Physics Research Collection

Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates

Thu, 31 Jan 2013 00:00:00 GMT

Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates Balobaid, Laila; Craig Carville, N.; Manzo, Michele; Gallo, Katia; Rodriguez, Brian J. Photoreduction on a periodically proton exchanged ferroelectric crystal leads to the formation of periodic metallic nanostructures on the surface. By varying the depth of the proton exchange (PE) from 0.59 to 3.10 µm in congruent lithium niobate crystals, the width of the lateral diffusion region formed by protons diffusing under the mask layer, can be controlled. The resulting deposition occurs in the PE region with the shallowest PE depth, and preferentially in the lateral diffusion region for greater PE depths. PE depth-control provides a route for the fabrication of complex metallic nanostructures with controlled dimensions on chemically patterned ferroelectric templates.

Photoreduction of SERS-active metallic nanostructures on chemically-patterned ferroelectric crystals

Tue, 28 Aug 2012 00:00:00 GMT

Photoreduction of SERS-active metallic nanostructures on chemically-patterned ferroelectric crystals Craig Carville, N.; Manzo, Michele; Damm, Signe; Castiella, Marion; Collins, Liam; Denning, Denise; Weber, Stefan A. L.; Gallo, Katia; Rice, James H.; Rodriguez, Brian J. Photodeposition of metallic nanostructures onto ferroelectric surfaces is typically based on patterning local surface reactivity via electric field poling. Here, we demonstrate metal deposition onto substrates which have been chemically patterned via proton exchange (i.e., without polarization reversal). The chemical patterning provides the ability to tailor the electrostatic fields near the surface of lithium niobate crystals and these engineered fields are used to fabricate metallic nanostructures. The effect of the proton exchange process on the piezoelectric and electrostatic properties of the surface is characterized using voltage modulated atomic force microscopy techniques, which combined with modeling of the electric fields at the surface of the crystal, reveal that the deposition occurs preferentially along the boundary between ferroelectric and proton exchanged regions. The metallic nanostructures have been further functionalized with a target probe molecule, 4-aminothiophenol, from which surface enhanced Raman scattering (SERS) signal is detected, demonstrating the suitability of chemically patterned ferroelectrics as SERS-active templates.

Note : Network random walk model of two-state protein folding : Test of the theory

Fri, 18 Jan 2013 00:00:00 GMT

Note : Network random walk model of two-state protein folding : Test of the theory Berezhkovskii, Alexander M.; Murphy, Ronan D.; Buchete, Nicolae-Viorel We study two-state protein folding in the framework of a toy model of protein dynamics. This model has an important advantage: it allows for an analytical solution for the sum of folding and unfolding rate constants [A. M. Berezhkovskii, F. Tofoleanu, and N.-V. Buchete, J. Chem. Theory Comput. 7, 2370 (2011)10.1021/ct200281d] and hence for the reactive flux at equilibrium. We use the model to test the Kramers-type formula for the reactive flux, which was derived assuming that the protein dynamics is described by a Markov random walk on a network of complex connectivity [A. Berezhkovskii, G. Hummer, and A. Szabo, J. Chem. Phys. 130, 205102 (2009)10.1063/1.3139063]. It is shown that the Kramers-type formula leads to the same result for the reactive flux as the sum of the rate constants.

Robust liquid metal collector mirror for EUV and soft X-ray plasma sources

Mon, 02 Aug 2010 00:00:00 GMT

Robust liquid metal collector mirror for EUV and soft X-ray plasma sources Fahy, Kenneth; O'Reilly, Fergal; Scally, Enda; Sheridan, Paul Recent work in UCD has centred on the development of a liquid metal coating process for EUV and soft X-ray collector optics. The work involves using a room temperature liquid metal coated on a solid metal substrate of the appropriate form. The advances made demonstrate that a stable thin coating film on the interior surface of a rotating optic substrate is possible, and this offers promise as a solution to the problem of producing an atomically flat reflector that remains unspoiled in front of a multi-kilowatt EUV plasma. We report on the results of preliminary EUV tests carried out on a simple focusing liquid metal mirror. Advances in X-Ray/EUV Optics and Components V, 2–3 August 2010 San Diego, California, United States

Configuration Interaction in Charge Exchange Spectra of Tin and Xenon

Sat, 01 Jan 2011 00:00:00 GMT

Configuration Interaction in Charge Exchange Spectra of Tin and Xenon D'Arcy, Rebekah; Morris, O.; Ohashi, H.; Suda, S.; Tanuma, H.; Fujioka, S.; Nishimura, H.; Nishihara, K.; Suzuki, C.; Kato, T.; Koike, F.; O'Sullivan, Gerry Charge state specific extreme ultraviolet spectra from both tin ions and xenon ions have been recorded at Tokyo Metropolitan University. The Electron Cyclotron Resonance Source spectra were produced from charge exchange collisions between the ions and rare gas target atoms. In order to identify unknown spectral lines of tin and xenon, atomic structure calculations were performed for Sn14+ - Sn17+ and for Xe 16+ - Xe20+ using the Hartree-Fock with Configuration Interaction code of Cowan. The energies of the capture states involved in the single electron process that occurs in these slow collisions are estimated using the classical over barrier model.

UTA versus line emission for EUVL : studies on xenon emission at the NIST EBIT

Wed, 01 Dec 2004 00:00:00 GMT

UTA versus line emission for EUVL : studies on xenon emission at the NIST EBIT Fahy, Kenneth; Dunne, Padraig; McKinney, Luke; O'Sullivan, Gerry; Sokell, Emma; White, John K.; Aguilar, A.; Pomeroy, J.M.; Tan, J.N.; Blagojevi, B.; LeBigot, E.-O.; Gillaspy, J.D. Spectra from xenon ions have been recorded at the NIST EBIT and the emission into a 2% bandwidth at 13.5 nm arising from 4d_5p transitions compared with that from 4d_4f and 4p_4d transitions in Xe XI and also with that obtained from the unresolved transition array (UTA) observed to peak just below 11 nm. It was found that an improvement of a factor of five could be gained in photon yield using the UTA rather than the 4d_5p emission. The results are compared with atomic structure calculations and imply that a significant gain in efficiency should be obtained using tin, in which the emission at 13.5 nm comes from a similar UTA, rather than xenon as an EUVL source material.

Measurement of EUV spectra from high Z elements in the Large Helical Device

Tue, 21 Sep 2010 00:00:00 GMT

Measurement of EUV spectra from high Z elements in the Large Helical Device Suzuki, C.; Kato, T.; Sakaue, H.A.; Kato, D.; Murakami, I.; Sato, K.; Tamura, N.; Sudo, S.; Yamamoto, N.; Tanuma, H.; Ohashi, H.; D’Arcy, Rebekah; Harte, Colm S.; O’Sullivan, Gerry Extreme ultra-violet (EUV) emission spectra from highly charged tin, xenon and tungsten ions have been measured in optically thin high-temperature plasmas produced in the Large Helical Device (LHD) at the National Institute for Fusion Science by using a grazing incidence spectrometer and a tracer-encapsulated solid pellet (TESPEL) injector. Quasi-continuous spectral features arising from unresolved transition array (UTA) of open 4d subshell ions were commonly observed for tin, xenon and tungsten around 13.5, 11, and 5 nm, respectively, when edge plasma was cooled enough. The spectral appearance obviously depends on edge electron temperature and atomic number. In the case of intermediate edge temperature, sharp discrete lines from highly charged open 4s or 4p subshell ions are clearly observed for tin and xenon in longer wavelength side of the UTAs but not for tungsten. Assignments of the strong discrete lines have been performed with the help of comparisons with the other experimental data and the theoretical calculations by Cowan code. Contribution of open 4f subshell ions should also be considered to interpret the whole spectra from tungsten ions. 7th International Conference On Atomic and Molecular Data and Their Applications - ICAMDATA-2010, 21–24 September 2010, Vilnius, (Lithuania)

Feasibility study of broad band efficient "water window" source

Sun, 01 Jan 2012 00:00:00 GMT

Feasibility study of broad band efficient "water window" source Higashiguchi, Takeshi; Otsuka, Takamitsu; Yugami, Noboru; Endo, Akira; Li, Bowen; Dunne, Padraig; O'Sullivan, Gerry We demonstrate a table-top broadband emission water window source based on laser-produced high-Z plasmas. Resonance emission from multiply charged ions merges to produce intense unresolved transition arrays in the 2 to 4 nm region, extending below the carbon K edge (4.37 nm). Arrays resulting from n = 4−4 transitions are overlaid with n = 4−5 emission and shift to shorter wavelength with increasing atomic number. From spectral analysis, a guideline for microscope construction design for single-shot live cell imaging is proposed based on the use of a bismuth plasma source, coupled with multilayer mirror optics.

Interpretation of spectral emission around 20 nm region from tungsten ions observed in fusion device plasmas

Wed, 24 Aug 2011 00:00:00 GMT

Interpretation of spectral emission around 20 nm region from tungsten ions observed in fusion device plasmas Suzuki, C.; Harte, Colm S.; Kilbane, Deirdre; Kato, T.; Sakaue, H.A.; Murakami, I.; Kato, D.; Sato, K.; Tamura, N.; Sudo, S.; Goto, M.; D’Arcy, Rebekah; Sokell, Emma; O’Sullivan, Gerry We have measured extreme ultraviolet (EUV) spectra from tungsten ions around 20 nm region in plasmas produced in the Large Helical Device at the National Institute for Fusion Science. The spectra after injecting a tungsten pellet into a hydrogen plasma were monitored by a grazing incidence spectrometer. Quasicontinuum spectral feature arising from unresolved transition array (UTA) was observed around 20 nm region in plasmas with temperatures below 1.0 keV. This structure is reasonably considered to be the same one as those observed in another tokamak device or laser produced plasmas under low temperature conditions. Atomic structure calculations have been performed for tungsten ions with open 5p, 5s and 4f subshells (W7+–W27+) to interpret this commonly observed feature around 20 nm. Wavelengths and gA values for these transitions were calculated, and their mean wavelengths and extent were compared with the observations, which suggests that the emission largely arises from n = 5–5 transitions in stages lower than W27+.

Ground-State Configurations and Unresolved Transition Arrays in Extreme Ultraviolet Spectra of Lanthanide Ions

Fri, 01 Jan 2010 00:00:00 GMT

Ground-State Configurations and Unresolved Transition Arrays in Extreme Ultraviolet Spectra of Lanthanide Ions Kilbane, Deirdre; O'Sullivan, Gerry Theoretical ground-state configurations of lanthanide ions calculated with the Cowan suite of codes are presented. Theoretical 4d - 4f and 4p - 4d spectra of Pd-like to Rb-like lanthanide ions calculated using the FAC relativistic code are also shown. The effects of configuration interaction are investigated and results compare favorably with experiments where, for increasing nuclear charge, strong emission peaks are observed to move towards shorter wavelength. The application of these strong emitters as extreme ultraviolet radiation sources, a topic of emerging interest, is discussed.

Extreme ultraviolet emission spectra of Gd and Tb ions

Fri, 01 Jan 2010 00:00:00 GMT

Extreme ultraviolet emission spectra of Gd and Tb ions Kilbane, Deirdre; O'Sullivan, Gerry Theoretical extreme ultraviolet emission spectra of gadolinium and terbium ions calculated with the Cowan suite of codes and the flexible atomic code (FAC) relativistic code are presented. 4d–4f and 4p–4d transitions give rise to unresolved transition arrays in a range of ions. The effects of configuration interaction are investigated for transitions between singly excited configurations. Optimization of emission at 6.775 nm and 6.515 nm is achieved for Gd and Tb ions, respectively, by consideration of plasma effects. The resulting synthetic spectra are compared with experimental spectra recorded using the laser produced plasma technique.

The effect of viewing angle on the spectral behavior of a Gd plasma source near 6.7 nm

Sun, 01 Jan 2012 00:00:00 GMT

The effect of viewing angle on the spectral behavior of a Gd plasma source near 6.7 nm O'Gorman, Colm; Otsuka, Takamitsu; Yugami, Noboru; Jiang, Weihua; Endo, Akira; Li, Bowen; Cummins, T. (Thomas); Dunne, Padraig; Sokell, Emma; O'Sullivan, Gerry; Higashiguchi, Takeshi We have demonstrated the effect of viewing angle on the extreme ultraviolet (EUV) emission spectra of gadolinium (Gd) near 6.7 nm. The spectra are shown to have a strong dependence on viewing angle when produced with a laser pulse duration of 10 ns, which may be attributed to absorption by low ion stages of Gd and an angular variation in the ion distribution. Absorption effects are less pronounced at a 150-ps pulse duration due to reduced opacity resulting from plasma expansion. Thus for evaluating source intensity it is necessary to allow for variation with both viewing angle and target orientation.

Optimizing conversion efficiency and reducing ion energy in a laser-produced Gd plasma

Sun, 01 Jan 2012 00:00:00 GMT

Optimizing conversion efficiency and reducing ion energy in a laser-produced Gd plasma Cummins, T. (Thomas); Otsuka, Takamitsu; Yugami, Noboru; Jiang, Weihua; Endo, Akira; Li, Bowen; O'Gorman, Colm; Dunne, Padraig; Sokell, Emma; O'Sullivan, Gerry; Higashiguchi, Takeshi We have demonstrated an efficient extreme ultraviolet (EUV) source at 6.7 nm by irradiating Gd targets with 0.8 and 1.06 μm laser pulses of 140 fs to 10 ns duration. Maximum conversion efficiency of 0.4% was observed within a 0.6% bandwidth. A Faraday cup observed ion yield and time of flight signals for ions from plasmas generated by each laser. Ion kinetic energy was lower for shorter pulse durations, which yielded higher electron temperatures required for efficient EUV emission, due to higher laser intensity. Picosecond laser pulses were found to be the best suited to 6.7 nm EUV source generation.

Transition wavelengths and unresolved transition array statistics of ions with Z = 72 − 89

Sun, 28 Aug 2011 00:00:00 GMT

Transition wavelengths and unresolved transition array statistics of ions with Z = 72 − 89 Kilbane, Deirdre Potential extreme ultraviolet and soft x-ray radiation sources have been identified, using the flexible atomic code (FAC), as emission peaks arising from the 4d–4f and 4p–4d transitions in Pd-like to Rb-like ions of hafnium through actinium. The effects of configuration interaction are investigated and for increasing nuclear charge, these strong emitters are seen to separate and move to shorter wavelengths. Each source is characterized using the unresolved transition array model. They are proposed to complement the currently used nitrogen and argon sources in the 'water window', and as possible successors to tin in next-generation lithography.

Charge resolved electrostatic diagnostic of colliding copper laser plasma plumes

Sat, 01 Jan 2011 00:00:00 GMT

Charge resolved electrostatic diagnostic of colliding copper laser plasma plumes Yeates, P; Fallon, Conor; Kennedy, E.T.; Costello, John T. The collision of two laser generated plasma plumes can result, under appropriate conditions, in the formation of ‘stagnation layer’. The processes underlying this phenomenon are complex and time dependent. The majority of experiments over the last few decades have focused upon spectroscopic diagnostic of colliding plasmas. We have performed electrostatic diagnosis of multiply charged copper ions (Cu+ to Cu5+) generated via Q-switched pulsed laser (λ=1.06 μm, τ=6 ns, EL=52-525 mJ) generation of copper plasma plumes from a planar target. Time dependent current traces, charge yields and kinetic energy (Ke) distributions are obtained for single plasma plumes (Sp) and colliding plasma plumes (Cp). The charge yield from a Cp relative to twice that from a Sp is characterized by a charge yield ratio (CYR) parameter. Superior ion yields for all charge states occur for a discrete range of fluences (F) from colliding plasma plumes leading to a CYR parameter exceeding unity. The kinetic energy distributions from colliding plasma plumes display well defined energy compression via narrowing of the distributions for all fluences and charge states. The extent of this energy compression is charge dependent. Space charge forces within the stagnation layer and the resulting charge dependent acceleration of ions is proposed to account for the transfer of ion kinetic energy in favour of collisional ionization mechanisms.

Systematic investigation of self-absorption property and conversion efficiency of 6.7-nm extreme ultraviolet sources

Wed, 01 Dec 2010 00:00:00 GMT

Systematic investigation of self-absorption property and conversion efficiency of 6.7-nm extreme ultraviolet sources Otsuka, Takamitsu; White, John; Kilbane, Deirdre; Higashiguchi, Takeshi; Yugami, Noboru; Yatagai, Toyohiko; Jiang, Weihua; Endo, Akira; Dunne, Padraig; O’Sullivan, Gerry We have demonstrated rare-earth plasma extreme ultraviolet sources at 6.7 nm to investigate the spectral behavior and the conversion efficiencies to different laser wavelength and the initial target densities. The conversion efficiency was maximized to be 0.9% at laser intensity of 7 × 1012 W/cm2 at its wavelength of 1064 nm, which is attributed to the minimum self-absorption effect by use of the low initial density target, together with the narrow spectrum. It is important to use a low initial density target and to produce low electron density plasmas for efficient EUV sources using the high-Z targets.

Spectral and temporal behavior of an alkali metal plasma extreme ultraviolet source for surface morphology applications

Mon, 28 Feb 2011 00:00:00 GMT

Spectral and temporal behavior of an alkali metal plasma extreme ultraviolet source for surface morphology applications Higashiguchi, Takeshi; Yamaguchi, Mami; Otsuka, Takamitsu; Terauchi, Hiromitsu; Yugami, Noboru; Yatagai, Toyohiko; D'Arcy, Rebekah; Dunne, Padraig; O'Sullivan, Gerry We have characterized the emission spectrum and temporal history of a pure potassium plasma in a capillary discharge. Strong broadband emission was observed around 40 nm due to 3s−3p, 3p−3d, and 3d−4f transitions in ions ranging from K2+ to K4+ at a time-integrated electron temperature of about 12 eV. The temporal behavior of this emission strongly follows the recombination phase in the plasma and it was successfully reproduced by a hydrodynamic simulation of the potassium plasma which accounted for atomic processes.

Dielectronic recombination of Pd-like gadolinium

Sun, 01 Jan 2012 00:00:00 GMT

Dielectronic recombination of Pd-like gadolinium Li, Bowen; O'Sullivan, Gerry; Fu, Y.B.; Dong, C.Z. As research and development of extreme ultraviolet lithography (EUVL) sources at 6.7 nm (which will be based on emission from ionized gadolinium) has already begun, reliable atomic data are required in order to determine the optimum plasma conditions. However, the complexity of the atomic structure means that ab initio level-resolved dielectronic recombination (DR) calculations are currently unavailable for the ions of interest. Here we report the first detailed calculation of the DR rate coefficients for the ground state and first excited states of Pd-like gadolinium. Energy levels, radiative transition probabilities, and autoionization rates of Ag-like gadolinium for [Kr]4d94fnl, [Kr]4p54d104fnl, [Kr]4d95l'nl, and [Kr]4d96l'nl (n ≤ 18) complexes were calculated using the flexible atomic code (FAC). It was found that inclusion of 4p54d104fnl configurations has significant influence on the total DR rate coefficient. The DR rate coefficients obtained here are compared with radiative recombination and three-body recombination coeffcients. The results show that the DR rate coefficient is almost an order of magnitude higher than the coefficients for the other two recombination processes combined at plasma electron temperatures around 110 eV, which suggests that the DR process should be included in theoretical modeling for Pd-like gadolinium in EUVL source plasmas.

Shorter-wavelength extreme-UV sources below 10nm

Fri, 07 Oct 2011 00:00:00 GMT

Shorter-wavelength extreme-UV sources below 10nm Higashiguchi, Takeshi; Otsuka, Takamitsu; Yugami, Noboru; Jiang, Weihua; Endo, Akira; Dunne, Padraig; Li, Bowen; O'Sullivan, Gerry A next-generation laser-produced plasma system based on rare-earth targets generates strong resonant line emissions at 6.5–6.7nm.

Tungsten spectra recorded at the LHD and comparison with calculations

Fri, 01 Oct 2010 00:00:00 GMT

Tungsten spectra recorded at the LHD and comparison with calculations Harte, Colm S.; Suzuki, C.; Kato, T.; Sakaue, H.A.; Kato, D.; Sato, K.; Tamura, N.; Sudo, S.; D'Arcy, Rebekah; Sokell, Emma; White, John K.; O'Sullivan, Gerry We have measured extreme ultraviolet (EUV) spectra from highly charged tungsten ions in low-density and high-temperature plasmas produced in the Large Helical Device at the National Institute for Fusion Science. The EUV spectra emitted after injection of a tungsten pellet into a hydrogen plasma were recorded at plasma temperatures of 1.5 and 3 keV and were dominated by an intense transition array in the 4.5–6.5 nm region, the profile and extent of which was different in both spectra. Some discrete lines present were identified by comparison with existing spectral data while atomic structure calculations showed that the dominant emission in both arose from Δn = 0, n = 4–n = 4 transitions and the main differences could be attributed to the appearance of the 4p–4d and 4s–4p transitions from W XXXIX to W XLVI in the higher temperature spectrum. Comparison with calculations showed that the dominant emission in both temperature regimes arose from stages where the 4f subshell was either almost or completely stripped. We also investigated if the effect of low density favours transitions to the lowest level as observed in recently reported results.

Scaling of laser produced plasma UTA emission down to 3 nm for next generation lithography and short wavelength imaging

Mon, 22 Aug 2011 00:00:00 GMT

Scaling of laser produced plasma UTA emission down to 3 nm for next generation lithography and short wavelength imaging Li, Bowen; Endo, Akira; O'Gorman, Colm; Otsuka, Takamitsu; Cummins, T. (Thomas); Donnelly, Tony; Kilbane, Deirdre; Dunne, Padraig; O'Sullivan, Gerry; Jiang, Weihua; Higashiguchi, Takeshi; Yugami, Noboru 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 CO2 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 CO2 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 Presented at a poster session at Advances in X-Ray/EUV Optics and Components VI, Monday 22 August 2011, San Diego, California, USA

Emission characteristics and dynamics of the stagnation layer in colliding laser produced plasmas

Fri, 15 Jan 2010 00:00:00 GMT

Emission characteristics and dynamics of the stagnation layer in colliding laser produced plasmas Hough, Pádraig; McLoughlin, Conor; Harilal, Sivanandan S.; Mosnier, Jean-Paul; Costello, John T. The expansion dynamics of ion and neutral species in laterally colliding laser produced aluminium plasmas have been investigated using time and space resolved optical emission spectroscopy and spectrally and angularly resolved fast imaging. The emission results highlight a difference in neutral atom and ion distributions in the stagnation layer where, at a time delay of 80 ns, the neutral atoms are localised in the vicinity of the target surface (< 1 mm from the target surface) while singly and doubly charged ions lie predominantly at larger distances, < 1.5 mm and < 2 mm respectively. The imaging results show that the ions were found to form a well defined, but compressed, stagnation layer at the collision front between the two seed plasmas at early times (Δt < 80 ns). On the other hand the excited neutrals were observed to form a V shaped emission feature at the outer regions of the collision front with enhanced neutral emission in the less dense, cooler regions of the stagnation layer.

Gd plasma source modeling at 6.7 nm for future lithography

Mon, 05 Dec 2011 00:00:00 GMT

Gd plasma source modeling at 6.7 nm for future lithography Li, Bowen; Dunne, Padraig; Higashiguchi, Takeshi; Otsuka, Takamitsu; Yugami, Noboru; Jiang, Weihua; Endo, Akira; O’Sullivan, Gerry Plasmas containing gadolinium have been proposed as sources for next generation lithography at 6.x nm. To determine the optimum plasma conditions, atomic structure calculations have been performed for Gd11+ to Gd27+ ions which showed that n=4 - n=4 resonance transitions overlap in the 6.5 – 7.0 nm region. Plasma modeling calculations, assuming collisional-radiative equilibrium, predict that the optimum temperature for an optically thin plasma is close to 110 eV and that maximum intensity occurs at 6.76 nm under these conditions. The close agreement observed between simulated and experimental spectra from laser and discharge produced plasmas indicates the validity of our approach.

Ion emission in collisions between two laser-produced plasmas

Wed, 07 Sep 2011 00:00:00 GMT

Ion emission in collisions between two laser-produced plasmas Hough, Pádraig; Hayden, Patrick; Fallon, Conor; Kelly, Thomas J.; McLoughlin, Conor; Yeates, P.; Mosnier, Jean-Paul; Kennedy, E.T.; Harilal, Sivanandan S.; Costello, John T. Measurements of the total ion emission from a pair of colliding laser-produced aluminium plasmas were obtained with the aid of a Faraday cup detector. The energy profile width at half height of the kinetic energy distribution for ions emitted normal to the target was found to be 30% narrower for colliding plasmas compared to a single plasma. Similar to ion emission from single plumes, the mean ion kinetic energy is observed to increase with the energy of the incident laser pulse. However, the width of the ion energy distribution increases at a significantly slower rate than in the single plume case.

Electron and ion stagnation at the collision front between two laser produced plasmas

Sat, 07 Mar 2009 00:00:00 GMT

Electron and ion stagnation at the collision front between two laser produced plasmas Hough, Pádraig; McLoughlin, Conor; Kelly, Thomas J.; Hayden, Patrick; Harilal, Sivanandan S.; Mosnier, Jean-Paul; Costello, John T. We report results from a combined optical interferometric and spectrally resolved imaging study on colliding laser produced aluminium plasmas. A Nomarski interferometer was used to probe the spatio-temporal distribution of the electron density at the collision front. Analysis of the resulting interferograms reveals the formation and evolution of a localised electron density feature with a well defined profile reminiscent of a stagnation layer. First signs of electron stagnation are observed at a time delay of 10 ns after the peak of the plasma generating laser pulse. The peak electron density was found to exceed 1019 cm−3 and the layer remained well defined up to a time delay of ca. 100 ns. Temporally and spectrally resolved optical imaging was also undertaken to compare the Al+ ion distribution, with that of the 2D electron density profile. This revealed nascent stagnation of singly charged ions at a delay time of 20 ns. We attribute these results to the effects of space charge separation in the seed plasma plumes.

Theory of AC-Stark splitting in core-resonant Auger decay under strong x-ray fields

Wed, 21 Dec 2011 00:00:00 GMT

Theory of AC-Stark splitting in core-resonant Auger decay under strong x-ray fields Nikolopoulos, L.A.A.; Kelly, Thomas J.; Costello, John T. In this work we report the modification of the normal Auger line shape under the action of an intense x-ray radiation. Under strong Rabi-type coupling of the core, the Auger line profile develops into a doublet structure with an energy separation mainly determined by the relative strength of the Rabi coupling. In addition, we find that the charge resolved ion yields can be controlled by judicious choice of the x-ray frequency.

Femtosecond X-ray pulse length characterization at the LCLS free electron laser

Thu, 01 Sep 2011 00:00:00 GMT

Femtosecond X-ray pulse length characterization at the LCLS free electron laser Düsterer, S.; Radcliffe, P.; Bostedt, C.; Bozek, J.; Cavalieri, A.L.; Coffee, R.; Costello, John T.; Cubaynes, D.; DiMauro, L.F.; Ding, Y.; Doumy, G.; Helml, W.; Schweinberger, W.; Kienberger, R.; Maier, A.R.; Grüner, F.; Messerschmidt, M.; Richardson, V.; Roedig, C.; Tschentscher, T.; Meyer, M. Two-color, single-shot time-of-flight electron spectroscopy of atomic neon was employed at the Linear Coherent Light Source (LCLS) to measure the laser-assisted Auger decay in the X-ray regime. This X-ray-optical cross correlation technique provides a straightforward, non-invasive and on-line means of determining the duration of femtosecond (> 40 fs) X-ray pulses. In combination with a theoretical model of the process based on the soft-photon approximation, we were able to obtain the LCLS pulse duration and to extract a mean value of the temporal jitter between the optical pulses from a synchronized Ti-Sapphire laser and X-ray pulses from the LCLS. We find that the experimentally determined values are systematically smaller than the length of the electron bunches. Nominal electron pulse durations of 175 and 75 fs yield X-ray pulse shapes of 120 ± 20 fs FWHM and an upper limit of 40 ± 20 fs FWHM, respectively. Simulations of the SASE process using the GENESIS code agree well with the experimental results.

Temperature accelerated Monte Carlo (TAMC) : a method for sampling the free energy surface of non-analytical collective variables

Sat, 01 Jan 2011 00:00:00 GMT

Temperature accelerated Monte Carlo (TAMC) : a method for sampling the free energy surface of non-analytical collective variables Ciccotti, Giovanni; Meloni, Simone We introduce a new method to simulate the physics of rare events. The method, an extension of the Temperature Accelerated Molecular Dynamics, comes in use when the collective variables introduced to characterize the rare events are either non- analytical or so complex that computing their derivative is not practical. We illustrate the functioning of the method by studying the homogeneous crystallization in a sample of Lennard-Jones particles. The process is studied by introducing a new collective variable that we call Effective Nucleus Size N . We have computed the free energy barriers and the size of critical nucleus, which result in agreement with data available in literature. We have also performed simulations in the liquid domain of the phase diagram. We found a free energy curve monotonically growing with the nucleus size, consistent with the liquid domain.

The influence of light intensity, active area and excitation wavelength on the temporal response of a dye sensitized solar cell

Sun, 02 Aug 2009 00:00:00 GMT

The influence of light intensity, active area and excitation wavelength on the temporal response of a dye sensitized solar cell O'Reilly, Thomas; Andrei, Codrin; O'Reilly, Jennifer; Zerulla, Dominic The temporal response of a biomimetic dye-sensitized solar cell (DSSC) is critically linked to the intensity of the incident light. When a DSSC is partially illuminated and the incoming light is of low intensity, the response time of the cell is prolonged dramatically. In this report, the major components of the DSSC are investigated to find the source and to provide a model of the driving mechanisms behind this delay. For low light level conditions,only deep traps states of the TiO2 layer participate in electron transport resulting in a slow temporal response. Increasing the illumination level thus increases the conductivity of the TiO2 electrode by filling these trap states and increases the response time. This study shows a strong correlation between the light intensity, active area and excitation wavelength on the temporal response time of a DSSC. Poster presentation at SPIE Optics + Photonics: Solar Energy and Technology, San Diego, California, USA, 2nd – 6th August 2009

Characterising dye-sensitized solar cells

Mon, 03 Aug 2009 00:00:00 GMT

Characterising dye-sensitized solar cells Tobin, Laura L.; O'Reilly, Thomas; Zerulla, Dominic; Sheridan, John T. Kafafi, Zakya H.; Lane, Paul A. With growing energy and environmental concerns due to fossil fuel depletion and global warming there is an increasing attention being attracted by alternative and/or renewable sources of power such as biomass, hydropower, geothermal, wind and solar energy. In today’s society there is a vast and in many cases not fully appreciated dependence on electrical power for everyday life and therefore devices such as PV cells are of enormous importance. The more widely used and commercially available silicon (semiconductor) based cells currently have the greatest efficiencies, however the manufacturing of these cells is complex and costly due to the cost and difficulty of producing and processing pure silicon. One new direction being explored is the development of dye-sensitised solar cells (DSSC). The SFI Strategic Research Centre for Solar Energy Conversion is a new research cluster based in Ireland, formed with the express intention of bringing together industry and academia to produce renewable energy solutions. Our specific area of research is in biomimetic dye sensitised solar cells and their electrical properties. We are currently working to develop test equipment, and optoelectronic models describing the performance and behaviors of dye-sensitised solar cells (Grätzel Cells). In this paper we describe some of the background to our work and also some of our initial experimental results. Based on these results we intend to characterise the opto-electrical properties and bulk characteristics of simple dye-sensitised solar cells and then to proceed to test new cell compositions. SPIE: SPIE Optics + Photonics: Solar Energy and Technology, 2nd – 6th August 2009, San Diego, California, USA

Investigating dye-sensitised solar cells

Tue, 13 Apr 2010 00:00:00 GMT

Investigating dye-sensitised solar cells Tobin, Laura L.; O'Reilly, Thomas; Zerulla, Dominic; Sheridan, John T. At present there is a global concern of environmental issues and future energy supplies, for instance global warming and the rapid depletion of fossil fuels. This trepidation has initiated a more critical investigation into alternative and renewable sources of power such as geothermal, biomass, hydropower, wind and solar energy. The immense dependence on electrical power in today’s society has prompted the manufacturing of devices such as photovoltaic (PV) cells to help alleviate and replace current electrical demands of the power grid. The most popular and commercially available PV cells are silicon solar cells which have to date the greatest efficiencies for PV cells. The drawback however is that the manufacturing of these cells is complex and costly due to the expense and difficulty of producing and processing pure silicon. One relatively inexpensive alternative to silicon PV cells that we are currently studying are dye-sensitised solar cells (DSSCs or Grätzel Cells). DSSCs are biomimetic solar cells which are based on the process of photosynthesis. The SFI Strategic Research Centre for Solar Energy Conversion is a research cluster based in Ireland formed with the express intention of bringing together industry and academia to produce renewable energy solutions. Our specific research area is in DSSC and their opto-electrical properties. We are currently developing testing equipment for multiple DSSC and optoelectronic models which will describe the performance and behaviour of DSSCs. SPIE Photonics Europe: Photonics for Solar Energy Systems III, 12th- 16th April, Brussels, 2010.

Simplified 1-D calculation of 13.5-nm emission in a tin plasma including radiation transport

Fri, 04 Dec 2009 00:00:00 GMT

Simplified 1-D calculation of 13.5-nm emission in a tin plasma including radiation transport White, John Kingston; Dunne, Padraig; Hayden, Patrick; O'Sullivan, Gerry Many next generation lithography schemes for the semiconductor industry are based on a 13.5-nm tin plasma light source, where hundreds of thousands of 4d-4f, 4p-4d, and 4d-5p transitions from Sn5+–Sn13+ ions overlap to form an unresolved transition array. To aid computation, transition arrays are treated statistically, and Hartree-Fock results are used to calculate radiation transport in the optically thick regime with a 1-D Lagrangian plasma hydrodynamics code. Time-dependent spectra and conversion efficiencies of 2% in-band 13.5-nm emission to laser energy are predicted for a Nd:YAG laser incident on a pure tin slab target as a function of laser power density and pulse duration at normal incidence. Calculated results showed a maximum conversion efficiency of 2.3% for a 10-ns pulse duration at 8.0 x 1010 W/cm2 and are compared to experimental data where available. Evidence for the need to include lateral expansion is presented.

A spatially resolved study on the Sn diffusion during the sintering process in the active layer of dye sensitised solar cells

Fri, 01 Jan 2010 00:00:00 GMT

A spatially resolved study on the Sn diffusion during the sintering process in the active layer of dye sensitised solar cells Andrei, Codrin; O'Reilly, Thomas; Zerulla, Dominic Dye sensitised solar cells (DSSCs) use a mesoporous TiO2 scaffold, typically assisted by an adsorbed dye, as the main active element, responsible for the photon absorption, exciton generation and charge separation functionality. The sintering process employed in the TiO2 active layer fabrication plays a crucial role in the formation of the nanoparticle scaffold and hence the performance of a dye sensitised solar cell, as it allows the particles to form efficient inter-crystalline electric contacts to provide high electron conductivity. The sintering temperature, with typical values in the range of 450–600 °C, is of particular importance for the formation as it reduces the amount of unwanted organics between the individual crystallites and determines the formation of interfaces between the nanoparticles. Furthermore, the cell design requires a conductive transparent top electrode which is typically made of fluorinated tin oxide or indium tin oxide. Here we report on a highly spatially resolved scanning electron microscopy study including focussed ion beam (FIB) milling and energy dispersive X-ray (EDX) mapping of the distribution of all relevant elements within a DSSC subsequent to a classical sintering process. We find that the above quoted temperatures cause the Sn of the transparent conductive oxide (TCO) to migrate into the TiO2 scaffold, resulting in unwanted alterations in the composition of the complex scaffold which has a direct effect on the DSSC performance. One potential solution to this problem is the invention of novel concepts in the manufacturing of DSSCs using lower sintering temperatures.

Characterising dye-sensitised solar cells

Fri, 01 Jul 2011 00:00:00 GMT

Characterising dye-sensitised solar cells Tobin, Laura L.; O'Reilly, Thomas; Zerulla, Dominic; Sheridan, John T. In today’s society there is a vast and in many cases not fully appreciated dependence on electrical power for everyday life. Furthermore, with growing energy and environmental concerns arising due to fossil fuel depletion and climate change/global warming, ever increasing attention is being given to alternative and/or renewable sources of energy such as biomass, hydropower, geothermal, wind and solar energy. Devices such as photovoltaic cells are therefore of enormous importance. The more widely used and commercially available silicon (semiconductor) based cells currently have the greatest reported efficiencies and have received considerable attention. However the manufacturing of these cells is complex and expensive due to the cost and difficulty of producing and processing pure silicon. One alternative technology being explored is the development of dye-sensitised solar cells (DSSCs) or Grätzel Cells. In this paper we report on our current work to develop simple test equipment and optoelectronic models describing the performance and behaviours of DSSCs. We describe some of the background to our work and also some of our initial experimental results. Based on these results we aim to characterise the opto-electrical properties and bulk characteristics of simple dye-sensitised solar cells and then to proceed to test new cell compositions.