Experiments With A High Resolution Field-Emission STEM

我们已经表明，电子能量损失光谱成像（EELS）在扫描透射电子显微镜（STEM）可以提供近单原子的元素，如钙，磷和铁结合到蛋白质吸附到薄碳膜的灵敏度。光谱成像系统，包括一个100 × 1340像素的CCD探测器，使并行收集EELS数据在每个图像像素。该系统的优点是（i）低噪声水平，其提供更高的分析灵敏度，（ii）约10 ms的短读出时间，其能够更快地采集，（iii）正方形像素的二维阵列，其允许对通道增益变化的精确校正，以及（iv）检测器阵列到闪烁体的光学耦合的改进的点扩散函数。通过互相关记录在每个扫描线的末端的环形暗场图像来实现对样品漂移的实时补偿。我们已经实施了新的软件来提高光谱分析的准确性，以进一步降低元素的检测限。

We have shown that electron energy loss spectroscopic imaging (EELS) in the scanning transmission electron microscope (STEM) can provide near single atom sensitivity for elements such as calcium, phosphorus and iron bound to proteins adsorbed onto thin carbon films. A spectrum-imaging system incorporating a 100x1340 pixel CCD detector has enabled the parallel collection of EELS data at each image pixel. Advantages of this system are (i) the low noise level, which provides higher analytical sensitivity, (ii) the short read-out time of around 10 ms, which enables faster acquisition, (iii) the two-dimensional array of square pixels, which allows exact correction for channel gain variations, and (iv) the improved point-spread function of the optical coupling of the detector array to the scintillator. Compensation for specimen drift is achieved in real-time by cross-correlating annular dark-field images recorded at the end of each scan line. We have implemented new software to improve the accuracy of spectral analysis to reduce the elemental detection limits further.