Charles H. Winter

Optical properties of Al2O3 thin films grown by atomic layer deposition

We employed the atomic layer deposition technique to grow Al(2)O(3) films with nominal thicknesses of 400, 300, and 200 nm on silicon and soda lime glass substrates. The optical properties of the films were investigated by measuring reflection spectra in the 400-1800 nm wavelength range, followed by numerical fitting assuming the Sellmeier formula for the refractive index of Al(2)O(3). The films grown on glass substrates possess higher refractive indices as compared to the films on silicon. Optical waveguiding is demonstrated, confirming the feasibility of high-index contrast planar waveguides fabricated by atomic layer deposition.

Synthesis, structure, and properties of magnesium complexes containing cyclopentadienyl and amidinate ligand sets

[CpMgMe(Et2O)]2 was prepared by dissolving Cp2Mg and dimethylmagnesium together in diethyl ether. It reacted readily with diphenylamine, 3-amino-2,4-dimethylpentane, 2,6-diisopropylaniline, N-isopropylbenzylamine, and diisopropylamine in diethyl ether to afford the dimeric amido complexes [CpMg(NPh2)]2 (83%), [CpMg(NHCH(CH(CH3)2)2)]2 (75%), [CpMg(NHiPr2C6H3)]2 (61%), [CpMg(N(iPr)(CH2Ph))]2 (62%), and [CpMg(NiPr2)]2 (81%) as colorless crystalline solids. Treatment of [CpMgMe(Et2O)]2 with N,N,N‘-trimethylethylenediamine in diethyl ether yielded dimeric [CpMg(MeNCH2CH2NMe2)]2 (76%). The reaction of [CpMgMe(Et2O)]2 with 2,5-bis(dimethylaminomethyl)pyrrole in diethyl ether led to the formation of the monomeric magnesium pyrrolato complex [CpMg(Et2O)(η2-Me2NCH2(C4H2N)CH2NMe2)] (70%). The X-ray crystal structures of [CpMg(NPh2)]2, [CpMg(NHCH(CH(CH3)2)2)]2, [CpMg(NHiPr2C6H3)]2, [CpMg(N(iPr)(CH2Ph))]2, and [CpMg(Et2O)(η2-Me2NCH2(C4H2N)CH2NMe2)] were determined. In the solid state structures, [CpMg(NPh2)]2, [CpMg(N...

Low-temperature deposition of titanium nitride films from dialkylhydrazine-based precursors

Abstract The deposition of titanium nitride films from single-source precursors bearing alkylhydrazine-derived ligands is reported. The complex [Ti2Cl4(NN(CH3)2)2(NH2N(CH3)2)2] sublimes at 140–150°C (0.1 mmHg) and affords titanium nitride films in a chemical vapor deposition reactor at substrate temperatures of ⩾400°C. By contrast, structurally related single-source precursors containing alkylamine- or ammonia-derived ligands deposit titanium (IV) nitride chloride films at 400°C in the same reactor, and only afford titanium nitride films at ⩾475°C. The hydrazide(1−) complex [TiCl2(N(CH3)N(CH3)2)2] sublimes at 130°C (0.1 mmHg) and affords titanium nitride films at 600°C. At substrate temperatures of ⩽550°C, poorly adherent blue-colored coatings were obtained. The atmospheric pressure chemical vapor deposition reaction of titanium tetrachloride and 1,1-dimethylhydrazine affords titanium nitride films at >500°C, but gives titanium (IV) nitride chloride films at ⩽500°C. Characterization of the films obtained from the depositions is described. The results demonstrate that ligands derived from 1,1-dialkylhydrazines can be powerful reducing sources for high valent early transition metals, depending on the ligand coordination mode, and can lead to a significant reduction in deposition temperatures compared to traditional nitrogen sources in cases where a high valent metal source compound must be reduced to a lower oxidation state.

Synthesis, structure and properties of volatile lanthanide complexes containing amidinate ligands: application for Er2O3 thin film growth by atomic layer deposition

Treatment of anhydrous rare earth chlorides with three equivalents of lithium 1,3-di-tert-butylacetamidinate (prepared in situ from the di-tert-butylcarbodiimide and methyllithium) in tetrahydrofuran at ambient temperature afforded Ln(tBuNC(CH3)NtBu)3 (Ln = Y, La, Ce, Nd, Eu, Er, Lu) in 57–72% isolated yields. X-Ray crystal structures of these complexes demonstrated monomeric formulations with distorted octahedral geometry about the lanthanide(III) ions. These new complexes are thermally stable at >300 °C, and sublime without decomposition between 180–220 °C/0.05 Torr. The atomic layer deposition of Er2O3 films was demonstrated using Er(tBuNC(CH3)NtBu)3 and ozone with substrate temperatures between 225–300 °C. The growth rate increased linearly with substrate temperature from 0.37 A per cycle at 225 °C to 0.55 A per cycle at 300 °C. Substrate temperatures of >300 °C resulted in significant thickness gradients across the substrates, suggesting thermal decomposition of the precursor. The film growth rate increased slightly with an erbium precursor pulse length between 1.0 and 3.0 s, with growth rates of 0.39 and 0.51 A per cycle, respectively. In a series of films deposited at 250 °C, the growth rates varied linearly with the number of deposition cycles. Time of flight elastic recoil analyses demonstrated slightly oxygen-rich Er2O3 films, with carbon, hydrogen and fluorine levels of 1.0–1.9, 1.7–1.9 and 0.3–1.3 atom%, respectively, at substrate temperatures of 250 and 300 °C. Infrared spectroscopy showed the presence of carbonate, suggesting that the carbon and slight excess of oxygen in the films are due to this species. The as-deposited films were amorphous below 300 °C, but showed reflections due to cubic Er2O3 at 300 °C. Atomic force microscopy showed a root mean square surface roughness of 0.3 and 2.8 nm for films deposited at 250 and 300 °C, respectively.

Magnesium Complexes Bearing η2‐Pyrazolato Ligands

Despite the small size of the magnesium ion, η2 -bound pyrazolato ligands are found in complexes 1-3. These complexes provide new insight into the design of volatile Group 2 metal complexes for use in chemical vapor deposition processes.

Volatility, high thermal stability, and low melting points in heavier alkaline earth metal complexes containing tris(pyrazolyl)borate ligands.

Treatment of MI(2) (M = Ca, Sr) or BaI(2)(THF)(3) with 2 equiv of potassium tris(3,5-diethylpyrazolyl)borate (KTp(Et2)) or potassium tris(3,5-di-n-propylpyrazolyl)borate (KTp(nPr2)) in hexane at ambient temperature afforded CaTp(Et2)(2) (64%), SrTp(Et2)(2) (64%), BaTp(Et2)(2) (67%), CaTp(nPr2)(2) (51%), SrTp(nPr2)(2) (75%), and BaTp(nPr2)(2) (39%). Crystal structure determinations of CaTp(Et2)(2), SrTp(Et2)(2), and BaTp(Et2)(2) revealed monomeric structures. X-ray structural determinations for strontium tris(pyrazolyl)borate (SrTp(2)) and barium tris(pyrazolyl)borate ([BaTp(2)](2)) show that SrTp(2) exists as a monomer and [BaTp(2)](2) exists as a dimer containing two bridging Tp ligands. The thermogravimetric analysis traces, preparative sublimations, and melting point/decomposition determinations demonstrate generally very high thermal stabilities and reasonable volatilities. SrTp(2) has the highest volatility with a sublimation temperature of 200 degrees C/0.05 Torr. [BaTp(2)](2) is the least thermally stable with a decomposition temperature of 330 degrees C and a percent residue of 46.5% at 450 degrees C in the thermogravimetric analysis trace. SrTp(Et2)(2), BaTp(Et2)(2), CaTp(nPr2)(2), SrTp(nPr2)(2), and BaTp(nPr2)(2) vaporize as liquids between 210 and 240 degrees C at 0.05 Torr. BaTp(Et2)(2) and BaTp(nPr2)(2) decompose at about 375 degrees C, whereas MTp(Et2)(2) and MTp(nPr2)(2) (M = Ca, Sr) are stable to >400 degrees C. Several of these new complexes represent promising precursors for chemical vapor deposition and atomic layer deposition film growth techniques.

Synthesis, structure, and properties of magnesium complexes containing mixed cyclopentadienyl and amido ligand sets

[CpMgMe(Et2O)]2 was prepared by dissolving Cp2Mg and dimethylmagnesium together in diethyl ether. It reacted readily with diphenylamine, 3-amino-2,4-dimethylpentane, 2,6-diisopropylaniline, N-isopropylbenzylamine, and diisopropylamine in diethyl ether to afford the dimeric amido complexes [CpMg(NPh2)]2 (83%), [CpMg(NHCH(CH(CH3)2)2)]2 (75%), [CpMg(NHiPr2C6H3)]2 (61%), [CpMg(N(iPr)(CH2Ph))]2 (62%), and [CpMg(NiPr2)]2 (81%) as colorless crystalline solids. Treatment of [CpMgMe(Et2O)]2 with N,N,N‘-trimethylethylenediamine in diethyl ether yielded dimeric [CpMg(MeNCH2CH2NMe2)]2 (76%). The reaction of [CpMgMe(Et2O)]2 with 2,5-bis(dimethylaminomethyl)pyrrole in diethyl ether led to the formation of the monomeric magnesium pyrrolato complex [CpMg(Et2O)(η2-Me2NCH2(C4H2N)CH2NMe2)] (70%). The X-ray crystal structures of [CpMg(NPh2)]2, [CpMg(NHCH(CH(CH3)2)2)]2, [CpMg(NHiPr2C6H3)]2, [CpMg(N(iPr)(CH2Ph))]2, and [CpMg(Et2O)(η2-Me2NCH2(C4H2N)CH2NMe2)] were determined. In the solid state structures, [CpMg(NPh2)]2, [CpMg(N...

Adducts of titanium tetrachloride with organosulfur compounds. Crystal and molecular structures of TiCl4(C4H8S)2 and (TiCl4)2(CH3SSCH3)

Abstract Treatment of titanium tetrachloride with a range of organothiols affords adducts of the formula TiCl4(HSR)2 in 77–89% yields. Reaction of titanium tetrachloride with organic sulfides gives sulfide adducts of the formula TiCl4(SR2)2 in 87–98% yields. These complexes are volatile and monomeric with cis-organosulfur ligands. Treatment of titanium tetrachloride with methyl disulfide affords the adduct (TiCl4)2(CH3SSCH3) in 98% yield, which adopts a dinuclear structure with a Ti2Cl8 core and a bridging disulfide ligand. The crystal structures of TiCl4(C4H8S)2 and (TiCl4)2(CH3SSCH3) were determined. The relevance of these observations to the chemical vapor deposition of titanium disulfide and trisulfide films is discussed.

Preparation and characterization of molybdenum and tungsten nitride nanoparticles obtained by thermolysis of molecular precursors

Treatment of Mo(NtBu)2Cl2 with [K(Ph2pz)(THF)]6 (pz = pyrazolyl) in tetrahydrofuran afforded Mo(NtBu)2(Ph2pz)2 (85%), while treatment of W(NtBu)2(NHtBu)2 with 3,5-diphenylpyrazole afforded W(NtBu)2(Ph2pz)2 (97%). The complexes M(NtBu)2(Ph2pz)2 were characterized completely by spectral and analytical data, and by an X-ray crystal structure determination for Mo(NtBu)2(Ph2pz)2. Thermolysis of M(NtBu)2(Ph2pz)2 at 800 °C under nitrogen afforded 2–3 nm metal nitride nanoparticles that were embedded in an amorphous carbon–oxygen matrix, as determined by X-ray powder diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. X-Ray photoelectron spectroscopy also revealed the presence of metal oxide phases, which were amorphous by X-ray powder diffraction. The nanoparticles prepared at 800 °C were insoluble. Thermolysis of M(NtBu)2(Ph2pz)2 at 425 °C afforded amorphous 2–3 nm nanoparticles, as determined by X-ray powder diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. X-Ray photoelectron spectroscopy suggested a molybdenum(IV) nitride and W2N/WN, as well as MoO3 and an oxidized tungsten nitride. Materials prepared at 425 °C were not embedded in a matrix, and were soluble in tetrahydrofuran. Infrared and NMR spectroscopy suggested the presence of surface organic fragments that contain alkyl-substituted phenyl groups. Such surface groups are most likely derived from decomposition of the heterocyclic ligands. Simultaneous differential thermal analysis/thermogravimetric analysis indicated that the amorphous nitride materials convert to crystalline nanoparticles consistent with M2N phases between 600–700 °C, along with a weight loss that may correspond to dinitrogen evolution. The amorphous carbon–oxygen matrix also forms upon heating from 425 to 800 °C. This work provides the first description of tungsten nitride nanoparticles, as well as the first description of soluble group 4–6 nanoparticles.

Synthesis, Structure, and Properties of Group 1 Metal Complexes Containing Nitrogen-Rich Hydrotris(tetrazolyl)borate Ligands

Nitrogen-rich hydrotris(tetrazolyl)borate salts of lithium, sodium, and potassium have been prepared for the first time by thermolysis of the borohydride ion with three equivalents of tetrazoles in ether solvents at 160-162 °C. Despite the high nitrogen contents, these complexes have low sensitivity to impact, electrostatic discharge, and friction.