Contract Report for FY 2019 & FY 2020 National Geological & Geophysical Data Preservation Project

The Bureau of Economic Geology has a rich history of mineral exploration and mining that predates its role as the Geological Survey of Texas, established in 1858. Many publications from the United States Geological Survey, United States Bureau of Mines, and Bureau of Economic Geology addressing mineral resources were published before the digital age and the development of the internet. Most of this valuable information is preserved and archived as annual mineral reports, reports of investigations, mineral circulars, and other products published between 1858 and 1990. As part of the National Geological and Geophysical Data Preservation Project funded through the United States Geological Survey, two project goals were developed to assist in the identification of critical minerals in Texas. Project Goal 1 for 2019 and 2020 aimed to acquire and review all publications, materials, and data that reference and describe mineral information, mineral deposits, and occurrences hosting critical minerals. This data was transcribed into provided spreadsheets and information templates, including details such as name, location, geology, resource information on contained commodities, production information, resource or reserve estimations, ore grade, deposit type, mining history, reference citations, and other relevant information. Project Goal 2 aimed to develop a statewide depth to Precambrian basement map in common geospatial digital data format using the national Geologic Map Schema (GeMS) and available seismic and drill core data. Although Precambrian basement has been mapped and interpolated in oil and gas basins, and identified as surface (and near-surface) exposure in central and western Texas, there had not been an effort to compile all of these data into a complete and distributable geospatial dataset and published basement map. The state of Texas boasts abundant well log data, and the Bureau of Economic Geology, functioning as the state geological survey, possesses numerous seismic and geophysical surveys, as well as thousands of cross-sections and drill core data. This project aimed to leverage these resources to create a comprehensive and accessible dataset and map of Precambrian basement depths across the state.Bureau of Economic Geolog

Atomic Layer Deposition of Aluminum Metal Films Using a Thermally Stable Aluminum Hydride Reducing Agent

Atomic Layer Deposition of Aluminum Metal Films Using a Thermally Stable Aluminum Hydride Reducing Agen

Aluminum Dihydride Complexes and their Unexpected Application in Atomic Layer Deposition of Titanium Carbonitride Films

Aluminum dihydride complexes containing amido-amine ligands were synthesized and evaluated as potential reducing precursors for thermal atomic layer deposition (ALD). Highly volatile monomeric complexes AlH2(tBuNCH2CH2NMe2) and AlH2(tBuNCH2CH2NC4H8) are more thermally stable than common Al hydride thin film precursors such as AlH3(NMe3). ALD film growth experiments using TiCl4 and AlH2(tBuNCH2CH2NMe2) produced titanium carbonitride films with a high growth rate of 1.6-2.0 Å/cycle and resistivities around 600 μΩ·cm within a very wide ALD window of 220-400 °C. Importantly, film growth proceeded via self-limited surface reactions, which is the hallmark of an ALD process. Root mean square surface roughness was only 1.3 % of the film thickness at 300 °C by atomic force microscopy. The films were polycrystalline with low intensity, broad reflections corresponding to the cubic TiN/TiC phase according to grazing incidence X-ray diffraction. Film composition by X-ray photoelectron spectroscopy was approximately TiC0.8N0.5 at 300 °C with small amounts of Al (6 at%), Cl (4 at%) and O (4 at%) impurities. Remarkably, self-limited growth and low Al content was observed in films deposited well above the solid-state thermal decomposition point of AlH2(tBuNCH2CH2NMe2), which is ca. 185 °C. Similar growth rates, resistivities, and film compositions were observed in ALD film growth trials using AlH2(tBuNCH2CH2NC4H8). </p

Aluminum Dihydride Complexes and their Unexpected Application in Atomic Layer Deposition of Titanium Carbonitride Films

<p>Aluminum dihydride complexes containing amido-amine ligands were synthesized and evaluated as potential reducing precursors for thermal atomic layer deposition (ALD). Highly volatile monomeric complexes AlH₂(tBuNCH₂CH₂NMe₂) and AlH₂(tBuNCH₂CH₂NC₄H₈) are more thermally stable than common Al hydride thin film precursors such as AlH₃(NMe₃). ALD film growth experiments using TiCl₄ and AlH₂(tBuNCH₂CH₂NMe₂) produced titanium carbonitride films with a high growth rate of 1.6-2.0 Å/cycle and resistivities around 600 μΩ·cm within a very wide ALD window of 220-400 °C. Importantly, film growth proceeded via self-limited surface reactions, which is the hallmark of an ALD process. Root mean square surface roughness was only 1.3 % of the film thickness at 300 °C by atomic force microscopy. The films were polycrystalline with low intensity, broad reflections corresponding to the cubic TiN/TiC phase according to grazing incidence X-ray diffraction. Film composition by X-ray photoelectron spectroscopy was approximately TiC_0.8N_0.5 at 300 °C with small amounts of Al (6 at%), Cl (4 at%) and O (4 at%) impurities. Remarkably, self-limited growth and low Al content was observed in films deposited well above the solid-state thermal decomposition point of AlH₂(tBuNCH₂CH₂NMe₂), which is ca. 185 °C. Similar growth rates, resistivities, and film compositions were observed in ALD film growth trials using AlH₂(tBuNCH₂CH₂NC₄H₈). </p

Low Temperature, Selective Atomic Layer Deposition of Nickel Metal Thin Films

We report the growth of nickel metal films by atomic layer deposition (ALD) employing bis­(1,4-di-<i>tert</i>-butyl-1,3-diazadienyl)­nickel and <i>tert</i>-butylamine as the precursors. A range of metal and insulating substrates were explored. An initial deposition study was carried out on platinum substrates. Deposition temperatures ranged from 160 to 220 °C. Saturation plots demonstrated self-limited growth for both precursors, with a growth rate of 0.60 Å/cycle. A plot of growth rate versus substrate temperature showed an ALD window from 180 to 195 °C. Crystalline nickel metal was observed by X-ray diffraction for a 60 nm thick film deposited at 180 °C. Films with thicknesses of 18 and 60 nm grown at 180 °C showed low root mean square roughnesses (<2.5% of thicknesses) by atomic force microscopy. X-ray photoelectron spectroscopies of 18 and 60 nm thick films deposited on platinum at 180 °C revealed ionizations consistent with nickel metal after sputtering with argon ions. The nickel content in the films was >97%, with low levels of carbon, nitrogen, and oxygen. Films deposited on ruthenium substrates displayed lower growth rates than those observed on platinum substrates. On copper substrates, discontinuous island growth was observed at ≤1000 cycles. Film growth was not observed on insulating substrates under any conditions. The new nickel metal ALD procedure gives inherently selective deposition on ruthenium and platinum from 160 to 220 °C

Axial Composition Gradients and Phase Segregation Regulate the Aspect Ratio of Cu₂ZnSnS₄ Nanorods

Cu₂ZnSnS₄ (CZTS) is a promising material for solar energy conversion, but synthesis of phase-pure, anisotropic CZTS nanocrystals remains a challenge. We demonstrate that the initial concentration (loading) of cationic precursors has a dramatic effect on the morphology (aspect ratio) and composition (internal architecture) of hexagonal wurtzite CZTS nanorods. Our experiments strongly indicate that Cu is the most reactive of the metal cations; Zn is next, and Sn is the least reactive. Using this reactivity series, we are able to purposely fine-tune the morphology (dots versus rods) and degree of axial phase segregation of CZTS nanocrystals. These results will improve our ability to fabricate CZTS nanostructures for photovoltaics and photocatalysis

Cu₂ZnSnS₄ Nanorods Doped with Tetrahedral, High Spin Transition Metal Ions: Mn²⁺, Co²⁺, and Ni²⁺

Because of its useful optoelectronic properties and the relative abundance of its elements, the quaternary semiconductor Cu₂ZnSnS₄ (CZTS) has garnered considerable interest in recent years. In this work, we dope divalent, high spin transition metal ions (M²⁺ = Mn²⁺, Co²⁺, Ni²⁺) into the tetrahedral Zn²⁺ sites of wurtzite CZTS nanorods. The resulting Cu₂M_<i>x</i>Zn_1–<i>x</i>SnS₄ (CMTS) nanocrystals retain the hexagonal crystalline structure, elongated morphology, and broad visible light absorption profile of the undoped CZTS nanorods. Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and infrared (IR) spectroscopy help corroborate the composition and local ion environment of the doped nanocrystals. EPR shows that, similarly to Mn_<i>x</i>Cd_1–<i>x</i>Se, washing Cu₂Mn_<i>x</i>Zn_1–<i>x</i>SnS₄ nanocrystals with trioctylphosphine oxide (TOPO) is an efficient way to remove excess Mn²⁺ ions from the particle surface. XPS and IR of as-isolated and thiol-washed samples show that, in contrast to binary chalcogenides, Cu₂Mn_<i>x</i>Zn_1–<i>x</i>SnS₄ nanocrystals aggregate not through dichalcogenide bonds, but through excess metal ions cross-linking the sulfur-rich surfaces of neighboring particles. Our results may help in expanding the synthetic applicability of CZTS and CMTS materials beyond photovoltaics and into the fields of spintronics and magnetic data storage