Wit Bareld, Gramse Georg, Müllegger Stefan
Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040 Linz, Austria.
Biophysics Institute, Johannes Kepler University, 4020 Linz, Austria.
Rev Sci Instrum. 2023 Oct 1;94(10). doi: 10.1063/5.0155029.
We outline calibrated measurements of the microwave reflection coefficient from the tunnel junction of an ultra-high vacuum low temperature scanning tunneling microscope. The microwave circuit design is described in detail, including an interferometer for an enhanced signal-to-noise ratio and a demodulation scheme for lock-in detection. A quantitative, in situ procedure for impedance calibration based on the numerical three-error-term model is presented. Our procedure exploits the response of the microwave reflection signal due to the change of the tunneling conductance caused by sub-nm variation of the tunneling distance. Experimental calibration is achieved by a least-squares numerical fit of simultaneously measured conductance and microwave reflection retraction curves at finite conductance. Our method paves the way for nanoscale microscopy and spectroscopy of dielectric surface properties at GHz frequencies and cryogenic temperatures. This opens a promising pathway even for dielectric fingerprinting at the single molecule limit.
我们概述了超高真空低温扫描隧道显微镜隧道结微波反射系数的校准测量。详细描述了微波电路设计，包括用于提高信噪比的干涉仪和用于锁相检测的解调方案。提出了一种基于数值三误差项模型的定量原位阻抗校准程序。我们的程序利用了由于隧道距离亚纳米变化引起的隧道电导变化而导致的微波反射信号的响应。通过在有限电导下同时测量的电导和微波反射回缩曲线的最小二乘数值拟合来实现实验校准。我们的方法为GHz频率和低温下介电表面性质的纳米级显微镜和光谱学铺平了道路。这甚至为单分子极限下的介电指纹识别开辟了一条有前景的途径。
