A. Abdi,A. Abdi, L.V. Titova L.V. Titova , L. M. Smith and H. E. JacksonL. M. Smith and H. E. JacksonDepartment of Physics, University of Cincinnati, Ohio 45221-0011

J. M. Yarrison-RiceJ. M. Yarrison-RiceDepartment of Physics, Miami University, Oxford, OH

J. L. LenschJ. L. Lensch** and L. J. Lauhon and L. J. LauhonDepartment of Materials Science and Engineering, Northwestern

University, Evanston, IL 60208

Supported by NSF and partially supported by the Petroleum Research Fund of the American Chemical Society and Northwestern University and a *National Science Foundation Graduate Research Fellowship.

Probing the Electronic and Vibronic Probing the Electronic and Vibronic Structure of Single and Ensemble Structure of Single and Ensemble CdS Nanowires using Resonant CdS Nanowires using Resonant

Raman ScatteringRaman Scattering

Outline …Outline …

Sample preparation

An ensemble of CdS nanowires Resonant Raman Scattering

Single CdS nanowire Resonant Raman Scattering

Summary

VLS Sample GrowthVLS Sample Growth

Alloy Liquid

Vapor

CdSNanowire

Au Catalysts

Si Substrate

Y. Wu and P. Yang, J. Am. Chem. Soc. 123, 3165 (2001)

SEM of CdS NanowiresSEM of CdS Nanowires

1 m

• An ensemble with an average diameter of 10 nm

2.35 2.40 2.45 2.50 2.550

10

20

30

40

50

exc : 458 nm

Inte

nsit

y (

arb

. unit

s)

Energy (eV)

PL

2.35 2.40 2.45 2.50 2.550

10

20

30

40

50

Si

: 488 nm

2 LO

1 LO

exc

2.35 2.40 2.45 2.50 2.550

10

20

30

40

50

: 496 nm

2 LO

Si1 LO

exc

Resonant Raman Spectrum at Resonant Raman Spectrum at Room Temperature for a CdS Room Temperature for a CdS

Nanowire EnsembleNanowire Ensemble

Background Subtracted Background Subtracted Resonant Raman ScatteringResonant Raman Scattering

200 400 600 800 1000

0

40

80

exc = 496 nm

Inte

nsit

y (

arb

. unit

)

3 LO

2 LO

Raman Shift (cm-1)

1 LO

Si

1 LO Resonance Raman 1 LO Resonance Raman Intensities vs. Excitation Energy Intensities vs. Excitation Energy for CdS Nanowire Ensemble for CdS Nanowire Ensemble

250

300

350

50

100

150

200

2.4 2.5 2.6 2.7

Inte

nsit

y (

arb

. unit

)T = 300K

2.3 2.4 2.5 2.6 2.7

0

10

20

30 34 meV

2LO Integ. Intensity

2.3 2.4 2.5 2.6 2.7

0

10

20

30

1 LO Integ. Intensity

42 meV

2.3 2.4 2.5 2.6 2.7

0

10

20

30

Inte

nsi

ty (

arb

. unit

s)

Energy (eV)

PL

Resonant Raman Intensity vs. Resonant Raman Intensity vs. EnergyEnergy for CdS Nanowire for CdS Nanowire Ensemble Ensemble

Outline …Outline …

Sample preparation

An ensemble of CdS nanowires Resonant Raman Scattering

Single CdS nanowire Resonant Raman Scattering

Summary

200 400 600 800 100010k

20k

30k

40k

50k

60k

70k

80k

90kSi 2 LO

Inte

nsit

y (

arb

. unit

)

Raman Shift (cm-1)

exc

: 488 nm

1 LO

200 400 600 800 100010k

20k

30k

40k

50k

60k

70k

80k

90kSi 2 LO

Inte

nsit

y (

arb

. unit

)

Raman Shift (cm-1)

: 496 nm

1 LO

Single (10 nm catalyst) CdS Single (10 nm catalyst) CdS NanaowireNanaowire

2.3 2.4 2.5 2.6 2.70

500

1000

1500

2000

2500

3000

3500

1 LO Integ. Intensity

Inte

gra

ted Inte

nsit

y (

arb

. unit

)

Energy (eV)

20 meV35 meV

PL

2 LO Integ. Intensity

Resonance Raman Intensities vs. Resonance Raman Intensities vs. Excitation Energy of a Single CdS Excitation Energy of a Single CdS NanowireNanowire

SummarySummary

RRS has been used to study successfully both an ensemble and a single of CdS nanowires at room temperature.

The similarity of the lineshapes of the PL and the RRS integrated intensities indicates that we probe the electronic states.

1 LO and 2 LO Energy differences are consistent with the bulk CdS values.