semiconductors, including Si and Ge, the mobility drastically degrades when the channel thickness of the conductor is below 5 nm due to thickness-fluctuationinduced scattering. [2] On the other hand, 2D materials maintain high mobility even under the monolayer limit (0.3-0.6 nm) [3][4][5] and exhibit inherently high on-current, as evidenced by the stronger quantummechanical effect that is observed. [6] In particular, transition metal dichalcogenides (TMDCs) are attractive materials for semiconductor channels of nanoscale FETs because of their high stability against oxidation [7] as well as their superior electrical properties, such as a large bandgap and relatively high carrier mobility. [3][4][5] Here, the large challenge with 2D-FET always involves the formation of highquality ultrathin high-κ oxide insulators. The atomic layer deposition (ALD) of dielectrics on TMDCs has a disadvantage in that high capacitive top gate stacks are formed on TMDCs because the nucleation of the oxide predominantly occurs at defect sites or through the physical adsorption of precursors onto the surface due to the absence of dangling bonds, [8] as shown in Figure 1a. Therefore, thick dielectrics are required to cover the whole surface without pinholes. [9] To form thin oxides with high dielectric constants by the ALD method, it is necessary to intentionally form nucleation sites on TMDCs. In fact, various surface modification methods, including surface treatment [10,11] and the formation of a buffer layer, [12][13][14][15][16][17][18] have been reported for oxide formation on TMDCs with high uniformity and dielectric properties. A surface treatment, including O 2 plasma [10] and ultraviolet ozone, [11] has improved the coverage and uniformity of ALD oxide on TMDCs; however, this treatment induces additional defects that produce extra scattering sites or dopants on TMDCs.The deposition of a buffer layer, including thin metal layers [12][13][14][15] and organic molecules, [16][17][18] is an effective method to provide nucleation sites without forming defects. To date, the thinnest equivalent oxide thickness (EOT) of 1 nm on monolayer TMDCs has been successfully reported by combining an organic monolayer of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) and ALD-HfO 2 for the top gate stack. [18] However, due to the quite low dielectric constant of PTCDA

For the complementary operation of two-dimensional (2D) material-based field-effect transistors (FETs), high-performance p-type FETs are essential. In this study, we applied surface charge-transfer doping from WO x , which has a large work function of ∼6.5 eV, selectively to the access region of WS2 and WSe2 by covering the channel region with h-BN. By reducing the Schottky barrier width at the contact and injecting holes into the valence band, the p-type conversion of intrinsically n-type trilayer WSe2 FET was successfully achieved. However, trilayer WS2 did not show clear p-type conversion because its valence band maximum is 0.66 eV lower than that of trilayer WSe2. Although inorganic WO x boasts high air stability and fabrication process compatibility due to its high thermal budget, the trap sites in WO x cause large hysteresis during back gate operation of WSe2 FETs. However, by using top gate (TG) operation with an h-BN protection layer as a TG insulator, a high-performance p-type WSe2 FET with negligible hysteresis was achieved.

Operando analysis of electron devices provides key information regarding their performance enhancement, reliability, thermal management, etc. For versatile operando analysis of devices, the nitrogen-vacancy (NV) centers in diamonds are potentially useful media owing to their excellent sensitivity to multiple physical parameters. However, in single crystal diamond substrates often used for sensing applications, placing NV centers in contiguity with the active channel is difficult. This study proposes an operando analysis method using a nanodiamond thin film that can be directly formed onto various electron devices by a simple solution-based process. The results of noise analysis of luminescence of the NV centers in nanodiamonds show that the signal-to-noise ratio in optically detected magnetic resonance can be drastically improved by excluding the large 1/ f noise of nanodiamonds. Consequently, the magnetic field and increase in temperature caused by the device current could be simultaneously measured in a lithographically fabricated metal microwire as a test device. Moreover, the spatial mapping measurement is demonstrated and shows a similar profile with the numerical calculation.