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Moon, Kiwon,Shin, Jun-Hwan,Lee, Il-Min,Park, Dong Woo,Lee, Eui Su,Park, Kyung Hyun IOP 2018 Nanotechnology Vol.29 No.47
<P>Rectifiers have been used to detect electromagnetic waves with very low photon energies. In these rectifying devices, different methods have been utilized, such as adjusting the bandgap and the doping profile, or utilizing the contact potential of the metal–semiconductor junction to produce current flow depending on the direction of the electric field. In this paper, it is shown that the asymmetric application of nano-electrodes to a metal–semiconductor–metal (MSM) structure can produce such rectification characteristics, and a terahertz (THz) wave detector based on the nano-MSM structure is proposed. Integrated with a receiving antenna, the fabricated device detects THz radiation up to a frequency of 1.5 THz with responsivity and noise equivalent power of 10.8 V/W and <img ALIGN='MIDDLE' ALT='$100\,{\rm{pW}}/\sqrt{{\rm{Hz}}},$' SRC='http://ej.iop.org/images/0957-4484/29/47/47LT01/nanoaae130ieqn1.gif'/> respectively, estimated at 0.3 THz. The unidirectional current flow is attributed to the thermionic emission of hot carriers accelerated by the locally enhanced THz field at the sharp end of the nano-electrode. This work not only demonstrates a new type of THz detector but also proposes a method for manipulating ultrafast charge-carrier dynamics through the field enhancement of the nano-electrode, which can be applied to ultrafast photonic and electronic devices.</P>
Terahertz Near-Field Microscope: Analysis and Measurements of Scattering Signals
Kiwon Moon,Euna Jung,Meehyun Lim,Youngwoong Do,Haewook Han IEEE 2011 IEEE transactions on terahertz science and technol Vol.1 No.1
<P>We present the analysis and measurements of scattering signals of a terahertz pulse scattering-type near-field microscope. We used a self-consistent line dipole image method for the quantitative analysis of the THz near-field interaction. The line scan across a gold film demonstrated that the terahertz microscope has a nanoscale resolution of ~80 nm. The measurements of scattering signals on gold and silicon substrates were in good agreement with calculations.</P>
Subsurface Nanoimaging by Broadband Terahertz Pulse Near-Field Microscopy
Moon, Kiwon,Park, Hongkyu,Kim, Jeonghoi,Do, Youngwoong,Lee, Soonsung,Lee, Gyuseok,Kang, Hyeona,Han, Haewook American Chemical Society 2015 NANO LETTERS Vol.15 No.1
<P>Combined with terahertz (THz) time-domain spectroscopy, THz near-field microscopy based on an atomic force microscope is a technique that, while challenging to implement, is invaluable for probing low-energy light-matter interactions of solid-state and biomolecular nanostructures, which are usually embedded in background media. Here, we experimentally demonstrate a broadband THz pulse near-field microscope that provides subsurface nanoimaging of a metallic grating embedded in a dielectric film. The THz near-field microscope can obtain broadband nanoimaging of the subsurface grating with a nearly frequency-independent lateral resolution of 90 nm, corresponding to ∼λ/3300, at 1 THz, while the AFM only provides a flat surface topography.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-1/nl503998v/production/images/medium/nl-2014-03998v_0005.gif'></P>
A NEXT GENERATION MULTI-BEAM FOCAL PLANE ARRAY RECEIVER OF TRAO FOR 86-115 GHZ BAND
Moon-Hee Chung,김효령,이창훈,김광동,Vladimir B.Khaikin,Kiwon Park 한국우주과학회 2006 Journal of Astronomy and Space Sciences Vol.23 No.1
The noise temperature of existing millimeter-wave receivers is already within two rthree times quantum noise limit. One of practical ways to increase the observationspeed of single dish radio telescope without longer integration time is use of multi-beam focal plane array receiver as demonstrated in several large single dish radiotelescopes. In this context the TRAO (Taeduk Radio Astronomy Observatory), whichoperates a 14 m Cassegrain radio telescope, is planning to develop a 4 x 4 beamsfocal plane array SIS receiver system for 86-115 GHz band. Even though millimeter-wave HEMT LNA-based receivers approach the noise temperature comparable to theSIS receiver at W-band, it is believed that the receiver based on SIS mixer seems tooffer a bit more advantages. The critical part of the multi-beam array receiver willbe sideband separating SIS mixers. Employing such a type of SIS mixer makes itpossible to simplify the quasi-optics of receiver. Otherwise, an SSB lter should beused in front of the mixer or some sophisticated post-processing of observation datais needed. In this paper we will present a preliminary design concept and componentsneededforthedevelopmentofanew3mbandmulti-beamfocalplanearrayreceiver.
Kim, Kiwon,Moon, Jun Hyuk American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.40
<P>A photoanode capable of high-efficiency water oxidation at low bias potential is essential for its practical application for photocathode-coupled tandem systems. To address this issue, a photoanode with low turn-on voltage for water oxidation and high charge separation efficiency at low bias potential is essential. In this study, we demonstrate the photoanode of the BiVO<SUB>4</SUB>/ZnO three-dimensional (3D) bicontinuous (BC) structure. ZnO has a relatively cathodic flat-band potential, which leads to low turn-on potential; the BiVO<SUB>4</SUB>/ZnO 3D BC photoanode shows an onset potential of 0.09 V versus the reversible hydrogen electrode (<I>V</I><SUB>RHE</SUB>). Moreover, we achieve remarkably high charge separation efficiency at low bias potential (78% at 0.6 V<SUB>RHE</SUB>); this is attributed to the application of thin-film BiVO<SUB>4</SUB> shells by high light-scattering properties of the 3D BC structure. As a result, the BiVO<SUB>4</SUB>/ZnO 3D BC photoanode generates a high water oxidation photocurrent of up to 3.4 ± 0.2 mA cm<SUP>-2</SUP> (with CoPi catalyst coating). This photocurrent value is reproducible, and the photocurrent-to-O<SUB>2</SUB> conversion efficiency is over 90%. To the best of our knowledge, this is the highest value among the values of the photocurrent at 0.6 V<SUB>RHE</SUB> in previous BiVO<SUB>4</SUB>-based heterojunction photoanodes.</P> [FIG OMISSION]</BR>
Kim, Kiwon,Nam, Seong Kyung,Park, Jong Hyeok,Moon, Jun Hyuk The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.9
<P>The BiVO4/WO3 heterojunction is the ideal photoanode for highly efficient solar water splitting. Despite much effort, the low light absorption efficiency near the BiVO4 band gap wavelength is still a major cause of loss of water-splitting efficiency. To address this issue, we introduce a BiVO4/WO3 photoanode in which BiVO4 single crystal nanoparticles (NPs) are decorated. In particular, we present a limited growth method in confined geometry to synthesize BiVO4 NPs. These BiVO4 NPs enhance Rayleigh-type light scattering, especially at the absorption edge wavelengths, resulting in increased light absorption efficiency (<I>η</I>abs) at the corresponding wavelengths; the BiVO4 NPs dramatically improved the <I>η</I>abs up to 60% at 500 nm, which is more than twice as high as the <I>η</I>abs values obtained for previously reported BiVO4 photoanodes. In addition, BiVO4 NPs exhibit high charge separation efficiency, especially at low bias potentials. This result indicates effective charge transport in the NP morphology. As a result, the BiVO4 NP-coated WO3 photoanode achieves a remarkably high water splitting photocurrent of 5.8 ± 0.18 mA cm<SUP>−2</SUP>. This is the highest water-splitting photocurrent among those previously reported for BiVO4-based photoanodes.</P>