Scanning Probe Microwave Reflectivity of Aligned Single-Walled Carbon Nanotubes: Imaging of Electronic Structure and Quantum Behavior at the Nanoscale

Abstract

Single-walled carbon nanotubes (SWNTs) are 1-dimensional nanomaterials with unique electronic properties that make them excellent candidates for next-generation device technologies. While nanotube growth and processing methods have progressed steadily, significant opportunities remain in advanced methods for their characterization, inspection, and metrology. Microwave near-field imaging offers an extremely versatile "nondestructive" tool for nanomaterials characterization. Herein, we report the application of nanoscale microwave reflectivity to study SWNT electronic properties. Using microwave impedance microscopy (MIM) combined with microwave impedance modulation microscopy (MIM(2)), we imaged horizontal SWNT arrays, showing the microwave reflectivity from individual nanotubes is extremely sensitive to their electronic properties and dependent on the nanotube quantum capacitance under proper experimental conditions. It is shown experimentally that MIM can be a direct probe of the nanotube-free carrier density and the details of their electronic band structure. We demonstrate spatial mapping of local SWNT impedance (MIM), the density of states (MIM(2)), and the nanotube structural morphology (AFM) simultaneously and with lateral resolution down to <50 nm. Nanoscale microwave reflectivity could have tremendous impact, enabling optimization of enriched growth processes and postgrowth purification of SWNT arrays while aiding in the analysis of the quantum physics of these important 1D materials.

Local characterization of mobile charge carriers by two electrical AFM modes: multi-harmonic EFM versus sMIM

“…sMIM was proposed by Lai et al and developing quickly these years [10,11,23,24]. It can detect many kinds of electrical properties of various samples (including conductors, semiconductors, insulators and other functional materials) at the micro/nano scale [14,[25][26][27][28][29][30][31][32][33][34][35]. Figure 1 illustrates the microwave electronics.…”

“…The newly-developing powerful method scanning microwave impedance microscopy (sMIM) is a promising tool for 2D mobile charge carriers profiling with nanometer resolution [10][11][12][13][14][15][16][17][18][19][20]. It also has advantages in sub-surface scanning ability and simple in sample preparation [21].…”

Quantitative microwave impedance microscopy with effective medium approximations

“…[1][2][3][4][5][6][7] The technique has been used, for example, to image the highly conductive domain walls in ferromagnetics, [2][3][4] and identify metallic and semiconducting carbon nanotubes individually and non-destructively. 6 Many of the existing studies using MIM are somewhat qualitative in nature and the technique is used generally to measure the contrast in the tip-sample admittance across an image; however, some effort has been given to quantification of results and analyzing the tip-sample system in detail. Wei et al have produced a Green's theorem approach to quantify the tip-sample capacitance and verified this approach by comparison of the MIM signal with an electrostatic force microscopy (EFM) approach curve, 8 and have also modeled effects of the height of the probe on the measurement.…”

Direct mapping of the electric permittivity of heterogeneous non-planar thin films at gigahertz frequencies by scanning microwave microscopy

“…nano-composite absorbers). 13,14 In addition, SMM has also been applied to the study of complex oxides, 15 graphene, 16,17 carbon nanotubes, 18 doped semiconductors, 19 and superconductors. 20 Furthermore, SMM will contribute to the emerging field of high frequency nanoelectronic devices, where there is the demand of on-wafer measurement systems sensitive to the microwave electromagnetic properties of dielectric materials.…”