Nanobubbles at Water-Solid Interfaces: Calculation of the Contact Angle Based on a Simple Model

Nanobubbles have been found to form at the interface of water and solid surfaces. We examine the conditions for such bubbles to form and estimate the pressure inside the bubble based on thermodynamic considerations. Using a simple model we calculate the contact angle for a wide range of temperatures and hypothetical substrates possessing a continuous range of strengths. We show that as the temperature increases the shape of a bubble changes continuously from a spherical cap with low curvature to a complete sphere. An equivalent effect results from either increasing the strength of the solid or decreasing the surface tension. A model of a substrate formed by layers of materials is proposed to obtain a nanobubble with a particular contact angle.     

Direct spectroscopic evidence for the formation of one-dimensional wetting wires during the growth of InGaAs/GaAs quantum dot chains

We report direct spectroscopic evidence for the formation of one-dimensional (1D) wetting wires (WWs) during the Stransky-Krastanov growth of InGaAs/GaAs quantum dot (QD) chains. The wire-like nature of these 1D WWs was demonstrated by their 1D density of states and absorption anisotropies from the photoluminescence excitation measurements. Two groups of QDs were found sitting on top of these 1D WWs and the traditional two-dimensional wetting layers, respectively, with size-dependent emission polarization anisotropies of ca. 6-25% because of their elongated shapes.     

Undercooling and demixing of copper-based alloys

Since the beginning of materials science research under microgravity conditions immiscible alloys have been an interesting subject. New possibilities to investigate such systems are offered by containerless processing techniques. Of particular interest is the ternary system Cu-Fe-Co, and its limiting binaries, Cu-Co and Cu-Fe. They all show a metastable miscibility gap in the regime of the undercooled melt. Within the ESA-MAP project “CoolCop”, different aspects of this alloy have been investigated; results obtained so far are reported here.     

Orientation relationships in multilayer ZnO/In<Subscript>2</Subscript>O<Subscript>3</Subscript> structures

Multilayer ZnO/In₂O₃ structures prepared by annealing Zn _x In₂S_3+x (x = 1, 5) single crystals have been studied by x-ray diffraction and optical microscopy. The results indicate limited texturing of the endotaxial oxide layers. The orientation relationships between the ZnO and In₂O₃ crystallites in neighboring layers are shown to be analogous to those between similar unit cells of single-crystal layers and substrates in epitaxial systems.     

White-light emission from a blend of CdSeS nanocrystals of different Se:S ratio

CdSeS nanocrystals with different bandgap energies have been synthesized by the colloidal method. The solution blend of blue-, green-?and red-emitting CdSeS nanocrystals, in appropriate proportions, showed strong white emission of different shades on excitation with a UV source. We observed that the CIE coordinate of the spectrum of a particular blend is independent of excitation wavelength. We also observed that the contribution of self-absorption in energy loss in the blend of CdSeS nanocrystals is not very significant. A white-light-emitting LED has been fabricated by coating a blend mixed with polymethylmethacrylate on a commercial UV-LED.     

Ball cocks for liquid abrasive media

Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 6, pp. 8–9, June, 1991.     

Time-delay/Doppler scattering function for suburban mobile radio propagation at 436 MHz

Time-delay/Doppler scattering functions are presented for two different suburban locations where multipath propagation is evident. The major features of the scattering functions are explained in terms of the surrounding environment and the street orientation with respect to the transmitter.     

Zone melting of indium phosphide

Bulk indium phosphide crystals have been prepared by zone melting with dislocation densities 104 ≤ N_d ≤ 105 cm^-2. The residual impurity level in nominally undoped crystals and the dopant distribution in Cd-, Sn- and Ge-doped zone melted ingots, as revealed by spark source mass spectrometric analyses, indicate a strong interaction between segregation at the solid/liquid interface and vapor transport. The effective distribution coefficients for Sn and Ge in zone melted InP are k_e(Sn) = 0.3 and k_e(Ge) = 0.4. The free electron concentration measured in the middle section of nominally undoped ingots is N_D-N_A = 1.9 × 10¹⁵ cm^-3 corresponding to a Hall mobility Μ_e = 3263 cm^2V-1sec^-l.