Fullerene‐like CNx thin films were synthesized by Pulsed‐Laser Ablation (PLA) of pyrolythic graphite (99.99%) target in nitrogen using a (500 mJ, 7 ns, 1064 nm) Nd:YAG‐pulsed laser. The films were deposited onto silicon substrates at 300 °C and nitrogen pressures within the 5–100 mTorr range. The composition and structure of these films were analyzed by means of Reflection Absorption Infrared Spectroscopy (RAIRS), XPS, and Raman spectroscopy and the morphology of the film surfaces by AFM. The RAIRS analysis of films deposited at different pressures shows the presence of the 2229 and 2273 cm–1 stretching peaks associated to CN triple bonds (C≡N) of nitriles and isocyanides. On the other hand, the XPS study of the N 1s bonding energy region provided typical spectra of the CNx materials. The spectra present the energy peaks at 400.8 (P2) and 398.4 eV (P3), which are usually assigned to nitrogen that is bonded to sp2 and sp3‐coordinated C atoms, respectively. For a fullerene‐like structure with developed basal planes, nitrogen is mostly bonded in a sp2‐rich environment. In our conditions, in films deposited at 5 mTorr the P2/P3 ratio is 1.41 indicating a fullerene‐like structure. Finally, the Raman analysis of films produced at different pressures, shows the characteristic D and G peaks at 1360–1370 cm–1 and 1580–1590 cm–1 related to the bond length in sp3 or sp2‐coordinated carbon respectively. The study demonstrated that laser ablation technique, by using an Nd:YAG‐pulsed laser, is a viable technique for the growth of fullerene‐like CNx films. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We used the theory of finite periodic systems to explain the photoluminescence spectra dependence on the average diameter of nanocrystals embedded in oxide matrices. Because of the broad matrix band gap, the photoluminescence response is basically determined by isolated nanocrystals and sequences of a few of them. With this model we were able to reproduce the shape and displacement of the experimentally observed photoluminescence spectra.

Carbon atoms form various allotropes with different physical and chemical natures originated from the variety of s-p orbital hybridization [1,2]. Carbon is a remarkable element showing a variety of stable forms ranging from 3D semiconducting diamond to 2D semi-metallic graphite to ID conducting and semiconducting carbon nanotubes to OD fullerenes, in this work we present a synthesis route to carbon with hierarchical morphology on the nanoscale.Carbon nanostructures have been synthetized by chemical reaction in aqueous solution using saccharose, deionized water, rongalite and sulfuric acid as precursor reagents. The main idea is to carbonize the saccharose by means of a dehydrolization process with sulfuric acid. Rongalite was used to complex some intermediate carbon structures due its powerful reductor capability.1gr of saccharose was mixed with 2ml of deionized water in a glass beaker at room temperature until it dissolved, then 0.3ml of polyethyleneimine (PEI, C 2 H 5 N 2 ), 0.3ml of rongalite (CH 3 NaO 3 S), 3ml of sulfuric acid (H 2 SO 4 ) and 0.3ml of ammonium hydroxide (NH 4 OH) buffer pH 11 was added to the mixture. At first the solution become darker and further addition of sulfuric acid made the solution completely black.The material obtained was characterized by FTIR and Raman spectroscopy and SEM-EDS studies.The samples where characterized by infrared transmission spectra carried out by a Horiba-Jobin-Yvon LabRam HR with a He-Ne laser at 632.8 nm, the chemical reaction give rise to a peak at 1645 cm -1 , which is corresponding to a stretching vibration mode of C=C bond, the intensities, positions and widths of the observed peaks are well consistent for the most part in the spectrum, it is inferred that the C=C bond was formed by a dehydration of the saccharose.The Raman spectra of the sample are show in figure 2, it was carried out by a Perkin Elmer Spectrum two with a UATR module, the spectrum was normalized by the maximum values of G-band peak, the spectrum was collected in the range from 0 to 4000 cm -1 , the peaks shown are the so called "G-peak" (for graphite) at 1584 cm -1 and "D-peak" (for disorder) at 1358cm -1 . Band peaks characteristics are strongly dependent on structure of the graphitization [3] and the Raman spectra are interpreted by models and theories [4]. The G-peak is due to the phonon mode that allowed by a break-up of selection rules for crystallite with sizes smaller than 100nm (nanocrystalline graphite), the spectra also shows a strong peak in the 2500 cm -1 characteristic of the sp 2 carbon materials.The scanning electron microscopy (SEM) were carried out by a FE-SEM JOEL jsm-7800F, images of the formed particles are shown in the figures 3 and 4, the sample has a ordained and homogenous morphology, the surface is covered by small nano-sized grains of about 100nm.

Noble metal nanoparticles, such as silver nanoparticles (AgNPs), have found technological applications due to their localized surface plasmon resonance (LSPR). In this context, a great quantity of synthetic methods for the preparation of AgNPs have been developed, including photo-chemical synthesis [1]. The photo-chemical synthesis is an advantageous technique because it is simple and environmentally friendly [2]. In this work, synthesis of AgNPs was performed via direct photo-reduction process of the silver nitrate and sodium citrate solutions without the previous addition of silver seeds.Silver nanoparticles were synthesized in aqueous solution using a mixture of silver nitrate (5 mM) as metallic precursor and sodium citrate (3 mM) as reducing agent. 300 µL of reaction mixture was placed in a polystyrene cuvette and was irradiated with laser light (λ = 488 nm, 130 mW) from an Ar ion CWLaser (Melles-Griot, USA) or direct sunlight (near noon) varying irradiation time from 5 to 60 minutes. Both synthesis took place at ~20 °C. Scanning Transmission Electron Microscopy (STEM) analysis was carried out with a field emission microscope JEOL JSM-7800F, operated at 30 kV.The synthesis is achieved by photo-oxidation of sodium citrate to acetone-1,3-dicarboxylate, reducing ionic silver to Ag 0 in the process. Furthermore, acetone-1,3-dicarboxylate can be chemisorbed on the nanoparticle surface controlling their growth and also stabilizing the nanostructures in the solution [3]. Therefore, the only residual product is CO2, which makes of this synthetic route a clean technique.In all cases laser synthesized AgNPs showed high size polydispersity. The size of the NPs ranges from a few nanometers (~10 nm) up to more than 100 nm, forming large aggregates with irregular morphology (Figure 1). Moreover, it can be seen that as the irradiation time elapses there is a decrease in the number of the smaller NPs. It is worth to mention that the agglomeration of NPs hampered to obtain the size distribution curve.Sunlight mediated AgNPs showed better size distribution and morphologies than that obtained by laser irradiation. The size of the nanoparticles increased with the increase of the irradiation time (Figure 2 a-c). It is proposed that the improvement in size and morphology is achieved thanks to the uniform illumination over the reaction cuvette when using sunlight. It is important to note that the laser beam passes through a small volume of reaction mixture causing a localized reaction in the sample. Sunlight mediated synthesis overcomes the later, so we can assume that all the solution receives the same quantity of light in every point at the same time, inducing a uniform nucleation and growth of the nanoparticles in the solution. In order to study the effect of silver/citrate ratio on the size and morphology of the NPs, we performed an experiment using a lower silver nitrate concentration (0.1 mM) keeping constant the sodium citrate concentration. This solution was exposed to 60 minutes of sunlight. Figure 2d shows the obtained n...

Over past decade, thin films have been important component in device fabrication of many technological applications such optical transmitters, gas sensors, conducting films, solar cells [1]. In recent years, a new category of thin films technology is based on luminescent materials which are mainly used in applications as white light emitting diodes (LED) and field emission displays (FED). Recently, luminescent thin films have been proposed to efficiency enhancement of solar cells [2]. Zinc oxide (ZnO) is currently one of the key functional materials in advanced optoelectronic and photonic applications, including photovoltaics, due to its high transparency across the solar spectrum, excellent electrical properties, and the possibility to synthesize a rich variety of nanostructures [3].In this study, the ZnO thin films were synthetized using a typical chemical bath process. Before the chemical bath, a ZnO layer was deposited on glass substrates by sol-gel method using dip-coating technique. The sol solution was prepared by mixing zinc acetate dihydrate (Zn(CH3COO)2·2H2O), diethylamine (DEA), and adequate volume of deionized water, the mixture was added to 25 ml ethyl alcohol. The cleaned glass was dipped in the sol-gel by a controlled withdrawal speed of 200 mm/min. The dip-coating process was repeated 1 and 3 times to get seed ZnO layers (ZnO-1C and ZnO-3C, respectively). The seed ZnO layers were then placed in the heated (80 ºC) aqueous solution containing 0.025M zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and hexamethylenetetramine (HMT) for 30 min.The morphological information about the ZnO thin films, prior and after coating with the chemical bath process, was obtained by SEM. Fig. 1a) shows the surface imagen of ZnO seed layer deposited by solgel method. It can be observed the formation of nanoparticles which are spherical in shape with a diameter around 30-50 nm. Figure 1b) and 1c) present the nanorods growth using seed ZnO layers with 1 and 3 cycles of deposit, respectively. Comparing the two figures, it can be seen that nanorods diameter slightly increases from 80 to 120 nm as the seed layer growth cycle is increased. However, for ZnO-3C thin film, it is evident that the nanorods grew disorderly which could be explained due to an inhomogeneous deposit of ZnO seed layer on the surface of glass substrate. In order to analyze the structural properties of obtained ZnO thin films, they were characterized by Raman spectroscopy. Both Raman spectra shown four fundamental bands located at 98, 380, 436, and 580 cm -1 , which correspond to the E2(low), A1(TO), E2(high), and E1(LO) vibrational modes of ZnO in hexagonal phase (Fig. 2a)). The Raman bands around 200 and 330 cm -1 are associated to the second order 2E2(low) and multi-phonon E2(high)-E2(low) modes, respectively. As can be observed, there is a decrease in the intensity of all the Raman bands for ZnO-3C film respect to the ZnO-1C film. This indicated that the film had a low degree of crystallinity, possibly due to the formation of structural defects induced by...