Hybrid density functional study of oxygen vacancies in KTaO3 and NaTaO3

Using the Heyd-Scuseria-Ernzerhof hybrid functional, we systematically study the energetics and electronic properties of oxygen vacancies in KTaO3 and NaTaO3. The oxygen vacancies in these systems show similar behavior. The 2+ charge state is the most stable for most positions of the Fermi level inside the band gap. The neutral and + charge states become comparable in formation energy with the 2+ charge state when the Fermi level is close to the conduction band minimum. Therefore, the oxygen vacancies are double shallow donors, which can provide carrier electrons. Two types of off-symmetric configurations, in which the two nearest tantalum atoms of the oxygen vacancies are asymmetrically located, also possibly form as metastable configurations. These metastable configurations show a striking difference in electronic structure from each other; one configuration has a delocalized characteristic as in the case of the stable configuration, while the other induces a deep, localized state in the band gap. On the basis of the predicted formation energies and electronic properties, the previous experimental and theoretical findings relevant to the oxygen vacancies are discussed

PRiSM: Enhancing Low-Resource Document-Level Relation Extraction with Relation-Aware Score Calibration

Document-level relation extraction (DocRE) aims to extract relations of all entity pairs in a document. A key challenge in DocRE is the cost of annotating such data which requires intensive human effort. Thus, we investigate the case of DocRE in a low-resource setting, and we find that existing models trained on low data overestimate the NA ("no relation") label, causing limited performance. In this work, we approach the problem from a calibration perspective and propose PRiSM, which learns to adapt logits based on relation semantic information. We evaluate our method on three DocRE datasets and demonstrate that integrating existing models with PRiSM improves performance by as much as 26.38 F1 score, while the calibration error drops as much as 36 times when trained with about 3% of data. The code is publicly available at https://github.com/brightjade/PRiSM.Comment: Accepted to Findings of IJCNLP-AACL 202

Synthesis of mono-to-multi-layer graphene for transparent electrode applications

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 82-83).In this thesis, mono-to-multilayer graphene for transparent electrode applications was synthesized by Atmospheric Pressure Chemical Vapor Deposition (APCVD) and the key factors that determine the electrical and optical properties of the graphene were isolated. This work involves optimizing APCVD conditions to grow the best quality graphene for transparent electrode applications as well as explaining the underlying mechanisms behind APCVD. The effects of methane and hydrogen in the growth step were studied along with the impact of the annealing step. Growth without hydrogen was also investigated. Sheet resistance, transmittance, and mobility data with carrier concentration information were obtained and analyzed for each growth condition. This work explored a large set of APCVD conditions with focus towards the electrical and optical properties; therefore it will be greatly beneficial for researchers who seek to the high quality graphene for the transparent electrodes and other electronic applications.by Minseok Choi.S.M