Nguyen Quang Liem

Raman study of the microstructure, composition and processing of ancient Vietnamese (proto)porcelains and celadons (13–16th centuries)

Selected ancient Vietnamese (proto)porcelains and celadons (13–16th centuries) from the Ha Lan (Nam Ð inh), Chu Ðâu (Nam Sach, Hai Duong) and Hop Le (Binh Giang, Hai Duong) ceramic kilns were studied by chemical analysis, macro- and micro-Raman spectroscopy, thermal expansion and differential thermal analysis. Raman spectra of quartz, cristobalite, rutile, mullite, anatase, iron oxide, amphibole and glassy phases were analysed and their evolutions are used to discuss the ancient ceramic technology (raw materials used, firing procedures of the glaze and body, etc.). Structural composition data taken from thermal expansion measurements and Raman spectroscopy are in good agreement. Particular attention is given to the analysis of glaze for the feasible discrimination between original artefacts and modern copies. On the basis of experimental results, the samples made at Chu Ð au can be considered as true porcelains, whereas those made at Hop Le and Ha Lan had evolutions towards porcelain and high-temperature-fired fine faience, respectively. Copyright

Microstructure, composition and processing of 15th century Vietnamese porcelains and celadons

Fifteenth century porcelains and celadons are the most interesting ancient Vietnamese ceramics, both from the material and aesthetic points of view. This paper reports on composition, microstructure and technological processing of the Chu Ðâu-My Xa (Hai Duong province) ceramics. Samples come either from the kiln site or from the Cu Lao Cham (Hoi An) shipwreck. Chemical analysis, scanning electron microscopy, EDX analysis, X-ray diffraction, Raman spectroscopy, thermal expansion/shrinkage and open porosity measurements were systematically performed. The results show the Ca (+K)-based glaze, high-temperature-fired bodies, by one- or multi-step firings. Mullite phase (3Al2O3·2SiO2) was formed in large amount indicating the true porcelain quality of the samples under study. The matrices used for overglaze colouring (e.g., the green, red and metallic-lustre) are lead-based low-firing-temperature glasses. Comparison was made for the structural elements and fluxing agents between the 15th century Vietnamese porcelains and the time-corresponding Chinese ones.

Optical transitions in polarized CdSe, CdSe/ZnSe, and CdSe/CdS/ZnS quantum dots dispersed in various polar solvents

The optical transitions in ensembles of colloidal CdSe-based quantum dots (QDs) have been systematically studied as a function of the net QDs’ polarity/polarization and of the solvent’s polarity. While the general trend observed for all QD systems dispersed in different solvents is similar, the spectral shifts are more pronounced in core QDs than in core/shell structures. Our results can be rationalized by taking account of the electric field experienced by the QDs that results from their effective polarization in solvents of different polarities (quantum confined Stark effect) as well as from the effect of the external dielectric environment (solvatochromatic effect).

Eu locations in Eu-doped InGaN/GaN quantum dots

We report on the photoluminescence and photoluminescence excitation studies of Eu-doped wurtzite InGaN quantum dots (QDs) embedded in a GaN matrix grown by plasma-assisted molecular-beam epitaxy. The location of Eu3+ ions either in InGaN QDs or in the GaN spacing layer is assigned by comparing the different behaviors of the D05→F27 emission around 620nm under various photoexcitation energies and temperatures to those observed in Eu-doped GaN∕AlN QDs and a Eu-doped GaN thick layer.

Time-resolved photoluminescence measurements of InP/ZnS quantum dots

This paper reports the results on the time-resolved photoluminescence study of InP/ZnS core/shell quantum dots. The ZnS shell played a decisive role to passivate imperfections on the surface of InP quantum dots, consequently giving rise to a strong enhancement of the photoluminescence from the InP core. Under appropriate excitation conditions, not only the emission from the InP core but also that from the ZnS shell was observed. The emission peak in InP core quantum dots varied as a function of quantum dots size, ranging in the 600 – 700 nm region; while the ZnS shell showed emission in the blue region around 470 nm, which is interpreted as resulting from defects in ZnS.

Biexciton photoluminescence in cubic ZnS single crystals

The near-band-edge emission of cubic zinc sulfide single crystals has been studied in detail by steady-state photoluminescence (PL) and time-resolved photoluminescence. Based on the peak energy positions, excitation power density and temperature dependencies of the PL spectra, we interpret the emission as recombination of the free and bound excitons and of the biexcitons. We observed the biexciton emission at 3.791 eV in cubic ZnS single crystals with very low excitation power density. Its binding energy and radiative lifetime were determined to be about 9 meV and 52 ps at 12 K, respectively.

Detection of the pesticide by functionalised quantum dots as fluorescence–based biosensor

In this paper, we present the new results of biosensor that is made from the surface–modified quantum dots with acetylcholinesterase enzymes (AChE) for optical detection of the pesticides. The quantum dots (QDs) mentioned in this study are CdTe, CdSe/ZnS and CdSe/ZnSe/ZnS - the thick shell QDs are totally new. The results pointed out that all of the quantum dots are fit for the role of transducers in biosensor. In the biosensor, the QD– streptavidine - AChE is used as the substrate for the detection of pesticide. The pesticides used in this work are Parathion Methyl (PM) and Acetamiprid. The acetylthiocholine (ATCh) is used as an indicator of the activity of the AChE enzyme. Alternatively, the organophosphorus (OP) pesticides are the inhibitor for the AChE enzymes. Therefore, the mixture of the pesticide and ATCh is used for the goal of the specification of pesticide. We can detect pesticides by the change in PL intensity of QDs biosensor, with the content ranges from 0.05 ppb to 10 ppb.

Assembly of Mid-Nanometer-Sized Gold Particles Capped with Mixed Alkanethiolate SAMs into High-Coverage Colloidal Films

We investigated the influence of the mixed n-alkanethiolate self-assembled monolayer (SAM) formed on gold nanoparticles (AuNPs: 50.0 ± 3.2 nm in diameter) on their assembly into colloidal films. Dodecanethiol and octadecanethiol were selected as the short- and long-chain alkanethiols, respectively. The mixed SAMs were formed by immersing AuNPs in a mixed alkanethiol solution at different molar ratios. Au colloidal films were fabricated on indium tin oxide substrates by our previously reported hybrid method. The composition of the two alkanethiolates in the SAM was deduced from the intensity ratio of two Raman bands at 1080 and 1105 cm(-1). The surface coverage of the colloidal films increased by forming equimolar or dodecanethiolate-dominant mixed SAMs on AuNPs instead of a pure dodecanethiolate or octadecanethiolate SAM. The highest coverage exceeded 80%. This improvement is attributed to the high dispersion stability of AuNPs covered with equimolar or dodecanethiolate-dominant mixed SAMs.

Enhanced Photocatalytic Activity of {110}-Faceted TiO2 Rutile Nanorods in the Photodegradation of Hazardous Pharmaceuticals

Rutile TiO2 with highly active facets has attracted much attention owing to its enhanced activity during the photocatalytic degradation of pollutants such as pharmaceuticals in wastewater. However, it is difficult to obtain by controlling the synthetic conditions. This paper reports a simple hydrothermal synthesis of rutile TiO2 nanorods with highly exposed {110} facets. The obtained rutile was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. The main contribution to the photocatalytic activity comes from rutile nanorods with highly dominant active {110} facets, which were studied in the photodegradation of reactive cinnamic acid and more recalcitrant ibuprofen. The contribution of active species was also investigated. The present work further confirmed the hydrothermal synthesis route for controlling the preparation of highly crystalline and active rutile nanocrystals.

Preparation of SERS Substrates for the Detection of Organic Molecules at Low Concentration

In this paper, we present the results of the preparation of Surface Enhanced Raman Spectroscopy (SERS) substrates by depositing silver nanoparticles (Ag NPs) onto a porous silicon wafer that is produced by the chemical etching process. The influences of the preparation parameters such as resistivity of the silicon wafer, the anodizing current density, etching time to the size of pores were systematically investigated. The SERS substrates prepared were characterised by using appropriate techniques: the morphology and pores size by scanning electron microscope (SEM), the SERS activity by Raman scattering measure of organic molecules malachite green (MG) embedded into the substrate at room temperature. Our experimental results show that a home-made Raman microscope system could be efficiently used to detect the MG molecules at the concentration lower than 10 -7 M with the prepared SERS substrates which have Ag NPs in the obtained pores of 10 – 40 nm.