SEMSEM是scanning electron microscope的缩写，中文即扫描电子显微镜，扫描电子显微镜的设计思想和工作原理，早在1935年便已被提出来了。1942年，英国首先制成一台实验室用的扫描电镜，但由于成像的分辨率很差，照相时间太长，所以实用价值不大。经过各国科学工作者的努力，尤其是随着电子工业技术水平的不断发展，到1956年开始生产商品扫描电镜。近数十年来，扫描电镜已广泛地应用在生物学、医学、冶金学等学科的领域中，促进了各有关学科的发展。
目录
特点
扫描电镜的结构
1．镜筒
2．电子信号的收集与处理系统
3．电子信号的显示与记录系统
4．真空系统及电源系统
工作原理
在化学化工里，SEM是scanning electron microscope的缩写，指扫描电子显微镜是一种常用的材料分析手段。
扫描电子显微镜于20世纪60年代问世，用来观察标本的表面结构。其工作原理是用一束极细的电子束扫描样品，在样品表面激发出次级电子，次级电子的多少与电子束入射角有关，也就是说与样品的表面结构有关，次级电子由探测体收集，并在那里被闪烁器转变为光信号，再经光电倍增管和放大器转变为电信号来控制荧光屏上电子束的强度，显示出与电子束同步的扫描图像。图像为立体形象，反映了标本的表面结构。为了使标本表面发射出次级电子，标本在固定、脱水后，要喷涂上一层重金属微粒，重金属在电子束的轰击下发出次级电子信号。 目前扫描电镜的分辨力为6~10nm，人眼能够区别荧光屏上两个相距0.2mm的光点，则扫描电镜的最大有效放大倍率为0.2mm/10nm=20000X。 它是依据电子与物质的相互作用。当一束高能的人射电子轰击物质表面时，被激发的区域将产生二次电子、俄歇电子、特征x射线和连续谱X射线、背散射电子、透射电子，以及在可见、紫外、红外光区域产生的电磁辐射。同时，也可产生电子-空穴对、晶格振动（声子）、电子振荡（等离子体）。原则上讲，利用电子和物质的相互作用，可以获取被测样品本身的各种物理、化学性质的信息，如形貌、组成、晶体结构、电子结构和内部电场或磁场等等。扫描电子显微镜正是根据上述不同信息产生的机理，采用不同的信息检测器，使选择检测得以实现。如对二次电子、背散射电子的采集，可得到有关物质微观形貌的信息；对x射线的采集，可得到物质化学成分的信息。
编辑本段特点
和光学显微镜及透射电镜相比，扫描电镜SEM（Scanning Electron Microscope）具有以下特点： (一) 能够直接观察样品表面的结构，样品的尺寸可大至120mm×80mm×50mm。 (二) 样品制备过程简单，不用切成薄片。 (三) 样品可以在样品室中作三度空间的平移和旋转，因此，可以从各种角度对样品进行观察。 (四) 景深大，图象富有立体感。扫描电镜的景深较光学显微镜大几百倍，比透射电镜大几十倍。 (五) 图象的放大范围广，分辨率也比较高。可放大十几倍到几十万倍，它基本上包括了从放大镜、光学显微镜直到透射电镜的放大范围。分辨率介于光学显微镜与透射电镜之间，可达3nm。 (六) 电子束对样品的损伤与污染程度较小。 (七) 在观察形貌的同时，还可利用从样品发出的其他信号作微区成分分析。
编辑本段扫描电镜的结构
编辑本段1．镜筒
镜筒包括电子枪、聚光镜、物镜及扫描系统。其作用是产生很细的电子束(直径约几个nm)，并且使该电子束在样品表面扫描，同时激发出各种信号。
编辑本段2．电子信号的收集与处理系统
在样品室中，扫描电子束与样品发生相互作用后产生多种信号，其中包括二次电子、背散射电子、X射线、吸收电子、俄歇(Auger)电子等。在上述信号中，最主要的是二次电子，它是被入射电子所激发出来的样品原子中的外层电子，产生于样品表面以下几nm至 几十nm的区域，其产生率主要取决于样品的形貌和成分。通常所说的扫描电镜像指的就是二次电子像，它是研究样品表面形貌的最有用的电子信号。检测二次电子的检测器(图15(2)的探头是一个闪烁体，当电子打到闪烁体上时，1就在其中产生光，这种光被光导管传送到光电倍增管，光信号即被转变成电流信号，再经前置放大及视频放大，电流信号转变成电压信号，最后被送到显像管的栅极。
编辑本段3．电子信号的显示与记录系统
扫描电镜的图象显示在阴极射线管(显像管)上，并由照相机拍照记录。显像管有两个，一个用来观察，分辨率较低，是长余辉的管子；另一个用来照相记录，分辨率较高，是短余辉的管子。
编辑本段4．真空系统及电源系统
扫描电镜的真空系统由机械泵与油扩散泵组成，其作用是使镜筒内达到 10(4～10(5托的真空度。电源系统供给各部件所需的特定的电源。
编辑本段工作原理
从电子枪阴极发出的直径20(m～30(m的电子束，受到阴阳极之间加速电压的作用，射向镜筒，经过聚光镜及物镜的会聚作用，缩小成直径约几毫微米的电子探针。在物镜上部的扫描线圈的作用下，电子探针在样品表面作光栅状扫描并且激发出多种电子信号。这些电子信号被相应的检测器检测，经过放大、转换，变成电压信号，最后被送到显像管的栅极上并且调制显像管的亮度。显像管中的电子束在荧光屏上也作光栅状扫描，并且这种扫描运动与样品表面的电子束的扫描运动严格同步，这样即获得衬度与所接收信号强度相对应的扫描电子像，这种图象反映了样品表面的形貌特征。 扫描电镜样品制备的主要要求是：尽可能使样品的表面结构保存好，没有变形和污染，样品干燥并且有良好导电性能。 另外，扫描电镜生物样品制备技术大多数生物样品都含有水分，而且比较柔软，因此，在进行扫描电镜观察前，要对样品作相应的处理。
开放分类：
搜索引擎，网络推广，网络营销，seo，百度SEM
2.搜索引擎营销 编辑本义项求助编辑sem目录
目标层次原理
服务方式一、 竞价排名
二、 购买关键词广告
三、 搜索引擎优化（SEO）
四、点击付费广告
SEM是Search Engine Marketing的缩写，中文意思是搜索引擎营销。SEM是一种新的网络营销形式。SEM所做的就是全面而有效的利用搜索引擎来进行网络营销和推广。SEM追求最高的性价比，以最小的投入，获最大的来自搜索引擎的访问量，并产生商业价值。 现在随着互联网的深入生活，方便人们的生活，例如现在大家都普遍使用的B2C网站，还有网上缴费等等，很多都运用了SEM。
编辑本段目标层次原理
搜索引擎营销可分为四个层次，可分别简单描述为：存在层、表现层、关注层和转化层。 第一层是搜索引擎营销的存在层，其目标是在主要的搜索引擎/分类目录中获得被收录的机会，这是搜索引擎营销的基础之一，第二个基础是通过竞价排名方式出现在搜索引擎中，离开这两个个层次，搜索引擎营销的其他目标也就不可能实现。搜索引擎登录包括免费登录、付费登录、搜索引擎关键词广告等形式。存在层的含义就是让网站中尽可能多的网页获得被搜索引擎收录（而不仅仅是网站首页），也就是为增加网页的搜索引擎可见性。 第二层的目标则是在被搜索引擎收录的基础上尽可能获得好的排名，即在搜索结果中有良好的表现，因而可称为表现层。因为用户关心的只是搜索结果中靠前的少量内容，如果利用主要的关键词检索时网站在搜索结果中的排名靠后，那么还有必要利用关键词广告、竞价广告等形式作为补充手段来实现这一目标。同样，如果在分类目录中的位置不理想，则需要同时考虑在分类目录中利用付费等方式获得排名靠前。 搜索引擎营销的第三个目标则直接表现为网站访问量指标方面，也就是通过搜索结果点击率的增加来达到提高网站访问量的目的。由于只有受到用户关注，经过用户选择后的信息才可能被点击，因此可称为关注层。从搜索引擎的实际情况来看，仅仅做到被搜索引擎收录并且在搜索结果中排名靠前是不够的，这样并不一定能增加用户的点击率，更不能保证将访问者转化为顾客。要通过搜索引擎营销实现访问量增加的目标，则需要从整体上进行网站优化设计，并充分利用关键词广告等有价值的搜索引擎营销专业服务。 搜索引擎营销的第四个目标，即通过访问量的增加转化为企业最终实现收益的提高，可称为转化层。转化层是前面三个目标层次的进一步提升，是各种搜索引擎方法所实现效果的集中体现，但并不是搜索引擎营销的直接效果。从各种搜索引擎策略到产生收益，期间的中间效果表现为网站访问量的增加，网站的收益是由访问量转化所形成的，从访问量转化为收益则是由网站的功能、服务、产品等多种因素共同作用而决定的。因此，第四个目标在搜索引擎营销中属于战略层次的目标。其他三个层次的目标则属于策略范畴，具有可操作性和可控制性的特征，实现这些基本目标是搜索引擎营销的主要任务。目前搜索营销，逐步被人们认识和运用。
编辑本段服务方式
一、 竞价排名
顾名思义就是网站付费后才能被搜索引擎收录并靠前排名，付费越高者排名越靠前；竞价排名服务，是由客户为自己的网页购买关键字排名，按点击计费的一种服务。客户可以通过调整每次点击付费价格，控制自己在特定关键字搜索结果中的排名；并可以通过设定不同的关键词捕捉到不同类型的的目标访问者。 而在国内最流行的点击付费搜索引擎有百度，雅虎和Google。值得一提的是即使是做了PPC（Pay Per Click，按照点击收费）付费广告和竞价排名，最好也应该对网站进行搜索引擎优化设计，并将网站登录到各大免费的搜索引擎中。
二、 购买关键词广告
即在搜索结果页面显示广告内容，实现高级定位投放，用户可以根据需要更换关键词，相当于在不同页面轮换投放广告；
三、 搜索引擎优化（SEO）
SEO（Search Engine Optimization），汉译为搜索引擎优化，是较为流行的网络营销方式，主要目的是增加特定关键字的曝光率以增加网站的能见度，进而增加销售的机会。分为站外SEO和站内SEO两种。SEO的主要工作是通过了解各类搜索引擎如何抓取互联网页面、如何进行索引以及如何确定其对某一特定关键词的搜索结果排名等技术，来对网页进行相关的优化，使其提高搜索引擎排名，从而提高网站访问量，最终提升网站的销售能力或宣传能力的技术。 seo就是通过对网站结构、关键字选择、网站内容规划进行调整和优化，使得网站在搜索结果中靠前。 搜索引擎优化（seo）又包括网站内容优化、关键词优化、外部链接优化、内部链接优化、代码优化、图片优化、搜索引擎登录等。 PPC 为 Pay Per Click的缩写 PPC是英文Pay Per Click的缩写形式,其中文意思就是点击付费广告。 目前，SEM正处于发展阶段，它将成为今后专业网站乃至电子商务发展的必经之路。 SEO是属于SEM的一部分，是实现SEM搜索引擎整合营销的一种手段。
四、点击付费广告
英文为PPC，是Pay Per Click的缩英文写 其中文意思就是点击付费广告。目前，SEM正处于发展阶段，它将成为今后专业网站乃至电子商务发展的必经之路。
扩展阅读：
1
sem吧 http://tieba.baidu.com/sem
3.经济管理学院 编辑本义项求助编辑semSEM还是School of Economics and Management的缩写，也就是经济管理学院（简称经管学院）的意思。随着市场经济的发展，经管学院正在为社会输送越来越多的管理、会计、金融类人才，为社会的建设与发展做出突出贡献。
4.结构方程模型 编辑本义项求助编辑sem结构方程模型是社会科学研究中的一个非常好的方法。该方法在20世纪80年代就已经成熟，可惜国内了解的人并不多。“在社会科学以及经济、市场、管理等研究领域，有时需处理多个原因、多个结果的关系，或者会碰到不可直接观测的变量（即潜变量），这些都是传统的统计方法不能很好解决的问题。20世纪80年代以来，结构方程模型迅速发展，弥补了传统统计方法的不足，成为多元数据分析的重要工具。 结构方程模型分析:结构方程模型是一种建立、估计和检验因果关系模型的方法。模型中既包含有可观测的显在变量，也可能包含无法直接观测的潜在变量。结构方程模型可以替代多重回归、通径分析、因子分析、协方差分析等方法，清晰分析单项指标对总体的作用和单项指标间的相互关系。
参考资料：SEM是Search Engine Marketing的缩写，中文意思是搜索引擎营销。SEM搜索引擎营销是一种新的网络营销形式。SEM搜索引擎营销所做的就是全面而有效的利用搜索引擎来进行网络营销和推广。SEM搜索引擎营销追求最高的性价比，以最小的投入，获最大的来自搜索引擎的访问量，并产生商业价值。
网络SEM搜索引擎营销整合营销是整合网络资源，综全网站推广。互联网每天都有无数网站崛起，无数网站倒闭，侯庆龙认为，网络整合营销对其方法起到很大的作用。
一、SEM搜索引擎营销
搜索引擎营销是指搜索引擎优化、关键词广告、关键词竞价排名、搜索引擎定位广告搜索引擎在网络营销中的地位尤其重要，每天各行各业的人使用搜索引擎搜索信息。通过搜索引擎营销能直接带来流量与终端客户。
二、电子邮件营销方法
以电子邮件为产品资料、刊物、介绍等方向发送到电子邮件广告等。 基于用户许可的电子邮件营销的推广方式，此种方法对可以提醒用户对产品的了解。
三、资源合作营销方法
网站交换链接、交换广告、内容合作、信息推广、信息合作、用户资源合作等方式，正所谓“人人为我，我为人人”，合作共赢，利益共享，共同发展。
四、网络广告营销方法
网络广告是常用的网络营销方式之一，直接通过网站的广告位置进行投放推广，可以直接借用其他网络媒体推广，网站广告的优势在于:范围广、形式多样、适用性强、投放及时等优点，适合于网站初期营销推广。
五、 信息推广营销方法
把网站的信息发布相关行业网站中，利用用户在访问这些网站同时，了解你网站信息，达到凿壁借光，可以把信息推广发布到黄页、分类广告、论坛、博客网站、供求信息平台、行业网站等，这也是免费网站推广的常用方法之一。
六、 网址营销方法
通过把一些网站信息提交到相关网址导航中，来获取巨大流量，有些网络用户常进入一些网址导航中来查询相关网站信息，而且此种推广，对网站的作用也显而易见。
SEM搜索引擎营销的服务主要有4种方式：
一、 竞价排名，顾名思义就是网站付费后才能被搜索引擎收录并靠前排名，付费越高者排名越靠前；竞价排名服务，是由客户为自己的网页购买关键字排名，按点击计费的一种服务。客户可以通过调整每次点击付费价格，控制自己在特定关键字搜索结果中的排名；并可以通过设定不同的关键词捕捉到不同类型的的目标访问者。
而在国内最流行的点击付费搜索引擎有百度，雅虎和Google。值得一提的是即使是做了PPC（Pay Per Click，按照点击收费）付费广告和竞价排名，最好也应该对网站进行搜索引擎优化设计，并将网站登录到各大免费的搜索引擎中。
二、 购买关键词广告，即在搜索结果页面显示广告内容，实现高级定位投放，用户可以根据需要更换关键词，相当于在不同页面轮换投放广告；
三、 搜索引擎优化（SEO优化），就是通过对网站建设结构、关键字选择、网站内容规划进行调整和优化，使得网站在搜索结果中靠前。 搜索引擎优化（SEO优化）又包括网站内容优化、关键词优化、外部链接优化、内部链接优化、代码优化、图片优化、搜索引擎登录等。
PPC 为 Pay Per Click的缩写 PPC是英文Pay Per Click的缩写形式,其中文意思就是点击付费广告。
目前，SEM正处于发展阶段，它将成为今后专业网站乃至电子商务发展的必经之路。
SEO是属于SEM的一部分，是实现SEM搜索引擎营销搜索引擎整合营销的一种手段。
纯英文，凑合着看吧摘自wiki
(http://en.wikipedia.org/wiki/Electron_Microscope)
Electron microscope
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The electron microscope is a type of microscope that uses electrons to create an image of the target. It has much higher magnification and resolving power than a normal light microscope, up to two million times, allowing it to see smaller objects and details.
Contents [hide]
1 History
2 Electron microscope manufacturers
3 Types
3.1 Transmission Electron Microscope (TEM)
3.2 Scanning Electron Microscope (SEM)
3.3 Reflection Electron Microscope (REM)
3.4 Scanning Transmission Electron Microscope (STEM)
4 Sample Preparation
5 Disadvantages
6 See also
7 External links
8 References
8.1 Archives
[edit] History
A transmission electron microscope.
An image of an ant from a scanning electron microscopeThe first electron microscope prototype was built in 1932 by the German engineers Ernst Ruska and Max Knoll. It was based on the ideas and discoveries of French physicist Louis de Broglie. Although it was primitive and not fit for practical use, the instrument was still capable of magnifying objects by four hundred times.
Reinhold Rudenberg, the research director of Siemens, had patented the electron microscope in 1931, although Siemens was doing no research on electron microscopes at that time. In 1937 Siemens began developing the electron microscope, funding Ruska and Bodo von Borries to develop the instrument. Siemens also employed Ruska's brother Helmut to work on applications, particularly with biological materials. [1][2]
Siemens produced the first commercial TEM in 1939, but the first practical electron microscope was built at the University of Toronto in 1938, by Eli Franklin Burton and students Cecil Hall, James Hillier and Albert Prebus.[3]
Although modern electron microscopes can magnify objects up to two million times, they are still based upon Ruska's prototype and his correlation between wavelength and resolution. The electron microscope is an integral part of many laboratories. Researchers use it to examine biological materials (such as microorganisms and cells), a variety of large molecules, medical biopsy samples, metals and crystalline structures, and the characteristics of various surfaces.
[edit] Electron microscope manufacturers
Major manufacturers include:
Delong Group
FEI Company - USA (formerly a division of Philips Electronics)
FOCUS GmbH - Germany
Hitachi - Japan
JEOL, Inc. - Japan (Japan Electro Optics Laboratory)
TESCAN - EU
Carl Zeiss NTS GmbH
[edit] Types
[edit] Transmission Electron Microscope (TEM)
Main article: Transmission electron microscopy
The original form of electron microscopy, Transmission electron microscopy (TEM) involves a high voltage electron beam emitted by a cathode and formed by magnetic lenses. The electron beam that has been partially transmitted through the very thin (and so semitransparent for electrons) specimen carries information about the inner structure of the specimen. The spatial variation in this information (the "image") is then magnified by a series of magnetic lenses until it is recorded by hitting a fluorescent screen, photographic plate, or light sensitive sensor such as a CCD (charge-coupled device) camera. The image detected by the CCD may be displayed in real time on a monitor or computer.
Resolution of the high-resolution TEM (HRTEM) is limited by spherical aberration and chromatic aberration, but a new generation of aberration correctors has been able to overcome spherical aberration. Software correction of spherical aberration has allowed the production of images with sufficient resolution to show carbon atoms in diamond separated by only 0.89 ångström (89 picometers) and atoms in silicon at 0.78 ångström (78 picometers) at magnifications of 50 million times. The ability to determine the positions of atoms within materials has made the HRTEM an indispensable tool for nano-technologies research and development in many fields, including heterogeneous catalysis and the development of semiconductor devices for electronics and photonics.
Transmission electron microscopes produce two-dimensional images.
[edit] Scanning Electron Microscope (SEM)
Main article: Scanning Electron Microscope
Unlike the TEM, where electrons are detected by beam transmission, the Scanning Electron Microscope (SEM)[4] produces images by detecting secondary electrons which are emitted from the surface due to excitation by the primary electron beam. In the SEM, the electron beam is rastered across the sample, with detectors building up an image by mapping the detected signals with beam position.
Generally, the TEM resolution is about an order of magnitude better than the SEM resolution, however, because the SEM image relies on surface processes rather than transmission it is able to image bulk samples and has a much greater depth of view, and so can produce images that are a good representation of the 3D structure of the sample.
[edit] Reflection Electron Microscope (REM)
In addition there is a Reflection Electron Microscope (REM). Like TEM, this technique involves electron beams incident on a surface, but instead of using the transmission (TEM) or secondary electrons (SEM), the reflected beam is detected. This technique is typically coupled with Reflection High Energy Electron Diffraction and Reflection high-energy loss spectrum (RHELS). Another variation is Spin-Polarized Low-Energy Electron Microscopy (SPLEEM), which is used for looking at the microstructure of magnetic domains [1].
[edit] Scanning Transmission Electron Microscope (STEM)
main article: Scanning Transmission Electron Microscopy STEM
[edit] Sample Preparation
Materials to be viewed under an electron microscope may require processing to produce a suitable sample. The technique required varies depending on the specimen and the analysis required:
Cryofixation - freezing a specimen so rapidly, to liquid nitrogen or even liquid helium temperatures, that the water forms vitreous (non-crystalline) ice. This preserves the specimen in a snapshot of its solution state. An entire field called cryo-electron microscopy has branched from this technique. With the development of cryo-electron microscopy of vitreous sections (CEMOVIS), it is now possible to observe virtually any biological specimen close to its native state.
Fixation - preserving the sample to make it more realistic. Glutaraldehyde - for hardening - and osmium tetroxide - which stains lipids black - are used.
Dehydration - replacing water with organic solvents such as ethanol or acetone.
Embedding - infiltration of the tissue with a resin such as araldite or epoxy for sectioning.
Sectioning - produces thin slices of specimen, semitransparent to electrons. These can be cut on an ultramicrotome with a diamond knife to produce very thin slices. Glass knives are also used because they can be made in the lab and are much cheaper.
Staining - uses heavy metals such as lead, uranium or tungsten to scatter imaging electrons and thus give contrast between different structures, since many (especially biological) materials are nearly "transparent" to electrons (weak phase objects). In biology, specimens are usually stained "en bloc" before embedding and also later stained directly after sectioning by brief exposure to aqueous (or alcoholic) solutions of the heavy metal stains.
Freeze-fracture or freeze-etch - a preparation method particularly useful for examining lipid membranes and their incorporated proteins in "face on" view. The fresh tissue or cell suspension is frozen rapidly (cryofixed), then fractured by simply breaking or by using a microtome while maintained at liquid nitrogen temperature. The cold fractured surface (sometimes "etched" by increasing the temperature to about -100°C for several minutes to let some ice sublime) is then shadowed with evaporated platinum or gold at an average angle of 45° in a high vacuum evaporator. A second coat of carbon, evaporated perpendicular to the average surface plane is often performed to improve stability of the replica coating. The specimen is returned to room temperature and pressure, then the extremely fragile "pre-shadowed" metal replica of the fracture surface is released from the underlying biological material by careful chemical digestion with acids, hypochlorite solution or SDS detergent. The still-floating replica is thoroughly washed from residual chemicals, carefully fished up on EM grids, dried then viewed in the TEM.
Ion Beam Milling - thins samples until they are transparent to electrons by firing ions (typically argon) at the surface from an angle and sputtering material from the surface. A subclass of this is Focused ion beam milling, where gallium ions are used to produce an electron transparent membrane in a specific region of the sample, for example through a device within a microprocessor. Ion beam milling may also be used for cross-section polishing prior to SEM analysis of materials that are difficult to prepare using mechanical polishing.
Conductive Coating - An ultrathin coating of electrically-conducting material, deposited either by high vacuum evaporation or by low vacuum sputter coating of the sample. This is done to prevent the accumulation of static electric fields at the specimen due to the electron irradiation required during imaging. Such coatings include gold, gold/palladium, platinum, tungsten, graphite etc. and are especially important for the study of specimens with the scanning electron microscope.
[edit] Disadvantages
Pseudocolored SEM image of the feeding basket of Antarctic krill. Real electron microscope images do not carry any color information, they are greyscale. The first degree filter setae carry in v-form two rows of second degree setae, pointing towards the inside of the feeding basket. The purple ball is one micrometer in diameter. To display the total area of this fascinating structure one would have to tile 7500 times this image.Electron microscopes are expensive to buy and maintain. They are dynamic rather than static in their operation: requiring extremely stable high-voltage supplies, extremely stable currents to each electromagnetic coil/lens, continuously-pumped high-/ultra-high-vacuum systems, and a cooling water supply circulation through the lenses and pumps. As they are very sensitive to vibration and external magnetic fields, microscopes aimed at achieving high resolutions must be housed in buildings (sometimes underground) with special services. Newer generations of TEM operating at lower voltages (around 5 kV) do not have stringent voltage supply, lens coil current, cooling water or vibration isolation requirements and as such are much less expensive to buy and far easier to install and maintain.
The samples have to be viewed in vacuum, as the molecules that make up air would scatter the electrons. Recent advances have allowed hydrated samples to be imaged using an environmental scanning electron microscope.
Scanning electron microscopes usually image conductive or semi-conductive materials best. Non-conductive materials can be imaged by an environmental scanning electron microscope. A common preparation technique is to coat the sample with a several-nanometer layer of conductive material, such as gold, from a sputtering machinehowever this process has the potential to disturb delicate samples.
The samples have to be prepared in many ways to give proper detail, which may result in artifacts purely the result of treatment. This gives the problem of distinguishing artifacts from material, particularly in biological samples. Scientists maintain that the results from various preparation techniques have been compared, and as there is no reason that they should all produce similar artifacts, it is therefore reasonable to believe that electron microscopy features correlate with living cells. In addition, higher-resolution work has been directly compared to results from X-ray crystallography, providing independent confirmation of the validity of this technique. Recent work performed on unfixated, vitrified specimens has also been performed, further confirming the validity of this technique.
[edit] See also
Wikibooks has more about this subject:
The Opensource Handbook of Nanoscience and NanotechnologyCategory:Electron microscope images
Field emission microscope
[edit] External links
Electron Microscopy Supplies - Ladd Research
Environmental Scanning Electron Microscope (ESEM)
X-ray element analysis in electron microscope - Information portal with X-ray microanalysis and EDX contents
http://www2.physics.utoronto.ca/overview/history/microsco/microscopy.htm (John H.L. Watson: VERY EARLY ELECTRON MICROSCOPY IN THE DEPARTMENT OF PHYSICS, THE UNIVERSITY OF TORONTO — A PERSONAL RECOLLECTION)
[edit] References
^ DH Kruger, P Schneck and HR Gelderblom (13). "Helmut Ruska and the visualisation of viruses" (in English). The Lancet 355 (9216): 1713-1717. DOI:10.1016/S0140-6736(00)02250-9.
^ Ernst Ruska (1986). Ernst Ruska Autobiography (English). Nobel Foundation. Retrieved on 2007-02-06.
^ MIT biography of Hillier
^ SCANNING ELECTRON MICROSCOPY 1928 - 1965
[edit] Archives
Rubin Borasky Electron Microscopy Collection, 1930-1988 Archives Center, National Museum of American History, Smithsonian Institution.
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