We report on commissioning experiments at the high-energy,high-temperature(HHT)target area at the GSI Helmholtzzentrum für Schwerionenforschung GmbH,Darmstadt,Germany,combining for the first time intense pulses o...We report on commissioning experiments at the high-energy,high-temperature(HHT)target area at the GSI Helmholtzzentrum für Schwerionenforschung GmbH,Darmstadt,Germany,combining for the first time intense pulses of heavy ions from the SIS18 synchrotron with high-energy laser pulses from the PHELIX laser facility.We demonstrate the use of X-ray diagnostic techniques based on intense laserdriven X-ray sources,which will allow probing of large samples volumetrically heated by the intense heavy-ion beams.A new target chamber as well as optical diagnostics for ion-beam characterization and fast pyrometric temperature measurements complement the experimental capabilities.This platform is designed for experiments at the future Facility for Antiproton and Ion Research in Europe GmbH(FAIR),where unprecedented ion-beam intensities will enable the generation of millimeter-sized samples under high-energy-density conditions.展开更多
Gradient index layers and rugate structures were fabricated on a Leybold Syrus pro deposition system by plasma-assisted coevaporation of the low index material silica and the high index material niobium pentoxide.To o...Gradient index layers and rugate structures were fabricated on a Leybold Syrus pro deposition system by plasma-assisted coevaporation of the low index material silica and the high index material niobium pentoxide.To obtain information about the compositional profiles of the produced layers,cross sectional transmission electron microscopy was used in assistance to deposition rate data recorded by two independent crystal monitors during the film preparation.The depth dependent concentration profiles were transformed to refractive index gradients by means of effective medium approximation.Based on the refractive index gradients the corresponding samples`transmission and reflection spectra could be calculated by utilizing matrix formalism.The relevance of the established refractive index profiles could be verified by comparison of the calculated spectra with the measured ones.展开更多
Reengineering the refractive index profile of inhomogeneous coatings is a troublesome task. Multiplicity of solutions may significantly reduced by providing additional information. For this reason an in-situ broadband...Reengineering the refractive index profile of inhomogeneous coatings is a troublesome task. Multiplicity of solutions may significantly reduced by providing additional information. For this reason an in-situ broadband monitoring system was developed to measure the transmittance of the growing film directly at the rotating substrate. For characterization of these coatings, a new model was developed, which significantly reduces the number of parameters. The refractive index profile may be described by a proper number of equally spaced volume fraction values using the Bruggeman effective media approach. A good initial approximation of the refractive index profile can be generated based on deposition rates for both materials recorded with quartz crystal monitor during manufacturing. During the optimization process, a second order minimization algorithm was used to vary the refractive index profile of the whole coating and film thickness of the intermediate stages. Finally, a significantly improved accuracy of the modelled transmittance was achieved.展开更多
The formation of a denuded zone(DZ)by conventional furnace annealing(CFA)and rapid thermal annealing(RTA)based denudation processing is investigated and the gettering of copper(Cu)atoms in germanium co-doped heavily p...The formation of a denuded zone(DZ)by conventional furnace annealing(CFA)and rapid thermal annealing(RTA)based denudation processing is investigated and the gettering of copper(Cu)atoms in germanium co-doped heavily phosphorus-doped Czochralski(GHPCZ)silicon wafers is evaluated.It is suggested that both a good quality defect-free DZ with a suitable width in the sub-surface area and a high density bulk micro-defect(BMD)region could be formed in heavily phosphorus-doped Czochralski(HPCZ)silicon and GHPCZ silicon wafers.This is ascribed to the formation of phosphorus-vacancy(P-V)related complexes and germanium-vacancy(GeV)related complexes.Compared with HPCZ silicon,the DZ width is wider in the GHPCZ silicon sample with CFA-based denudation processing but narrower in the one with two-step RTA pretreatments.These phenomena are ascribed to the enhancing effect of germanium on oxygen out-diffusion movement and oxygen precipitate nucleation,respectively.Furthermore,fairly clean DZs near the surface remain in both the HPCZ and GHPCZ silicon wafers after Cu in-diffusion,except for the HPCZ silicon wafer which underwent denudation processing with a CFA pretreatment,suggesting that germanium doping could improve the gettering of Cu contamination.展开更多
We present in situ measurements of spectrally resolved X-ray scattering and X-ray diffraction from monocrystalline diamond samples heatedwith an intense pulse of heavy ions.In this way,we determine the samples’heatin...We present in situ measurements of spectrally resolved X-ray scattering and X-ray diffraction from monocrystalline diamond samples heatedwith an intense pulse of heavy ions.In this way,we determine the samples’heating dynamics and their microscopic and macroscopic structuralintegrity over a timespan of several microseconds.Connecting the ratio of elastic to inelastic scattering with state-of-the-art density functionaltheory molecular dynamics simulations allows the inference of average temperatures around 1300 K,in agreement with predictions fromstopping power calculations.The simultaneous diffraction measurements show no hints of any volumetric graphitization of the material,butdo indicate the onset of fracture in the diamond sample.Our experiments pave the way for future studies at the Facility for Antiproton andIon Research,where a substantially increased intensity of the heavy ion beam will be available.展开更多
We present a stochastic procedure to investigate the correlation spectra of quantum dot superluminescent diodes. The classical electric field of a diode is formed by a polychromatic superposition of many independent s...We present a stochastic procedure to investigate the correlation spectra of quantum dot superluminescent diodes. The classical electric field of a diode is formed by a polychromatic superposition of many independent stochastic oscillators. Assuming fields with individual carrier frequencies, Lorentzian linewidths and amplitudes we can form any relevant experimental spectrum using a least square fit. This is illustrated for Gaussian and Lorentzian spectra, Voigt profiles and box shapes. Eventually, the procedure is applied to an experimental spectrum of a quantum dot superluminescent diode which determines the first- and second-order temporal correlation functions of the emission. We find good agreement with the experimental data and a quantized treatment. Thus, a superposition of independent stochastic oscillators represents the first- and second-order correlation properties of broadband light emitted by quantum dot superluminescent diodes.展开更多
The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes.In radiation environments with high transmutation helium p...The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes.In radiation environments with high transmutation helium production rates such as in fusion and spallation applications,even materials with otherwise acceptable radiation stability may suffer from radiation embrittlement related to helium bubble formation.While theoretical modeling of helium-assisted cavity nucleation in pure metals and simple alloys provides some useful guidelines at the atomic scale level,these,however,do not overlap with the size resolution of available experimental techniques.In this study,we employed slow positron beam spectroscopy to characterize the nucleation and growth of nano-scale helium bubbles in martensitic steels strengthened by thermodynamically stable nano-oxide dispersoids.In combination with transmission electron microscopy,we experimentally characterized the evolution of helium bubbles from small clusters of radiation-induced vacancies to large cavities well resolvable by TEM.Superior radiation resistance of oxide-dispersion strengthened steels dominates only in the early stages of bubble evolution,where positron lifetime measurements provide a missing piece of the microstructural puzzle conventionally constructed by TEM.展开更多
Although silicon is an indirect semiconductor, light emission from silicon is governed by the same gener- alized Planck＇s radiation law as the emission from direct semiconductors. The emission intensity is given by t...Although silicon is an indirect semiconductor, light emission from silicon is governed by the same gener- alized Planck＇s radiation law as the emission from direct semiconductors. The emission intensity is given by the absorptance of the volume in which there is a difference of the quasi Fermi energies. A difference of the Fermi energies may result h＇om the absorption of external light （photoluminescence） or from the injection of electrons and holes via selective contacts （electroluminescence）. The quantum efficiency may be larger than 0.5 for carrier densities below 10^15 cm^-3. At larger densities, non-radiative recombination, in particular Auger recombination dominates. At all carrier densities, the relation between emission intensity and difference of the quasi Fermi energies is maintained. Since this difference is equal to the voltage of a properly designed solar cell, luminescence is the key indicator of material quality for solar cells.展开更多
Near-field holography（NFH）, with its virtues of precise critical dimensions and high throughput, has a great potential for the realization of soft x-ray diffraction gratings. We show that NFH with reflections reduce...Near-field holography（NFH）, with its virtues of precise critical dimensions and high throughput, has a great potential for the realization of soft x-ray diffraction gratings. We show that NFH with reflections reduced by the integration of antireflective coatings（ARCs） simplifies the NFH process relative to that of setups using refractive index liquids. Based on the proposed NFH with ARCs, gold-coated laminar gratings were fabricated using NFH and subsequent ion beam etching. The efficiency angular spectrum shows that the stray light of the gratings is reduced one level of magnitude by the suppression of interface reflections during NFH.展开更多
The high-energy/high-intensity laser facility PHELIX of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt,Germany,has been in operation since 2008.Here,we review the current system performance,which ...The high-energy/high-intensity laser facility PHELIX of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt,Germany,has been in operation since 2008.Here,we review the current system performance,which is the result of continuous development and further improvement.Through its versatile frontend architecture,PHELIX can be operated in both long-and short-pulse modes,corresponding to ns-pulses with up to 1 kJ pulse energy and sub-ps,200 J pulses,respectively.In the short-pulse mode,the excellent temporal contrast and the control over the wavefront make PHELIX an ideal driver for secondary sources of high-energy ions,neutrons,electrons and X-rays.The long-pulse mode is mainly used for plasma heating,which can then be probed by the heavy-ion beam of the linear accelerator of GSI.In addition,PHELIX can now be used to generate X-rays for studying exotic states of matter created by heavy-ion heating using the ion beam of the heavy-ion synchrotron of GSI.展开更多
Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is ...Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is field-effect transistors(FETs),that witness increased attention for application as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies,where they exhibit very good sensitivity even high above the cut-off frequency defined by the carrier transit time.Transport theory predicts that the coupling of radiation at THz frequencies into the channel of an antenna-coupled FET leads to the development of a gated plasma wave,collectively involving the charge carriers of both the two-dimensional electron gas and the gate electrode.In this paper,we present the first direct visualization of these waves.Employing graphene FETs containing a buried gate electrode,we utilize near-field THz nanoscopy at room temperature to directly probe the envelope function of the electric field amplitude on the exposed graphene sheet and the neighboring antenna regions.Mapping of the field distribution documents that wave injection is unidirectional from the source side since the oscillating electrical potentials on the gate and drain are equalized by capacitive shunting.The plasma waves,excited at 2 THz,are overdamped,and their decay time lies in the range of 25-70 fs.Despite this short decay time,the decay length is rather long,i.e.,0.3-0.5μm,because of the rather large propagation speed of the plasma waves,which is found to lie in the range of 3.5-7×10^(6)m/s,in good agreement with theory.The propagation speed depends only weakly on the gate voltage swing and is consistent with the theoretically predicted 1/4 power law.展开更多
Ionic liquids(ILs)have been used effectively in many applications for reducing problems related to friction and wear.In this work,the potential of ILs as an anti-wear and extreme pressure lubricant additive for high l...Ionic liquids(ILs)have been used effectively in many applications for reducing problems related to friction and wear.In this work,the potential of ILs as an anti-wear and extreme pressure lubricant additive for high load-carrying gearbox applications such as helicopter transmissions has been studied.Two halide-free ILs:P_(8881)(BuO)_(2)PO_(2)^(-)(1)and P_(8881)(MeO)_(2)PO_(2)^(-)(2),which are blended at 5 wt%each into a standard non-additivated FVA2 base oil(BO)are examined.Their solid-liquid interface,friction and load-carrying capacity,and wear(scuffing)behavior are studied on the nano-,lab-,and component-scale,respectively,at a different range of temperature and loading conditions by using the atomic force microscopy(AFM),Schwing-Reib-Verschleiβ(SRV)friction tests,and Brugger tests,as well as forschungsstelle für zahnrader und getriebebau(FZG)back-to-back gear test rig.The AFM analysis shows nearly no change of adhesion over the full range of studied temperature for the IL blends compared to the BO.Similarly,IL blends demonstrate a very stable coefficient of friction(COF)of around 0.16,which even decreases with increasing test temperatures ranging from 40 to 120℃.A clear reduction in COF up to 25%is achieved by adding only 5 wt%of the investigated Ils in the BO,and the Brugger tests also show a pronounced enhancement of load-carrying capacity.Finally,on the component-scale,a significant improvement in gear scuffing performance has been observed for both used IL blends.A detailed characterization of the wear tracks from the SRV friction tests via the transmission electron microscopy(TEM)revealed the formation of a phosphate(P-O)-based amorphous tribo-chemical layer of about 20 nm thickness.Therefore,this work may present an approach for Ils to be used as an additive in conventional lubricants due to their ability to enhance the lubrication properties,making them an alternative lubricant solution for high load-carrying gearbox applications.展开更多
This paper presents the development and experimental utilization of a synchronized off-harmonic laser system designed as a probe for ultra-intense laser±plasma interaction experiments. The system exhibits a novel...This paper presents the development and experimental utilization of a synchronized off-harmonic laser system designed as a probe for ultra-intense laser±plasma interaction experiments. The system exhibits a novel seed-generation design,allowing for a variable pulse duration spanning over more than three orders of magnitude, from 3.45 picoseconds to 10 nanoseconds. This makes it suitable for various plasma diagnostics and visualization techniques. In a side-view configuration, the laser was employed for interferometry and streaked shadowgraphy of a laser-induced plasma while successfully suppressing the self-emission background of the laser±plasma interaction, resulting in a signal-to-self-emission ratio of 110 for this setup. These properties enable the probe to yield valuable insights into the plasma dynamics and interactions at the PHELIX facility and to be deployed at various laser facilities due to its easy-to-implement design.展开更多
The spatial distribution of beams with orbital angular momentum in the far field is known to be extremely sensitive to angular aberrations,such as astigmatism,coma and trefoil.This poses a challenge for conventional b...The spatial distribution of beams with orbital angular momentum in the far field is known to be extremely sensitive to angular aberrations,such as astigmatism,coma and trefoil.This poses a challenge for conventional beam optimization strategies when a homogeneous ring intensity is required for an application.We developed a novel approach for estimating the Zernike coefficients of low-order angular aberrations in the near field based solely on the analysis of the ring deformations in the far field.A fast,iterative reconstruction of the focal ring recreates the deformations and provides insight into the wavefront deformations in the near field without relying on conventional phase retrieval approaches.The output of our algorithm can be used to optimize the focal ring,as demonstrated experimentally at the 100 TW beamline at the Extreme Light Infrastructure-Nuclear Physics facility.展开更多
基金supported by GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, as part of the R & D Project No. SI-URDK2224 with the University of Rostocksupport by the Federal Ministry of Education and Research (BMBF) under Grant No. 05P21RFFA2supported by the Helmholtz Association under Grant No. ERC-RA-0041。
文摘We report on commissioning experiments at the high-energy,high-temperature(HHT)target area at the GSI Helmholtzzentrum für Schwerionenforschung GmbH,Darmstadt,Germany,combining for the first time intense pulses of heavy ions from the SIS18 synchrotron with high-energy laser pulses from the PHELIX laser facility.We demonstrate the use of X-ray diagnostic techniques based on intense laserdriven X-ray sources,which will allow probing of large samples volumetrically heated by the intense heavy-ion beams.A new target chamber as well as optical diagnostics for ion-beam characterization and fast pyrometric temperature measurements complement the experimental capabilities.This platform is designed for experiments at the future Facility for Antiproton and Ion Research in Europe GmbH(FAIR),where unprecedented ion-beam intensities will enable the generation of millimeter-sized samples under high-energy-density conditions.
文摘Gradient index layers and rugate structures were fabricated on a Leybold Syrus pro deposition system by plasma-assisted coevaporation of the low index material silica and the high index material niobium pentoxide.To obtain information about the compositional profiles of the produced layers,cross sectional transmission electron microscopy was used in assistance to deposition rate data recorded by two independent crystal monitors during the film preparation.The depth dependent concentration profiles were transformed to refractive index gradients by means of effective medium approximation.Based on the refractive index gradients the corresponding samples`transmission and reflection spectra could be calculated by utilizing matrix formalism.The relevance of the established refractive index profiles could be verified by comparison of the calculated spectra with the measured ones.
文摘Reengineering the refractive index profile of inhomogeneous coatings is a troublesome task. Multiplicity of solutions may significantly reduced by providing additional information. For this reason an in-situ broadband monitoring system was developed to measure the transmittance of the growing film directly at the rotating substrate. For characterization of these coatings, a new model was developed, which significantly reduces the number of parameters. The refractive index profile may be described by a proper number of equally spaced volume fraction values using the Bruggeman effective media approach. A good initial approximation of the refractive index profile can be generated based on deposition rates for both materials recorded with quartz crystal monitor during manufacturing. During the optimization process, a second order minimization algorithm was used to vary the refractive index profile of the whole coating and film thickness of the intermediate stages. Finally, a significantly improved accuracy of the modelled transmittance was achieved.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50832006 and 60906001the National Basic Research Program of China under Grant No 2007CB6130403,and the China Postdoctoral Science Foundation.
文摘The formation of a denuded zone(DZ)by conventional furnace annealing(CFA)and rapid thermal annealing(RTA)based denudation processing is investigated and the gettering of copper(Cu)atoms in germanium co-doped heavily phosphorus-doped Czochralski(GHPCZ)silicon wafers is evaluated.It is suggested that both a good quality defect-free DZ with a suitable width in the sub-surface area and a high density bulk micro-defect(BMD)region could be formed in heavily phosphorus-doped Czochralski(HPCZ)silicon and GHPCZ silicon wafers.This is ascribed to the formation of phosphorus-vacancy(P-V)related complexes and germanium-vacancy(GeV)related complexes.Compared with HPCZ silicon,the DZ width is wider in the GHPCZ silicon sample with CFA-based denudation processing but narrower in the one with two-step RTA pretreatments.These phenomena are ascribed to the enhancing effect of germanium on oxygen out-diffusion movement and oxygen precipitate nucleation,respectively.Furthermore,fairly clean DZs near the surface remain in both the HPCZ and GHPCZ silicon wafers after Cu in-diffusion,except for the HPCZ silicon wafer which underwent denudation processing with a CFA pretreatment,suggesting that germanium doping could improve the gettering of Cu contamination.
基金support by the Federal Ministry of Education and Research(BMBF)under Grant No.05P21RFFA2supported by the Helmholtz Association under Grant No.ERC-RA-0041.
文摘We present in situ measurements of spectrally resolved X-ray scattering and X-ray diffraction from monocrystalline diamond samples heatedwith an intense pulse of heavy ions.In this way,we determine the samples’heating dynamics and their microscopic and macroscopic structuralintegrity over a timespan of several microseconds.Connecting the ratio of elastic to inelastic scattering with state-of-the-art density functionaltheory molecular dynamics simulations allows the inference of average temperatures around 1300 K,in agreement with predictions fromstopping power calculations.The simultaneous diffraction measurements show no hints of any volumetric graphitization of the material,butdo indicate the onset of fracture in the diamond sample.Our experiments pave the way for future studies at the Facility for Antiproton andIon Research,where a substantially increased intensity of the heavy ion beam will be available.
文摘We present a stochastic procedure to investigate the correlation spectra of quantum dot superluminescent diodes. The classical electric field of a diode is formed by a polychromatic superposition of many independent stochastic oscillators. Assuming fields with individual carrier frequencies, Lorentzian linewidths and amplitudes we can form any relevant experimental spectrum using a least square fit. This is illustrated for Gaussian and Lorentzian spectra, Voigt profiles and box shapes. Eventually, the procedure is applied to an experimental spectrum of a quantum dot superluminescent diode which determines the first- and second-order temporal correlation functions of the emission. We find good agreement with the experimental data and a quantized treatment. Thus, a superposition of independent stochastic oscillators represents the first- and second-order correlation properties of broadband light emitted by quantum dot superluminescent diodes.
基金the contribution of the Slovak Research and Development Agency under the project APVV-20-0010financial contributions from the Scientifc Grant Agency of the Ministry of Education,Science,Research and Sport of the Slovak Republic and the Slovak Academy of Sciences,grant numbers VEGA 1/0382/20 and VEGA 1/0395/20the European Regional Development Fund project No.ITMS2014+:313011W085。
文摘The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes.In radiation environments with high transmutation helium production rates such as in fusion and spallation applications,even materials with otherwise acceptable radiation stability may suffer from radiation embrittlement related to helium bubble formation.While theoretical modeling of helium-assisted cavity nucleation in pure metals and simple alloys provides some useful guidelines at the atomic scale level,these,however,do not overlap with the size resolution of available experimental techniques.In this study,we employed slow positron beam spectroscopy to characterize the nucleation and growth of nano-scale helium bubbles in martensitic steels strengthened by thermodynamically stable nano-oxide dispersoids.In combination with transmission electron microscopy,we experimentally characterized the evolution of helium bubbles from small clusters of radiation-induced vacancies to large cavities well resolvable by TEM.Superior radiation resistance of oxide-dispersion strengthened steels dominates only in the early stages of bubble evolution,where positron lifetime measurements provide a missing piece of the microstructural puzzle conventionally constructed by TEM.
文摘Although silicon is an indirect semiconductor, light emission from silicon is governed by the same gener- alized Planck＇s radiation law as the emission from direct semiconductors. The emission intensity is given by the absorptance of the volume in which there is a difference of the quasi Fermi energies. A difference of the Fermi energies may result h＇om the absorption of external light （photoluminescence） or from the injection of electrons and holes via selective contacts （electroluminescence）. The quantum efficiency may be larger than 0.5 for carrier densities below 10^15 cm^-3. At larger densities, non-radiative recombination, in particular Auger recombination dominates. At all carrier densities, the relation between emission intensity and difference of the quasi Fermi energies is maintained. Since this difference is equal to the voltage of a properly designed solar cell, luminescence is the key indicator of material quality for solar cells.
基金supported by the Sino-German Center for Research Promotion (No.GZ 983)the German Science Foundation DFG (No.IRTG 2101)+1 种基金the Joint Fund of the National Natural Science Foundation of Chinathe China Academy of Engineering Physics (No.U1230104)
文摘Near-field holography（NFH）, with its virtues of precise critical dimensions and high throughput, has a great potential for the realization of soft x-ray diffraction gratings. We show that NFH with reflections reduced by the integration of antireflective coatings（ARCs） simplifies the NFH process relative to that of setups using refractive index liquids. Based on the proposed NFH with ARCs, gold-coated laminar gratings were fabricated using NFH and subsequent ion beam etching. The efficiency angular spectrum shows that the stray light of the gratings is reduced one level of magnitude by the suppression of interface reflections during NFH.
基金funding from the European Union’s Horizon 2020 research and innovation programme via the transnational access and joint research activity programmes of Laserlab(grant agreement Nos.871124 and 654148)funding from the European Union’s HORIZON-INFRA-2022-TECH-01 call under grant agreement number 101095207(THRILL)financed via the BMBF Er UM-APPA collaborative research scheme(contract numbers 05P19RFFA1-Goethe-Universität Frankfurt,05P21RDFA2-Technische Universität Darmstadt,05P19SJFA1 and 05P21SJFA2-Friedrich-Schiller Universität Jena)。
文摘The high-energy/high-intensity laser facility PHELIX of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt,Germany,has been in operation since 2008.Here,we review the current system performance,which is the result of continuous development and further improvement.Through its versatile frontend architecture,PHELIX can be operated in both long-and short-pulse modes,corresponding to ns-pulses with up to 1 kJ pulse energy and sub-ps,200 J pulses,respectively.In the short-pulse mode,the excellent temporal contrast and the control over the wavefront make PHELIX an ideal driver for secondary sources of high-energy ions,neutrons,electrons and X-rays.The long-pulse mode is mainly used for plasma heating,which can then be probed by the heavy-ion beam of the linear accelerator of GSI.In addition,PHELIX can now be used to generate X-rays for studying exotic states of matter created by heavy-ion heating using the ion beam of the heavy-ion synchrotron of GSI.
基金funding from the Adolf Messer Stiftungthe Friedrich-Ebert Stiftung+5 种基金the Rosa Luxemburg Stiftungthe EU-funded action H2020-MSCA-ITN-2015-ETN CELTAfunded by the Deutsche Forschungsgemeinschaft(DFG project RO 770/40)support via the BMBF projects 05K16ODA,05K16ODC,05K19ODA,and 05K19ODBfunding from the Swedish Research Council(grant no.2017.-04504)funding from the Academy of Finland(grant nos.325810,312297,320167,and 314810).
文摘Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is field-effect transistors(FETs),that witness increased attention for application as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies,where they exhibit very good sensitivity even high above the cut-off frequency defined by the carrier transit time.Transport theory predicts that the coupling of radiation at THz frequencies into the channel of an antenna-coupled FET leads to the development of a gated plasma wave,collectively involving the charge carriers of both the two-dimensional electron gas and the gate electrode.In this paper,we present the first direct visualization of these waves.Employing graphene FETs containing a buried gate electrode,we utilize near-field THz nanoscopy at room temperature to directly probe the envelope function of the electric field amplitude on the exposed graphene sheet and the neighboring antenna regions.Mapping of the field distribution documents that wave injection is unidirectional from the source side since the oscillating electrical potentials on the gate and drain are equalized by capacitive shunting.The plasma waves,excited at 2 THz,are overdamped,and their decay time lies in the range of 25-70 fs.Despite this short decay time,the decay length is rather long,i.e.,0.3-0.5μm,because of the rather large propagation speed of the plasma waves,which is found to lie in the range of 3.5-7×10^(6)m/s,in good agreement with theory.The propagation speed depends only weakly on the gate voltage swing and is consistent with the theoretically predicted 1/4 power law.
基金funded by the Endowed Professorship on“Tribology”at the Vienna University of Technology(Grant No.WST3-F-5031370/001-2017).
文摘Ionic liquids(ILs)have been used effectively in many applications for reducing problems related to friction and wear.In this work,the potential of ILs as an anti-wear and extreme pressure lubricant additive for high load-carrying gearbox applications such as helicopter transmissions has been studied.Two halide-free ILs:P_(8881)(BuO)_(2)PO_(2)^(-)(1)and P_(8881)(MeO)_(2)PO_(2)^(-)(2),which are blended at 5 wt%each into a standard non-additivated FVA2 base oil(BO)are examined.Their solid-liquid interface,friction and load-carrying capacity,and wear(scuffing)behavior are studied on the nano-,lab-,and component-scale,respectively,at a different range of temperature and loading conditions by using the atomic force microscopy(AFM),Schwing-Reib-Verschleiβ(SRV)friction tests,and Brugger tests,as well as forschungsstelle für zahnrader und getriebebau(FZG)back-to-back gear test rig.The AFM analysis shows nearly no change of adhesion over the full range of studied temperature for the IL blends compared to the BO.Similarly,IL blends demonstrate a very stable coefficient of friction(COF)of around 0.16,which even decreases with increasing test temperatures ranging from 40 to 120℃.A clear reduction in COF up to 25%is achieved by adding only 5 wt%of the investigated Ils in the BO,and the Brugger tests also show a pronounced enhancement of load-carrying capacity.Finally,on the component-scale,a significant improvement in gear scuffing performance has been observed for both used IL blends.A detailed characterization of the wear tracks from the SRV friction tests via the transmission electron microscopy(TEM)revealed the formation of a phosphate(P-O)-based amorphous tribo-chemical layer of about 20 nm thickness.Therefore,this work may present an approach for Ils to be used as an additive in conventional lubricants due to their ability to enhance the lubrication properties,making them an alternative lubricant solution for high load-carrying gearbox applications.
文摘This paper presents the development and experimental utilization of a synchronized off-harmonic laser system designed as a probe for ultra-intense laser±plasma interaction experiments. The system exhibits a novel seed-generation design,allowing for a variable pulse duration spanning over more than three orders of magnitude, from 3.45 picoseconds to 10 nanoseconds. This makes it suitable for various plasma diagnostics and visualization techniques. In a side-view configuration, the laser was employed for interferometry and streaked shadowgraphy of a laser-induced plasma while successfully suppressing the self-emission background of the laser±plasma interaction, resulting in a signal-to-self-emission ratio of 110 for this setup. These properties enable the probe to yield valuable insights into the plasma dynamics and interactions at the PHELIX facility and to be deployed at various laser facilities due to its easy-to-implement design.
基金funded through IOSIN,Nucleu PN-IFIN-HH 23-26 Code PN 2321Extreme Light Infrastructure-Nuclear Physics(ELI-NP)Phase II+2 种基金a project co-financed by the Romanian Government and the European Union through the European Regional Development Fund and the Competitiveness Operational Programme(1/07.07.2016,COP,ID 1334)through IFA project ELI-RO 03/2020 Pulse-Mereadreceived funding from the European Union’s HORIZON-INFRA-2022-TECH-01 call under grant agreement number 101095207
文摘The spatial distribution of beams with orbital angular momentum in the far field is known to be extremely sensitive to angular aberrations,such as astigmatism,coma and trefoil.This poses a challenge for conventional beam optimization strategies when a homogeneous ring intensity is required for an application.We developed a novel approach for estimating the Zernike coefficients of low-order angular aberrations in the near field based solely on the analysis of the ring deformations in the far field.A fast,iterative reconstruction of the focal ring recreates the deformations and provides insight into the wavefront deformations in the near field without relying on conventional phase retrieval approaches.The output of our algorithm can be used to optimize the focal ring,as demonstrated experimentally at the 100 TW beamline at the Extreme Light Infrastructure-Nuclear Physics facility.
