We report our investigation of the atomic layer deposition (ALD) of HfO2 on the MoS2 surface. In contrast to previous reports of conformal growth on MoS2 flakes, we find that ALD on MoS2 bulk material is not uniform. No covalent bonding between the HfO2 and MoS2 is detected. We highlight that individual precursors do not permanently adsorb on the clean MoS2 surface but that organic and solvent residues can dramatically change ALD nucleation behavior. We then posit that prior reports of conformal ALD deposition on MoS2 flakes that had been exposed to such organics and solvents likely rely on contamination-mediated nucleation. These results highlight that surface functionalization will be required before controllable and low defect density high-κ/MoS2 interfaces will be realized. The band structure of the HfO2/MoS2 system is experimentally derived with valence and conduction band offsets found to be 2.67 and 2.09 eV, respectively.
The effect of room temperature ultraviolet-ozone (UV-O 3) exposure of MoS 2 on the uniformity of subsequent atomic layer deposition of Al 2 O 3 is investigated. It is found that a UV-O 3 pre-treatment removes adsorbed carbon contamination from the MoS 2 surface and also functionalizes the MoS 2 surface through the formation of a weak sulfur-oxygen bond without any evidence of molybdenum-sulfur bond disruption. This is supported by first principles density functional theory calculations which show that oxygen bonded to a surface sulfur atom while the sulfur is simultaneously back-bonded to three molybdenum atoms is a thermodynamically favorable configuration. The adsorbed oxygen increases the reactivity of MoS 2 surface and provides nucleation sites for atomic layer deposition of Al 2 O 3. The enhanced nucleation is found to be dependent on the thin film deposition temperature. V
The contact resistance of metal-graphene junctions has been actively explored and exhibited inconsistencies in reported values. The interpretation of these electrical data has been based exclusively on a side-contact model, that is, metal slabs sitting on a pristine graphene sheet. Using in situ X-ray photoelectron spectroscopy to study the wetting of metals on as-synthesized graphene on copper foil, we show that side-contact is sometimes a misleading picture. For instance, metals like Pd and Ti readily react with graphitic carbons, resulting in Pd- and Ti-carbides. Carbide formation is associated with C-C bond breaking in graphene, leading to an end-contact geometry between the metals and the periphery of the remaining graphene patches. This work validates the spontaneous formation of the metal-graphene end-contact during the metal deposition process as a result of the metal-graphene reaction instead of a simple carbon diffusion process.
Effects of interface oxidation on the transport behavior of the two-dimensional-electron-gas in AlGaN/GaN heterostructures by plasma-enhanced-atomic-layer-deposited AlN passivation
The interfacial reactions between atomic layer deposited Al 2 O 3 films on various chemically treated InP(100) surfaces have been investigated by in situ X-ray photoelectron spectroscopy at each half cycle in the deposition process. With the first cycle of trimethyl aluminum, a significant decrease in the amount of indium oxides present on the surface is seen, consistent with the ''clean up'' effect reported for other III-V semiconductor surfaces. However, a concurrent increase in the amount of phosphorous oxide is seen, suggesting oxygen transfer from indium oxides to phosphorous during indium oxide decomposition. #
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