S.H. Hu

Preparation and optical waveguide property of metal alkoxide solution-derived Pb(Zr0.5Ti0.5)O3 thick films

Pb(Zr0.5Ti0.5)O3 films with thickness of about 1.5 and 3.7 μm have been deposited on single-crystal SrTiO3 substrate by a sol-gel process from nonhydrolyzed metal alkoxide precursor. X-ray diffraction shows that the films exhibit a single perovskite phase with (001)-preferred orientation. Atomic force microscopy study indicates that the PZT film possesses a crack-free and smooth surface. The optical waveguide property has been examined by the prism-film coupling experiment. Four and 12 TE modes are observed for 1.5 and 3.7 μm PZT films, respectively.

Electrical bistability in self-assembled hybrid multilayers of phospholipid and nanoparticles

A novel kind of biomolecule-based electrical bistable device composed of phospholipid-CdTe nanoparticle multilayered films was demonstrated. The composite film was fabricated by a facile solution-cast method. X-ray reflectivity and transmission electron microscopy measurements showed the homogeneous distribution of nanoparticles within the lamellar lipid matrix with long-range ordering. Current-voltage scans on the Al/(lipid-nanoparticle composite film)/ITO/glass structures at room temperature exhibited an obvious current bistable phenomenon. Further investigation of such bionanoparticle composite film promises to show its importance for applications in future memory nanodevices with tailored performance.

Structure and Phase Transformation of Oligodeoxynucleotide/Lipid Lipoplexes on Solid Supports

Lipoplexes are composed of lipids and nucleic acids and have an ordered multilamellar structure with a periodic 1D array of parallel nucleic acid strands in the lipid bilayers. We report a low-angle X-ray diffraction study on solid-supported lipoplex films composed of synthetic single-stranded oligodeoxynucleotides (ssODN) and lipids. The ssODN molecules distribute sparsely in the headgroup regions when the weight concentration of the ssODN in the lipoplex is low. The lipoplex separates into two phases, an ODN-poor phase and an ODN-rich phase, when the weight concentration of the ssODN is increased beyond a level at which the ssODN molecules contact each other so that some regions of the lipid bilayers must accommodate two layers of the ssODN. The phase separation is a result of the fusion of such regions to minimize the total interfacial energy of the system. The ssODN molecules distort the lipid bilayers in the ODN-poor phase. The local area per lipid molecule is increased by the distortions so that the interbilayer distance of the lipoplex film is smaller than that of the lipid film without the ssODN. The ODN-rich phase has a much larger interbilayer distance because two layers of ssODN are intercalated into each lipid bilayer. The ssODN molecules are tightly compacted, and the lipid bilayers are not distorted in the ODN-rich phase.

Thermotropic phase behavior of multilamellar membranes of dioleoylphosphatidylcholine.

We use the X-ray diffraction method to examine the thermotropic phase behavior of multilamellar membranes of dioleoylphosphatidylcholine. We find that when the temperature is reduced from room temperature to below 0 degrees C, both the lipid bilayers and the amount of water in the bilayers increase. But the interbilayer distance descends abruptly at a certain temperature between -6 and -15 degrees C, the actual value depending on the relative humidity of the atmosphere, solely due to the thinning of the water layer, d(w). There are several L(alpha) and L(c) phase coexistence states both in the cooling process and in the heating process. In the cooling process, only a part of the lipid molecules accomplish the L(alpha)-to-L(c) main phase transition at -16 degrees C, with the rest of the lipids being frozen down to a very low temperature. In the heating process, however, these frozen lipid molecules are able to move to complete the L(alpha)-to-L(c) main phase transition at -12 degrees C. The reverse of the main phase transition begins at -9 degrees C and is completed at -5 degrees C, after which the water is absorbed into the lipid bilayer to increase the thickness of the water layer, while the thickness of the lipid membranes remain unchanged. This process continues until all the ice on top of the samples melts.

Temperature dependence of interfacial fluctuations of polymerized fatty acid salt multilayers

X-ray scattering was used to study the temperature dependence of the profile structure of polymerized 10,12-tricosadiynoic acid salt multilayers. The stacking periodicity of the multilayers was found to decrease with increasing temperature due to the conformational changes of the alkyl chains. When the samples were fully hydrated in water, the reflectivity measurement showed that the thermal fluctuations of the interfaces are enhanced with temperature, resulting in reduced ordering. Meanwhile, the diffuse scattering indicated that the thermal fluctuations renormalize the elasticity of the multilayers; both the bending and the compression moduli are reduced. Similar measurements performed in air, however, do not show this thermal enhancement although the stacking periodicity decreases in the same manner. It is implied that water might weaken the interaction between the carboxyl groups and the metal ions so that the polymerized bilayers are softened in water.

Real time observation of partial dislocations in thin colloidal crystals

We use laser diffraction microscopy to visualize in real time the motion of partial dislocations in thin colloidal crystals confined in flat capillaries. The results show that the formation of partial dislocation loops with their associated stacking faults is an energetically preferred strain-relaxation channel for colloidal crystals. The local residual stress in the crystal can be estimated by measuring the velocity of the dislocations. Two types of interactions between the dislocations are observed, namely, that between two dislocations in two intersecting slide planes and that between two dislocations in two parallel slide planes.

Electronic transitions and hybrid resonance in InAsSb films by reflectance spectra

Electronic properties of InAs1−xSbx films with x up to 0.09 have been investigated by reflectance spectra in 1.5–5 eV energy range at room temperature. The real and imaginary parts of the dielectric function were derived by Kramers–Kronig analysis on the reflectance spectra, which show satisfactory agreement with the spectroscopic ellipsometry data. The E1′ and E1′+Δ1′ peaks are attributed to electronic interband transitions at the E1 and E1+Δ1 critical points, respectively. The prominent E2′ peaks, which exhibit high reflectivity and large blueshift, are found to be contributed by hybrid resonance due to the cooperative behavior of both E2-state electrons and plasmons.

Subnanometer-Thick PbS Film on Organic Substrate and Its Usage as Buffer for Homo- and Heteroepitaxial Overgrowth

We report on the fabrication of a subnanometer-thick epitaxial PbS film on polydiacetylene (PDA) substrate. The film is formed by cation-absorption in PbCl2 solution followed by sulfidation in mixed H2S/N2 gas, exhibiting a flat and smooth surface morphology. The strong adsorbate-surface interaction between the lead hydrolysis complexes and the carboxyl headgroups on the surface of PDA accounts for such a growth mode. We further demonstrate that such an ultrathin film can be used as a buffer layer for both homo- and heteroepitaxial growth of sulfide films. The X-ray and electron diffraction results reveal that the (001) planes of PbS are parallel to the surface of PDA and the (110) planes of PbS are parallel to the (110) planes of PDA.