5 research outputs found
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
<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 AlH<sub>2</sub>(tBuNCH<sub>2</sub>CH<sub>2</sub>NMe<sub>2</sub>)
and AlH<sub>2</sub>(tBuNCH<sub>2</sub>CH<sub>2</sub>NC<sub>4</sub>H<sub>8</sub>)
are more thermally stable than common Al hydride thin film precursors such as
AlH<sub>3</sub>(NMe<sub>3</sub>). ALD film growth experiments using TiCl<sub>4</sub> and AlH<sub>2</sub>(tBuNCH<sub>2</sub>CH<sub>2</sub>NMe<sub>2</sub>) 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<sub>0.8</sub>N<sub>0.5</sub> 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 AlH<sub>2</sub>(tBuNCH<sub>2</sub>CH<sub>2</sub>NMe<sub>2</sub>), which is ca. 185 °C. Similar growth rates,
resistivities, and film compositions were observed in ALD film growth trials
using AlH<sub>2</sub>(tBuNCH<sub>2</sub>CH<sub>2</sub>NC<sub>4</sub>H<sub>8</sub>). </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 bisÂ(1,4-di-<i>tert</i>-butyl-1,3-diazadienyl)Ânickel
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 Ã…/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 Cu<sub>2</sub>ZnSnS<sub>4</sub> Nanorods
Cu<sub>2</sub>ZnSnS<sub>4</sub> (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
Cu<sub>2</sub>ZnSnS<sub>4</sub> Nanorods Doped with Tetrahedral, High Spin Transition Metal Ions: Mn<sup>2+</sup>, Co<sup>2+</sup>, and Ni<sup>2+</sup>
Because
of its useful optoelectronic properties and the relative abundance
of its elements, the quaternary semiconductor Cu<sub>2</sub>ZnSnS<sub>4</sub> (CZTS) has garnered considerable interest in recent years.
In this work, we dope divalent, high spin transition metal ions (M<sup>2+</sup> = Mn<sup>2+</sup>, Co<sup>2+</sup>, Ni<sup>2+</sup>) into
the tetrahedral Zn<sup>2+</sup> sites of wurtzite CZTS nanorods. The
resulting Cu<sub>2</sub>M<sub><i>x</i></sub>Zn<sub>1–<i>x</i></sub>SnS<sub>4</sub> (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<sub><i>x</i></sub>Cd<sub>1–<i>x</i></sub>Se, washing
Cu<sub>2</sub>Mn<sub><i>x</i></sub>Zn<sub>1–<i>x</i></sub>SnS<sub>4</sub> nanocrystals with trioctylphosphine
oxide (TOPO) is an efficient way to remove excess Mn<sup>2+</sup> ions
from the particle surface. XPS and IR of as-isolated and thiol-washed
samples show that, in contrast to binary chalcogenides, Cu<sub>2</sub>Mn<sub><i>x</i></sub>Zn<sub>1–<i>x</i></sub>SnS<sub>4</sub> 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