Modification of Si nanocrystallites in SiO2 matrixby swift heavy ion irradiation

By: V. E. Thelelo & A. Rossouw

In co-operation with,University of Fort Hare & Stellenbosch University

Supervised By:

N.S.Kirilkin, V.A.SkuratovJoint Institute for Nuclear Research, Dubna, Russia

Brief project overview

The irradiation testing of nuclear ceramics and oxides with heavy ions of fission fragment energy

Our irradiation testing experiments will be focused on study of:

– correlation between surface and material bulk radiation damage induced by heavy ions with energies above 1 MeV/atomic mass unit (amu).

– temperature dependence of swift heavy ion-induced phase transformations and dense ionization effect on pre-existing defect structure in irradiating materials.

The project fulfillment allows us to acquire new knowledge concerning evolution of defect structure in nuclear ceramics under dense electronic excitations simulating the fission fragment impact.

G. Schiwietz et al. NIMB 226 (2004) 683

The source of structural changes in tracks of high energy (E > 1 MeV/amu) heavy ions is a huge energy deposition (Se tens keV/nm) in electron subsystem of irradiating material

SHI cause exotic effects in different classes of materials which cannot be generated by any other means.

Irradiation with swift heavy ions (SHI)

SiO2 layers with variable NC concentration

1. Deposition of SiO2 and Si on Si substrate from two sources separated by distance of 100 mm 2. dSiO2 = 400 - 1000 nm3. Si content in oxide: 5 - 90 vol.%4. Annealing: 1140оС, 40 min, N2

NC size: 3 – 5 nm

Si

Ordered arrays of Si nanocrystals in SiO2: structural, optical and propertiesOrdered arrays of Si nanocrystals in SiO2: structural, optical and properties

The ordering of composites under high-energy ion irradiation and formation of elongated particles (up to 250 nm length with diameter 3-5 nm) is known for metal nanoparticales in SiO2

Pt in SiO2

185 MeV AuNIM B 266 (2008), 3158

Kr, 90 MeV, 1012 cm-2

Formation of the ordered NC distribution

substrate

surface

Ion pass

30 nm

20 nm

Irradiated NC-SiO2 layer (37 % Si)

Kr, 90 MeV, 1012 cm-2 non-irradiated layer

HREM cross sectional images for the Si NCs in irradiated layer

Atomic planes of NCs in the irradiated samples are oriented along the ion tracks

500 550 600 650 700 750 800 850 9000

50

100

150

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350

X, %: 57 51 40 33 26 22

PL in

tens

ity, a

rb. u

nits

Wavelength, nm500 550 600 650 700 750 800 850 9000

50

100

150

200

250

300

350

X, %:

51 40 33 26 22 18 14.5

PL in

tens

ity, a

rb. u

nits

Wavelength, nm

Bi, 670 MeV , ex. = 488 nm, Ar laser

Initial 1x1012 cm-2 8x1012 cm-2

500 550 600 650 700 750 800 850 9000

5

10

15

20

25

30SiO-3

X, vol.% 57 51 40 33 26 22 18

PL in

tens

ity, a

rb. u

nits

Wavelength, nm

Photoluminescence of irradiated layer

10 20 30 40 50 600

50

100

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350

I PL, a

rb.u

nits

X, vol %

initial

Bi, 1012 cm-2

Bi, 8.1x1012 cm-2

Photoluminescence of 670 MeV Bi ion irradiated layer

Experimental Setup

Spectrometer

Diod380nm

Nc Si specimen

SpectrometerANDOR iDUS

1. Diod with 380nm wavelength produces excitation of Nc Si

2. Nc Si specimen emit light

3. Spectrometer register this light and cuts off signal less than 550nm wavelength

Extra Si concentration

1 2 3 654

5% 90%

Max effect for points 3 and 4

PL intensity of initial Si NCs as a function of Si concentration

Acknowledgments

Dr. N. M. Jacobs Prof. M. L. Lekala Dr. V. A. Skuratov Mr. N. S. Kirilkin JINR UFH US And everyone else involved in making this practice

possible.

Thank you for your attention!