Nm Line Of He-Cd Laser Research Articles

C and O doped BN nanoflake and nanowire hybrid structures for tuneable photoluminescence

Abstract C and O doped BN nanoflakes and hybrid nanoflake-nanowire structures were synthesized in N2+H2 environment using plasma-enhanced hot filament chemical vapour deposition with solid B4C as boron and carbon precursor. Structure and chemical composition of the C and O doped BN nanoflakes and hybrid nanoflake-nanowire hybrid structures were systemically studied using advanced characterization instruments including high resolution transmission electron microscope, micro-Raman spectroscope, Fourier transform infrared spectroscope, X-ray diffractometer, field emission scanning electron microscope, and X-ray photoelectron spectroscope. The obtained results evidence that the C and O doped BN nanowires nucleate and grow directly on the tops of C and O doped BN nanoflakes due to the presence of dangling bonds on the surfaces of tips of C and O doped BN nanoflakes, which were formed by the ion bombardment in plasma. The photoluminescence (PL) properties of C and O doped BN nanoflakes and C and O doped BN nanoflake-nanowire hybrid structures were studied at room temperature using a micro-Raman system with the 325 nm line of He-Cd laser as the excitation source. The results of PL measurements indicate that the PL properties of C and O doped BN nanoflake-nanowire hybrid structures significantly change with the length of C and O doped BN nanostructures due to the interface zones caused by the nanowire length. Thus, the PL properties can be efficiently tuned by the length of nanowires. These achievements can contribute to the synthesis of novel BN-based hybrid nanostructures and the development of the next generation BN-based optoelectronic nanodevices.

Conversion of vertically-aligned boron nitride nanowalls to photoluminescent CN compound nanorods: Efficient composition and morphology control via plasma technique

Two-dimensional BN/CN nanomaterials of various composition and morphology were synthesized in N2H2 plasma by plasma-enhanced hot filament chemical vapor deposition, with B4C used as precursor. The results of field emission scanning electron microscopy, X-ray diffractometer, transmission electron microscopy, micro-Raman and X-ray photoelectron spectroscopy evidence that the hexagonal boron nitride nanowalls with carbon and oxide phases were synthesized under about 1:1 ratio of H2 to N2, while the CN nanorods with boron and oxide phases are formed under other ratios of H2 to N2, and the nanowires made of oxide phases are grown without the plasma. Efficient control over the nanostructure composition and morphology was demonstrated, thus proposing a cheap and convenient fabrication technique for the advanced composite boron nitride/graphene materials. The photoluminescence properties of the synthesized BN and CN nanomaterials were also studied using the 325 nm line of HeCd laser as the excitation source. The fabricated nanomaterials can generate the ultraviolet, blue and green multi-PL bands, which are associated to the defects formed in these nanomaterials and the carbon clusters, respectively. These outcomes can make a great contribution to the design of functional BN- and CN-nanomaterials of various morphologies and compositions for the applications in various electronic and carbon-based optoelectronic nanodevices.

Structure and photoluminescence properties of carbon nanotip-vertical graphene nanohybrids

We report on the effective enhancement and tuning of photoluminescence (PL) by combining vertical graphene nanoflakes (VGs) and carbon nanotips (CNTPs). The VGs are grown on the vertical CNTPs by hot filament chemical vapor deposition in the methane environment, where the CNTPs are synthesized on silicon substrates by CH4-H2-N2 plasma-enhanced hot filament chemical vapor deposition. The results of field emission scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy indicate that the VGs can be grown on the CNTP and silicon substrate surfaces with the orientation perpendicular to the surfaces of CNTPs and silicon substrates. The PL properties of VG, CNTP, and CNTP-VG structures are studied using a 325 nm line of He-Cd laser as the excitation source. The PL results indicate that the PL of VGs is enhanced by the CNTPs due to the increasing density of PL emitters, while the PL properties of the nanohybrid system can be tuned. Furthermore, the potential applications of CNTP-VG structures in optoelectronic devices are analyzed. These results contribute to the design of functional graphene-based materials and the development of next-generation optoelectronic devices.

Microstructure and Optical Characteristics of Rod-Like Nanoscale CeO<SUB>2</SUB> Synthesized by Hydrothermal Method

The rod-like nanoscale CeO2 were successfully synthesized by an ethanediamine-assisted hydrothermal synthesis process using CeCl3 x 7H2O as cerium source and N2H4 x H2O as mineralizer. The morphology, microstructure, and optical properties of nanoscale CeO2 were characterized by the scanning electron microscope, transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectrometer, UV-Vis spectrophotometer and photoluminescence spectrometer. The lattice parameter decreases with the increase of crystallite size due to the effect of lattice relaxation and Ce ions. Suitable amount of ethylenediamine is beneficial for the growth of CeO2 nanorods. The as-growth rod-like nanoscale CeO2 is polycrystalline materials, and the main valence of cerium was +4. The spectra exhibit a strong absorption band at the near UV region due to the charge-transfer transitions from O 2p to Ce 4f. The band gap energy increases with the increase of ethylenediamine from 0 up to 3 mL and then decreases. Photoluminescence properties were measured using the 325 nm line of He-Cd laser and were also discussed.

The diffusion redistribution of hydrogen and oxygen in porous silicon films

A porous silicon (PS) layer prepared by electrochemical anodization of a single crystal silicon surface has been known for many years. Crystalline structure of the PS is network of silicon is nanometer-sized regions, surrounded by void space, with very large surface to volume ratios [1]. The PS surfaces are covered by silicon hydrides and silicon oxides. Observation of visible photoluminescence from PS has generated widespread interest because of the potential application of PS in Si-based optoelectronic technology. The luminescence, optical and other properties of PS are determined by incorporation of hydrogen and oxygen on surfaces and the formation of Si-H, Si-H2 and Si-O bonds. Therefore stability of luminescence and optical characteristics of PS depend on processes of concentration redistribution of hydrogen and oxygen atoms under treatments. This, in turn, is limited by oxygen and hydrogen diffusion along inner PS surfaces with simultaneous penetration into silicon. The formation mechanism of PS and the luminescence mechanism have been actively discussed, whereas the composition changes of PS caused by hydrogen and oxygen diffusion, and by appropriate changes in the number of Si-H, Si-H2 and Si-O bonds due to thermal treatments are rarely considered. From FTIR measurements, a reduction of photoluminescence intensity of PS with simultaneous decrease of intensity of Si-H2 peaks as results of annealing at 25–400 ◦C was observed by Tsai et al. [2]. Hydrogenand oxygenrelated bonds changes during PS oxidation for the range 20–500 ◦C at atmospheric pressure has also been reported [3, 4]. The aim of the present work is to determine the diffusion parameters of hydrogen and oxygen atoms in free-standing PS films from analysis of changes intensity of Si-H and Si-O absorption peaks as a function of temperature and duration of annealing in air. The PS films were prepared on n-type Si (100) substrates of resistivity ρ= 0,09A cm by anodic etching in a solution HF : H2O= 1 : 3 at a current density of 15 mA/cm2 under the white light illumination. The PS films were then detached from silicon substrate by electropolishing under former solution with a current density of 0.8–1.0 A/cm2. The free-standing PS films and PS film on Si substrates were characterized by porosity, photoluminescence and FTIR measurements at room temperature. Porosity of films was determined by gravimetry. Freestanding PS films of thickness 10–20μm and porosities 70–80% were obtained. FTIR spectra of free-standing PS films were measured at room temperature by using a Mattson 1000 spectrometer. The photoluminescence spectra were excited by the 325 nm line of He-Cd laser under a power output of 20 mW. This investigation focuses on the analysis of changes of absorption coefficients of Si-H, Si-H2 (doublet at 2100 cm−1) and Si-O (1100 cm−1) peaks as a result of isothermal annealing at temperatures in the range 65–185 ◦C at atmospheric pressure. Isothermal annealings of PS films were carried out at 65, 80, 110, 150 and 185 ◦C. Time-dependence FTIR and photoluminescence spectra were measured after 5-min cycles of isothermal annealings. The distribution of photoluminescence intensity along thickness of PS films (on silicon substrates) has been analyzed by sequential removal of thin layers (about 1μm) from PS film and the photoluminescence intensity measurements. The absorption coefficient (α) is deduced from transmission spectra by solving α in the equation

Excitation energy dependence of photoluminescence in nanocrystalline silicon deposited by remote plasma chemical vapor deposition

The photoluminescence (PL) spectra of nanocrystalline silicon (nc-Si) films excited by the 488 nm line of an Ar laser show a single peak at about 2.1 eV, similar to the optical band gap. The PL spectra of nc-Si films excited by 325 nm line of HeCd laser, very similar to those of thermally grown silicon oxide films, show three peaks at about 1.6, 2.5, and 3.1 eV. The estimation of the skin depth shows that the 488 nm laser line penetrates into the sample by about 410 Å, 4.5 times more than the 325 nm laser line. These results combined with data from previously published literature suggest that the PL excited at 325 nm is produced by Si–O related effects in the surface oxide layer of nc-Si films, while the PL excited at 488 nm is caused by light emission in the amorphous silicon-like bulk region of nc-Si films.

Growth and characterisation of GaN epitaxial layers

Layers of monocrystalline GaN were grown at different temperatures by atmospheric pressure metalorganic chemical vapour deposition (MOCVD) method on the sapphire substrates. The high quality of the layers was confirmed by X-ray diffraction and photoluminescence spectra measurements. For comparison purposes, simultaneous growth on a-plane and c-plane sapphire substrates was performed for each of the experiments. The GaN layers grown on either a-plane or c-plane sapphire were oriented with the GaN c-plane (0001) parallel to the substrate. The 325 nm line of He-Cd laser was used as an excitation source for photoluminescence experiments. Photoluminescence spectra showed near band peaks and broad yellow band emission at 77 K.

Pyrene sulphonyl chloride as a reagent for quantitation of oestrogens in human serum using HPLC with conventional and laser-induced fluorescence detection.

A highly sensitive HPLC method with conventional and laser-induced fluorescence detection for the analyses of oestrogens is described. beta-oestradiol (beta-ES) was chosen as a model and derivatized with pyrenesulphonyl chloride (PSCL), a novel derivatizing reagent, using a two-phase system with tetrapentylammonium bromide (TPABR) as a phase transfer catalyst. Derivatization was complete in 30 s at room temperature and concentrations as low as 5 x 10(-10) M could be derivatized and detected. The concentration detection limit PSCL derivatized beta-ES was 2 x 10(-11) M which corresponds to an on-column detection limit of one femtomole using conventional chromatography and detection. The relative standard deviation (n = 6) of the derivatization carried out at 2.5 x 10(-9) M was 4%. No significant loss of peak-height of the derivative was observed at room temperature over 24 h period. Baseline resolution of PSCL derivatized oestrone, equilin and beta-oestradiol was achieved with ACN:H2O (75:25 v/v) using a Bondclone C-18 column. The method described here is sufficiently sensitive for analyses of beta-oestradiol at low pg/mL concentrations in 1 mL of human serum. The PSCL derivatives of oestrogens demonstrate excellent potential for excitation by laser-induced fluorescence using the 351 nm line of an Ar ion laser or the 325 nm line of He-Cd laser. A concentration limit of detection of 4 x 10(-12) M for beta-oestradiol was achieved using the 325 nm line of an He-Cd laser. This corresponds to 0.2 fmol of derivatized beta-oestradiol on-column.