Polymer‐free,low tension graphene mechanical resonators

Graphene resonators are fabricated using a polymer‐free, direct transfer method onto metal reinforced holey carbon grids. The resonators are distinguished by the absence of organic residues and excellent crystallinity. The normal mode frequencies are measured using a Fabry–Perot technique; resonance curves indicate highly linear behaviour but very little built‐in strain, which is consistent with device geometry examined by atomic force microscopy. We conclude that the oscillators' restoring force is due instead to graphene's intrinsic bending rigidity; our measurements indicate a value of approximately 1.0 eV, consistent with previous theoretical and experimental work. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Piezoresponse imaging and local characterization of ferroelectric domains in Pb(Zn1/3Nb2/3)O3–7%PbTiO3 single crystals

Ferroelectric domain structures of (001)‐oriented Pb(Zn_1/3Nb_2/3)O₃–7%PbTiO₃ (PZN‐7%PT) single crystals were visualized and characterized by piezoresponse force microscopy (PFM). Locally regular domain configurations are found to be possibly related to the stable macroscopic properties in the PZN‐7%PT single crystals. Nanoscale piezoresponse hysteresis loops measured by PFM tip revealed no evidence of local domain switching behavior in the PZN‐7%PT single crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Correlation of atomic force microscopy detecting local conductivity and micro‐Raman spectroscopy on polymer–fullerene composite films

Thin hetero‐junction composite films of polymer (electron donor) and fullerene (electron acceptor) are prepared on indium‐tin‐oxide coated glass by spin‐coating from solution in dichlorobenzene. Optimized atomic force microscopy (AFM) parameters allowed us to scan these soft composite films in contact mode and to measure their local conductivity with high lateral resolution by current‐sensing AFM. The morphology and local conductivity data are correlated with Kelvin force microscopy and micro‐Raman mapping and discussed with view to their photovoltaic properties. Regions with both compounds present are compared to areas where the components segregated, acting as shunts of the junction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Probe Indentation: A Mesoscale Approach to Characterise Powder Systems: Experimental Investigation of Monomodel and Bimodal Diameter Distributions of Glass Spheres

An experimental study investigating a novel power characterisation method is investigated. The scope of this experimental work is to assess the feasibility, suitability and sensitivity of small scale probe indentation as a mechanism by which Discrete element method (DEM) may be calibrated. This meso–scale approach is chosen for investigation since it bridges the gap between the single‐particle methodologies of atomic force microscopy (AFM) and bulk measurements such as shear cell testing. Five different mono‐modal populations of glass bead and bi‐modal blends of these populations have been examined. The force‐displacement profile from a spherical probe was measured during indentation into a powder bed. Discernable differences in the resultant force‐profile are quantifiable and a mechanism has been proposed for the physical basis of these different characteristics.     

Single atomic contact adhesion and dissipation in dynamic force microscopy

By combining dynamic force microscopy experiments and first-principles calculations, we have studied the adhesion associated with a single atomic contact between a nanoasperity--the tip apex--and a semiconductor surface--the Ge(111)-c(2 x 8). The nanoasperity's termination has been atomically characterized by extensive comparisons of the measured short-range force at specific sites with the chemical forces calculated using many atomic models that vary in structure, composition, and relative orientation with respect to the surface. This thorough characterization has allowed us to explain the dissipation signal observed in atomic-resolution images and force spectroscopic measurements, as well as to identify a dissipation channel and the associated atomic processes.     

Effect of C60 molecular rotation on nanotribology

The effect of C60 molecular rotation on the nanotribological properties of C60 single crystal surfaces has been studied by atomic/frictional force microscopy. The orientational order-disorder phase transition, in which the high temperature C60 free rotation is reduced to a low temperature hindered rotation, is shown to give rise to an abrupt change in friction and adhesion. This change in frictional force is quantitatively consistent with the observed change in adhesion. The similar slopes of the friction versus load curves in both phases indicate that the friction coefficient in the two phases remains about the same. Hence the C60 rotation does not provide an additional energy dissipation channel in the friction process.     

Microwave specific loss power of magnetic fluids subjected to a static magnetic field

This paper reports on the frequency dependence of the magnetic and electric power dissipation in a magnetic fluid sample, in the microwave frequency range (0.5 to 8GHz), at various values of the static magnetic field (0 to 167.8kA/m). The computation of the power dissipation relies on the experimental values measured for the complex dielectric permittivity, ɛ = ɛ′ - iɛ″, and the complex magnetic permeability, μ = μ′ - iμ″, over the same frequency range. The results show that the magnetic power dissipation is much larger than the electric one for the investigated sample. At a specific frequency, f (Hz) , the power dissipation, p, depends on the external magnetic field, and exhibits a maximum. The result obtained suggests the possibility of controlling the energy absorption in the microwave range by means of the application of an external magnetic field.     

Lead‐free piezoelectric (Na0.5Bi0.5)0.94TiO3–Ba0.06TiO3 nanofiber by electrospinning

Lead‐free (Na_0.5Bi_0.5)_0.94TiO₃–Ba_0.06TiO₃ (NBT‐BT6) nanofibers were synthesized by the sol–gel process and electrospinning, and a butterfly‐shaped piezoelectric response was measured by scanning force microscopy. NBT‐BT6 nanofibers with perovskite phase were formed, after being cleaned at 700 °C for 1 hour, and the diameters are in the range of 150 nm to 300 nm. The average value of the effective piezoelectric coefficient d₃₃ is 102 pm/V. The high piezoelectricity may be attributed to the easiness for the electric field to tilt the polar vector of the domain and to the increase of the possible spontaneous polarization direction. There is a potential for the application of NBT‐BT6 nanofibers in nanoscale piezoelectric devices. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Damping mechanism in dynamic force microscopy

A general theory is presented which describes the damping in dynamic force microscopy due to the proximity of the surface, consistently with resonant frequency shift effects. Orders of magnitude for the experimentally measured "dissipation" and image corrugation are reproduced. It is suggested that the damping does not mainly result from energy dissipation, but arises because not all solutions of the microlever equation of motion are accessible. The damping is related to the multivalued nature of the analytical resonance curve, which appears at some critical tip-surface separation.     

高频电磁波驱动等离子体电流

本文分析了高频电磁波驱动等离子体电流的效应,指出,波的电场力和洛仑兹力都对驱动电流有贡献;l=0或l≠0的共振都可能成为主要驱动机制,不同l的驱动效果有区别;非共振效应也可能超过共振效应而成为主要驱动机制,同时,波的碰撞耗散可能超过共振耗散而成为主要耗散机制。 关键词：     

Local chemical state change in Co–O resistance random access memory

Kelvin probe force microscopy (KFM) and conductive atomic force microscopy (C‐AFM) together with micro X‐ray photoelectron spectroscopy (XPS) were performed for the stacking structure comprising of the transition metal oxide Co–O and metal electrode, which exhibits large reproducible resistance switching. The application of the external voltage by the C‐AFM cantilever decreases the resistance of Co–O, which well accords with the non‐polar forming process observed in the Pt/Co–O/Pt trilayer, known as the candidate of resistance random access memory (ReRAM). Furthermore, the KFM and micro XPS experimentally revealed that the local reductive reaction of Co–O possibly nucleates the defect related energy levels which dominates the current conduction in the low resistance state. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Screen charge transfer by grounded tip on ferroelectric surfaces

We have investigated polarization reversal and charge transfer effects by a grounded tip on 50 nm thick ferroelectric thin films using piezoelectric force microscopy and Kelvin force microscopy. We observed the polarization reversal in the center of written domains, and also identified another mechanism, which is the transfer of screen charges toward the grounded tip. In order to overcome these phenomena, we successfully applied a modified read/write scheme featuring a bias voltage. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of tip–sample interaction forces from measured dynamic force spectroscopy curves

The forces between a sharp tip and a sample are characteristic for different sample materials. A new method for quantifying the elastic tip–sample interaction forces from measured frequency vs. distance curves is presented. The dynamic force–spectroscopy curves investigated were obtained by dynamic force microscopy under ultrahigh vacuum (UHV) conditions for large vibration amplitudes with commercial levers/tips. The full non-linear force–distance relationship is deduced via a numerical algorithm, where the equation of motion describing the oscillation of the tip is solved explicitly. The elastic force distance dependence can be determined by fitting the results of a computer simulation to experimental frequency vs. distance data. The obtained force–distance curves can be compared quantitatively with theoretical models.     

Atomic structure of alkali halide surfaces

The atomic structure of surfaces of alkali halide crystals has been revealed by means of high-resolution dynamic force microscopy. True atomic resolution is demonstrated both on steps surrounding islands or pits, and on a chemically mixed crystal. We have directly observed the enhanced interaction at low-coordinated sites by force microscopy. The growth of NaCl films on metal surfaces and radiation damage in a KBr surface is discussed based on force microscopy results. The damping of the tip oscillation in dynamic force microscopy might provide insight into dissipation processes on the atomic scale. Finally, we present atomically resolved images of wear debris found after scratching a KBr surface. PACS 68.37.-d; 68.37.Ps; 75.55.Fv     

Small‐signal lock‐in thermography at the maximum power point of an a‐Si solar mini‐module

The paper introduces a small‐signal lock‐in thermography (MPP‐SLIT) technique based on voltage modulations around the maximum power point (MPP) of an illuminated solar cell or module. At MPP the differential power dissipation of the entire device turns from negative (less dissipation with increasing voltage) to positive (more dissipation with increasing voltage). Pictures taken around the MPP unveil a positive or negative response depending on the respective local maximum power point. This paper presents qualitative discussions for two situations; firstly, where opposite signs of the LIT signal arise due to the parallel connection of areas with different photovoltaic quality on a single cell, and second, the interaction of cells of different quality connected in series in a solar module. The experimental verification of our method is obtained from an amorphous silicon thin‐film mini‐module. The experimental results demonstrate the validity of the method, especially the fact that positive and negative signs are observed in the same picture and depend on the position of the local operating point with respect to the local MPP. It is also observed that the signal arising from power dissipation at the cell interconnects is always negative. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Domain wall thickness variations of ferroelectric BaMgF4 single crystals in the tip fields of an atomic force microscope

The ferroelectric domain wall thickness of a fluoride BaMgF₄ single crystal was investigated by piezoresponse force microscopy. It was found that the domain wall thickness shows a strong spatial variation in the as‐grown crystal and the polarization reversal process. The original wall thickness is greater (about two to seven times) than that switched by the tip fields of the atomic force microscope. A significantly narrower domain wall was obtained in the higher tip‐field. The trapped defects at the domain wall play an important role in the spatial variation of the polarization width of 180° domain wall in the BaMgF₄ single crystal. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-Contact to Contact Transition： Direct Measurements of Interaction Forces between a Solid Probe and a Planar Air-Water Interface

The interaction force between a solid probe and a planar air-water interface is measured by using an atomic force microscope. It is demonstrated that during the approach of the probe to the air-water interface, the force curves decline all the time due to the van der Waals attraction and induces a stable profile of water surface raised. When the tip approaches very close to the water surface, force curves jump suddenly, reflecting the complex behaviour of the unstable water surface. With a theoretical analysis we conclude that before the tip touches water surface, two water profiles appear, one stable and the other unstable. Then, with further approaching, the tip touches water surface and the non-contact to contact transition occurs.     

Local spectroscopy and atomic imaging of tunneling current, forces, and dissipation on graphite

Theory predicts that the currents in scanning tunneling microscopy (STM) and the attractive forces measured in atomic force microscopy (AFM) are directly related. Atomic images obtained in an attractive AFM mode should therefore be redundant because they should be similar to STM. Here, we show that while the distance dependence of current and force is similar for graphite, constant-height AFM and STM images differ substantially depending on the distance and bias voltage. We perform spectroscopy of the tunneling current, the frequency shift, and the damping signal at high-symmetry lattice sites of the graphite (0001) surface. The dissipation signal is about twice as sensitive to distance as the frequency shift, explained by the Prandtl-Tomlinson model of atomic friction.     

Mesoscopic thermal and thermoelectric measurements of individual carbon nanotubes

We discuss the mesoscopic experimental measurements of electron energy dissipation, phonon thermal transport, and thermoelectric phenomena in individual carbon nanotubes. The temperature distributions in electrically heated individual multiwalled carbon nanotubes have been measured with a scanning thermal microscope. The temperature profiles along the tube axis in nanotubes indicate the bulk dissipation of electronic energy to phonons. In addition, thermal conductivity of an individual multiwalled nanotube has been measured using a microfabricated suspended device. The observed thermal conductivity is two orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. Finally, we present thermoelectric power (TEP) of individual single walled carbon nanotubes using a novel mesoscopic device. A strong modulation of TEP as a function of the gate electrode was observed.     

Measurement of the energy dissipated in the hand and arm whilst using vibratory tools

Acceleration levels during hand-held grinding have been measured. By controlling the input to a vibration shaker the same acceleration levels were introduced into a specially designed handle gripped by a human hand. From measurements of force, acceleration and phase the power dissipated in the hand was calculated in third-octave bands. Approximate agreement was achieved with power dissipation estimates obtained from the acceleration alone by assuming the hand-arm system to be a linear, single degree of freedom system. The power dissipated is proposed as an important parameter affecting vibration-induced white finger.