Molecular engineered silica surfaces with an assembled anthracene monolayer as a fluorescent sensor for organic copper(II) salts

A novel fluorescence film has been fabricated by covalently coupling anthracene on a glass plate surface via a long flexible “Y” type spacer. Fluorescence measurement demonstrated that the emission of the film is dominated by anthracene monomer emission, and the emission can be selectively quenched by organic copper(II) salts including copper acetate, copper citrate, copper tartrate, etc. Addition of inorganic copper(II) salts like Cu(NO₃)₂, CuSO₄, CuCl₂, etc., however, has little effect upon the emission of the film. This observation was explained by considering the screening effect of the spacer layer, or spacer clusters, or even spacers adopting compact coiled conformation. Different from the reported fluorescence films with similar structures, immobilization of anthracene via a “Y” type spacer on a glass plate surface makes the fluorophore moieties exist in two different states, that is some of them were embedded within the spacer structures, and some of them might stay out of the structures. This hypothesis has been confirmed by model system, solvent effect and quenching mechanism studies. The emission of the film is sensitive to the presence of organic copper(II) salts like copper acetate. The response of the film to copper acetate is fully reversible. Presence of other inorganic salts, including Pb(Ac)₂, Cd(Ac)₂, Zn(Ac)₂, and inorganic copper(II) salts has little effect upon the sensing performance of the film to copper acetate.     

The gas-sensing potential of nanocrystalline SnO2 produced by a mechanochemical milling via centrifugal action

In this work, the synthesis of undoped nanocrystalline tin dioxide powders and the subsequent preparation of SnO₂ thick-films were studied. An initial mixture of SnCl₂ and Ca(OH)₂ was sealed in a vial for milling in an air atmosphere. Heat treatment of the milled powder resulted in the formation of tetragonal and orthorhombic SnO₂ phases, which was confirmed by X-ray diffraction (XRD) analysis. It was found that crystallite size could be controlled by varying the milling time, the rotation speed and the temperature used for the heat treatment. Crystallite sizes in the range 20 to 30 nm (determined by XRD measurements) were obtained. The total pore volume was 0.22 ml/g for a measured particle size of 37 m²/g. No contamination of the powder during milling was found. The response of the prepared thick-films to H₂S gas in the concentration range 0.5 to 10 ppm in air was investigated as a function of the preparation conditions. The advantage of mechanochemical synthesis of powder is its relative simplicity, low cost and possibility of obtaining isolated, unagglomerated nanosized grains. It is shown that chemical reactions, which usually occur in the vibratory mill to produce the SnO phase, can also be initiated during a short processing time in the centrifugal mill. Received: 25 July 2001 / Accepted: 4 September 2001 / Published online: 20 December 2001     

Crystal growth, thermal and optical studies of nonlinear optical material: Glycine potassium sulphate

A new nonlinear optical material glycine potassium sulphate (GPS) has been synthesized and optical quality crystals were grown from aqueous solution. This material has positive temperature coefficient revealed from the solubility studies. The grown crystals were characterized by employing several techniques such as single crystal and powder X-ray diffraction, thermo gravimetric analysis, FTIR and UV-vis-NIR spectra. The etching studies have been done on the (1 0 0) plane of the grown crystal. Preliminary measurements to find second harmonic generation efficiency of GPS has been carried out.     

Age-induced oxide on cleaved surface of layered GaSe single crystals

It is shown that a long-term keeping of a layered gallium monoselenide at room temperature results in formation of the intrinsic oxide at a cleaved surface of semiconductor. It is found that the chemical compositions of the intrinsic oxide at the surfaces of the intentionally undoped and doped samples of GaSe are different. The electrical properties of the GaSe-intrinsic oxide system are presented. It is established that intrinsic oxide films at the surface of GaSe are characterized by current instability with N-type current-voltage characteristic. The influence of relative humidity on changes of capacitance and surface resistivity of the intrinsic oxide is also discussed.     

Effect of patterns and inhomogeneities on the surface of waveguides used for optical waveguide lightmode spectroscopy applications

It has been found that patterns and inhomogeneities on the surface of the waveguide used for optical waveguide lightmode spectroscopy applications can produce broadening and fine structure in the incoupled light peak spectra. During cell spreading on the waveguide, a broadening of the incoupling peaks is observed, while regular microstructures on the incoupling grating produce shifts and splitting of the peaks. A theoretical model, based on the zigzag wave representation of light propagation in a planar optical waveguide has been developed in order to understand the physical background of the observed effects. Numerical results are given for the different cases observed, and they are compared with the experimental data. Several possible applications of these effects are considered. Received: 10 July 2000 / Revised version: 9 October 2000 / Published online: 21 February 2001     

Effects of Mg and Zn on the surface of doped melt-derived glass for biomaterials applications

Bioactive glasses in the system SiO₂-CaO-Na₂O-P₂O₅ were synthesized pure and doped with magnesium or zinc by melt-derived method. The bioactivity was studied during in vitro assays: the ability of hydroxycarbonate apatite (HCA) layer to form on the glass surface was examined after contact with simulated body fluid (SBF). The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) studies were performed before and after immersion in vitro assays. The SBF solutions were also analyzed using inductively coupled plasma-optical emission spectroscopy (ICP-OES).Introduction of magnesium and zinc as trace element induces several modifications on the observed phenomena at the glass surface and in SBF solution after immersion of the samples. The chemical durability of the glasses, the formation of the silica-rich layer and the crystallization of the HCA layer were affected, but not present the same modifications as the introduced doping element.     

Effect of process parameters on surface morphology and characterization of PE-ALD SnO2 thin films for gas sensing

Tin dioxide (SnO₂) thin films were deposited by plasma enhanced-atomic layer deposition (PE-ALD) on Si(1 0 0) substrate using dibutyl tin diacetate (DBTA) ((CH₃CO₂)₂Sn[(CH₂)₃-CH₃]₂) as precursor. The process parameters were optimized as a function of substrate temperature, source temperature and purging time. It is observed that the surface phenomenon of the thin films was changed with film thickness. Atomic force microscopy (AFM) images and X-ray diffraction (XRD) pattern were used to observe the texture and crystallanity of the films. The films deposited for 100, 200 and 400 cycles were characterized by XPS to determine the chemical bonding properties. XPS results reveal that the surface dominant oxygen species for 100, 200 and 400 cycles deposited films are O₂⁻, O⁻ and O²⁻, respectively. The 200 cycles film has exhibited highest concentration of oxygen (O⁻) species before and after annealing. Conductivity studies revel that this film has best adsorption strength to the oxygen ions forming on the surface. The sensor with 200 cycles SnO₂ thin film has shown highest sensitivity to CO gas than other films. A correlation between the characteristics of Sn3d_5/2 and O1s XPS spectra before and after annealing and the electrical behavior of the SnO₂ thin films is established.     

The interpretation of the LII signal in optically dense combusting sprays

A numerical investigation was made of the generation and behaviour of the LII signal in optically dense combusting sprays at conditions similar to those in the combustion chamber of compression ignition engines and gas turbines. The influence of particle size, particle morphology and size distribution on the behaviour of the LII signal, and the scattering and absorption of light, and the consequences that different calibration procedures have on the accuracy of the results were studied. Results show that, as the particle size or aggregation increases, light extinction is not caused only by absorption but also by scattering, which contributes more than 10% to the total extinction of light. Particle shape effects are important, irrespective of particle size. The form, soot concentration gradients and optical thickness of the flame cause an uneven laser fluence across the measuring volume that affects the generation of the LII signal. In addition, the quotient between the transmitted and incoming laser pulses across the flame borders can be as small as a percentage of unity. The interpretation of the induced signal is further challenged by the loss of signal between the measuring volume and the detection arrangement, thus causing the detection of spectrally distorted and weaker signals with an erroneous profile of the local amount of carbonaceous particles. An appropriate calibration procedure must be followed to obtain results that are quantitatively representative. External calibration was found to be inappropriate for these systems since it can lead one to underestimate the local volume fraction for almost two orders of magnitude. Implementing an in situ calibration along a line can lead to underestimate or overestimate the local mean volume fraction by a factor of two. However, the use of an in situ calibration procedure using a laser sheet that propagates through the complete measuring volume can reduce the error in estimating the mean soot volume fraction to a 30%. The latter was found to be the most adequate among the studied calibration routines.     

High-resolution scanning tunneling microscopy and dI/dV map studies of peptidenucleic acid and fluorescein isothiocyanate

We used scanning tunneling microscopy (STM) to spatially map the local density of states of individual PNA molecules labeled with fluorescein isothiocyanate (FITC) on a Cu(1 1 1) surface. From the observed bias voltage dependences of the topographic height and the dI/dV map of FITC and individual PNA molecules, we confirmed that FITC and PNA have different electrical properties. We clearly differentiated the FITC and PNA molecules by mapping the density of states feature. This study shows that STM with the dI/dV map method is useful in FITC mapping.     

Study of quantum effects on atomic displacements in quartz

The crystal structure of quartz (SiO₂) was analyzed by neutron powder diffraction at several temperatures in the range of 10-250 K. The temperature dependence of the structure parameters was consistent with our previous results obtained using single-crystal X-ray diffraction above room temperature. Atomic displacements are order parameters for displacive structural phase transitions. The temperature evolution of Si atomic displacement in quartz was analyzed by studying the quantum expansion of the Landau potential. The expansion was found to accurately describe the evolution of the atomic displacement over the entire temperature interval. To the best of our knowledge, such a verification of atomic displacement is the first of its kind. A proportional relationship between spontaneous strain and the square of the atomic displacement was observed over the entire temperature interval. The validity of the obtained characteristic temperature for the quantum effect is discussed and compared with the results of previous Raman-scattering studies.