Engineering topics

Allen, Amy J.

Publications and source records attributed to Allen, Amy J..

3 records

DOE OSTI2016

Indium Oxide Thin Films by Atomic Layer Deposition Using Trimethylindium and Ozone

We investigated the atomic layer deposition (ALD) of indium oxide (In2O3) thin films using alternating exposures of trimethylindium (TMIn) and a variety of oxygen sources: ozone (O-3), O-2, deionized H2O, and hydrogen peroxide (H2O2). We used in situ quartz crystal microbalance measurements to evaluate the effectiveness of the different oxygen sources and found that only O-3 yielded viable and sustained 111203 growth with TMIn. These measurements also provided details about the In2O3 growth mechanism and enabled us to verify that both the TMIn and O-3 surface reactions were self-limiting. In2O3 thin films were prepared and characterized using X-ray diffraction, ultraviolet visible spectrophotometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and scanning electron microscopy. The electrical transport properties of these layers were studied by Hall probe measurements. We found that, at deposition temperatures within the range of 100-200 degrees C, the In2O3 growth per cycle was nearly constant at 0.46 angstrom/cycle and the films were dense and pure. The film thickness was highly uniform (<0.3% variation) along the 45 cm length of our tubular ALD reactor. At higher growth temperatures the In2O3 growth per cycle increased due to thermal decomposition of the TMIn. The ALD In2O3 films showed resistivities as low as 3.2 x 10(-3) Omega cm, and carrier concentrations as large as 7.0 x 10(19) cm(-3). This TMIn/O-3 process for In2O3 ALD should be suitable for eventual scale-up in photovoltaics.

atomic layer deposition↗

DOE OSTI2013

Corrosion behavior of mesoporous transition metal nitrides

Transition metal nitrides (TMN) have many desirable characteristics such as high hardness and good thermal stability under reducing conditions. This work reports an initial survey of the chemical stability of mesoporous TMNs (TM=Nb, V, Cr and Ti) in water at 80 °C at neutral, acidic and alkaline pH. The mesoporous TMNs had specific surface areas of 25–60 m{sup 2}/g with average pore sizes ranging from 10 to 50 nm. The high surface areas of these materials enhance the rate of corrosion per unit mass over that of a bulk material, making detection of corrosion much easier. The products were characterized by Rietveld refinement of powder X-ray diffraction (PXRD) patterns and by scanning electron microscopy (SEM). Several nitrides have corrosion rates that are, within error, not distinguishable from zero (±1 Å/day). Of the nitrides examined, CrN appears to be the most corrosion resistant under acidic conditions. None of the nitrides studied are corrosion resistant under alkaline conditions. - Graphical abstract: Corrosion behavior of mesoporous transition metal nitrides (TM=Nb, V, Cr and Ti) in acidic and alkaline solutions at 80 °C for 2 weeks. Display Omitted - highlights: • Corrosion rates of mesoporous transition metal nitrides in aqueous solution is reported. • The mesoporous TMNs had surface areas of 25–60 m{sup 2}/g. • CrN is the most corrosion resistant under the conditions studied.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2013

Mesoporous VN prepared by solid-solid phase separation

We recently reported a simple route to prepare mesoporous, conducting nitrides from Zn containing ternary transition metal oxides. Those materials result from the condensation of atomic scale voids created by the loss of Zn by evaporation, the replacement of 3 oxygen anions by 2 nitrogen anions, and in most cases the loss of oxygen to form water on the reduction of the transition metal. In this report, we present a different route to prepare mesoporous VN from K containing vanadium oxides. In this case, ammonolysis results in a multiphase solid product that contains VN, and other water soluble compounds such as KOH or KNH{sub 2}. On removing the K containing products by washing with degassed water, only mesoporous VN remains. VN materials with different pore sizes (10 nm-20 nm) were synthesized at 600 Degree-Sign C by varying the reaction time, while larger pores are obtained at higher temperatures (50 nm at 800 Degree-Sign C). - Graphical Abstract: The synthesis process of mesoporous VN from solid-solid separation. Highlights: Black-Right-Pointing-Pointer Mesoporous VN has been prepared by solid-solid phase separation. Black-Right-Pointing-Pointer Mesoporous VN was characterized by Rietveld refinement of PXRD, SEM and nitrogen physisorption. Black-Right-Pointing-Pointer VN materials with different pore sizes (10 nm-50 nm) were synthesized.

36 MATERIALS SCIENCE↗