澳洲护理代写essay:电子显微镜

2020-01-22 12:18

扫描电子显微镜(SEM)能产生高倍、低分辨率的图像。与传统的光学显微镜使用光和物镜来放大样品不同，扫描电子显微镜使用聚焦的高能电子束和电磁电容器来形成图像。SEMs的放大倍数可达10万倍，分辨率可达1纳米以下(Goldstein et al.， 2003)。电子在电子枪中产生。离开电子枪或阴极的电子被向下拉向阳极，并在强电场作用下被取样。通过阳极后，电子被压缩成一束，在那里它们到达并通过物镜来满足样品(JoVE, 2018)。入射电子与样品之间的相互作用产生三个主要信号:次级电子(SE)、反向散射电子(BSE)和x射线(Vernon-Parry, 2000)。这三个信号携带不同的样本信息。各个信号由各自的探测器识别，并根据需要的信息被处理成图像。SEs、BSEs和x射线来自不同的样本区域;因此，它们提供了不同的样本信息。SEs由样品表面的原子发射，并产生具有高空间分辨率的详细的地形显微照片。显微照片阐明了样品的整体形态和独特的微观特征。当从不同角度拍摄的两张显微照片通过立体观察器(Taylor, 1973)或特殊软件进行观察时，就可以生成三维图像
澳洲护理代写essay:电子显微镜
Scanning electron microscopes (SEM) produce high magnification, low resolution images. Unlike traditional optical microscopes that use light and objective lenses to magnify a sample, SEM uses a focused, high-energy beam of electrons and an electromagnetic condenser to form an image. SEMs are capable of exceeding magnifications of 100,000X and resolutions below 1nm (Goldstein et al., 2003). Electrons are generated in the electron gun. Electrons leaving the gun, or cathode, are pulled down towards the anode and sample by a strong electric field. After passing though the anode, the electrons are condensed into a fine beam where they reach and pass through the objective lens to meet the sample (JoVE, 2018). The interaction between the incident electrons and the sample produce three primary signals: secondary electrons (SE), backscattered electrons (BSE), and X-rays (Vernon-Parry, 2000). The three signals carry different sample information. The individual signals are recognized by their respective detectors and, depending on what information is desired, are processed into an image.SEs, BSEs, and X-rays originate from disparate sample regions; therefore, they provide different sample information. SEs emanate from atoms on the sample’s surface, and produce detailed, topographic micrographs with high-spatial resolution. SE micrographs elucidate the overall morphology and unique, microscopic characteristics of a sample. A three-dimensional image can be produced when two micrographs, taken from different angles, are viewed through a stereoviewer (Taylor, 1973) or through specialty software