Two-particle microrheology of quasi-2D viscous systems

We study the spatially correlated motions of colloidal particles in a quasi-2D system (human serum albumin protein molecules at an air-water interface) for different surface viscosities eta s. We observe a transition in the behavior of the correlated motion, from 2D interface dominated at high eta s to bulk fluid dependent at low eta s. The correlated motions can be scaled onto a master curve which captures the features of this transition. This master curve also characterizes the spatial dependence of the flow field of a viscous interface in response to a force. The scale factors used for the master curve allow for the calculation of the surface viscosity eta s that can be compared to one-particle measurements.     

Formation of oxygen-deficient type structural defects and state of ions in SiO2 glasses implanted with transition metal ions

The properties and concentrations of oxygen-deficient type structural defects in type III SiO₂ glasses implanted with Ti⁺, Cr⁺, Mn⁺, Fe⁺, or Cu⁺ to doses from 0.5×10¹⁶ to 6×100¹⁶ ions/cm² at an energy of 160 keV have been measured by using vacuum UV and EPR spectroscopies. An intense absorption band centered around 7.5 eV is observed in all the samples except for Cu-implanted ones and is attributed primarily to Si---Si homo-bonds with the bond distance close to that of the Si₂H₆ molecule. The homo-bond and implanted ion concentrations are of the same order of magnitude in the implanted layers. An E′ type center associated with the homo-bond is observed in all the samples except for Cu-implanted ones. Anomalous behaviors of the Cu-implanted samples are attributed to the formation of Cu-colloids. An enhanced formation of metallic particles or colloids is suggested for the samples implanted with Cr, Mn or Fe to doses higher than 3×10¹⁶ ions/cm².     

Si(1 1 1)-H(1 × 1): A mirror for atoms characterized by AFM, STM, He and H2 diffraction

AFM, STM and diffraction of He and H₂ have been used to assess Si(1 1 1)-H(1 × 1) surfaces for their potential as mirrors for matter-waves. The H-passivated samples are produced by wet-chemical methods and delivered to a different laboratory for diffraction measurements. We show that the surface is flat and homogenous over lateral scales of microns and that absolute He and H₂ reflectivities of the order of ∼3% are obtained, even after 20 h storage under Ar and several days’ storage in UHV. These characteristics allow the use of Si(1 1 1)-H(1 × 1) as a highly reflective mirror for atoms and molecules, with application in a future He microscope or focused hydrogen nano-lithography system.     

Anomalous diffusion probes microstructure dynamics of entangled F-actin networks

We study the thermal motion of colloidal tracer particles in entangled actin filament (F-actin) networks, where the particle radius is comparable to the mesh size of the F-actin network. In this regime, the ensemble-averaged mean-squared displacement of the particles is proportional to tau(gamma), where 0相似文献