Tony Donnelly | University College Dublin (original) (raw)

Papers by Tony Donnelly

Time evolution of electron density in a laser ablation plume has been investigated using a floati... more Time evolution of electron density in a laser ablation plume has been investigated using a floating hairpin resonance probe in conjunction with the ion density measured using a planar Langmuir probe. The laser plasma plume is produced by ablation of silver using a 248 nm, 26 ns, KrF, YiG laser. Due to supersonic flow of ions in the plume; measuring the electron density is difficult using a Langmuir probe, because of energetic ions bombarding the probes surface. Therefore we used a floating hairpin resonance probe for measuring time varying electron density of the plume. This technique depends only on the local electron density and is independent of the ion fluxes received by the probe. The ion density on the other hand is simply obtained from the ion flux and ion flight-time measure to a negatively biased probe, at some distance from the target. We observe a good agreement between the electron and ion density measured using two distinct techniques.

Society of Photo-Optical …, Jan 1, 2009

To form a better uniform metal nano-particles (Nps) film, the spatial distribution of Nps produce... more To form a better uniform metal nano-particles (Nps) film, the spatial distribution of Nps produced by femtosecond (fs) pulsed-laser deposition (PLD) method has been studied in detail. Firstly, the spatial distribution of Nps is collected by a slice of harden plastic under different laser fluence. Secondly, the deposition slices are scanned into jpg images. Then, the gray intensity of Nps deposit in the images has been used to have information of the number of deposited Nps. The data are analyzed by Matlab, Excel and Origin software. Experimental results show that the Nps' spatial distribution is following the Anisimov gas expansion model, in which a k value shows a descending trend with the increasing of laser fluence. Most Nps are flying to a narrow angle θ (θ≈0-30 degree), which is departing away the vertical direction of material surface. A 3cm deposition distance and θ≈30 degree are chosen to deposit Cu Nps film. The deposited Cu film seems not very compact and the Nps can be seen clearly in 0.7 J/cm 2 with 500s deposition time, and the growing velocity of Cu film is near 0.14-0.16 nm/s.

Plasma Science, Jan 1, 2007

Summary form only given. Laser ablation is a useful technique for applications such as nanomateri... more Summary form only given. Laser ablation is a useful technique for applications such as nanomaterial production, micromachining and pulsed laser deposition. For laser ablation plumes which are significantly ionised, Langmuir probes have proved to be a relatively simple and inexpensive tool for measuring the plume shape, ion energy distribution and electron temperature. The supersonic flow in the ablation plume complicates

ocs.ciemat.es

Measurements of the in-band Extreme-Ultraviolet (EUV) emission from CO2 laser produced Sn (tin) p... more Measurements of the in-band Extreme-Ultraviolet (EUV) emission from CO2 laser produced Sn (tin) plasma were recorded in order to obtain conversion efficiency values for next generation EUV Lithography sources. CE values were recorded for different laser gas mixtures, with maximum CE values of around 1.5% achieved.

Proceedings of …, Jan 1, 2011

An engineering prototype high average power 13.5-nm source has been shipped to semiconductor faci... more An engineering prototype high average power 13.5-nm source has been shipped to semiconductor facilities to permit the commencement of high volume production at a 100 W power level in 2011. In this source, UTA (unresolved transition array) emission of highly ionized Sn is optimized for high conversion efficiency and full recovery of the injected fuel is realized through ion deflection in a magnetic field. By use of a low-density target, satellite emission is suppressed and full ionization attained with short pulse CO 2 laser irradiation. The UTA is scalable to shorter wavelengths, and Gd is shown to have similar conversion efficiency to Sn (13.5 nm) at a higher plasma temperature, with a narrow spectrum centered at 6.7 nm, where a 70% reflectivity mirror is anticipated. Optimization of short pulse CO 2 laser irradiation is studied, and further extension of the same method is discussed, to realize 100 W average power down to a wavelength of 3 nm.

ocs.ciemat.es

Confined laser ablation is used to form long lived dense plasma for single shot deposition of a m... more Confined laser ablation is used to form long lived dense plasma for single shot deposition of a metal nanoparticle film. Laser ablation of a silver target, using 1064 nm laser radiation at 1.5 J cm -2 , is performed in vacuum and the expansion of the plasma produced is restricted by placing a glass substrate over the target with a target-substrate distance of 50 µm. Time resolved optical emission spectroscopy shows that the confined plasma is sustained for longer than for free ablation. Electron microscopy revealed the presence of a silver nanoparticle layer deposited on the inside of the confining substrate. The nanoparticle layer formed by confined laser ablation is compared to films grown by conventional pulsed laser deposition (PLD). It is shown that a layer of nanoparticles, with similar surface coverage can be grown using a single shot in the confined geometry as opposed to the several thousand shots required for the PLD films.

Journal of Applied …, Jan 1, 2010

We have analyzed ultrafast laser ablation of a metallic target ͑Nickel͒ in high vacuum addressing... more We have analyzed ultrafast laser ablation of a metallic target ͑Nickel͒ in high vacuum addressing both expansion dynamics of the various plume components ͑ionic and nanoparticle͒ and basic properties of the ultrafast laser ablation process. While the ion temporal profile and ion angular distribution were analyzed by means of Langmuir ion probe technique, the angular distribution of the nanoparticulate component was characterized by measuring the thickness map of deposition on a transparent substrate. The amount of ablated material per pulse was found by applying scanning white light interferometry to craters produced on a stationary target. We have also compared the angular distribution of both the ionic and nanoparticle components with the Anisimov model. While the agreement for the ion angular distribution is very good at any laser fluence ͑from ablation threshold up to Ϸ1 J/ cm 2 ͒, some discrepancies of nanoparticle plume angular distribution at fluencies above Ϸ0.4 J / cm 2 are interpreted in terms of the influence of the pressure exerted by the nascent atomic plasma plume on the initial hydrodynamic evolution of the nanoparticle component. Finally, analyses of the fluence threshold and maximum ablation depth were also carried out, and compared to predictions of theoretical models. Our results indicate that the absorbed energy is spread over a length comparable with the electron diffusion depth L c ͑Ϸ30 nm͒ of Ni on the timescale of electron-phonon equilibration and that a logarithmic dependence is well-suited for the description of the variation in the ablation depth on laser fluence in the investigated range. to 134.226.1.234. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 043309-2 Donnelly et al. J. Appl. Phys. 108, 043309 ͑2010͒ Downloaded 08 Oct 2010 to 134.226.1.234. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 043309-3 Donnelly et al.

Applied surface science, Jan 1, 2006

Ultra-thin (0.5-5 nm) films of Ag have been prepared by pulsed laser deposition in vacuum using a... more Ultra-thin (0.5-5 nm) films of Ag have been prepared by pulsed laser deposition in vacuum using a 26 ns KrF excimer laser at 1 J cm À2 . The deposition was controlled using a Langmuir ion probe and a quartz crystal thickness monitor. Transmission electron microscopy showed that the films are not continuous, but are structured on nanometer size scales. Optical absorption spectra showed the expected surface plasmon resonance feature, which shifted to longer wavelength and increased in strength as the equivalent film thickness was increased. It is shown that Maxwell Garnett effective medium theory can be used to calculate the main features of optical absorption spectra. #

Time evolution of electron density in a laser ablation plume has been investigated using a floati... more Time evolution of electron density in a laser ablation plume has been investigated using a floating hairpin resonance probe in conjunction with the ion density measured using a planar Langmuir probe. The laser plasma plume is produced by ablation of silver using a 248 nm, 26 ns, KrF, YiG laser. Due to supersonic flow of ions in the plume; measuring the electron density is difficult using a Langmuir probe, because of energetic ions bombarding the probes surface. Therefore we used a floating hairpin resonance probe for measuring time varying electron density of the plume. This technique depends only on the local electron density and is independent of the ion fluxes received by the probe. The ion density on the other hand is simply obtained from the ion flux and ion flight-time measure to a negatively biased probe, at some distance from the target. We observe a good agreement between the electron and ion density measured using two distinct techniques.

Society of Photo-Optical …, Jan 1, 2009

To form a better uniform metal nano-particles (Nps) film, the spatial distribution of Nps produce... more To form a better uniform metal nano-particles (Nps) film, the spatial distribution of Nps produced by femtosecond (fs) pulsed-laser deposition (PLD) method has been studied in detail. Firstly, the spatial distribution of Nps is collected by a slice of harden plastic under different laser fluence. Secondly, the deposition slices are scanned into jpg images. Then, the gray intensity of Nps deposit in the images has been used to have information of the number of deposited Nps. The data are analyzed by Matlab, Excel and Origin software. Experimental results show that the Nps' spatial distribution is following the Anisimov gas expansion model, in which a k value shows a descending trend with the increasing of laser fluence. Most Nps are flying to a narrow angle θ (θ≈0-30 degree), which is departing away the vertical direction of material surface. A 3cm deposition distance and θ≈30 degree are chosen to deposit Cu Nps film. The deposited Cu film seems not very compact and the Nps can be seen clearly in 0.7 J/cm 2 with 500s deposition time, and the growing velocity of Cu film is near 0.14-0.16 nm/s.

Plasma Science, Jan 1, 2007

Summary form only given. Laser ablation is a useful technique for applications such as nanomateri... more Summary form only given. Laser ablation is a useful technique for applications such as nanomaterial production, micromachining and pulsed laser deposition. For laser ablation plumes which are significantly ionised, Langmuir probes have proved to be a relatively simple and inexpensive tool for measuring the plume shape, ion energy distribution and electron temperature. The supersonic flow in the ablation plume complicates

ocs.ciemat.es

Measurements of the in-band Extreme-Ultraviolet (EUV) emission from CO2 laser produced Sn (tin) p... more Measurements of the in-band Extreme-Ultraviolet (EUV) emission from CO2 laser produced Sn (tin) plasma were recorded in order to obtain conversion efficiency values for next generation EUV Lithography sources. CE values were recorded for different laser gas mixtures, with maximum CE values of around 1.5% achieved.

Proceedings of …, Jan 1, 2011

An engineering prototype high average power 13.5-nm source has been shipped to semiconductor faci... more An engineering prototype high average power 13.5-nm source has been shipped to semiconductor facilities to permit the commencement of high volume production at a 100 W power level in 2011. In this source, UTA (unresolved transition array) emission of highly ionized Sn is optimized for high conversion efficiency and full recovery of the injected fuel is realized through ion deflection in a magnetic field. By use of a low-density target, satellite emission is suppressed and full ionization attained with short pulse CO 2 laser irradiation. The UTA is scalable to shorter wavelengths, and Gd is shown to have similar conversion efficiency to Sn (13.5 nm) at a higher plasma temperature, with a narrow spectrum centered at 6.7 nm, where a 70% reflectivity mirror is anticipated. Optimization of short pulse CO 2 laser irradiation is studied, and further extension of the same method is discussed, to realize 100 W average power down to a wavelength of 3 nm.

ocs.ciemat.es

Confined laser ablation is used to form long lived dense plasma for single shot deposition of a m... more Confined laser ablation is used to form long lived dense plasma for single shot deposition of a metal nanoparticle film. Laser ablation of a silver target, using 1064 nm laser radiation at 1.5 J cm -2 , is performed in vacuum and the expansion of the plasma produced is restricted by placing a glass substrate over the target with a target-substrate distance of 50 µm. Time resolved optical emission spectroscopy shows that the confined plasma is sustained for longer than for free ablation. Electron microscopy revealed the presence of a silver nanoparticle layer deposited on the inside of the confining substrate. The nanoparticle layer formed by confined laser ablation is compared to films grown by conventional pulsed laser deposition (PLD). It is shown that a layer of nanoparticles, with similar surface coverage can be grown using a single shot in the confined geometry as opposed to the several thousand shots required for the PLD films.

Journal of Applied …, Jan 1, 2010

We have analyzed ultrafast laser ablation of a metallic target ͑Nickel͒ in high vacuum addressing... more We have analyzed ultrafast laser ablation of a metallic target ͑Nickel͒ in high vacuum addressing both expansion dynamics of the various plume components ͑ionic and nanoparticle͒ and basic properties of the ultrafast laser ablation process. While the ion temporal profile and ion angular distribution were analyzed by means of Langmuir ion probe technique, the angular distribution of the nanoparticulate component was characterized by measuring the thickness map of deposition on a transparent substrate. The amount of ablated material per pulse was found by applying scanning white light interferometry to craters produced on a stationary target. We have also compared the angular distribution of both the ionic and nanoparticle components with the Anisimov model. While the agreement for the ion angular distribution is very good at any laser fluence ͑from ablation threshold up to Ϸ1 J/ cm 2 ͒, some discrepancies of nanoparticle plume angular distribution at fluencies above Ϸ0.4 J / cm 2 are interpreted in terms of the influence of the pressure exerted by the nascent atomic plasma plume on the initial hydrodynamic evolution of the nanoparticle component. Finally, analyses of the fluence threshold and maximum ablation depth were also carried out, and compared to predictions of theoretical models. Our results indicate that the absorbed energy is spread over a length comparable with the electron diffusion depth L c ͑Ϸ30 nm͒ of Ni on the timescale of electron-phonon equilibration and that a logarithmic dependence is well-suited for the description of the variation in the ablation depth on laser fluence in the investigated range. to 134.226.1.234. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 043309-2 Donnelly et al. J. Appl. Phys. 108, 043309 ͑2010͒ Downloaded 08 Oct 2010 to 134.226.1.234. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 043309-3 Donnelly et al.

Applied surface science, Jan 1, 2006

Ultra-thin (0.5-5 nm) films of Ag have been prepared by pulsed laser deposition in vacuum using a... more Ultra-thin (0.5-5 nm) films of Ag have been prepared by pulsed laser deposition in vacuum using a 26 ns KrF excimer laser at 1 J cm À2 . The deposition was controlled using a Langmuir ion probe and a quartz crystal thickness monitor. Transmission electron microscopy showed that the films are not continuous, but are structured on nanometer size scales. Optical absorption spectra showed the expected surface plasmon resonance feature, which shifted to longer wavelength and increased in strength as the equivalent film thickness was increased. It is shown that Maxwell Garnett effective medium theory can be used to calculate the main features of optical absorption spectra. #