Scanning Probe Microscopy Cantilever Research Articles

Microwave synthesis of molybdenene from MoS2

Dirac materials are characterized by the emergence of massless quasiparticles in their low-energy excitation spectrum that obey the Dirac Hamiltonian. Known examples of Dirac materials are topological insulators, d-wave superconductors, graphene, and Weyl and Dirac semimetals, representing a striking range of fundamental properties with potential disruptive applications. However, none of the Dirac materials identified so far shows metallic character. Here, we present evidence for the formation of free-standing molybdenene, a two-dimensional material composed of only Mo atoms. Using MoS2 as a precursor, we induced electric-field-assisted molybdenene growth under microwave irradiation. We observe the formation of millimetre-long whiskers following screw-dislocation growth, consisting of weakly bonded molybdenene sheets, which, upon exfoliation, show metallic character, with an electrical conductivity of ~940 S m−1. Molybdenene when hybridized with two-dimensional h-BN or MoS2, fetch tunable optical and electronic properties. As a proof of principle, we also demonstrate applications of molybdenene as a surface-enhanced Raman spectroscopy platform for molecular sensing, as a substrate for electron imaging and as a scanning probe microscope cantilever.

Volcano-Shaped Scanning Probe Microscopy Probe for Combined Force-Electrogram Recordings from Excitable Cells.

Atomic force microscopy based approaches have led to remarkable advances in the field of mechanobiology. However, linking the mechanical cues to biological responses requires complementary techniques capable of recording these physiological characteristics. In this study, we present an instrument for combined optical, force, and electrical measurements based on a novel type of scanning probe microscopy cantilever composed of a protruding volcano-shaped nanopatterned microelectrode (nanovolcano probe) at the tip of a suspended microcantilever. This probe enables simultaneous force and electrical recordings from single cells. Successful impedance measurements on mechanically stimulated neonatal rat cardiomyocytes in situ were achieved using these nanovolcano probes. Furthermore, proof of concept experiments demonstrated that extracellular field potentials (electrogram) together with contraction displacement curves could simultaneously be recorded. These features render the nanovolcano probe especially suited for mechanobiological studies aiming at linking mechanical stimuli to electrophysiological responses of single cells.

Variations in Electric Switching and Transverse Resistance of GeTe/ Sb2Te3 Superlattices at Elevated Temperature Studied by Conductive Scanning Probe Microscopy

ABSTRACTTemperature-dependent variations in electric switching and transverse resistance of phase-change [(GeTe)2(Sb2Te3)]n (n=4 and 8) chalcogenide superlattice (CSL) films were studied using conductive scanning probe microscopy (SPM). Three temperature regions with different electric transport properties were recognized in point current-voltage (I-V) spectra and the surface potential maps measured with tantalum and platinum-coated SPM cantilevers. At around 80°C the switching voltage decreased abruptly from ∼2 V to 0.5 V and the thermal coefficient of resistance changes its sign, indicating different carrier transport mechanisms. The observed changes correlated with decrease in the surface potential by ∼150 meV from 25 to 150°C. The results were ascribed to an opening of the CSL electronic band gap near the Fermi energy caused by thermal stress, which led to the transition from a Dirac-like semimetal to a narrow-gap semiconductor.

A novel method for formation of single crystalline tungsten nanotip

A point electron source is desired to improve performance of high brightness electron beam instruments. It is valuable to create nano-sized tungsten (W) tip from sharp ordinary polycrystalline W needle. The sharp W needle, which is manufactured by electrochemical etching, has been practically utilized as a cold field emission electron source. A novel method for formation of single crystalline W nanotip on the top of h-BN coated conventional polycrystalline tungsten, by supplying high voltage, has been found. The W nanotip with an apex radius as small as a few times 10 nm would be grown on the top of the polycrystalline W needle. Field emission characteristics of obtained W nanotip are measured, and the field emission microscopic (FEM) and transmission emission microscopic (TEM) images are observed. The emission current from the W nanotip is measured to exceed 0.1 mA. The FEM image shows significant electron emission from the crystallographic facets of the W single crystal. From these results, the present method for formation of the single crystalline W nanotip would be expected as a key technology to realize a point electron source with a nano-sized apex which makes it possible to improve the performance of high brightness electron beam instruments, especially tiny X-ray tubes for medical use, as well as a cantilever of scanning probe microscope.

Noninvasive Measurement of Electrical Events Associated with a Single Chlorovirus Infection of a Microalgal Cell.

Chlorovirus Paramecium bursaria chlorella virus 1 (PBCV-1) contains a viral-encoded K(+) channel imbedded in its internal membrane, which triggers host plasma membrane depolarization during virus infection. This early stage of infection was monitored at high resolution by recording the cell membrane depolarization of a single Chlorella cell during infection by a single PBCV-1 particle. The measurement was achieved by depositing the cells onto a network of one-dimensional necklaces of Au nanoparticles, which spanned two electrodes 70 μm apart. The nanoparticle necklace array has been shown to behave as a single-electron device at room temperature. The resulting electrochemical field-effect transistor (eFET) was gated by the cell membrane potential, which allowed a quantitative measurement of the electrophysiological changes across the rigid cell wall of the microalgae due to a single viral attack at high sensitivity. The single viral infection signature was quantitatively confirmed by coupling the eFET measurement with a method in which a single viral particle was delivered for infection by a scanning probe microscope cantilever.

Design and Analysis of Scanning Probe Microscopy Cantilevers With Microthermal Actuation

The scanning probe microscope has revolutionized our ability to image and characterize the physical and chemical properties of material with atomic resolution. It has evolved as a versatile instrument for nanofabrication including atomic deposition, nanolithography, nanomachining, atomic manipulation, and assembly. However, in order to enable practical nanofabrication with scanning probe tips, it is critical to address the issues of throughput, tip wear effects, chemical cross contamination, and scalability. In this paper, we address these issues by designing, optimizing, fabricating, and testing active electromechanical cantilever probes with an integrated microgripper for automated modular tip exchange. The cantilevers are designed and optimized to be compatible with existing atomic force microscope systems. Mechanical performance and optimization are carried out by the development of an analytical electrothermomechanical model and multiphysics finite-element analysis. The silicon cantilevers are formed by microfabrication processes and characterized by scanning electron microscopy, laser vibrometry, and in situ optical microscopy current–voltage studies. The cantilever grippers are shown to actuate with a maximum displacement of $3~\mu \text{m}$ for each arm at an applied voltage of 4 V 6- $\mu \text{m}$ total displacement for grasping modular tool-tips. Gripping is demonstrated by grasping and releasing of a cylindrical microtool (wire). [2014-0332]

Method for Measuring the Distribution of Adhesion Forces on Continuous Nanoscale Protrusions Using Carbon Nanofiber Tip on a Scanning Probe Microscope Cantilever

The adhesion force on surfaces has received attention in numerous scientific and technological fields, including catalysis, thin-film growth, and tribology. Many applications require knowledge of the strength of these forces as a function of position in three dimensions, but until now such information has only been theoretically proposed. Here, we demonstrate an approach based on scanning probe microscopy that can obtain such data and be used to image the three-dimensional surface force field of continuous nanoscale protrusions. We present adhesion force maps with nanometer and nanonewton resolution that allow detailed characterization of the interaction between a surface and a thin carbon nanofiber (CNF) rod synthesized by plasma-enhanced chemical vapor deposition (PECVD) at the end of a tip on a scanning probe microscope cantilever in three dimensions. In these maps, the positions of all continuous nanoscale protrusions are identified and the differences in the adhesive forces among limited areas at inequivalent sites are quantified.

Magnetic Vortices Induced by a Monopole Tip

A ferromagnetic monolayer with an easy-plane anisotropy scanned by a magnetic tip that is moved with constant velocity ν is studied using atomistic computer simulations. The spin dynamics are treated using the Landau-Lifshitz-Gilbert equation. To study the influence of the tip's field, it is modeled by a monopole field instead of a dipole field, which is a common near-field approximation of a scanning probe microscopy cantilever. The magnetic structures induced by the moving tip are analyzed with respect to the strength of the coupling as well as the scanning velocity, and the energy dissipation is calculated. The results agree with calculations in a continuum model using Thiele's equation, as well as with earlier results obtained from simulations using a dipolar tip. The quantitative influence of the field is illustrated using energetic arguments.

Systematic characterization of optical beam deflection measurement system for micro and nanomechanical systems

Optical beam deflection (OBD) measurement method is very popular in various types of scanning probe microscopy (SPM) and micro/nanomechanical sensors to measure a mechanical motion. This paper reports the detail design and implementation of a very low drift (2nm over 1000s), high bandwidth (40MHz) and low noise (15fm/Hz) OBD measurement setup that can be used in metrological SPM. The noise, bandwidth and stability of the setup and the thermo-mechanical behavior of SPM cantilevers were systematically characterized. The influences of optical beam spot size, power of the laser beam and the type of position sensitive detector on the total measurement noise for different preamplifications were analyzed in detail. Consequently, recommendations for further improvements of the OBD systems in SPMs and MEMS sensors are given. The results can be used in future high speed, high accurate and low drift SPMs and MEMS sensors applications.

An Evaluation of Local Thermal Analysis of Polymers on the Sub-Micrometer Scale Using Heated Scanning Probe Microscopy Cantilevers

A basic understanding of thermal properties of polymers is of fundamental importance for the development of advanced polymers. However, up to now, mainly bulk properties have been investigated. To characterize local softening processes in polymers, a local thermal analysis (LTA) technique is applied as an add-on to a scanning probe microscope. The development of a new generation of heatable cantilever probes enables thermal analysis in the sub-μm range. This method is based on an appropriate temperature calibration, which provides a reliable correlation of the applied voltage heating the tip and the actual temperature at the tip-sample interface. As the presented technique is more susceptible to environmental changes than comparable macroscopic methods, different parameters that might influence its performance are evaluated like a strong dependence on sample temperature. It is shown that the measured softening temperature on a polystyrene (PS) sample decreases from 102.2 to 66.4 °C as the temperature of the substrate is increased by 50 °C. The interaction between heat from the cantilever and the substrate is the reason for local sample softening, which opens new perspectives to understand the temperature calibration process using the melting standard method. A stepwise guideline for a suitable temperature calibration is provided.

Multifunctional nanoanalytics and long-range scanning probe microscope using a nanopositioning and nanomeasuring machine

An interferometer-based metrological scanning probe microscope (SPM) is successfully integrated into our nanopositioning and nanomeasuring machine (NPM machine) for high-precision measurements with nanometre uncertainty over a range of 25 mm × 25 mm × 5 mm. Both devices were developed at the Institute of Process Measurement and Sensor Technology of Ilmenau University of Technology, Germany. Outstanding results were achieved for different measurement tasks. With the NPM machine, truly long-range and long-term measurements are possible. Due to the tip wear, an automatic SPM cantilever replacement is preferable. Such a tip replacement is also required for the integration of multifunctional nanoanalytics. For example, for Kelvin probe force microscopy (KPFM), the measurement of topography and surface potential with different SPM tips is necessary. For this purpose, an electromagnetic tip changer was designed. The tip changer comprises three SPM probes. In order to retrieve the previous tip positions, additional fiducial marks were developed. The repeatability of relocation is less than 10 nm. The automatic tip changer and fiducial marks are integrated into a sample holder. The tip changer in combination with fiducial marks allows scanning distances three times longer (with the same type of SPM probes) and multifunctional nanoanalytics (with different SPM probes with special properties). Sample KPFM measurements are demonstrated. The developed tip changer, including special fiducial marks, improves the performance and functionality of the NPM machine crucially.

On the operating stability of a scanning force microscope with a nanowhisker at the top of the probe

The functioning of the scanning probe microscope cantilever with a metal-carbon whisker at the top is studied. Metal-carbon whiskers grown by focused ion beam deposition in the presence of precursor gases have an aspect ratio in the range α = 10−200 and hold shape upon multiple scanning in the constant force mode. The advantage of probes with whiskers at the top in examining rough surfaces with vertical walls and narrow grooves is demonstrated experimentally. At high α, the scanning probe microscope is found to operate unstably, because the lateral surface of the whisker interacts with the specimen. It is shown that the axis of the whisker should be set normally to the specimen’s surface for the microscope to operate reliably at high aspect ratios.

Cooling of the SPM cantilever by nonlinear mechanical frequency modulation with cavity‐induced radiation force

AbstractWe perform a systematic analysis of the dynamics of a scanning probe microscope (SPM) cantilever incorporating the mechanical nonlinearity by the cavity‐induced radiation force (CIRF) under the random noise depending on the ambient conditions. It has been clarified that higher vibration modes emerge and modulate the mechanical frequency of the cantilever to greatly suppress its amplitude by increasing CIRF.Particularly, we have revealed that the cooling efficiency of translational motion of cantilever can be controlled by changing the properties of ambient environment. The results and discussion here will give us guiding principles to control the sensitivity of SPM by utilizing CIRF (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Density measurement of pillar structure fabricated via nanoimprinting using a poly(dimethylsiloxane) mold

The authors report density measurements of a pillar structure that was fabricated via nanoimprinting using a poly(dimethylsiloxane) mold. The imprinted pillars were fabricated using two types of resin, SU-8 and hydrogen silsesquioxane, and were characterized by measuring the spring constant using a scanning probe microscopy cantilever, which was manipulated with a three-axis actuator. The spring constant determined Young's modulus of the imprinted pillars. The authors measured the resonant frequency using the alternating current electrostatic force. Using the results for Young's modulus and the resonant frequency, they determined the density of the pillar structure fabricated via nanoimprinting.

Micromachined self-actuated piezoresistive cantilever for high speed SPM

This paper presents high resonance frequency (~400-1000kHz) thermally actuated piezoresistive cantilevers for scanning probe microscopy (SPM). A novel technological fabrication process for the cantilever is presented. Theoretical calculations and simulations using the finite element method (FEM) are done to optimize the mechanical as well as the thermal properties. We investigate the cantilever's dynamics, the actuation and sensing mechanism, keeping focus on electrical crosstalk between sensor and actuator. High-speed imaging with a fast x-y scanning stage combined with a custom build AFM controller shows the potential of the cantilever. Images with scan rates up to oneimagepersecond are obtained.

Mechanical characteristics of imprinted nanostructures fabricated with a poly(dimethylsiloxane) mold

Nanoscale imprinted pillars were fabricated with three resin systems and characterized by measuring the spring constant using a scanning probe microscopy cantilever manipulated with a three-axis actuator. The functional dependence of the spring constant on the height and diameter of the pillar was then used to determine the Young’s modulus. Nanoindentation was used to determine the Young’s modulus of the base film. Before high temperature annealing, the Young’s modulus of the imprinted pillar was nearly the same as that of film. After the annealing, the Young’s modulus of the imprinted pillar was lower than that of the film.

Quartz-crystal scanning probe microcantilevers with a silicon tip based on direct bondingof silicon and quartz

This paper reports on the design, fabrication and characterization of cantilever-shapedquartz-crystal resonators for scanning probe microscopy (SPM) in order to operate undervarious environments, especially in liquids for biological applications. The cantilevers havefunctions of self-sensing and self-actuation using piezoelectric effects, and these propertiesare demonstrated experimentally. Compared to conventional SPM cantilevers, this quartzcantilever is easy to utilize as a SPM based force sensor in liquids because theself-actuating properties can lead to no spurious resonant peaks. In addition,the self-sensing properties will enable its use even in an opaque liquid and cansimplify the SPM system. In this research, quartz cantilevers are fabricated onsilicon using a silicon–quartz direct bonding technique, and the sharp silicontip is integrated at the end of the cantilever as well. Additionally, the electricalQ-enhancement(active Q-control) was tested.

Size Control of Carbon Nanofiber Probes Fabricated by Ion Irradiation

The effect of ion species and fabrication temperature on the size of ion-induced carbon nanofibers (CNFs) grown on tips of scanning probe microscope cantilevers was investigated in detail. Similarly to that using Ar+ ions, the fabrication of CNF probes using Ne+ and Xe+ ions was possible. Xe+ sputtering yielded the shortest CNF probes owing to its large sputtering effect; however, a significant difference in the size of the CNF probes between Ne+ and Ar+ ion irradiation was not observed. The CNFs increased in length with fabrication temperature owing to the enhanced diffusion of C atoms at elevated temperatures; however, the CNF diameter remained almost constant independent of fabrication temperature. Therefore, the fabrication at elevated temperatures was effective for the rapid fabrication of practical CNF probes. Thus, the CNF probe size was controllable by adjusting the fabrication temperature and ion species.

Electrical Modes in Scanning Probe Microscopy

Scanning probe microscopy methods allow the investigation of a variety of sample surface properties on a nanometer scale, even down to single molecules. As molecular electronics advance, the characterization of electrical properties becomes more and more important. In both research and industry, films made from composite materials and lithographically structured elements have already reached structure sizes down to a few nanometers. Here, we review the major scanning probe microscopy modes that are used for electrical characterization of thin films, that is, scanning conductive force microscopy, Kelvin probe force microscopy and scanning electric field microscopy. To demonstrate the possibilities and capabilities of these modes, reference samples were fabricated by means of focused ion beam deposition and analyzed using the described methods. Furthermore, two upcoming modes are presented that are based on: i) local current measurements while the SPM-cantilever is excited into torsional vibrations, and, ii) changes in a backscattered microwave that was coupled into a scanning probe microscopy-cantilever. The scanning-probe-based electrical modes are applicable for studies of functional layers used in soft matter electronic devices under realistic environmental conditions.

A hybrid scanning probe microscope (SPM) module based on a DVD optical head

The development of a highly sensitive (sub-nanometer) and multi-platform scanning probe microscope (SPM) module is presented. The module is based on an optical DVD pick-up head and uses its astigmatic detection scheme to detect the vertical displacement of the SPM cantilevers. The complete hybrid SPM module is capable of scanning in SPM intermittent contact, SPM contact and optical profilometry modes. The module can be used in a modified optical microscope or be implemented in a stand-alone system. Measurement results prove that the mechanical stability of this SPM module is high enough for atomic resolution imaging. Both scanning-sample and scanning-probe-type SPM setups have been tested based on this SPM module. The noise level and drift rate in the z-direction of the stand-alone system are 10 pm (rms) and 0.2 nm min−1, respectively.