MoAl Alloy Research Articles

Back-Channel-Etched IGZO TFTs With Cu-Based Multilayer Electrodes Using MoAl Alloy and MoMn Alloy as Buffer Layers

We report high-performance IGZO TFTs with MoAl/Cu/MoAl and MoMn/Cu/MoMn three-layer electrodes, where MoAl or MoMn alloy is used as the buffer layer. The multilayer electrode has good electrical properties and can effectively prevent the oxidation and diffusion of the middle Cu layer. In addition, the multilayer electrode can be etched in a PAN etchant solution and match the etching rate with Cu. Based on these MoAl/Cu/MoAl and MoMn/Cu/MoMn electrodes, vacuum-processed IGZO TFTs exhibit a turn-on voltage of 0 V, an on-off ratio of 10⁹, and a mobility of 10.7 cm² V⁻¹ s⁻¹ after annealing at 115 °C in N₂. Under the gate bias stress test, devices with MoMn electrodes, which exhibit a small threshold voltage shift, show better performance than those with MoAl electrodes. The presented studies may provide another option for the Cu buffer layer.

Suppressing channel-shortening effect of self-aligned coplanar Al-doped In-Sn-Zn-O TFTs using Mo-Al alloy source/drain electrode as Cu diffusion barrier

Developing high-resolution displays to achieve realistic images have been in a great demand recently regardless of the display size. However, in the backplane technology, the channel-shortening effect is a serious obstacle in realizing oxide thin film transistors (TFTs) with short channel lengths. In this study, we investigated the channel-shortening effect of Al-doped InSnZnO (Al:ITZO) thin-film transistors (TFTs) with Mo and Mo-based alloy Cu diffusion barriers and proposed Mo‒Al alloy as a Cu diffusion barrier to effectively reduce the channel-shortening effect. The TFTs with the Mo (Cu diffusion barrier) exhibited negative Von shifts and a channel-shortening length (ΔL) of 3.52 µm at an annealing temperature of 290 °C, although no chemical reaction occurred at the Mo/Al:ITZO interfaces. In addition, the TFTs with the Mo‒Ti (Cu diffusion barrier) showed the largest ΔVon and ΔL values at various annealing temperatures. The material and electrical analysis results confirmed that the hydrogen diffusion from the source/drain region is the main cause of the channel-shortening effect. Thus, the TFTs with the Mo‒Al (Cu diffusion barrier) exhibited excellent characteristics against the channel-shortening effect by forming a uniform and thin Al2O3 layer at the Mo‒Al/Al:ITZO interface and preventing the hydrogen diffusion. The ΔVon remained almost unchanged, and the ΔL was 1.61 µm up to an annealing temperature of 290 °C. This study suggests a highly beneficial method for producing oxide TFTs, while suppressing the channel-shortening effect by tailoring the interface between source/drain and active layer using an appropriate Cu diffusion electrode.

Oxidation‐induced crack healing and erosion life assessment of Ni–Mo–Al–Cr7C3–Al2O3 composite coating

AbstractThe present investigation focuses on the effect of Cr2AlC MAX phase addition on erosion and oxidation‐induced crack healing behavior of Ni–Mo–Al alloy. For this, Ni–Mo–Al and 20 wt% Cr2AlC‐blended Ni–Mo–Al powders were coated by Air Plasma Spray (APS). For oxidation‐induced crack healing studies, the samples were heat treated at 500, 800, and 1100°C in the air for 5 hours. The heat‐treated samples were analyzed by X‐Ray Diffraction (XRD) analysis, Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS) for the phases, morphology, and composition. Erosion behavior studies were carried out at 30, 250, 500, 800, and 1000°C temperatures. The average hardness was obtained to be 400 ± 10 HV for Ni–Mo–Al coating and 580 ± 10 HV for 20 wt% Cr2AlC‐blended Ni–Mo–Al coating. The addition of Cr2AlC MAX into Ni–Mo–Al matrix reduces the overall erosion rate and improved the crack healing ability. This was attributed to the presence of in‐situ‐formed Cr7C3 and Al2O3 phases.

Alpha phase precipitation from phase-separated beta phase in a model Ti–Mo–Al alloy studied by direct coupling of transmission electron microscopy and atom probe tomography

Nucleation and growth of alpha precipitates during low-temperature annealing of Ti–10 at.% Mo–10 at.% Al alloy was investigated using direct coupling of transmission electron microscopy and atom probe tomography. The initial stages of annealing at 400 °C showed structurally well-defined alpha precipitates that were depleted in Mo as well as Al, and were confined within the Ti-rich beta phase separated pockets. The Al-enriched alpha phase was only observed after further annealing at 600 °C.

High-pressure synthesis of cubic BN using Fe–Mo–Al and Co–Mo–Al alloy solvents

The pressure and temperature regions of cubic BN formation were determined using Fe–Mo–Al and Co–Mo–Al ternary alloys as synthetic solvents of cubic BN. The alloy compositions employed in the present study were (in weight percent) Fe60.14–Mo36.86–Al3 and Co57.6–Mo38.4–Al4. The cubic BN was successfully synthesized at minimum pressure of about 4.4 GPa and temperature of about 1250 °C. Pressure and temperature of cubic BN synthesis were decreased drastically by small amount of Al addition into Fe–Mo or Co–Mo alloy solvents. The growth of cubic BN was started at the interface between the molten alloy and the source hexagonal BN. In the present study, we proposed that Fe–Mo and Co–Mo work as solvent of B and N atoms and Al acts as a nucleation agent of cubic BN.

Probing reaction pathways on model catalyst surfaces: Vinyl acetate synthesis and olefin metathesis

The reaction pathway for the palladium-catalyzed synthesis of vinyl acetate from acetic acid, ethylene and oxygen is investigated using reflection–absorption infrared spectroscopy by monitoring the rate of acetate titration by gas-phase ethylene. This reveals that acetate species are removed by reaction with gas-phase ethylene resulting in vinyl acetate formation. Reaction with C 2D 4 reveals a large (∼6) isotope effect indicating that hydrogen is involved in the rate-limiting step. This also results in the appearance of an infrared feature that is assigned to an acetoxyethyl-palladium intermediate. Acetate reaction rates are different for the isotopomers, CH 2CD 2 and CHDCHD. These observations are consistent with a reaction pathway first proposed by Samanos in which ethylene reacts with an acetate species to form an acetoxyethyl-palladium intermediate, which then reacts to form vinyl acetate by a β-hydride elimination reaction. The Hérisson–Chauvin pathway for olefin metathesis, which proposes that reaction occurs between a surface carbene and alkene to form a C 3 metallacycle, which decompose by the reverse of this pathway to form metathesis products, is tested on a MoAl alloy formed by reactions with Mo(CO) 6 with an alumina thin film grown on a refractory metal substrate. This is the accepted pathway in homogeneous phase, and is demonstrated to occur on the alloy surface by grafting intermediates using iodine-containing precursors.

The Surface Chemistry of Propylene, 1-Iodopropane, and 1,3-Diiodopropane on MoAl Alloy Thin Films Formed on Dehydroxylated Alumina

The adsorption of C3 hydrocarbons propylene, 1-iodopropane, and 1,3-diiodopropane is studied in ultrahigh vacuum on a molybdenum-aluminum alloy formed by molybdenum hexacarbonyl reaction with a planar alumina film grown on a Mo(100) substrate. Carbon-iodine bond scission occurs below approximately 200 K to deposit iodine, and form propyl species from 1-iodopropane and a C3 metallacycle from 1,3-diiodopropane. Propyl species either undergo beta-hydride elimination to yield propylene or hydrogenate to form propane. Propylene adsorbs as both pi- and di-sigma-bonded species, and the di-sigma form hydrogenates to yield propane, where the addition of the first hydrogen to form propyl species is slower than the second hydrogenation step to yield propane. Propylene also thermally decomposes on the surface to desorb hydrogen and deposit carbon where the methylyne group is the most, and the methyl group the least reactive. The metallacyclic intermediate reacts to give an allylic intermediate, which forms propylene, but also decomposes by C-C bond cleavage to evolve ethylene and deposit methylene species on the surface. This is a key step in the mechanism proposed for heterogeneously catalyzed olefin metathesis and this is the first time that this chemistry has been directly identified in ultrahigh vacuum.

Formation and Decomposition of C3 Metallacycles from Ethylene and Methylene on MoAl Alloy Thin Films

The reaction between adsorbed ethylene and methylene species has been investigated on a molybdenum-aluminum alloy grown from Mo(CO)(6) on a planar alumina film formed on a Mo(100) single crystal in ultrahigh vacuum. Di-sigma-bonded ethylene reacts with carbene species, formed on the surface from methylene iodide, to form a C(3) metallacycle. This predominantly decomposes to yield propylene, while a smaller portion yields cross-metathesis products since (12)C(13)CH(4) is formed from reaction between (13)C(2)H(4) and (12)CH(2). This work demonstrates for the first time that the reaction proceeds in heterogeneous phase via a C(3) metallacycle as proposed in the Hérisson-Chauvin mechanism.

The chemistry of ethylene on MoAl alloy thin films formed on dehydroxylated alumina: Hydrogenation, dehydrogenation and H–D exchange reactions

The chemistry of ethylene adsorbed on a thin MoAl layer grown in ultrahigh vacuum on a thin alumina film is studied using a combination of temperature-programmed desorption and X-ray, Auger and reflection absorption infrared spectroscopies. Both di-σ-bonded and a small proportion of π-bonded ethylene are found, where the di-σ-bonded ethylene has a σ/π parameter of ∼0.8 and a heat of adsorption of ∼70 kJ/mol. The ethylene self-hydrogenates to yield ethane and a small amount of methane is detected. The surface hydrogenation activation energy of di-σ-bonded ethylene is ∼65 kJ/mol, while the π-bonded species hydrogenates more easily. Adsorbed ethyl species grafted onto the surface by decomposing ethyl iodide predominantly undergo β-hydride elimination to yield ethylene. Ethyl species hydrogenate to ethane at a lower temperature than does di-σ-bonded ethylene implying that addition of hydrogen to adsorbed ethylene is slower than the rate of ethyl hydrogenation.

Ethylene hydrogenation on Mo(CO) 6 derived model catalysts in ultrahigh vacuum: From oxycarbide to carbide to MoAl alloy

The ethylene hydrogenation activity is compared for molybdenum oxycarbides, molybdenum carbides and a molybdenum alloy formed by reaction of molybdenum hexacarbonyl with alumina in ultrahigh vacuum using temperature-programmed desorption. It is found that molybdenum oxycarbides are inactive for ethylene hydrogenation. It is shown by forming carbides by reaction between alumina and ethylene that this is due to site blocking by oxygen. The carbide is found to be moderately active for hydrogenation and some ethylene decomposition and self-hydrogenation is also detected. The alloy is found to be the most reactive surface where substantial ethylene hydrogenation and also H–D are detected.

Interaction of molybdenum hexacarbonyl with hydroxylated alumina thin films at high temperatures: Formation and removal of surface carbides

The chemistry of Mo(CO) 6 is studied on a thin hydroxylated alumina (HA) film grown in ultrahigh vacuum on a Mo(1 0 0) substrate using temperature-programmed desorption, and X-ray and Auger spectroscopies. The uptake of molybdenum on HA at ∼700 K is about six times larger than on a dehydroxylated surface and this is ascribed to a combination of a higher surface area for the hydroxylated alumina film and the presence of surface hydroxyl groups. This reaction results in the formation of molybdenum carbides where the stoichiometry is close to MoC at low exposures, while it approaches Mo 2C as the exposure increases. The carbide incorporates a small amount of oxygen and measuring the Mo 3d 5/2 chemical shifts suggests that the carbides are present as small particles at low Mo(CO) 6 exposures. With increasing exposure, the surface carbide forms a thin film. Heating the surface evolves predominantly carbon monoxide due to alumina reduction to form metallic aluminum and, at high Mo(CO) 6 exposures, the molybdenum diffuses into the bulk while, at lower Mo(CO) 6 exposures, a surface MoAl alloy is formed.

The Chemistry of CH2I2 on MoAl Alloy Thin Films Formed on Dehydroxylated Alumina: Insight into Methylene Insertion Reactions

The chemistry of diiodomethane is explored in ultrahigh vacuum on a MoAl alloy film grown on planar, dehydroxylated alumina by reaction with molybdenum hexacarbonyl. The majority of the diiodomethane forms methylene species below approximately 250 K, although a small proportion forms CH(2)I((ads)), which hydrogenates to form iodomethane. The majority ( approximately 90%) of the adsorbed methylene species thermally decomposes to carbon and hydrogen. The remainder undergoes several reactions, including partial hydrogenation to form adsorbed methyl species or total hydrogenation to form methane. The methyl species can couple forming ethane or undergo methylene insertion reactions to form alkyl species up to C(4). These form alkenes via a beta-hydride elimination reaction. This chemistry is relatively unique, only having been found previously for Ni(110) surfaces. No such chemistry is found on Ni(100) and Ni(111).

The chemistry of iodomethane on MoAl alloy thin films formed on dehydroxylated alumina: Formation and reaction of surface methyl species

The surface chemistry of iodomethane is studied in ultrahigh vacuum using X-ray and Auger spectroscopies and temperature-programmed desorption, on a MoAl alloy film formed by reacting molybdenum hexacarbonyl with dehydroxylated alumina. The alloy is grown by reacting Mo(CO) 6 with a thin alumina film on a molybdenum substrate at 700 K and heating to 1500 K. A portion of the iodomethane dissociates following adsorption at ∼150 K. Heating to ∼220 K desorbs molecular iodomethane from the surface leaving adsorbed methyl species and iodine, where the iodine appears to adsorb preferentially on the aluminum. The resulting methyl species can either decompose to deposit carbon and evolve hydrogen, hydrogenate to yield methane or oligomerize yielding predominantly ethylene and propylene, and a small amount of ethane is formed. Both methyl and ethyl radicals are found to desorb from the surface suggesting that the ethylene is formed by methylene insertion into the methyl surface bond to form an ethyl intermediate, which forms ethylene by β-hydride elimination, or hydrogenates to yield ethane. Propylene is likely to form by further methylene insertion into the ethyl-surface bond.

Interaction of molybdenum hexacarbonyl with dehydroxylated alumina thin films at high temperatures: Formation and removal of surface carbides

The reaction of Mo(CO) 6 with thin films of dehydroxylated alumina grown on a Mo(1 0 0) substrate above 500 K is studied in ultrahigh vacuum using temperature-programmed desorption and Auger and X-ray photoelectron spectroscopies. This results in the formation of a molybdenum carbide that incorporates a small amount of oxygen, where MoC is formed initially, becoming closer to Mo 2C as the Mo(CO) 6 exposure increases. Heating the (oxy)carbide-covered surface desorbs CO in two states at ∼1130 and 1320 K. Forming the alumina films with H 2 18O shows that the majority of the oxygen in the CO derives from the substrate. The lower-temperature desorption state arises from both oxycarbide decomposition and alumina reduction by the carbide, while the high-temperature state results only from reduction of the alumina, finally resulting in the formation of a MoAl alloy.

Thermal stability of Mo–Al Schottky metallizations on n-GaAs

The contact stability and electrical characteristics of sputtered Mo–Al alloy metallizations (Mo74Al26, Mo27Al73, Mo12Al88) on n-GaAs have been investigated. The contacts were annealed by rapid thermal processing in the temperature range of 500–1000 °C for 20 s. X-ray diffraction, Auger depth profiling, scanning electron microscopy, and transmission electron microscopy (TEM) were used to study the structural characteristics. The Schottky diodes were assessed using the current–voltage measurements. The Mo74Al26/GaAs and Mo27Al73/GaAs contacts were stable up to 900 °C anneal, while interfacial reactions in 800 °C annealed Mo12Al88/GaAs contact were observed. Variations of the film surface morphologies and the degradation of the diodes after annealing can be well correlated to the interfacial stabilities. For all thermally stable Mo–Al/GaAs diodes, the Schottky barrier heights increased with annealing temperature. The AlxGa1−xAs at the interface, which contributes to the enhancement of the barrier height, has been clearly verified by the dark field cross-sectional TEM viewed along the 〈100〉 of GaAs.

Solid-state amorphization reaction by temperature-dependent ion mixing

A layer of amorphous Mo–Al alloy is formed by ion-assisted solid-state interdiffusion reaction of a Mo/Al bilayer. Xe ion irradiation at 200 °C enhances the long-range diffusion of the dominant moving species while the formation of equilibrium compounds remains inhibited. The idea of using the temperature-dependent ion mixing at intermediate temperatures to promote a solid-state amorphization reaction opens the possibility of growing an amorphous phase in a system where both compound formation and interdiffusion are difficult

On the valence state of molybdenum ions in silica-molybdenum catalysts photoreduced in carbon monoxide

The chemistry of Mo(CO)6 is studied on a thin hydroxylated alumina (HA) film grown in ultrahigh vacuum on a Mo(1 0 0) substrate using temperature-programmed desorption, and X-ray and Auger spectroscopies. The uptake of molybdenum on HA at ∼700 K is about six times larger than on a dehydroxylated surface and this is ascribed to a combination of a higher surface area for the hydroxylated alumina film and the presence of surface hydroxyl groups. This reaction results in the formation of molybdenum carbides where the stoichiometry is close to MoC at low exposures, while it approaches Mo2C as the exposure increases. The carbide incorporates a small amount of oxygen and measuring the Mo 3d5/2 chemical shifts suggests that the carbides are present as small particles at low Mo(CO)6 exposures. With increasing exposure, the surface carbide forms a thin film. Heating the surface evolves predominantly carbon monoxide due to alumina reduction to form metallic aluminum and, at high Mo(CO)6 exposures, the molybdenum diffuses into the bulk while, at lower Mo(CO)6 exposures, a surface MoAl alloy is formed.