Electronic behavior of the Zn- and O-polar ZnO surfaces studied using conductive atomic force microscopy

We have used conducting atomic force microscopy (CAFM) to study the morphology and electronic behavior of as-received and air-annealed (0001) Zn- and (0001¯) O-polar surfaces of bulk ZnO. Both polar surfaces exhibit relatively flat morphologies prior to annealing, which rearrange to form well-defined steps upon annealing in air at 1050 °C for 1 h. Long-term exposure to air results in surface layer pitting and the destruction of steps for both the as-received and air-annealed (0001¯)surfaces, indicating its enhanced reactivity relative to the (0001) surface. CAFM I-V spectra for polar surfaces are similar and indicate Ohmic to rectifying behavior that depends on the maximum applied ramp voltage, where higher voltages result in more conducting behavior. These data and force-displacement curves suggest the presence of a physisorbed H2O layer, which is removed at higher voltages and results in higher conduction

Pickup velocity of nanoparticles

This paper represents the first systematic study of the pneumatic conveying of nanoparticles. The minimum pickup velocity, Upu, of six nanoparticle species of different materials (i.e., silicon dioxide (SiO2), aluminum oxide (Al2O3) and titanium dioxide (TiO2)) and surfaces (i.e., apolar and polar) were determined by the weight loss method. Specifically, the weight loss method involves measuring the mass loss from the particle sample at various superficial gas velocities (U), and the Upu is the U value at which mass loss is zero. Nanoparticles were picked up as agglomerates rather than individually. Results show that (a) due to relative lack of hydrogen bonding, apolar nanoparticles have higher mass loss values at the same velocities, mass loss curves with accentuated S-shaped profiles, and lower Upu values; (b) among the three species, SiO2, which has the lowest Hamaker coefficient, exhibited the greatest discrepancy between apolar and polar surfaces with respect to both mass loss curves and Upu values; (c) Umf,polar/Umf,apolar was between 1 – 3.5 times that of Upu,polar/Upu,apolar due to greater extents of hydrogen bonding associated with Umf ; (d) Upu values are at least an order-of-magnitude lower than that expected from the well-acknowledged Upu correlation (1) due to agglomeration; (e) although nanoparticles should be categorized as Zone III (1) (or Geldart Group C (2)), the nanoparticles, and primary and complex agglomerates agree more with the Zone I (or Geldart Group B) correlation (Figure 1, whereby Rep* and Ar are the particle Reynolds number and Archimedes number, respectively (1)). In view of the importance of surface polarity on the pneumatic conveying of nanoparticles, more studies are on-going to further understand such surface effects. Please click Additional Files below to see the full abstract

Fast and Simple Methods For Computing Control Points

The purpose of this paper is to present simple and fast methods for computing control points for polynomial curves and polynomial surfaces given explicitly in terms of polynomials (written as sums of monomials). We give recurrence formulae w.r.t. arbitrary affine frames. As a corollary, it is amusing that we can also give closed-form expressions in the case of the frame (r, s) for curves, and the frame ((1, 0, 0), (0, 1, 0), (0, 0, 1) for surfaces. Our methods have the same low polynomial (time and space) complexity as the other best known algorithms, and are very easy to implement.Comment: 15 page

The Relation Between Offset and Conchoid Constructions

The one-sided offset surface Fd of a given surface F is, roughly speaking, obtained by shifting the tangent planes of F in direction of its oriented normal vector. The conchoid surface Gd of a given surface G is roughly speaking obtained by increasing the distance of G to a fixed reference point O by d. Whereas the offset operation is well known and implemented in most CAD-software systems, the conchoid operation is less known, although already mentioned by the ancient Greeks, and recently studied by some authors. These two operations are algebraic and create new objects from given input objects. There is a surprisingly simple relation between the offset and the conchoid operation. As derived there exists a rational bijective quadratic map which transforms a given surface F and its offset surfaces Fd to a surface G and its conchoidal surface Gd, and vice versa. Geometric properties of this map are studied and illustrated at hand of some complete examples. Furthermore rational universal parameterizations for offsets and conchoid surfaces are provided