Unknown X -Rays:high penetration

Transcription

1 The nobel prize in physics 1901 Wilhelm Conrad Röntgen Germany in recognition of the extraordinary services he has rendered by the discovery of the remarkable rays subsequently named after him" Discovery of X-RaysX 1895, W.C. Röntgen: Unknown X -Rays:high penetration 1

2 The nobel prize in physics 1903: Discovery of radioactivity (1896) Henri Becquerel France in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity" Pierre Curie France Marie Curie France "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel" Discovery of radioactivity Rutherford, different types of atomic radiation - artificial transmutation of one element into another - Atoms contain small nucleus Atoms are not elementary particles. They have complicated structure 2

3 The nobel prize in chemistry 1908 Ernest Rutherford, UK for his investigations into the disintegration of the elements, and the chemistry of radioactive substances" The nobel prize in physics 1906 Joseph John Thomson United Kingdom "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases" 3

4 Discovery of electron 1897, JJ. Thomson: Rays of discharge: Have negative charge, Consist of discrete particles Determined the ratio e/m m e ~0.001 m hydrogen Electrons Discovery of electron 1912, R.A.Millikan: Charge of electron e = 1.6x10-19 C 4

5 Structure of atoms Thomsons: pudding model Structure of atoms Rutherford's Experiment - Planetar model 5

6 Structure of atoms Atoms emit sharp spectral lines Why? Structure of atoms Bohr: - electrons are orbiting the nucleus -only orbits of certain radii (energies) are "permitted, where electron : has a defined energy state will not radiate energy will not spiral into the nucleus E=R h /n 2 6

7 The nobel prize in physics 1922 Niels Henrik David Bohr Denmark for his services in the investigation of the structure of atoms and of the radiation emanating from them" LIGHT - WAVE OR PARTICLE: Black Body Radiation Black body: an idealized object which absorbs and emits all frequencies Rayleign-Jean law Ultraviolet catastrophe Planck, 1905: The energy of vibrating molecules can only have certain discrete values: E=n*hf hf, n=0, 1, 2,... Birth of quantum physics! h = 6.6 x Js Planck s constant 7

8 LIGHT - WAVE OR PARTICLE: Photovoltaic effect An appearance of current in a vacuum tube under illumination Hertz, 1887: - maximum electron energy is independent of the light intensity - existence of cutoff frequency Lenard,, maximum electron energy is determined by the light frequency Einstein, 1905: light= quanta or photons E=hf LIGHT - WAVE OR PARTICLE: 8

9 LIGHT - WAVE OR PARTICLE: Photovoltaic effect Millikan,, 1916 Attempts (10 years of work!!!) to disprove Einstein's theory Most convincing evidence for Einstein's theory LIGHT - WAVE AND PARTICLE: E=hf The nobel prize in physics Max Karl Ernst Ludwig Planck Germany in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta" Albert Einstein Germany and Switzerland for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect" 9

10 The nobel prize in physics 1923 Robert Andrews Millikan USA for his work on the elementary charge of electricity and on the photoelectric effect" Matter: Particle or Wave De Broglie, 1923: Atomic orbits should be quantized because each particle is also a wave: λ=h/mv λel = 7*10-10 m, i.e. several times size of atom 10

11 Matter: Particle or Wave C. J. Davisson, 1927: Electron diffraction from nickel crystal G.P.Thomsom, 1927: Electron diffraction by thin foil Electron is a wave The nobel prize in physics Prince Louis-Victor Pierre Raymond de Broglie, France "for his discovery of the wave nature of electrons" Clinton J.Davisson USA George P.Thomson UK "for their experimental discovery of the diffraction of electrons by crystals" 11

12 The nobel prize in physics Werner Karl Heisenberg Germany for the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen" Erwin Schrödinger Austria Paul Adrien Maurice Dirac, UK for the discovery of new productive forms of atomic theory" New Quantum Mechanics A. Einstein: God does not play dice R. Feynman: No one understands quantum mechanics Heisenberg - Matrix mechanics Uncertainty principle Δx Δp > h/2 ΔE Δt >h/2 12

13 New Quantum Mechanics Schrödinger - Wave mechanics H Ψ= EΨ Ψ - wavefunction ΨΨ*dx = 1 New Quantum Mechanics: Tunneling 13

14 New Quantum Mechanics: Tunneling After the barrier: Ψ 0 Tunneling Transmission probability T e 2kL k = [8π 2 m(u 0 E)] ½ /h New Quantum Mechanics Dirac - Prediction of spin - Prediction of antiparticles (positron) 14

15 The nobel prize in physics 1945 Wolfgang Pauli Austria "for the discovery of the Exclusion Principle, also called the Pauli Principle" The nobel prize in physics 1986 Ernst Ruska Germany "for his fundamental work in electron optics, and for the design of the first electron microscope" Gerd Binning Germany Heinrich Rocher Germany "for their design of the scanning tunneling microscope" 15

16 Seeing with electrons: Transmission Electron Microscope Electron: Particle and Wave Light microscope: Size of an object is limited by the wavelength of light. Transmission Electron microscopes Use electrons as a "light source" much lower wavelength a resolution of a thousand times better than with a light microscope. Seeing with electrons: Scanning Electron Microscope Scanning electron microscopy (SEM): scanning a focused probe across the surface of the sample. Detection: Secondary electrons emitted from the sample detected by a photomultiplier system. The output - modulate the brightness of a TV monitor that is rastered in synchronisation with the the electron beam scan. The more electrons a particular region emits, the brighter the image at that point. 16

17 Seeing with electrons: Scanning Electron Microscope Black Widow spider claw An ant holding a microchip Seeing with electrons: Scanning Tunneling Microscope Electrons tunnel between the surface and the stylus an electrical signal. Size of the stylus tip - single atom. It slowly scans across the surface. The stylus is raised and lowered in order to keep the signal constant and maintain the distance. Smallest details of the surface! 17

18 Seeing with electrons: Scanning Tunneling Microscope Platinum Silicon Individual atoms (10-10 m) can clearly be seen!!! 18