Abstract: Many interactions drive the adsorption of molecules on surfaces, all of which can result in a measurable change in surface stress. This article compares the contributions of various possible interactions to the overall induced surface stress for cantilever-based sensing applications. The surface stress resulting from adsorption-induced changes in the electronic density of the underlying surface is up to 2-4 orders of magnitude larger than that resulting from intermolecular electrostatic or Lennard-Jones interactions. We reveal that the surface stress associated with the formation of high quality alkanethiol self-assembled monolayers on gold surfaces is independent of the molecular chain length, supporting our theoretical findings. This provides a foundation for the development of new strategies for increasing the sensitivity of cantilever-based sensors for various applications.
Abstract: Non-contact atomic force microscopy is rapidly expanding from ultra-high vacuum to include the study of surfaces and biomolecules in liquids by high resolution imaging and force spectroscopy. This is despite the additional frequency shift noise due to the inherently low Q factor of the cantilever oscillating in a liquid. In this paper we present a tip based on an optical fiber which can operate in liquid with Q factors in excess of 100 using a âdiving bellâ arrangement which allows only a small portion of the tip to be submerged. We demonstrate stable imaging and force spectroscopy using this set-up. The tips are based on scanning near-field optical microscopy tips and, when used with NC-AFM, provide a method of combining both high resolution mechanical and fluorescence studies of biomolecules and cells.
Abstract: There has been increasing focus on the use of Kelvin probe force microscopy (KPFM) for the determination of local electronic structure in recent years, especially in systems where other methods, such as scanning tunnelling microscopy/spectroscopy, may be intractable. We have examined three methods for determining the local apparent contact potential difference (CPD): frequency modulation KPFM (FM-KPFM), amplitude modulation KPFM (AM-KPFM), and frequency shift-bias spectroscopy, on a test system of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on NaCl, an example of an organic semiconductor on a bulk insulating substrate. We will discuss the influence of the bias modulation on the apparent CPD measurement by FM-KPFM compared to the DC-bias spectroscopy method, and provide a comparison of AM-KPFM, AM-slope detection KPFM and FM-KPFM imaging resolution and accuracy. We will also discuss the distance dependence of the CPD as measured by FM-KPFM for both the PTCDA organic deposit and the NaCl substrate.
Abstract: A technique for highly reproducible deposition of nanoscale sized gold dots in an atomic force microscopy (AFM) configuration is described. This is achieved by precisely controlling the tip-sample separation, using feedback control enabled by the application of an external electrostatic servo force. Application of a voltage pulse of either polarity to a gold coated oscillating cantilever tip leads to the deposition of the Au dot. Dimensions for the fabricated dots are 6-100 nm in width, and $<$1-10 nm in height. The well controlled deposition process allowed the study of dot formation and the obtaining of relevant statistics. We found that the deposition process is the field emission of Au ions. Nevertheless, threshold values obtained are higher than previously reported ones and were found to be dependent on the tip shape. Depositions are independent of substrate morphology and lithographically patterned lines formed by overlapping Au nanodots as long as 55 um have been fabricated.
Abstract: Tunneling measurements of dI/dV, d2I/dV2, and d 3I/dV3 were performed along the C3 axis (normally to layers) for Bi2Te3 and Sb2Te 3 layered semiconductors in the temperature range 4.2 < T < 295 K. Temperature dependences of the forbidden band energy Eg were obtained. The forbidden band energy in Bi2Te3 was 0.20 eV at room temperature and increased to 0.24 eV at T = 4.2 K. The Eg value for Sb2Te3 was 0.25 eV at 295 K and 0.26 eV at 4.2 K. The distance between the top of the higher valence band of light holes and the top of the valence band of heavy holes situated lower was found to be ÎEV $\approx$19 meV in Bi2Te3; this distance was independent of temperature. The conduction bands of Bi2Te 3 and Sb2Te3 each contain two extrema with distances between them of ÎEc $\approx$ 25 and 30 meV, respectively. \copyright 2003 MAIK "Nauka/Interperiodica".
Abstract: A non-contact atomic force microscope (NC-AFM) based on a microfabricated piezoelectric cantilever is presented. A single piezoelectric lead zirconate titanate thin film layer on the cantilever serves as deflection sensing, cantilever oscillation and feedback actuation. Since such an AFM requires neither external oscillator nor external deflection sensor, considerably simple instrumentation becomes possible even for extreme environments such as low temperature or ultra-high vacuum. Also feedback control by the integrated actuator in the cantilever makes faster scanning possible. Images of atomic steps on annealed sapphire (0001) surfaces have been observed in air atmosphere in frequency modulation mode.
Abstract: A new atomic force microscope(AFM)was developed and its performance was evaluated experimentally and theoretically. First, a self-sensing and self-actuating probe with PZT film was fabricated, which simplifies AFM structure and increases imaging speed. Next, its dynamic characteristics were clarified by forced-vibration tests and follow-up tests, and the measured response time agreed with theoretical one obtained by a transient response analysis of a 1-DOF system. Finally a sapphire surface was measured by the developed AFM and the atomic size resolution was obtained.
Abstract: The effect of doping with Hf atoms on the nearly commensurate (NC) charge-density-wave (CDW) structures of 1T-TaS2 was investigated using scanning tunnelling microscopy (STM) at room temperature, for levels of substitution of Hf for Ta up to 6.9%. It was found that the Hf atom introduces a point defect to the CDW superlattice at the CDW domain boundary for lower contents. For Hf contents higher than 1%, the CDW superlattice melted and a distorted structure was observed instead of the usual CDW superlattice. The change of the CDW structure observed by STM was compared with the change of the Ï-T characteristics.
Abstract: Noncontact atomic force microscopy with frequency modulation detection is a promising technique for surface observation with true atomic resolution. The piezoelectric material itself can be an actuator and sensor of the oscillating probe simultaneously, without the need for additional electro-mechanical transducers or other measurement systems. A vertical resolution of 0.01 nm rms has been achieved using a microfabricated cantilever with lead zirconate titanate thin film in noncontact mode frequency modulation detection. The cantilever also has a sharpened pyramidal stylus with a radius of about 10 nm for noncontact atomic force microscopy.
Abstract: Scanning tunneling microscopy has been used to investigate the effects of hafnium impurities on the charge density wave (CDW) state in 1T-TaS2 at room temperature. The STM images have shown that Hf atom strongly affects the CDW state to destroy its long range order and the CDW state has changed to a characteristic one, which has a parallel-line structure in small regions. It suggests that the CDW state has become a single-q CDW state from a triple-q CDW state in the regions due to the strong pinning by Hf.
Abstract: Single crystals of (LaO)CuS with size 100x100x5 μm3 have been prepared by annealing of small crystals and polycrystalline powders of (LaO)CuS in iodine atmosphere at 1373 K. The iodine pressure at this temperature is about 5 atm. The present study indicates that there are optimum values both of iodine pressure and annealing temperature.
Abstract: Tunnelling spectroscopy measurements were carried out on the mixed crystal TiSe2-xSx (0 $\leq$ $\times$ $\times$ 0.55) to investigate the change in the density of states in the CDW state. The temperature dependences of the CDW energy gap widths were obtained. Experiments showed that the flattening of the peak in the Ï-T curve with increasing x corresponds to the decrease in the CDW energy gap. A model was proposed in which the anomalous Ï-T characteristics in this system were explained in terms of the competition of the two conduction mechanisms associated with the metallic carriers and the âexcitonicâ carriers.
Abstract: Tunneling measurements were carried out to investigate the valence band structure of Pb1-xEuxTe with x = 0.038. A marked decrease in the dI/dV has been observed in the energy range of Eu-4f states. It was found that the top edge of the Eu-4f states lies 0.13 eV below the top of the valence band for x = 0.038.
Abstract: The CDW energy gap structure of TiSe2 has been observed by tunnelling spectroscopy and its temperature dependence obtained for 77 K$<$or=T$<$or=295 K. In addition to the energy gap associated with the CDW with Tc=201 K, a narrower gap structure was observed to persist at higher temperature, which explains the negative temperature coefficient of the rho -T curve above Tc.
Abstract: The monolithic approach described in this work proposes the use of a laser cut small bulk piezoceramic designed as a fully integrated flat scanning stage. Some zones are active and others purely passive. The piezoelectric deformation is amplified by a lever mechanism designed in the bulk piezoceramic. One or several degrees of freedom (DOF) are possible for a single monolithic structure. They are suited for a wide range of applications specially all kind of microscopy (optical and scanning probe) or microrobotics. MPA prototypes of 2 and 3 DOFs have been modelled, characterised and implemented. Displacements between 10 and 20 microns have been measured at low frequencies and a bipolar voltage of ï±150V in the plane XY. The 3 DOF prototype still in development yields a similar displacement in the plane and 50 microns in the Z axis.
Abstract: A novel position sensor based on atomic force microscope (AFM) and nanometric scale reference is presented. The scale reference is fixed to the object whose position is to be measured and the AFM to the reference frame or vice versa. The AFM tip is brought in proximity to the scale and relative displacement is determined by counting the number of periods in the AFM signal. A compact and potentially low cost AFM called the Credit Card AFM (CCAFM) has been developed to serve as the sensor head of the position sensing system. 1-d and 2-d nano gratings are used as scale reference. Monolithic piezo XY stages and electromagnetic linear XY stages are used as test platforms.
Abstract: The angle-resolved tunneling spectroscopy has been performed on the conduction band of Si. Heavily doped n-Si(111) wafer pairs were bonded to form the SIS tunnnel junctions with various in-plane crystal-axis angles between the two crystals. The angle dependence of tunneling originates from the condition of the conservation of transverse component of momentum, together with the energy conservation, of the tunneling Bloch electrons. Rom the angle dependence of the tunneling characteristics, the conduction band structure of Si was derived along the orbit in the k-space, whose projection on the (111) plane forms a circle centered at k=0 and passes the bottom of the conduction band.
Notes: 25th International Conference on the Physics of Semiconductors (ICPS25), OSAKA, JAPAN, SEP 17-22, 2000
Abstract: Tunneling study was made on Bi2Te3 and Sb2Te3 at 4.2 K, 77 K and 295 K. Energy gap of Bi2Te3 was estimated to be 0.25 eV, 0.22 eV and 0.20 eV at 4.2 K, 77 K and 295 K, respectively.
