Adsorption-induced modification of the hot electron lifetime in a Pb/Ag111 quantum well system
Florian Haag, Tobias Eul, Lisa Grad, Norman Haag, Johannes Knippertz, Mirko Cinchetti, Martin Aeschlimann, Benjamin Stadtmüller
AAdsorption-induced modification of the hot electron lifetime in a Pb/Ag111 quantumwell system
Florian Haag,
1, 2, ∗ Tobias Eul, Lisa Grad, † Norman Haag, JohannesKnippertz, Mirko Cinchetti, Martin Aeschlimann, and Benjamin Stadtm¨uller
1, 2 Department of Physics and Research Center OPTIMAS, TU Kaiserslautern,Erwin-Schroedinger-Straße 46, 67663 Kaiserslautern, Germany Graduate School of Excellence Materials Science in Mainz,Erwin-Schroedinger-Straße 46, 67663 Kaiserslautern, Germany Experimentelle Physik VI, Technische Universit¨at Dortmund, 44221 Dortmund, Germany
The interfacial band structures of multilayer systems play a crucial role for the ultrafast charge andspin carrier dynamics at interfaces. Here, we study the energy- and momentum-dependent quasipar-ticle lifetimes of excited states of a lead monolayer film on Ag(111) prior and after the adsorption ofa monolayer of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA). Using time-resolved two-photon momentum microscopy, we show that the electron dynamics of the bare Pb/Ag(111) bilayersystem is dominated by isotropic intraband scattering processes within the quantum well state aswell as interband scattering processes from the QWS into the Pb sideband. After the adsorptionof PTCDA on the Pb monolayer, the interband scattering is suppressed and the electron dynamicsis solely determined by intraband or inelastic scattering processes. Our findings hence uncover anew possibility to selectively tune and control scattering processes of quantum well systems by theadsorption of organic molecules.
1. INTRODUCTION
Interfaces between different types of functional mate-rials are decisive building blocks for the next generationof nano-sized optoelectronic, photonic and spintronic ap-plications [1, 2]. They do not only determine the effi-ciency of charge and spin transport through the devicestructure but can also mediate device relevant functional-ities, such as spin filtering or charge-to-spin and spin-to-charge conversion processes [3–6]. These functionalitiesare thereby closely linked to the interfacial band struc-ture and the corresponding ultrafast carrier dynamics ofthe interfaces.For this reason, countless studies focused on this cor-relation between the ultrafast single particle electron dy-namics and the (spin-dependent) interfacial band struc-ture of ultrathin metallic or molecular films on metallicsurfaces [7–24]. The most commonly used experimentaltechnique for such studies is time-resolved two-photon-photoemission spectroscopy (tr-2PPE) [25–30], which al-lows one to characterize the ultrafast electron dynamicsby the quasiparticle lifetime of the optically excited elec-trons in the so-called single-particle limit. These stud-ies laid the foundation for today’s understanding of thedifferent energy and momentum dissipation mechanismsof (optically) excited charge and spin carriers at sur-faces, interfaces and bulk materials. For heterostructuresand interfaces without structural order and well-definedbands, the quasiparticle lifetime only depends on the ex-cited state energy of the excited electrons and is deter-mined by inelastic electron-electron scattering processes ∗ Electronic address: f˙[email protected] † Current address: Department of Physics, University of Z¨urich,Winterthurerstrasse 190, 8057 Z¨urich, Switzerland [30]. Energy- and momentum-dependent quasiparticlelifetimes are in contrast only observed for sample systemswith well-defined (interfacial) band structures [12, 15,31–35]. Typical model systems with well-dependent bandstructures are e.g. quantum well states, image poten-tial states or adsorption-induced shifted Shockley-surfacestates [12, 36, 37]. For these cases, electron-phonon orelectron-defect scattering processes can lead to coupledenergy and momentum dissipation processes of excitedelectrons, which are typically classified as inter- or in-traband scattering processes. These scattering processescan be directly identified in a time- and angle-resolved2PPE experiment due to the strong correlation betweenthe energy- and momentum-dependent quasiparticle life-times of optically excited electrons and the band struc-ture of metal-metal or metal-organic interfaces.To gain further insights into the inter- or intrabandscattering processes at interfaces, we turn to the single-particle electron dynamics of one layer lead (Pb) on anAg(111) single crystal surface. This model system wasselected as an exemplary case from the manifold of ul-trathin layers on surfaces that can host quantum con-fined electrons and quantum well states (QWSs) [9, 11,12, 15, 38]. In the particular case of the Pb/Ag(111) in-terface, the band structure reveals two distinct bands inthe Pb layer: (i) a parabolic, free electron-like QWS withparabolic dispersion in the center of the surface Brillouinzone and p z orbital character and (ii) a Pb side band withalmost linear dispersion and p x/y orbital character [38].These two bands are expected to dominate the ultrafastelectron dynamics of such ultrathin Pb films.Previous tr-2PPE studies of similar ultrathin Pb layersalready proposed complex inter- and intraband scatter-ing processes between different Pb and Pb-derived states[12, 15] in a limited part of the surface Brilliouin zone(either conducted without angular (momentum) resolu-tion or along one high symmetry direction in momen- a r X i v : . [ c ond - m a t . m e s - h a ll ] J a n tum space). We build on these pioneering studies us-ing time-resolved two-photon momentum microscopy (tr-2PMM) [39]. This approach combines the optical setupof a conventional tr-2PPE experiment with a photoemis-sion electron microscope operated in momentum spacemode, i.e., a momentum microscope [40–43], which al-lows us to study inelastic as well as (quasi-)elastic in-terband and intraband scattering processes in the wholeaccessible momentum space with a parallel detectionscheme and a fixed experimental geometry. In a sec-ond step, we explore the tuneability of the electron dy-namics of the Pb/Ag(111) bilayer system by adding theprototypical molecule 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on top of the Pb/Ag(111). Theadsorption of PTCDA alters the band structure of thePb/Ag interface thereby suppressing one of the promi-nent scattering channels.Our tr-2PMM experiments allow us to disentangle theintrinsic quasiparticle lifetime of the Pb side band at thebare Pb/Ag(111) interface. We find that the electron dy-namics of the Pb/Ag(111) bilayer system is dominatedby isotropic scattering processes of electrons of the PbQWS in momentum space. They lead to a lifetime of τ ≈
12 fs, which is isotropic in momentum and increasesslightly when approaching the band minimum due to in-traband scattering. Additionally, we observe isotropicinterband scattering of electrons from the QWS into thePb side band with p x / y orbital character. This scat-tering process is responsible for an increased lifetime inthe Pb side band despite its intrinsically vanishing quasi-particle lifetime. After the adsorption of PTCDA on thePb monolayer, all interband scattering processes are sup-pressed and the electron dynamics is solely determinedby intraband or inelastic scattering processes. In thisway, our study demonstrates an alternative way for tun-ing and controlling scattering processes in QWS systemsby the adsorption of organic molecules.
2. EXPERIMENTAL DETAILS2.1. Sample Preparation
All experiments and the sample preparation proce-dures were performed under ultrahigh-vacuum conditionswith a base pressure better than 1 · − mbar. Thesurface of the (111)-oriented silver crystal was cleanedby several cycles of argon ion bombardments and subse-quent annealing at a temperature of T Sample = 730 K.The cleanliness of the Ag(111) surface was verified bythe width of the diffraction spots in low energy elec-tron diffraction (LEED) measurements and the linewidthof the Shockley surface state at the Γ-point using two-photon photoemission momentum microscopy. After-wards, more than a ML Pb was evaporated onto the sub-strate at room temperature. Subsequent annealing for10 minutes up to 420 K leads to desorption of higher Pblayers resulting in a uniform single Pb layer. The resultwas checked with LEED and momentum-resolved pho- toemission spectroscopy. The coverage of the moleculePTCDA was controlled by the evaporation time and theflux of the evaporator.
The time-resolved two-photon momentum microscopymeasurements (tr-2PMM) were performed with a pho-toemission electron microscope (PEEM) operated in k-space mode. We used a time-of-flight detector as en-ergy analyzer [43–45] for the Pb ML measurements anda double hemispherical analyzer [40–42] for the one layerPTCDA on Pb/Ag(111) system. Both microscopes arecombined with optical beamlines for pump-probe spec-troscopy [39]. As light sources for the optical part ofour experiments, we used the second harmonics (SHG)of titanium-sapphire laser oscillators with a central wave-length of 800 nm (1 .
55 eV) for the fundamental emissionline, sub 30 fs pulse width (FWHM), and a repetitionrate of 80 MHz. The polarization was changed withinthe experiments using a λ -half-wave plate. A mirror lo-cated within the PEEM optics was used for the nearlynormal incidence angle measurements (4 ° incidence an-gle with respect to the surface normal) [46].The multi-dimensional data sets I ( k x , k y , E-E F , ∆ t )were analyzed using the same approach as describedin our previous work [39]. The momentum-dependentlifetimes were determined by extracting autocorrelationcurves at each point in the momentum space for eachintermediate state energy E-E F . These traces were an-alyzed within the framework of optical Bloch equationswhich yields lifetimes in momentum space [47–49]. Theselifetimes are plotted as color code in so-called lifetimemaps, which reflect the lifetimes of electrons through-out the entire accessible momentum space in a tr-2PMMexperiment. Note that these lifetimes do not necessaryreflect the pure intrinsic quasiparticle lifetime of the cor-responding state in energy and momentum space but alsocontains signatures of energy- and momentum-dependentrefilling processes.
3. RESULTS AND DISCUSSION
We start our discussion with the hot electron dynam-ics of the bare Pb/Ag(111) bilayer system. The unoc-cupied band structure of the material system is illus-trated in Fig.1 as an energy vs. momentum cut alongthe M (cid:48)
Γ-direction. Here, we only review the most im-portant spectroscopic features of the unoccupied bandstructure which are sketched on the right side of Fig.1.A more detailed discussion can be found elsewhere [38].The unoccupied band structure of the Pb/Ag(111) bi-layer system is dominated by two Pb-derived states: (i) afree electron-like quantum well state (labelled QWS p z )with p z orbital character and a parabolic dispersion cen-tred at the Γ-point of the surface Brillouin zone and (ii) PE signal [arb. Units] -0.5 0.0 0.5k ∥ [ Å -1 ] E - E F [ e V ] QWS p z Mahan conePb p x/y
Figure 1: Left: Intermediate state energy E-E F over k (cid:107) cutalong the M (cid:48) Γ-direction. Right: Sketch of the Γ M-direction.The parabolic features refer to the Pb QWS having a p z or-bital character and the hybridized sp-sp Mahan cone transi-tion. The straight lines belong to the Pb side band, having ap x / y orbital character. All bands are named accordingly. a Pb-derived side band (labelled Pb p x / y ) with almostlinear dispersion and p x / y orbital character. The thirdspectroscopic feature with parabolic dispersion (labelledMahan cone) is not a band of the unoccupied Pb/Agband structure, but can be attributed to a so-called Ma-han Cone transition [50, 51]. It is caused by a resonanttransition of electrons from an occupied valence bandinto an unoccupied band above the vacuum energy via astrongly detuned intermediate state (virtual intermediatestate). For the Pb/Ag(111) system, this transition onlybecomes visible for exciting light with a non-vanishingout-of-plane electric field vector.The energy- and momentum-dependent electron dy-namics of the Pb-derived side band can be extractedfrom the tr-2PMM data set shown in Fig.2. These datawere obtained in a monochromatic (3 . k x -direction(see sketch in Fig.2(f)). In this experimental geometry,the light pulses of the pump- and probe beam only exhibitan electric field component parallel to the surface andhence can only excite and probe states with predominantin-plane orbital character. This is clearly reflected in theenergy vs. momentum cut along the M (cid:48) Γ M-direction inFig.2(a), which only shows the spectroscopic signature ofthe Pb side band with p x / y orbital character (marked bya green dotted line). The dispersion of this state in mo-mentum space is reflected in the exemplary constant en-ergy (CE) maps in Fig.2(b) which were recorded at threeintermediate state energies of E-E F = 2 .
65 eV, 2 .
85 eVand 3 . (cid:48) Γ M-direction inFig.2(d), which does not show any pattern following thelinear dispersion of the Pb side bands. The energy-dependent and momentum averaged quasiparticle life-time is quantified in Fig.2(e), which reveals an increasefrom τ ≈ F = 3 . τ ≈ F = 1 . ◦ withrespect to the surface normal (the in-plane componentof the electric field vector oscillates parallel to the k x -direction). The results are summarized in Fig.3. Theenergy vs. momentum cut through the unoccupied bandstructure along the M (cid:48) Γ M-direction in Fig.3(a) revealsspectroscopic signatures of the QWS, the Pb side bandas well as of the Mahan cone transition. All Pb-derivedstates are now accessible in our 2PMM experiment due tothe out-of-plane component of the electronic field vectorof the pump and probe pulses in gracing incidence geom-etry (see sketch in Fig.3(e)). Again, the dispersions of allstates are shown in the exemplary constant energy (CE)maps in Fig.3(b), which were recorded at three interme-diate state energies E-E F = 2 .
65 eV, 2 .
85 eV and 3 . F = 2 .
65 eV(bottom CE map of panel (b)). In contrast, the predom-inant p z orbital character of the Pb QWS and the statesinvolved in the Mahan cone transition results in ring-likeemission pattern of these features with a homogeneousazimuthal intensity distribution.The lifetimes of these states are reflected in the CE life- -0.5 0.0 0.5k x [ Å -1 ] k y [ Å - ] x [ Å -1 ]k x Light (3.1eV)
AgPb Lifetime [fs]3 12-0.5 0.0 0.5k ∥ [ Å -1 ]PE signal [arb. Units]0 1 E - E F [ e V ] -0.5 0.0 0.5k ∥ [ Å -1 ] (d)(f) (b) (c)(a) Lifetime [fs]100 E - E F [ e V ] Figure 2: Time-resolved two-photon momentum microscopy experiment of the Pb ML on Ag(111) system performed withan incidence angle of 4 ° (nearly normal incidence, in-plane electric field vector parallel to the k x -direction) and a photonenergy of 3 . k (cid:107) cut along the M (cid:48) Γ M-direction. (b) Constant energy maps for E-E F = 2 .
65 eV, 2 .
85 eV and3 . time maps in Fig.3(c). These CE maps reveal a disc-likeand a ring-like feature with quasiparticles lifetimes thatare distinguishable from those of the homogeneous back-ground in the L-bandgap of the Ag(111) crystal. Bothfeatures follow the dispersion of the QWS (dashed circles)as well as of the Pb side band (dotted circles) closely inall CE maps and hence allow us to gain insights into themomentum-dependent lifetimes of both states.The disc-like feature reflects the lifetimes of the QWSin momentum space. Its radius in momentum space fol-lows very closely the energy-dependent band dispersionof the QWS as indicated by the dashed green circles inthe CE lifetime maps in Fig.3(c). This is even moreclearly visible in the energy vs. momentum lifetime mapin Fig.3(d), where the energy and momentum regionswith distinct lifetime resembles closely the parabolic dis-persion of the QWS (green dashed curve). Along thisparabolic dispersion, we find slight increase of the life-time of the QWS from ≈ . F = 3 . ≈ . F = 2 . x / y -orbital character (seegreen dotted line) as shown in the energy vs. momentumlifetime map in Fig.3(d). The lifetime of this featureis τ ≈
11 fs for all energies and azimuthal orientations.This value is significantly larger than the lifetimes of thePb side band obtained in normal incidence geometry andhence does not reflect the intrinsic quasiparticle lifetimeof this state. Instead, we propose that this apparentlylarger lifetime is due to a momentum-dependent refillingof electrons from the QWS to the Pb side band mediatedby a interband scattering process. Such a process wasalready proposed for the QWS system Pb/Cu(111) [15].Altogether, the electron dynamics and the differentinter- and intraband scattering processes are summarizedin Fig.3(f). Optically excited electrons in the QWS dissi-pate energy and momentum by isotropic intraband scat-tering following the band dispersion towards the bandbottom of the QWS. Additional (quasi-)elastic scatter-ing processes can isotropically redistribute electrons fromthe QWS either towards the center of the Brillouin zone,most likely by electron-defect scattering, or into the Pbside bands via interband scattering between both Pb-derived bands. Most importantly, only the interbandscattering process from the QWS into the Pb side bandleads to an increased lifetime of the Pb side band which -0.5 0.0 0.5k x [ Å -1 ] k y [ Å - ] -0.50.5 -0.5 0.0 0.5k x [ Å -1 ]k x Ag Pb Lifetime [fs]6 14 -0.5 0.0 0.5 k ∥ [ Å -1 ]PE signal [arb. Units]0 1 E - E F [ e V ] -0.5 0.0 0.5 k ∥ [ Å -1 ] (d)(f)(b) (c)(a) Γ intra k ∥ [ Å -1 ] E - E F [ e V ] QWS
Pb side band Γ intra Γ Defect (e) Γ inter E - E F [ e V ] Figure 3: Time-resolved two-photon momentum microscopy experiment of the Pb ML on Ag(111) system performed withp-polarized light, a gracing incidence angle of 65 ° and a photon energy of 3.1 eV. (a) E over k (cid:107) cut along the M (cid:48) Γ M-direction.(b) Constant energy maps for E-E F = 2 .
65 eV, 2 .
85 eV and 3 . otherwise reveals a vanishing intrinsic quasiparticle life-time for all energies and momenta addressed in our ex-periment.In the next step, we focus on the modifications ofthe ultrafast electron dynamics of the Pb/Ag(111) bi-layer system by the adsorption of the aromatic moleculePTCDA. In this multilayer system, the interaction andcorresponding charge transfer across the PTCDA/Pb in-terface quench the QWS in the Pb layer [38]. This canpotentially alter the momentum-dependent refilling pro-cesses within the Pb/Ag(111) bilayer system.Upon the adsorption of PTCDA on Pb/Ag(111), theoverall shape of the autocorrelation traces changes sig-nificantly. Fig.4(a) shows an exemplary autocorrelationtrace averaging the total momentum-resolved photoemis-sion yield of the tr-2PMM experiment for a single in-termediate state energy. The data was recorded withmonochromatic radiation of 3 . δt ≈
50 fs. Thisunderestimation of the experimental data by the mod- elled autocorrelation trace has already been observed formolecular adsorbates on surfaces and is a signature ofan additional electronic state at this energy [52]. Thissecond state must be an excited molecular state at thisenergy.To consider both states in our data analysis,we modelled the autocorrelation traces of thePTCDA/Pb/Ag(111) multilayer system with a lin-ear combination of two autocorrelation traces exhibitingone lifetime τ PTCDA for the molecular adsorbate statesand one lifetime τ Pb for the Pb-derived states. Therelative contributions of both individual autocorrelationtraces is modelled by weighting factors A and (1 − A )respectively, with A ∈ [0 , τ Pb = 8 . τ PTCDA = 50 . A = 0 . A for each energy to a constant value. -150 -100 -50 0 50 100 150Delay [fs] P E y i e l d [ a . u ] P E y i e l d [ a . u ] Fit PTCDA
Fit Pb Fit curveDataFit curve(b)(a)
Figure 4: Exemplary normalized autocorrelation curves ex-tracted from the k-space integrated photoemission yield ofa time-resolved momentum microscopy experiment of thePTCDA/Pb/Ag(111) surface. As light source, a monochro-matic laser setup with p-polarized light and 3.1 eV photonenergy was used. The fits based on optical Bloch equationsare plotted as black solid lines. The measured data in bothpanel is the same and presented as black circles. The datain panel (a) was fitted with one autocorrelation revealing alifetime of τ = 14 . τ PTCDA is 50 . τ Pb is 8.3 fswith a weighting of 67 % (A = 0.33). The energy-dependent weighting factor was determinedby analyzing the autocorrelation trace of the momentumintegrated photoemission yield using A as a free fittingparameter.Our findings for the momentum-dependent electrondynamics of the PTCDA/Pb/Ag(111) multilayer systemis shown in Fig.5. The monochromatic tr-2PMM datawas obtained with p-polarized light, a gracing incidenceangle of 65 ° and a photon energy of 3.1 eV. Constant en-ergy maps of the momentum-dependent photoemissionyield as well as the lifetime maps of the PTCDA- andPb-derived states are exemplarily shown for an interme-diate state energy of E-E F = 2 .
65 eV in Fig.5(a). TheCE lifetime maps were obtained for a constant weightingfactor A = 0 . k y [ Å - ] P E y i e l d [ a . u . ] τ P b [ f s ] k y [ Å - ] -0.5 k y [ Å - ] E-E F =2.65 eV A = 0.33 τ P T C D A [ f s ] x [ Å -1 ] 2.0 2.5 3.0E-E F [eV]5001020304060 L i f e t i m e [ f s ] + τ Pb GI p-pol + τ Pb/Ag(111) NI + τ PTCDAGI p-pol + τ Pb/Ag(111) GI p-pol
Figure 5: Time-resolved two-photon momentum microscopyexperiments performed with p-polarized light, a gracing inci-dence angle of 65 ° and a photon energy of 3.1 eV. (a) Con-stant energy map and constant energy momentum-dependentlifetime maps of the PTCDA and Pb contributions for E-E F = 2 .
65 eV of the one layer PTCDA/Pb/Ag(111) system.(b) PTCDA (red) and Pb (blue) lifetimes extracted from amomentum-integrated autocorrelation trace in dependence ofthe intermediate state energy of the PTCDA/Pb/Ag(111)sample. The lifetimes for the Pb/Ag(111) system are depictedin green (p-pol, grazing incidence (GI)) and black (normal in-cidence (NI)) for comparison.
However, we also do not observe any signature of a ring-like feature in the CE lifetime map of the Pb-derivedside band as found for the CE lifetime map of the barePb/Ag(111) bilayer system for identical excitation con-ditions (p-polarized excitation). This directly points to asuppressing of any refilling process of electrons into thePb side bands due to the adsorption of PTCDA.Similar results were obtained for the intermediatestate energies E-E F = 2 .
15 eV ( A = 0 .
34) and E-E F = 2 .
85 eV ( A = 0 . τ PTCDA ≈
50 fs for the molecular state and of τ Pb ≈ x / y -like orbitals of the Pb sidebands with the molecular p z -like orbitals of the excitedstates. This observation points to a rather weak, orbital-selective chemical interaction across the PTCDA/Pb in-terface.
4. SUMMARY
In our work, we have investigated the momentum-dependent electron dynamics of the quantum well sys-tem one layer Pb on Ag(111) prior and after the adsorp-tion of PTCDA using tr-2PMM in different excitationgeometries. The unoccupied band structure of the barePb/Ag(111) bilayer system is dominated by two excitedstates: (i) a free electron-like quantum well state withp z orbital character and parabolic dispersion centeredat the Γ-point of the surface and (ii) a Pb side bandwith almost linear dispersion and p x / y orbital character.The hot electron dynamics of electrons of the QWS isdetermined by isotropic intraband scattering leading to an increase of the lifetime from 12 fs to 13 . τ PTCDA ≈
50 fs for all energies.The electron dynamics of the Pb-derived states is signif-icantly altered by the adsorption induced suppression ofthe Pb QWS band structure. This modification of the Pbband structure prevents any refilling of electrons withinthe Pb layer. In addition, no interlayer refilling processesare observed which leads to vanishing lifetime of the Pbside band.We attribute the adsorption-induced modification ofthe electron dynamics in the Pb layer to a weak, orbital-selective chemical interaction across the PTCDA/Pb in-terface. This interaction selectively tunes the band struc-ture and the corresponding intralayer scattering pro-cesses within the Pb quantum well systems. In this way,our work lays the first steps towards controlling scatter-ing processes of low dimensional systems and quantum(well) materials by the adsorption of organic molecules.
Acknowledgments
The experimental work was funded by the DeutscheForschungsgemeinschaft (DFG, German Research Foun-dation) - TRR 173 – 268565370 Spin + X: spin in its col-lective environment (Project B05). BS and FH acknowl-edge financial support from the Graduate School of Ex-cellence MAINZ (Excellence Initiative DFG/GSC 266).MC acknowledges funding from the European ResearchCouncil (ERC) under the European Union ´ s Horizon2020 research and innovation programme (grant agree-ment No. 725767—hyControl). [1] M. Cinchetti, V. A. Dediu, and L. E. Hueso, “Activat-ing the molecular spinterface,” Nature materials , vol. 16,no. 5, pp. 507–515, 2017.[2] T.-C. Chiang, “Photoemission studies of quantum wellstates in thin films,”
Surface Science Reports , vol. 39,no. 7-8, pp. 181–235, 2000.[3] J. C. R. S´anchez, L. Vila, G. Desfonds, S. Gambarelli,J. P. Attan´e, J. M. de Teresa, C. Mag´en, and A. Fert,“Spin-to-charge conversion using Rashba coupling at theinterface between non-magnetic materials,”
Nature com-munications , vol. 4, no. 1, 2013.[4] M. Isasa, M. C. Mart´ınez-Velarte, E. Villamor, C. Mag´en,L. Morell´on, J. M. de Teresa, M. R. Ibarra, G. Vig-nale, E. V. Chulkov, E. E. Krasovskii, L. E. Hueso, and F. Casanova, “Origin of inverse rashba-edelstein effectdetected at the cu/bi interface using lateral spin valves,”
Physical Review B , vol. 93, no. 1, 2016.[5] S. Oyarz´un, A. K. Nandy, F. Rortais, J.-C. Rojas-S´anchez, M.-T. Dau, P. No¨el, P. Laczkowski, S. Pouget,H. Okuno, L. Vila, C. Vergnaud, C. Beign´e, A. Marty,J.-P. Attan´e, S. Gambarelli, J.-M. George, H. Jaffr`es,S. Bl¨ugel, and M. Jamet, “Evidence for spin-to-chargeconversion by Rashba coupling in metallic states at theFe/Ge(111) interface,”
Nature communications , vol. 7,no. 1, 2016.[6] I. Bergenti and V. Dediu, “Spinterface: A new platformfor spintronics,”
Nano Materials Science , vol. 1, no. 3,pp. 149–155, 2019. [7] F. J. Himpsel, “Low-dimensional electronic states atmetal surfaces: Quantum wells and quantum wires,”
Sur-face Review and Letters , vol. 02, no. 01, pp. 81–88, 1995.[8] M. Bauer, S. Pawlik, and M. Aeschlimann, “Resonancelifetime and energy of an excited Cs state on Cu(111),”
Physical Review B , vol. 55, no. 15, pp. 10040–10043, 1997.[9] S. Ogawa, H. Nagano, and H. Petek, “Optical in-tersubband transitions and femtosecond dynamics inAg/Fe(100) quantum wells,”
Physical review letters ,vol. 88, no. 11, p. 116801, 2002.[10] E. V. Chulkov, J. Kliewer, R. Berndt, V. M. Silkin,B. Hellsing, S. Crampin, and P. M. Echenique, “Hole dy-namics in a quantum-well state at Na/Cu(111),”
PhysicalReview B , vol. 68, no. 19, p. 3060, 2003.[11] D. Wegner, A. Bauer, and G. Kaindl, “Electronic struc-ture and dynamics of quantum-well states in thin Ybmetal films,”
Physical review letters , vol. 94, no. 12,p. 126804, 2005.[12] P. S. Kirchmann and U. Bovensiepen, “Ultrafast electrondynamics in Pb/Si(111) investigated by two-photon pho-toemission,”
Physical Review B , vol. 78, no. 3, p. 4160,2008.[13] A. Zugarramurdi, N. Zabala, V. M. Silkin, A. G. Borisov,and E. V. Chulkov, “Lifetimes of quantum well statesand resonances in Pb overlayers on Cu(111),”
PhysicalReview B , vol. 80, no. 11, p. 171, 2009.[14] I.-P. Hong, C. Brun, F. Patthey, I. Y. Sklyadneva, X. Zu-bizarreta, R. Heid, V. M. Silkin, P. M. Echenique, K. P.Bohnen, E. V. Chulkov, and W.-D. Schneider, “Decaymechanisms of excited electrons in quantum-well states ofultrathin Pb islands grown on Si(111): Scanning tunnel-ing spectroscopy and theory,”
Physical Review B , vol. 80,no. 8, 2009.[15] S. Mathias, A. Ruffing, F. Deicke, M. Wiesenmayer,M. Aeschlimann, and M. Bauer, “Band structure depen-dence of hot-electron lifetimes in a pb/cu(111) quantum-well system,”
Physical Review B , vol. 81, no. 15, 2010.[16] S. Link, A. Scholl, R. Jacquemin, and W. Eberhardt,“Electron dynamics at a Ag/C metal–semiconductorinterface,” Solid State Communications , vol. 113, no. 12,pp. 689–693, 2000.[17] X. Zhu, “Electronic structure and electron dynamicsat molecule–metal interfaces: implications for molecule-based electronics,”
Surface Science Reports , vol. 56,no. 1-2, pp. 1–83, 2004.[18] G. Dutton, D. P. Quinn, C. D. Lindstrom, and X.-Y.Zhu, “Exciton dynamics at molecule-metal interfaces:C /Au(111),” Physical Review B , vol. 72, no. 4, p. 972,2005.[19] J. G¨udde, W. Berthold, and U. H¨ofer, “Dynamics of elec-tronic transfer processes at metal/insulator interfaces,”
Chemical reviews , vol. 106, no. 10, pp. 4261–4280, 2006.[20] L. Gundlach, R. Ernstorfer, and F. Willig, “Dynamics ofphotoinduced electron transfer from adsorbed moleculesinto solids,”
Applied Physics A , vol. 88, no. 3, pp. 481–495, 2007.[21] A. Hotzel, “Electron dynamics of image potential statesin weakly bound adsorbate layers: A short review,”
Progress in Surface Science , vol. 82, no. 4-6, pp. 336–354, 2007.[22] S. Hagen, Y. Luo, R. Haag, M. Wolf, and P. Tegeder,“Electronic structure and electron dynamics at an or-ganic molecule/metal interface: interface states of tetra-tert -butyl-imine/Au(111),”
New Journal of Physics ,vol. 12, no. 12, p. 125022, 2010. [23] A. Zugarramurdi, N. Zabala, V. M. Silkin, E. V. Chulkov,and A. G. Borisov, “Quantum-well states with imagestate character for Pb overlayers on Cu(111),”
PhysicalReview B , vol. 86, no. 7, 2012.[24] B. Stadtm¨uller, S. Emmerich, D. Jungkenn, N. Haag,M. Rollinger, S. Eich, M. Maniraj, M. Aeschlimann,M. Cinchetti, and S. Mathias, “Strong modification of thetransport level alignment in organic materials after op-tical excitation,”
Nature communications , vol. 10, no. 1,p. 1470, 2019.[25] Schmuttenmaer, Aeschlimann, Elsayed-Ali, Miller, Man-tell, Cao, and Gao, “Time-resolved two-photon photoe-mission from Cu(100): Energy dependence of electron re-laxation,”
Physical review. B, Condensed matter , vol. 50,no. 12, pp. 8957–8960, 1994.[26] M. Wolf, “Femtosecond dynamics of electronic excita-tions at metal surfaces,”
Surface Science , vol. 377-379,pp. 343–349, 1997.[27] H. Petek and S. Ogawa, “Femtosecond time-resolvedtwo-photon photoemission studies of electron dynamicsin metals,”
Progress in Surface Science , vol. 56, no. 4,pp. 239–310, 1997.[28] M. Weinelt, “Time-resolved two-photon photoemissionfrom metal surfaces,”
Physical review. B, Condensedmatter , vol. 14, no. 43, pp. R1099–R1141, 2002.[29] U. Bovensiepen and P. S. Kirchmann, “Elementary relax-ation processes investigated by femtosecond photoelec-tron spectroscopy of two-dimensional materials,”
Laser& Photonics Reviews , vol. 6, no. 5, pp. 589–606, 2012.[30] M. Bauer, A. Marienfeld, and M. Aeschlimann, “Hotelectron lifetimes in metals probed by time-resolvedtwo-photon photoemission,”
Progress in Surface Science ,vol. 90, no. 3, pp. 319–376, 2015.[31] W. Berthold, U. H¨ofer, P. Feulner, E. V. Chulkov, V. M.Silkin, and P. M. Echenique, “Momentum-resolved life-times of image-potential States on Cu(100),”
Physical re-view letters , vol. 88, no. 5, p. 056805, 2002.[32] A. S. Syed, V. M. Trontl, M. Ligges, S. Sakong,P. Kratzer, D. L¨ukermann, P. Zhou, I. Avigo, H. Pfn¨ur,C. Tegenkamp, and U. Bovensiepen, “Unoccupied elec-tronic structure and momentum-dependent scatteringdynamics in Pb/Si(557) nanowire arrays,”
Physical Re-view B , vol. 92, no. 13, 2015.[33] C. Monney, M. Puppin, C. W. Nicholson, M. Hoesch,R. T. Chapman, E. Springate, H. Berger, A. Magrez,C. Cacho, R. Ernstorfer, and M. Wolf, “Revealing therole of electrons and phonons in the ultrafast recovery ofcharge density wave correlations in 1 T -TiSe ,” PhysicalReview B , vol. 94, no. 16, p. 2791, 2016.[34] S. Aeschlimann, R. Krause, M. Ch´avez-Cervantes,H. Bromberger, R. Jago, E. Mali´c, A. Al-Temimy, C. Co-letti, A. Cavalleri, and I. Gierz, “Ultrafast momen-tum imaging of pseudospin-flip excitations in graphene,”
Physical Review B , vol. 96, no. 2, 2017.[35] A. S. Ketterl, S. Otto, M. Bastian, B. Andres, C. Gahl,J. Min´ar, H. Ebert, J. Braun, O. E. Tereshchenko, K. A.Kokh, T. Fauster, and M. Weinelt, “Origin of spin-polarized photocurrents in the topological surface statesof Bi Se ,” Physical Review B , vol. 98, no. 15, 2018.[36] M. Weinelt, A. B. Schmidt, M. Pickel, and M. Donath,“Spin-polarized image-potential-state electrons as ultra-fast magnetic sensors in front of ferromagnetic surfaces,”
Progress in Surface Science , vol. 82, no. 4-6, pp. 388–406,2007.[37] M. Marks, A. Sch¨oll, and U. H¨ofer, “Formation of metal– organic interface states studied with 2PPE,”
Journal ofElectron Spectroscopy and Related Phenomena , vol. 195,pp. 263–271, 2014.[38] B. Stadtm¨uller, L. Grad, J. Seidel, F. Haag, N. Haag,M. Cinchetti, and M. Aeschlimann, “Modification ofPb quantum well states by the adsorption of organicmolecules,”
Journal of Physics: Condensed Matter ,vol. 31, no. 13, p. 134005, 2019.[39] F. Haag, T. Eul, P. Thielen, N. Haag, B. Stadtm¨uller,and M. Aeschlimann, “Time-resolved two-photon mo-mentum microscopy—A new approach to study hot car-rier lifetimes in momentum space,”
Review of ScientificInstruments , vol. 90, no. 10, p. 103104, 2019.[40] M. Escher, N. Weber, M. Merkel, C. Ziethen, P. Bern-hard, G. Sch¨onhense, S. Schmidt, F. Forster, F. Reinert,B. Kr¨omker, and D. Funnemann, “Nanoelectron spec-troscopy for chemical analysis: a novel energy filter forimaging x-ray photoemission spectroscopy,”
Journal ofPhysics: Condensed Matter , vol. 17, no. 16, pp. S1329–S1338, 2005.[41] B. Kr¨omker, M. Escher, D. Funnemann, D. Hartung,H. Engelhard, and J. Kirschner, “Development of a mo-mentum microscope for time resolved band structureimaging,”
The Review of scientific instruments , vol. 79,no. 5, p. 053702, 2008.[42] C. Tusche, A. Krasyuk, and J. Kirschner, “Spin resolvedbandstructure imaging with a high resolution momentummicroscope,”
Ultramicroscopy , vol. 159 Pt 3, pp. 520–529,2015.[43] G. Sch¨onhense, K. Medjanik, C. Tusche, M. de Loos,B. van der Geer, M. Scholz, F. Hieke, N. Gerken,J. Kirschner, and W. Wurth, “Correction of the de-terministic part of space-charge interaction in momen-tum microscopy of charged particles,”
Ultramicroscopy ,vol. 159 Pt 3, pp. 488–496, 2015.[44] A. Oelsner, O. Schmidt, M. Schicketanz, M. Klais,G. Sch¨onhense, V. Mergel, O. Jagutzki, and H. Schmidt-B¨ocking, “Microspectroscopy and imaging using a de-lay line detector in time-of-flight photoemission mi-croscopy,”
Review of Scientific Instruments , vol. 72,no. 10, pp. 3968–3974, 2001.[45] A. Oelsner, M. Rohmer, C. Schneider, D. Bayer,G. Sch¨onhense, and M. Aeschlimann, “Time- and energyresolved photoemission electron microscopy-imaging ofphotoelectron time-of-flight analysis by means of pulsedexcitations,”
Journal of Electron Spectroscopy and Re-lated Phenomena , vol. 178-179, pp. 317–330, 2010.[46] P. Kahl, S. Wall, C. Witt, C. Schneider, D. Bayer, A. Fis-cher, P. Melchior, M. Horn-von Hoegen, M. Aeschlimann,and F.-J. Meyer zu Heringdorf, “Normal-Incidence Pho- toemission Electron Microscopy (NI-PEEM) for ImagingSurface Plasmon Polaritons,”
Plasmonics , vol. 9, no. 6,pp. 1401–1407, 2014.[47] M. Aeschlimann, M. Bauer, and S. Pawlik, “Compet-ing nonradiative channels for hot electron induced sur-face photochemistry,”
Chemical Physics , vol. 205, no. 1-2, pp. 127–141, 1996.[48] Hertel, Knoesel, Wolf, and Ertl, “Ultrafast electron dy-namics at Cu(111): Response of an electron gas to op-tical excitation,”
Physical review letters , vol. 76, no. 3,pp. 535–538, 1996.[49] S. Ogawa, H. Nagano, and H. Petek, “Hot-electron dy-namics at Cu(100), Cu(110), and Cu(111) surfaces: Com-parison of experiment with Fermi-liquid theory,”
PhysicalReview B , vol. 55, no. 16, pp. 10869–10877, 1997.[50] G. D. Mahan, “Theory of Photoemission in Simple Met-als,”
Physical Review B , vol. 2, no. 11, pp. 4334–4350,1970.[51] A. Winkelmann, A. Akin ¨Unal, C. Tusche, M. Ellguth,C.-T. Chiang, and J. Kirschner, “Direct k -space imag-ing of Mahan cones at clean and Bi-covered Cu(111) sur-faces,”
New Journal of Physics , vol. 14, no. 8, p. 083027,2012.[52] S. Steil, N. Großmann, M. Laux, A. Ruffing, D. Steil,M. Wiesenmayer, S. Mathias, O. L. A. Monti,M. Cinchetti, and M. Aeschlimann, “Spin-dependenttrapping of electrons at spinterfaces,”
Nature Physics ,vol. 9, no. 4, pp. 242–247, 2013.[53] P. Puschnig, S. Berkebile, A. J. Fleming, G. Koller,K. Emtsev, T. Seyller, J. D. Riley, C. Ambrosch-Draxl,F. P. Netzer, and M. G. Ramsey, “Reconstruction ofmolecular orbital densities from photoemission data,”
Science (New York, N.Y.) , pp. 702–706, 2009.[54] B. Stadtm¨uller, M. Willenbockel, E. M. Reinisch, T. Ules,F. C. Bocquet, S. Soubatch, P. Puschnig, G. Koller,M. G. Ramsey, F. S. Tautz, and C. Kumpf, “Orbital to-mography for highly symmetric adsorbate systems,”
EPL(Europhysics Letters) , vol. 100, no. 2, p. 26008, 2012.[55] R. Wallauer, M. Raths, K. Stallberg, L. M¨unster,D. Brandstetter, X. Yang, J. G¨udde, P. Puschnig,S. Soubatch, C. Kumpf, F. C. Bocquet, F. S. Tautz,and U. H¨ofer, “Tracing orbital images on ultrafast timescales.”[56] C. H. Schwalb, M. Marks, S. Sachs, A. Sch¨oll, F. Reinert,E. Umbach, and U. H¨ofer, “Time-resolved measurementsof electron transfer processes at the PTCDA/Ag(111) in-terface,”