcal/mol) is of the order of magnitude of the thermal energy at the operating temperature. The formation of hydrogen bonds with surface hydroxyl groups plays a key role in aiding the dissociation of a Zn-O bond. In the square-pyramidal complex, the Zn center has a free coordination position, which might promote the interaction with incoming reagents on the deposition surface. These results provide a valuable atomistic insight on the molecule-to-material conversion process which, in perspective, might help to tailor by design the first nucleation stages of the target ZnO-based nanostructures.

Vacuum versus ambient pressure inert gas thermogravimetry: a study of silver carboxylates

A comparative study of vacuum versus ambient pressure inert gas thermogravimetry was performed on silver carboxylates compounds. Some of the complexes from this group have been previously successfully applied as precursors for both chemical vapour deposition and electron beam-induced deposition. Considerable differences were found between the thermogravimetry methods, which we associate with changes in evaporation dynamics. Vacuum thermogravimetry sublimation onsets consistently occurred at lower temperatures than ambient pressure N2-flow thermogravimetry, where the differences reached up to 120 °C. Furthermore, compound sublimation during N2-TGA was suppressed to such an extent that significant thermal decomposition of the compounds into metal and volatile organic fragments was observed while at vacuum the same complexes sublimed as intact molecules. Moreover, thermal stability of silver complexes was investigated using isothermal thermogravimetry. These findings are interesting for the field of thin film synthesis and nanomanufacturing via chemical vapour deposition, atomic layer deposition and focused electron beam induced deposition. In all three methods, delivery of functional precursor over the substrate is crucial. The presented results prove that vacuum thermogravimetry can be used as fast method of pre-screening for novel, especially low-volatility precursors.Graphic abstract

Thermal ranges and figures of merit for gold-containing precursors for atomic layer deposition

This is a survey of known gold-containing chemical vapor deposition (CVD) and atomic layer deposition (ALD) precursors with a focus on collecting their volatilization and decomposition data. These data were applied to a figure of merit (σ) developed to easily assess the thermal characteristics (“volatilization temperature” and the onset of decomposition]) important in the initial assessment of molecules as potential ALD precursors. Of the 46 compounds that were identified, 23 had sufficient thermal data reported in the literature to determine a σ value. The two known gold ALD precursors (15, σ = 104 and 22, σ = 44) were both shown to be in a cluster of excellent precursors. They were each the best in their families of precursors, measured by their σ and their onset of volatility. It was also found that many potentially excellent gold ALD precursors had gold in the +3 oxidation state. Some gold(I) compounds were identified as having good figures of merit (28, σ = 78, 29, σ = 32, 36, σ = 31), but 28 and 29 were found to undergo a reductive elimination reaction at growing gold surfaces, which is a common CVD deposition route for gold(I) compounds. β-diketonates and β-ketoiminates of gold were the most encouraging family of compounds, with σ values of greater than 50. This family contained the precursor with the highest figure of merit (9, σ = 212). These compounds are difficult to make in high yield, but an alternate synthetic route that was identified during this survey might serve to make this class of gold compound competitive as a precursor.

Synthesis and Characterization of Strontium N,N-Dimethylaminodiboranates as Possible Chemical Vapor Deposition Precursors.

The reaction of SrBr2 with 2 equiv of sodium N,N-dimethylaminodiboranate (DMADB; Na(H3BNMe2BH3)) in Et2O at 0 °C followed by crystallization and drying under vacuum gives the unsolvated strontium compound Sr(H3BNMe2BH3)2 (1). Before the vacuum-drying step, the colorless crystals obtained by crystallization consist of the diethyl ether adduct Sr(H3BNMe2BH3)2(Et2O)2 (2). If the reaction of SrBr2 with 2 equiv of Na(H3BNMe2BH3) is carried out in the more strongly coordinating solvent thf, the solvate Sr(H3BNMe2BH3)2(thf)3 (3) is obtained. Treating the thf adduct 3 with 1,2-dimethoxyethane (dme), bis(2-methoxyethyl) ether (diglyme), or N,N,N',N'-tetramethylethylenediamine (tmeda) in thf affords the new compounds Sr(H3BNMe2BH3)2(dme)2 (4), Sr(H3BNMe2BH3)2(diglyme) (5), and Sr(H3BNMe2BH3)2(tmeda) (6), respectively, in greater than 60% yields. Treatment of 3 with 2 equiv of the crown ether 12-crown-4 affords the charge-separated salt [Sr(H3BNMe2BH3)(12-crown-4)2][H3BNMe2BH3] (7). Crystal structures of all the Lewis base adducts are described. Compounds 2-6 all possess chelating κ2-BH3NMe2BH3-κ2 groups, in which two hydrogen atoms on each boron center are bound to strontium. Compound 6 is dinuclear because each metal atom is also coordinated to one hydrogen atom on a BH3NMe2BH3- ligand that chelates to the neighboring metal center. Compound 7 possesses an unusual κ1-BH3NMe2BH3- group owing to the near-complete encapsulation of the Sr atom by two 12-crown-4 molecules; the other BH3NMe2BH3- anion is a charge-separated counterion. When they are heated, the diglyme and tmeda compounds 5 and 6 melt without decomposition and can be sublimed readily under reduced pressure (1 Torr) at 120 °C. The diglyme and tmeda adducts are some of the most volatile strontium compounds known and are promising candidates as CVD precursors for the growth of strontium-containing thin films.

Platinum ω-Alkenyl Compounds as Chemical Vapor Deposition Precursors: Synthesis and Characterization of Pt[CH2CMe2CH2CH═CH2]2 and the Impact of Ligand Design on the Deposition Process

We describe the synthesis and characterization of three platinum(II) ω-alkenyl complexes of stoichiometry Pt[CH2CMe2(CH2)xCH═CH2]2 where x is 0, 1, or 2, as well as some related platinum(II) compounds formed as byproducts during their synthesis. The ω-alkenyl ligands in all three complexes, cis-bis(η1,η2-2,2-dimethylbut-3-en-1-yl)platinum (2), cis-bis(η1,η2-2,2-dimethylpent-4-en-1-yl)platinum (3), and cis-bis(η1,η2-2,2-dimethylhex-5-en-1-yl)platinum (4), bind to Pt by means of a Pt–alkyl sigma bond at one end of the ligand chain and a Pt–olefin pi interaction at the other; the olefins reversibly decomplex from the Pt centers in solution. The good volatility of 3 (10 mTorr at 20 °C), its ability to be stored for long periods without decomposition, and its stability toward air and moisture make it an attractive platinum chemical vapor deposition (CVD) precursor. CVD of thin films from 3 shows no nucleation delay on several different substrates (SiO2/Si, Al2O3, and VN) and gives films that are unusually smooth. At 330 °C in the absence of a reactive gas, the precursor deposits platinum containing 50% carbon, but in the presence of a remote oxygen plasma, the amount of carbon is reduced to below the Rutherford backscattering spectroscopy (RBS) detection limit without affecting the film smoothness. Under hot wall CVD conditions at 250 °C in the absence of a co-reactant, 72% of the carbon atoms in 3 are released as hydrogenated products (largely 4,4-dimethylpentenes), 22% are released as dehydrogenated products (all of which are the result of skeletal rearrangements), and 6% remain in the film. Some conclusions about the CVD mechanism are drawn from this product distribution.

Platinum ω-Alkenyl Compounds as Chemical Vapor Deposition Precursors. Mechanistic Studies of the Thermolysis of Pt[CH2CMe2CH2CH═CH2]2 in Solution and the Origin of Rapid Nucleation

The compound cis-bis(η1,η2-2,2-dimethylpent-4-en-1-yl)platinum, Pt[CH2CMe2CH2CH═CH2]2 (3), is a recently discovered chemical vapor deposition (CVD) precursor for the deposition of highly smooth pla...

An Amidinato-Cerium Compound and Its Application as CVD Precursor for CeOx-Based Materials

A cerium compound with asymmetric amidinate ligands [Ce(iPrNC(Me)NtBu)3] has been reported and characterized in this paper. The compound showed good volatility and thermal stability, which were evaluated by TGA (thermogravimetric analysis). Corresponding results indicated the great potential of this compound for the chemical vapor deposition (CVD) process. Therefore, CeOx film and particle (loaded on TiO2) deposition were conducted by CVD using Ce(iPrNC(Me)NtBu)3 and O2 as precursors. Meanwhile, the photocatalytic activity of the CVD CeOx–TiO2 composite was evaluated by degrading methylene blue solution under the irradiation of ultraviolet light (365 nm).

Tuning Coordination Geometry of Nickel Ketoiminates and Its Influence on Thermal Characteristics for Chemical Vapor Deposition of Nanostructured NiO Electrocatalysts.

Nickel-based nanostructured materials have gained widespread attention, particularly for energy-related applications. Employing chemical vapor deposition (CVD) for NiO necessitates suitable nickel precursors that are volatile and stable. Herein, we report the synthesis and characterization of a series of new nickel β-ketoiminato complexes with different aliphatic and etheric side chain substitutions, namely, bis(4-(isopropylamino)-pent-3-en-2-onato)nickel(II) ([Ni(ipki)2], 1), bis(4-(2-methoxyethylamino)pent-3-en-2-onato)nickel(II) ([Ni(meki)2], 2), bis(4-(2-ethoxyethylamino)pent-3-en-2-onato)nickel(II) ([Ni(eeki)2], 3), bis(4-(3-methoxy-propylamino)-pent-3-en-2-onato)nickel(II) ([Ni(mpki)2], 4), and bis(4-(3-ethoxypropylamino)pent-3-en-2-onato)nickel(II) ([Ni(epki)2], 5). These compounds have been thoroughly characterized with regard to their purity and identity by means of nuclear magnetic resonance spectroscopy (NMR) and electron impact mass spectrometry (EI-MS). Contrary to other transition metal β-ketoiminates, the imino side chain strongly influences the structural geometry of the complexes, which was ascertained via single-crystal X-ray diffraction (XRD). As a result, the magnetic momenta of the molecules also differ significantly as evidenced by the magnetic susceptibility measurements employing Evan's NMR method in solution. Thermal analysis revealed the suitability of these compounds as new class of precursors for CVD of Ni containing materials. As a representative precursor, compound 2 was evaluated for the CVD of NiO thin films on Si(100) and conductive glass substrates. The as-deposited nanostructured layers were stoichiometric and phase pure NiO as confirmed by XRD, Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). X-ray photoelectron spectroscopy (XPS) indicated the formation of slightly oxygen-rich surfaces. The assessment of NiO films in electrocatalysis revealed promising activity for the oxygen evolution reactions (OER). The current densities of 10 mA cm-2 achieved at overpotentials ranging between 0.48 and 0.52 V highlight the suitability of the new Ni complexes in CVD processes for the fabrication of thin film electrocatalysts.

Sustained and Controlled Release of Volatile Precursors for Chemical Vapor Deposition of Graphene at Atmospheric Pressure.

Precursors and catalysts play vital roles in chemical reactions. Considerable efforts have been devoted to the investigation of catalysts for graphene growth by chemical vapor deposition in recent years. However, there has been little research on precursors because of a lack of innovation in term of creating a controllable feeding method. Herein, we present a novel sustained and controlled release approach, and develop a convenient, safe, and potentially scalable feeding system with the assistance of matrix materials and a simple portable feeder. As a result, a highly volatile liquid precursor can be fed accurately to grow large-area, uniform graphene films with optimal properties. This feeding approach will further benefit the synthesis of other two-dimensional materials from various precursors.

High-rate synthesis of SiCN films using single-source silicon precursor with high-density helicon plasma

A novel type of compound, namely Si-guanidinate, where the Si center of alkylsilyl is linked with pyrrolyl-guanidinate ligand, has been synthesized as potential chemical vapor deposition (CVD) precursor and characterized by 1H, 13C, EI-MS, and elemental analysis. The thermal properties of the Si-guanidinate, including vapor pressure and thermal stabilities which were investigated by simultaneous thermal analyses (STA) exhibit a promising precursor in CVD process. The Si-guanidinate was used as a single-source liquid organosilicone precursor to deposit silicon carbon nitride (SiCN) films with the helicon plasma-enhanced chemical vapor deposition (HWP-CVD) method. The effect of the substrate pules negative bias voltage (-Vs) on the microstructure, morphology, composition and optical properties (including refractive index) of the SiCN films has been studied. The deposition rate of the films exhibits a maximum of 15.3 μm/min, which is contributed by the high-density plasma generation of HWP. By X-ray photoelectron spectroscopy (XPS) analysis, the film is mainly composed of Si–C–N. The SiCN films deposited at -VS of 1500 V appear to be high N content of 30.0% (k = 1.83) materials with quite small surface roughness (Root mean square (RMS)~0.7 nm).

Synthesis and Evaluation of Molybdenum Imido-Thiolato Complexes for the Aerosol-Assisted Chemical Vapor Deposition of Nitrogen-Doped Molybdenum Disulfide

Molybdenum bis(imido) bis(thiolato) complexes of the type Mo(NtBu)2(SR)2 (R = tBu (1), iPr (2)) were synthesized and evaluated as precursors for the aerosol-assisted chemical vapor deposition (AACV...