Cantilever Probe Research Articles

Fabrication of Microstructure Arrays via Localized Electrochemical Deposition

Localized electrochemical deposition microadditive manufacturing (AM) (LECD-µAM) technology represents a nontraditional manufacturing method applied for the layer-by-layer fabrication of metal microstructures via a fully automatic feedback mechanism. In terms of material utilization and complex structure formation, the proposed technology exhibits great potential for microstructure fabrication. The LECD-µAM technology introduced in this study involves the reduction of metal cations in the electrolyte to form metal microstructures. This study showed the flow simulation of an electrolyte in the cantilever probe and pressure distribution at the probe tip. In addition, the effect of extrusion pressure on the deposition structure was investigated experimentally. Combined with the experimental results, we discussed the effects of LECD-µAM technology on deposition outcomes and optimized parameters and designed a printing route for the deposition of complex metal microstructure arrays with smooth surfaces. The proposed technology attained a deposition rate and a microstructural copper content of 0.961 µm/s and 99.5%. In addition, LECD-µAM technology can be performed at room temperature, has low environmental requirements and cost, provides a good deposition surface, and holds great potential for the manufacture of three-dimensional and other complex microstructure arrays.

Johnson-noise-limited cancellation-free microwave impedance microscopy with monolithic silicon cantilever probes

Microwave impedance microscopy (MIM) is an emerging scanning probe technique for nanoscale complex permittivity mapping and has made significant impacts in diverse fields. To date, the most significant hurdles that limit its widespread use are the requirements of specialized microwave probes and high-precision cancellation circuits. Here, we show that forgoing both elements not only is feasible but also enhances performance. Using monolithic silicon cantilever probes and a cancellation-free architecture, we demonstrate Johnson-noise-limited, drift-free MIM operation with 15 nm spatial resolution, minimal topography crosstalk, and an unprecedented sensitivity of 0.26 zF/√Hz. We accomplish this by taking advantage of the high mechanical resonant frequency and spatial resolution of silicon probes, the inherent common-mode phase noise rejection of self-referenced homodyne detection, and the exceptional stability of the streamlined architecture. Our approach makes MIM drastically more accessible and paves the way for advanced operation modes as well as integration with complementary techniques.

Microstructured Cantilever Probe on Optical Fiber Tip for Microforce Sensor

Benefiting from the great advances of the femtosecond laser two-photon polymerization (TPP) technology, customized microcantilever probes can be accurately 3-dimensional (3D) manufactured at the nanoscale size and thus have exhibited considerable potentials in the fields of microforce, micro-vibration, and microforce sensors. In this work, a controllable microstructured cantilever probe on an optical fiber tip for microforce detection is demonstrated both theoretically and experimentally. The static performances of the probe are firstly investigated based on the finite element method (FEM), which provides the basis for the structural design. The proposed cantilever probe is then 3D printed by means of the TPP technology. The experimental results show that the elastic constant k of the proposed cantilever probe can be actively tuned from 2.46 N/m to 62.35 N/m. The force sensitivity is 2.5 nm/µN, the Q-factor is 368.93, and the detection limit is 57.43 nN. Moreover, the mechanical properties of the cantilever probe can be flexibly adjusted by the geometric configuration of the cantilever. Thus, it has an enormous potential for matching the mechanical properties of biological samples in the direct contact mode.

The aggregation of micro-particles based on hydraulic vortices

The large-scale and nondestructive aggregation of micro-particles in the solvent has a crucial role on cell detection and the preparation of micro-nano drugs. To achieve directional aggregation of micro-particles, a piezoelectric cantilever probe structure can be utilized to generate a vortex region by driving the liquid with low-frequency oscillation. By adjusting the driving voltage and frequency of the piezoelectric oscillator, polystyrene microspheres in the liquid can be effectively aggregated and manipulated. Experimental results using fixed concentration polystyrene solvent demonstrated that micro-particle aggregation occurred within the frequency range of 20–70 Hz and voltage range of 20–80 V. The particles were stably concentrated in front of the probe, with a maximum aggregation area of 0.71 mm2 and a maximum number of aggregated particles reaching 2495, when the driving voltage was 60 V and the driving frequency was 60 Hz. Furthermore, the flow field particle image velocimetry experiment revealed that when four main vortices with opposite rotation directions were present, the micro-particle aggregation exhibited a regular Arc and Witch-shaped pattern. Conversely, in the presence of an indefinite number of large main vortices in the flow field, the micro-particle aggregation displayed an irregular Small symmetry and Large symmetry-shaped pattern. This method of micro-particle aggregation manipulation using hydraulic vortices has the potential to meet the demands of biomedical and fine chemical fields for precise micro-particle manipulation.

Dual Cantilever Probe for Crack Probability Analysis of Multilayer Substrates During Wafer Probing

Dual Cantilever Probe for Crack Probability Analysis of Multilayer Substrates During Wafer Probing

Effect of Audible Sounds on the Forces Acting between Charged Surfaces in Water.

We aimed to determine if audible sounds could change the forces acting between charged surfaces in water and their electric double layers (EDLs). This was achieved by using an atomic force microscope to measure force-distance curves between a microsized silica particle attached to a cantilever (probe) and a silicon wafer in water in the absence and presence of sound. Sound decreased the repulsive forces acting between the probe and silicon wafer, where the range and magnitude of the forces decreased with an increase in the sound frequency from 300 to 15000 Hz. The decrease in the force range was explained by a decrease in the EDL thickness. This result was explained by (1) the shrinkage of the EDL by a high-pressure region of the sound wave, where an increased sound frequency caused the number of high-pressure regions that passed between the probe and the substrate to increase and (2) the inability of the EDL to fully re-expand to its original thickness during the time that a low-pressure region of the sound wave was applied. The decrease in the force magnitude with a sound frequency increase was explained by the increased screening of charged surfaces that accompanies a decrease in the EDL thickness. An increase in the force measurement speed caused the sound waves to reduce the repulsive forces less. A faster speed decreased the time to measure a force curve, which reduced the number of high-pressure regions of the sound wave to pass through the water between the probe and the substrate. This reduced the number of times that the EDL was compressed by the sound wave.

Analytical solution for size-dependent nonlinear behavior of AFM microcantilever with assembled probe in liquid environments

Using modified strain gradient theory, this study aims to examine the size-dependent nonlinear behavior of atomic force microscopy (AFM) with an assembled cantilever probe (ACP) in various liquid environments. The largest contribution of this theory lies in its consideration of the material length scale parameter (MLSP) to analyze the effect of size on physical characteristics. When studying ACP in liquids, the hydrodynamic force creates a different behavior compared to an ACP beam enclosed in air. In this study, Hamilton’s principle is used to derive the nonlinear partial differential equation (PDE) of motion and associated boundary conditions (BCs) of the ACP in liquid environments. To achieve this, a combination of Euler-Bernoulli’s theory and strain gradient concepts are employed. As the next step, a reduced order model of the system is developed using the Galerkin method. To assess the nonlinear frequency response of the ACP in various liquid environments, perturbation technique, including the method of multiple scales (MMS), is applied to the developed reduced order model. The study also calculates resonance frequencies, phase planes, stability, and the potential function of the system analytically. The results of this study indicate that the system becomes nonlinear as the ratio of beam thickness to MLSP decreases. Several factors, including the ratio of beam thickness to MLSP as well as the viscous damping coefficient, can influence the jump phenomenon. Furthermore, the results of the phase and amplitude of the ACP in liquid environments demonstrate that an increase in the (h/l) ratio results in a decrease in response amplitude and a leftward shift in the phase of the response diagram. This phenomenon is indicative of a softening behavior exhibited by the system. Lastly, the paper examines the validity and accuracy of the MMS solution by comparing it to a numerical solution.

A 3D-Printed Microforce Sensor for Microscopic Objects

A cantilever probe microstructure is designed using mechanical metamaterials for an optical fiber microforce sensor tip.

Three-dimensional printed microcantilever with mechanical metamaterial for fiber-optic microforce sensing

Mechanical metamaterials can adjust mechanical properties of structures flexibly through a mechanical structural design based on the premise that the materials remain unchanged. Here, a cantilever probe microstructure is designed using mechanical metamaterials for an optical fiber microforce sensor tip that can be prepared by femtosecond laser-induced two-photon polymerization. The elastic constant k of the fabricated fiber-optic microforce sensor has been adjusted by two orders of magnitude from 0.165 to 46 N/m, and the geometric configuration of the cantilever beam can be tailored to match the mechanical properties of biological specimens. This fiber microforce sensor shows an ultra-high force sensitivity of 154 nm/µN and a force resolution of up to 130 pN. The optical fiber microforce sensor that shows the lowest force resolution in a direct-contact mode has high potential for biosensing applications, and the results reveal a potential design strategy for special scanning tunneling microscope probes with unique physical properties.

AFM SMILER: A Scale Model Interactive Learning Extended Reality Toolkit for Atomic Force Microscopy Created With Digital Twin Technology

The Atomic Force Microscope (AFM) is a precision mechatronic system for nanoscale imaging of surfaces. Due to limited instrument access and lack of visualization techniques, understanding its principles can be challenging. Digital twin technology allows the creation of virtual representations of physical systems, which can be particularly useful to address challenges in AFM education. To realistically simulate nanoscale physics, we first developed new efficient algorithms for four virtual scale models, including cantilever mechanics, probe transducers, controller tuning, and contact mechanics. Second, three simulated experiment interactive learning modules are developed for instrument operation, including virtual imaging, system overview, and imaging modalities. In the end, three hardware systems are integrated for an extended reality experience, including a macroscopic AFM scale model, a haptic device for probe-sample interaction force feedback, and an upgraded low-cost educational AFM for nanoscale imaging and instrumentation. This completes the eight total modules for the AFM SMILER: A scale model interactive learning extended reality toolkit. Preliminary studies show the toolkit being helpful for AFM education. In addition to mechatronics and nanotechnology education, techniques developed in this work can be generally applied to computationally efficient realistic digital twin creation.

Method to Measure Surface Tension of Microdroplets Using Standard AFM Cantilever Tips.

Surface tension is a physical property that is central to our understanding of wetting phenomena. One could easily measure liquid surface tension using commercially available tensiometers (e.g., Wilhelmy plate method) or by optical imaging (e.g., pendant drop method). However, such instruments are designed for bulk liquid volumes on the order of milliliters. In order to perform similar measurements on extremely small sample volumes in the range of femtoliters, atomic force microscope (AFM) is considered as a promising tool. It was previously reported that by fabricating a special "nanoneedle"-shaped cantilever probe, a Wilhelmy-like experiment can be performed with AFM. By measuring the capillary force between such special probes and a liquid surface, surface tension could be calculated. Here, we carried out measurements on microscopic droplets with AFM, but instead, using standard pyramidal cantilever tips. The cantilevers were coated with a hydrophilic polyethylene glycol-based polymer brush in a simple one-step process, which reduced its contact angle hysteresis for most liquids. Numerical simulations of a liquid drop interacting with a pyramidal or conical geometry were used to calculate surface tension from the experimentally measured force. The results on micrometer-sized drops agree well with bulk tensiometer measurement of three test liquids (mineral oil, ionic liquid, and glycerol), within a maximum error of 10%. Our method eliminates the need for specially fabricated "nanoneedle" tips, thus reducing the complexity and cost of measurement.

Active Probe Atomic Force Microscopy with Quattro-Parallel Cantilever Arrays for High-Throughput Large-Scale Sample Inspection.

An Atomic Force Microscope(AFM) isa powerful and versatile tool for nanoscale surface studies to capture 3D topography images of samples. However, due to their limited imaging throughput, AFMs have not been widely adopted for large-scale inspection purposes. Researchers have developed high-speed AFM systems to record dynamic process videos in chemical and biological reactions at tens of frames per second, at the cost of a small imaging area of up to several square micrometers. In contrast, inspecting large-scale nanofabricated structures, such as semiconductor wafers, requires nanoscale spatial resolution imaging of a static sample over hundreds of square centimeters with high productivity. Conventional AFMs use a single passive cantilever probe with an optical beam deflection system, which can only collect one pixel at a time during AFM imaging, resulting in low imaging throughput. This work utilizes an array of active cantilevers with embedded piezoresistive sensors and thermomechanical actuators, which allows simultaneous multi-cantilever operation in parallel operation for increased imaging throughput. When combined with large-range nano-positioners and proper control algorithms, each cantilever can be individually controlled to capture multiple AFM images. With data-driven post-processing algorithms, the images can be stitched together, and defect detection can be performed by comparing them to the desired geometry. This paper introduces principles of the custom AFM using the active cantilever arrays, followed by a discussion on practical experiment considerations for inspection applications. Selected example images of silicon calibration grating, highly-oriented pyrolytic graphite, and extreme ultraviolet lithography masks are captured using an array of four active cantilevers ("Quattro") with a 125 µm tip separation distance. With more engineering integration, this high-throughput, large-scale imaging tool can provide 3D metrological data for extreme ultraviolet (EUV) masks, chemical mechanical planarization (CMP) inspection, failure analysis, displays, thin-film step measurements, roughness measurement dies, and laser-engraved dry gas seal grooves.

Multipurpose active scanning probe cantilevers for near-field spectroscopy, scanning tunnel imaging, and atomic-resolution lithography

In this work, we report progress on developing a multipurpose scanning probe cantilever applying gallium nitride nanowires as the probe tip. Gallium nitride nanowires possess high potential as probes due to their straight profile, tunable electrical and optical properties, high Young’s Modulus, durability, and high-yield fabrication process. Their wide bandgap enables them to be pumped to emit ultraviolet pulses which can be used for optical imaging and spectroscopy. They can be doped during growth to be electrically conductive, and their sharp tips obtained during epitaxial growth enable confinement of a high electric field at tip–sample interface. Their sharp tips are obtained during fabrication by their epitaxial growth which eliminates the need for postprocess sharpening that is typically required for standard STM tips. We present results of using gallium nitride nanowires for scanning tunnel microscopy applications of atomic-resolution imaging and lithography, and atomic force microscopy applications of imaging and lithography in vacuum and atmospheric environments.

Customization of an atomic force microscope for multidimensional measurements under environmental conditions.

Atomic force microscopy (AFM) is an analytical surface characterization tool that reveals the surface topography at a nanometer length scale while probing local chemical, mechanical, and even electronic sample properties. Both contact (performed with a constant deflection of the cantilever probe) and dynamic operation modes (enabled by demodulation of the oscillation signal under tip-sample interaction) can be employed to conduct AFM-based measurements. Although surface topography is accessible regardless of the operation mode, the resolution and the availability of the quantified surface properties depend on the mode of operation. However, advanced imaging techniques, such as frequency modulation, to achieve high resolution, quantitative surface properties are not implemented in many commercial systems. Here, we show the step-by-step customization of an atomic force microscope. The original system was capable of surface topography and basic force spectroscopy measurements while employing environmental control, such as temperature variation of the sample/tip, etc. We upgraded this original setup with additional hardware (e.g., a lock-in amplifier with phase-locked loop capacity, a high-voltage amplifier, and a new controller) and software integration while utilizing its environmental control features. We show the capabilities of the customized system with frequency modulation-based topography experiments and automated voltage and/or distance spectroscopy, time-resolved AFM, and two-dimensional force spectroscopy measurements under ambient conditions. We also illustrate the enhanced stability of the setup with active topography and frequency drift corrections. We believe that our methodology can be useful for the customization and automation of other scanning probe systems.

Mechanism of near-field optical nanopatterning on noble metal nano-films by a nanosecond laser irradiating a cantilevered scanning near-field optical microscopy probe.

To overcome the diffraction limit, a laser irradiating cantilevered scanning near-field optical microscopy (SNOM) probe has been used in near-field optical nanopatterning. In this paper, the mechanism of nanopatterning on noble metal nano-films by this technique is investigated by the finite element method. It is proposed that the main mechanism of this phenomenon is the melt and reshaping of the nano-film under the SNOM tip. The melt is caused by the surface plasmon polariton-assisted enhancement and restriction within the SNOM tip aperture. The impacts of the gap g between the tip and substrate and the polarization of the laser are further analyzed.

The Development of 3D Atomic Force Microscopy with Magnetically Driven-Orthogonal Cantilever Probes

This paper presents a three-dimensional (3D)-atomic force microscopy (AFM) method based on magnetically driven (MD)-orthogonal cantilever probes (OCPs), in which two independent scanners with three degrees of freedom are used to achieve the vector tracking of a sample surface with a controllable angle. A rotating stage is integrated into the compact AFM system, which helps to achieve 360° omnidirectional imaging. The specially designed MD-OCP includes a horizontal cantilever, a vertical cantilever, and a magnetic bead that can be used for the mechanical drive in a magnetic field. The vertical cantilever, which has a protruding tip, can detect deep grooves and undercut structures. The design, simulation, fabrication, and performance analysis of the MD-OCP are described first. Then, the amplitude compensation and home positioning for 360° rotation are introduced. A comparative experiment using an AFM step grating verifies the ability of the proposed method to characterize steep sidewalls and corner details, with a 3D topography reconstruction method being used to integrate the images. The effectiveness of the proposed 3D-AFM based on the MD-OCP is further confirmed by the 3D characterization of a micro-electromechanical system (MEMS) device with microcomb structures. Finally, this technique is applied to determine the critical dimensions (CDs) of a microarray chip. The experimental results regarding the CD parameters show that, in comparison with 2D technology, from which it is difficult to obtain sidewall information, the proposed method can obtain CD information for 3D structures with high precision and thus has excellent potential for 3D micro–nano manufacturing inspection.

Direct force measurement and loading on developing tissues in intact avian embryos.

Developmental morphogenesis is driven by tissue stresses acting on tissue rheology. Direct measurements of forces in small tissues (100 µm-1 mm) in situ, such as in early embryos, require high spatial precision and minimal invasiveness. Here, we introduce a control-based approach, tissue force microscopy (TiFM), that integrates a mechanical cantilever probe and live imaging with closed-loop feedback control of mechanical loading in early chicken embryos. By testing previously qualitatively characterized force-producing tissues in the elongating body axis, we show that TiFM quantitatively captures stress dynamics with high sensitivity. TiFM also provides the means to apply stable, minimally invasive and physiologically relevant loads to drive tissue deformation and to follow the resulting morphogenetic progression associated with large-scale cell movements. Together, TiFM allows us to control tissue force measurement and manipulation in small developing embryos, and promises to contribute to the quantitative understanding of complex multi-tissue mechanics during development.

Preparation of a spherical biochar colloidal probe and its application in deciphering the mechanism of biochar mitigating membrane fouling

To better unravel biochar’s interface behavior and mitigation mechanism on membrane fouling, spherical biochar colloidal probes were prepared by adhering microspheres to the free end of the probe cantilever. The prepared colloidal probes were used to measure the interaction forces between the membrane and foulant/biochar and between the foulant and foulant/biochar by atomic force microscopy (AFM). The study investigated the differences in physicochemical properties of biochars and their mitigating effects on membrane fouling caused by bovine serum albumin (BSA). Results indicated that dosing biochar strengthened the electrostatic repulsion between BSA and membranes, thereby, mitigating the adhesion or deposition of BSA on the membrane surface. Additionally, spherical biochar (SBC) and hydrochar (HC) exhibited better membrane fouling mitigation than conventional biochar (CBC) due to better physicochemical properties, adsorption capacity, and a more porous fouling layer structure composed of microparticles. Importantly, the stronger adhesion force of SBC-PVDF (0.90 mN/m) than BSA-PVDF (0.50 mN/m) alleviated membrane fouling in the initial stage of the filtration, and the adhesion force of SBC-BSA (0.049 mN/m) alleviated membrane fouling in the later stage, resulting in higher water flux. The interaction force between mature SBC and BSA was comparable to that between BSA and BSA (0.14 mN/m) and stronger than that between original SBC and BSA (0.049 mN/m), implying further membrane fouling mitigation.

Dynamic Metal-Phenolic Coordination Complexes for Versatile Surface Nanopatterning.

We report a general nanopatterning strategy that takes advantage of the dynamic coordination bonds between polyphenols and metal ions (e.g., Fe3+ and Cu2+) to create structures on surfaces with a range of properties. With this methodology, under acidic conditions, 29 metal-phenolic complex-based precursors composed of different polyphenols and metal ions are patterned using scanning probe and large-area cantilever free nanolithography techniques, resulting in a library of deposited metal-phenolic nanopatterns. Significantly, post-treatment of the patterns under basic conditions (i.e., ammonia vapor) triggers a change in coordination state and results in the in situ generation of more stable networks firmly attached to the underlying substrates. The methodology provides control over feature size, shape, and composition, almost regardless of substrate (e.g., Si, Au, and silicon nitride). Under reducing conditions (i.e., H2) at elevated temperatures (180-600 °C), the patterned features have been used as nanoreactors to synthesize individual metal nanoparticles. At room temperature, the ammonia-treated features can reduce Ag+ to form metal nanostructures and be modified with peptides, proteins, and thiolated DNA via Michael addition and/or Schiff base reaction. The generality of this technique should make it useful for a wide variety of researchers interested in modifying surfaces for catalytic, chemical and biological sensing, and template-directed assembly purposes.

Electron-beam lithography of nanostructures at the tips of scanning probe cantilevers

We developed a process to fabricate nanoscale metallic gate electrodes on scanning probe cantilevers, including on the irregular surface of protruding cantilever tips. The process includes a floating-layer technique to coat the cantilevers in an electron-beam resist. We demonstrate gate definition through a lift-off process and through an etching process. The cantilevers maintain a high force sensitivity after undergoing the patterning process. Our method allows the patterning of nanoscale devices on fragile scanning probes, extending their functionality as sensors.