In this work, nitrogen-doped graphene quantum dots (N-GQDs) were synthesized by pulsed laser ablation in liquid using Nd:YAG laser (532 nm). Graphite target was ablated in dimethylformamide, as ...solvent and nitrogen source, and the microstructure as well as optical properties of N-GQDs were studied. The N-GQDs structure consists of a graphitic core with oxygen and nitrogen functionalities and particle size about 3 nm, as demonstrated by X-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. The as-prepared N-GQDs structure was modified by solvothermal treatment at 65, 90 and 120 °C reducing the oxygen functional groups, adding nitrogen and restoring the π-conjugated structure of N-GQD. The N-GQDs exhibit UV–Vis absorption spectrum with the characteristic π-π* and n – π* electronic transitions of the GQDs with a large amount of oxygen and nitrogen functionalities. These N-GQDs exhibited a visible light photoluminescence centered at 486 nm upon an excitation of 410 nm and the photoluminescence intensity enhanced up to 4.05% of quantum yield after solvothermal treatment. The N-GQDs dispersion was used for selective detection of ascorbic acid, through a signal-off and signal-on system. The results show the use of N-GQDs as a competent photoluminescence sensor for metal ions and ascorbic acid.
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In the present article, antimony sulfide nanoparticles have been synthesized by pulsed laser ablation of an antimony sulfide pellet in distilled water and isopropyl alcohol. The target was irradiated ...by 1064 and 532 nm from a pulsed Nd:YAG laser operated at 10 Hz and pulse width of 10 ns at room temperature. Analysis of the morphology, crystalline phase and elemental composition were done using transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The optical band gap energies of these colloidal nanoparticles were evaluated from UV–Visible absorption spectra. It was observed that the morphology, size, and optical properties of the antimony sulfide nanoparticles depend on the wavelength of the laser and the liquid media.
Carbon surfaces become significantly activated with plasma treatment enhancing the surface energy, wettability, and bio-conjugation. However, the activated surfaces are influenced by aging effect or ...reorientation phenomenon, a rarely reported occurrence, that refers to the loss of surface activity with time. Generated plasma-activated surface functional groups suffer from a brief shelf life as they reorient themselves to occupy lower states of energy. This study thoroughly assesses plasma-treated pyrolyzed carbon platforms with O2, N2, and Ar plasma radiations over 3 weeks. Pristine, immediately treated, and aged carbon samples were analyzed by SEM, AFM, WCA, and XPS to observe physical and chemical changes of the surfaces. Moreover, the electrochemical analyses demonstrated radical alterations of the surface characteristics immediately after the treatment; an activation which did not last long regardless of the plasma choice. With time, clear signs of surface inactivation were recorded manifesting in the form of decreased roughness, increased water contact angle, and major alterations of surface chemical composition, capacitance, and resistance. Our observations confirm that the plasma-treated carbon samples return to the pristine surface characteristics within a brief period of time thus demonstrating the loss of surface activity irrespective of the treatment choice.
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•Pd nanoparticle colloids were synthesized using PLAL technique.•Characterized by TEM, XPS and UV–vis spectroscopy.•Average size distribution was affected by different liquid media.•Laser ...post-irradiation was effective to regain optical properties.•Ultrasonic treatment helped to regain the optical properties.
Pulsed laser ablation in liquid (PLAL) as a prominent technique for nanofabrication was employed to synthesize palladium (Pd) nanoparticles in different liquids. The synthesis of Pd nanoparticles was developed using a pulsed Nd:YAG laser with its fundamental wavelength output of 1064nm (10Hz, 10ns) in a range of energy fluence (40.5–8J/cm2). Pure Pd metal target was immersed in distilled water, methanol–water mixture (1:1) and sodium dodecyl sulfate (SDS) to study the effect of the nature of the liquid media. Laser post-irradiation and ultrasonic treatments were applied to the precipitated colloidal solution to investigate their effects on the re-dispersion and stability. The mean size, size distributions, shape, elemental composition, optical properties and stability of nanoparticles synthesized by PLAL were examined by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–vis absorption spectroscopy. TEM characterizations showed smaller nanoparticles in methanol–water mixture in comparison with the other liquids. Spherical morphology was observed for Pd nanoparticles synthesized in distilled water and methanol–water mixture. In the case of SDS, spherical nanoparticles embedded on the surfactant were observed. The effect of energy fluence was different for each liquid media. Laser post-irradiation and ultrasonic agitation worked as efficient methods to re-disperse the precipitates of NPs and to recover their optical properties.
•CdS thin films by conventional CBD and laser assisted CBD.•Characterized these films using XRD, XPS, AFM, optical and electrical measurements.•Accelerated growth was observed in the laser assisted ...CBD process.•Improved dark conductivity and good photocurrent response for the LACBD CdS.
In this work, we report the preparation and characterization of CdS thin films by laser assisted chemical bath deposition (LACBD). CdS thin films were prepared from a chemical bath containing cadmium chloride, triethanolamine, ammonium hydroxide and thiourea under various deposition conditions. The thin films were deposited by in situ irradiation of the bath using a continuous laser of wavelength 532nm, varying the power density. The thin films obtained during deposition of 10, 20 and 30min were analyzed. The changes in morphology, structure, composition, optical and electrical properties of the CdS thin films due to in situ irradiation of the bath were analyzed by atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–vis spectroscopy. The thin films obtained by LACBD were nanocrystalline, photoconductive and presented interesting morphologies. The results showed that LACBD is an effective synthesis technique to obtain nanocrystalline CdS thin films having good optoelectronic properties.
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•Highlights•TiO2 nanomaterials were prepared by PLALM.•Characterized these nanomaterials using TEM, XPS, XRD, optical and luminescence measurements.•Morphology of these nanomaterials ...were dependent on ablation wavelength, fluence and post-irradiation time.•Laser post irradiation modified the size, morphology and structure of these TiO2 nanomaterials.
Nanomaterials of titanium oxide were prepared by pulsed laser ablation of a titanium metal target in distilled water. The ablation was performed at different laser energy (fluence) using a nanosecond pulsed Nd:YAG laser output of 1064 and 532nm. A post-irradiation of titanium oxide nanocolloids obtained by ablation using 532nm was carried out to explore its effects on the structure and properties. Analysis of morphology, crystalline phase, elemental composition, chemical state, optical and luminescent properties were performed using Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), UV–-vis absorption spectroscopy and room temperature photoluminescence spectroscopy. It was found that titanium oxide nanomaterial morphologies and optical properties were determined by ablation wavelength and fluence. Further, nanocolloids prepared by 532nm ablation showed a crystalline phase change by laser post-irradiation. The results showed that pulsed laser ablation in liquid as well as post-irradiation were effective in modifying the final structure and properties of titanium oxide nanocolloids.
Zinc oxide (ZnO) thin films were grown at 70 °C by plasma-enhanced atomic layer deposition using H
2
O and O
2
plasmas. Plasma oxidants were used in order to improve the ZnO crystallinity and ...optoelectronic properties, avoiding high-temperature synthesis. The deposition parameters were optimized to achieve saturation in each reaction step. X-ray photoelectron spectroscopy (XPS) reveals high purity of the obtained ZnO films. X-ray diffraction (XRD) measurements indicate that the grown layers are polycrystalline and that the H
2
O plasma synthesis leads to better crystallinity than the O
2
plasma as inferred from the intensity of the (100) and (002) peaks. The films are with high optical transmission, ~90%, as inferred from UV–visible (UV–Vis) transmittance measurements, and optical band gaps of 3.22 and 3.23 eV for H
2
O and O
2
plasma, respectively. Atomic force microscopy (AFM) indicates that the films are smooth, with an average roughness of ~ 0.22 nm. The growth rate was found to be in the range of 1.2–1.4 Å/cycle. The XPS, XRD, UV–Vis, and AFM results prove the possibility to obtain high-quality ZnO films by O
2
and H
2
O plasma processes at 70 °C with chemical, structural, and optical properties promising for flexible electronics. ZnO films were successfully deposited on polyethylene terephthalate substrates using the optimal conditions for H
2
O plasma process. No damage of the film surface or substrate was observed.
Thin film transistors (TFT) were fabricated by plasma-enhanced atomic layer deposition (PE-ALD) of aluminum oxide (Al2O3) and zinc oxide (ZnO) on glass substrates at 70 °C. The thicknesses of the ...Al2O3 (gate dielectric) and ZnO (n-type semiconductor) were 25 and 60 nm, respectively. Prior to Al2O3 deposition Cr/Au gate contacts were patterned using photolithography. Photolithography was also used to define aluminum source and drain contacts with thickness of 200 nm. The W/L ratio of the fabricated transistors was varied between 1 and 8 by varying the channel length L (40, 20 10 and 5 μm), while the channel width W was kept constant to 40 μm. Capacitance-voltage measurements revealed good uniformity of the Al2O3 layer with a dielectric constant value of ~8. The sheet resistance of the ZnO layer was found to be ~2400 Ω/sq. The TFT electrical characterization showed that the saturation mobility does not depend substantially on W/L ratio and had values between 0.82 and 1.1 cm2/V-s, while the subthreshold slope varied between 190 and 207 mV/dec. Moreover, a high on/off current ratio of ⁓107 was determined. The threshold voltage (Vth) instability was also characterized by positive and negative bias stress leading to a Vth shift of about −0.3 V and − 0.8 V, respectively.
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•Low temperature fabrication of thin-film transistors below 115 °C.•Full lithography fabrication process and minimum channel length of 5um.•Reliability of the VTH under gate bias stress of ±2.4 MV/cm.•ΔVTH between −0.30 to 0.03 V under PBS.•ΔVTH between −1.01 to −0.73 V under NBS.
Pulsed laser ablation in liquid media (PLALM) is a prominent technique for the controlled fabrication of nanomaterials via rapid reactive quenching of ablated species at the interface between the ...plasma and liquid. Results on nanoparticles and nanocrystals formed by PLALM of silver (Ag) and antimony (Sb) solid targets in different liquid environments (Sodium Dodecyl Sulfate, distilled water) are presented. These experiments were done by irradiating solid targets of Ag and Sb with a nanosecond pulsed Nd:YAG laser output of wavelength 532 nm. Nanoparticles of silver and nanocrystals of antimony oxide (Sb
2
O
3
) obtained were characterized using UV-Vis spectrometry, Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), X-ray Energy Dispersion Analysis (EDAX) and X-ray diffractometry (XRD). The morphology of nanomaterials formed is studied as a function of surfactant environment. The silver nanoparticles obtained were spherical of size in the order of 10–35 nm in solution of SDS having different concentrations. In case of the Sb target, ablation was performed in two different molarities of SDS solution and distilled water. Nanocrystals of Sb
2
O
3
in powder form having cubic and orthorhombic phases were formed in SDS solution and as fibers of nanocrystals of cubic Sb
2
O
3
in distilled water.
•Self-powered photodetector based on NiOx/Si heterostructure was fabricated.•At 0 V the responsivity was between 0.85 and 0.55 A/W for the 365 – 635 nm range.•At -1.5 V the responsivity varies ...between 59 and 33 A/W for the same range.
Thin NiOx layers were prepared by oxidation at 400, 500 and 600 °C of metallic Ni deposited by electron beam evaporation. The bandgap of NiOx determined from optical measurements increases from 3.6 to 3.7 eV with the increase of oxidation temperature from 400 to 500°C. Higher temperature leads to larger grain sizes, 12.6 nm at 400 °C, 15.3 nm at 500 °C and 16.1 nm 600 °C. Photodiodes based on NiOx/Si heterostructure were fabricated by evaporation of semitransparent Au top contacts. The structures with NiOx obtained at 500 °C showed superior diode characteristics compared to the other two types of devices with dark current < 3.5 × 10-8 A (current density J < 3.9 × 10−4 A/cm2) for reverse biases between 0 and -2 V and forward current of 3.3 × 10−5 A (J = 0.36 A/cm2) at bias of 1.5 V. The responsivity of these devices at 0 V is between 0.85 and 0.55 A/W for wavelengths in the 365 – 635 nm range, values higher than those previously reported for self-powered NiOx/Si photodiodes. The responsivity at reverse bias of -1.5 V increases more than 60 times to values of 33, 32, 50 and 59 A/W for red, green, blue, and ultraviolet light, values among the highest reported for broadband photodetectors. The excellent properties of the photodiodes with NiOx obtained at 500 °C are the result of a higher quality of the Si/NiOx interfacial region, which leads to lower recombination rate of the photogenerated carriers.
