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
Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit high-quality, ultrathin dielectric insulators on graphene to modulate the channel potential. Here, we study a novel and facile approach based on atomic layer deposition through ozone functionalization to deposit high-κ dielectrics (such as Al(2)O(3)) without breaking vacuum. The underlying mechanisms of functionalization have been studied theoretically using ab initio calculations and experimentally using in situ monitoring of transport properties. It is found that ozone molecules are physisorbed on the surface of graphene, which act as nucleation sites for dielectric deposition. The physisorbed ozone molecules eventually react with the metal precursor, trimethylaluminum to form Al(2)O(3). Additionally, we successfully demonstrate the performance of dual-gated GFETs with Al(2)O(3) of sub-5 nm physical thickness as a gate dielectric. Back-gated GFETs with mobilities of ~19,000 cm(2)/(V·s) are also achieved after Al(2)O(3) deposition. These results indicate that ozone functionalization is a promising pathway to achieve scaled gate dielectrics on graphene without leaving a residual nucleation layer.
We present characteristics of dual-gated graphene devices with an Al2O3 gate dielectric formed by an O3-based atomic-layer-deposition process. Raman spectra reveal that a O3 process at 25°C on single-layered graphene introduces the least amount defects, while a substantial number of defects appear at 200 °C. This graphene device with O3-based Al2O3 dielectric demonstrates a heterojunction within the graphene sheet when applying VTG and VBG and possesses good dielectric properties with minimal chemical doping, including a high dielectric constant ∼8, low hysteresis width ∼0.2 V, and low leakage current and a carrier mobility of 5000 cm2/V s 25°C in ambient.
During chemical-vapor-deposited graphene transfer onto target substrates, a polymer film coating is necessary to provide a mechanical support. However, the remaining polymer residues after organic solvent rinsing cannot be effectively removed by the empirical thermal annealing in vacuum or forming gas. Little progress has been achieved in the past years, for little is known about the chemical evolution of the polymer macromolecules and their interaction with the environment. Through in situ Raman and infrared spectroscopy studies of PMMA transferred graphene annealed in nitrogen, two main processes are uncovered involving the polymer dehydrogenation below 200 °C and a subsequent depolymerization above 200 °C. Polymeric carbons over the monolayer graphitic carbon are found to constitute a fundamental bottleneck for a thorough etching of PMMA residues. The dehydrogenated polymeric chains consist of active CC bonding sites that are readily attacked by oxidative gases. The combination of Raman spectroscopy, X-ray photoemission spectroscopy, and transmission electron microscopy reveals the largely improved carbon removal by annealing in oxidative atmospheres. CO2 outperforms other oxidative gases (e.g., NO2, O2) because of its moderate oxidative strength to remove polymeric carbons efficiently at 500 °C in a few minutes while preserving the underlying graphene lattice. The strategy and mechanism described here open the way for a significantly improved oxidative cleaning of transferred graphene sheets, which may require optimization tailored to specific applications.
Patterned fabrication depends on selective deposition that can be best achieved with atomic layer deposition (ALD). For the growth of TiO2 by ALD using TiCl4 and H2O, X-ray photoelectron spectroscopy reveals a marked difference in growth on oxidized and hydrogen-terminated silicon surfaces, characterized by typical and predictable deposition rates observed on SiO2 surfaces that can be 185 times greater than the deposition rates on hydrogen-terminated Si(100) and Si(111) surfaces. Large-scale patterning is demonstrated using wet chemistry, and nanometer-scale patterned TiO2 growth is achieved through scanning tunneling microscopy (STM) tip-based lithography and ALD. The initial adsorption mechanisms of TiCl4 on clean, hydrogen-terminated, and OH-terminated Si(100)-(2 × 1) surfaces are investigated in detail through density functional theory calculations. Varying the reactive groups on the substrate is found to strongly affect the probability of precursor nucleation on the surface during the ALD process. Theoretical studies provide quantitative understanding of the experimental differences obtained for the SiO2, hydrogen-terminated, and clean Si(100) and Si(111) surfaces.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.