Repetition: Refractive Index

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Beatrix Golden
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1 Repetitio: Refractive Idex (ω) κ(ω) 1 0 ω 0 ω 0 The real part of the refractive idex correspods to refractive idex, as it appears i Sellius law of refractio. The imagiary part correspods to the absorptio of eergy i the medium.

2 Repetitio: Optics - Coservatio Law For optics the followig coservatio law is valid: T + R + A + S = 1 T Trasmissio R Reflectio A Absorptio S Scatterig For geometric optics the refractio idex ca be cosidered as frequecy idepedet.

3 Repetitio: Optics - Iterfaces Reflectio: α = α α β α' 1 Refractio: si si α β = 1 Wavelegth: λ i = λ Vak i

4 Repetitio: Fresel's Equatios Media, idices of refractio 1,, perpedicular impigemet, i. e.: ϕ 1 = ϕ = 0 Reflectio: 1 1 k p k r r + = = Trasmissio: 1 1 k p k t t + = =

5 Repetitio: Optical Film Thickess Electromagetic radiatio passes from Vacuum ito a Medium with refractive idex : Frequecy ω: Wavelegth λ: ω = ω Vak λ = λ Vak If a film thickess is give as the moltiple of a wavelegth, λ is meat. This film thickess is called optical film thickess", d opt. It is: d Opt = d

6 Repetitio: Reflectio Suppressio 0 1 t 0 t 1 0 < 1 1 > d d = λ/4 λ Itesities of reflected radiatio: 0 1 r 0 r 1 1 r r I I ) ( ) ( I ) ( ) ( I = = + = + = Amplitude requiremet

7 Repetitio: Sigle Layer o absorptio, ifiite thickess absorptio, fiite thickess, reflexio at lower iterface Trasmitted itesity [%] d=100 m = =1.5 1 =1.57 0,4 0,5 0,6 0,7 0,8 Wavelegth [µm]

8 Repetitio: Reflectio Ehacemet I

9 Repetitio: Reflectio Ehacemet II A dielectric mirror cosists of a multilayer made from λ/4-coatigs with alteratig high (H) ad low (L) idices of refractio.

10 Magetic Properties I Motivatio: permaet data storage Logitudial Recordig Perpedicular Recordig

11 Magetic Properties II Motivatio: volatile data storage Spi Valve Magetic Radom Access Memory (MRAM)

12 Switchig "Switchig" of a magetic elemet meas the complete reversal of the magetizatio M by a exteral field H. To achieve this, the total eergy E of the elemet which results from M ud H has to be miimized. Eergy cotributios: Exteral field Stray field Aisotropy Exchage eergy Domai walls

13 Eergy Cotributios Grafik: Arbeitsgruppe Mikromagetismus, T. Schrefl

14 Eergy Cosideratio I Focus o the followig eergy cotributios: Exteral field Aisotropy Magetically aisotropic medium: z y easy directio H M x Magetizatio cosidered to rotate coheretly!

15 Eergy Cosideratio II Total magetic eergy (referred to uit volume); aisotropy costat K: z y easy directio M x E r r = M H + K si θ = M H H cos( φ θ) + K si θ = = M H x cosθ M H y si θ + K si θ Aditio theorem cos( φ θ) = cosθ cosφ + si θ si φ H x = H cosφ H y = H si φ

16 Magetic Reversal I H parallel to easy directio: M x K K M M H x A hysteresis loop is observable. H K = K M Exteral Coercitivity H K

17 Magetic Reversal II H perpedicular to easy directio: M y K K M M H y There is o hysteresis loop. M turs cotiously. Each itermediate positio is stable.

18 Further Cosideratios Magetic reversal may ot occur via coheret rotatio of M ia all cases. Further iflueces: Domai ucleatio Domai wall mobility Volume of magetized regios Superparamagetic limit: Volumia of magetized regios (bit size) ca become so small, that the aisotropy eergy ca be surpassed by thermal fluctuatios istability

19 Superparamagetic Limit Estimate: Typical aisotropy eergies: E Ais = J m 3 Thermal eergy withi a grai of volume V: 3 k B T k B T = EAis V V = l = l = 3 E T = 300K : l = m Ais k E B T Ais

20 Giat Mageto Resistace (GMR) Mageto Resistace is the pheomeo that the electric resistivity ca be iflueced by the directio of the magetizatio. The effect is based o differet scatterig probabilities betwee electros of equal ad opposite spis. It has extremely importat techological ad scietific applicatios (Nobel prize 007!): Hard disk readig heads Spi valves

21 Chemical Compositio For the chemical aalysis of thi filmsas well as for the aalysis of the surface of bulk materials a wide rade of physical aalysis methds is available. Most of these methods are based o the followig priciple: + Bombardemet of the material with probe particles + Detectio of the geerated radiatio or of the geerated particles Oly electro optic methods (TEM, LEED, RHEED) ad scaig probe methods (STM, AFM,...) do ot ecessarily ivolve this priciple.

22 Physical Aalytics - Survey

23 Electro Beam Micro Aalysis Iteractio volumes: Backscattered electros: approx. 1-5µm ejectio depth Secodary electros: ear surace regio Auger electros: approx. 10 m ejectio depth X-rays: approx. 1-5µm ejectio depth

24 Auger Electro Spectroscopy (AES) Characteristics: + Surface sesitive (ejectio depth 1 10 m) + Sesitive to light elemets + Sesitivity limit: approx. 0.1 At%

25 Eergy Cispersive X-Ray Aalysis (EDX) Ejectio volume Surface effects EDX-spectrum Nachweisgreze: ca. 0.1 At%

26 XPS, UPS Photoelectro spectroscopy by excitatio with X-rays (XPS) or UV-radiatio (UPS) Observable properties: + Electro work fuctio + Desity of states

27 EELS Electro Eergy Loss Spectroscopy Characteristics: + High lateral resolutio (TEM) + Sesitivity limit: ca. 1 At% + Possibility of local chemical mappig

28 SIMS, SNMS Secodary Io Mass Spectroscopy (SIMS) or Secodary Neutral Mass Spectroscopy (SNMS): Mass spectroscopy of directly sputtered ios (SIMS) or post ioized eutrals (SNMS): Characteristics: Cautio: Ioizatio cross sectio withi the bulk does ot correspod to the oe of a sigle atom " matrix effect " + High chemical sesitivity (mass spectroscopy) + Quatificatio possible (SNMS) + Sesitivity limit: ppm

29 LEISS Low Eergy Io Surface Spectroscopy Characteristics: + High surface sesitivity (1. Moolayer) + Absolute quatificatio possible (simple collisio mechaism)

30 GDOS Glow Discharge Optical Spectroscopy Characteristics: + Fast depth profilgg + Good chemical sesitivity + Reasoable quatificatio possible (Spectroscopy)

31 RBS Rutherford Backscatterig Characteristics: + No destructive depth aalysis + Quatificatio possible (Coulomb potetial)

$LEED Low Eergy Electro Diffractio W(100) 45 ev 145 ev Characteristics:$

32 LEED Low Eergy Electro Diffractio W(100) 45 ev 145 ev Characteristics: + Surface sesitive + Yields surface crystallography ad adsorbate positios

33 RHEED Reflected High Eergy Electro Diffractio Ideal situatio: Characteristics: + Surface sesitive + Yields detailed iformatios about growth modes (Layer By Layer/rougheig/stochastic)

Repetition: Micro Hardness

Repetition: Micro Hardness Repetitio: Micro Hardess Defied by the residual deformatio of a material due to the peetratio of a (ideally) udeformable test body. Test body material: + Diamod Test body geometries: + Vicers: Pyramid