Nanoscale microwave microscopy using shielded cantilever probes

Abstract

Quantitative dielectric and conductivity mapping in the nanoscale is highly desirable for many research disciplines, but difficult to achieve through conventional transport or established microscopy techniques. Taking advantage of the micro-fabrication technology, we have developed cantilever-based near-field microwave probes with shielded structures. Sensitive microwave electronics and finite-element analysis modeling are also utilized for quantitative electrical imaging. The system is fully compatible with atomic force microscope platforms for convenient operation and easy integration of other modes and functions. The microscope is ideal for interdisciplinary research, with demonstrated examples in nano electronics, physics, material science, and biology.

Quantitative microwave impedance microscopy with effective medium approximations

“…The tip is actually pyramidal in shape, 16 though we instead approximate the tip as a cone so that the geometry can be reduced to a two-dimensional axisymmetric simulation to avoid a more computationally intense threedimensional model. A similar simulation geometry has already been demonstrated for a non-contact mode, 11 though the sMIM mode is used only in the contact mode. Furthermore, it is informative to perform the simulation over a range of conductivities and permittivities to observe the complete response of the system.…”

“…Choosing a value of and fitting with respect to σ, the goodness of fit is high for both the real and imaginary parts, with R 2 > 0.99. Previous studies interpret the results of simulations qualitatively with a two-element equivalent circuit 11 or with a more complicated circuit of arbitrary size, 17 though the three element circuit is the simplest to quantitatively fit the results of the non-Ohmic contact-mode simulation.…”

“…10 Furthermore, Lai et al have demonstrated a quantitative calibration scheme for MIM by imaging samples of known bulk permittivity, comparing the average output (in arbitrary units) of the instrument with finite element simulations. 7 Lai et al 11 and Tselev et al 4 have also offered estimates of the ratio of capacitance to the signal output. Their estimates differ somewhat, Tselev et al citing 1.6 aF/mV (the ratio of the tip-sample capacitance to the output voltage of the imaginary sMIM-C or MIM-Im channel), and Lai et al reporting 0.1 aF/mV.…”

Nanoscale dielectric microscopy of non-planar samples by lift-mode electrostatic force microscopy

“…Among them, we can cite nanoscale capacitance microscopy [1][2][3], electrostatic force microscopy (EFM) [4][5][6][7][8][9][10], nanoscale impedance microscopy [11,12], scanning polarization force microscopy [13][14][15][16], scanning microwave microscopy (SMM) [17,18] and nanoscale non-linear dielectric microscopy [19]. These techniques have allowed measuring the electric permittivity with nanoscale spatial resolution on planar samples, such as thin oxides, polymer films and supported biomembranes [2][3][4]8,10], and on non-planar ones, such as, single carbon nanotubes, nanowires, nanoparticles, viruses and bacterial cells [20][21][22][23][24][25][26][27][28][29][30].…”

Uncovering edge states and electrical inhomogeneity in MoS 2 field-effect transistors

“…In this paper, we report the microwave impedance microscopy (MIM) (24,25) study on the nanoscale conductance distribution during the normal operation of MoS 2 FETs. The experimental setup for our simultaneous transport and MIM measurements is schematically illustrated in Fig.…”