scholarly journals Carbon doping of WS2 monolayers: Bandgap reduction and p-type doping transport

2019 ◽  
Vol 5 (5) ◽  
pp. eaav5003 ◽  
Author(s):  
Fu Zhang ◽  
Yanfu Lu ◽  
Daniel S. Schulman ◽  
Tianyi Zhang ◽  
Kazunori Fujisawa ◽  
...  
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
Transition Metal Dichalcogenides ◽  
Carbon Doping ◽  
Chemical Doping ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Metal Dichalcogenides ◽  
P Type ◽  
Electronic Chemical ◽  
Type Conduction

Chemical doping constitutes an effective route to alter the electronic, chemical, and optical properties of two-dimensional transition metal dichalcogenides (2D-TMDs). We used a plasma-assisted method to introduce carbon-hydrogen (CH) units into WS2 monolayers. We found CH-groups to be the most stable dopant to introduce carbon into WS2, which led to a reduction of the optical bandgap from 1.98 to 1.83 eV, as revealed by photoluminescence spectroscopy. Aberration corrected high-resolution scanning transmission electron microscopy (AC-HRSTEM) observations in conjunction with first-principle calculations confirm that CH-groups incorporate into S vacancies within WS2. According to our electronic transport measurements, undoped WS2 exhibits a unipolar n-type conduction. Nevertheless, the CH-WS2 monolayers show the emergence of a p-branch and gradually become entirely p-type, as the carbon doping level increases. Therefore, CH-groups embedded into the WS2 lattice tailor its electronic and optical characteristics. This route could be used to dope other 2D-TMDs for more efficient electronic devices.

Pristine edge structures of T′′-phase transition metal dichalcogenides (ReSe2, ReS2) atomic layers

Nanoscale ◽  
2020 ◽  
Vol 12 (32) ◽  
pp. 17005-17012
Author(s):  
Xiya Chen ◽  
Bao Lei ◽  
Yong Zhu ◽  
Jiadong Zhou ◽  
Zheng Liu ◽  
...  
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
Density Functional ◽  
Transition Metal Dichalcogenides ◽  
Density Functional Theory Calculations ◽  
Microscopy Imaging ◽  
Functional Theory ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Metal Dichalcogenides ◽  
T Phase

Atomically sharp pristine edges of ReSe2 atomic layers were identified with scanning transmission electron microscopy imaging and density functional theory calculations.

NANOSTRUCTURAL ANALYSIS OF A GaN-BASED VIOLET LASER DIODE

2008 ◽  
Vol 15 (01n02) ◽  
pp. 189-193
Author(s):  
J. R. YANG ◽  
H. L. TSAI ◽  
T. Y. WANG ◽  
H. W. YEN ◽  
C. Y. CHEN ◽  
...  
Keyword(s):  
Laser Diode ◽  
Scanning Transmission Electron Microscopy ◽  
Dark Field ◽  
Threading Dislocation ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Strained Layer Superlattice ◽  
P Type

The nanostructure of p-type AlGaN / GaN strained-layer superlattice (SLS) cladding in a GaN -based violet laser diode (LD) has been investigated by high-angle annular dark-field (HAADF) scanning-transmission electron microscopy (STEM). The pairs of the AlGaN and GaN layers in SLS cladding are observed, where the AlGaN and GaN layers appear as dark and bright bands. It is also found that the threading dislocations disappeared within the SLS; this evidence manifests the role of SLS in suppressing threading dislocation propagation.

scholarly journals Single-atom doping of MoS2 with manganese enables ultrasensitive detection of dopamine: Experimental and computational approach

2020 ◽  
Vol 6 (32) ◽  
pp. eabc4250 ◽  
Author(s):  
Yu Lei ◽  
Derrick Butler ◽  
Michael C. Lucking ◽  
Fu Zhang ◽  
Tunan Xia ◽  
...  
Keyword(s):  
Density Functional ◽  
Transition Metal Dichalcogenides ◽  
Density Functional Theory Calculations ◽  
Single Atom ◽  
Buffer Solution ◽  
Dopamine Detection ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Metal Dichalcogenides ◽  
Metal Doped

Two-dimensional transition metal dichalcogenides (TMDs) emerged as a promising platform to construct sensitive biosensors. We report an ultrasensitive electrochemical dopamine sensor based on manganese-doped MoS2 synthesized via a scalable two-step approach (with Mn ~2.15 atomic %). Selective dopamine detection is achieved with a detection limit of 50 pM in buffer solution, 5 nM in 10% serum, and 50 nM in artificial sweat. Density functional theory calculations and scanning transmission electron microscopy show that two types of Mn defects are dominant: Mn on top of a Mo atom (MntopMo) and Mn substituting a Mo atom (MnMo). At low dopamine concentrations, physisorption on MnMo dominates. At higher concentrations, dopamine chemisorbs on MntopMo, which is consistent with calculations of the dopamine binding energy (2.91 eV for MntopMo versus 0.65 eV for MnMo). Our results demonstrate that metal-doped layered materials, such as TMDs, constitute an emergent platform to construct ultrasensitive and tunable biosensors.

Determination of Thickness for the Individual Layer of Strained P-Type Al0.11Ga0.89NGaN Superlattice by High Angle Annular Dark Field Scanning Transmission Electron Microscopy

2010 ◽  
Vol 152-153 ◽  
pp. 879-882 ◽  
Author(s):  
Hui Liao ◽  
Wei Hua Chen ◽  
Fen Fen Wei ◽  
Juan Hou
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Dark Field ◽  
High Angle ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
P Type

AlGaN/GaN superlattice are the important structure of optoelectronic devices such as light-emitting diodes and laser diodes. The nanostructure of the superlattice can greatly influences the optical electrical properties of final LD and LED . It is impossible to evaluate their thickness by TEM when it’s aluminum component lower than 14%.We investigated the nanostructure of strained p-type Al0.11Ga0.89N/GaN superlattice grown on sapphire by high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).By an average filtering technique, the thickness of the AlGaN layers and GaN layers were determined to be 2.409±0.092 nm and 2.371±0.062 nm from the HAADF-STEM images, respectively.

High-Voltage Scanning Electron Microscopy

1970 ◽  
Vol 28 ◽  
pp. 6-7
Author(s):  
J. M. Cowley
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Wave Optics ◽  
Contrast Effects ◽  
Transmission Electron ◽  
Mode Of Operation ◽  
Scanning Transmission ◽  
Types Of Information ◽  
Voltage Scanning

The comparison of scanning transmission electron microscopy (STEM) with conventional transmission electron microscopy (CTEM) can best be made by means of the Reciprocity Theorem of wave optics. In Fig. 1 the intensity measured at a point A’ in the CTEM image due to emission from a point B’ in the electron source is equated to the intensity at a point of the detector, B, due to emission from a point A In the source In the STEM. On this basis it can be demonstrated that contrast effects In the two types of instrument will be similar. The reciprocity relationship can be carried further to include the Instrument design and experimental procedures required to obtain particular types of information. For any. mode of operation providing particular information with one type of microscope, the analagous type of operation giving the same information can be postulated for the other type of microscope. Then the choice between the two types of instrument depends on the practical convenience for obtaining the required Information.

Imaging and diffraction modes in Scanning Transmission Electron Microscopy

1986 ◽  
Vol 44 ◽  
pp. 684-687
Author(s):  
J. M. Cowley ◽  
R. Glaisher ◽  
J. A. Lin ◽  
H.-J. Ou
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
High Efficiency ◽  
Fiber Optic ◽  
Image Intensifier ◽  
Detector System ◽  
Detector Plane ◽  
Secondary Electrons ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Special Detector

Some of the most important applications of STEM depend on the variety of imaging and diffraction made possible by the versatility of the detector system and the serial nature, of the image acquisition. A special detector system, previously described, has been added to our STEM instrument to allow us to take full advantage of this versatility. In this, the diffraction pattern in the detector plane may be formed on either of two phosphor screens, one with P47 (very fast) phosphor and the other with P20 (high efficiency) phosphor. The light from the phosphor is conveyed through a fiber-optic rod to an image intensifier and TV system and may be photographed, recorded on videotape, or stored digitally on a frame store. The P47 screen has a hole through it to allow electrons to enter a Gatan EELS spectrometer. Recently a modified SEM detector has been added so that high resolution (10Å) imaging with secondary electrons may be used in conjunction with other modes.

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