Otto Stern (Sohrau 1888 Berkeley 1969) Nobel Laureate 1943

Otto Stern, O.R. Frisch, I. Estermann (Hamburg, 1929-1933)He NaCl(001)a

These experiments are of interest not only because of their confirmation of the predictions of quantum mechanics, but also because they introduce the possibility of applying atom diffraction to investigations of the atomic constitution of surfaces. (T. M. Johnson, Phys. Rev. 37 (1931) 847).

Bound-state resonancesFrisch-Stern (1933) J. E. Lennard-Jones and A. F. Devonshire, Nature 137 (1936) 1069. I00

Gas Surface Interactions:- energy transfer- sticking (adsorption)

INELASTIC SCATTERINGINELASTIC RESONANCESLattice vibrations (phonons) J.M. Jackson and N.F. Mott, Proc. Roy. Soc. A 137 (1932) 703: Quantum DWBA

L.D. Landau, Phys. Z. Sowjet. 8 (1935) 489.B.L. Bonch-Bruevich, Usp. Fiz. Nauka 40 (1950) 369 ClassicalRarified Gas DynamicsSupersonic Molecular Beams

Supersonic nozzle beam sources

v

Supersonic He-atom beam sourcesTime-of-flight spectroscopyHigh-resolution diffraction

J. P. Toennies: HUGO (MPI-SF, Goettingen)

Angular distributionsDiffractionInelastic processes: inelastic bound state resonances - kinematical focussing- surfing

Time of Flight (TOF)Inelastic scatteringPhononsvia the mechanical action (Pauli repulsion) on the electron densityForces between atomsForces between ions and electrons (electron-phonon interaction)& electronic susceptibilityPhonon dispersion curves

phonon excitations probe interatomic forcesinelastic He atom scattering excites phonons

Surface wavesLord Rayleigh (1887)Irpinia 1980 (Polo Sismico Alberto Gabriele, FCCSEM Erice)

Surface phonons 1: from 3D lattice to slab

rl r(l1 l2 l3,) = l1a1 + l2a2 + l3a3 + d() rl r(l1 l2 l3,) = l1a1 + l2a2 + d(l3,) interatomicpotentialforce constant matrixharmonic eq. of motion3D2D slabBloch wavessecular equation

Surface phonons 2: from one monolayerto a slab of Nz layers

TOF spectrumEnergy-transfer spectrumscan curves for 90 geometry

HAS versus theorytheory: Green Function surface dynamics + DWBA scattering theoryLiF(001)NaF(001)end of lecture 3

Metals: Skin & Bones ICu(111)HAS

Anomalous longitudinal resonanceCu(111) HAS dataC. Kaden et al. PRB (1992)

G. Benedek et al. PRB 1993Cu(001)a giant resonance

There is something fundamental in the anomalous longitudinal resonance

A feature common to all metal surfaces

A strong amplitude in HAS but weak in EELS

Unphysical fitting with force-constant models

The Multipole Expansion (ME) Method Equilibrium:

Adiabatic conditionSecular equationDynamic electron density oscillationsNon-local dielectric response (susceptibility)

Density-functional Hellmann-Feynman vs. Multipole expansion ynk Kohn-Sham wavefunctions:

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parametrized ME method

Ion-coredisplacementsElectron density oscillationsMEDFPT

Metals: Skin & Bones II

1D conductorPeierls instabilityelectron-hole excitationsHAS hole-electron pairs!

The Helium-3 Spin-Echo SpectroscopyP. Fouquet, A.P. Jardine, S. Dworski, G. Alexandrowicz, W. Allison and J. Ellis"Thermal energy 3He spin-echo spectrometer for ultrahigh resolution surface dynamics measurements Rev. Sci. Inst. 76, 053109 (2005).

The Cavendish He3 Spin-Echo Apparatus

ParameterValue

Total scattering angle44.4 degrees3He Angular Resolution0.1 degreeNominal beam energy8 meVMeasured beam intensity1e14 atoms/secondBeam diameter at target2 mmEnergy resolution (QE peak width)20 neVScattering chamber base pressure2e-10 mbarSample manipulator6 axis, titaniumSample manipulator resolution0.003 degreesSample heatingRadiation / E-beamSample coolingLiquid Nitrogen or HeliumSample temperature range 55 K - >1200 K

First tests for He3 Spin-Echo: Bound states of He3 on LiF(001) Surface Transport Measurements using Quasi-elastic Helium Atom Scattering (QHAS)A.P. Jardine, S. Dworski, P. Fouquet, G. Alexandrowicz, G.Y.H. Lee, D.J. Riley, J. Ellis, W. Allison, "Ultrahigh resolution spin-echo measurement of surface potential energy landscapes", Science 304, 1790-1793 (2004). back to Frisch & Stern!

4He liquid jetscluster, droplets at 0.37 Knano-scale superfluididitytargets for high-energy physicstargets for laser accelerators (e.g., for hadrotherapy)4He gas jetsatom microscopeatom interferometrysuperfluid 4He (p-H2) clusters inside 3He droplets jets from expansion of solid 4He: the geyser effect

PMCSsubstratetime of flight mass spectrometerquartz MB2000 l/s diff. pump500 l/s turbo pump700 l/s diff. pumpHe linesample manipulatortargetto pulsed power supplySOURCE CHAMBERDEPOSITION CHAMBERTOF-MSCHAMBERSUPERSONIC CLUSTER BEAM DEPOSITION at the Department of Physics, University of MilanoGrenoble - 9

Giorgio Benedek J. Peter Toennies Helium Atom Scattering Spectroscopy of Surface Phonons

Springer-VerlagBerlin Heidelberg New York 2007

something more on inelastic atom scattering:end of lecture 4

JPTBibi Bortolani