Atomic-scale defects in two-dimensional transition metal dichalcogenides (TMDs) often dominate their physical and chemical properties. Introducing defects in a controllable manner can tailor properties of TMDs. For example, chalcogen atom defects in TMDs were reported to trigger phase transition, induce ferromagnetism, and drive superconductivity. However, reported strategies to induce chalcogen atom defects including postgrowth annealing, laser irradiation, or plasma usually require high temperature (such as 500 °C) or cause unwanted structural damage. Here, we demonstrate low-temperature (60 °C) partial surface oxidation in 2D PdSe2 with low disorder and good stability. The combination of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations provide evidence of atomic-scale partial oxidation with both atomic resolution and chemical sensitivity. We also experimentally demonstrate that this controllable oxygen incorporation effectively tailors the electronic, optoelectronic, and catalytic activity of PdSe2. This work provides a pathway toward fine-tuning the physical and chemical properties of 2D TMDs and their applications in nanoelectronics, optoelectronics, and electrocatalysis.

It is widely reported that a significant amount of germanium is incorporated in HfO 2 gate dielectric during the formation of highgate stack on germanium substrate. In this paper, the dependences of germanium incorporation in HfO 2 on dielectric deposition method, annealing temperature, and annealing ambient were extensively studied by physical methods such as time-of-flight secondary ion mass spectroscopy. The results indicate that the high thermal budget of processes, including deposition and annealing, is the most critical factor to the Ge incorporation. The Ge incorporation in HfO 2 is identified by two mechanisms: Ge atoms out-diffusion from substrate and gaseous GeO diffusion downward into HfO 2 via airborne transportation in the chamber.Germanium is a promising channel material for metal-oxide semiconductor field effect transistor ͑MOSFET͒ applications. It has much higher mobility over silicon ͑two times higher for electrons and four times higher for holes͒. However, germanium oxide has a poor electrical quality and is water soluble. It is not possible to form a high-quality gate dielectric on germanium substrate by conventional oxidation techniques. With the recent successful development of high-material deposition, germanium MOSFETs with highgate dielectrics have attracted much research interest. High-mobility long-channel bulk germanium, germanium-on-insulator, and strained germanium MOSFETs with various high-gate dielectrics have been reported. 1-4 Deep submicrometer: ͑0.15 m͒ Ge MOSFETs with HfO 2 were also demonstrated in a 200-mm Si prototyping line, 5 illustrating that Ge MOSFET fabrication is compatible with mainstream Si processing technology. Compared to many reports on HfO 2 deposition on silicon, there is little knowledge of HfO 2 deposition on germanium substrates. Recently, it was reported that a large amount of germanium was found inside HfO 2 film deposited by metallorganic chemical vapor deposition ͑MOCVD͒ on germanium substrate. 6 Similar germanium incorporation was also observed in physical vapor deposition ͑PVD͒ HfO 2 on Ge substrate after high-temperature annealing. 7 However, there is no detailed investigation on the dependence of germanium incorporation in HfO 2 on process conditions. In this paper, the germanium incorporation in HfO 2 is extensively evaluated on bulk germanium wafers with varied deposition techniques and postdeposition annealing conditions. ExperimentalHfO 2 films were deposited on germanium ͑100͒ substrates by either MOCVD or PVD. Before deposition, the wafers were cleaned by diluted HF. MOCVD deposition used Hf t-butoxide precursor and O 2 at 400°C in the MOCVD chamber of a Jusung gate cluster. To evaluate the dependence of Ge incorporation on the deposition method, reactive sputtering using a pure Hf target in O 2 ambient at room temperature was used to prepare HfO 2 films. To study the Ge incorporation in HfO 2 upon subsequent thermal processes, postdeposition annealing ͑PDA͒ was performed in a rapid thermal processing ͑RTP͒ machine in N 2 or O 2 ambient at tem...

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