Monochromatic ion beams are invaluable tools in material sciences, in the emerging nanotechnology industry, and in studies of biological materials. In these domains, where ions are used to modify,

image or analyze surfaces and materials, the ability to convey large ion currents into smaller and smaller spot sizes is considered as a primary figure of merit [1]. State-of-the-art Focused Ion Beams (FIBs)

are commercially available, based mainly on plasma, liquid metal tip or Helium ion sources for large, intermediate, and low currents, respectively. On the other extreme of the current range, single ion

delivery and implantation onto a surface with nanometric precision opens exciting research possibilities and leads to the ultimate frontiers of the solitary dopant optoelectronics - solotronics - for

engineering few atoms devices [2].

Recently, experimental realizations of novel ion or electron sources based on the ionization of laser-cooled atoms have been reported [3,4] and have shown the potential of these new sources. Due to

the low temperatures associated with laser cooling, the ion (or electron) beam originating from the cold sample has an extremely narrow angular spread. This means that ion or electron sources based on the

ionization of cold atoms would have the ability to create very small focal spots with relatively strong currents.

A cold cesium atom source for Focused Ion Beams and Single Ion ImplantationM. Allegrini1,4, Y. Bruneau2, D. Ciampini1,4, D. Comparat2, A. Fioretti4,1, F. Fuso1,4,

I. Guerri1, g. Khalili2, L. Kime3, P. Pillet2, B. Rasser3, G. Shayeganrad1, P. Sudraud3, and M. Viteau3

1Dipart. di Fisica, Univ. di Pisa,and CNISM, Largo Pontecorvo 3, 56127 PISA, Italy

2Laboratoire Aimé Cotton, CNRS, Un. Paris-Sud, ENS Cachan, Bât. 505, 91405 Orsay, France

3Orsay Physics, 95 Avenue des Monts Aurélien, ZAC Saint Charles, 13710 Fuveau, France

4Istituto Nazionale di Ottica, CNR, U.O.S. Pisa, via Moruzzi 1, 56124, Pisa, Italy

Introduction

Cold Cs atoms as a Focused Ion Beam source

References and Acknowledgements These activities on ion beam production are carried out within a Marie

Curie PEOPLE Industry-Academia Partnerships and Pathways network in

a collaboration among the University of Pisa, the Laboratoire Aimé-Cotton

in Orsay and the private company Orsay Physics in Fuveau.

D. Comparat, F. Fuso and P. Sudraud acknowledge gratefully the support

of the European Union Seventh Framework Program FP7/2007-2013 under

Grant Agreement No. 251391 MC-IAPP ”COLDBEAMS”.

G. Shayeganrad and M. Viteau are or have been Research Fellows hired

under this program.

COLDBEAMS

[1] J. Orloff, M. Utlaut, and L. Swanson, High Resolution Focused Ion Beams: FIB and its applications (Springer-Verlag, New York,

2002).

[2] P.M. Koenraad and M.A.. Flatté, single dopants in semiconductors, Nature Materials, 10 (2011) 91

[3] B. Knuffman, A.V. Steele, J. Orloff and J.J. McClelland, Nanoscale focused ion beam from laser-cooled lithium atoms, New

Journal of Physics 13 (2011) 103035

[4] L. Kime, A. Fioretti, Y. Bruneau, N. Porfido, F. Fuso, M. Viteau, G. Khalili, N. Šantić, A. Gloter, B. Rasser, P. Sudraud, P. Pillet, and

D. Comparat, High-flux monochromatic ion and electron beams based on laser-cooled atoms, Phys. Rev. A, 88 (2013) 033424

Objectives:

Oven, collimation and compression

Rydberg excitation/ionisation FIB coupling

Results and perspectives

LMIS

Suppressor

Extractor Lens

Condensor Lens

Variable Apertures

Blanking

Faraday Cup

Deflectors

Objective Lens

Ion Beam

Sample

18.5 kV

-21.4 kV

The 3 ionizing electrodes

Field ionization

area

Rydberg excitation lasers

Atomic Beam

Cold Cs atoms as a Single Ion source

New ion beam source, starting from cold atoms

- Continuous beam- Low energy dispersion (<0.5ev)- High brihtness (>>106 A.m-2.sr-1.V-1)

Stainless steel grid on silicon. Silicon scale is 10 mm. Ion energy = 3 keV, current = 10 pA, Dt/pixel = 50 ms

Tin balls on carbon. Ion energy = 5 keV, current = 7 pA, Dt/pixel = 50 ms

The results demonstrate that ions possessing an average energy as small as 10 eV and energy spread slightly above 0.5 eV can be extracted from the ionization volume, in order to be used in technological applications.Concerning the deterministic nature of the ion delivery, our system is still statistical in nature. Nevertheless, given the very high collection efficiency that can be reached also for electrons, ion delivery could be crosschecked by electron detection, resulting in an almost deterministic delivery of single ion.

Atomic beam

[A.Camposeo et al., Optics Comm. 200 231 (2001)A.Camposeo et al., Mat.Sci.Eng. C 23 217 (2003)]

6 2S1/2

6 2P3/2

continuum

852 nm

405 nm

F = 4

F’ = 3F’ = 4

F’ = 5

Hyperfine levels

Cs energy level scheme

3.9 eV

+0.6 eV

Excitation laser

Ionization laser

Currents attained: up to 500 pA

Objectives: - Low energy (< 1 keV)- Low energy dispersion (<0.5ev)- Possible low emittance

Deterministic delivery of single ion or ion bunch with few nanometer resolution

Proof-of-principle experiment

Ionization scheme

A slow and cold Cs beam (109 at/s) is outsourced from a pyramidal MOT, transversally cooled and ionized.Ions are extracted and directed onto an electron multiplier

- Excitation 6s-6p3/2: ECDL laser @ 852nm- Ionization 6p3/2 – continuum:

DL @ 405 nm or SHG Nd-YAG @ 473nm

Results and perspectives

(a) Ion count rate versus ionization laser power Pion for Pexc = 1 mW

(b) Ion count rate versus excitation laser power Pexc for Pion = 25 mW; the solid lines are a fit to the data.

Ion beam rms energy spread, ΔUrms, as a function of the bias V1 applied to grid G1. Experimental data are obtained in the co-propagating (red circles) and crossed (blue squares) laser beam configurations.

Ion counts as a function of laser pulse duration for ions which are produced through (a) the pushing method and (b) the pulsed excitation method. The continuous lines represent linear fit to experimental data.

Actual resolution (100 nm) limited by source-FIB coupling. New ionization electrodes under construction