The sensing behavior of graphitic carbon nitride (g-C3N4) allotropes (fabricated with thermal polymerization of urea or melamine) by monitoring their laser induced room temperature photoluminescence (PL) emission, is demonstrated. Their sensing behavior has been investigated at oxygen atmosphere, upon optical excitation with a laser source (248 and 355 nm) in wavelength for different energy densities. The observed variability of PL features of g-C3N4, such as spectral intensity and wavelength, offers a systematic way to monitor the environmental changes in a reliable manner, opening the path for exploiting g-C3N4, as optical sensing material.
In this work, we review our recent results demonstrating the effectiveness of pulsed laser irradiation to fabricate nanostructures on various substrates, which are then used to enhance the Hydrogen Evolution Reaction (HER). Femtosecond (fs) laser pulses were used to fabricate nanostructures directly on nickel and iron sheets, while nanosecond laser pulses were used to fabricate nanostructures on Ni foam (NF) substrates via pulsed laser deposition. Electrodeposition was further employed complementary to the fs laser-surface direct nanostructuring to deposit Ni nanoparticles on top of the laser-modified nanostructures. A thorough electrochemical, structural, and morphological comparison has been conducted between laser-nanostructured and flat (i.e., untreated) Ni and Fe electrodes. In addition, the Ni-deposited (with PLD) NF electrodes were compared to an untreated NF electrode. The prepared electrodes show enhanced electrochemical characteristics and superior performance in HER. Morevover, the laser-nanostructured and electrodeposited electrodes were found to be as much as 4.6 times more efficient in actual Hydrogen production conditions. We propose that scaling up in the fabrication of such nanostructured electrodes should be pursued to address global energy and environmental concerns.
In the area of optoelectronics, Epsilon Near Zero (ENZ) materials possess a special place, as due to them, high nonlinearities can be achieved. Our interest is focused at the telecommunication wavelengths, as a lot of nanophotonic phenomena are taking place. Transparent Conductive Oxides (TCOs) is a group of materials that are used in the ENZ regime. Aluminum Zinc Oxide (AZO) is a TCO that has been proved that is preferred for telecom applications. In order to achieve higher nonlinearities in ENZ regime, we fabricate 3D photonic nanostructures, via Multiphoton lithography and we cover them with AZO via Pulsed Laser Deposition.
Zinc oxide (ZnO) is one of the most studied materials in nanoscience and chemical sensing research area. Monitoring the variations of electrical conductance of different ZnO nanostructure has enabled the detection of different gases and volatile organic compounds (VOCs). Another interesting perspective emerges from the development of optical sensors and experiments based on the photoluminescence of the semiconductor, has shown excellent sensing properties towards different chemical substances, ranging from oxygen, NO2, CO and volatile compounds (ethanol, H2S), to biomolecules, such as glucose, in aqueous solutions.
In the present study ZnO has been investigated as optical sensing material towards ozone (O3) detection, by monitoring its laser induced room temperature photoluminescence (PL) emission. The optical material consists of ZnO/polymer nanohybrids (ZnO/poly(poly(ethylene glycol) methyl ether methacrylate) (ZnO/PPEGMA) and ZnO/polydimethylsiloxane (ZnΟ)/PDMS)) which are excited with a UV pulsed laser source (λex= 248 nm, τex= 15 ns).
The performance of these sensing systems has been investigated with respect to response, reversibility, and dynamic characteristics (response/recovery time) as a function of ozone concentration in synthetic air (1600 down to 50 ppb).
We present our latest results into the freeform 3D nanoprinting of arrays of TiO2 nanorods. We demonstrate that the rate of photocatalysis of Methylene Blue increases significantly, due to increase in active surface area. Our results open the route to using 3D-printed TiO2 nanorods for other energy applications, such as hydrogen generation.
The sensing properties of zinc oxide (ZnO) combined with tilted fiber Bragg gratings have been studied in this work for the development of organic vapor optical fiber sensors. ZnO has been deposited onto tilted optical fiber Bragg gratings by drop casting technique to obtain coatings with thickness below 100nm. For a title angle of 4°, cladding modes up to 4 dB peak to peak amplitude were obtained and, as a consequence, the fundamental mode strength dropped below 0.5dB. The sensing features were evaluated by exposing the sensor to saturated atmospheres of three different alcohols and acetone. A negligible change was registered for methanol but in the case of ethanol and isopropanol a 24pm red shift was observed; in the case of acetone, the shift was 96pm which is of the order of spectral width of certain cladding modes. For all cases, the shifts were reversed once the organic vapors were removed. Ongoing studies are focused on the optimization of the sensing layer as well as the tilted angle to enhance the spectral response of the sensor.
AlN thin films with thickness in the nanometer range were prepared by Pulsed Laser Deposition technique. The extension of PLD/RPLD for obtaining good AlN nanostructures is a consequence of high reproducibility, control of the film growth rate and stoichiometry, and low impurity contamination. We investigated in this paper the effect of laser wavelength, pulse duration, and ambient gas pressure on the composition and morphology of the deposited films. We demonstrate that we deposited stoichiometric and even textured AlN thin films by PLD from AlN targets using 3 laser sources generating pulses of 34 ns@248 nm (source A), 450 fs@248 nm (source B), and 50 fs@800 nm (source C). Plamsa investigations by Optical Emission Spectroscopy and Time-of-Flight Mass Spectrometry are in agreement with the studies of films, showing plasma richer in Al ions for source A, and the prevalent presence of AlN positive ions in the plasma generated under the action of sources B and C.
Er- doped YAG and YAP layers were grown by nanosecond (20 ns) and subpicosecond (450 fs) KrF laser ablation under a wide set of deposition conditions. Results of characterization of films crystallinity and luminescence are presented and discussed. Films grown in ns regime were almost amorphous for substrate temperature to Ts ~ 1000 oC, while films grown in subps regime were partly crystalline, even at low Ts. Film crystallinity was also studied after annealing of amorphous layers under vacuum with CO2 and KrF excimer lasers. Luminescence corresponding to Er+3 ions was observed for all samples.
We report on the reproducible growth of stoichiometric thin films of ferromagnetic intermetallic compound NiMnSb by pulsed laser deposition (PLD) on various substrates. The films are grown at moderate temperature (around 200 degree(s)C) using polycrystalline targets. Two different substrates were employed - single crystalline silicon and InAs polycrystalline - to investigate the influence of the thin layer/substrate lattice mismatch on the quality of the grown film. XRD and EDX analyses indicate that the layers are of high crystalline quality and their stoichiometry is very close to that of the corresponding targets, respectively. SEM images show that there are droplets on the surface of the films and their composition is similar to that of the targets. Magnetic measurements performed at both room temperature and 5K find that the investigated samples have small Hc values.
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