Karl Johnston

HRS

GPS

MEDICIS

Belgium CERN Denmark Spain Finland France Germany Greece Italy Norway Romania Sweden S. Africa Slovakia U. Kingdom Poland

x angle []

y a

ng

le [

]

-2 -1 0 1

-1

0

1

2

P+: 1.4 GeVLUCRECIA

ISS

Medical

Isotopes

ISS

Oct 16th 2017: 50 years of beams at ISOLDE1975

"

H. Haas„First results are described in theHMI-AR/1976. First conferencecontribution: HFI-IV in Madison(1977): 79Kr/Zn,Cd,Sb.

ISOLDE today offers the largest range of available isotopes of any ISOL facility worldwide. 1000 isotopes of >70 elements For materials science…yields

typically >1e7 s-1

10% of ISOLDE experimental programme (beamtime)Currently 22 approved experiments (out of 129)

Biophysics and medicine7%

Coulomb excitation22%

Nuclear Astrophysics6%

nuclear reactions3%

Nuclear structure from beta-decay21%

Nuclear structure from ground state properties

22%

reserve4%

Solid state11%

TISD4%

ISOLDE Pie 2016

SENSITIVITY / TRACEABILITY:Very low concentrations of radioactive impurity atoms in materials, surfaces or interfaces can be detected.

SELECTIVITY:Element transmutation due to radioactivedecay add chemical selectivity to “classical”spectroscopy techniques, e.g.,photoluminescence, resistivity,deep level transientspectroscopy...

NANOSCOPIC SCALE INFORMATION:Hyperfine interactions (ME, PAC, b-NMR)

local information on magnetic and electric neighborhood

e-, b-,b+, a Emission Channelingdirect and precise lattice site location.

Key features of RIB for materials research

PRODUCTION / AVAILABILITYElement and isotope

Variety, Intensity and Purity

MethodsInteractionsNuclear probes

Muons ß+

Positrons

Neutrons

Ions

NuclearReaction

ß+-e-

Interaction

HyperfineInteraction

CoulombInteraction

ScatteringDiffraction

Nuclear Reaction Analysis

Positron AnnihilationPositron Angular DistributionPositron Energy Distribution

Nuclear Magnetic resonanceNuclear orientation

Ion ChannelingBackscatteringElastic RecoilResonant ScatteringNeutron Scattering

DLTSPhotoluminescenceTracer Diffusion

RadioactiveNucleig, a, b

Radioactivedecay

Mößbauer effecte--g, g-g angular correlation

Emission Channeling

HyperfineInteractions

CoulombInteraction

ScatteringDiffraction

NuclearPhysics

SOLID STATEPHYSICS RESEARCH @ ISOLDE

Applying radioactivity to solid state physics

ISOLDE table of elements

Isotopes of this element used for solid state

physics or life science

NiCoCr

Pt

Workhorse probes:

111Cd, 199Hg, 117Cd, 57Mn, 73As

New promising probes:

68Cu, 149Gd, 172Lu, 151Gd, 197Hg

OnlineOffline

Offline labs at ISOLDE: B. 508

Staying relevant: Materials studied at ISOLDE

graphene Topological Insulators

Hyperfine techniques are particularly successful in unravelling subtle magnetic behaviour in materials

Dietl et al, Science 287 (2000) 1019

Next generation semiconductors: doping

Incoming 40-60 keV 57Mn+ beamIntensity: ~2108 57Mn+/cm2 Implantation

chamber

Mössbauer drive with resonance detector

Sample

Hyperfine Interactions with Mossbauer spectroscopy

Laser Ionised 57Mn beam : a new era for Mossbauer experiments at ISOLDE. 20th anniversary in 2016

• Very clean, intense beam of 57Mn (>3x108 ions sec-1)

• Allows collection of single Mossbauer spectrum in ~ 3 mins.

• Able to collect many hundreds over course of a 3 day run.

• Allows low concentrations of probe atoms to be used (~10-

4At%)

0

EAES

δ = EA - ES

E

v (mm.s-1)

I (v)

Isomer Shift Quadrupole Splitting

mI

21

2

31

2

ZZ

Q

eQVE

Lattice asymmetry Clustering of atoms

)()( 00sa

a -IS

Chemical bondingCharge states

Local information….

6 fold spectrum: characteristic of magnetic structure (at room temperature!!!).

Results in an external magnetic field show that the spectrum shown to be a

slowly relaxing paramagnetic system .

Gunnlaugsson et al (APL 97 142501 2010)

After high-dose implantations, precipitates ofFe-III are formed. These form clusters yieldingmisleading information about the nature ofmagnetism in ZnO (as reported by many groupsover the last number of years).

Gunnlaugsson et al APL 100 042109 (2012)

Fe: ZnO a ferromagnetic semiconductor?

(no!)

ZnO C axis

B

B

18

Fe

Sn

Green – reproducible good beamRed – low quality beam

19

181Hf(42d)

67 Zn(62h)

73Ga (5h)

Mössbauer periodic table

3.345 3.350 3.355

4.64 t1/2

1.99 t1/2

0.22 t1/2

0.98 t1/2

Energy (eV)

I10

3.360 3.365 3.370 3.375

Sb

4.64 t1/2

1.99 t1/2

0.98 t1/2

Energy (eV)

0.22 t1/2 10 100

No

rmal

ised

In

teg

rate

d

Inte

nsi

ty (

arb

.un

its.

)

Time (hours)

J Cullen et al Appl. Phys. Lett. 102 192110 (2013)

Ag Cd In Sn SbIs

oe

lectr

on

ic

Single

DonorGroup IV

impurityGroup V

impurity

ZnO: wideband gapsemiconductor

1. K. Johnston et al Phys Rev B 73 165212 (2006).2. K. Johnston et al Phys Rev B 83 125205 (2011).3. J Cullen et al Appl. Phys. Lett. 102 192110 (2013)4. J. Cullen et al Phys Rev B 87 165202 (2013)5. J. Cullen et al J. Appl Phys (2013)

• Radio PL allows for the subtle chemical identification of luminescence through different decay chains.

• Has allowed for the identification of neutral and ionised donors [1, 2], complexed impurities [3], “double donor” centres [2, 4], and isoelectronic centres [5].

Radiotracer PL has allowed for the full classification of the dominant impurities in ZnO

Implantation

Diffusion annealing up to

1800 °C

Sample serial sectioning by ion sputtering

Catching the sputtered ions by

a tape system (allow D < 10-

19m2/s)

In situ activity measurement

Remote control

DIFFUSION

New collaboration withUni Munster: diffusionprocesses in CIGS (CopperIndium Gallium Selenide)solar cells: in particular Cu

Why? Cu diffusion in CIGS: the entire literature...

Cu 1, Cu 2, Cu 3:• various authors,• various (electrical) methods

64Cu: • tracer experiment• bulk single-crystal CIS

Lubomirsky et al., JAP 83 (1998) 4678

10-15

10-13

10-11

10-9

10-7

10-5

1 2 3

450 300 200

64Cu in sc-CIS

Cu 1

Cu 2Cu 3

Ag

1/T (10–3

K–1

)

D (

cm

2s

-1)

T (°C)

Beamtime scheduled for Nov 2017

Emission channeling: (b-, b+, c.e., a)

b- decay, CE

electron yield

angle

What do you need to do Emission Channeling

Position-sensitivedetector

Vacuum chamber

Goniometer

Lattice sites of 27Mg in different pre-doped GaN

● Electron emission channeling

patterns show mix of substitutional +

interstitial 27Mg

● Interstitial Mg fraction highest in p-GaN:Mg

● Lowest in n-GaN:Si

Direct evidence for amphoteric character of

Mg that is coupled to the doping type

● Site change interstitial - substitutional MgGa

Activation energy for migration of interstitial

Mg: EM » 1.3 - 2.0 eV

-2

-1

0

1

2

-1 0 1 2 3

(01-

10)

(11-20)

(11-20

)

(01-

10)

1.42 - 1.50

1.33 - 1.42

1.25 - 1.33

1.16 - 1.25

1.07 - 1.16

0.99 - 1.07

0.90 - 0.99

0.82 - 0.90

-1 0 1 2 3

-2

-1

0

1

2

(11-20

)

(11-20)

(b) best fit

1.42 - 1.50

1.33 - 1.42

1.25 - 1.33

1.16 - 1.25

1.07 - 1.16

0.99 - 1.07

0.90 - 0.99

0.82 - 0.90

-1 0 1 2 3

-2

-1

0

1

2

(01-10)

(01-

10)

(11-

20) (11-20)

(d) 100% Mgi(c) 100% SGa

1.59 - 1.70

1.48 - 1.59

1.37 - 1.48

1.26 - 1.37

1.15 - 1.26

1.04 - 1.15

0.93 - 1.04

0.82 - 0.93

-1 0 1 2 3

-2

-1

0

1

2

(01-10)

(11-20)

(a) experiment

1.34 - 1.43

1.26 - 1.34

1.17 - 1.26

1.08 - 1.17

1.00 - 1.08

0.91 - 1.00

0.82 - 0.91

0.74 - 0.82

0 100 200 300 400 500 600 700 800-5

0

5

10

15

20

25

30

35

Interstitial 27

Mg (t1/2

=9.5 min) in GaN of different doping types

Arrhenius step models:

N=1 EM

=2.0 eV

N=105 E

M=1.3 eV

implantation current [pA]: 0.20 0.27 1.4-3.0

nid-GaN

p-GaN

GaN:Mg

n-GaN:Si

inte

rsti

tial

27M

g [

%]

implantation temperature T [°C]

Phys. Rev. Lett. 118, 095501(2017)

Nobel Prize in Physics 2016

"for theoretical discoveries of topological phase transitions and topological phases of matter"Source: "The Nobel Prize in Physics 2016". Nobelprize.org. Nobel Media AB 2014. Web. 4 Dec 2016.

<http://www.nobelprize.org/nobel_prizes/physics/laureates/2016/>

Semi-metalic surface states originatingfrom non-trivial topology of theelectronic band structure in the bulk(insulator)

Dirac fermions at the surface(equivalent to graphene)+ spin-locking → spin current in a non-magneticmaterial

(spintronics, quantum computation...)

Z2 topological insulators: time reversal symmetry

Topological crystalline insulators: crystal mirror symmetry

Nature Physics 8, 800 (2012) Nature Materials 13, 178 (2014)Phys. Rev. Lett. 112, 186801 (2014) Nature Communications 3, 982 (2012)

Topological insulators

cubic

rhombohedral

Pb, Sn or Ge

Te

PbTe

↓

(Pb,Sn)Te

↓

SnTe

↓

(Ge,Sn)Te

↓

GeTe

topologicalcrystallineinsulator

(TCI)

ferroelectricRashba

semiconductor(FERS)

Topological crystalline insulators

Rhombohedral distortion: breaking crystal mirror symmetry

Perturbed angular correlation

... with hyperfine interactions

0.0 0.1 0.2 0.3 0.4

-2

-1

0

1

2

3

Vzz [

1

02

1 V

/m2]

r [Å]

GeTe

SnTe

PbTe

technique parent t1/2 Q [b]

Pb PAC 204mPb 67 min 0.44

Sn eMS119In 2.4 min

0.094119mSn 293 d

Ge PAC 73As 80 d 0.70

𝜔𝑄 or ∆𝐸𝑄 ∝ 𝑄 𝑉𝑧𝑧

Δr

density functional theorycalculations

to establish relation between measure HFI parameters and

structural parameters

... with hyperfine interactions

Δr

-10 -5 0 5 10

exp.

fit

Sn2+

Sn0

Sn4+

velocity (mm/s)

95 K

50 100 150 200 250 3000.0

0.1

0.2

0.3

0.4

0.5

E

Q (

mm

/s)

T (K)

119In → 119Sn emission Mössbauer (PbTe)

> <10 % precision in Δr (corresponding to < 0.05 Å)

> non-regular sites: OK

> damage: OK

Proof-of-principle with

most challenging case:

> PbTe is cubic

> smallest Δr (< 0.10 Å)

> 119Sn – smallest Q

Mossbauer spectroscopy

See also:

Successful emission channeling measurements on topological insulators

-1

0

1

2

3

<211>

<111>

<110>

0.94

0.99

1.03

1.08

1.13

1.17-1

0

1

2

3

-2 -1 0 1 2

-2 -1 0 1 2

-2

-1

0

1

2

-1

0

1

2

3

<211>

<111>

<110>

-1

0

1

2

3-3 -2 -1 0 1

-3 -2 -1 0 1-3

-2

-1

0

1

2

0.94

0.99

1.05

1.10

1.16

1.21

56Mn (2.6 h)

• Mn as magnetic dopant

• EC is used to determine the lattice location

123Sn (40 min)

• parent: 123In

• isotope used for first time for EC

• EC is used to characterize the distortion

Mn-doped PbTe Sn-doped PbTe

…with emission channeling

Combination with multitude of techniques, at ISOLDE and beyond, and strong link to theory

Challenges

• Still a niche field, unfamiliar beyond the core community, or necessarily small: emission channelling needs to be attached to an ISOLDE …

• Limitations with beamtime shift requests can be comparatively modest compared to nuclear physics. only one run a year….(Mossbauer work previously mentioned took about 2.5 years to complete).

• Core community e.g. in Germany not being renewed, nuclear solid state physics not popular at home labs: licenses etc… Leads to problems with training.

• Pace of materials science is very fast… difficult to react to new developments/materials….experiments which don’t get beam within one year can lose relevance….

• Safety administration becoming ever heavier

New developments

• Upgrading of detectors/spectrometers/upgrade DAQ.

• LaBr and CeBr detectors, allow for wider range of probes to be used.

• Spectrometer for biophysics for Mossbauer spectroscopy.

CERN-MEDICIS: new Facility for medicalisotopes (and solid state/materials?)

36

HRS

Summary• Solid State programme at ISOLDE: well established and a unique

combination of techniques on site.

• Varied experimental programme capable of resolving otherwise difficult problems. Remaining relevant in spite of the difficulties in obtaining beam time..

• New developments should help make spectrometers more user friendly

• Possible link with MEDICIS could allow for wider community to be served (beyond ISOLDE)

•

Funding and Acknowledgements

• Manfred Deicher, Herbert Wolf, University of Saarlandes, Germany• Juliana Schell University of Essen, Germany• Guilherme Correia, Uli Wahl ITN, Lisbon, Portugal• Lino Pereira, KU Leuven• Martin Henry, Dublin City university, Ireland• Monika Stachura, TRIUMF• Bruce Marsh, Sebastian Rothe, Valentin Fedesseov, CERN