nanoquebec 2006-11-16 09:55
扫描电子显微镜，透射电子显微镜学习资源汇集
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[b][背景][/b]扫描电子显微镜和透射电子显微镜是纳米结构和形貌分析的最基本的手段之一。所以有必要掌握其基本的原理。希望此帖除了能全面介绍基本原理外，能够汇集其它相关的资源。以便大家能够将这个传统的技术得到更深入和全面的应用[/color]
[b]1. SEM and TEM仪器样本照片[/b]
SEM
[img]http://www.siliconfareast.com/sem.jpg[/img]
TEM
[img]http://www.tut.fi/units/mol/materiaalioppi/kuvat/tem2.jpg[/img]
[b]2. Scanning Electron Microscopy (SEM)[/b]
Scanning electron microscopy is used for inspecting topographies of specimens at very high magnifications using a piece of equipment called the scanning electron microscope. SEM magnifications can go to more than 300,000 X but most semiconductor manufacturing applications require magnifications of less than 3,000 X only. SEM inspection is often used in the analysis of die/package cracks and fracture surfaces, bond failures, and physical defects on the die or package surface.
During SEM inspection, a beam of electrons is focused on a spot volume of the specimen, resulting in the transfer of energy to the spot. These bombarding electrons, also referred to as primary electrons, dislodge electrons from the specimen itself. The dislodged electrons, also known as secondary electrons, are attracted and collected by a positively biased grid or detector, and then translated into a signal.
To produce the SEM image, the electron beam is swept across the area being inspected, producing many such signals. These signals are then amplified, analyzed, and translated into images of the topography being inspected. Finally, the image is shown on a CRT.
The energy of the primary electrons determines the quantity of secondary electrons collected during inspection. The emission of secondary electrons from the specimen increases as the energy of the primary electron beam increases, until a certain limit is reached. Beyond this limit, the collected secondary electrons diminish as the energy of the primary beam is increased, because the primary beam is already activating electrons deep below the surface of the specimen. Electrons coming from such depths usually recombine before reaching the surface for emission.
Aside from secondary electrons, the primary electron beam results in the emission of backscattered (or reflected) electrons from the specimen. Backscattered electrons possess more energy than secondary electrons, and have a definite direction. As such, they can not be collected by a secondary electron detector, unless the detector is directly in their path of travel. All emissions above 50 eV are considered to be backscattered electrons.
Backscattered electron imaging is useful in distinguishing one material from another, since the yield of the collected backscattered electrons increases monotonically with the specimen's atomic number. Backscatter imaging can distinguish elements with atomic number differences of at least 3, i.e., materials with atomic number differences of at least 3 would appear with good contrast on the image. For example, inspecting the remaining Au on an Al bond pad after its Au ball bond has lifted off would be easier using backscatter imaging, since the Au islets would stand out from the Al background.
A SEM may be equipped with an EDX analysis system to enable it to perform compositional analysis on specimens. EDX analysis is useful in identifying materials and contaminants, as well as estimating their relative concentrations on the surface of the specimen.
[img]http://www.siliconfareast.com/semphoto.jpg[/img]
When performing SEM inspection, the following must be observed:
1) The EHT must be high enough to provide a good image but low enough to prevent specimen charging.
2) To maximize contrast due to material differences, use as low an EHT as possible.
3) If possible, sputter-coat the specimen to prevent specimen charging. Sputter-coating is considered destructive. Never sputter-coat units that still need to undergo electrical testing, curve tracing, EDX analysis, inspection, etc.
4) The probe current must be set to its default value, unless a higher probe current is needed to focus the point of interest properly.
[quote] 1. The "Virtual Source" at the top represents the electron gun, producing a stream of monochromatic electrons.
2. The stream is condensed by the first condenser lens (usually controlled by the "coarse probe current knob"). This lens is used to both form the beam and limit the amount of current in the beam. It works in conjunction with the condenser aperture to eliminate the high-angle electrons from the beam
3. The beam is then constricted by the condenser aperture (usually not user selectable), eliminating some high-angle electrons
4. The second condenser lens forms the electrons into a thin, tight, coherent beam and is usually controlled by the "fine probe current knob"
5. A user selectable objective aperture further eliminates high-angle electrons from the beam
6. A set of coils then "scan" or "sweep" the beam in a grid fashion (like a television), dwelling on points for a period of time determined by the scan speed (usually in the microsecond range)
7. The final lens, the Objective, focuses the scanning beam onto the part of the specimen desired.
8. When the beam strikes the sample (and dwells for a few microseconds) interactions occur inside the sample and are detected with various instruments
9. Before the beam moves to its next dwell point these instruments count the number of interactions and display a pixel on a CRT whose intensity is determined by this number (the more reactions the brighter the pixel).
10. This process is repeated until the grid scan is finished and then repeated, the entire pattern can be scanned 30 times per second.
[img]http://www.unl.edu/CMRAcfem/gifs/semoptic.gif[/img]
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3. Transmission Electron Microscopy (TEM)
Transmission Electron Microscopy (TEM) is a technique used for analyzing the morphology, crystallographic structure, and even composition of a specimen. TEM provides a much higher spatial resolution than SEM, and can facilitate the analysis of features at atomic scale (in the range of a few nanometers) using electron beam energies in the range of 60 to 350 keV.
Unlike the SEM which relies on dislodged or reflected electrons from the specimen to form an image, the TEM collects the electrons that are transmitted through the specimen. Like the SEM, a TEM uses an electron gun to produce the primary beam of electrons that will be focused by lenses and apertures into a very thin, coherent beam.
This beam is then controlled to strike the specimen. A portion of this beam gets transmitted to the other side of the specimen, is collected, and processed to form the image.
For crystalline materials, the specimen diffracts the incident electron beam, producing local diffraction intensity variations that can be translated into contrast to form an image. For amorphous materials, contrast is achieved by variations in electron scattering as the electrons traverse the chemical and physical differences within the specimen.
The greatest consideration when performing TEM analysis is sample preparation. The quality of sample preparation contributes greatly to whether the micrograph will be good or not, so analysts are required to exercise the necessary diligence in preparing the sample for TEM analysis.
A TEM works much like a slide projector. A projector shines a beam of light through (transmits) the slide, as the light passes through it is affected by the structures and objects on the slide. These effects result in only certain parts of the light beam being transmitted through certain parts of the slide. This transmitted beam is then projected onto the viewing screen, forming an enlarged image of the slide.
[quote]
TEMs work the same way except that they shine a beam of electrons (like the light) through the specimen(like the slide). Whatever part is transmitted is projected onto a phosphor screen for the user to see. A more technical explanation of a typical TEMs workings is as follows (refer to the diagram below):
1. The "Virtual Source" at the top represents the electron gun, producing a stream of monochromatic electrons.
2. This stream is focused to a small, thin, coherent beam by the use of condenser lenses 1 and 2. The first lens(usually controlled by the "spot size knob") largely determines the "spot size"; the general size range of the final spot that strikes the sample. The second lens(usually controlled by the "intensity or brightness knob" actually changes the size of the spot on the sample; changing it from a wide dispersed spot to a pinpoint beam.
3. The beam is restricted by the condenser aperture (usually user selectable), knocking out high angle electrons (those far from the optic axis, the dotted line down the center)
4. The beam strikes the specimen and parts of it are transmitted
5. This transmitted portion is focused by the objective lens into an image
6. Optional Objective and Selected Area metal apertures can restrict the beam; the Objective aperture enhancing contrast by blocking out high-angle diffracted electrons, the Selected Area aperture enabling the user to examine the periodic diffraction of electrons by ordered arrangements of atoms in the sample
7. The image is passed down the column through the intermediate and projector lenses, being enlarged all the way
8. The image strikes the phosphor image screen and light is generated, allowing the user to see the image. The darker areas of the image represent those areas of the sample that fewer electrons were transmitted through (they are thicker or denser). The lighter areas of the image represent those areas of the sample that more electrons were transmitted through (they are thinner or less dense)
[img]http://www.unl.edu/CMRAcfem/gifs/tem2.gif[/img][/quote]
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nanoquebec 2006-11-16 10:04
SEM and FIB
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The manufactoring and characterization of smallest structures play a key role in the field of modern micro-/nanoelectronics and related areas. Systems for ion beam milling utilizing a focuses ion beam (FIB) become increasingly important. These systems have been commercially available for more than ten years mostly applied in semiconductor research.
More recently, FIB technology has supported development of next-generation microelectronic devices1, microelectromechanical systems (MEMS)2,3, research into novel materials4,5, and manufacturing of scanning probe tips6,7. Application examples include transmission electron microscope (TEM) sample preparation8, failure analysis of semiconductor devices9,10, integrated circuit device repair11, maskless focused ion beam lithography12, and ion beam assisted deposition13. An excellent overview on the fundamental principles and applications is given by Melngailis14 and more recently by Reyntjens and Puers15.
The fundamental operation principle of FIB systems is comparable to scanning electron microscopes (SEM). However, instead of an electron beam, a finely focused beam of ions with a diameter down to approx. 5 nm is applied. As shown schematically, an ion beam emitted from a liquid metal (alloy) field ionization source is focused onto the sample surface by a set of electrostatic lenses. In the case of an alloy ion source, a mass separator enables selection of the desired ionic species. Operating the primary ion beam at low beam currents allows imaging of the sample; at high beam currents sputtering or milling processes are induced.
Surface collision with energetic ions leads to sputtered material which leaves the surface either as secondary ions or neutral atoms (substrate milling). Furthermore, secondary electrons are generated at the surface. If the beam is scanned across the sample surface the signal generated by the secondary ions or electrons may be collected for imaging purposes with resolution in the nanometer range. At high primary ion beam currents significant material ablation is induced enabling precise milling, cutting drilling and structuring at the nanolevel. While e-beam lithography allows nanofabrication with higher lateral resolution, for many of the proposed applications short processing time (e.g. prototyping and characterization of novel devices and structures) and high throughput (e.g. TEM sample preparation) is an essential need.
Among the most compelling features of the dualbeam instrumentation is the integration of field emission scanning electron microscopy and focused ion beam technology into one FIB/SEM system.
One examples for FIB manufacturing
[img]http://www.brucherseifer.com/assets/images/fib_05e.gif[/img]
FIB-milling of a gold layer on silicon simultaneously observed with SEM
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[1] F. A. Stevie, et. al., Surf. Interface Anal. 23, 61 (1995).
[2] T.W. Kim, et. al., Appl. Phys. Lett. 80, 2168 (2002).
[3] G.M. Kim, et. al. Microelectr. Engineering 67-68, 609 (2003).
[4] R. Hull, et. al., Materials Research Society Symposium Proc. 523, 141 (1998).
[5] N. Motta, J. Phys. Cond. Matter 14, 8353 (2002).
[6] A. Olbrich, et. al., J. Vacuum Sci. & Technol. B, 17, 1570 (1999).
[7] J.R. Krogmeier, et. al., Appl. Phys. Lett., 79, 4494 (2001).
[8] H. Bender, Eds. B. O. Kolbesen et al, Elchem. Soc. Pennington 99, 232 (1999).
[9] M. Abramo, et. al., Semicond. International, 133 (1997).
[10] D. Verkleij, Microelectron. Reliab. 38, 869 (1998).
[11] K. N. Hooghan, et. al., Proc. 25th Int. Symp. f. Test. a. Fail. Anal. 247 (1999).
[12] J. Melngailis, Nuclear Instr. and Meth. in Phys. Res., B80/81, 1271 (1993).
[13] E.J. Sanchez, et. al., Rev. Sci. Instr. 73, 3901 (2002).
[14] J. Melngailis, J. Vac. Sci. Technol. B, 5, 469 (1987).
[15] S. Reyntjens, et. al., J. Micromech. Microeng., 11, 287 (2001).
nanoquebec 2006-11-16 10:06
http://www.rodenburg.org/guide/index.html
[size=4]Learn to use a TEM quickly...
[quote][size=4][color=blue]
[i]Tutorials:[/i]
TEM alignment
STEM alignment
Wave interference
[i]Research:[/i]
Diffractive imaginging
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1. A single lens: get hands-on experience right from the start
2. Understand shift and tilt
3. : this is how we correct misalignments. We also practice adjusting an aperture position Two or more lenses: understand how the microscope magnifies and learn how to take an image
4. The gun: learn how to turn on the beam
5. The condenser system: understand how to align two lenses
6. Astigmatism
7. : Learn to adjust this important variable The objective lens: understand the heart of the electron microscope, and how the other lenses fit above and below the objective
8. Eucentric height: all about where the specimen sits
9. Pivots points: understand why you have to get those two blobs to be coincident
10. Diffraction mode: understand the next most important mode after 'image mode'
11. . The schemetic diagram
12. : Understand the entire microscope Twin objective lens
13. : Understand the pre-field and other realities The computer
14. : What I love to hate... Alignment schedules
15. : and other alignment hints The vacuum system:
16. In brief Gun tilt
17. : A more advanced discussion Focussing the diffraction pattern
18. : more advanced details Homepage
: With sections on STEM alignment and elementary theory of electron interference
Alphabetical list of subjects
These links point to the page where the term is first introduced...
* alignment (general)
* alignment coils
* aperture mechanism
* astigmatism
* beam stopper
* bias
* binoculars
* brightness
* CCD camera
* cold finger
* coma-free axis
* computer control
* condenser aperture
* condenser astigmatism
* condenser system
* current centre
* deflection coils
* differential pumping aperture
* diffraction lens
* diffusion pump
* diffraction lens and diffraction mode
* diffraction mode
* double deflection coils
* emission
* eucentric height
* exposure meter
* filament
* filament saturation
* fine focus
* focus
* focus diffraction pattern
* focus step size
* Fraunhofer diffraction
* getter
* gun
* gun align
* gun shift
* gun tilt
* gun tilt (advanced)
* High tension
* high vacuum pump
* HT
* intensity
* intermediate lens
* ion pump
* magnification
* multifunction knobs
* objective focus
* objective lens
* optic axis
* optical analogue
* over-focus
* Pirani gauge
* pivot points
* photographic film
* projector system
* pure shift
* pure tilt
* reversal centre
* riot act
* rocking point
* roughing manifold
* rough pump
* rule of rays
* saturation (filament)
* selected area aperture
* shift purity
* shift-x (electrical shift)
* shift-y (electrical shift)
* specimen height
* specimen shift
* specimen loading
* spreading the beam
* spot size
* STEM and STEM/TEM alignment
* stigmator sensitivity
* tilt purity
* trap
* turbo pump
* turn off the beam
* turn on the beam
* twin objective lens
* UHV
* under-focus
* vacuum gauges
* voltage centre
* weak lens
* z-shift
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For more information, please visit website
[b]http://www.rodenburg.org/guide/index.html
[/b]
nanochip 2007-10-27 18:19
Scanning Electron Microscopy (SEM)
What is Scanning Electron Microscopy
[url=http://serc.carleton.edu/images/research_education/geochemsheets/techniques/UWSEM.jpg][img]http://serc.carleton.edu/images/research_education/geochemsheets/techniques/UWSEM_250.jpg[/img][/url]
[i]
A typical SEM instrument, showing theelectron column, sample chamber, EDS detector, electronics console, andvisual display monitors.[/i]
The scanning electron microscope(SEM) uses a focused beam of high-energy electrons to generate avariety of signals at the surface of solid specimens. The signals thatderive from [url=http://serc.carleton.edu/research_education/geochemsheets/electroninteractions.html]electron-sample interactions[/url]reveal information about the sample including external morphology(texture), chemical
composition, and crystalline structure andorientation of materials making up the sample. In most applications,data are collected over a selected area of the surface of the sample,and a 2-dimensional image is generated that displays spatial variationsin these properties. Areas ranging from approximately 1 cm to 5 micronsin width can be imaged in a scanning mode using conventional SEMtechniques (magnification ranging from 20X to approximately 30,000X,spatial resolution of 50 to 100 nm). The SEM is also capable ofperforming analyses of selected point locations on the sample; thisapproach is especially useful in qualitatively or semi-quantitativelydetermining chemical compositions (using [url=http://serc.carleton.edu/research_education/geochemsheets/eds.html]EDS[/url]), crystalline structure, and crystal orientations (using [url=http://serc.carleton.edu/research_education/geochemsheets/ebsd.html]EBSD[/url]). The design and function of the SEM is very similar to the [url=http://serc.carleton.edu/research_education/geochemsheets/techniques/EPMA.html]EPMA[/url], and considerable overlap in capabilities exists between the two instruments.Fundamental Principles of Scanning Electron Microscopy (SEM)Acceleratedelectrons in an SEM carry significant amounts of kinetic energy, andthis energy is dissipated as a variety of signals produced by [url=http://serc.carleton.edu/research_education/geochemsheets/electroninteractions.html]electron-sample interactions[/url]when the incident electrons are decelerated in the solid sample. Thesesignals include secondary electrons (that produce SEM images),backscattered electrons ([url=http://serc.carleton.edu/research_education/geochemsheets/bse.html]BSE[/url]), diffracted backscattered electrons ([url=http://serc.carleton.edu/research_education/geochemsheets/ebsd.html]EBSD[/url] that are used to determine crystal structures and orientations of minerals), photons ([url=http://serc.carleton.edu/research_education/geochemsheets/xrays.html]characteristic X-rays[/url] that are used for elemental analysis and continuum X-rays), visible light ([url=http://serc.carleton.edu/research_education/geochemsheets/semcl.html]cathodoluminescence--CL[/url]),and heat. Secondary electrons and backscattered electrons are commonlyused for imaging samples: secondary electrons are most valuable forshowing morphology and topography on samples and backscatteredelectrons are most valuable for illustrating contrasts in compositionin multiphase samples (i.e. for rapid phase discrimination). [url=http://serc.carleton.edu/research_education/geochemsheets/xrays.html]X-ray generation[/url]is produced by inelastic collisions of the incident electrons withelectrons in discrete ortitals (shells) of atoms in the sample. As theexcited electrons return to lower energy states, they yield X-rays thatare of a fixed wavelength (that is related to the difference in energylevels of electrons in different shells for a given element). Thus,characteristic X-rays are produced for each element in a mineral thatis "excited" by the electron beam. SEM analysis is considered to be"non-destructive"; that is, x-rays generated by electron interactionsdo not lead to volume loss of the sample, so it is possible to analyzethe same materials repeatedly.
Scanning Electron Microscopy (SEM) Instrumentation - How Does It Work?[float=right][url=http://serc.carleton.edu/images/research_education/geochemsheets/techniques/SEM_schematic.JPG.jpg][img=250,295]http://serc.carleton.edu/images/research_education/geochemsheets/techniques/SEM_schematic.JPG_250.jpg[/img][/url][/float]
Essential components of all SEMs include the following:[list][*]Electron Source ("Gun")[*]Electron Lenses[*]Sample Stage[*]Detectors for all signals of interest[*]Display / Data output devices[*]Infrastructure Requirements:[list][*]Power Supply[*]Vacuum System[*]Cooling system[*]Vibration-free floor[*]Room free of ambient magnetic and electric fields[/list][/list]SEMs always have at least one detector (usually a secondary electrondetector), and most have additional detectors. The specificcapabilities of a particular instrument are critically dependent onwhich detectors it accommodates.
Applications [float=right][url=http://serc.carleton.edu/images/research_education/geochemsheets/techniques/radio3.gif][img=250,202]http://serc.carleton.edu/images/research_education/geochemsheets/techniques/radio3_250.jpg[/img][/url][/float]
The SEM is routinely used to generate high-resolution imagesof shapes of objects (SEI) and to show spatial variations in chemicalcompositions (usually EDS, also BSE and CL [add images here later]).This instrument is also widely used to identify phases based onqualitative chemical analysis and/or crystalline structure [add imageshere later]. Precise measurement of measurement of very small featuresand objects down to 50 nm in size is also accomplished using the SEM.Backescattered electron images can be used for rapid discrimination ofphases in multiphase samples. SEMs equipped with diffractedbackscattered electron detectors can be used to examine microfabric andcrystallographic orientation in many materials.Strengths and Limitations of Scanning Electron Microscopy (SEM)? StrengthsThereis arguably no other instrument with the breadth of applications in thestudy of solid materials that compares with the SEM. The SEM iscritical in all fields that require characterization of solidmaterials. While this contribution is most concerned with geologicalapplications, it is important to note that these applications are avery small subset of the scientific and industrial applications thatexist for this instrumentation. Most SEM's are comparatively easy tooperate, with user-friendly "intuitive" interfaces. Many applicationsrequire minimal sample preparation. For many applications, dataacquisition is rapid (less than 5 minutes/image for SEI, BSE, spot EDSanalyses.) Modern SEMs generate data in digital formats, which arehighly portable.
LimitationsSamples must be solid and they must fitinto the microscope chamber. Maximum size in horizontal dimensions isusually on the order of 10 cm, vertical dimensions are generally muchmore limited and rarely exceed 40 mm. For most instruments samples mustbe stable in a vacuum on the order of 10-5 - 10-6torr. Samples likely to outgas at low pressures (rocks saturated withhydrocarbons, "wet" samples such as coal, organic materials or swellingclays, and samples likely to decrepitate at low pressure) areunsuitable for examination in conventional SEM's. However, "low vacuum"and "environmental" SEMs also exist, and many of these types of samplescan be successfully examined in these specialized instruments. [url=http://serc.carleton.edu/research_education/geochemsheets/eds.html]EDS detectors[/url]on SEM's cannot detect very light elements (H, He, and Li), and manyinstruments cannot detect elements with atomic numbers less than 11(Na). Most SEMs use a solid state x-ray detector ([url=http://serc.carleton.edu/research_education/geochemsheets/eds.html]EDS[/url]),and while these detectors are very fast and easy to utilize, they haverelatively poor energy resolution and sensitivity to elements presentin low abundances when compared to wavelength dispersive x-raydetectors ([url=http://serc.carleton.edu/research_education/geochemsheets/wds.html]WDS[/url]) on most electron probe microanalyzers ([url=http://serc.carleton.edu/research_education/geochemsheets/techniques/epma.html]EPMA[/url]).An electrically conductive coating must be applied to electricallyinsulating samples for study in conventional SEM's, unless theinstrument is capable of operation in a low vacuum mode.
User's Guide - Sample Collection and Preparation Samplepreparation can be minimal or elaborate for SEM analysis, depending onthe nature of the samples and the data required. Minimal preparationincludes acquisition of a sample that will fit into the SEM chamber andsome accommodation to prevent charge build-up on electricallyinsulating samples. Most electrically insulating samples are coatedwith a thin layer of conducting material, commonly carbon, gold, orsome other metal or alloy. The choice of material for conductivecoatings depends on the data to be acquired: carbon is most desirableif elemental analysis is a priority, while metal coatings are mosteffective for high resolution electron imaging applications.Alternatively, an electrically insulating sample can be examinedwithout a conductive coating in an instrument capable of "low vacuum"operation.
Data Collection, Results and Presentation
Representative SEM images of asbestiform minerals from the
[url=http://usgsprobe.cr.usgs.gov/index.html]USGS Denver Microbeam Laboratory[/url]
[url=http://serc.carleton.edu/images/research_education/geochemsheets/techniques/chrysotile.jpg][img=300,300]http://serc.carleton.edu/images/research_education/geochemsheets/techniques/chrysotile_300.jpg[/img][/url][url=http://serc.carleton.edu/images/research_education/geochemsheets/techniques/asbestos_2.jpg][img=300,300]http://serc.carleton.edu/images/research_education/geochemsheets/techniques/asbestos_2_300.jpg[/img][/url]
UICC Asbestos Chrysotile 'A' standard Tremolite asbestos, Death Valley, California
[url=http://serc.carleton.edu/images/research_education/geochemsheets/techniques/asbestos_3.jpg][img=300,300]http://serc.carleton.edu/images/research_education/geochemsheets/techniques/asbestos_3_300.jpg[/img][/url][url=http://serc.carleton.edu/images/research_education/geochemsheets/techniques/asbestos_4.jpg][img=300,300]http://serc.carleton.edu/images/research_education/geochemsheets/techniques/asbestos_4_300.jpg[/img][/url]
Anthophyllite asbestos, Georgia Winchite-richterite asbestos, Libby, Montana
Literature
The following literature can be used to further explore Scanning Electron Microscopy (SEM)
[list][*]Goldstein, J. (2003) Scanning electron microscopy and x-ray microanalysis. Kluwer Adacemic/Plenum Pulbishers, 689 p.[*]Reimer, L. (1998) Scanning electron microscopy : physics of image formation and microanalysis. Springer, 527 p.[*]Egerton, R. F. (2005) Physical principles of electron microscopy : an introduction to TEM, SEM, and AEM. Springer, 202.[*]Clarke, A. R. (2002) Microscopy techniques for materials science. CRC Press (electronic resource)[/list] Related LinksFor more information about Scanning Electron Microscopy (SEM) follow the links below.
[list][*][url=http://www.microbeamanalysis.org/masjh/GSA/gsa.php]Microbeam Analysis Society[/url]- contains GSA presentations from the 'Teaching Instrumentation toGeoscience Students: Course design, objectives and presentations'session[/list]
[url=http://serc.carleton.edu/research_education/geochemsheets/techniques/SEM.html]http://serc.carleton.edu/researc ... techniques/SEM.html[/url]
[[i] 本帖最后由 vanaxu 于 2007-10-27 18:36 编辑 [/i]]
baogangguo 2007-10-28 13:05
好好学习一下！！！！
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