哈工大-sem实验报告

《先进材料表征技术》课程学生实验报告

实验名称：扫描电镜与能谱仪的原理及应用

姓名：

实验时间：2015 年11 月 6 日

哈尔滨工业大学深圳研究生院

I. Purpose

1. Be familiar with the structure and principle of scanning electron microscope .

2. Be familiar with the requirement of sample preparation.

3. Know about the operation specification of SEM, be familiar with the differences between image of secondary electron and backscatter electron.

4. Know about the operation specification of EDS, be familiar with the point analysis, line analysis and mapping.

II. Principles

2.1Resolution and contrast

For imaging, resolution means the minimum distance between two distinct points.For composition analysis, resolution means the minimum region can be analyzed. In SEM system, resolution depends on the diameter of the incident electron beam and signal type.

Contrast means the difference of brightness , and it can be caused by morphology or atomic number. The morphology contrast is always observed in SE image, and the atomic contrast is always observed in BSE image.

2.2 Electron microscopy imaging

The beam emitted from the electron gun is focused at the surface of the sample through a series of electromagnetic lens (Fig 1.). The last lens equipped with a scanning coil can drive electron beam scan on the surface. The interaction between high energy electron beam and sample generate various signals, and the signals can be received by the detector. Do this point by point and we can get a image (Fig 2.).

Fig 1.

Fig 2. the scanning process to form a image

2.3 SE image and BSE image

Secondary electron signal are generated from the very surface (Fig 3.), so the intensity of the signal sensitive to the orientation of the incident beam. Along angle formed by surface and incident beam increases, the secondary electron yield increase. Therefore, the SE image is suitable for display the morphology contrast.

From Fig 2. we can see that backscatter electron is generated from a relative big volume near to the surface, so the image has poorer resolution .The BSE yield is sensitive to the atomic number (<40), as a result, the regions where the heavier atomic exists are brighter than other regions.

Fig 3. the region of SE (left) and BSE (right)

2.4 EDS--Primary X-rays

X-ray is a result of inelastic collision between the incident beam and sample. When high energy electron interact with atomic, it can stimulate inner electron. The inner energy level has a hole, and the outer electron will move to the hole and the atom emits the

number, so we can identify the elements by primary and roughly measure the relative quantity of different elements by calculate the area between the peak on spectrum.

Fig . the generation of X-ray

III. Equipment

3.1扫描电镜

电镜主体主要是由电子光学系统、样品室、检测器以及真空抽气系统组成。电子光学系统包括电子枪、电磁透镜、扫描线圈等。电源电路系统由控制镜体部分的各种电源、信号处理、图象显示和记录系统以及用于全部电气部分的操作面板构成。真空系统由用于低真空抽气的旋转机械泵(RP)和高真空抽气的油扩散泵（DP）或离子泵构成。

图1所示为我院实验室使用的扫面电子显微镜，该扫描电镜主要技术参数如下：

图1 实验室所用的扫描电子显微镜

a) 电子枪：冷场发射型

b) 分辨率：15KV：≤1.5nm（WD：12mm），1kV：≤2.1nm

c) 加速电压：0.5～30kV

d) LOWMAG 模式：×30～2,000

e) HIGHMAG 模式：×250～500,000

3.2能谱仪

能谱仪主要由控制及指令系统、X射线信号检测系统、信号转换及储存系统、数据输出及显示系统组成，能谱仪剖析图如图2所示。电子束从样品中所激发的X 射线信号由X射线探测器接收，形成电压脉冲，其脉冲高度与进入的X射线的能量成正比，然后经放大器进一步放大成型，送到多道分析器，按照X射线能量大小分别在不同的信道内记数，最后在记录仪或显示器上把脉冲数即X射线的强度与X射线能量的关系曲线显示出来，即X射线能谱图，横坐标是X射线的能量，纵坐标是

X-射线强度。

图2 EDAX能谱仪剖析组成图

EDAX 能谱仪的能谱可对元素（4Be—92U）范围进行定性和定量分析，性能包括：

a) 定点分析--获得样品中一个选定点的全谱分，确定夹杂、第二相等选定点所含元素的种类和浓度（定量分析）；

b) 线分析--获得样品在一个选定线上的某一元素的浓度变化（定性分析）；

c) 元素的面分布--获得样品在一个选定区域内某一元素的浓度分布图（定性分析）。

IV. Procedure

1）Know about the structure and principle of the SEM and EDS, and be familiar with the operation spefication.

2）Cleaning the contamination on the surface is required in sample preparation. The insulator sample should be coated with Pt or C. Keep the sample dry before tested.

3）To obtain high quality SEM image, we should modify various parameters such as

angle of sample, focus and astigmatism correction, magnification, brightness and contrast ratio.

4）EDS microanalysis

Start up the SEM.;Make vacuum for 10~15min, then start up the EDS;Select proper parameter and click “Image ” to get SEM image; Click “Spc ” to do a full spectrum analysis of the selected area; Right-click and do point analysis, line analysis and mapping.

5）Export and analyze the experiment data.

V . Results and analysis

First, we should clarify what the sample is.

The EDS result is shown as Fig 5. We can see that there are some peaks are marked as the primary X-ray of element O, Mn and Co. But some peaks are

not marked. We should know whether these peaks belong to the above 3 elements.

I found the Primary X-ray of the 3 elements online, as chart 1. Shown. We found that a peak with energy about 2.1keV is not belong to the 3 elements. It may be the K β of element P, but I don ’t why this peak is not marked.

So, the sample is mainly composed by element O, Mn, and Co, maybe element P also exist in the sample.The atomic ratio O:Mn:Co is about 9:7:4.

What is this sample used for? From the Internet, I got that Co-Mn-O composite oxides were also prepared and studied in details as the catalyst for CO selective oxidation.

image with 20.0k magnification(Fig .), we can see that the particle is balls consist of numerous smaller sticks. As the Fig shows, there are many holes on the surface of every stick. This structure make the balls have very big specific and the sample will have better performance as catalyst.

VI. Summary

宋体四号字