1,720,966 research outputs found
Atomic Healing of Chalcogen Vacancies in Monolayer WSe2
No full textTwo-dimensional (2D) transition-metal dichalcogenide (TMDC) semiconductors are the atomically thin platforms for a new type of photonics. Therein, atomic-scale deformations such as point defects and grain boundaries, often generate novel 2D physical properties. For example, single point defects in WSe2 and WS2 monolayers (MLs) serve as sources for single-photon emissions or electronic dopants, and mirror twin boundaries in MoSe2 MLs provide topologically protected edge-states. In order to exploit these local physical properties into practical device platforms, such atomic-scale deformations must be deterministically controlled in the 2D host lattices of TMDC MLs. Here, we report a simple process for the healing of chalcogen point vacancies on the synthetic ML WSe2 by metal-organic selenium passivation. We verified such atomic healing process from substantial reduction of the localized exciton states by low temperature photoluminescence. Our work suggests steps to realize the higher quality photonics with atomic precision.1
Sub Band-Gap Photoresponse by Hot Electron Injections in AU-Nanorod Decorated Van Der Waals Semiconductor Monolayers
No full textHot electrons in metal nanostructures can be exploited in a wide range of optical functions, including photocatalysis, surface-enhanced Raman scattering, photodetectors and photovoltaics. Here, we report the sub band-gap (Eg) photoresponse in Au-nanorod decorated van der Waals (vdW) semiconductor, MoS2 and WSe2, monolayers (MLs). It was found that hot electrons, optically excited in Au nanorod (NR) arrays at the sub band-gap (Eg) radiations, can be injected to vdW ML semiconductors over Schottky barriers, producing substantial photocurrents in n-type MoS2 and p-type WSe2 ML photodetectors, as well as photovoltages in n-MoS2/p-WSe2 ML stack junctions. Moreover, by spectrally and light-polarization resolved measurements, we showed that these sub band-gap (Eg) excitations of hot electrons can be modulated by tuning the plasmon resonance at the shape controlled Au NRs.1
Atomistic Probing of Defect-Engineered 2H-MoTe2 Monolayers
No full textPoint defects dictate various physical, chemical, and optoelectronic properties of two-dimensional (2D) materials, and therefore, a rudimentary understanding of the formation and spatial distribution of point defects is a key to advancement in 2D material-based nanotechnology. In this work, we performed the demonstration to directly probe the point defects in 2H-MoTe2 monolayers that are tactically exposed to (i) 200 degrees C-vacuum-annealing and (ii) 532 nm-laser-illumination; and accordingly, we utilize a deep learning algorithm to classify and quantify the generated point defects. We discovered that tellurium-related defects are mainly generated in both 2H-MoTe2 samples; but interestingly, 200 degrees C-vacuum-annealing and 532 nm-laser-illumination modulate a strong n-type and strong p-type 2H-MoTe2, respectively. While 200 degrees C-vacuum-annealing generates tellurium vacancies or tellurium adatoms, 532 nm-laser-illumination prompts oxygen atoms to be adsorbed/chemisorbed at tellurium vacancies, giving rise to the p-type characteristic. This work significantly advances the current understanding of point defect engineering in 2H-MoTe2 monolayers and other 2D materials, which is critical for developing nanoscale devices with desired functionality.11Nsciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Identification of Point Defects in Atomically Thin Transition-Metal Dichalcogenide Semiconductors as Active Dopants
No full textSelective doping in semiconductors is essential not only for monolithic integrated circuity fabrications but also for tailoring their properties including electronic, optical, and catalytic activities. Such active dopants are essentially point defects in the host lattice. In atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDCs), the roles of such point defects are particularly critical in addition to their large surface-to-volume ratio, because their bond dissociation energy is relatively weaker, compared to elemental semiconductors. In this Mini Review, we review recent advances in the identifications of diverse point defects in 2D TMDC semiconductors, as active dopants, toward the tunable doping processes, along with the doping methods and mechanisms in literature. In particular, we discuss key issues in identifying such dopants both at the atomic scales and the device scales with selective examples. Fundamental understanding of these point defects can hold promise for tunability doping of atomically thin 2D semiconductor platforms.11Nsciescopu
Full automation of point defect detection in transition metal dichalcogenides through a dual mode deep learning algorithm
No full textPoint defects often appear in two-dimensional (2D) materials and are mostly correlated with physical phenomena. The direct visualisation of point defects, followed by statistical inspection, is the most promising way to harness structure-modulated 2D materials. Here, we introduce a deep learning-based platform to identify the point defects in 2H-MoTe2: synergy of unit cell detection and defect classification. These processes demonstrate that segmenting the detected hexagonal cell into two unit cells elaborately cropped the unit cells: further separating a unit cell input into the Te2/Mo column part remarkably increased the defect classification accuracies. The concentrations of identified point defects were 7.16 x 1020 cm2 of Te monovacancies, 4.38 x 1019 cm2 of Te divacancies and 1.46 x 1019 cm2 of Mo monovacancies generated during an exfoliation process for TEM sample-preparation. These revealed defects correspond to the n-type character mainly originating from Te monovacancies, statistically. Our deep learning-oriented platform combined with atomic structural imaging provides the most intuitive and precise way to analyse point defects and, consequently, insight into the defect-property correlation based on deep learning in 2D materials. We advocate for the development of expertise in visualizing and identifying point defects in two-dimensional (2D) materials, a skillset intimately linked to a wide array of physical phenomena.11Nsciescopu
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
