VITO–Versatile Ion-polarized Techniques On-line at ISOLDE (former

CERN-INTC-2013-013 / INTC-O-017

29/05/2013

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

Letter of Interest

to the ISOLDE and Neutron Time-of-Flight Committee

VITO – Versatile Ion-polarized Techniques On-line at ISOLDE

(former ASPIC UHV beamline)

29 May 2013

M. Deicher

, M. Stachura

, V.S. Amaral

, M. Bissell

, J.G. Correia

, A. Gottberg

, L. Hemmingsen

S-W Hong

, K. Johnston

1,2

,Y. Kadi

2,8

, M. Kowalska

, J. Lehnert

, A.M.L. Lopes

, G. Neyens

K. Potzger

, D. Pribat

, N. Severijns

, C. Tenreiro

8,10

, P.W. Thulstrup

, T. Trindade

, Th. Wichert

H. Wolf

, D.T. Yordanov

, Z. Salman

University of Saarlandes, Saarbrücken, Germany

PH-Department, ISOLDE, CERN, Switzerland

3 University of Aveiro, Aveiro, Portugal

4 KU Leuven, Leuven, Belgium

5 University of Lisboa, Lisboa, Portugal

6 CSIC, Madrid, Spain

7 University of Copenhagen, Copenhagen, Denmark

8 Sungkyunkwan University, Seoul, Korea

9 Helmholtz-Zentrum Dresden-Rossendorf, Germany

10 University of Talca, Chile

11 Max-Planck Institute, Heidelberg, Germany

12 PSI, Villigen, Switzerland

Spokesperson(s): M. Deicher (manfred.deicher@tech-phys.uni-sb.de)

M. Stachura (monika.stachura@cern.ch)

Local contact(s): M. Stachura (monika.stachura@cern.ch)

A. Gottberg (alexander.gottberg@cern.ch)

K. Johnston (karl.johnston@cern.ch)

Initial Remark

This letter of interest expresses the wide and general motivation of performing numerous

experiments at a dedicated beamline for producing polarized beams at ISOLDE/CERN by

modifying the former UHV beamline hosting the ASPIC apparatus. The usual letter of

intents and full proposals for beamtimes at ISOLDE will be submitted to the INTC

committee after the approval of the upgrade of the UHV beamline by the ISCC committee

in July 2013. The presented scientific program in the near future will request approx.

70 shifts which will be spread over several runs for a period of 2 years, starting in 2014.

The planned upgrade of the UHV beamline is to be presented to the ISCC committee in July

2013. The major enhancement will be introducing the laser-based nuclear spin polarisation

of the isotope beam at RB0 line, which will allow for establishing β-NMR and

beta-asymmetry studies in a wide range of sample environments realized in all end-stations.

Figure 1. An overview of the beamline system at ISOLDE around RB0.

1 SCIENTIFIC MOTIVATION

The interest in using polarized beams for addressing various scientific phenomena has

constantly increased over the past few years. Only at ISOLDE, there is one and frequently

running experimental setup employing such beams (COLLAPS), besides other systems such

as NICOLE or more recently the tilted foil setup using post-accelerated isotopic beams.

However, neither of them provides the particular specifications needed for either of the

following cases without major modification.

Therefore, we aim to establish a dedicated beamline for laser-induced nuclear orientation, which will

open a wide range of possibilities for carrying out versatile and multidisciplinary experiments at

ISOLDE by modifying the existing UHV beamline at the RB0 branch.

As shown in figure 2, the new beamline will provide three end stations after the intended

upgrade: the ASPIC end station, the β-NMR spectroscopy end station and an open station

for movable experiments requiring rare polarized ions e.g. for nuclear or fundamental

physics studies. The UHV and low temperature ASPIC station will remain for PAC studies

on sensitive surfaces and interfaces (see suggested experiments by M. Deicher et al.,

V. Amaral et al., and J. Röder et al., in section 2.1) and shall later be extended for β-NMR

spectroscopy (suggested experiment by Z. Salman in section 2.1). The second station will

be open for movable experiments or UHV environment. The β-NMR spectroscopy station

will be equipped with a strong differential pumping system allowing for online bio-β-NMR

on liquid samples (suggested experiment by L. Hemmingsen in the section 2.2) and online

PAC spectroscopy in volatile matter, such as biochemically relevant aqueous solution.

Furthermore, after chamber exchange, this station will allow for other, non-biological

experiments e.g. for weak interaction physics research (suggested experiment by

N. Severijns and G. Neyens, and D.T. Yordanov et al., in section 2.2). A short description

of the two permanent end stations is presented below.

Figure 2. A schematic view of the three end stations.

1.1 The ASPIC end station

The Apparatus for Surface Physics and Interfaces at CERN (ASPIC) achieves high

resolution of local electronic and magnetic properties and high surface sensitivity at the

same time. Therefore it combines nuclear Perturbed Angular Correlation (PAC)

spectroscopy with state-of-the-art sample preparation and manipulation hosted in a

common ultra-high vacuum system. Samples can be prepared in-situ by molecular beam

epitaxy (MBE), argon ion beam sputtering and heat treatment between 77K and 2800K. A

low energy electron diffractometer (LEED) and an Auger spectrometer (AES) are in place

for chemical and structural characterisation. A base pressure of 10

-10

mbar ensures the

required high surface quality throughout the time required for detailed measurements.

Once the sample is prepared, suitable radioactive probe nuclei are collected from ISOLDE

through a dedicated UHV beamline and transferred to the sample’s surface by soft-landing,

where the ions are deposited with thermal energy only on top of the first atomic layer.

Additional preparation steps help to integrate the probes into defined crystalline sites on the

surface or at an interface. Different detection geometries allow for PAC spectroscopy along

and perpendicular to all surface directions at variable temperatures (4K to 500K) and

variable magnetic field (0.01T to 0.8T).

The setup has been successfully used from 1990 until 2008, generating numerous results of

relevance in the field of the interaction of single add-atoms with magnetic metallic surfaces.

In 2009 it was left in a widely operating state under conserving conditions. In 2012 the UHV

chamber was re-started and the individual connected elements were mostly commissioned,

repaired or replaced by existing spares.

1.2 The β-NMR spectroscopy end station

Nuclear spin polarization induced by circular polarized laser light [1] appears to be the most

appropriate technique for a β-NMR end station for applied research since it does not require

stopping or extreme cooling of the ion, and it has provided very good and reproducible

results for over a dozen of isotopes. After passing the polarization section, the ion beam is

implanted into the NMR sample placed inside a strong magnetic field of some kG. Due to

both, the high degree of nuclear polarization and the sensitive detection of asymmetry via

the beta decay as little as 10

nuclei are required for observing a resonance, compared to 10

for conventional NMR spectroscopy. Except for this difference, β-NMR spectroscopy

provides the same information as conventional NMR: chemical shifts, line broadening or

relaxation times providing information about energies and dynamics of chemical bonding.

The best polarization schemes are found by identifying strong transitions in atomic-

transition databases, performing atomic calculations which involve coupled differential

equations for light absorption and emission, and finally testing the schemes “online” with

radioactive beam from ISOLDE. For

29,31

Mg such schemes have been already identified (see

[2] for details on the calculations and their comparison to experimental data). For Cu strong

excitation schemes have been already used online [3] (see figure 3), so calculations and

“online” polarization tests have good starting points. For Zn, the candidate transitions have

been identified and they will be tested on radioactive beams in 2014 [4].

Figure 3. Top: Hyperfine splitting of the 2S1/2 and 2P3/2 levels for a Cu isotope nuclear spin I = 1. Bottom:

Hyperfine spectra for 64Cu and 66Cu, observed in fluorescence (not β-asymmetry). Reprinted from [3].

A prototype spectrometer was successfully tested in August 2012, when the first β-NMR

spectrum was recorded on a liquid sample. This spectrometer will be available for use at this

end station.

2.1 The study cases at the ASPIC end station

2.1.1 Surface mediated magnetism in metal-oxide semiconductors

M. Deicher, K. Johnston, J. Lehnert, Th. Wichert, H. Wolf

Dilute magnetic semiconductors (DMS) are of great interest due to their potential

applications in spintronics, which uses the electronic and magnetic properties of the

semiconductor [5]. Especially, transition metal doped wide band gap metal oxide

semiconductors, such as ZnO, are expected to exhibit ferromagnetism at room temperature

[6]. A large number of studies on ZnO based DMS has been reported, but there is no clear

agreement about the nature and origin of the ferromagnetism in this system. However,

many studies, both experimental and theoretical, during the last years show strong evidence

that defect-induced magnetism is a key mechanism for ferromagnetism in ZnO as well as in

other non-magnetic oxides with a Curie temperature above room temperature. It seems that

doping with magnetic elements is not the only and most promising way to achieve magnetic

ordering in these oxides. The introduction of intrinsic defects of the order of a few percent,

such as vacancies (with or without doping with magnetic or non-magnetic ions) plays a

dominant role in triggering magnetic ordering.

It has been shown both for thin ZnO films [7] and nanostructured ZnO [8,9] that surface

defects which can reach high concentrations play a critical role for achieving

ferromagnetism in ZnO. There is also evidence that room-temperature ferromagnetism can

be triggered by hydrogen adsorption at the surface of ZnO [10]. The ASPIC setup allowing

the soft landing of radioactive isotopes on surfaces and nuclear spectroscopic techniques like

PAC opens the possibilty to gain microscopic information both on the magnetic and

structural properties of ZnO surfaces.

PAC studies using the probe atom

111m

Cd:

• Determine via magnetic hyperfine interaction the magnetic properties of surfaces of

undoped ZnO with different native defects (O or Zn vacancies).

• Investigate the effect of native surface defects and hydrogen-related defect complex on

ferromagnetism on undoped ZnO.

• PAC experiments on the ferromagnetic interplay between surface defects and transition

metals in ZnO.

Estimated number of shifts: about 10 shifts for

111m

Cd.

2.1.2 Interaction and Dynamics of add-atoms with 2-Dimensional Structures

(PAC studies of mono- and low- number of stacking layers)

V.S. Amaral, A. Gottberg, J.G. Correia, K. Johnston

Y. Kadi, S-W Hong, D. Pribat, J. Röder, L. Hemmingsen, V.M. Pereira, K. Potzger,

T. Trindade, J.P. Araújo, A.M.L. Lopes, C. Tenreiro, A.S. Fenta, S. Cottenier, S. Casassa

IDADS Collaboration

An international collaboration is being settled by grouping people and institutes from

Belgium, Chile, Denmark, Italy, Korea, Portugal, Singapore and Spain to establish the (so

far called) IDADS-Collaboration, aiming the study of interactions and dynamics of add-

atoms with two-dimensional – single or few – atomic layers with the Perturbed Angular

Correlation – PAC – technique. Graphene and derivate structures and new bi-dimensional

materials like dicalcogenides (e.g. MoS

, MgB

) are the substrates where radioactive probe

atoms will be deposited with the soft-landing technique under the UHV conditions

proportionated by the ASPIC setup at ISOLDE. The hyperfine fields obtained under such

clean environment are expected to reveal in detail the basic bricks of the 2D surface’s unique

phenomena.

1 Motivation in brief

Graphene presents unique physical and structural properties, and has captured the attention

of a large number of researchers, as a strong candidate for a variety of electronic and energy-

related devices and structures. It has recently been chosen as the subject of one of the two

Europe’s first 10-year FET flagship projects, and a R&D roadmap was elaborated. Among

the properties of graphene outstands the tuneable electronic transport properties, with

exceptional quantum characteristics associated to the massless Dirac fermions

characteristics. Its stiffness, stretchability and impermeability, as well as optical absorption

features are also distinctive. From a technological point of view, devices like ultrahigh

frequency transistors, ultrafast photoactive structures, and transparent flexible electrodes for

optoelectronics or photovoltaics were demonstrated and are being developed, combining

also graphene with other 2D materials, such as atomically thin boron nitride or

molybdenum disulfide. The growth of graphene (single or multiple) layers on metallic and

semiconducting surfaces, which can then be transferred, goes already beyond wafer

dimensions (several cm

). Moreover, the low electronic noise in graphene makes its

properties very sensitive to the presence of add-atoms or molecules (e.g. for sensors) and the

manipulation of its properties by chemical functionalization is also focus of strong attention.

In the context of condensed-matter physics, radioactive ion beams and associated nuclear

techniques available at ISOLDE-CERN have been applied to modify (dope) and probe

materials with the exceptional possibility to “see and feel” at the nanoscale, to determine the

positions and functions of atoms and electrons, of electric and magnetic fields, at a certain

element/isotope with extreme sensitivity (doses of ppm or less). By using the soft-landing

technique of add-atoms, ASPIC @ ISOLDE, allows doing all of this unique research under

UHV conditions at surfaces and interfaces.

2 Case Studies

The opportunities for the application of radioactive ions in the study of graphene are

numerous. The hyperfine properties of pure graphene were addressed theoretically, in the

presence of a sea of 2D Dirac electrons, with a linear dispersion and the role of spin

coherence relaxation mechanisms with nuclei for spintronics and quantum information

processing applications was highlighted. The presence of a probe was not considered,

although.

We propose to use Perturbed Angular Correlations (PAC) to study the interaction of the

add-atom probe element, nucleus and the surrounding electrons with the surfaces, by

assessing the Electric Field Gradient and the Hyperfine Magnetic Fields. Following the

LOI132 first studies, drafted below, we will address the following topics of add-atoms

physics that require the UHV ASPIC environment:

1- Charge renormalization in graphene was predicted to change considerably the electron

motion in a strong Coulomb field of an ad-atom impurity, leading to quantum relativistic

atomic collapse and the supercritical instability already at charges Z~1-2 in contrast to the

heavy nuclei charge (Z>170) for free atoms. The crossover was very recently observed by

Scanning Tunnel Microscopy in clusters of charged Ca dimers on electronically gated

graphene on BN, thus, producing resonances in conductivity. It is our intent to probe such

catastrophic charge renormalization phenomena using hyperfine effects with radioactive ions of different

valences soft-landed onto graphene.

2- The concept of topological insulator (TI), or Quantum spin-Hall state was predicted initially to

occur in graphene, but such new quantum state, with spin-filtered edge states (quantized

conductance, with opposite spin electrons propagating in opposite directions), were first

observed in HgTe quantum wells and in the surface states of Bi2Se3 and other materials

with sufficiently strong spin-orbit coupling Recently, graphene as a viable candidate for TI

was revived by predicting that a few % of heavy add-atoms (In, Os, Ir,.. ) can produce a

robust gapped topological insulator state. However, the mechanism is still controversial,

either involving electron tunnelling from graphene onto an add-atom or considering that

despite their dilute character add-atoms form impurity states that hybridize with graphene.

Further, it is found that the electronic structure of add-atoms (e.g. Co) deposited on back-

gated devices, could be tuned by application of voltage and screening clouds around a single

atom as large as 10 nm observed. Such tunability by external control and the emergence of

extended screening effects are fundamental for electronic applications. These issues highlight

the need for locally and internally probing the add-atom physics on graphene, which we here propose

now by using the PAC technique within the ASPIC environment.

3- Physics of add-atoms on other 2D materials, such as MoS

, MgB

and similar dichalcogenides, is

also poorly known in spite of its importance for understanding the catalytic properties, and

for helping the designing of heterostructures with tuned properties, for which the first

examples start to appear. Again these are ideal subjects to be addressed with add-atoms probed by

PAC under the UHV environment of ASPIC.

4- Addressing the preparation of isotopically pure graphene layers or their modifications. Study of the

growth on transition metal template coatings/ substrates. Graphene synthesis by ion

implantation was demonstrated (carbon implanted at 30 keV on metal (Ni)

coatings/substrates, and subsequently segregated to the surface at lower temperature). The

use of add-atoms probes of PAC within the UHV ASPIC environment challenges our understanding of

these processes and in-situ doping.

5- Studying of nucleation of nanostructures and clusters on graphene and related phases requires

the complementary use of ASPIC and wet chemical methods.

Graphene and graphene oxide have been investigated as new platforms for growing

semiconductor nanostructures aiming diverse devices, such as quantum dots. Fundamental

studies that address their nucleation are lacking. We intend to monitor the nucleation of

CdS nanophases on graphene sheets. This task will involve the controlled generation of CdS

seeds, in situ, using wet chemistry methods developed in our laboratories. Radioactive

111m

Cd will be implanted in the CdS precursors and then synthetic samples will be analysed

for distinct reaction times to inquire the local environment of the CdS dots on the graphene

surface. Complementary studies in UHV will allow comparing the Cd local environment and the role

of solvent (water).

3 Short report on LOI I132: Radioactive Local Probing and Doping on Graphene

Experiments were performed using radioactive

111m

Cd/

111

Cd and

199m

Hg/

199

Hg on graphene

laying into Si/SiO

wafers and PET polymer sheet substrates. Additional experiments on

related materials, like graphite, graphene oxide and carbon nanotubes suspensions were

done for comparison. On these preliminary studies two different methods were used to

deliver the isotopes to the sample’s surfaces. The first method consisted on implanting the

ions on ice that, once melted, was used to wet the samples until some ions bind to graphene.

In the second method, direct implantation of radioactive ions through graphene samples

standing on a Si/SiO

wafer, was followed by subsequent annealing up to 800 º C and 1100

º C, in order to promote the diffusion of ions from the substrate to the graphene interface.

The aim was to study the process of recovery of the substrate and graphene itself after

suffering the 50kV ion beam bombarding. From these experiments we got amazing results

regarding the determinant contribution of the still surviving graphene layer to the damage

recovery of the implanted substrates (to be reported in detail elsewhere).

Hereby, are shown results obtained at different temperatures, after wetting with melted ice

containing

111m

Cd and

199m

Hg, the graphene samples laying at PET and Si substrates: Figure

4 and Figure 5 show the experimental PAC observable, the R(t) function, as measured in

graphene on Si and PET substrates with

111m

199m

Hg. The different spectra show multiple

Electric Field Gradients, which reveal that the substrate is able to influence the binding of

Hg and Cd ions to graphene. Due to the temperature dependence of the R(t) spectra, we

further believe that water molecules are interfering with the bonding, and consequently,

with the places where the Cd and Hg metal ions sit. DFT first principle simulations are in

progress, which model atomic configurations containing metal ions and water molecules on

graphene, aiming to reproduce the experimental data and help on explaining the interaction

of metal ions with graphene in, e.g., catalytic processes.

Figure 4. R (t) functions and respective Fourier Transforms (FT) obtained using PAC, with

111m

Cd isotope,

measured at room temperature (RT) and 3 º C. The samples analyzed were graphene on PET - a) and b), and

graphene on Si - c) and d).

Figure 5. R (t) functions and respective Fourier Transforms (FT) obtained using PAC, with

199m

isotope, measured at 3 ºC. The samples analyzed were graphene on PET - a), and graphene on Si - b).

Estimated number of shifts: 18 shifts, (over two years) regarding the following probes:

Br/

Se,

Se/

(M)

80m

Br/

Br,

111m

Cd/

111

Cd,

111

In/

111

Cd,

140

La/

140

(M)

147

Gd/

147

(M)

172

Lu/

172

Yb,

199m

Hg/

199

Hg. (M) accounts for magnetic probing only.

0,0

0,1

R(t)

(a) graphene/PET, T=RT

0 100 200 300

0,0

(b) graphene/PET T=3ºC

0 100 200

time (ns)

Ω (Mrad/s)

R(t)

0,0

0,1

0 100 200 300

0,0

(d) graphene/Si,T=3ºC

0 100 200

time (ns)

Ω (Mrad/s)

0 5 10 15

0,0

0,1

(a) graphene/PET, T=3

0 2000 4000

time (ns)

Ω

(Mrad/s)

0 5 10 15

0,0

0,1

(b) graphene/Si, T=3

time (ns)

Ω (Mrad/s)

0 2000 4000

2.1.3 Surface and interface investigations of first, second, and third

generation solar cells using ASPIC

J. Röder, A. Gottberg, T. Beckers, M. Martin

Solar cells of the third generation use multilayers of different semiconductors to overcome

the Shockley-Queisser efficiency limit for conventional first generation solar cells. This

limits the efficiency of converting the power of irradiated sun light to electrical power

theoretically to about 34% up to about 87% for an infinite number of layers. Laboratory

examples have already shown efficiencies of more than 43% while best examples one layer

silicon cells may reach 25%. Understanding the behaviour of complex multilayer systems as

shown in Figure 6 below is crucial for their implementation and in addition for addressing

aging processes. At contact of interfaces additional phases may form at certain

temperatures, or diffusion may take place, changing the designed properties. Due to the

typical layer thicknesses in the range of nanometres to micrometres and the challenging

conditions of interfaces, available methods to investigate the concerned material properties

are challenging themselves.

Figure 6. Typical solar cell multilayer (A) Coverage of the natural Sun spectrum for each of the layers (B)

Second generation solar cells are significantly simpler to implement with the advantage of

requiring only a low amount of high purity semiconductor material as layer on a cheap and

free to design carrier material, such as glass. Although a monolayer solar cell, the layer itself

consists of several layers of different materials. One specific example is the question of

sodium diffusion from the glass into the CIGS layers, which is crucial for a good

performance and till now a poorly understood process.

Figure 7. CIGS solar cell.

First generation solar cells with high efficiency are produced from wafers, mainly silicon, see

Figure 8. The roughness of the surface is enlarged in order to increase the performance.

Investigation of the defect structure of the surface and its influence of additional anti-

reflexion coatings may result in better understanding of the involved processes.

Furthermore, the contact conjunctions are produced of different layers, introducing various

interfaces that are subject of aging and thermal changes, which are poorly understood.

Figure 8. Typical single crystal solar cell.

PAC spectroscopy in combination with ASPIC can be a powerful tool to investigate the

local structure in these materials as well as in the interfaces or surfaces. ASPIC is a decisive

tool for preparing samples in ultra-high vacuum under controlled conditions in order to

perform investigations in all fields described above.

As a first experiment Cu(In,Ga)Se semiconductor layers could be investigated temperature

dependent, focussing on its properties in contact with the surrounding layers. Glass -

molybdenum and Cu(In,Ga)Se will be studied, investigating the influence of sodium in the

local structure.

In a second step, contact interfaces of silicon and common coatings for the solar cell

production are planned to be studied. Finally multilayer systems of InGaP and AlInP and

GaAs will be a challenging research interest.

Intermetallic conjunctions of aluminum and gold are used for contacts in space devices and

on solar cells. Gold and aluminium have a complex phase diagram producing at contact

different intermetalic phases. Phases causing mainly problems are Au

, known as white

plague, AuAl

as purple plague, and Au

Al. These phases have different material

properties, cause an increase of resistance and reduction in volume causing cavities.

Solutions are using ultrasound welding or adding additional metals such as Ni and V as

intermediate layer. To increase the understanding of the undergoing processes, intermetalic

phase formations will be studied on Au-Al contact and with intermediate layers Ni:V/Ag as

well as Ga as amalgam forming metal. Investigations will be performed in layers and

temperature dependant. The preparation will be performed using ASPIC and phase changes

will be studied by using PAC.

2.1.4 Low energy β-NMR for studies on condensed matter

Z. Salman

Nuclear magnetic resonance (NMR) and related nuclear methods are widely used in

condensed matter physics. The magnetic moment of a nucleus acts as a sensitive probe of

the local magnetic and electronic environment. All forms of magnetic resonance require

generation of nuclear spin polarization out of equilibrium followed by a detection of how

that polarization evolves in time. The spin precession rate or Larmor frequency is a measure

of the local magnetic field at the nucleus, whereas the spin relaxation rate is determined by

spin dynamics near the Larmor frequency. However, there are also significant differences

which influence the specific applications. For example, in conventional magnetic resonance

a relatively small nuclear polarization is generated by applying a large magnetic field after

which it is tilted with a small RF magnetic field. An inductive pickup coil is used to detect

the resulting precession of the nuclear magnetization. Typically one needs about 10

nuclear spins to generate a good NMR signal with stable nuclei. Consequently conventional

NMR is mostly a bulk probe of matter. On the other hand, in related nuclear methods such

as muon spin rotation (mSR) or b-detected NMR (β-NMR) a beam of highly polarized

radioactive nuclei (or muons) is generated and then implanted into the material. The

polarization can be made much higher - between 50 and 100% . Most importantly, the time

evolution of the spin polarization is monitored through the anisotropic decay properties of

the nucleus or muon which requires about 10 orders of magnitude fewer spins. Furthermore

one can control the depth of implantation of the probe on an interesting length scale (1-

300~nm). Thus depth controlled low energy b-NMR [11-14] and mSR (LE-mSR) [15-17]

are well suited to studies of dilute impurities, nano-structures or interfaces where there are

few nuclear spins.

The low energy β-NMR technique used for condensed matter studies has the advantage of

not being limited to a specific material or properties. It can be used to study any material

whether they are conducting, insulating, magnetic or non-magnetic. This makes it extremely

versatile and useful for different fields in condensed matter, and therefore has the potential

of attracting many new users to ISOLDE. The low implantation energy of the spin probes in

β-NMR, makes the technique useful mainly for studies of surfaces and interfaces. The

electronic, magnetic and structural properties of an interface between two materials (or near

the surface) are in general different from the bulk properties of both. In such systems the

technique can provide depth resolved information of the properties of such systems.

A dramatic example which was discovered recently [18–20], is the high mobility two-

dimensional electron gas (2DEG) at the interface between two insulating perovskite oxides;

TiO

-terminated SrTiO

(STO) and LaAlO

(LAO). Surprisingly, there is evidence that this

interface can be both magnetic and even superconducting below 300 mK [18-21]. In this

example the high magnetic sensitivity of β-NMR was used (at TRIUMF) to detect weak

magnetism at these interfaces and its dependence on the thickness of the LAO layers [22].

Another important example where β-NMR can provide unique information is the newly

discovered class of materials called topological insulators (TIs) [23]. These are 3D insulating

materials with a band gap in the bulk electronic structure but with metallic gapless surface

states. The protected surface states are believed to be robust to disorder, interactions, and

thermal fluctuations, potentially leading to room temperature device applications [24]. In

this case we expect β-NMR to provide novel information regarding the depth dependence of

these surfaces states, and more importantly, study the properties of interfaces between TIs

and other superconducting or magnetic materials. Such buried interfaces cannot be

investigated using the commonly used techniques in TI studies such as angle resolved

photo-emission spectroscopy and scanning tunneling microscopy.

Several isotopes have been identified as suitable for development as probes for condensed

matter applications.

Li is the lightest and is relatively easy to polarize. There are, however,

several other probes which could be very useful for β-NMR studies in the near future,

including

O and

Be. Different nuclei offer complementary information since they have

different nuclear dipole and quadrupole moments as well as a different decay lifetime. For

example, since

Li has a nuclear moment of I=2 it experiences both the local magnetic field

as well as electric field gradient. This may complicate the measured resonance results and

makes it hard to disentangle the local magnetic and electronic information in the studied

system. In contrast,

Be which has nuclear spin 1/2 will have a purely magnetic interaction

with the system.

2.2 The study cases at the β-NMR spectroscopy end station

2.2.1 Bio-β-NMR spectroscopy on liquid samples

L. Hemmingsen, M. Stachura, A. Gottberg, M. Kowalska, P.W. Thulstrup

Metal ions are essential for life, and various functions have developed depending on the

intrinsic properties of each metal ion. The current letter of interest is focused on establishing

new spectroscopic possibilities for studies of the biologically highly important metal ions

, Ca

, Cu

, and Zn

. Mg

is involved in practically all phosphate metabolism as well

as an integral component of chlorophyll in photosynthesis. Ca

is involved in a plethora of

biochemical reactions, for example kinase reactions, muscle contraction, cell division, as

well as biomineralization etc. Both of these ions also take part in the control of formation of

negatively charged polymers, and thereby in the control of membrane stability and cell-cell

interactions, a property that may be exploited in this project, vide infra [25]. Cu

+/2+

essential in both various oxidases (enzymes) and in electron transfer processes, for example

in photosynthesis, where so-called small blue copper-proteins play key roles as electron

transporters. Finally Zn

is both an integral structural component of proteins, involved in

many enzymes, and in biochemical control of the expression of genes. All these metal ions

usually evade spectroscopic characterization, as they are invisible to most standard

spectroscopic techniques. Thus, the application of radioactive ion beams and nuclear

spectroscopic techniques would constitute an important, novel and most notably highly

sensitive approach to the elucidation the biological chemistry of these elements.

The short term aim (1-3 years) of this project is to establish a proof-of-principle that on-line

β-NMR and PAC spectroscopy on liquid samples using short lived radioisotopes of Mg, Ca,

Cu, and Zn is feasible. The long term aim is to apply these spectroscopic techniques to

elucidate both local structure and dynamics at the probe sites in biological systems. Only the

short term aim is addressed in detail in the following. Once the short term aim is achieved,

and the experimental setup has been optimized to allow for experiments on aqueous

solutions (test experiments have indicated that this is within reach), a number of

experiments elucidating the biological chemistry of the metal ions, vide supra, will be

designed

In the following specific experiments on the different metal ions are described. They are all

to be conducted using ionic liquid as solvent, as it displays very low vapor pressure, and

thus is suitable for UHV beam lines:

• Mg

Mg β-NMR experiments have already been successfully carried out using

ionic liquid as solvent [26]. Conventional

Mg NMR spectroscopy will be applied to

validate the results.

o The binding of

to a molecule in the ionic liquid solution would

complete the experiment series, demonstrating that not only a signal from

in the solvent, but also the process of binding to high affinity site may

be achieved within the lifetime of the radioisotope. As the chemical shift

range for

in a variety of compounds is rather small (about 200 ppm),

and this is close to the limit of what can be resolved (with the current setup), it

will be very difficult directly to observe different chemical shifts. Thus we

adopt a different strategy, and aim to bind Mg

to different sizes of

molecules, using anionic molecules exhibiting Mg

dependent

polymerization, vide supra. The origin of this strategy is that for molecular

species experiencing rotational diffusion on a time scale comparable to the

inverse of the Larmor frequency, the spin-lattice relaxation time is minimal,

and thus the signal is lost or reduced in intensity. That is, the binding of

to a certain size of polymer will give rise to loss of signal, and thus

demonstrate that the metal ion is in fact bound.

In addition a number of test experiments are important:

o The resonance frequency in a reference (single crystal of MgO) must be

recorded to calibrate the system

o A β-NMR experiment without any sample in the chamber, in order to test if

the recently designed setup in itself gives rise to a signal (a fraction of the

beam is deposited in the walls of the final pin-hole, and we suspect that

the Knight shift of Mg in aluminum is consequently observed)

o Conventional

Mg NMR spectroscopic data indicate a strong temperature

dependence of the signal, and we aim to carry out a similar series (20 ⁰C –

100 ⁰C) using β-NMR.

• For Ca

, Cu

and Zn

: For these elements conventional NMR experiments are

difficult, and we resort to other conventional techniques for validation of the results

(electronic absorption and fluorescence spectroscopy), see the second bullet below.

o The first experiments to be carried out will be simply implanting the spin-

polarized radioisotope into ionic liquid, in analogy to the initial

Mg β-NMR

experiments. The binding of the metal ions will most likely occur to the anion

of the ionic liquid (acetate).

o Next, a molecule with high affinity for each of the respective metal ions will

be added to the solution. Fortunately, such metal ion specific chromophores

and fluorophores exist, and additionally independently allow for

spectroscopic characterization of the process of metal ion binding, using so-

called stopped flow techniques (where the chromophore/fluorophore is mixed

with the relevant metal ion, and then rapidly (with a dead time of ~1 ms) the

time trace of the spectroscopic signal is followed.

Estimated number of shifts:

Mg, Ca,

Cu,

Cu or

Cu,

77m

Zn (10 shifts each element)

2.2.2 β-decay studies of laser-polarized radioactive beams

D.T. Yordanov for the proponents of INTC-I-090

Currently there is a strong interest in β-decay studies of laser-polarized radioactive beams.

This technique has the capability of measuring spins of excited nuclear states and as such is

expected to be an important tool for nuclear-structure studies. The basic principles, as well

as a physics case were presented in a letter of intent [27] in the context of collinear laser

spectroscopy at HIE-ISOLDE. The intention to establish a dedicated beam line for laser-

induced nuclear orientations opens the possibility to employ an alternative geometry for

optical-pumping, as shown in figure 9. The ion beam is deflected at 90° which is equivalent

to, and therefore removes the need of, a 90° turn of the orientation axis. Under these

conditions the nuclei will be delivered at the implantation point with a higher degree of

polarization. Furthermore, the magnetic field needed to bend the orientation axis is obsolete

in this configuration. In the absence of a large electromagnet the solid angle around the

sample can be used instead for an efficient detection system.

Figure 9. Geometry of β-delayed spectroscopy with optical pumping of ions.

2.2.3 Fundamental weak interaction physics using polarized beams: Precision

measurements of the beta asymmetry parameter for mirror β transitions in

Na,

and

Ar for determination of the V

element of the CKM quark mixing matrix

N. Severijns, G. Neyens, M. Bissell

Measurements of correlations in nuclear beta decay (e.g. the beta-neutrino correlation or the

beta emission asymmetry) are a sensitive means to search for the presence of new charged

gauge bosons mediating scalar or tensor type weak interactions not included in the Standard

Model [28]. Moreover, when results of such measurements for mirror beta transitions are

combined with the ft-value of the transition, then also the V

element of the Cabibbo-

Kobayashi-Maskawa (CKM) quark mixing matrix is obtained. E.g the beta-asymmetry

parameter A yields the Fermi-Gamow-Teller mixing ratio,

1 11



= −



++ +



which in turn yields V

when combined with the corrected Ft-value

00 2

2 / 1

mirror

→



ℑ=ℑ +





. Via the unitarity requirement of the CKM matrix additional

information on physics beyond the Standard Model is then obtained, such as e.g. on the

existence of heavy Z bosons [29].

Recently, it was shown that existing results of correlation measurements in the beta decay of

five mirror nuclei, originally not intended for this purpose, provide a value for V

of similar

precision to that obtained in neutron decay [30]. Further, it was shown that the beta

asymmetry parameter of the mirror beta decay of

Ar provides unrivaled sensitivity to V

[31] within the series of mirror nuclei. A measurement of the beta-asymmetry parameter

with a relative precision of 0.5 %, would provide a value for V

that is only a factor of 3 less

precise than the value for V

that is obtained from the entire set of superallowed pure Fermi

beta transitions [32]. Furthermore, if the current ft-value [33]) can be improved by a factor of

5, the V

would be obtained with a precision that is half of the current precision as obtained

from all data available till now. A measurement of the beta asymmetry parameter in the

decay of

Ar would thus allow further improving the precision of the value of V

and thus

the sensitivity to different types of new physics.

A measurement of the beta asymmetry parameter requires a polarized beam that is

implanted in a suitable host material selected so as to maintain the nuclear polarization

sufficiently long. Using optical pumping with a circularly polarized laser beam allows

producing high degrees of polarization, as illustrated e.g. for Na and Mg isotopes [34, 35].

The polarization is maintained after implantation by placing the host crystal in a magnetic

field of a few 1000 Gauss. The beta asymmetry will be observed with two ∆E-E telescopes

(to reduce background counts) placed perpendicular to the polarization symmetry axis. As

the measured asymmetry will provide the product of the nuclear polarization, P, and the

beta asymmetry parameter, A, the nuclear polarization has to be determined with a

precision better than 0.5%. Such methods have recently been developed at TRIUMF [36]

and at Los Alamos Natl. Laboratory [37]. Alternatively, determining the polarization can be

avoided by measuring simultaneously the asymmetry for the mirror beta transition and for

the pure Gamow-Teller transition to the first excited state of

Ar (with a branching ratio of

1.2 %). The nuclear polarization then cancels in the ratio of both beta-asymmetries. This

method has successfully been applied in the past already [38-40] and requires gamma

detectors to be installed as well, in order to select the two individual beta transitions via

beta-gamma coincidences.

As polarizing of a noble gas such as

Ar requires some development, the method and setup

will first be tested with

Mg and/or

Na which, apart from the dominant g.s.  g.s. mirror

beta transition, also have a Gamow-Teller transition to the first excited state (branching

ratio respectively 8.2 % and 4.8 %).

References:

[1] R. Neugart and G. Neyens, in J. Al-Khalili and E. Roeckl, The Euroschool Lectures on

Physics with Exotic Beams, Vol. 2, Lect. Notes Phys. 700 (2006)

[2] M. Kowalska, D. Yordanov et al., Phys. Rev. C 77 (2008), 034307

[3] P. Vingerhoets, K. T. Flanagan, et al., Phys. Rev. C 82 (2010), 064311

[4] B. Cheal et al., Proposal to INTC, INTC-P-300 (2011)

[5] H. Ohno, Science 281 (1998), 951

[6] T. Dietl et al., Science 287 (2000), 101

[7] M. Kapilashrami et al., Appl. Phys. Lett. 95 (2009), 033104

[8] S. Ghosh et al., J. Appl. Phys. 109 (2011), 123927

[9] R.N. Aljawfi et al., J. Magnetism and Magnetic Materials 332 (2013), 130

[10] M. Khalid and P. Esquinazi, Phys. Rev. B 85 (2012), 134424

[11] G. D. Morris et al., Phys. Rev. Lett. 93 (2004), 157601

[12] Z. Salman et al., Phys. Rev. Lett. 96 (2006), 147601

[13] Z. Salman et al., Nano Lett. 7 (2007), 1551

[14] Z. Salman et al., Phys. Rev. Lett. 109 (2012), 257207

[15] E. Morenzoni et al., J. Phys.: Condens. Matter 16 (2004), S4583

[16] T. Prokscha et al., Nucl. Instr. and Meth. A 595 (2008), 317

[17] Boris et al., 332 (2011), 937

[18] A. Ohtomo and H.Y. Hwang, Nature (London) 427 (2004), 423

[19] S. Thiel, et al., Science 313 (2006), 1942

[20] M. Huijben et al., Nat. Mater. 5 (2006), 556

[21] A. Brinkman et al., Nat. Mater. 6 (2007), 493

[22] Salman et al., Phys. Rev. Lett. 109 (2012), 257207

[23] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82 (2010), 3045

[24] J. Moore, Nat. Phys. 5 (2009), 378

[25] J.J.R Frausto da Silva and R.J.P Williams, “The biological Chemistry of the Elements

– The Inorganic Chemistry of Life”, Oxford University Press, 1991

[26] A. Gottberg et al., manuscript in preparation

[27] Proposal to INTC, INTC-2010-21 (2010) https://cds.cern.ch/record/1266236/

[28] N. Severijns et al., Rev. Mod. Phys. 78 (2006), 991

[29] I.S. Towner and J.C. Hardy Rep. Prog. Phys. 73 (2010), 046301

[30] O. Naviliat-Cuncic and N. Severijns, Phys. Rev. Lett. 102 (2009), 142302

[31] N. Severijns and O. Naviliat-Cuncic, Physica Scripta T152 (2013), 014018

[32] J.C. Hardy and I.S. Towner, Phys. Rev. C 79 (2009), 055502

[33] N. Severijns et al., Phys. Rev. C 78 (2008), 055501

[34] K. Kura et al., Phys. Rev. C 85 (2012), 034310

[35] G. Neyens et al., Phys. Rev. Lett. 94 (2005), 022501

[36] D. Meconian et al, Phys. Lett. B 649 (2007), 370

[37] F. Fang et al, Phys. Rev. A 83 (2011), 013416

[38] D. Garnett et al., Phys. Rev. Lett. 60 (1988), 499

[39] G.S. Masson and P.A. Quin, Phys. Rev. C 42 (1990), 1110

[40] A. Converse et al., Phys. Lett. B 304 (1993), 60

Appendix

DESCRIPTION OF THE PROPOSED EXPERIMENT

The experimental setup comprises: (name the fixed-ISOLDE installations, as well as flexible

elements of the experiment)

Part of the Choose an item.

Availability

Design and manufacturing

Dedicated beamline for producing

polarized beams at ISOLDE

Existing

To be used without any modification

New

Standard equipment supplied by a manufacturer

CERN/collaboration responsible for the design and/or

manufacturing

ASPIC apparatus

Existing

To be used without any modification

To be modified

New

Standard equipment supplied by a manufacturer

CERN/collaboration responsible for the design and/or

manufacturing

β-NMR apparatus

Existing

To be used without any modification

To be modified

New

Standard equipment supplied by a manufacturer

CERN/collaboration responsible for the design and/or

manufacturing

bio-β-NMR apparatus

New

Standard equipment supplied by a manufacturer

CERN/collaboration responsible for the design and/or

manufacturing

UNIVERSITÄT

DES

SAARLANDES

PD Dr. Manfred Deicher

Naturwissenschaftlich-

Technische Fakultät II

Fakultät 7

Physik und Mechatronik

Campus E2 6

D-66123 Saarbrücken

Tel.: +49 (0)681 302 58198

Fax: +49 (0)681 302 4315

e-mail:

manfred.deicher@

tech-phys.uni-sb.de

Datum: 28.05.2013

Universität des Saarlandes - Fakultät 7 Physik und Mechatronik

Postfach 15 11 50, D-66041 Saarbrücken

Letter of support for ASPIC

Together with the radioactive isotopes provided by ISOLDE, ASPIC

opens world-wide unique possibilities to combine “classical” surface

and interface experiments with nuclear solid state physic techniques

like perturbed angular correlation spectroscopy (PAC) or spin

polarization methods like β-NMR.

I hereby strongly support an upgraded ASPIC beamline at ISOLDE.

Using ASPIC, we plan to perform PAC experiments in

semiconductors, especially on surface and interface magnetism in

spintronic systems.

Saarbrücken, May 28, 2013

Dr. Manfred Deicher

ISOLDE and Neutron Time

-of-Flight

Experiments Committee (INTC)

CERN

-1211 Geneva 23

Switzerland

May 28, 2013

Letter of support for the “Letter of Interest” for a beam line at ISOLDE, for the production and

application of spin polarized nuclei,

The possibility to carry out research in the fields of biochemistry and biophysics at ISOLDE, using

ion beams with spin polarized nuclei represents a unique opportunity. It will allow us to conduct

experiments that cannot be carried out elsewhere, and which are expected to significantly

advance both basic and applied biochemistry, most notably concerning the role of metal ions in

biological system, which is the core expertise of my group at the University of Copenhagen.

The group in Copenhagen has been fortunate enough to have had beam time grants for several

years at ISOLDE, leading to publications in high ranking international chemistry and biochemistry

journals, and expect to continue carrying out research for at this facility for many years to come.

Similarly, the group has attracted funding for this research for several years, and hope and aim to

attract future funding for biochemistry and biophysics projects to be carried out at this beam line

at ISOLDE.

Thus, my group will greatly benefit from the facilities at proposed beam line, both on a short and

on a longer time scale.

Sincerely,

Lars Hemmingsen,

Associate Professor, Ph.D.

Biophysical and Bioinorganic Chemistry

Department of Chemistry

Faculty of Science

University of Copenhagen

Thorvaldsensvej 40

DK-1871 Frederiksberg

Denmark

TEL +45 35332307 / +45 22341782

Vítor Amaral

Departamento de Física

Universidade de Aveiro

3810-193 Aveiro

Portugal

Fax +351-234378197

Email: [email protected]

To whom it may concern

Having in mind research projects requiring the use of radioactive ion beams for hyperfine

measurements in demanding conditions I hereby state my support to the UHV RB0 beam line upgrade

project. This will allow the continuation of current activities and the enrichment of conditions to

foster demanding experiments in solid-state, soft-matter and biophysics applications.

I will do my best to contribute to the progress of research in its multiple and interdisciplinary

aspects, looking forward to the improvements well expressed, and justifiable, by the UHV RB0 beam-

line upgrade project.

Aveiro, 28

May 2013

(Vítor Brás de Sequeira Amaral)

Full Professor,

Physics Department University of Aveiro