The photoluminescence (PL) origin of bright blue emission arising from intrinsic states in graphene quantum dots (GQDs) is investigated. The bright PL of intercalatively acquired GQDs is attributed to favorably formed subdomains composed of four to seven carbon hexagons. Random and harsh oxidation which hinders the energetically favorable formation of subdomains causes weak and redshifted PL.

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Nickel oxide (NiO) thin films were grown on soda-lime glass substrates by RF magnetron sputtering method at room temperature (RT), and they were post-annealed at the temperatures of 100 o C, 200 o C, 300 o C and 400 o C for 30 minutes in vacuum. The electronic structure, optical and electrical properties of NiO thin films were investigated using X-ray photoelectron spectroscopy (XPS), reflection electron energy spectroscopy (REELS), UV-spectrometer and Hall Effect measurements, respectively. XPS results showed that the NiO thin films grown at RT and post annealed at temperatures below 300 o C had the NiO phase, but, at 400 o C, the nickel metal phase became dominant. The band gaps of NiO thin films post annealed at temperatures below 300 o C were about 3.7 eV, but that at 400 o C should not be measured clearly because of the dominance of Ni metal phase. The NiO thin films post-annealed at temperatures below 300 o C showed p-type conductivity with low electrical resistivity and high optical transmittance of 80% in the visible light region, but that post-annealed at 400 o C showed n-type semiconductor properties, and the average transmittance in the visible light region was less than 42%. Our results demonstrate that the post-annealing plays a crucial role in enhancing the electrical and optical properties of NiO thin films.

The electronic structure of a Ta 2 O 5 thin film on SiO 2 /Si (100) after Ar Gas Cluster Ion Beam (GCIB) sputtering was investigated using X-ray photoemission spectroscopy and compared with those obtained via mono-atomic Ar ion beam sputtering. The Ar ion sputtering had a great deal of influence on the electronic structure of the oxide thin film. Ar GCIB sputtering without sample rotation also affected the electronic structure of the oxide thin film. However, Ar GCIB sputtering during sample rotation did not exhibit any significant transition of the electronic structure of the Ta 2 O 5 thin films. Ar GCIB can be useful for potential applications of oxide materials with sample rotation. 1．IntroductionIon beam sputtering has been widely used in secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) for depth profiling or surface cleaning. One of the drawbacks of ion beam sputtering is an induced matrix effect such as surface segregation, surface composition change and surface damage, which causes difficulties in characterization of organic/inorganic interfaces and oxide materials [1,2]. Therefore, the surface matrix effects caused by ion beam sputtering should be minimized to use facile surface analysis. C 60 ion sputtering has been used for low damage surface cleaning and depth profiling of many organic materials, but the depth profiling of organic has not been successful because of a composition change due to preferential sputtering as well as degradation of chemical states of C 1s, N 1s, and O1s [3]. Recently, Ar GCIB has attracted a lot of attention as a promising method for depth profiling of organic thin films due to extremely low degradation of surface during depth profiling [4,5]. The effects of an Ar GCIB sputtering process on the structural and chemical properties of an organic material as well as the energy level alignment at the interface between the organic semiconductor and the electrode were studied. The molecular structure and the orientation of pentacene stayed the same after the Ar GCIB process. Furthermore, there was no change in the chemical bonding states in the organic materials including pentacene and poly (3, 4-ethylene dioxy thiophene) polymerized with poly (4-styrene sulfonate) (PEDOT: PSS). The Ar GCIB sputtering process did not cause any variation in the primary valence band structure including the chemical state and the configuration of pentacene/PEDOT:PSS and pentacene/Au. The Ar GCIB sputtering is a damage-free process for organic thin films [6,7]. In our previous work, we applied GCIB sputtering to measure the damage profile on Si (100) surfaces [8]. The damage thickness was about 10 nm, 6.4 nm and 4.2 nm for 20, 10, and 5 keV Ar GCIB sputtering, respectively. We also applied Ar GCIB sputtering to SiO 2 thin films [9]. The Ar GCIB sputtering at surface normal incidence had a deal of influence on the surface potential and the chemical structure of a SiO 2 thin film. However, the Ar GCIB sputtering at the grazing incidence...