A number of studies of tungsten disulfide (WS2) have been conducted because monolayer WS2 has a relatively high photoluminescence quantum yield. However, the defect-related Raman scattering which determines the quality of monolayer WS2 has been rarely studied. In this study, we perform tip-enhanced Raman scattering experiments for the WS2 monolayer to investigate the defect-induced Raman scattering properties. We demonstrate that the red-shifted A1g mode with the D and D′ modes can be attributed to the defect in monolayer WS2. Furthermore, we also identify that the emergence of new Raman vibrational modes can be induced by sulfur vacancies through the density functional theory calculations.
Monolayer tungsten disulfide (WS2) has emerged as a material for optoelectronic applications because of its remarkable quantum yield of photoluminescence. However, the existing studies of defects in monolayer WS2 are insufficient to specifically discern Raman scattering properties caused by the defect. Here, we report that resonance tip-enhanced Raman spectroscopy imaging and correlation study with scanning tunneling microscopy can reveal defect-induced Raman modes denoted as D and D′ modes in monolayer WS2. Furthermore, our density functional theory calculations demonstrate that sulfur vacancies introduce not only the red-shifted A1g mode but also the D and D′ modes. The observed defect-related Raman modes can be utilized to evaluate the quality of monolayer WS2 and will be helpful to improve the performance of WS2 optoelectronic devices.
Nanobiotechnology is the convergent field of nanotechnology and biotechnology, and it has received a lot of attention in the 21st century. Typical technical fields of nanobiotechnology are the design and synthesis of biological molecules with new functionality, nanobiosensors, nanoimaging technology of cell and biosystems, and nanomaterials for drug delivery and therapy. Nanotechnology based on the structure and principle of biomaterials is the emerging field to develop new nanodevices and systems that were not possible with existing macroscale technology. It is evaluated as a core technology that can lead to new industries in the 21st century.
We report the application of an optical microscope equipped with a high-resolution dark-field condenser for detecting dynamic responses of cellular nanostructures in real time. Our system provides an easy-to-use technique to visualize biological specimens without any staining. This system can visualize the dynamic behavior of nanospheres and nanofibers, such as F-actin, at the leading edges of adjacent neuronal cells. We confirmed that the nanofibers imaged with this high-resolution optical microscopic technique are F-actin by using fluorescence microscopy after immunostaining the F-actin of fixed cells. Furthermore, cellular dynamics are enhanced by applying noncontact electric field stimulation through a transparent graphene electric field stimulator. High-resolution label-free optical microscopy enables the visualization of nanofiber dynamics initiated by filopodial nanofiber contacts. In conclusion, our optical microscopy system allows the visualization of nanoscale cellular dynamics under various external stimuli in real time without specific staining.
In this study, an apertureless near-field scanning optical microscope-Raman spectroscopy system is constructed and the topography and Raman scattering image of carbon nano-materials are simultaneously measured with high spatial resolution by using a sharp Au tip. The Rayleigh scattering image, and Raman scattering image of the carbon nanotubes showed improved spatial resolution and enhanced scattering intensity owing to the optical antenna effect of Au tip.
Kyoung In Min, Ki Kang Kim, Myoung-Kyu Oh, Soo Bong Choi, Heesuk Rho, Ha Jin Lee, Kay Hyeok An, Young Chul Choi, Jong Hun Han, Kyung Hui Oh, Young-Hee Lee, Mun Seok Jeong
We investigated single wall carbon nanotubes (SWCNTs) synthesized by the HiPCO method and further processed with nitronium hexafluoroantimonate (NO2SbF6 : NHFA) treatment using continuous resonant Raman scattering in the range of 570-900 nm. According to the population ratio calculation results from Raman scattering data, it is obvious that semiconducting SWCNTs with small diameter and metallic SWCNTs were selectively removed by NHFA.
Chandan Biswas, Seung Yol Jeong, Seong Chu Lim, Dong Jae Bae, Young Hee Lee, Hyun Jin Shin, Seon-Mi Yoon, Jae Young Choi, Ok Hwan Cha, Mun Seok Jeong, David Perello, Minhee Yun
CdSe/ZnS core/shell quantum dots have been decorated on thin multiwalled and singlewalled carbon nanotubes (CNTs)
by chemical functionalization and substrate gate-bias control. CdSe quantum dots were negatively charged by adding
mercaptoacetic acid (MAA). The silicon oxide substrate was decorated by octadecyltrichlorosilane (OTS) and converted
to hydrophobic surface. The negatively charged CdSe/ZnS NCs were adsorbed on the SWCNT surface by applying the
negative gate bias. The selective adsorption of CdSe/ZnS quantum dots on SWCNTs was confirmed by confocal laser
scanning microscope. Quantum dots decorated carbon nanotubes have been used for effective photogenaration and
carrier transport through the organic photovoltaic device which has fabricated using effective polymers. The results
clearly indicate the efficient photocurrent generation and carrier transport which effectively increased the efficiency of
the device for the next generation organic solar cell applications.
KEYWORDS: Silicon, Stereolithography, Superlattices, Electron transport, Excitons, Signal processing, Phonons, Germanium, Electrodes, Temperature metrology
The photoelectric transient process of a 99 period Si0.823Ge0.177/Si superlattices (SL) was investigated by the photocurrent decay (PCD) method. Decay lifetimes of electron and hole in SL, Si cap and buffer layers are extracted from the transient intensity and polarity of the PCD signal. The temperature and bias dependences of lifetime exhibit the thermalization of heavy hole, the dissociation of free exciton, and the thermal activation of shallow impurity and dislocation. The thermalized hole jumps in and out of the well at low temperature and weak electric field, while it jumps or surfs over the well region by a strong electric field or at high temperature. The lifetimes of electron and hole are nearly the same in the Si cap layer, while the lifetime of hole is about one order of magnitude longer than that of electron in SL, possibly due to the quantum confinement of hole in the SL region.
A successful fabrication of semiconductor optical switch, similar in function to the self- electro-optic effect devices, is reported for the first time from MOCVD-grown GaAs/AlGaAs low barrier quantum well pin diodes (Al fraction, x equals 4%). A reflective 16 X 8 switch array and its performance are also reported. The maximum contrast ratio was found to be 2.9:1 at 5 V bias.
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