Sampling distance

Figure Bl.19.37. Nonual force versus tip-sample distance curves for a Si3N4 tip on a Si02 surface under 1 luM NaCl solution at pH 4 and pH 9. (Taken from [189], figure 2.)...

This corresponds to the physician s stethoscope case mentioned above, and has been realized [208] by bringing one leg of a resonatmg 33 kHz quartz tiinmg fork close to the surface of a sample, which is being rastered in the x-y plane. As the fork-leg nears the sample, the fork s resonant frequency and therefore its amplitude is changed by interaction with the surface. Since the behaviour of the system appears to be dependent on the gas pressure, it may be assumed that the coupling is due to hydrodynamic mteractions within the fork-air-sample gap. Since the fork tip-sample distance is approximately 200 pm -1.120), tire teclmique is sensitive to the near-field component of the scattered acoustic signal. 1 pm lateral and 10 mn vertical resolutions have been obtained by the SNAM. 

Figure Bl.19.39. Schematic of the themiocoiiple probe in a scaiming themial profiler. The probe is supported on a piezoelectric element for modulation of tip-sample distance at frequency oi and to provide positioning. The AC thennal signal at oi is detected, rectified, and sent to the feedback loop, which supplies a voltage to the piezostack to maintain the average tip-sample spacing constant. (Taken from [209], figure 1.)...

Pitot-static traverse The set positions of a Prandtl tube m a duct run required to provide a statistically valid set of readings, A series of measurements of the torn 1 and static pressure taken across an area of a duct to determine the air veloc-it> at that point. The sampling distance should be at least 7.5 times the diameter of the duct away from any disturbances of air flow. 

FIG. 3 Dependence of the electrostatic force on tip-surface distance. The experimental data (square points) can he fit reasonably weU with a A/z + B function (solid curve) predicted hy the model in the previous figure for tip-sample distances smaller than the tip radius. 

FIG. 28 Changes in contact potential of mica relative to a hydrophobic tip as a function of relative humidity. The tip-sample distance during measurements was maintained at 400 A. At room temperature the potential first decreases by about 400 mV. At -30% RH it reaches a plateau and stays approximately constant until about 80% RH. At higher humidity the potential increases again, eventually becoming more positive than the initial dry mica surface. The changes in surface potential can be explained by the orientation of the water dipoles described in the previous two figures. 

Figure 5.2 Tunnel current as a function oftip-sample distance for Au(l 1 1) in 0.1 M H2S04 for three different electrode potentials (vs. SCE) Positive of ( ), negative of (- -), and at the pzc (—). s = 0 refers to the tip position at the closest approach that could be experimentally achieved. (Reproduced with permission from Ref. [19].)...

The polymers were dissolved in methylisobutylketone (MIBK) and spin-coated on oxjdized silicon wafers (1100 X thick Si02 layers) to form 5000 A thick films. After a prebaking to improve adhesion to the substrate, the resist samples were irradiated 0 through the mask (A) using the Al K 152 emission line at 8.3 A as X-ray source. The electron beam gun was operated at a 300 W power and the source to sample distance was U.9 cm. Taking into account the absorption of the aluminum foil mask,the different X-ray fluxes available on the sample were calculated from the relation given by (9) ... 

Deng W, Hipps KW (2003) Tip-sample distance dependence in the STM-based orbital-mediated tunneling spectrum of nickel(II) tetraphenylporphyrin deposited on Au(lll). J Phys Chem B 107 10736-10740... 

Gopakumar TG, Meiss J, Pouladsaz D, Hietschold M (2008) HOMO-LUMO gap shrinking reveals tip-induced polarization of molecules in ultrathin layers tip-sample distance-depen-dent scanning tunneling spectroscopy on d8 (Ni, Pd, and Pt) phthalocyanines. J Phys Chem C 112 2529-2537... 

In the upper stream of the Meza River, including significant tributaries (e.g. Topla, Helenski potok, Musenik, Jazbinski potok, Juncarjev potok), the stream sediment samples were collected approximately 1 km apart. From Mezica to the Drava River the sampling distance was increased to 10 km. Additionally, two samples of the Drava River sediments were taken before and after its confluence with the Meza River (Fig. 1). 

Experimentally, this quantity can be conveniently measured by varying the tip-sample distance through the z piezo, often with an ac voltage. The measured values often varies with distance. Eq. (1.13) is the definition of the... 

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