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Abstract：
We increase the dynamical range of a scanning tunneling microscope (STM) by actively subtracting dominant current-harmonics generated by nonlinearities in the current-voltage characteristics that could saturate the current preamplifier at low junction impedances or high gains. The strict phase relationship between a cosinusoidal excitation voltage and the current-harmonics allows excellent cancellation using the displacement-current of a driven compensating capacitor placed at the input of the preamplifier. Removal of DC currents has no effect on, and removal of the first harmonic only leads to a rigid shift in differential conductance that can be numerically reversed by adding the known removal current. Our method requires no permanent change of the hardware but only two phase synchronized voltage sources and a multi-frequency lock-in amplifier to enable high dynamic range spectroscopy and imaging. • Active power filter • Dynamic range compression • High gain preamplifier.
摘要：
我们通过主动减去由电流-电压特性中的非线性产生的主要电流谐波来增加扫描隧道显微镜（STM）的动态范围，这些谐波可能会在低结阻抗或高增益下使电流前置放大器饱和。余弦激励电压与电流谐波之间的严格相位关系允许使用放置在前置放大器输入处的驱动补偿电容器的位移电流进行出色的消除。直流电流的去除对，并且去除一次谐波只会导致微分电导的刚性偏移，可以通过添加已知的去除电流在数值上进行反转。我们的方法不需要永久更改硬件，而只需要两个相位同步电压源和一个多频锁定放大器即可实现高动态范围的光谱和成像。•有源电力滤波器•动态范围压缩•高增益前置放大器。
