Woehl Taylor J, White Ryan M, Keller Robert R
Applied Chemicals and Materials Division,Material Measurement Lab,NIST, Boulder,CO 80301,USA.
Microsc Microanal. 2016 Jun;22(3):544-50. doi: 10.1017/S1431927616000775. Epub 2016 May 6.
A microchannel plate was used as an ion sensitive detector in a commercial helium ion microscope (HIM) for dark-field transmission imaging of nanomaterials, i.e. scanning transmission ion microscopy (STIM). In contrast to previous transmission HIM approaches that used secondary electron conversion holders, our new approach detects forward-scattered helium ions on a dedicated annular shaped ion sensitive detector. Minimum collection angles between 125 mrad and 325 mrad were obtained by varying the distance of the sample from the microchannel plate detector during imaging. Monte Carlo simulations were used to predict detector angular ranges at which dark-field images with atomic number contrast could be obtained. We demonstrate atomic number contrast imaging via scanning transmission ion imaging of silica-coated gold nanoparticles and magnetite nanoparticles. Although the resolution of STIM is known to be degraded by beam broadening in the substrate, we imaged magnetite nanoparticles with high contrast on a relatively thick silicon nitride substrate. We expect this new approach to annular dark-field STIM will open avenues for more quantitative ion imaging techniques and advance fundamental understanding of underlying ion scattering mechanisms leading to image formation.
在商用氦离子显微镜(HIM)中,微通道板被用作离子敏感探测器,用于纳米材料的暗场透射成像,即扫描透射离子显微镜(STIM)。与先前使用二次电子转换支架的透射HIM方法不同,我们的新方法在专用的环形离子敏感探测器上检测向前散射的氦离子。在成像过程中,通过改变样品与微通道板探测器之间的距离,获得了125毫弧度至325毫弧度之间的最小收集角。蒙特卡罗模拟用于预测能够获得具有原子序数对比度的暗场图像的探测器角度范围。我们通过对二氧化硅包覆的金纳米颗粒和磁铁矿纳米颗粒进行扫描透射离子成像,展示了原子序数对比度成像。尽管已知STIM的分辨率会因衬底中的束展宽而降低,但我们在相对较厚的氮化硅衬底上对磁铁矿纳米颗粒进行了高对比度成像。我们期望这种用于环形暗场STIM的新方法将为更定量的离子成像技术开辟道路,并推动对导致图像形成的潜在离子散射机制的基本理解。