Avogadro Project
• Redefine the kilogram based on the lattice constant and density of 28 Si.
• Final ~ 5 kg crystal grown in 2007
• Enrichment: 99.991% 28 Si
[P] ~ 5 x 10 11 cm -3
[B] ~ 5 x 10 13 cm -3
• Dislocation free!
G. G. Devyatykh et al., Dokl. Chem. 421, 157 (2008)
M. Cardona and M. L. W. Thewalt, RMP 77, 1173 (2005)
28
M. L. W. Thewalt, M. Steger, A. Yang, T. Sekiguchi
H. Riemann, 1 N. V. Abrosimov, 1 A. V. Gusev, 2 A. D. Bulanov, 2 A. K. Kaliteevskii, 3 O. N. Godisov, 3 P. Becker, 4 and H.-J. Pohl 5
1
2
3
4
5
31
b c
Cu
0
0 luminescence line. Formerly described as a 2-Cu-atom complex. We demonstrate that at least 4 atoms form this complex by observing five different combinations of the two natural Cu isotopes (63 & 65) through their different exciton binding energies.
Cu
3
Ag
1
, formerly known as Cu*. Thought to be a 2-Cu-atom complex (different than Cu
0
0 ). Via its isotopic fingerprint we can determine that it is a complex of 3 Cu and 1 Ag atoms.
This is a novel characterization method for many deep centers containing for example Cu, Ag, Au, Li and possibly Pt.
M. Steger, A. Yang, N. Stavrias, M. L. W. Thewalt, et al., Phys. Rev. Lett. 100, 177402 (2008) a a , A schematic of the transitions between the neutral donor ground state (D 0 ) and the bound exciton ground state (D 0 X). The two electrons (
) of D 0 X form a spin singlet which cannot couple to the hole (
), the nuclear spin, or the magnetic field.
b , Zeeman splitting of the D 0 and D 0 X states, and allowed optical transitions, numbered in order of increasing energy. c , Schematic for the optical polarization mechanism. A laser pumps neutral donors (D 0 ) in only one selected electronic and nuclear spin state into a D 0 X state. This decays to an ionized donor plus free electron by the predominant Auger decay of D 0 X; subsequent electron capture may then populate the opposite electronic spin state.
9
10
5
6
T = 2.0 K
B = 440 G
1
2
3
4
7
8
11
12
Laser Energy ( µ eV) 1,149,850 1,149,855
A photoconductivity spectrum of the 31 P bound exciton in the most perfect available sample of 28 Si.
Zeeman spectrum of the phosphorus bound exciton no-phonon transitions in a sample enriched to 99.991% 28 Si, at T=1.4 K with a
490 G magnetic field parallel to the [100] axis. For comparison, the spectrum of natural Si is shown, shifted to compensate for the dependence of the band gap energy on the average isotopic mass.
Spectra of the 31 P bound exciton in an n-type 28 Si sample, revealing electronic and nuclear polarizations obtained by selective optical pumping. At the bottom is a spectrum without any pumping. The upper three spectra show the PLE signal when the pump laser is located at the peak of either line 6, 6' or 8.
A. Yang, M. Steger, T. Sekiguchi, M.L.W. Thewalt, T.D. Ladd, et al., Simultaneous sub-second hyperpolarization of the nuclear and electron spins of phosphorus in silicon …, accepted for Phys. Rev. Lett. on June 3, 2009
A. Yang, M. Steger, D. Karaiskaj, M.L.W. Thewalt, et al., Optical detection and ionization of donors in specific electronic and nuclear spin states , Phys. Rev. Lett. 97, 227401 (2006)
77 Se
Absorption spectra of Se +
1S(T
2
)
7 of different combinations of impurity and host isotopic composition.
Transitions due to stable isotopes of Se are well resolved in the 28 Si: nat Se spectrum.
The 77 Se Hyperfine doublet dominates the spectrum of the 28 Si: 77 Se sample at the bottom.
( nat Si: nat Se spectrum used with permission of B. Pajot)
3445
Se
+
1 s ( T
2
) Γ
7 nat
Si: nat
Se nat
Si:
77
Se
28
Si: nat
Se
28
Si:
77
Se
74 76 78 80 82
3446 3447
Photon energy (cm
-1
)
T=1.5 K
3448
3446.6
77
Se
+
1 s ( T
2
) Γ
7
3446.4
3446.2
0 500 1000 1500 2000
Magnetic field (G)
2500 3000
The Zeeman splitting components of the 77 Se + 1S(T
2
)
7 transitions in
28 Si are shown as a fan diagram, where the brightness corresponds to the magnitude of the absorbance. The level diagram indicates the origin of the these components. 1S(A
1
) is the Se + ground state, and
e and
I are the electronic and nuclear spins, respectively.
M. L. W. Thewalt, M. Steger, A. Yang, et al., Physica B 401-402, 587 (2007)
High energy end of the IR absorption spectrum of boron
(B) doped nat Si and of 28 Si.
In 28 Si absorption lines are up to 20x narrower than in nat Si. Different B isotopes can be resolved.
The arrow marks the part shown in the spectrum below.
7 Γ
6
7 Γ
7 a
Low P
16 Γ
8
17 Γ
8 b
20 Γ
8 c d
9 Γ
7 e
10 Γ
6 g h f i j k l p,q,r s m,n,o t u v,w x y z aa ab ac ad ae af ag ah ai aj ak am an ao ap aq ar as al
28
Si
T=1.5K
at au av
10 B removed synthetically
5p
±
High P
6p
±
6h
±
7p
±
7f
±
7h
±
8f
±
8h
±
9f
±
355 356 357 358 359
Photon Energy (cm
-1
360
)
361 362 363
The top two spectra are from a sample with low-P concentration. All identified 10 B11 B pairs are labeled. The instrumental resolution is
0.006 cm −1 . The bottom spectrum and inset show phosphorus (P) absorption lines, both at a resolution of 0.02 cm −1 .
M. Steger, A. Yang, D. Karaiskaj, M. L. W. Thewalt, et al., Phys. Rev. B 79, 205210, (2009)