Spin dependent transport of hot electrons through ultrathin epitaxial metallic films [Elektronische Ressource] / by Emanuel Heindl

Sujets

• Physik

Informations

• Publié par: universitat_regensburg
• Publié le: 01 janvier 2010
• Nombre de lectures: 15
• Langue: English
• Poids de l'ouvrage: 58 Mo

Extrait

Spin dependent transport of hot electrons
through ultrathin epitaxial metallic films
by
Emanuel Heindl
(2010)
Thesis submitted in partial fulfillment
of the requirements for the degree of
Doctor of Natural Sciences (Dr. rer. nat.)
in the department of Physics
of the university of RegensburgTo my son
Sascha Heindl- III -
Promotionsgesuch eingereicht am 23.06.2010
Die Arbeit wurde angeleitet von Prof. Dr. Christian H. Back
Prufungsaussc¨ huss: Vorsitzender: Prof. Dr. John Schliemann
1. Gutachter: Prof. Dr. Christian H. Back
2. Gutachter: Prof. Dr. Jascha Repp
weiterer Prufer:¨ Prof. Dr. Dieter WeissContents
Contents II
Figures IV
1 Introduction 1
2 Theory of Hot Electron Transport 7
2.1 The emitter - creation of hot electrons . . . . . . . . . . . . . . . . . . . 7
2.1.1 Hot electron momentum distribution . . . . . . . . . . . . . . . . 10
2.1.2 Hot electron energy distribution . . . . . . . . . . . . . . . . . . 11
2.2 The base - hot electron propagation and relaxation . . . . . . . . . . . . 13
2.2.1 Electron-electron scattering . . . . . . . . . . . . . . . . . . . . . 16
2.2.2 Electron-phonon scattering . . . . . . . . . . . . . . . . . . . . . 19
2.2.3 Electron-magnon scattering . . . . . . . . . . . . . . . . . . . . . 21
2.2.4 Electron-defect . . . . . . . . . . . . . . . . . . . . . . 23
2.2.5 Electron-plasmon scattering . . . . . . . . . . . . . . . . . . . . . 24
2.2.6 Electron relaxation at the surface . . . . . . . . . . . . . . . . . . 24
2.2.7 and optical excitations . . . . . . . . . . . . . 24
2.2.8 Spin-orbit interaction . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3 The collector - hot electron filtering . . . . . . . . . . . . . . . . . . . . 25
2.3.1 Electron reflection and refraction . . . . . . . . . . . . . . . . . . 26
2.3.2 The shape of the Schottky barrier . . . . . . . . . . . . . . . . . 31
2.3.3 Spectroscopy and microscopy . . . . . . . . . . . . . . . . . . . . 33
2.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3 Instrumentation and sample fabrication 39
3.1 Electrical Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.1.1 Detection of the collector current . . . . . . . . . . . . . . . . . . 39
3.1.2 of the tunneling current . . . . . . . . . . . . . . . . . 43
3.1.3 Other parameters of the setup . . . . . . . . . . . . . . . . . . . 45
3.2 Mechanical Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.3 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48- II - Contents
4 Results 51
4.1 Characterization of the base/collector contact . . . . . . . . . . . . . . . 51
4.2 Features of hot electron characteristics . . . . . . . . . . . . . . . . . . . 53
4.3 Hot electron transport and magnetic anisotropy of
Fe Co /Au/Fe Co spin valves . . . . . . . . . . . . . . . . . . . . . 5734 66 34 66
4.4 Hot electron transport in bcc Fe Co . . . . . . . . . . . . . . . . . . . 6434 66
4.4.1 Magnetocurrent and hot electron spin polarization . . . . . . . . 65
4.4.2 Spin dependent attenuation lengths of bcc Fe Co . . . . . . . 6834 66
4.5 Hot electron transport in fcc Au . . . . . . . . . . . . . . . . . . . . . . 75
4.6 Temperature dependence of hot electron transport . . . . . . . . . . . . 77
4.6.1 Hot electron transport in Fe Co /Au/Fe Co spin valves . . . 7734 66 34 66
4.6.2 Hot transport in Fe/Au/Fe Co spin valves . . . . . . 8234 66
5 Conclusion 93
Publications 103
Acknowledgements 105
Declaration 107List of Figures
1.1 Experimental setups: SVT, MTT and BEEM . . . . . . . . . . . . . . . 2
1.2 Spin detection based on hot electron filtering . . . . . . . . . . . . . . . 4
2.1 Emitter/base contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Electron tunneling visualized in momentum and energy space . . . . . . 9
2.3 flux and tunneling . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4 Hot electron momentum distribution . . . . . . . . . . . . . . . . . . . . 11
2.5 Hot energy distribution . . . . . . . . . . . . . . . . . . . . . . . 12
2.6 Brillouin zone of fcc Au: bulk and (100) surface . . . . . . . . . . . . . . 13
2.7 The role of spin dependent group velocities . . . . . . . . . . . . . . . . 14
2.8 Density of states and hot electron scattering lengths . . . . . . . . . . . 15
2.9 Spin resolved lifetimes of hot electrons . . . . . . . . . . . . . . . . . . . 16
2.10 Electron mediated electron relaxation . . . . . . . . . . . . . . . . . . . 18
2.11 Phonon . . . . . . . . . . . . . . . . . . . . 20
2.12 Magnon mediated electron relaxation . . . . . . . . . . . . . . . . . . . . 22
2.13 The relevance of spin orbit interaction . . . . . . . . . . . . . . . . . . . 25
2.14 Electron refraction at the base/semiconductor interface . . . . . . . . . 27
2.15 Angle dependent electron transmission into GaAs P . . . . . . . . . . 2967 33
2.16 Spatial electronic bandstructure in BEEM . . . . . . . . . . . . . . . . . 32
2.17 Bell-Kaiser model and I U-characteristics . . . . . . . . . . . . . . . . . 34C
2.18 Influence of atomic steps and surface gradients on I . . . . . . . . . . . 35C
2.19 Overview of the capabilities of BEEM . . . . . . . . . . . . . . . . . . . 37
3.1 Preamplifier circuits for I and I . . . . . . . . . . . . . . . . . . . . . 41T C
3.2 Characterization of the electronic setup . . . . . . . . . . . . . . . . . . 42
3.3 Current noise of I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44T
3.4 STM/BEEM head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.5 vacuum chamber . . . . . . . . . . . . . . . . . . . . . . . 47
3.6 Surface morphology of GaAs P (100) . . . . . . . . . . . . . . . . . . . 4967 33
3.7 Conduction band profile of GaAs P (100) and crystallinity of67 33
Fe Co /Au/Fe Co spin valve overlayers . . . . . . . . . . . . . . . . 5034 66 34 66- IV - List of Figures
4.1 Current voltage characteristics of the metallized semiconductors . . . . . 52
4.2 Overview of hot electron characteristics . . . . . . . . . . . . . . . . . . 54
4.3 Noise in hot electron characteristics . . . . . . . . . . . . . . . . . . . . . 55
4.4 Definition of Magnetocurrent . . . . . . . . . . . . . . . . . . . . . . . . 57
4.5 Ferromagnetic resonance on spin valves . . . . . . . . . . . . . . . . . . 59
4.6 Hysteresis loops for the magnetic easy and hard axis . . . . . . . . . . . 60
4.7 Coercive fields of Fe Co /Au/Fe Co spin valves . . . . . . . . . . . 6134 66 34 66
4.8 Hysteresis loops for the magnetic intermediate axis . . . . . . . . . . . . 63
4.9 Magnetocurrent and tunneling voltage . . . . . . . . . . . . . . . . . . . 66
4.10current and hot electron spin polarization . . . . . . . . . . . . 67
4.11 Spin attenuation lengths of bcc Fe Co . . . . . . . . . . . . . . . . . . 6834 66
4.12 Comparison of the attenuation lengths of bcc Fe Co to literature . . 7034 66
4.13 Electronic bandstructure of fcc Au and bcc Fe Co . . . . . . . . . . . 7134 66
4.14 Spin resolved electronic bandstructure of bcc Fe Co . . . . . . . . . . 7434 66
4.15 Group velocity and integrated DOS of bcc Fe Co . . . . . . . . . . . 7534 66
4.16 Attenuation length of fcc Au . . . . . . . . . . . . . . . . . . . . . . . . 76
4.17 Temperature dependence of hot electron transport through Fe Co /34 66
Au/Fe Co spin valves . . . . . . . . . . . . . . . . . . . . . . . . . . . 7934 66
4.18 Normalized temperature dependence of hot electron transport through
Fe Co /Au/Fe Co spin valves . . . . . . . . . . . . . . . . . . . . . 8134 66 34 66
4.19 Crystallinity of Fe/Au/Fe Co spin valves . . . . . . . . . . . . . . . . 8334 66
4.20 Magnetic response of Fe/Au/Fe Co spin valves . . . . . . . . . . . . . 8434 66
4.21 Hysteresis loops of Fe/Au/Fe Co spin valves . . . . . . . . . . . . . . 8534 66
4.22 Temperature dependence of hot electron transport through
Fe/Au/Fe Co spin valves . . . . . . . . . . . . . . . . . . . . . . . . . 8734 66
4.23 Normalized temperature dependence of hot electron transport through
Fe/Au/Fe Co spin valves . . . . . . . . . . . . . . . . . . . . . . . . . 8834 66
4.24 Spin resolved electronic bandstructure of bcc Fe . . . . . . . . . . . . . . 89
4.25 Group velocity, integrated electronic and magnonic DOS of bcc Fe . . . 90
4.26 Hot electron spin polarization for bcc Fe Co and bcc Fe thin films . . 9134 661 Introduction
When a material is exposed to an incident beam of particles, the particles may interact
with the in such a way that the particle characteristics measured thereafter
reflect some material properties. A thorough interpretation of the acquired results de-
mands the determination of the states of the initially incident and outgoing particles.
Many experiments in natural sciences and even everyday occurrences are based on this
principle. By way of example, we determine the color of a leaf by illuminating it and
identifying the frequencies of the reflected light by means of our eyes. However, the
leaf appears green when white light is utilized and black when monochromatic red light
shines on it as a consequence of absorption. In some situations interaction is weak and
some of the particles do not feel the presence of the material at all. These become
transmitted through the material in a ballistic manner. However, information about
the material can still be gained, yet in a complementary way to