Pressure Optical Sensors for Diamond Anvil Cell

Transcription

1 Pressure Optical Sensors for Diamond Anvil Cell Jesús González CENTRO DE ESTUDIOS DE SEMICONDUCTORES Facultad de Ciencias, Departamento de Física, Universidad de Los Andes Mérida, Venezuela Alfa Meeting Highfield Vienne 26 th to 30 th April 2004

2 A Slice of DAC

3 An open DAC The pressure changing machine

4 Shematic optical set-up Modulator DAC with light focussed on ruby Beam splitter Argon laser Neon lamp Focussing lens Primary Objective Secondary Objective Exit lens Eyepiece Screen

5 Ruby luminiscence Spectra

6 Photo luminiscence of Ruby at 300 K RUBI (Al 2 O 3 :Cr 3+ ), luminiscence, R 1 -R 2 splitting λ (R 1 ) = 6942 A 0 Γ= 6 A 0

7 Lineal variation as compare with the equation of state of Decker for NaCl, valid up to 30 GPa λ/ P = A 0 Kbar -1 λ/ P = cm -1 Kbar -1

8 Fixed Point scale

9 Criostat for pressure measurements at low temperatures

10 Low temperature photoluminiscence spectra of ruby 9000 Photoluminiscence (A.U) Al 2 O 3 : Cr K 296 K wave number (cm -1 )

11 Ruby at Low Temperatures : in-situ termometer 10 < T < 100 K, T=A/ln(ηI 1 /I 2 ) A = / K= K = 29.1 cm -1 between 10 and 100 K (splitting between R 1 and R 2 ruby lines) K Boltzmann s constant η= quantum efficiency between R 2 and R 1, transition η= Under hydrostatic conditions the calibration was done up to 12 GPa. The relative error in T is less than 10% between 12 and 25 GPa. The pressure is given by the shift of the ruby line R 1 P (GPa) = 380.8[(σ 0 /σ) 5-1] σ 0 = cm -1, T< 108 K

12 Range 108< T < 300 K T (K) = [A 1 -A 2 / 1+(T-T 0 ) p ]+ A 2 A 1 = , A 2 = , p=1.188, T 0 =1.966 The pressure is given by P (GPa) = 380.8[(σ 0 /σ) 5-1] σ 0 is not constant in this range and is given by: σ 0 (cm -1 ) = (T-108) (T-108) 2

13 Equations for pressure measurements Under cuasi-hydrostatic conditions, for pressure bigger than 30 GPa: P (Mbar) = 3.808[( λ/6942+1) 5-1] λ (nanometers) In He: P (GPa) = 0.274x λ R1 (0)/7.665[{λ R1 (P)/ λ R1 (0)} ] λ (nanometers)

14 Major drawbacks of Ruby The R 1 line belongs to a doublet and its line width is very sensitive to nonhydrostatic stress and to temperature. In the presence of one or both factors, the doublet broadens, which results in the overlapping of the two lines and the formation of a broad asymmetrical band. The accuracy of the pressure measurement is then significantly reduced The signal-to-background ratio of the fluorescence rapidly decrease above 700 K. A similar effect is observed in nonhydrostatic environments, making the measurements difficult above 100 GPa The R 1 line presents a relatively large wavelength shift with temperature and any error in the temperature measurement will directly contribute to an erroneous determination of the pressure

15 Fig 24: Rubi Lumenescense at 5 kbar Fig 25: Samarium Luminescence at 40kbar Luminescense / Arbritary units ºC 75ºC 125ºC 175ºC 225ºC 275ºC x ºC x 10 Luminescence / Arbitrary units ºC 125ºC 175ºC 225ºC 275ºC 325ºC 400ºC Wavelength / nm Wavelength / nm

16 SAMARIUM (SrB 4 O 7 :Sm 2+ ) Fluorescence of line 7 D 0-5 F 0 λ 0-0 = A 0 Γ= 1.4 A 0 Up to 120 GPa at 300K λ 0-0 (P)= P + 8.9x 10-4 P 2

17 Luminescence spectra of (a) ruby and (b) of the Samarium at Gpa in helium. The laser power was 10 mw and the accumulation time, 10 s. The star indicate the plasma lines from Ar + laser

18 Luminiscence spectra of the Samarium compound and of ruby in ice (H2O). The stars indicate the plasma lines from the Ar + laser. (a) Ruby at 95 Gpa. The laser power (P 1 ) was 13 mw and the accumulation time (t acc ), 10s; (b) Samarium at 95 Gpa (P t =13mW, t acc =10 s) and, in the inset, at 130 Gpa (P t =13 mw, t acc =20 s)

19 SAMARIUM λ 0-0 (T> 500)= 1.06x10-4 (T-500)+1.5x10-7 (T-500) 2 Pressure and temperature In- Situ measurements with both sensors T= ( λ R λ 0-0 )

20 Calibration of the wavelength shift of the 7 D 0-5 F 0 line of samarium and he R 1 line of ruby with temperature at ambient pressure. Solid line: linear fit to the ruby data from 300 to 600 K ( λ R1 / T=7.3x10-3 nm/k); dashed line: quadratic fit to the ruby data between 600 and 800 K

21 Calibration of the 7 D 0-5 F 0 line wavelength shift with pressure in helium. Squares and up-triangules: incresing prresure runs; circles and down-triangules: drecrease pressure run; the solid line is a numerical fit to the experimental data: P λ = 2 λ λ The dotted line is the linear fit (P= λ0.255 obteined by Lacam et al. In 4:1 M-E mixture up to 20 GPa

22 High Temperatures External Resistive Furnaces up to 900 K in the air, and up to 1400 K in the vacum or inert gas. Ruby: 300< T< 600 K lineal law λ R1 / T= 7.3x10-3 nmk < T < 1300 K λ R1 = x10-3 T+5.5x10-6 T 2 T=T-600

23 External Heater

24 High Temperature Setup

25 Diamond Types Type Ia = contains nitrogen in clusters (aggregates) Type IaA contains predominantly A- aggregates (pair of nitrogen atoms, forms at lower geological temperatures) Type IaB contains predominantly B- aggregates (four nitrogen atoms surrounding a vacancy, forms at higher geological temperatures)

26 Many type Ia diamonds contain similar amounts of A- aggregates as well as B- aggregates and are the called type laa/b. In these stones one can frequently detect a certain amount of N3 centers, which cause the light yellow coloration of "cape" diamonds. Nitrogen may also be present in platelets which have a large extent and low thickness and which represent probably a structure of carbon and nitrogen atoms

27 Type Ib = contains mostly isolated substitutional nitrogen (i.e. one nitrogen atom substitutes one carbon atom)

28 Type IIa = does not show any impurity-related absorption in the UV, visible or infrared parts of the spectrum (the optically most transparent diamonds) Type IIb = contains boron as an isolated substitutional impurity, is therefore electrically conductive and always has a gray to blue color. Stones with a very low boron content may appear near colorless Type IIc = type II diamonds which contain hydrogen as a substitutional impurity with a dominating absorption around 2900cm -1 in the infrared

29 INFRARED ABSORPTION OF DIFFERENT TYPES OF DIAMOND

30 Firts Order Raman

31 Second Order Raman

32 Raman Sintetic Diamond

33 FTIR Diamond IIa

34 FTIR diamonds Ia, IIa and IIb