Gallium oxide (Ga2O3) is an ultrawide bandgap semiconductor with promising applications in power electronics and UV-photodetectors. Herein, we present thermal atomic layer deposition (ALD) of Ga2O3 thin films using tris(1,3-diisopropyltriazenide)gallium(iii) and water. The deposition process shows saturation in the growth per cycle of ∼1.5 Å at precursor pulses ≥2 s with a narrow ALD temperature interval between 400 and 415 °C, and a nucleation delay of ∼15 cycles. Time-of-flight elastic recoil detection analysis revealed near-stoichiometric Ga2O3 with <3.5 at%, of C, H, N, and Cl, all of which decreases after annealing. Grazing Incidence X-ray diffraction reveals that annealing at 700 °C converts as-deposited amorphous films into phase-pure β-Ga2O3. The as-deposited films were highly transparent (>96%) with an optical bandgap of ∼3.74 eV, which increased to ∼4.0 eV upon annealing. Electrical conductivity also increased from ∼3 mS cm−1 in the as deposited films to ∼30 mS cm−1 after annealing. This work extends the ALD chemistry of triazenide precursors, previously validated for GaN, InN, InGaN and In2O3, to Ga2O3.

The present study reports on the structure formation in thin epitaxial nickel-aluminum films (Ni<inf>1-x</inf>Al<inf>x</inf>; Al atomic fraction x up to x = 0.24 ) grown on MgO ( 001 ) substrates by magnetron sputtering. Experimental and computational data demonstrate that for x &lt; 0.11 , the films exhibit the face-centered cubic random solid-solution Ni<inf>1-x</inf>Al<inf>x</inf> structure ( γ phase). Whereas in the range x = 0.11–0.24 the γ phase coexists with the ordered L 1 2 structure ( γ ′ phase). The two phases are homogenously intermixed forming a strained coherent nanocomposite , which exhibits a single lattice parameter that expands as the Al content increases. Isothermal annealing of films containing x = 0.14 of Al, coupled with structural and nano-mechanical characterization, reveal that the coherent nanocomposite retains its overall integrity for temperatures up to 673 K , while the film hardness increases from 5.5 GPa (as deposited films) to 6 GPa . Further increase of the annealing temperature to 873 K and 1073 K causes the coherent nanocomposite to dissolve into distinct γ and γ ′ phase domains and the hardness to decrease down to values of 4 GPa . These findings confirm the metastable nature of the as-deposited thin Ni<inf>1-x</inf>Al<inf>x</inf> alloy films and underpin the effectiveness of high supersaturation/undercooling for creating non-equilibrium phases and self-organized nanostructures upon synthesis of multicomponent materials.

The present study investigates photochromic oxygen-containing yttrium hydride (YHO) thin films deposited by reactive high power impulse magnetron sputtering (HiPIMS) and compares their photochromic, optical, and structural properties with those of films synthesized by reactive pulsed direct current magnetron sputtering (pulsed-DCMS). Optical emission spectroscopy reveals that, unlike pulsed-DCMS where Ar+ ions dominate, HiPIMS discharges are characterised by strong Y+ emission, evidencing high yttrium ionisation and substantial self-sputter recycling. The critical working pressure (P_c) required to obtain transparent and photochromic films is higher for HiPIMS (P_c ≈ 1.0 Pa) than for pulsed-DCMS (P_c ≈ 0.5 Pa). Although films deposited near P_c exhibit similar solar transmittance (∼72 %) and lattice parameters (5.38–5.39 Å), the pulsed-DCMS film shows a substantially higher relative photochromic contrast (34 %) and a lower optical band gap (2.70 eV) compared with the HiPIMS film (9 % contrast and 2.94 eV). This difference is partly attributed to a lower oxygen-to-hydrogen atomic ratio in the pulsed-DCMS film. Structurally, HiPIMS films are largely polycrystalline with random out-of-plane crystallographic orientation, whereas pulsed-DCMS films exhibit a pronounced <100> out-of-plane preferred orientation. These results demonstrate that, beyond composition, thin-film growth conditions and microstructure play a crucial role in governing the photochromic performance of YHO.

The present study investigates photochromic oxygen-containing yttrium hydride (YHO) thin films deposited by reactive high power impulse magnetron sputtering (HiPIMS) and compares their photochromic, optical, and structural properties with those of films synthesized by reactive pulsed direct current magnetron sputtering (pulsed-DCMS). Optical emission spectroscopy reveals that, unlike pulsed-DCMS where Ar+ ions dominate, HiPIMS discharges are characterised by strong Y+ emission, evidencing high yttrium ionisation and substantial self-sputter recycling. The critical working pressure (P-c) required to obtain transparent and photochromic films is higher for HiPIMS (P-c approximate to 1.0 Pa) than for pulsed-DCMS (P-c approximate to 0.5 Pa). Although films deposited near P-c exhibit similar solar transmittance (similar to 72 %) and lattice parameters (5.38-5.39 & Aring;), the pulsed-DCMS film shows a substantially higher relative photochromic contrast (34 %) and a lower optical band gap (2.70 eV) compared with the HiPIMS film (9 % contrast and 2.94 eV). This difference is partly attributed to a lower oxygen-to-hydrogen atomic ratio in the pulsed-DCMS film. Structurally, HiPIMS films are largely polycrystalline with random out-of-plane crystallographic orientation, whereas pulsed-DCMS films exhibit a pronounced <100> out-of-plane preferred orientation. These results demonstrate that, beyond composition, thin-film growth conditions and microstructure play a crucial role in governing the photochromic performance of YHO.

Aluminum titanium nitride (AlxTi1-xN, 0 < x < 1) is a critical hard coating material for cutting tools due to its exceptional hardness, thermal stability, wear resistance, and oxidation resistance, all of which are influenced by its Al content. A common method to swiftly estimate the Al content in production of such coatings is by the size of the AlxTi1-xN unit cell-determined by standard 0-20 X-ray diffraction-and the equilibrium cell size of the binary constituents AlN and TiN in the framework of Vegard's law. However, in most cases, the measured unit cell size does not merely depend on Al content as AlxTi1-xN is a metastable phase that may exhibit crystalline defects, non-ideal mixing of the binaries, differences in bonding characteristics, strain relaxation, and phase separation. We seek to investigate the resulting uncertainty in Vegard's-law-based estimation by comparing estimated Al content with elemental composition of AlxTi1-xN coatings-grown industrially by chemical vapor deposition on cemented tungsten carbide substrates-using energy-dispersive X-ray spectroscopy, hard X-ray photoelectron spectroscopy, time-of-flight elastic recoil detection analysis, and Rutherford backscattering spectrometry. Our results demonstrate that the uncertainties in Al content estimated by Vegard's law are relatively small, rendering this method a good first-order approach for compositional analysis of the metal sub-lattices in AlxTi1-xN. Moreover, our data indicate that a multimethod strategy is required for precise composition determination that includes both the metal and the non-metal sublattices and impurity level.

We study the effect of impurities on the morphological evolution of thin silver (Ag) and copper (Cu) films deposited by direct current and high-power impulse magnetron sputtering on weakly-interacting silicon dioxide and amorphous carbon substrates. We systematically vary the ratio of impurity-to-metal particle flux [Formula presented] arriving at the substrate in the range ∼10−4−10 and assess the character of film morphological evolution and the overall growth dynamics by means of real-time in-situ diagnostic tools and ex-situ analyses. We find that both thin-film materials exhibit a three-dimensional morphological evolution, which for the case of Ag is governed by the effect of metal vapor flux magnitude on the dynamic competition among island nucleation, growth, and coalescence (vapor-controlled growth regime). At all deposition conditions, small amounts (of the order of 1at.%) of impurities (comprising oxygen, carbon, and hydrogen) are incorporated in the Ag films, while an increase of [Formula presented] suppresses three-dimensional growth for layers deposited on silicon dioxide. Cu exhibits a similar (vis-à-vis Ag) behavior with respect to the overall morphology and impurity incorporation for [Formula presented] below a critical value of ∼1. For [Formula presented] above ∼1, the impurity content in the Cu layers increases sharply (reaching ∼10at.% for [Formula presented]) and film morphological evolution is seemingly determined by the effect of impurities on the fundamental structure-forming process of island nucleation, grain growth, and crystal growth (impurity-controlled growth regime).

The present work models temperature-dependent ( 500 − 1300 K ) diffusion dynamics of Ag, Au, and Cu adatoms on MoS2 as well as electronic and magnetic properties of adatom (Ag, Au, and Cu)/MoS2 systems. Modeling is done by means of ab initio molecular dynamics (AIMD) simulations that account for van der Waals corrections and electronic spin degrees of freedom in the framework of density functional theory. It is found that Ag and Au adatoms exhibit super-diffusive motion on MoS2 at all temperatures, while Cu adatoms follow a random walk pattern of uncorrelated surface jumps. The observed behavior is consistent with AIMD-calculated effective migration barriers E a ( E a Ag = 190 ± 50 meV , E a Au = 67 ± 7 meV , and E a Cu = 300 ± 100 meV ) and can be understood on the basis of the considerably flatter potential energy landscapes encountered by Ag and Au adatoms on the MoS2 surface (corrugation of the order of tens of meV), as compared to Cu adatoms (corrugation > 100 meV ). Moreover, evaluation of the electronic and magnetic properties of AIMD configurations suggest that Ag, Au, and Cu monomer adsorption induces semimetallic features in at least one spin channel of the adatom/MoS2 electronic structure at elevated temperatures. The overall results presented herein may provide insights into fabricating 2D-material-based heterostructure devices beyond graphene.

The use of superconducting radio frequency (rf) cavities in particle accelerators necessitates that copper (Cu) surfaces are coated by thin niobium (Nb) films, predominantly synthesized by magnetron sputtering. A key feature of the rf cavities is that they exhibit a complex three-dimensional geometry, such that during Nb film growth vapor is not deposited on a flat substrate. The latter, combined with the line-of-sight nature of the deposition flux in conventional magnetron sputtering methods (including direct current magnetron sputtering; DCMS) yields films with porous columnar morphologies on surfaces of the cavities that do not face the magnetron source. High-power impulse magnetron sputtering (HiPIMS) is a variant of sputtering that generates highly-ionized fluxes. Using electrical fields, such fluxes can be deflected to trajectories that are closer to the substrate normal and, thereby, dense and uniform layers can be deposited on all surfaces of the rf cavities. In the present work, we use classical molecular dynamics simulations to model Nb film growth on Cu substrates at conditions consistent with those prevailing during DCMS and HiPIMS. Our computational results are in qualitative agreement with experimental data (also generated in the present study), with respect to film morphology. Based on this agreement and by studying the evolution of the simulated systems, we suggest that the morphology of HiPIMS-grown films (as compared to their DCMS counterparts) is the result of the combined effects of deflection of ionized sputtered particles to trajectories parallel to the substrate normal, bombardment-induced interruption of crystal growth, and ballistic atomic rearrangement along with dynamic thermal annealing caused by energetic film-forming species. Moreover, the predictions of our model with respect to dynamic processes at the film-substrate interface and their effect on local epitaxial growth are discussed.

We study the effect of nitrogen on the morphological evolution of thin silver (Ag) films deposited on weakly-interacting amorphous carbon (a-C) and silicon oxide (SiOx) surfaces. Films are synthesized at a deposition rate of 0.1nm·s-1 by direct current magnetron sputtering (DCMS), high power impulse magnetron sputtering (HiPIMS), and electron-beam evaporation (EBE). We monitor growth in situ and in real time by measuring the evolution of film stress and optical properties, complemented by ex situ analyses of discontinuous-layer morphologies, film crystal structure, and film composition. We find that addition of molecular nitrogen (N2) to the plasmagenic gas (Ar) during DCMS and HiPIMS promotes a two-dimensional (2D) morphology. Concurrently, EBE-deposited films exhibit a significantly more pronounced three-dimensional morphological evolution, independently from the gas atmosphere composition. We argue that the 2D morphology in DCMS- and HiPIMS-grown films is enhanced due to incorporation of atomic nitrogen (N)—result of plasma-induced N2 dissociation—that hinders island reshaping during coalescence. This mechanism is not active during EBE due to the absence of energetic plasma electrons driving N2 dissociation. The overall results of the study show that accurate control of vapor-phase chemistry is of paramount importance when using gaseous species as agents for manipulating growth in weakly-interacting film-substrate systems.

Here we investigate the interface properties of gold (Au) decorated graphenized surfaces of 4H-SiC intended for electrochemical electrodes. These are fabricated using a two-step process: discontinuous Au layers with a nominal thickness of 2 nm are sputter-deposited onto 4H-SiC substrates with different graphenization extent—zero-layer graphene (ZLG) and monolayer epitaxial graphene) —followed by thermal annealing. By performing combined morphometric analysis, Raman mapping analysis, conductive atomic force microscopy, and electrochemical impedance spectroscopy measurements, we shed light on the relationship between physical processes (Au intercalation, particle re-shaping, and de-wetting) caused by thermal annealing and the intrinsic properties of graphenized SiC (vertical electron transport, charge-transfer properties, vibrational properties, and catalytic activity). We find that the impedance spectra of all considered structures exhibit two semicircles in the high and low frequency regions, which may be attributed to the graphene/ZLG/SiC (or Au/graphene/ZLG/SiC) and SiC/ZLG/graphene/electrolyte (or SiC/ZLG//Au/electrolyte) interfaces, respectively. An equivalent circuit model is proposed to estimate the interface carrier transfer parameters. This work provides an in-depth comprehension of the way by which the Au/2D carbon/SiC interaction strength influences the interface properties of heterostructures, which can be helpful for developing high performance catalytic and sensing devices.