PHYSICS/BK21 SEMINAR (08/04/16)
관련링크
본문
"제목: Development of ultra-coherent electron beam and its application to electron microscopy
연사: Dr. B. Cho[Waseda University]
일시: 2008 년 4 월 16 일 15:00
장소: 물리학과 세미나실(3-201호)
ABSTRACT:
COHERENCE IS ONE OF THE MOST FUNDAMENTAL CONCEPTS OF WAVE PHYSICS INCLUDING PHYSICAL OPTICS AND QUANTUM MECHANICS. IN CLASSICAL TERMS, “HIGHLY COHERENTWAVES” MEANSTHAT THE WAVES VIBRATE IN UNISON FOR A LONG PERIOD OF TIME OVER A WIDE SPACE. THE HIGHLY COHERENT ELECTRON BEAM FROM FIELD EMITTERS IS THECORNERSTONE FOR THE ATOMIC RESOLUTIONELECTRON MICROSCOPY AND ELECTRON INTERFEROMETRY. BY REDUCING THE ELECTRON SOURCE SIZE, DECREASING THE ENERGY WIDTH OF THE BEAM, OR COOLING DOWN THE SOURCE, WE HAVE DEVELOPED ULTRA-COHERENT ELECTRON BEAMS. THE COHERENCY OF ELECTRONBEAM HAS BEEN EVALUATED BY MEASURING ITS ENERGY WIDTH DE OR BY MONITORINGTHE ELECTRON INTERFERENCE PATTERNS GENERATED FROM THE BEAM. SUPERCONDUCTING NIOBIUM FIELD EMITTERS EMITTED MONOCHROMATIC ELECTRON BEAM OFDE≒20 MEV.1 CONVENTIONAL TUNGSTEN FIELD EMITTERS PRODUCED MORE HIGHLY COHERENT ELECTRON BEAMS AT LOW TEMPERATURE, GENERATING THE BEST ELECTRON INTERFERENCE PATTERN.2,3 CARBON NANOTUBES EMITTED MUTUALLY COHERENT MULTIPLE ELECTRON BEAMS FROM SEPARATED EMISSION SITES AT PENTAGON CARBONRINGS.4 THEENHANCEMENT OF COHERENCY AT LOW TEMPERATURE AND THE MUTUALCOHERENCE OF MULTIPLEELECTRON BEAMS DEMONSTRATED THE DIRECT RELATIONSHIPBETWEEN THE COHERENCY OF ELECTRONBEAM AND THE ORIGINAL ELECTRONIC STATES.VERY HIGHLY COLLIMATED AND COHERENT ELECTRONBEAM WAS EXTRACTED FROM SINGLEATOM ELECTRON SOURCES.5 FIELD EMITTERS OPERATING UNDEREXTREME HIGH VACUU(XHV) IN A 10-10 PA RANGE PRODUCED THE MOST STABLE ELECTRON BEAM WHOSE CURRENT FLUCTUATION WAS DOMINATED BY THE INHERENT QUANTUM SHOT NOISE, ALLOWING THE LOWEST FREQUENCY SHOT NOISE MEASUREMENT BELOW 10 HZ.6 A SINGLE ATOM ELECTRON SOURCE SHOWED A SUPPRESSION OF THE SHOT NOISE OFBEAM CURRENT UNDER XHV, INDICATINGSTRONG QUANTUM CORRELATION BETWEEN ELECTRONS.7 TO UTILIZE THE ULTRA-COHERENT ELECTRONBEAM, WE HAVE DEVELOPED A VERSATILE LOW-ENERGY ELECTRON MICROSCOPE EQUIPPED WITH A SINGLE-ATOM SOURCE ELECTRON GUN8 AND AN OPTIMIZED ELECTRON OPTICS. THE MICROSCOPEWAS DESIGNED TO FUNCTION AS A SCANNING ELECTRON MICROSCOPE (SEM), A SCANNING TRANSMISSION ELECTRON MICROSCOPE (STEM) AND AN ELECTRON DIFFRACTION MICROSCOPE. SEMAND STEM IMAGES ARE SHOWN AND PRELIMINARY DIFFRACTION IMAGES OF THIN SAMPLESARE PRESENTED. THE OVERSAMPLING METHOD IS SUGGESTED TO RETRIEVE THE STRUCTURALINFORMATION OF NANO OBJECTS FORM THE LOW-ENERGY DIFFRACTOGRAM.
문의처: 정석민(054-279-2067, smc@postech.ac.kr)
"
연사: Dr. B. Cho[Waseda University]
일시: 2008 년 4 월 16 일 15:00
장소: 물리학과 세미나실(3-201호)
ABSTRACT:
COHERENCE IS ONE OF THE MOST FUNDAMENTAL CONCEPTS OF WAVE PHYSICS INCLUDING PHYSICAL OPTICS AND QUANTUM MECHANICS. IN CLASSICAL TERMS, “HIGHLY COHERENTWAVES” MEANSTHAT THE WAVES VIBRATE IN UNISON FOR A LONG PERIOD OF TIME OVER A WIDE SPACE. THE HIGHLY COHERENT ELECTRON BEAM FROM FIELD EMITTERS IS THECORNERSTONE FOR THE ATOMIC RESOLUTIONELECTRON MICROSCOPY AND ELECTRON INTERFEROMETRY. BY REDUCING THE ELECTRON SOURCE SIZE, DECREASING THE ENERGY WIDTH OF THE BEAM, OR COOLING DOWN THE SOURCE, WE HAVE DEVELOPED ULTRA-COHERENT ELECTRON BEAMS. THE COHERENCY OF ELECTRONBEAM HAS BEEN EVALUATED BY MEASURING ITS ENERGY WIDTH DE OR BY MONITORINGTHE ELECTRON INTERFERENCE PATTERNS GENERATED FROM THE BEAM. SUPERCONDUCTING NIOBIUM FIELD EMITTERS EMITTED MONOCHROMATIC ELECTRON BEAM OFDE≒20 MEV.1 CONVENTIONAL TUNGSTEN FIELD EMITTERS PRODUCED MORE HIGHLY COHERENT ELECTRON BEAMS AT LOW TEMPERATURE, GENERATING THE BEST ELECTRON INTERFERENCE PATTERN.2,3 CARBON NANOTUBES EMITTED MUTUALLY COHERENT MULTIPLE ELECTRON BEAMS FROM SEPARATED EMISSION SITES AT PENTAGON CARBONRINGS.4 THEENHANCEMENT OF COHERENCY AT LOW TEMPERATURE AND THE MUTUALCOHERENCE OF MULTIPLEELECTRON BEAMS DEMONSTRATED THE DIRECT RELATIONSHIPBETWEEN THE COHERENCY OF ELECTRONBEAM AND THE ORIGINAL ELECTRONIC STATES.VERY HIGHLY COLLIMATED AND COHERENT ELECTRONBEAM WAS EXTRACTED FROM SINGLEATOM ELECTRON SOURCES.5 FIELD EMITTERS OPERATING UNDEREXTREME HIGH VACUU(XHV) IN A 10-10 PA RANGE PRODUCED THE MOST STABLE ELECTRON BEAM WHOSE CURRENT FLUCTUATION WAS DOMINATED BY THE INHERENT QUANTUM SHOT NOISE, ALLOWING THE LOWEST FREQUENCY SHOT NOISE MEASUREMENT BELOW 10 HZ.6 A SINGLE ATOM ELECTRON SOURCE SHOWED A SUPPRESSION OF THE SHOT NOISE OFBEAM CURRENT UNDER XHV, INDICATINGSTRONG QUANTUM CORRELATION BETWEEN ELECTRONS.7 TO UTILIZE THE ULTRA-COHERENT ELECTRONBEAM, WE HAVE DEVELOPED A VERSATILE LOW-ENERGY ELECTRON MICROSCOPE EQUIPPED WITH A SINGLE-ATOM SOURCE ELECTRON GUN8 AND AN OPTIMIZED ELECTRON OPTICS. THE MICROSCOPEWAS DESIGNED TO FUNCTION AS A SCANNING ELECTRON MICROSCOPE (SEM), A SCANNING TRANSMISSION ELECTRON MICROSCOPE (STEM) AND AN ELECTRON DIFFRACTION MICROSCOPE. SEMAND STEM IMAGES ARE SHOWN AND PRELIMINARY DIFFRACTION IMAGES OF THIN SAMPLESARE PRESENTED. THE OVERSAMPLING METHOD IS SUGGESTED TO RETRIEVE THE STRUCTURALINFORMATION OF NANO OBJECTS FORM THE LOW-ENERGY DIFFRACTOGRAM.
문의처: 정석민(054-279-2067, smc@postech.ac.kr)
"
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