1,218 research outputs found
Metal-organic chemical vapor deposition of 2D van der Waals materials-The challenges and the extensive future opportunities
The last decade has witnessed significant progress in two-dimensional van der Waals (2D vdW) materials research; however, a number of challenges remain for their practical applications. The most significant challenge for 2D vdW materials is the control of the early stages of nucleation and growth of the material on preferred surfaces to eventually create large grains with digital thickness controllability, which will enable their incorporation into high-performance electronic and optoelectronic devices. This Perspective discusses the technical challenges to be overcome in the metal-organic chemical vapor deposition (MOCVD) growth of 2D group 6 transition metal dichalcogenide (TMD) atomic crystals and their heterostructures, as well as future research aspects in vdW epitaxy for 2D TMDs via MOCVD. In addition, we encourage the traditional MOCVD community to apply their expertise in the field of "2D vdW materials," which will continue to grow at an exponential rate
Two-dimensional heterogeneous photonic bandedge laser
We proposed and realized a two-dimensional (2D) photonic bandedge laser
surrounded by the photonic bandgap. The heterogeneous photonic crystal
structure consists of two triangular lattices of the same lattice constant with
different air hole radii. The photonic crystal laser was realized by
room-temperature optical pumping of air-bridge slabs of InGaAsP quantum wells
emitting at 1.55 micrometer. The lasing mode was identified from its spectral
positions and polarization directions. A low threshold incident pump power of
0.24mW was achieved. The measured characteristics of the photonic crystal
lasers closely agree with the results of real space and Fourier space
calculations based on the finite-difference time-domain method.Comment: 14 pages, 4 figure
Single-Port Transumbilical Laparoscopic-Assisted Adnexal Surgery
Single-port transumbilical laparoscopic-assisted surgery for large, benign adnexal tumors was found to be a feasible alternative to conventional laparoscopic or open surgical methods
Violet-light spontaneous and stimulated emission from ultrathin In-rich InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition
We investigated the spontaneous and stimulated emission properties of violet-light-emitting ultrathin In-rich InGaN/GaN multiple quantum wells (MQWs) with indium content of 60%-70%. The Stokes shift was smaller than that of In-poor InGaN MQWs, and the emission peak position at 3.196 eV was kept constant with increasing pumping power, indicating negligible quantum confined Stark effect in ultrathin In-rich InGaN MQWs despite of high indium content. Optically pumped stimulated emission performed at room temperature was observed at 3.21 eV, the high-energy side of spontaneous emission, when the pumping power density exceeds ???31 kW/ cm2.open6
Redirected Walking in Infinite Virtual Indoor Environment Using Change-blindness
We present a change-blindness based redirected walking algorithm that allows
a user to explore on foot a virtual indoor environment consisting of an
infinite number of rooms while at the same time ensuring collision-free walking
for the user in real space. This method uses change blindness to scale and
translate the room without the user's awareness by moving the wall while the
user is not looking. Consequently, the virtual room containing the current user
always exists in the valid real space. We measured the detection threshold for
whether the user recognizes the movement of the wall outside the field of view.
Then, we used the measured detection threshold to determine the amount of
changing the dimension of the room by moving that wall. We conducted a
live-user experiment to navigate the same virtual environment using the
proposed method and other existing methods. As a result, users reported higher
usability, presence, and immersion when using the proposed method while showing
reduced motion sickness compared to other methods. Hence, our approach can be
used to implement applications to allow users to explore an infinitely large
virtual indoor environment such as virtual museum and virtual model house while
simultaneously walking in a small real space, giving users a more realistic
experience.Comment: https://www.youtube.com/watch?v=s-ZKavhXxd
Recent advances in metallic transition metal dichalcogenides as electrocatalysts for hydrogen evolution reaction
Layered metallic transition metal dichalcogenides (MTMDs) exhibit distinctive electrical and catalytic properties to drive basal plane activity, and, therefore, they have emerged as promising alternative electrocatalysts for sustainable hydrogen evolution reactions (HERs). A key challenge for realizing-MTMDs-based electrocatalysts is the controllable and scalable synthesis of high-quality MTMDs and the development of engineering strategies that allow tuning their electronic structures. However, the lack of a method for the direct synthesis of MTMDs retaining the structural stability limits optimizing the structural design for the next generation of robust electrocatalysts. In this review, we highlight recent advances in the synthesis of MTMDs comprising groups VB and VIB and various routes for structural engineering to enhance the HER catalytic performance. Furthermore, we provide insight into the potential future directions and the development of MTMDs with high durability as electrocatalysts to generate green hydrogen through water-splitting technology
Effect of growth interruption on optical properties of In-rich InGaN/GaN single quantum well structures
In-rich InGaN/GaN single quantum well (SQW) structures with and without growth interruption (GI) were successfully grown on sapphire substrates by metal-organic chemical vapor deposition. The optical properties were systematically investigated by photoluminescence (PL), selectively excited PL, PL excitation (PLE), and cathodoluminescence (CL) techniques. The integrated PL intensity of the main In-rich InGaN emissions for the sample grown without GI decreased only by a factor of 15.5 when the temperature increased from 11 to 300 K, while that of the sample with GI decreased by about 1040, showing very good quantum efficiency for the sample without GI. The In-rich InGaN SQW emissions have been verified by selectively excited PL spectra and by the different PLE absorption edges. CL observations showed that the epilayer of the sample without GI agglomerated together to form clusters due to the large lattice and thermal mismatches with GaN, which confine the carriers in the clusters and ensure the relatively high quantum efficiency of the sample. The sample with GI showed relatively smooth surface with cluster structures jointed together, which gives two-dimensional QW environment in its energy band structure, and its optical emission is more sensitive to temperatures than that of the sample grown without GI.open7
Computer-Aided Designing and Manufacturing of Lingual Fixed Orthodontic Appliance Using 2D/3D Registration Software and Rapid Prototyping
The availability of 3D dental model scanning technology, combined with the ability to register CBCT data with digital models, has enabled the fabrication of orthognathic surgical CAD/CAM designed splints, customized brackets, and indirect bonding systems. In this study, custom lingual orthodontic appliances were virtually designed by merging 3D model images with lateral and posterior-anterior cephalograms. By exporting design information to 3D CAD software, we have produced a stereolithographic prototype and converted it into a cobalt-chrome alloy appliance as a way of combining traditional prosthetic investment and cast techniques. While the bonding procedure of the appliance could be reinforced, CAD technology simplified the fabrication process by eliminating the soldering phase. This report describes CAD/CAM fabrication of the complex anteroposterior lingual bonded retraction appliance for intrusive retraction of the maxillary anterior dentition. Furthermore, the CAD/CAM method eliminates the extra step of determining the lever arm on the lateral cephalograms and subsequent design modifications on the study model
Evaluation of genetic diversity and linkage disequilibrium in Korean-bred rice varieties using SSR markers
Background: In order to evaluate the variation among different rice
types, the genetic diversity in a rice collection composed by 59
breeding lines, 23 landraces, 18 weedy rice lines, and 35 introduced
lines that collected from countries worldwide was analyzed using 134
simple sequence repeat markers. Results: In total, 1264 alleles were
identified (average, 9.43 per locus). Rare alleles made up a large
portion (58.4%) of the detected alleles, and 29 unique alleles
associated with rice accessions were also discovered. A model-based
structural analysis revealed the presence of three subpopulations. The
genetic relationships revealed by the neighbour-joining tree method
were fairly consistent with the structure-based membership assignments
for most of the accessions. A total of 105 accessions (79.5%) showed a
clear relationship to each cluster, while the remaining 27 accessions
(20.5%) were categorized as admixtures. Linkage disequilibrium (LD)
patterns and distributions are of fundamental importance for
genome-wide association mapping. The mean r2 value for all
intrachromosomal loci pairs was 0.1286. The LD between linked markers
decreased with the genetic distance between pairs of linked loci.
Conclusions: These results will provide an effective aid for future
allele mining, association genetics, mapping and cloning gene(s),
germplasm conservation, and improvement programs
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