Dual-probe Atomic Force Microscopy Research Articles

In Situ Quantification of Strain-Induced Piezoelectric Potential of Dynamically Bending ZnO Microwires.

The piezoelectric properties of semiconductor micro/nanowires (M/NWs) are crucial for optimizing semiconductors' electronic structure and carrier dynamics. However, the dynamic characterization of the piezoelectric properties of M/NWs remains challenging. Here, a Kelvin probe force microscopy technique based on a dual-probe atomic force microscope is developed to achieve in situ piezoelectric potential measurements of dynamic bending MWs. This technique can not only characterize the surface potential on different crystal faces of ZnO MWs in a natural state through controllable axial rotation, but also investigate the piezoelectric potential of the dynamically bending flake-like ZnO MW at different points and under different strain loads. The results show that the surface potentials of different faces/positions of the ZnO MWs are varied significantly, and determine that the quasi-static conditions piezo-strain factor of the flake-like ZnO MW is 0.28 V/%, while the factor was0.14 V/% under low-frequency (⩽5 Hz) sinusoidal strain loading. This work provides a significant methodology to further study piezoelectric materials, and it aims to facilitate their applications in piezoelectric devices andsystems.

Dual-Probe Atomic Force Microscopy based on tuning fork probes for critical dimension metrology

Atomic force microscopy (AFM) is widely used for nano-dimensional metrology in semiconductor manufacturing and metrological system. However, the conventional AFM can't provide accurate CD characterization of nanostructures, due to its top-down configuration and probe-size effect. In this paper, we develop a dual-probe atomic force microscopy (DPAFM). Compared to conventional optical-lever based AFM, the DPAFM exploits two tuning fork probes that simplifies significantly the setup and can be controlled based on frequency-modulation (FM) mode. The developed DPFAM is implemented that builds a zero-reference point by dual-probe alignment firstly, following which, characterizes nanostructures from two sides independently with the two probes. The final CD feature is determined by matching profiles from the two probes based on the zero-reference point. The capability of the DPAFM is validated by experiments on a CD-standard structure, that achieves the true CD assessment with good accuracy and repeatability.

Design and Control of a Dual-Probe Atomic Force Microscope

Current atomic force microscopes (AFMs) support single-probe operation, in which one nanosized tip enables versatile operations such as surface imaging, nanomanipulation, and nanomanufacturing to be performed, although one at a time. Some AFM operations involve switching between imaging and the operational mode, which is cumbersome, challenging, and limiting, particularly when different probe geometries are preferred for each mode. This paper presents a new dual-probe atomic force microscope (DP-AFM) that has two independent probes operating in a common workspace. Such a setup enables two AFM operations to be carried out simultaneously. For instance, one probe can be used to image, while the other probe performs one of the many tip-based processes. The hardware and software design involved in developing the DP-AFM is discussed in detail. Furthermore, to demonstrate the capability of dual-probe arrangement, a controller is developed for real-time plowing depth control, where one probe is used to plow the surface, while the other is used to image the plow profile, thus enabling real-time feedback control of the AFM plow process. Experimental results show that the plow depth can be regulated with nanometer-level accuracy.

A nondestructive calibration method for maximizing the range and accuracy of AFM force measurement

In this paper, a nondestructive method for the normal and lateral sensitivity calibrations of the optical lever in atomic force microscope (AFM) is presented. The practical application of this method in a dual-probe AFM is discussed in detail. To calibrate the conversion factors between photodiode responses and probe's deflection angles accurately without applying forces to the probe, a two-degrees-of-freedom flexure-hinge-based calibration device (FHCD) is developed. The device, which mainly consists of two mutually perpendicular flexure-hinge levers that share the same rotational center, serves as a switching mechanism for precise translation-to-rotation conversions both in the normal and lateral directions. During the calibration, a probe is attached to the FHCD at the meeting of the rotational axes of two levers. The FHCD is mounted on an AFM sample platform. The probe in this method acts as a mirror to be normally and laterally tilted at nanoscale angles to deflect the reflected laser beam by twisting the corresponding flexure-hinge levers, rather than the force-inducing probe deflection in traditional AFM calibration methods. With this method, the nondestructive calibration of the local and full-range sensitivities of the optical levers can be completed without destroying the probe tip or modifying the actual system setup of an AFM. Moreover, the nonlinearities of the optical levers are accurately compensated. Experimental results show that the linear ranges (with a deviation of 5% in the full range) of the force measurement are extended to 3.6 and 4.5 times in the normal and lateral directions, respectively, increasing to over 90% of the full range of the force measurement.

Influence of grain boundary on electrical properties of organic crystalline grains investigated by dual-probe atomic force microscopy

We performed electrical transport measurements on α-sexithiophene crystalline grains using a dual-probe atomic force microscopy system having two independently controlled cantilever probes. The field-effect transistor characteristics were measured by varying the distances between the two probes brought in contact with the surface of the grains. It was clearly shown by the transfer line method that the grain boundary is the dominant factor limiting the electrical properties of organic thin films. Moreover, the hole transport across the grain boundary was found to be more affected by the oxygen hole doping than that within the crystalline grain.

Development of multi-environment dual-probe atomic force microscopy system using optical beam deflection sensors with vertically incident laser beams

We developed a dual-probe atomic force microscopy (DP-AFM) system with two cantilever probes that can be operated in various environments such as in air, vacuum, and liquid. The system employs the optical beam deflection method for measuring the deflection of each cantilever mounted on a probe scanner. The cantilever probes mounted on the probe scanners are attached to inertia sliders, which allow independent control of the probe positions. We constructed three types of probe scanners (tube, shear-piezo, and tripod types) and characterized their performance. We demonstrated AFM imaging in ambient air, vacuum, and ultrapure water, and also performed electrical measurement and pick-up manipulation of a Au nanorod using the DP-AFM system.

Visualization of Charge Injection Processes in Polydiacetylene Thin Film Grains by Dual-Probe Atomic Force Microscopy

We have recently developed a dual-probe atomic force microscopy (DP-AFM) system having two AFM cantilever probes whose positions can be independently controlled with a precision on the order of ten nanometers. In this study, we visualized charge injection processes in polydiacetylene thin film grains using the DP-AFM system. One of the two probes was used to apply bias voltages to the grains while the other probe was used to obtain surface potential images of the grains. The surface potential of the polymerized grain changed according to the applied bias voltages. The potential profiles at the edge of the grain were not sharp when negative voltages were applied to the grain, which suggests the existence of an electron injection barrier at the interface. Moreover, it is suggested from the same experiment conducted in vacuum that the p-type semiconductor characteristics of the polydiacetylene is due to the O2 hole doping.

Development of dual-probe atomic force microscopy system using optical beam deflection sensors with obliquely incident laser beams

We developed a dual-probe (DP) atomic force microscopy (AFM) system that has two independently controlled probes. The deflection of each cantilever is measured by the optical beam deflection (OBD) method. In order to keep a large space over the two probes for an objective lens with a large numerical aperture, we employed the OBD sensors with obliquely incident laser beams. In this paper, we describe the details of our developed DP-AFM system, including analysis of the sensitivity of the OBD sensor for detection of the cantilever deflection. We also describe a method to eliminate the crosstalk caused by the vertical translation of the cantilever. In addition, we demonstrate simultaneous topographic imaging of a test sample by the two probes and surface potential measurement on an α-sexithiophene (α-6T) thin film by one probe while electrical charges were injected by the other probe.

Investigations of Local Electrical Properties of Pentacene Thin Films by Dual-Probe Atomic Force Microscopy

We performed local electrical transport measurement on single grains of a pentacene thin film using a lab-built dual-probe atomic force microscopy (DP-AFM) system. We brought two conducting cantilever tips in contact with a single grain and successfully measured the p-type field-effect characteristics. Moreover, we investigated the effect of contact resistance on the measured characteristics by performing a series of transport measurements while varying tip distance. The contact resistance and hole mobility of the channel region were estimated as 3.1 GΩ and 2.7×10-2 cm2 V-1 s-1, respectively. The results demonstrate the applicability of the DP-AFM system to the nanometer-scale transport measurement of molecules.

Visualization of anisotropic conductance in polydiacetylene crystal by dual-probe frequency-modulation atomic force microscopy/Kelvin-probe force microscopy

The authors recently developed a dual-probe atomic force microscope (DP-AFM) system as a powerful measurement or fabrication tool in the fields of nanoelectronics and nanobiology. In this study, they performed frequency-modulation Kelvin-probe force microscopy (FM-KFM) experiments on a polydiacetylene (PDA) single crystal using the DP-AFM system. While a bias voltage was locally applied to the PDA surface with one probe, the surface potential on the surrounding area was mapped with the other probe by FM-KFM. The surface potential images showed anisotropic distributions, which are explained by the anisotropic conductance of the PDA crystal due to the quasi-one-dimensional electronic band structure along the diacetylene main chain. They also discuss the mechanisms of charge injection from a probe to the PDA crystal and the difference in the anisotropic conductance ratio for electrons and holes.