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 resonances Frisch-Stern (1933) J. E. Lennard-Jones and A. F. Devonshire, Nature 137 (1936) 1069. I 00
Gas – Surface Interactions: - energy transfer - sticking (adsorption) INELASTIC SCATTERING INELASTIC RESONANCES Lattice 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 Classical Rarified Gas Dynamics Supersonic Molecular Beams
Time of Flight (TOF)Inelastic scattering Phonons via the mechanical action (Pauli repulsion) on the electron density Forces between atoms Forces between ions and electrons (electron-phonon interaction) & electronic susceptibility Phonon dispersion curves
phonon excitations probe interatomic forces inelastic He atom scattering excites phonons
Surface waves Lord Rayleigh (1887) Irpinia 1980 (Polo Sismico Alberto Gabriele, FCCSEM Erice)
r l r(l 1 l 2 l 3, ) = l 1 a 1 + l 2 a 2 + l 3 a 3 + d( ) r l r(l 1 l 2 l 3, ) = l 1 a 1 + l 2 a 2 + d(l 3, ) interatomic potential force constant matrix harmonic eq. of motion 3D 2D slab Bloch waves secular equation
Surface phonons 2: from one monolayer… …to a slab of N z layers
TOF spectrum Energy-transfer spectrum scan curves for 90° geometry
HAS versus theory theory: Green Function surface dynamics + DWBA scattering theory LiF(001) NaF(001) end of lecture 3
Rayleigh wave Longitudinal resonance Metals: Skin & Bones I Cu(111) HAS
Anomalous longitudinal resonance Cu(111) HAS data C. Kaden et al. PRB (1992)
G. Benedek et al. PRB 1993 Cu(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:
1D conductor Peierls instability electron-hole excitations HAS hole-electron pairs!
The Helium-3 Spin-Echo Spectroscopy P. 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).
ParameterValue Total scattering angle44.4 degrees 3He Angular Resolution0.1 degree Nominal beam energy8 meV Measured beam intensity1e14 atoms/second Beam diameter at target2 mm Energy resolution (QE peak width)20 neV Scattering chamber base pressure2e-10 mbar Sample manipulator6 axis, titanium Sample manipulator resolution0.003 degrees Sample heatingRadiation / E-beam Sample coolingLiquid Nitrogen or Helium Sample temperature range55 K - >1200 K The Cavendish He3 Spin- Echo Apparatus
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!
4 He liquid jets cluster, droplets at 0.37 K nano-scale superfluididity targets for high-energy physics targets for laser accelerators (e.g., for hadrotherapy) 4 He gas jets atom microscope atom interferometry superfluid 4 He (p-H 2 ) clusters inside 3 He droplets jets from expansion of solid 4 He: the geyser effect
PMCS substrate cluster beam time of flight mass spectrometer quartz MB 2000 l/s diff. pump 500 l/s turbo pump 700 l/s diff. pump He line sample manipulator target cluster assembled film to pulsed power supply SOURCE CHAMBER DEPOSITION CHAMBER TOF-MS CHAMBER SUPERSONIC CLUSTER BEAM DEPOSITION at the Department of Physics, University of Milano Grenoble - 9
Giorgio Benedek J. Peter Toennies Helium Atom Scattering Spectroscopy of Surface Phonons Springer-Verlag Berlin Heidelberg New York 2007 something more on inelastic atom scattering: end of lecture 4