扫描电子显微镜1要点.pptVIP

SE的形貌衬度的应用p183-187 1.断口形貌的观察 2.高倍金相组织的观察 3.高分子复合材料及无机非金属材料研究 4.动态研究中的应用 2．BSE像衬度及特点 当观察成分衬度时，需将样品磨平、抛光。 成分衬度 形貌衬度(P188) 背散射电子能量高，离开样品后沿直线轨迹运动，检测器只能检测到直接飞向检测器的BSE 分辨率 立体感远不及SE电子像(见书P189) * /microscopy/proimage.html To produce an image on the screen, the electron beam scans over the area to be magnified and transfers this image to the TV screen. The electron beam stops at 1,000 points as it scans horizontally across the sample and down 1,000 lines vertically. This gives 1,000,000 points of information. The signal read from the electrons coming off each point is transferred to a corresponding point on the TV screen. Since the TV screen also has 1,000 points horizontally and 1,000 lines vertically, there is a 1:1 correspondance between the scan on the specimen and the TV screen. Since the length (x) of the electron beam scan on the specimen is smaller than the length (c) of the TV screen, a magnification is produced equal to the following equation: M=c/x By changing the size of the scan on the sample, the magnification can be changed. The smaller the area of the electron beam scan, the higher the magnification. Obtaining different degrees of magnifications are important in any practical uses of the SEM. * Ideally the field emission tip is used in a vacuum of 10nPa or better. Even in that condition, however, a few gas molecules will still land on the tip from time to time and these will cause fluctuations in the emission current. Eventually the whole tip will be covered and the output will become very unstable. The cathode must then be cleaned by rapidly heating it to a high T (2000C) for a few seconds (Cold FEG). Alternatively the tip can be kept warm (800-1000C, thermal FEG), in which case the majority of impinging molecules are immediately reevaporated. In this case acceptably stable emission is maintained even in a vacuum of 100 nPa or so. * （一）扫描电镜工作原理 透镜将电子束聚焦成非常细的电子束，射在试样表面上，激发出各种物理信号，由探测器接收，输送到阴极射线管成像。 主要收集信号是二次电子（ＳＥ）和背散射电子（ＢＳＥ）的信号。(p171) Beam is scanned over