B A
Methods of microstructure analysis
The most commonly used microstructure analysis methods in materials science and engineering
• • • optical microscopy X-ray diffraction electron microscopy
Sumio Iijima (饭岛澄男）discovered carbon nanotubes using TEM in 1991 Nature，354 (1991) 56.
TEM images
Structure model of carbon nanotubes
High resolution TEM (HREM)
Thin specimen
• resolution： <1Å • specimen： thin specimen (10-100nm)
Screen/detector
JEM-2010F FEG TEM
various TEMs
FEI Titan
Characterization of nanomaterials
Why learn electron microscopy
• The properties of materials are mainly determined by its microstructure. By controlling the microstructure of the materials, one can make a material with the required properties. • To achieve such goal, one should first “know” the microstructure of the materials. • Electron microscopy is a method to analyses the microstructure of the materials， especially for nanomaterials and nanotechnology
GraphiБайду номын сангаасe
Energy (eV)
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10000
Evaporated Carbon
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DLC
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Why learn this course?
Question? If we have a materials with heterogeneous composition and we want to know its structure , phase and composition, what microstructural analysis technique shall we use ?
Electron Diffraction Pattern
Phase analysis
Single crystal polycrystal amorphous
X-ray energy dispersive spectrometer （EDS）
• composition analysis
(from element of Z=4 to Z=92)
Topics of this lecture
• Comparison of electron microscopy with other microstructure analysis techniques • Briefly introduce various electron microscopes and their application • History of development of electron microscope and electron microscopy • course contents, teaching target, teaching arrangement and reference books
• Analysis of chemical composition from H (Z=1) to U (Z=92).
determination of nature of chemical bonding
Diamond
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Energy (eV)
Energy (eV)
Virus structure
Influenza virus
SARS virus
Scanning Electron Microscope (SEM)
• Interaction of incident electron beam with materials at surface of specimen results in many useful signals. • Using these signals one can do surface morphology observation and composition analysis • resolution： 4Å • specimen： thick specimen
Transmission Electron Microscope (TEM)
• Electron beam go through the thin specimen. Due to the interaction between the incident electron beam with the specimen, the transmitted beam will give out the structural and compositional information of materials. • Can do
Disadvantage:
– Can not “see” image – Can not do “localized” analysis
microstructural analysis
• Electron microscopy Advantage:
– High resolution: TEM (<1Å)， SEM (4Å） – Do image observation (BF, DF, HREM), structure analysis (SAD, CBED), composition analysis (EDS) and electronic structure analysis (EELS) on one instrument (TEM) – Can do analysis in very small volume (~nm3)
microstructural analysis
• Electron microscopy Disadvantage:
– – – – – only give localized information very expensive (US$:0.1-1million) interpretation is not straightforward operation is complex Specimen preparation is difficult
• resolution
– Horizontal (x-y direction ): 0.1nm – Vertical (z direction): 0.01nm
• detection depth: 1-2 atomic layer (no damage on the specimen) • Can work in air, solution, vacuum • can only be used for conductor and semiconductor
Different type of electron microscopes
• • • • Transmission Electron Microscope (TEM) Scanning Electron Microscope (SEM) Electron Probe Microanalyzer (EPMA) Scanning Transmission Electron Microscope (STEM)
Electron beam lithography system in SEM
Scanning Probe Microscope（SPM)
• Scanning Tunneling Microscope (STM) • Atomic Force Microscope (AFM)
STM
SPM
Scanning Tunneling Microscope (STM)
清华大学精品课
电子显微分析
授课教师：章晓中教授 办公室：东主楼(11区）一楼电镜实验室 Tel： 62773999 e-mail: xzzhang@
教学手段
• 双语教学：
– 讲课：英文 – 作业、实验、考试用中文
• • • •
使用多媒体和板书 教学内容课后会放在清华大学“网络学堂”上 无英文教材，有英文ppt课件和自编中文教材 推荐参考书
microstructural analysis
• Optical Microscopy Advantage:
– observe surface morphology – Easy to operate – Result interpretation is straightforward