Tuning Fork Atomic Force Microscope Research Articles

Compact quartz tuning fork-atomic force microscope with a low thermal drift at room temperature

A quartz tuning fork-atomic force microscope (QTF-AFM) is one of the useful research instruments for studying atomic or molecular-level dynamics in an ultra-high vacuum and low-temperature environment. In such conditions, movement of atoms or molecules is minimized, eliminating concerns about thermal drift. However, if it is possible to accurately measure atomic or molecular-level dynamics at room temperature, valuable information about atomic or molecular motion in real-life scenarios can be obtained. Nonetheless, the biggest obstacle in observing molecular-level motion at room temperature is the difficulty in precisely determining the position due to thermal drift. In this study, to address this issue, glass material was used instead of conventional metal materials as a system body, and the size was significantly reduced to create a compact QTF-AFM system. The aim was to minimize the system's thermal drift (∼2 p.m./s), thereby compensating for the challenge of accurately confirming positions affected by thermal drift.

Strong Electronic Winds Blowing under Liquid Flows on Carbon Surfaces

Solid-liquid interfaces display a wealth of emerging phenomena at nanometer scales, which are at the root of their technological applications. While the interfacial structure and chemistry have been intensively explored, the potential coupling between liquid flows and the solid’s electronic degrees of freedom has been broadly overlooked up till now. Despite several reports of electronic currents induced by liquids flowing in various carbon nanostructures, the mechanisms at stake remain controversial. Here, we unveil the molecular mechanisms of interfacial liquid-electron coupling by investigating flow-induced current generation at the nanoscale. We use a tuning fork atomic force microscope to deposit and displace a micrometric liquid droplet on a multilayer graphene sample, and observe an electronic current induced by the droplet displacement. The measured current is several orders of magnitude larger than previously reported for water on carbon, and further boosted by the presence of surface wrinkles on the carbon surface. Our results point to a peculiar momentum transfer mechanism between the fluid molecules and graphene charge carriers, mediated mainly by the solid’s phonon excitations. These findings open new avenues for active control of nanoscale liquid flows through the solid walls’ electronic degrees of freedom.Received 28 June 2022Revised 27 October 2022Accepted 12 January 2023DOI:https://doi.org/10.1103/PhysRevX.13.011020Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNanofluidicsPhysical SystemsGrapheneCondensed Matter, Materials & Applied Physics

Research work in the Microscope-based Nanoscale Physics Lab

Assistant Professor Sangmin An is head of the Microscope-based Nanoscale Physics Laboratory (MNPL), Jeonbuk National University, South Korea. He and his team are using atomic force microscope (AFM)-based technology as the basis of their work to make advances in materials science on the atomic and molecular levels. The researchers are combining their AFM-based technology with the scanning tunnelling microscope (STM), Raman spectroscopy systems and scanning electron microscope (SEM). Using this variety of techniques is enabling the team to drive progress in their field and also assisting with advances in semiconductor technology, including improving surface roughness measurement technology, which directly impacts consumer electronics. An and the team are also focused on nanoscale 3D printing with a view to overcoming limitations associated with the resolution of 3D printing. The researchers have fabricated nanopipettes through laser irradiation of perforated glass or quartz using a mechanical puller. The nanopipettes are then attached to a crystal oscillator to enable 3D printing at the nanoscale. The team has developed a process in which physical properties of materials can be measured directly using AFM + in situ Raman spectroscopy. By combining AFM-based nanoscale 3D printing technology and optical apparatus, it is possible to measure the physical, electrical, chemical, and optical properties of target materials. An and the team are also performing investigations related to Kelvin probe force microscope (KPFM) and friction measurement, as well as improving AFM technology for AFM and quartz tuning fork AFM (QTF-AFM) systems.

Measuring Dielectrophoresis Force for Metallic and Non-metallic Particle Manipulations via a Quartz Tuning Fork Atomic Force Microscope

Dielectrophoresis (DEP) force is a widely studied topic because it has high utility in various research areas. Understanding DEP force is significant from the point of view of its efficient usage. Here, we confirmed the directions and magnitudes of DEP forces for metallic and non-metallic particle manipulations as well as force measurements via a quartz tuning fork atomic force microscopy (QTF-AFM) system. The 100 nm non-metallic silica particles having negative DEP force move toward the minimum point of the square of the electric field while the 60 nm metallic Au particles have positive DEP force. We also measured the magnitude of the DEP force in a liquid environment with electrodes. The experimentally measured DEP force magnitude was about 1 nN, which was similar to the simulation results, and the tendency of the measured force was consistent with that of the simulated case. This shows the possibility of using a QTF-AFM system as the fine force sensor in a liquid environment.

Nanopipette/Nanorod-Combined Quartz Tuning Fork⁻Atomic Force Microscope.

We introduce a nanopipette/quartz tuning fork (QTF)–atomic force microscope (AFM) for nanolithography and a nanorod/QTF–AFM for nanoscratching with in situ detection of shear dynamics during performance. Capillary-condensed nanoscale water meniscus-mediated and electric field-assisted small-volume liquid ejection and nanolithography in ambient conditions are performed at a low bias voltage (~10 V) via a nanopipette/QTF–AFM. We produce and analyze Au nanoparticle-aggregated nanowire by using nanomeniscus-based particle stacking via a nanopipette/QTF–AFM. In addition, we perform a nanoscratching technique using in situ detection of the mechanical interactions of shear dynamics via a nanorod/QTF–AFM with force sensor capability and high sensitivity.

A Unique Self-Sensing, Self-Actuating AFM Probe at Higher Eigenmodes.

With its unique structure, the Akiyama probe is a type of tuning fork atomic force microscope probe. The long, soft cantilever makes it possible to measure soft samples in tapping mode. In this article, some characteristics of the probe at its second eigenmode are revealed by use of finite element analysis (FEA) and experiments in a standard atmosphere. Although the signal-to-noise ratio in this environment is not good enough, the 2 nm resolution and 0.09 Hz/nm sensitivity prove that the Akiyama probe can be used at its second eigenmode under FM non-contact mode or low amplitude FM tapping mode, which means that it is easy to change the measuring method from normal tapping to small amplitude tapping or non-contact mode with the same probe and equipment.

Nanopipette combined with quartz tuning fork-atomic force microscope for force spectroscopy/microscopy and liquid delivery-based nanofabrication

This paper introduces a nanopipette combined with a quartz tuning fork-atomic force microscope system (nanopipette/QTF-AFM), and describes experimental and theoretical investigations of the nanoscale materials used. The system offers several advantages over conventional cantilever-based AFM and QTF-AFM systems, including simple control of the quality factor based on the contact position of the QTF, easy variation of the effective tip diameter, electrical detection, on-demand delivery and patterning of various solutions, and in situ surface characterization after patterning. This tool enables nanoscale liquid delivery and nanofabrication processes without damaging the apex of the tip in various environments, and also offers force spectroscopy and microscopy capabilities.

Position-resolved Surface Characterization and Nanofabrication Using an OpticalMicroscopeCombined with a Nanopipette/Quartz Tuning Fork Atomic Force Microscope

In this work, we introduce position-resolved surface characterization and nanofabrication using an optical microscope (OM) combined with a nanopipette-based quartz tuning fork atomic force microscope (nanopipette/QTF-AFM) system. This system is used to accurately determine substrate position and nanoscale phenomena under ambient conditions. Solutions consisting of 5 nm Au nanoparticles, nanowires, and polydimethylsiloxane (PDMS) are deposited onto the substrate through the nano/microaperture of a pulled pipette. Nano/microscale patterning is performed using a nanopipette/QTF-AFM, while position is resolved by monitoring the substrate with a custom OM. With this tool, one can perform surface characterization (force spectroscopy/microscopy) using the quartz tuning fork (QTF) sensor. Nanofabrication is achieved by accurately positioning target materials on the surface, and on-demand delivery and patterning of various solutions for molecular architecture.

Position-resolved Surface Characterization and Nanofabrication Using an Optical Microscope Combined with a Nanopipette/Quartz Tuning Fork Atomic Force Microscope

Abstract In this work, we introduce position-resolved surface characterization and nanofabrication using an optical microscope (OM) combined with a nanopipette-based quartz tuning fork atomic force microscope (nanopipette/QTF-AFM) system. This system is used to accurately determine substrate position and nanoscale phenomena under ambient conditions. Solutions consisting of 5 nm Au nanoparticles, nanowires, and polydimethylsiloxane (PDMS) are deposited onto the substrate through the nano/microaperture of a pulled pipette. Nano/microscale patterning is performed using a nanopipette/QTF-AFM, while position is resolved by monitoring the substrate with a custom OM. With this tool, one can perform surface characterization (force spectroscopy/microscopy) using the quartz tuning fork (QTF) sensor. Nanofabrication is achieved by accurately positioning target materials on the surface, and on-demand delivery and patterning of various solutions for molecular architecture.

Oscillation control electronics for a Quartz Tuning Fork Atomic Force Microscope (AFM)

This paper presents oscillation control electronics for Frequency Modulation Atomic Force Microscope (FMAFM). It presents a Phase Locked Loop circuit performing the function of Frequency Control and its complete analysis.

Enhanced Formation of a Confined Nano-Water Meniscus Using a 780 nm Laser with a Quartz Tuning Fork-Atomic Force Microscope

Demonstrated herein is the optical-field-induced enhancement of the formation of a confined nanowater meniscus using a distance-regulated quartz tuning fork-atomic force microscope (QTF-AFM) with a 780 nm laser. While a pulled optical fiber tip approaches the surface, the laser is suddenly turned on and focuses on the front spot of the tip by the shape of the pulled optical fiber, which plays the role of an objective lens and induces the gathering effect of the water molecules directed to the electromagnetic-field gradient in air. This phenomenon facilitates a new boundary condition to form a long-range confined nano-scale liquid bridge between the tip and the surface. After the pulling of the optical fiber, 20-nm-thick gold was sputtered on the apex (diameter: approximately 100 nm) of the tip to guide and focus the beam on the spot. The critical power of the laser to overcome the barrier for the formation of a new boundary is 100 microW at the distance of 22 nm from the substrate.

Low-volume liquid delivery and nanolithography using a nanopipette combined with a quartz tuning fork-atomic force microscope

Electric-field-induced low-volume liquid ejection under ambient conditions was realized at a low bias potential of 12 V via a nanopipette (aperture diameter of 30 nm) combined with a non-contact, distance-regulated (within 10 nm) quartz tuning fork-atomic force microscope. A capillary-condensed water meniscus, spontaneously formed in the tip-substrate nanogap, reduces the ejection barrier by four orders of magnitude, facilitating nanoliquid ejection and subsequent liquid transport/dispersion onto the substrate without contact damage from the pipette. A study of nanofluidics through a free-standing liquid nanochannel and nanolithography was performed with this technique. This is an important breakthrough for various applications in controlled nanomaterial-delivery and selective deposition, such as multicolor nanopatterning and nano-inkjet devices.

Substructures high resolution imaging of individual IgG and IgM antibodies with piezoelectric tuning fork atomic force microscopy

Atomic force microscopy (AFM) has been widely used in biotechnological research to visualize proteins or cell components with a sub-nanometric resolution. Most of the commercial AFM systems use the standard optical lever method of detection. However, the optical beam deflection technique integrated in AFM presents some disadvantages such as the thermal drift due to cantilever elongation and bending caused by the heat dissipation of the laser diode. Also, optical artifacts and interferences are usually observed in liquid environment with the optical detection, and the laser beam alignment procedure can be an elaborate process in liquid environment. Thus, it is extremely interesting to find an alternative approach to resolve such type of problems. Herein, we introduce a self-sensing piezoelectric tuning fork atomic force microscope (AFM) for molecular imaging on individual proteins. AFM measurements were performed on antibodies samples (IgG and IgM) to study the stability and applicability of this sensor for investigation of soft materials with high dynamical tendency. In this work, we could characterize the substructure of isolated IgG and IgM antibodies adsorbed onto mica surface in air with high resolution imaging. Moreover, we have identified clearly different conformations and substructure differences of individual antibodies with AFM operating in Amplitude Modulation (AM-AFM) and Phase Modulation (PM-AFM) imaging. The used methodology revealed to be very promising approach for high resolution imaging of isolated proteins with well-defined structures.

Force spectroscopy by dynamic atomic force microscopy on bovine serum albumin proteins changing the tip hydrophobicity, with piezoelectric tuning fork self-sensing scanning probe

A tuning fork AFM (atomic force microscope) scanning probe has been used to study the chemical grafting between a functionalized tip and BSA (bovine serum albumin) protein. A non-conventional chemistry based on diazonium salts has been applied to control the hydrophobicity and hydrophilicity of the tip termination, and to graft proteins on surface. Unfolding signatures during the protein stretching have been observed, using amplitude modulation (AM-AFM) control of the probe. We propose a methodology to obtain quantitative information of the withdrawal forces from the amplitude and phase signals. Our results demonstrate the great potential of this new piezoelectric probe combined in term of sensitivity and versatility of the chemical functionalization of the tip to analyze biological materials.

Refined tip preparation by electrochemical etching and ultrahigh vacuum treatment to obtain atomically sharp tips for scanning tunneling microscope and atomic force microscope

A modification of the common electrochemical etching setup is presented. The described method reproducibly yields sharp tungsten tips for usage in the scanning tunneling microscope and tuning fork atomic force microscope. In situ treatment under ultrahigh vacuum (p ≤10(-10) mbar) conditions for cleaning and fine sharpening with minimal blunting is described. The structure of the microscopic apex of these tips is atomically resolved with field ion microscopy and cross checked with field emission.

Dynamic Force Microscopy Study on Si(111).RAD.3*.RAD.3-Ag Using a Tuning Fork Atomic Force Microscope

By evaporating silver onto Si(111)7× 7 surfaces, heterogeneous samples can be prepared that enable the direct comparison of surfaces with very different characteristics. In contrast to the bare Si(111)7× 7 reconstructed surface, the silver film assumes reconstructions such as √3×√3, and (111) oriented silver islands may also be present depending on the degree of coverage and the annealing or growth temperature. In the present study, force-distance spectra are measured using a home-built low-temperature tuning fork atomic force microscope. The focus of this work is a comparative study of different types of surfaces using the same tip in order to form an understanding of dissipation in non-contact atomic force microscopy. Force spectroscopic studies of the Ag islands revealed two different types of spectra occurring with the same probability. In some cases, the frequency shift-distance (df-z) spectra exhibited the commonly observed distance dependence in the attractive regime with a single minimum. In other cases, df-z spectra exhibited a double minimum, which corresponds to the dissipation process. In contrast to the measurements on the Ag islands, all df-z spectra from the √3×√3 reconstructed surface showed a double-well structure. We found evidence that the dissipation processes on the Ag islands and the √3×√3 reconstructed surface are induced by reversible tip modifications. [DOI: 10.1380/ejssnt.2011.26]

Measuring the Charge State of an Adatom with Noncontact Atomic Force Microscopy

Charge states of atoms can be investigated with scanning tunneling microscopy, but this method requires a conducting substrate. We investigated the charge-switching of individual adsorbed gold and silver atoms (adatoms) on ultrathin NaCl films on Cu(111) using a qPlus tuning fork atomic force microscope (AFM) operated at 5 kelvin with oscillation amplitudes in the subangstrom regime. Charging of a gold atom by one electron charge increases the force on the AFM tip by a few piconewtons. Moreover, the local contact potential difference is shifted depending on the sign of the charge and allows the discrimination of positively charged, neutral, and negatively charged atoms. The combination of single-electron charge sensitivity and atomic lateral resolution should foster investigations of molecular electronics, photonics, catalysis, and solar photoconversion.

Aperture based Raman spectroscopy on SiGe film structures with high spatial resolution

AbstractWe have investigated silicon–germanium (SiGe) line structures employing metallic apertures in combination with Raman spectroscopy to obtain high‐spatial strain resolution below the diffraction limit. The apertures were cut into specifically shaped electrochemically etched tungsten tips, which were adjusted within the Raman laser beam on the sample surface by a tuning fork atomic force microscope. With this setup, line structures on patterned SiGe films with a center‐to‐center distance down to 200 nm were resolved in the Raman scans, evidently indicating a resolution clearly below the far‐field Raman resolution of about 600 nm for the used instrument. This setup allows improved local strain analysis by Raman spectroscopy and shows potential for further near‐field Raman applications. Copyright © 2008 John Wiley & Sons, Ltd.