查看完整版本: Closing the Imaging Gap Between Optical and Electron Microscopy

Closing the Imaging Gap Between Optical and Electron Microscopy

[color=DarkGreen][size=4][font=黑体]一种重要的新型显微镜填补了光学和电子显微镜之间的成像空白[/font][/size]
!Ke.z*^,s2S A new tabletop SEM combines the high magnification of electronmicroscopy with the ease of use of optical microscopy to improveperformance in a benchtop instrument.[/color]
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[color=DarkGreen]A radical new breed of microscope fills the critical gap betweenoptical and electron microscopy. Optical microscopes are easy to usebut generally limited to useful magnifications of 1,000x or less.Electron microscopes routinely operate at magnifications of 100,000xbut can also be orders of magnitude more difficult to operate. The newmicroscopes, known commonly as tabletop or benchtop scanning electronmicroscopes (SEM), provide useful magnifications up to 20,000x and areas easy to use as the typical laboratory-grade optical microscopes. [/color]
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[color=DarkGreen]The new instruments could not have come at a better time since theperformance gap they fill corresponds to the ability to resolvefeatures with sizes between 5 nm and 100 nm, a range that is criticalin the booming field of nanotechnology. Microelectronics,microelectromechanical systems (MEMS), composite materials, andpharmaceuticals are but a few of the most obvious technologies with apressing need for fast, easy access to structural and morphologicalcharacterization in this size range.[/color] `~%^J
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[font=verdana][size=1] [i][b]The tabletop Phenom. All images: FEI Co.[/b][/i][/size][/font]
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[color=DarkGreen]The most striking development in the new tabletop SEM is its ease ofuse. Although small, inexpensive SEMs have been introduced more thanonce over the half century history of the technology, their widespreadacceptance has been hindered by their operational difficulty. One ofthe new tabletop SEMs, the Phenom, from FEI Co., Hillsboro, Ore., is aseasy to use as an optical microscope and accepts virtually any samplethat will fit into the sample holder. Achieving this level ofoperational simplicity required much more than simply scaling downexisting SEM technology; it required a redesign of many of themicroscope’s core components. [/color]oppL8H azA

q'H/eG9a/Y6F [b]Back to basics[/b]A'_? vY K
[color=DarkGreen]Optical microscopes use transparent lenses to focus light from thespecimen into a real image, either directly onto the retina of the eyeor into a camera or digital imaging system for capture and storage.SEMs create a virtual image by scanning a finely focused beam ofelectrons over the sample surface and mapping the intensity of varioussignals emitted at each point into an image array that is captured anddisplayed electronically. [/color]
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[color=DarkGreen]Operating an optical microscope requires little more than placing thesample on the stage and focusing the image and is usually accomplishedin a matter of seconds. Conventional SEMs, which require a high vacuumin the sample chamber, typically require several minutes to pump downthe sample chamber in addition to any preparation required to make thesample compatible with the vacuum (cleaning, drying, coating techniquesetc.). The time required to get an SEM image can easily become manyminutes or hours. The Phenom cuts away the time, difficulty, andexpense of the conventional SEM. The operator simply places the samplein the sample holder on the microscope. The automatically focused imageis displayed less than 30 seconds later, with the resolution and depthof field typical of full-size SEMs.[/color] L6nj%X^@H5d"f@
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[font=verdana][color=DarkGreen][size=1] [i][b]Tabletop SEMs can be used in forensic analysis, showing traces of materials found on clothing, such as this diatom.[/b][/i] [/size][/color][/font] Z.]/A;`3R
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n:Q3M$UP [font=verdana][color=DarkGreen][size=1] [i][b]A quick look with a tabletop SEM at bulk particles can show their morphology. This sample has primarily spheroidal morphology.[/b][/i] [/size][/color][/font]
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0tdy%p/Z6P*b [b]Improving performance[/b]Igq7]d&f3Pt+c
[color=DarkGreen]To achieve this level of performance, engineers focused on a few basicrequirements: size (including facility requirements), image quality,sample requirements, and easy operation.[/color]O"r"i8IGx"v'T
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[b]Size[/b][color=DarkGreen] –Successful imaging at high magnification in aconventional SEM requires a quiet environment. The presence of generallab equipment and a lively, vocal workforce in the same room as the SEMcauses vibrations that distort the image. It is not unusual for acustomized SEM room to cost as much as the SEM itself. [/color]ig0h(f+\(B/J+MXT P

*zAu"t,L [color=DarkGreen]The SEM’s sensitivity to vibration is a function of the resonantfrequency of the column and sample holder, determined primarily by itslength and diameter. The Phenom’s miniaturized column is approximately10 times smaller than a conventional SEM column and is energized bypermanent magnets rather than the commonly used electromagnets. Thesample holder is also smaller and rigidly mounted to the SEM column.The result is a dramatic increase in the resonant frequency and asystem that is virtually unaffected by the noise and vibration of atypical lab environment.[/color]
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*J#opC] d^] [b]Image quality[/b][color=DarkGreen] –The key determinants of image qualityin an SEM are resolution and signal-to-noise ratio. In simple terms,these factors are themselves determined by the choice of electronsource and the accelerating voltage of the electrons. SEMs use one ofthree types of electron sources. Field emission sources produce veryhigh resolution but require expensive high vacuum systems inconsistentwith the cost and sample requirements of a tabletop SEM. At the otherextreme, tungsten sources have the lowest vacuum requirements but needto operate at relatively high accelerating voltages to provideacceptable signal-to-noise characteristics. Unfortunately, increasingthe accelerating voltage decreases the image resolution as a result ofelectron penetration into the sample. The third choice, LaB6, hasproperties and requirements that lie between those of field emissionand tungsten sources. As a result, this type of source can be run at5kV, providing the optimal combination of resolution andsignal-to-noise in a tabletop SEM.[/color]q'n+q@d

!j&a1V8q;@9yJ EBz3BJ [b]Sample requirements[/b][color=DarkGreen] –The vacuum requirements in anSEM’s sample chamber affect many aspects of its operation. Highersample chamber vacuum requirements increase pump down and sampleexchange time and impose tighter constraints on sample type andcondition. The Phenom’s sliding vacuum seal reduces chamber volume andsample exchange time. Reduced vacuum levels in the chamber alsocontribute to faster sample exchange, but, more importantly, relax theconstraints on sample type. FEI pioneered the development of low vacuum(ESEM) technologies that allow just about any sample that will fit inthe holder, with little or no need for coating, cleaning, drying orother preparations.[/color]
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1['sN-V+gQHQ$},{0A [b]Ease of use[/b][color=DarkGreen]—Perhaps the most important characteristicof a lab instrument is its ease of use. A traditional electronmicroscope has an often bewildering user interface with an extremelylarge set of choices and parameters to optimize. A large majority ofthe variables of a traditional SEM are not needed in a workhorse tool.By eliminating variables, automating adjustments, and creative softwaredesign, the Phenom has reduced operating the microscope to driving thestage and changing the magnification. With this kind of softwareinterface, training a novice to use the system takes a matter ofminutes— the instrument becomes productive almost immediately.[/color]
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[font=verdana][color=DarkGreen][size=1] [i][b]This image of a fruit fly shows the underside of the head.  One of the compound eyes, the mandible, and two palps are visible.[/b][/i]  [/size][/color][/font]
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kf1]BS#T [b]Industrial applications[/b][color=DarkGreen]SEMs are used in many fields of industry, such as pharmaceuticals,composite materials, and life science. These industries, as well asmany others, will benefit from the new tabletop SEMs in characterizingstructures and morphologies in the nanometer range easily and quicklyin the lab. Some industrial applications include:[/color]
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[b]Particle characterization:[/b][color=DarkGreen] Size, distribution, andmorphology of particles and powders are critical parameters forindustries such as pharmaceuticals, composites, cosmetics, andcatalysts. [/color]9ieZ1j)_ M
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[color=DarkGreen]Often these measurements are derived from bulk analyses such as laserscattering; however, interpreting the data requires some knowledge ofthe particles themselves, i.e., are they spherical, rod-shaped, a mixof large and very small particles, etc. Tabletop microscopes withmagnification ranges up to 20,000x are ideal for this requirement. A“quick look” at these materials can greatly improve the efficiency ofanalysis and characterization. Measuring the dimensions and uniformityof coatings is also of critical importance in materials research. [/color]
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[b]Quality assurance in MEMS:[/b][color=DarkGreen] MEMS are miniaturizedcomponents commonly used in high volume, low-cost applications, such asthe automotive and electronic industries. One of the most commonapplications is the use of a MEMS accelerometer inside automotive airbags. The reliability of this class of device is paramount soinspection and quality assurance are frequent steps in themanufacturing process. Images of 3-D objects at magnifications in therange 100-5,000 are required, which is a task ideally suited for atabletop SEM microscope. [/color]jfl:h?/^YX.M
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[color=DarkGreen]Crime scene investigation: Forensic scientists have long usedmicroscopic images as an aid to their investigations, and the trend inthis field is to look at finer and finer levels of detail. Traces offoreign material found on clothing can often be used to help establishwhere the clothing has been. For example, the presence of a specificspecies of pollen can potentially indicate a particular area where theclothing must have been. Similarly, the presence of specific species ofalgae attached to clothing can indicate conclusively that the clothinghas been in water and potentially which body of water.[/color]
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_,kA$BD~0Em [color=DarkGreen]It is a common complaint that increasingly fewer students are enrollingin science and technology degree programs. Of the many reasons for thisdecline, one seems to be perennial: the difficulty for students tobecome excited about science when it is so hard to visualize andinternalize the basic concepts. The opportunity to have an easy tolearn and easy to use use table top electron microscope inside theclassroom could help mitigate this problem. [/color]
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[color=DarkGreen][color=Purple]This new class of tabletop microscope that goes far beyond theresolution capabilities of a light microscope, but does not require allthe cost and complexity of using a typical scanning electronmicroscope, will find applications in many industries and educationalenvironments. It is not unreasonable to speculate that this capabilitycould have the same kind of effect on the efficiency of development of new methods and materials as the PC had on the productivity of the office.[/color][/color]
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T*\&{q2ns [color=DarkGreen]—[/color][b]Steven Berger[/b][color=DarkGreen], Senior Vice President, [/color](DW9v]M k0y
[color=DarkGreen]—[/color][b]Diane Stewart[/b][color=DarkGreen], Senior Manager, Business Development,FEI Co., Newburyport, Mass., [/color][url=http://www.fei.com/]www.fei.com[/url]
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\AM rp1t8?%Cze [color=DarkGreen]Source：[/color][img]http://rdmag.com/images/logo.gif[/img] y^V(i,O!eL/@LG

)p(Q{C!Ic(Yq;MS(g [[i] 本帖最后由 vanaxu 于 2007-08-20 12:23 编辑 [/i]]

Very good, thanks for sharing!

确实是一大进展，相关的一则短评在我们的论坛里可以看看
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