Academia Sinica

About: Academia Sinica is a facility organization based out in Taipei, Taiwan. It is known for research contribution in the topics: Population & Galaxy. The organization has 52086 authors who have published 65998 publications receiving 1728114 citations. The organization is also known as: Central Research Academy.

Band Gap Engineering of Chemical Vapor Deposited Graphene by in Situ BN Doping

Abstract: Band gap opening and engineering is one of the high priority goals in the development of graphene electronics. Here, we report on the opening and scaling of band gap in BN doped graphene (BNG) films grown by low-pressure chemical vapor deposition method. High resolution transmission electron microscopy is employed to resolve the graphene and h-BN domain formation in great detail. X-ray photoelectron, micro-Raman, and UV–vis spectroscopy studies revealed a distinct structural and phase evolution in BNG films at low BN concentration. Synchrotron radiation based XAS-XES measurements concluded a gap opening in BNG films, which is also confirmed by field effect transistor measurements. For the first time, a significant band gap as high as 600 meV is observed for low BN concentrations and is attributed to the opening of the π–π* band gap of graphene due to isoelectronic BN doping. As-grown films exhibit structural evolution from homogeneously dispersed small BN clusters to large sized BN domains with embedded d...

Opening an Electrical Band Gap of Bilayer Graphene with Molecular Doping

Abstract: The opening of an electrical band gap in graphene is crucial for its application for logic circuits. Recent studies have shown that anenergy gap in Bernal-stacked bilayer graphene can begeneratedbyapplyinganelectricdisplacement field.Moleculardopinghasalsobeenproposedto open the electrical gap of bilayer graphene by breaking either in-plane symmetry or inversion symmetry; however, no direct observation of an electrical gap has been reported. Here we discover that the organic molecule triazine is able to form a uniform thin coating on the top surface of a bilayergraphene,whichefficientlyblockstheaccessibledopingsitesandpreventsambientp-doping onthetoplayer.Thechargedistributionasymmetrybetweenthetopandbottomlayerscanthenbe enhanced simply by increasing the p-doping from oxygen/moisture to the bottom layer. The on/off current ratio for a bottom-gated bilayer transistor operated in ambient condition is improved by at least 1 order of magnitude. The estimated electrical band gap is up to ∼111 meV at room temperature. The observed electrical band gap dependence on the hole-carrier density increase agrees well with the recent density-functional theory calculations. This research provides a simple method to obtain a graphene bilayer transistor with a moderate on/off current ratio, which can be stably operated in air without the need to use an additional top gate.

Voice conversion from non-parallel corpora using variational auto-encoder

Abstract: We propose a flexible framework for spectral conversion (SC) that facilitates training with unaligned corpora. Many SC frameworks require parallel corpora, phonetic alignments, or explicit frame-wise correspondence for learning conversion functions or for synthesizing a target spectrum with the aid of alignments. However, these requirements gravely limit the scope of practical applications of SC due to scarcity or even unavailability of parallel corpora. We propose an SC framework based on variational auto-encoder which enables us to exploit non-parallel corpora. The framework comprises an encoder that learns speaker-independent phonetic representations and a decoder that learns to reconstruct the designated speaker. It removes the requirement of parallel corpora or phonetic alignments to train a spectral conversion system. We report objective and subjective evaluations to validate our proposed method and compare it to SC methods that have access to aligned corpora.

Overview of the SDSS-IV MaNGA Survey: Mapping Nearby Galaxies at Apache Point Observatory

Abstract: We present an overview of a new integral field spectroscopic survey called MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV) that began on 2014 July 1. MaNGA will investigate the internal kinematic structure and composition of gas and stars in an unprecedented sample of 10,000 nearby galaxies. We summarize essential characteristics of the instrument and survey design in the context of MaNGA's key science goals and present prototype observations to demonstrate MaNGA's scientific potential. MaNGA employs dithered observations with 17 fiber-bundle integral field units that vary in diameter from 12" (19 fibers) to 32" (127 fibers). Two dual-channel spectrographs provide simultaneous wavelength coverage over 3600-10300 A at R~2000. With a typical integration time of 3 hr, MaNGA reaches a target r-band signal-to-noise ratio of 4-8 (per A, per 2" fiber) at 23 AB mag per sq. arcsec, which is typical for the outskirts of MaNGA galaxies. Targets are selected with stellar mass greater than 1e9 Msun using SDSS-I redshifts and i-band luminosity to achieve uniform radial coverage in terms of the effective radius, an approximately flat distribution in stellar mass, and a sample spanning a wide range of environments. Analysis of our prototype observations demonstrates MaNGA's ability to probe gas ionization, shed light on recent star formation and quenching, enable dynamical modeling, decompose constituent components, and map the composition of stellar populations. MaNGA's spatially resolved spectra will enable an unprecedented study of the astrophysics of nearby galaxies in the coming 6 yr.