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Time dependent STM has been used to evaluate step fluctuations as a function of temperature (300-450 K) on Ag(111) films grown on mica. The temporal correlation function scales as a power law in time, t 1/n with measured values of 1/n varying over a range of 0.19 ± 0.04 to 0.29 ± 0.04 with no correlation on temperature. The average value of 1/n = 0.24 ± 0.01 is consistent with step-edge diffusion limited fluctuations (n = z = 4, conserved noise). The magnitude of the time correlation function and the width of the fluctuations both scale with temperature with the same apparent activation energy of E eff = 0.21 ± 0.02 eV, indicating that the correlation time is at most weakly temperature dependent. Direct analysis of the autocorrelation function confirms that the correlation time is at most weakly temperature dependent, and thus the apparent correlation length is strongly temperature dependent. This behavior can be reproduced by assuming that the apparent correlation length is governed by the longest wavelength of step fluctuations that can be sampled in the measurement time interval. Evaluation of the correlation time for previous measurements for Al/Si(111) ( z =2) yields the same conclusion about measurement time interval. In both cases the ratio of the measurement time to the effective correlation time is on the order of 10.

We determine the statistics of the local tube width in F-actin solutions, beyond the usually reported mean value. Our experimental observations are explained by a segment fluid theory based on the binary collision approximation. In this systematic generalization of the standard mean-field approach, effective polymer segments interact via a potential representing the topological constraints. The analytically predicted universal tube width distribution with a stretched tail is in good agreement with the data.

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Spurred by recent theoretical predictions [Phys. Rev. E 69, 035102(R) (2004)10.1103/PhysRevE.69.035102; Surf. Sci. Lett. 598, L355 (2005)10.1016/j.susc.2005.09.023], we find experimentally using STM line scans that the fluctuations of the step bounding a facet exhibit scaling properties distinct from those of isolated steps or steps on vicinal surfaces. The correlation functions go as t0.15 +/- 0.03 decidedly different from the t0.26 +/- 0.02 behavior for fluctuations of isolated steps. From the exponents, we categorize the universality, confirming the prediction that the nonlinear term of the Kardar-Parisi-Zhang equation, long known to play a central role in nonequilibrium phenomena, can also arise from the curvature or potential-asymmetry contribution to the step free energy.