Laser based efficient new nanofabrication methods with technical feasibility for the fast uptake ... more Laser based efficient new nanofabrication methods with technical feasibility for the fast uptake in industrial application are of significant global demand. A recent simplest approach in this way is the standard pulsed laser deposition (PLD), used since 1960s after the development of high power lasers. Over all, PLD is a fit method towards the preparation of a variety of nanomaterials only for research purpose. Nevertheless, the method is relatively slow and could not adopted in industrial scale application. A recent new-fangled development in this direction is the atmospheric-PLD (APLD), where ablation of the target by a laser pulse occurs at atmospheric gas pressure and the ablated material is delivered to the substrate using a flowing medium such as gas or atmospheric plasma. With this method, a variety of nanomaterials such as plasmonic metal NP film could be produced for practical ap
For the fast uptake into industrial applications, the further development of fabrication methods ... more For the fast uptake into industrial applications, the further development of fabrication methods for nanomaterials which are inexpensive and simultaneously technologically feasible is one of the major key factors. One technological approach, which has great potential for industrial scale application, is pulsed laser deposition (PLD) in a gas at atmospheric pressure, since it allows flexible environmental conditions for nanofabrication. This makes the newly introduced atmospheric PLD (APLD) a rapid and robust method, so that the further development of the method is of great scientific and technical interest. In the laser ablation at atmospheric gas pressure, there is strong collisional coupling of the ablation plume and the ambient gas. The expansion of the plume is restricted and confined close to the target surface and forms a nanoparticle (NP) aerosol by collisional condensation. For the fabrication of NP films at atmospheric pressure, the NP aerosols have to be effectively transported away from the target to the substrate. In this thesis, the fabrication of plasmonic silver NP films with APLD was developed and investigated. A variety of methods based on: normal gas flow, supersonic gas flow, atmospheric flowing DBD plasma and a laser-triggered-spark discharge, were devised and applied to develop this technique. In each method, the ablation of a silver target was done using a ns excimer laser (248 nm, 25 ns), ns fiber laser (1060 nm, 0.6 ?s), or fs laser (800 nm, 130 fs), in gas at atmospheric pressure. The NP aerosol produced by laser ablation was entrained in a gas flow or flowing atmospheric plasma and was transported to a substrate. In the flowing gas methods, a normal flowing gas jet, or a supersonic gas jet, was used to transport the NP aerosol. In the plasma assist methods, an atmospheric plasma jet of Ar or He from a dielectric-barrier-discharge (DBD) plasma source, or a hot plasma from a laser-triggered-spark discharge, was used to drive the NP aerosol towards the substrate. The DBD plasma assist method was used in the two different geometries, the open and closed geometry. In the open geometry, the aerosol was directly entrained with the flowing plasma jet, whereas in the closed geometry, the aerosol was first transported to the plasma active region by the gas flow and then in the downstream plasma jet to a substrate. Each method was successful in making plasmonic NP films at atmospheric gas pressure. The NP films produced by these methods were characterised to asses the efficacy of each approach. The DBD plasma significantly enhanced the deposition rate and altered the film morphology. The laser-triggered-spark method was more efficient than the DBD plasma assist method, but with a smaller deposition area. Supersonic APLD method was effective to produce a microparticulate, or NP film. The Ag NP films produced by these methods were also used in SERS for molecular detection of Rhodamnine 6G (R6G) to test their performance as SERS substrates, with the highest enhancement observed for the supersonic APLD Ag NP film
This paper describes a study where an argon cold plasma jet, generated by a dielectric‐barrier di... more This paper describes a study where an argon cold plasma jet, generated by a dielectric‐barrier discharge (DBD), is combined with nanosecond laser ablation (248 nm, 25 ns, 10 Hz) to deposit silver particle aerosols onto the substrate at atmospheric pressure. The deposition of the particle is examined using various microscopy techniques and absorption spectroscopy for the plasma jet produced by operating DBD in the normal and reversed mode. Plasma facilitated the deposition process by delivering the particle to the substrate and significantly influenced its morphology depending on the jet interaction, length, and substrate position. In both cases, the particles are clustered; however, there is less deposit for the plasma ignited in the reverse mode. The theoretical analysis of the deposition process is performed using ANSYS software and evaluated in terms of plasma‐induced flow velocity. This study infers that the hybrid plasma‐laser deposition scheme considered is attractive for material processing and deposition, especially overextended substrate distances, and for altering the properties of the deposited particles for practical utilization in surface‐enhanced Raman spectroscopy, solar cells, and catalysis.
Abstract Spray pyrolysis technique was employed to synthesize NiO and NiO:Cu thin films (0.1–25% ... more Abstract Spray pyrolysis technique was employed to synthesize NiO and NiO:Cu thin films (0.1–25% Cu) on soda-lime glass substrate. Optical properties, as well as electrical resistivity of these films, were investigated. UV–Visible spectrophotometer was employed to measure the optical properties. The absorption edge of the films was located within the UV range i.e. λ = 280–380 nm. The average reflectance of the films was 16.9% in the range λ = 280–900 nm. On increasing the Cu/Ni ratio, the optical band gap decreased whereas the refractive index and Urbach energy increased. Quantitatively, the measured average value of the refractive index and the value calculated from the Reddy-Ahammed empirical formula, which connects refractive index with optical band gap, were in good agreement. Optical conductivity was found to be in the range 1014–1015 s−1 while the dielectric loss was rather very low; it points to the good optical response of the films. The average oscillator energy as well as dispersion energy evaluated from Wemple–DiDomenico model decreased rapidly to begin with as Cu/Ni ratio was increased up to 5% but later on decreased rather slowly. Optical band gap values calculated by the Wemple-DiDomenico model and by Tauc relation agreed very well. The PL spectra of all the films displayed an intense peak at 403 nm and two secondary peaks at 426 nm and 365 nm. The PL intensity of each peak decreased monotonically with an increase in Cu content in NiO:Cu thin film from 0 to 3%. However, it remained almost independent of Cu content in the range of 4–25%. With an increase in Cu/Ni ratio, electrical resistivity and carrier mobility decreased whereas carrier concentration increased.
The energy and charge state distribution of atomic carbon ions, carbon cluster ions, and protons ... more The energy and charge state distribution of atomic carbon ions, carbon cluster ions, and protons emitted during Q-switched Nd:YAG laser (1064 nm/6 ns) laser irradiation of high purity graphite target was investigated by employing a time of flight ion energy analyzer (TOF-IEA). Laser fluence on the target surface was varied from 2 to 26 J cm−2. At the lower fluence range (2–6 J cm−2), multiply charged low mass odd numbered cluster ions C n q + with n = 3, 5, 7 and charge state up to 5 + and carbon atomic ions up to the charge state of 3 + were detected. For the fluence greater than 6.4 J cm−2, carbon atomic ions up to a charge state of 6 + and protons were observed. The energy distribution of various carbon ions and protons was measured at the fluence of 5.1 and 25.5 J cm−2. At 5.1 J cm−2, the measured energy range for carbon cluster ions C 3 q + and carbon C 1 q + was 0.2–3.1 keV and 0.2–1.2 keV, respectively. At 25.5 J cm−2, the energy of carbon ions C 1 q + (q = 2–4) was in the ra...
Thermal oxidation and annealing of zinc nitride sputtered films are described in this paper. Zinc... more Thermal oxidation and annealing of zinc nitride sputtered films are described in this paper. Zinc nitride films were produced by the sputtering a zinc target (99.999%) in the plasma, ignited in a mixture of Ar:N2 (20:10 sccm) gas at 60 W and working pressure of [Formula: see text][Formula: see text]mbar. The films were initially micro-annealed in H2O2 solution (35[Formula: see text]vol.%) at room temperature and subsequently in ambient air in the low temperature range of 100–[Formula: see text]C. The as-sputtered and annealed films were examined using X-ray diffraction (XRD), spectrophotometer, Raman and photoluminescence spectroscopies. Annealing oxidation leads to the transformation of the cubic crystal structure of zinc nitride into wurtzite ZnO through the oxygen diffusion process. The XRD peak of (002) plane and the principal [Formula: see text] (high) phonon mode, detected for the annealed film, are clear signature on the conversion of zinc nitride film into crystalline ZnO. T...
Laser based efficient new nanofabrication methods with technical feasibility for the fast uptake ... more Laser based efficient new nanofabrication methods with technical feasibility for the fast uptake in industrial application are of significant global demand. A recent simplest approach in this way is the standard pulsed laser deposition (PLD), used since 1960s after the development of high power lasers. Over all, PLD is a fit method towards the preparation of a variety of nanomaterials only for research purpose. Nevertheless, the method is relatively slow and could not adopted in industrial scale application. A recent new-fangled development in this direction is the atmospheric-PLD (APLD), where ablation of the target by a laser pulse occurs at atmospheric gas pressure and the ablated material is delivered to the substrate using a flowing medium such as gas or atmospheric plasma. With this method, a variety of nanomaterials such as plasmonic metal NP film could be produced for practical ap
For the fast uptake into industrial applications, the further development of fabrication methods ... more For the fast uptake into industrial applications, the further development of fabrication methods for nanomaterials which are inexpensive and simultaneously technologically feasible is one of the major key factors. One technological approach, which has great potential for industrial scale application, is pulsed laser deposition (PLD) in a gas at atmospheric pressure, since it allows flexible environmental conditions for nanofabrication. This makes the newly introduced atmospheric PLD (APLD) a rapid and robust method, so that the further development of the method is of great scientific and technical interest. In the laser ablation at atmospheric gas pressure, there is strong collisional coupling of the ablation plume and the ambient gas. The expansion of the plume is restricted and confined close to the target surface and forms a nanoparticle (NP) aerosol by collisional condensation. For the fabrication of NP films at atmospheric pressure, the NP aerosols have to be effectively transported away from the target to the substrate. In this thesis, the fabrication of plasmonic silver NP films with APLD was developed and investigated. A variety of methods based on: normal gas flow, supersonic gas flow, atmospheric flowing DBD plasma and a laser-triggered-spark discharge, were devised and applied to develop this technique. In each method, the ablation of a silver target was done using a ns excimer laser (248 nm, 25 ns), ns fiber laser (1060 nm, 0.6 ?s), or fs laser (800 nm, 130 fs), in gas at atmospheric pressure. The NP aerosol produced by laser ablation was entrained in a gas flow or flowing atmospheric plasma and was transported to a substrate. In the flowing gas methods, a normal flowing gas jet, or a supersonic gas jet, was used to transport the NP aerosol. In the plasma assist methods, an atmospheric plasma jet of Ar or He from a dielectric-barrier-discharge (DBD) plasma source, or a hot plasma from a laser-triggered-spark discharge, was used to drive the NP aerosol towards the substrate. The DBD plasma assist method was used in the two different geometries, the open and closed geometry. In the open geometry, the aerosol was directly entrained with the flowing plasma jet, whereas in the closed geometry, the aerosol was first transported to the plasma active region by the gas flow and then in the downstream plasma jet to a substrate. Each method was successful in making plasmonic NP films at atmospheric gas pressure. The NP films produced by these methods were characterised to asses the efficacy of each approach. The DBD plasma significantly enhanced the deposition rate and altered the film morphology. The laser-triggered-spark method was more efficient than the DBD plasma assist method, but with a smaller deposition area. Supersonic APLD method was effective to produce a microparticulate, or NP film. The Ag NP films produced by these methods were also used in SERS for molecular detection of Rhodamnine 6G (R6G) to test their performance as SERS substrates, with the highest enhancement observed for the supersonic APLD Ag NP film
This paper describes a study where an argon cold plasma jet, generated by a dielectric‐barrier di... more This paper describes a study where an argon cold plasma jet, generated by a dielectric‐barrier discharge (DBD), is combined with nanosecond laser ablation (248 nm, 25 ns, 10 Hz) to deposit silver particle aerosols onto the substrate at atmospheric pressure. The deposition of the particle is examined using various microscopy techniques and absorption spectroscopy for the plasma jet produced by operating DBD in the normal and reversed mode. Plasma facilitated the deposition process by delivering the particle to the substrate and significantly influenced its morphology depending on the jet interaction, length, and substrate position. In both cases, the particles are clustered; however, there is less deposit for the plasma ignited in the reverse mode. The theoretical analysis of the deposition process is performed using ANSYS software and evaluated in terms of plasma‐induced flow velocity. This study infers that the hybrid plasma‐laser deposition scheme considered is attractive for material processing and deposition, especially overextended substrate distances, and for altering the properties of the deposited particles for practical utilization in surface‐enhanced Raman spectroscopy, solar cells, and catalysis.
Abstract Spray pyrolysis technique was employed to synthesize NiO and NiO:Cu thin films (0.1–25% ... more Abstract Spray pyrolysis technique was employed to synthesize NiO and NiO:Cu thin films (0.1–25% Cu) on soda-lime glass substrate. Optical properties, as well as electrical resistivity of these films, were investigated. UV–Visible spectrophotometer was employed to measure the optical properties. The absorption edge of the films was located within the UV range i.e. λ = 280–380 nm. The average reflectance of the films was 16.9% in the range λ = 280–900 nm. On increasing the Cu/Ni ratio, the optical band gap decreased whereas the refractive index and Urbach energy increased. Quantitatively, the measured average value of the refractive index and the value calculated from the Reddy-Ahammed empirical formula, which connects refractive index with optical band gap, were in good agreement. Optical conductivity was found to be in the range 1014–1015 s−1 while the dielectric loss was rather very low; it points to the good optical response of the films. The average oscillator energy as well as dispersion energy evaluated from Wemple–DiDomenico model decreased rapidly to begin with as Cu/Ni ratio was increased up to 5% but later on decreased rather slowly. Optical band gap values calculated by the Wemple-DiDomenico model and by Tauc relation agreed very well. The PL spectra of all the films displayed an intense peak at 403 nm and two secondary peaks at 426 nm and 365 nm. The PL intensity of each peak decreased monotonically with an increase in Cu content in NiO:Cu thin film from 0 to 3%. However, it remained almost independent of Cu content in the range of 4–25%. With an increase in Cu/Ni ratio, electrical resistivity and carrier mobility decreased whereas carrier concentration increased.
The energy and charge state distribution of atomic carbon ions, carbon cluster ions, and protons ... more The energy and charge state distribution of atomic carbon ions, carbon cluster ions, and protons emitted during Q-switched Nd:YAG laser (1064 nm/6 ns) laser irradiation of high purity graphite target was investigated by employing a time of flight ion energy analyzer (TOF-IEA). Laser fluence on the target surface was varied from 2 to 26 J cm−2. At the lower fluence range (2–6 J cm−2), multiply charged low mass odd numbered cluster ions C n q + with n = 3, 5, 7 and charge state up to 5 + and carbon atomic ions up to the charge state of 3 + were detected. For the fluence greater than 6.4 J cm−2, carbon atomic ions up to a charge state of 6 + and protons were observed. The energy distribution of various carbon ions and protons was measured at the fluence of 5.1 and 25.5 J cm−2. At 5.1 J cm−2, the measured energy range for carbon cluster ions C 3 q + and carbon C 1 q + was 0.2–3.1 keV and 0.2–1.2 keV, respectively. At 25.5 J cm−2, the energy of carbon ions C 1 q + (q = 2–4) was in the ra...
Thermal oxidation and annealing of zinc nitride sputtered films are described in this paper. Zinc... more Thermal oxidation and annealing of zinc nitride sputtered films are described in this paper. Zinc nitride films were produced by the sputtering a zinc target (99.999%) in the plasma, ignited in a mixture of Ar:N2 (20:10 sccm) gas at 60 W and working pressure of [Formula: see text][Formula: see text]mbar. The films were initially micro-annealed in H2O2 solution (35[Formula: see text]vol.%) at room temperature and subsequently in ambient air in the low temperature range of 100–[Formula: see text]C. The as-sputtered and annealed films were examined using X-ray diffraction (XRD), spectrophotometer, Raman and photoluminescence spectroscopies. Annealing oxidation leads to the transformation of the cubic crystal structure of zinc nitride into wurtzite ZnO through the oxygen diffusion process. The XRD peak of (002) plane and the principal [Formula: see text] (high) phonon mode, detected for the annealed film, are clear signature on the conversion of zinc nitride film into crystalline ZnO. T...
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Papers by Taj M . Khan