Amorphous WO3 Films via “Wet” CVD of a WVI Oxoalkoxide Precursor

Abstract

Amorphous WO 3 films are obtained by using the oxoalkoxide precursor WO(O t Bu) 4 . This compound is easily evaporated at 80 C, and reacts with water at the surface of the substrate (Si(100) or soda lime glass (KGlass)) to give films of tungsten oxide in a combined CVD sol±gel process. The films deposited at low temperatures (150 C, Si(100), or 100 C, KGlass) can be defined as tungstic species (of general formula WO n (OH) m ), having interesting electrochromic properties. Thermal treatment at temperatures over 400 C converts the material to a more typical WO 3 film.

AACVD of WO3 thin films from W(O)(OPri)3[O(CH2)nNMe2] (n = 2, 3)

“…Sol-gel, [6] sputtering [7] and spray pyrolysis [8] methods have been reported, but CVD offers the greatest potential for large-scale coatings. We have reported the use of W(OR) 6 (R = C 6 H 5 , C 6 H 4 F-4, C 6 H 3 F 2 -3,4) precursors in this latter regard, [9] which compliments other studies involving tunsten(IV) halides, [10,11] various tungsten alkoxides [W(OEt) n , n = 5, 6] [12] and oxo-alkoxides [W(O)(OR) 4 , R = Et, Pr i , Bu t , CH 2 Bu t ], [13,14] and organometallic precursors such as W(CO) 6 , [15] W(CO) 4 (PR 3 ) 2 (R = OEt) or W(η 3 -C 3 H 4 ) 4 . [16] More recently, the innovative use of poly-tungstates in an aerosolassisted delivery route has been reported by Parkin.…”

“…The surface of the deposited film appears rough, possibly grown via an island growth method, and bears a resemblance to the film grown from W(O)(OBu t ) 4 /H 2 O under sol-gel conditions. [14] The surface roughness can also be clearly seen in Fig. 5(b), which also indicates a columnar structure to the film, despite its amorphous nature.…”

“…The superior optical properties of the amorphous film derived from 3 in comparison to the two crystalline films from 1 and 2 are consistent with an earlier report that also notes that amorphous films (usually deposited at T < ca 300 • C to avoid crystallization) have better electrochromic properties than polycrystalline films. [14]…”

Volatile Hexavalent Oxo-amidinate Complexes: Molybdenum and Tungsten Precursors for Atomic Layer Deposition

“…In particular, we envisioned volatile metal–organic complexes bearing intact metal-dioxo functionalities on Mo­(VI) and W­(VI) centers, as sources for the growth of such centers. While vapor-phase deposition of molybdenum and tungsten oxide films has been realized through ALD and chemical vapor deposition (CVD), − including examples using volatile oxo-bearing tungsten precursors, , precise control of deposited surface structures has not yet been reported. Previously, Gordon and co-workers − reported that amidinato- and acetamidinato- ligand platforms are viable for volatile metal–organic ALD precursors.…”

Growth of WOx from Tungsten(VI) Oxo-Fluoroalkoxide Complexes with Partially Fluorinated β-Diketonate/β-Ketoesterate Ligands: Comparison of Chemical Vapor Deposition to Aerosol-Assisted CVD

“…As an alternative, the use of single-source precursors facilitates control of film stoichiometry and precursor decomposition through consideration of ligand choice . Single-source precursors for WO x CVD include tungsten alkoxides, such as W­(OEt) 6 , but their manipulation is difficult because of their sensitivity to moisture. , This sensitivity can be lessened through use of chelating ligands. Preparation of WO x material through AACVD has been successfully demonstrated by using precursors that contain both alkoxide and chelating ligands. , Fluorination of the ligands can improve the volatility of these complexes because of the repulsive nature of the fluorine atoms .…”