Metal and Ceramic Thin Film Growth by Reaction of Alkali Metals with Metal Halides:  A New Route for Low-Temperature Chemical Vapor Deposition

Abstract

A new low-temperature chemical vapor deposition (CVD) method for the growth of metal and ceramic thin films has been demonstrated. This method involves the use of a lowpressure coflow diffusion reactor to react alkali metal vapor with metal halide vapor. The reaction chemistry is described by the following general equation: mnNaHere, Na is an alkali metal (e.g. Na, K, Cs, or Rb), M is a metal (e.g. Ti, Ta, Pt, W, ...) or nonmetal (e.g. B, C, Si, ...), X is a halogen (e.g. F, Cl, Br, or I), Ar is an inert gas (e.g. Ar or He), and m and n are integers. In this reaction, the alkali metal strips halogen from the metal halide. The metal is then free to grow into a thin film on a substrate placed in the reaction zone. Metal nitride or metal oxide ceramic films are easily formed by the introduction of nitrogen or oxygen gases into the reactor. Previously, this technique has been successfully employed for the production of nanoparticles and as an industrial synthesis route for the reduction of bulk metals from their metal halides. Now, for the first time, this reaction chemistry has been demonstrated to be a viable technique for thin film growth as well. Using the precursors of sodium metal vapor, titanium tetrachloride (the limiting reagent), and either Ar or N 2 gas, salt-free titanium (Ti), titanium nitride (TiN), and titanium silicide (Ti x Si y ) thin films have been grown on copper and silicon substrates. Guided by theoretical modeling calculations, reactant concentrations were adjusted to prevent gasphase particle nucleation and growth. Using this technique, we have produced salt-free titanium and titanium nitride thin films on copper substrates heated to 610 °C. This temperature is considerably lower than the 900-1200 °C required for the conventional thermal CVD of titanium. A composite salt/Ti film was grown on a silicon wafer at 260 °C, while at 610 °C, a salt-free titanium silicide thin film was produced. The quality and composition of the thin films were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM).

A versatile low temperature solid-state synthesis of vanadium nitride (VN) via a “guanidinium-route”: experimental and theoretical studies from the key-intermediate to the final product

“…Conventionally, they are prepared by different and complex methods which include selfpropagating high temperature synthesis (SHS), 10 nitridation via the urea pathway, 11,12 chemical vapor deposition, 13 reductionnitridation reactions, 14 reaction of vanadium metallic with nitrogen, 1 carbothermal reduction and nitridation of vanadium oxides in N 2 , 15 and temperature programmed reactions. [16][17][18][19][20][21] The search for a more general, inexpensive, safe and efficient methodology to produce new classes of materials is highly desired and attempted by materials chemists, physicists and engineers. As may be seen in the literature, methods to produce a variety of nitrides and carbides are already known.…”

Rotational and hyperfine analysis of the near infrared Φ43–X 3Φ4 transitions of CoCl and CoI

“…[2][3][4] Spectroscopic studies of transition metal diatomic halides have been an active area of research for many years. [5][6][7][8] The diatomic metal monohalides are simple model systems that can provide insight into the role of the d orbitals in chemical bonding.…”

A Combined Experimental and Theoretical Study on the Formation of Crystalline Vanadium Nitride (VN) in Low Temperature through a Fully Solid-State Synthesis Route

“…Conventionally, they are prepared, among other methods, [13][14][15]22 by self-propagating high-temperature synthesis (SHS), 7 chemical vapor deposition, 8 reduction−nitridation, 9 direct reaction of vanadium metallic with nitrogen, 1 carbothermal reduction and nitridation of vanadium oxides in N 2 , 10 or temperature-programmed reactions. 11,12 In a previous article, we reported recent experimental findings on the crystallization of vanadium nitride (VN) in the NaCl-type structure via a method named "guanidinium route".…”

“…On the other hand, the synthesis of vanadium nitride is usually difficult, requiring elevated temperatures and long reaction times. Conventionally, they are prepared, among other methods, − , by self-propagating high-temperature synthesis (SHS), chemical vapor deposition, reduction–nitridation, direct reaction of vanadium metallic with nitrogen, carbothermal reduction and nitridation of vanadium oxides in N 2 , or temperature-programmed reactions. , …”