Ioan Stamatin

New results in pulsed laser deposition of poly-methyl-methacrylate thin films

Abstract Thin organic films based on poly-methyl-methacrylate (PMMA) polymer have been obtained by pulsed laser deposition (PLD) on silicon substrates. The films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Raman spectroscopy (RS). We observed that the film composition and structure depend on the laser fluence and on the temperature of the substrate during deposition.

Field emission properties of silicon carbide and diamond-like carbon (DLC) films made by chemical vapour deposition techniques

Abstract Chemical vapour-deposited (CVD) amorphous silicon carbide (a-SiC) and diamond-like carbon (DLC) thin films were realised on p-type silicon field emitter arrays (FEAs) in order to investigate their field emission properties. The FEA geometry was investigated by scanning electron microscopy (SEM), the film morphology by scanning force microscopy (SFM) and by SEM, and the film structure by X-ray photoelectron spectroscopy (XPS). Field emission properties of FEAs were determined in high vacuum conditions. a-SiC/p-Si in comparison with DLC/p-Si emitter arrays have higher current emission at lower external fields. The upper limits of the field emission current densities were 2.4 mA/cm 2 for an electric field of 25 V/μm in the case of SiC and 0.8 mA/cm 2 for the electric field of 42 V/μm in the case of DLC films.

A chemically intuitive proposal for the structure of n-diamond

Structural analysis on carbonaceous samples produced from high temperature–pressure conditions by Palatnik et al. in 1984 indicate the existence of a metallic allotrope of carbon with a diffraction pattern closely matching that of cubic diamond. A structure proposed for this phase by Konyashin et al. and others suggests that the four interstitial carbon atoms occupying the tetrahedral holes in the ordinary cubic diamond lattice are vacant in the new structure. This leads to a transformation of the Fd3m, ordinary cubic diamond structure-type, to a simple face centred cubic carbon lattice in space group Fm3m, with a lattice parameter of 3.56 Å, identical with that of cubic diamond. The new structure supports the diffraction evidence accumulated for this so-called ‘n-diamond’ phase, but does not hold up to a first principles total energy optimization at the DFT level of theory for the fcc lattice, which reports the Konyashin et al. structure to be unstable. Here we report an alternative tetragonal carbon structural-type, which we have called ‘glitter’, that explains the observed diffraction pattern of n-diamond reasonably well, and that is stabilized by extensive spiroconjugation in three dimensions leading to a metallic status for the carbonaceous structural-type.

Effect of different concentrations of olive oil and oleic acid on the mechanical properties of albumen (egg white) edible films

The main objective of this study was to investigate the effect of olive oil and oleic acid addition to albumin (egg white) through emulsification to produce films on mechanical properties. Plasticizer was necessary to maintain film and coating integrity and to avoid pores cracks. Edible composite films were prepared from albumin and lipid material at (1 and 1.5%), respectively. The effect of unsaturated oleic acid with glycerol and monounsaturated olive oil on tensile strength, elongation at break, water vapor permeability (WVP), opacity (OP), solubility, colour and atomic force microscopy (AFM) was investigated. In general, the incorporation of lipid materials resulted in the increase (P < 0.05) of tensile strength and elongation at break, and the reduction of WVP with some exceptions. Overall, the effect of monounsaturated was greater than that of unsaturated. The surface microstructure of the films was analyzed using atomic force microscopy (AFM).

On the structure of i-carbon

In the carbon science literature, there have been various reports over the past few decades of potentially novel crystalline forms of carbon emerging as nanometer scale fragments recovered from the explosive remnants of heated, shock compressed graphite and other precursors of C. Two nanometric and crystalline forms of C that are particularly prominent in these studies are known as n-diamond and i-carbon forms. In our previous work, we have shown that the commonly observed diffraction pattern of n-diamond nanocrystals, recorded by several research groups around the world, is consistent with the calculated diffraction pattern of a novel form of carbon that we propose to call glitter. Glitter is a tetragonal allotrope of carbon with a calculated density of similar to 3.08 g/cm(3), and the density functional theory (DFT) optimized lattice paxameters given as a = 0.2560 nm and c = 0.5925 nm. In addition to the diffraction evidence for n-diamond having the glitter structure, the DFT calculated band structure of glitter shows it to be metallic, like the observed electrical characteristics of n-diamond. In this communication, we report on a comparison of the diffraction pattern observed for nanocrystalline i-carbon by the investigative team of Yamada et al. in 1994, with the calculated diffraction pattern of glitter based upon the optimized lattice parameters. The close fit of the latter dataset to that observed for i-carbon, as reported herein, suggests that indeed i-carbon may be of the same structure as n-diamond, and that they both may have the tetragonal glitter structure.

SELECTIVE DPV METHOD OF DOPAMINE DETERMINATION IN BIOLOGICAL SAMPLES CONTAINING ASCORBIC ACID

A modified carbon paste electrode that incorporates the anionic surfactant sodium dodecyl sulfate (SDS) in the paste (SDS-CP) is reported. It is shown that the SDS-CP electrode discriminates effectively between the cationic form of dopamine and the anionic electroactive species existing in biological fluids at the physiological pH. Therefore, a differential pulse voltammetry method has been developed. It has the detection limit comprised in the submicromolar range and the capability to remove the interference of the ascorbic acid and to diminish the interference of the uric acid. The method has been tested with good results on real samples of deproteinized serum.

Thermal properties of ecological phosphate and silicate glasses

The present work deals with ecological phosphate and silicate glasses that belong to the oxide systems: Li2O-MgO-P2O5, Li2O-CaO-P2O5, Li2O-MgO-P2O5-Fe2O3; Li2O-CaO-P2O5-Fe2O3 and SiO2-R2O-R′O (R = Na, K; R′ = Mg, Ca), the last system contains certain amounts of ZrO2, ZnO, TiO2. These ecological glasses do not contain toxic substances as BaO, PbO, As2O3, As2O5, fluorine, CdS, CdSe and they have applications as regards the retention and counteracting action of the harmful compounds resulted from the nuclear plants. The replacement of MgO by CaO leads to an insignificant increasing of the thermal expansion index and a slight decreasing of the characteristic temperatures, except the softening point where the effect is opposite. Adding of iron oxide in the phosphate glass composition causes the increasing of characteristic temperatures and the decreasing of thermal expansion index, both in MgO and CaO-containing phosphate glasses. The ecological silicate glasses are used as opal glasses free of fluorine as well as for lead-free crystal glass (CFP) where BaO and PbO are replaced by non-toxic oxides as K2O, MgO, ZrO2, and TiO2. The paper presents different glass compositions and the technological parameters to prepare the ecological glass samples. Both ecological phosphate and silicate glasses have been characterized as regards the characteristic temperatures (vitreous transition point, low and high annealing points, softening point) and the thermal expansion coefficient. This study presents the changes of the thermal parameters when CaO replaces MgO in phosphate glass samples and the role of iron oxide in the vitreous network. In the case of silicate glasses, the viscosity and wetting angle dependency of temperature are presented. The elemental analysis of the ecological glasses was made by XPS (X-ray photoelectron spectroscopy) which also put in evidence the iron species from the vitreous network.

Thin films growth parameters in MAPLE; application to fibrinogen

Increasingly requirements on the thin film quality of functionalized materials are efficiently met by a novel laser processing technique – Matrix Assisted Pulsed Laser Evaporation (MAPLE). Examples of deposition conditions and main features characteristic to film growth rate of MAPLE-fabricated organic materials are summarized. MAPLE experimental results are compared with ones corresponding to the classical Pulsed Laser Deposition (PLD). In particular, the results of investigation of MAPLE-deposited fibrinogen blood protein thin films using a KrF* excimer laser and characterized by FTIR and Raman spectrometry are reported.

Electropolymerized molecular imprinting on glassy carbon electrode for voltammetric detection of dopamine in biological samples.

A simple and reliable method for preparing a selective dopamine (DA) sensor based on a molecularly imprinted polymer of ethacridine was proposed. The molecularly imprinted polymer electrode was prepared through electrodepositing polyethacridine-dopamine film on the glassy carbon electrode and then removing DA from the film via chemical induced elution. The molecular imprinted sensor was tested by cyclic voltammetry as well as by differential pulse voltammetry (DPV) to verify the changes in oxidative currents of DA. In optimized DPV conditions the oxidation peak current was well-proportional to the concentration of DA in the range from 2.0×10(-8)M up to 1×10(-6)M. The limit of detection (3σ) of DA was found to be as low as 4.4nM, by the proposed sensor that could be considered a sensitive marker of DA depletion in Parkinsons disease. Good reproducibility with relative standard deviation of 1.4% and long term stability within two weeks were also observed. The modified sensor was validated for the analysis of DA in deproteinized human serum samples using differential pulse voltammetric technique.

Matrix assisted pulsed laser evaporation of pullulan tailor-made biomaterial thin films for controlled drug delivery systems

We report the first successful deposition of cinnamate-pullulan polysaccharide thin films by Matrix Assisted Pulsed Laser Evaporation (MAPLE). Thin film depositions were performed in vacuum using a KrF* excimer laser source (λ = 248 nm, τ ≈ 20 ns) operated at a repetition rate of 10 Hz. The dependence on incident laser fluence of the induced surface morphology is studied. We demonstrated by Raman spectroscopy that our MAPLE-deposited cinnamate-pullulan thin films are composed of starting materials preserving their chemical structures, with no impurities.