EUV spectra from the NIST EBIT

D. Kilbane and G. O’SullivanAtomic and Molecular Plasma Physics group, UCD, IrelandAtomic and Molecular Plasma Physics group, UCD, Ireland

J. D. Gillaspy, Yu. Ralchenko and J. ReaderNational Institute of Standards and Technology,

Gaithersburg, MD 20899, USA

The 17th ADAS WORKSHOP23 – 25 September 2012Château de Cadarache

Outline

Motivation

EBIT • Experimental set up• Collisional-radiative modeling of plasma

EUV SpectraGadolinium

2

• Gadolinium• Dysprosium • Tungsten

‘Potential lowering’ of 4fn ions

Summary

Motivation

Atomic and Plasma Theory• Hf, Ta, W, Au ions

advance atomic / plasma codespredict trends in atomic structure

Next-Generation

Lithography

3

ITER• Diagnostics of hot

plasmas in fusion devices

• Modeling of sources at 6.x nm

NIST Electron Beam Ion Trap (EBIT)

EBIT creates, traps and excites HCI

Electron beam• collides with, ionizes and excites atoms• monoenergetic, width ~60 eV• tuneable, 1 - 30 keV• radius ~30 µm• density ~1011 cm-3

4

• density ~10 cm

Ions are trapped• radially by space charge• axially by electrodes and magnetic field

EUV radiation• from the ions is observed with a flat

field grazing incidence spectrometer

http://physics.nist.gov/ebitGillaspy Phys. Scr. T 71 99 (1997)Blagojević et al. Rev. Sci. Instrum. 76 083102 (2005)

Collisional-Radiative Modeling

Atomic Data –Flexible Atomic Code (FAC)

• Relativistic potential to solve the Dirac eqn (CI and QED):

energy levels, radiative decay rates,

CR model –NOMAD

• non-Maxwellian time-dependent CR plasma code

• ~103 levels/ion

All important physical processes in the EBIT plasma

5

energy levels, radiative decay rates, radiative recombination cross sections

• e- ion collisions are treated with distorted wave/Coulomb Born-exchange approx:

electron impact excitation, de-excitation, ionization cross sections

Gu Can. J. Phys. 86 675 (2008)Ralchenko and Maron J. Quant. Spectrosc. Radiat. Transfer 71 609 (2001)

• ~103 levels/ion typically 6-8 ions several million transitionsruns in minutes

• one free parameter – charge exchange CX between ions and neutrals

EBIT Spectra of Gd

Ion IP (eV)Rb-like 936Kr-like 1100Br-like 1142Se-like 1189As-like 1233Ge-like 1320Ga-like 1369

0

2×104

0

2×104

2×104

Cou

nts

(AD

U)

0.974

1.047

1.120

RbRb

Kr

KrKr

Br

BrBr

Br

0

5×104

0

1×105

1×105

Cou

nts

(AD

U)

1.320

1.378

1.450

Ge

Ge

Ga

Ga Ga

Ga

Rb-like to Cu-like gadolinium ion spectra

Ga-like 1369Zn-like 1481Cu-like 1531

Kilbane et al. accepted Phys. Rev. A (2012)Rodrigues et al. At. Data Nucl. Data Tables 86 117 (2004)

6

0

0

2×104

0

5×104

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17Wavelength (nm)

0

5×104

Cou

nts

(AD

U)

1.170

1.242

1.278

Br

Se Se

Se

As

AsAs

0

0

2×105

0

2×105

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17Wavelength (nm)

0

1×105

7 7.2 7.4 7.6 7.8 8

Cou

nts

(AD

U)

1.520

1.588

1.697

Cu

Zn

Ga

Cu

GaCu

Zn

EBIT Spectra of Gd

Ge-like Gd ion

CR database of singly + doubly excited 4s24p2, 4p4, 4s24d2, 4s4p3, 4s24p4d, 4s24p4f, 4s4p24d, 4s4p24f, 4s24p5l, 4s4p25l, 4s24p6l, 4s4p26l

Energy levels of all singly, doubly, triply and quadruply excited n=4 complex 0

2

4

6

8

Cou

nts

(104 A

DU

)

EXP: 1.320 keV

second order

As

7

Kilbane et al. accepted Phys. Rev. A (2012)

and quadruply excited n=4 complex 4s4d3, 4s4f3, 4d4, 4f4 4p24d2, 4p24f2 and 4p24d4f

CR database is updated with new energies of the lowest levels

Excellent agreement between measured and simulated spectra e.g. Se, As, Ge-like

0

4 5 6 7 8 9 10 11 12 13 14 15 16 17Wavelength (nm)

0

0.5

1

1.5

2

2.5

Em

issi

vity

(ar

b.un

its)

TH: 1.28 keV

Se

Ge

As

GeAs

As

Se

Gadolinium Data Tables

59 new lines: 4s-4p , 4p-4d and 4d-4f transitions ranging from 6.630 nm to 17.279 nm (mostly E1)

8

Kilbane et al. accepted Phys. Rev. A (2012)Suzuki et al. J. Phys. B 45 135002 (2012)

‘Forbidden lines’Kr-like (9.726 nm) (M2)4p6(4p4

+)0 – 4p54d(4p3+,4d+)2

Se-like (9.684 nm) (M2)4s24p4(4p2

+)2 – 4p34d(4p+,4d+)4

Se-like (7.826 nm) (M2)4s24p4(4p2

+)2– 4p34d((4p-,4p2

+)3/2,4d-)0

Spectra were calibrated with known lines of Ba, Xe, C and O ions – accuracy 0.003 nm

Cu-like linesNIST EBIT NIFS9.086 nm 9.091(2) nm7.527 nm 7.524(2) nm

Next-Generation EUV Lithography at 6.x nm4d-4f + 4p-4d UTAs

Intense emission due to overlap of many open 4d and 4f subshell ions

Churilov identified Gd and Tb in LPPs and spark discharges

7

7

7

7

7

7(a)La

15+

Ce16+

Pr17+

Nd18+

Pm19+

Sm20+ 14

15

16(b)

9

Churilov et al. Phys. Scr. 80 045303 (2009) Kilbane and O’Sullivan Phys. Rev. A 82 062504 (2010)

4 5 6 7 8 9 100

7

7

7

7

7

7

7

7

7Eu

21+

Gd22+

Tb23+

Dy24+

Ho25+

Er26+

Tm27+

Yb28+

Lu29+

Wavelength (nm)gA

(10

13 s

−1)

50 55 60 65 70 7510

11

12

13

Z

E(eV)

Spectra of Gd and Dy at 6.x nm

Ag-like4d104f – 4d94f26.7423, 6.7465, 6.7884 nm

Pd-like4d10 – 4d94f 6.7636 nm

Ag-like4d104f – 4d94f26.6437, 6.5967, 6.2587, 6.3125 nm

Pd-like4d10 – 4d94f 6.2778 nm

DysprosiumGadolinium

2468

0.609

5

10

150.684

5

10

150.720

10 0.800

Cou

nts

(10

AD

U)

32

4

6 0.588

4

6

8

100.607

Cou

nts

(10

AD

U)

310

Sugar et al. J. Opt. Soc. Am. B 10 799, 1321, 1977 (1993)

Rodrigues et al. At. Data Nucl. Data Tables 86 117 (2004)

Gd Ion IP (eV)

Ag-like 358

Pd-like 565

Rh-like 601

Note: Very low current ~5 mA at 0.609 keVAbsence of strong resonant transitions

Dy Ion IP (eV)

Ag-like 423

Pd-like 664

Rh-like 702

5

0.800

5

100.877

6.4 6.6 6.8 7 7.2 7.4 7.6 7.8Wavelength (nm)

5

10

15 0.913

Cou

nts

(10

AD

U)

2

4

6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8Wavelength (nm)

2

4

6

8

10 0.653

Cou

nts

(10

AD

U)

Spectra of W

W Ion IP (eV)

Ag-like 881.4

Pd-like 1132.2

Rh-like 1179.9

Ag-like 4d104f – 4d94f2

5.1457, 5.0895, 4.8729, 4.9403 nm

Pd-like 4d10 – 4d94f4.8948, 5.9852 nm

Rh-like 4d9 – 4d84f4.9856, 4.9785, 4.9938,

2

3

4 0.849

4

6

8

10 1.025

Cou

nts

(10

AD

U)

3

11

Sugar et al. J. Opt. Soc. Am. B 10 799, 1321, 1977 (1993)

Kramida and Shirai At. Data Nucl. Data Tables 95 305 (2009)

Strong resonant transitions observed at lower beam energies in Pd-like ions

Note: Feature observed at ~4.5 nm at 1.03 and 1.15 keV at the Berlin EBIT is absent

Biedermann et al. Phys. Scr. T 92 85 (2001)

4.9856, 4.9785, 4.9938, 5.0265 nm

2

4

4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 6Wavelength (nm)

2

4

6

8

10

121.137

Cou

nts

(10

AD

U)

‘Potential Lowering’ of 4fn ions

Metastable states

• Many low lying excited states of Ag-like ions are populated by collisions

• These metastable states remain well populated

• Beam energy required to 0

100

200

300

400

500

600

700

800

900

1000

Ene

rgy

(eV

)

4s24p64d10nl

4d104f

4d105s

4d105p

4d105d

4d105f

4d105g4d106s4d106p

4d106d4d106f

4d106g4d106h

4s24p64d94fnl

4d94f2

4d94f5s4d94f5p

4d94f5d

4d94f5f

4d94f5g

IP=881.4 eV

Ag−like W

12

• Beam energy required to generate excited states of Pd-like ions is reduced

0 Ag−like W

0

100

200

300

400

500

Ene

rgy

(eV

)

4s24p64d10nl

4d104f4d105s

4d105p

4d105d

4d105f

4d105g

4d106s4d106p

4d106d4d106f

4d106g4d106h

4s24p64d94fnl

4d94f24d94f5s

4d94f5p

4d94f5d

4d94f5f

4d94f5g

IP=358 eV

Ag−like Gd

Summary

EUV spectra of Gd, Dy and W ions from the NIST EBIT

• 59 new lines identified in Rb-like to Cu-like gadolinium

• ‘Potential lowering’ observed in 4fn ions

• Uses:

13

• validate atomic / plasma codes predict trends in atomic structure

• model EUV sources for next-generation lithography

• diagnostics of hot plasmas in fusion devices such as ITER

Thanks

The Atomic Spectroscopy Group at NIST

14

Acknowledgement : This work was supported by Science Foundation Ireland under grant number 07/IN.1/I1771 and in part by the Office of Fusion Energy Sciences of the U.S. Department of Energy.

The 17th ADAS WORKSHOP23 – 25 September 2012Château de Cadarache