A5026133216- Gyrotron and Vacuum Electronics Research
- Particle Accelerators and Free-Electron Lasers
- Photonic and Optical Devices
- Particle accelerators and beam dynamics
- Photonic Crystals and Applications
- Microwave Engineering and Waveguides
- Terahertz technology and applications
- Plasmonic and Surface Plasmon Research
- Optical Coatings and Gratings
- Graphene research and applications
- Advanced X-ray Imaging Techniques
- Advanced Electron Microscopy Techniques and Applications
- Superconducting and THz Device Technology
- 2D Materials and Applications
- Metamaterials and Metasurfaces Applications
- Pulsed Power Technology Applications
- Isotope Analysis in Ecology
- Mass Spectrometry Techniques and Applications
- Laser-Matter Interactions and Applications
- Topological Materials and Phenomena
- Crystallography and Radiation Phenomena
- Semiconductor Quantum Structures and Devices
- Quantum and electron transport phenomena
- Fern and Epiphyte Biology
- Astro and Planetary Science
Korea Atomic Energy Research Institute
2015-2024
Foundry (United Kingdom)
2024
Samsung (United States)
2024
Budker Institute of Nuclear Physics
2020
Korea University of Science and Technology
2015-2019
Daejeon University
2019
Seoul National University
2003-2011
Saratov State University
2004
Abstract Microscopic structures and magnetic properties are investigated for Fe 5− x GeTe 2 single crystal, recently discovered as a promising van der Waals (vdW) ferromagnet. An atom (Fe(1)) located in the outermost 5 Ge sublayer has two possible split‐sites which either above or below atom. Scanning tunneling microscopy shows √3 × superstructures attributed to ordering of Fe(1) layer. The have different phases due symmetry ordering. Intriguingly, observed breaks inversion resulting...
The authors show that evanescent tunneling transmission of effective surface plasmon polaritons between two counterstreaming electron beams noticeably increases Smith-Purcell radiation (SPR) intensity by about orders magnitude as well lower its transition threshold from a spontaneous emission to stimulated one. An mechanism the superradiant SPR is theoretically analyzed dielectric conversion structured metal and boundary matching condition Maxwell’s equations in comparison with numerical simulations.
Low-voltage operation of millimeter-wave folded waveguide traveling-wave tube (TWT) was investigated using a 12 kV linear electron beam. Backward wave oscillation operated at second space harmonic observed with output power 20 W, tunability 6% within 0.01 dB/MHz, and voltage-frequency stability 0.56 MHz/V. The measured frequency are in good agreement the predicted values particle-in-cell (PIC) code. In addition, backward-wave interaction second-space as an amplifier gain 15 dB bandwidth...
The circuits for millimeter wave vacuum electron devices with all circuit elements including an beam tunnel are microfabricated by two-step deep-etch x-ray lithography (x-ray LIGA). discrepancies of eigenfrequency between experiment and simulation within 1.1% in a coupled-cavity structure 1.4% folded waveguide when the operating frequency is about 100GHz. Furthermore, measured tolerance below 2μm, surface roughness 20–70nm, LIGA-fabricated implies LIGA microfabrication has potential...
We introduce the subwavelength transmission of an effective surface plasmon beyond light zone via proximity interaction convection electrons with a metal grating. A comparative analysis dielectric homogenization and finite-difference-time-domain simulation shows that out-of-phase-like modes (pi modes) have strong below cutoff frequency relying on parametric condition structural dimension electronic energy. The synchronous spatial field charge distribution pi mode system confirms evanescent...
The electromagnetic response of a metallic metamaterial to fast-moving electrons is studied by numerical simulations. considered one-dimensional array slits perforated on film and found generate Cerenkov wakes when the electron beam travels near its surface. There no energy threshold for generation such wakes, which would be promising lower operation in compact free-electron-lasers. Moreover, analyzing spectral dependence light, it possible map dispersion relation guided modes supported metamaterial.
Abstract In this paper, we propose a terahertz (THz) guided-mode resonance (GMR) notch filter made of monolithic polyethylene terephthalate (PET) film, which has monolayer grating structure. The proposed configuration shows both polarization-dependent and polarization-independent characteristics for the incident THz wave depending on rotation angle second film. When is 0°, filtering strength (transmittance) at frequency changes from 0.4 (0.996) to 99.0% (0.010) according polarization....
We investigated the foundations for high-frequency vacuum electron devices experimentally, with emphasis on deep etch X-ray lithography: lithographie, galvanoformung, abformung (LIGA) to fabricate a miniaturized interaction circuit and photonic crystal (PC) resonator excite stable high-order mode. The successful operation of LIGA-fabricated folded-waveguide traveling-wave tube was reported. From such physical considerations as Debye length band gap, we proposed reflex klystron adopting cold...
A vacuum tube oscillator fabricated by the deep etch X-ray lithography: lithographie, galvanoformung, abformung (LIGA) process was successfully developed for first time. For proof-of-concept experiment involving a delayed feedback oscillator, folding-waveguide traveling-wave (FWTWT) computer numerical control milling in advance. With 12.4-kV and 150-mA electron beam, Ka-band FWTWT amplifier shows linear gain of 25 dB bandwidth 10%. Applying scheme, threshold strengths onset oscillation...
A combined study of scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) is conducted to understand the multiple charge density wave (CDW) phases monolayer (ML) VSe2 films manifested by graphene substrates. Submonolayer (∼0.8 ML) are prepared on two different substrates single-layer (SLG) bi-layer (BLG) a 6H-SiC(0001). We find that ML less coupled SLG substrate compared VSe2/BLG. Then, grown BLG reveals very topography in STM. While VSe2/BLG shows one...
TM 330 -like higher order mode was excited in a multibeam reflex klystron oscillator employing hybrid photonic-band-gap (PBG) cavity using three-dimensional particle-in-cell simulation. One side of conventional metal replaced with dielectric photonic crystal lattice to form PBG resonator that uses band-gap effects resulting more uniform field as well the exclusion some conventional-cavity-type modes, thereby reducing competition. Simulated produced an output power much than could be delivered cavity.
We realized a variable-period permanent-magnet helical undulator with high ($\ensuremath{\sim}1\text{ }\text{ }\mathrm{T}$) field amplitude, which is almost constant over periods of 23--26 mm. Each period has four modular sections iron poles and permanent magnets embedded in nonmagnetic disks holes along the axis. Modular plates undergo longitudinal repulsive force from magnetic pressure spring coils between plates. The can thus be controlled by mechanically changing end plate position. This...
We propose an all-dielectric single-layer guided-mode resonance filter (GMRF) operating in the high-frequency terahertz (THz) region. For fabrication of thin gratings to achieve strong region, refractive index and absorption must be small, while tensile strength high. Cyclic olefin copolymer (COC) films have a lower than polyethylene terephthalate (PET) higher yield polytetrafluoroethylene (PTFE) films. Therefore, COC film was found suitable fabricate GMRF THz fabricated COC-based GMRFs with...
Bilayer VSe<sub>2</sub> shows polymorphic 1T′ structure which can transit to the dynamic state of lattice vibrations, triggered by tunneling current.
All-dielectric binary gratings, with and without slab waveguides, are designed to generate polarization-independent guided-mode resonance filters (GMRFs) operating in the THz frequency region using rigorous coupled-wave analysis (RCWA) method. The filling factor thickness of grating were adjusted have equal frequencies transverse electric (TE)- magnetic (TM)-polarized beams. single for a waveguide was obtained at 0.459 full width half maximum (FWHM) values 8.3 8.5 GHz TE TM modes,...
Cu2O has been investigated for decades to understand the complex nature of oxidation and utilize its high catalytic activity intrinsic p-type character. However, structures defects Cu2O(111) surfaces have not fully explored at atomistic level, which is required clarify some issues such as termination surfaces. Here, our combined scanning tunneling microscopy (STM) density functional theory (DFT) studies show that a stoichiometric surface where coordinately unsaturated Cu atoms appear with...
Abstract The deflection of charged particles is an intuitive way to visualize electromagnetic oscillation coherent light. Here, we present a real-time ultrafast oscilloscope for time-frozen visualization terahertz (THz) optical wave by probing light-driven motion relativistic electrons. We found the unique condition subwavelength metal slit waveguide preserving distortion-free waveform during its propagation. Momentary stamping wave, transversely travelling inside slit, on ultrashort wide...
The electromagnetic field distribution obtained from a finite-difference-time-domain simulation shows that hybrid photonic-band-gap (PBG) cavity enveloped by dielectric lattice and three metallic walls provides better uniformity of high order mode, TMmn0, than conventional one does under an external coupling with the maintenance quality factor cavity. Experimentally measured reflection transmission scattering matrices TM550 mode show PBG structure improves to within 10% compared larger...
The experimental observation of femtosecond dynamics in atoms and molecules by stroboscopic technologies utilizing x ray or electron flashes has attracted much attention rapidly developed. We propose a feasible ultrafast diffraction (UED) technology with high brightness sub-10 fs temporal resolution. previously demonstrated UED system an overall resolution 31 using RF photoelectron gun 90° achromatic bending structure. This structure enabled bunch duration 25 low timing jitter less than 10...
Understanding the characteristics of intrinsic defects in crystals is great interest many fields, from fundamental physics to applied materials science. Combined investigations scanning tunneling microscopy/spectroscopy (STM/S) and density functional theory (DFT) are conducted understand nature Se vacancy monolayer (ML) ReSe2 grown on a graphene substrate. Among four possible sites, we identify Se4 close Re layer by registry between STM topography DFT simulated images. The also...