n Song Li

Structure and characterization of surfactant-capped CdS nanoparticle films by the Langmuir-Blodgett technique

Abstract Oligomer-polymaleic acid octadecanol esters (PMAO) with different ratios between carboxylic groups and hydrocarbon chains stabilized CdS nanoparticles were produced in the form of reversed micelles. The PMAO-capped CdS nanoparticles were transferred from the air–water interface onto CaF 2 and silicon substrates. Surface pressure–area isotherms gave the information that both the two kinds of pure PMAO and PMAO-capped CdS could form stable monolayers on the water subphase. From the area occupied by average molecular unit (0.24 and 0.11 nm 2 ), it was concluded that the size of two kinds of PMAO-capped CdS nanoparticles was different. The results of UV-vis spectra gave us information that the diameter of CdS nanoparticles could be controlled to less than 2 nm. The measurement of Fourier transform infrared spectroscopy (FTIR) confirmed the formation of CdS. The average tilt angle of hydrocarbon chains revealed by polarized IR spectra was 50 and 60°, respectively. The long spacing of the multilayer of PMAO-capped CdS determined by small angle X-ray diffraction was 6.3 and 4.8 nm, which also maintained the conclusion that the ratio between carboxylic groups and hydrocarbon chains effect the size of reversed micelles.

Nanoscale organized assembly of nanoparticulate TiO2-stearate monolayers through the Langmuir–Blodgett method

Nanoparticulate titanium dioxide-stearate (TiO2-St) monolayer was directly obtained using TiO2 hydrosol as the subphase. The atomic force microscopy images of monolayer, show that the higher coverage were obtained through deposition on the hydrophilic Si(100) surface rather than the hydrophobic Si(100) surface. From the surface photovoltage spectra of TiO2-St monolayer, it can be followed that the photovoltage response of the n-type silicones increased by a factor of 25, and 5 times after a monolayer of TiO2-St Langmuir–Blodgett (LB) films was transferred onto hydrophobic and hydrophilic Si surface, respectively. On the contrary, the photovoltage response value is reduced by ∼40 and 5 times by the deposition of the LB monolayer in the case of the hydrophobic and hydrophilic p-type Si surface, respectively. It is considered that the enhancement of the photovoltage response may be due to the ordered electrostatic potential orientation of the Si(100)/TiO2-St/ITO heterostructures.

Preparation of titanium dioxide and barium titanate nanothick film by Langmuir–Blodgett technique

Abstract The TiO 2 and BaO(TiO 2 ) x thin film was prepared by the Langmuir–Blodgett (LB) technique. The mixture of octadecyl polymaleicate and tetrabutoxytitanium was spread on the surface of water subphase, then transferred onto substrates. The obtained LB multilayer was converted into a nano-thick TiO 2 film by calcination at 500°C for 30 min. When an appropriate amount of BaCl 2 was added into a water subphase, it was co-transferred onto a LB multilayer film. After calcination at the same condition, BaO(TiO 2 ) x thin films with different ratios of x could be obtained by adjusting the pH value of the water subphase. The Fourier transform infrared spectroscopy and X-ray photoelectron spectra measurements were used to confirm the formation of TiO 2 and BaO(TiO 2 ) x thin films. The integrated peak area in X-ray photoelectron spectra gave the atomic ratio of Ti/O and Ti/Ba. The surface morphology of the LB multilayer before and after calcination was investigated by atomic force microscopy. The image showed that the smooth and high cover surface of TiO 2 and BaO(TiO 2 ) x thin films were obtained after calcination. The rms roughness for a 21-layer film after calcination was approximately 25 A, which was less than that of before calcination of approximately 45 A. The resulting particle size was approximately 0.05 μm and almost uniform.

Comparison of photovoltaic behaviors for horseradish peroxidase and its mimicry by surface photovoltage spectroscopy

Surface photovoltage spectroscopy (SPS) was chosen to study the photovoltaic behavior of horseradish peroxidase (HRP), hemin and immobilized hemin (poly(NIPAAm/MBA/hemin)). Different photovoltaic behaviors were observed in these three systems. In air, similar SPS curves were found for HRP and poly(NIPAAm/MBA/hemin) with different response intensities. However, poly(NIPAAm/MBA/hemin) showed a wider changing range upon increasing the positive and negative bias to 1.0 V. The SPS of hemin showed a total different behavior when an external positive potential was applied. In vacuum, clearly different photovoltaic behaviors were found. Moreover, the response value decreased when HRP was exposed to O2, the SPS intensity was different from that in air, and could be altered by changing the external biases. On the other hand, the SPS could not be changed before and after poly(NIPAAm/MBA/hemin) was exposed to O2. These differences may result from different chemical microenvironments for hemin in HRP versus that in poly(NIPAAm/MBA/hemin). It could be concluded that H2O and O2 were important factors affecting the photovoltage response in HRP, but only H2O played this important role in poly(NIPAAm/MBA/hemin).

Preparation and structure of quantum-sized cadmium sulfide grown in amphiphilic oligomer Langmuir–Blodgett films

Abstract An amphiphilic oligomer, polymaleic acid with octadecanol ester (PMAO), with ratios of 2:1, 3.7:1 and 6:1 between the carboxylic groups and the hydrocarbon chains, was synthesized and has been used as a matrix to form and grow quantum dot-sized CdS particles. The formation of quantum-sized CdS particles during exposure of Langmuir–Blodgett (LB) films of CdPMAO to hydrogen sulfide has been studied using Fourier transform infrared spectroscopy and UV-vis absorption spectra. This showed that hydrogen bonding of the PMAO molecules were replaced by the metal ion (Cd 2+ ) bridges to form the bridging complex structures before the reaction with H 2 S. The intensities of the asymmetric ν a (COO − ) and symmetric ν s (COO − ) stretching modes were reduced after the reaction. But the presence of the asymmetric ν a (COO − ) and symmetric ν s (COO − ) stretching mode in spectra implied that not all the CdPMAO oligomers in the film were converted to PMAO after exposure to H 2 S gas. The result from the UV-vis absorption spectra indicated that the CdS within PMAO LB films showed a larger blue shift of the optical absorption edge with the decrease of the ratio between the carboxylic groups and the hydrocarbon chains. Moreover, it could be deduced that the size of the aggregate of the sulfides within PMAO LB films was smaller than that formed in stearic acid LB films.

Organized Langmuir-Blodgett Monolayers and Multilayers Based on Semi-Amphiphilic Binuclear Phthalocyanine: AFM Investigation and Photovoltaic Characteristics

Abstract A water-soluble binuclear cobalt phthalocyanine-sulphonate was used to prepare LB films by semi-amphiphilic technique. Atomic force microscopy (AFM) was applied to investigate the surface morphology of C18NH2-OME/bi-CoPc LB multilayer on silicon substrate and surface photovoltage spectra (SPS) was used to study the interfacial charge transfer properties.

Calculation of electronic energy levels in artificially confined cavities of a sphere and a circular cylinder

Based on the results of experiments of the nanostructured materials, the electronic structures of the spherical and circular cylindrical well in nanometer scale are calculated using a constant potential by direct solution of the Schrodinger equation. According to the result of the bound states existing only under certain conditions, the calculated results show that the energy level structures of these modes are quite distinct from that of the hydrogen atom. The number of energy levels is finite and it depends strongly on the potential parameter. The order of energy levels is E1s<E2p<E3d<E2s<E3p<E4d<… in the case of the artificially confined cavity of the sphere. It was exactly consistent with an investigation reported by T. Inoshita et al. [Phys. Rev. Lett. 57, 2560 (1986)]. The calculated results of the circular cylindrical wells have similar properties on the level structure compared with that of a square spherical artificial atom well.