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.

Energy band profile of ultrathin Hf silicate dielectrics, grown by atomic layer deposition, was studied by using x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap energy only slightly increases from 5.52eV for (HfO2)0.75(SiO2)0.25 to 6.10eV for (HfO2)0.25(SiO2)0.75, which is much smaller than 8.90eV for SiO2. For ultrathin Hf silicate dielectrics, the band gap is mainly determined by the Hf 5d conduction band state and the O 2p valence band state. The corresponding conduction band offsets are in the vicinity of 1eV, which satisfies the minimum requirement for the carrier barrier heights.

No abstract

The electronic and optical properties of Al 2 O 3 /SiO 2 dielectric thin films grown on Si(1 0 0) by the atomic layer deposition method were studied by means of x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy (REELS). The band gaps of the Al 2 O 3 /SiO 2 thin films before annealing and after annealing were 6.5 eV and 7.5 eV, respectively, and those of the γ-Al 2 O 3 and α-Al 2 O 3 phases were 7.1 eV and 8.4 eV, respectively. All of these were estimated from the onset values of the REELS spectra. The dielectric functions were determined by comparing the effective cross-section determined from experimental REELS with a rigorous model calculation based on dielectric response theory, using available software packages. The determined energy loss function obtained from the Al 2 O 3 /SiO 2 thin films before annealing showed a broad peak at 22.7 eV, which moved to the γ-Al 2 O 3 position at 24.3 eV after annealing. The optical properties were determined from the dielectric function. The optical properties of the Al 2 O 3 /SiO 2 thin films after annealing were in good agreement with those of γ-Al 2 O 3. The changes in band gap, electronic and optical properties of the Al 2 O 3 /SiO 2 thin films after annealing indicated a phase transition from an amorphous phase to the γ-Al 2 O 3 phase after annealing.

No abstract