1D nanomaterials: Plasma-stimulated synthesis elucidates nanowire nucleation and growth mechanisms

S. Tom Picraux, DMR0413523

Arizona State University

SiH4

Au seed

Si substrate

Plasma stimulatedThermal growth

350ºC 0.5 nm Au Scale bars: 500 nm

SiH4

SiH2

SiH3

PlasmaThermal

430470510 400 350

1000 / T (1/K) G

row

th R

ate

(nm

/min

)

plasma

C

thermal0.74 eV

0.26 eV

Vapor-liquid-solid Si nanowire growth

• One objective of this research is to understand the mechanisms of nanowire (NW) growth during metal catalytically seeded vapor-liquid-solid (VLS) synthesis.• We have used plasma excitation to gain new insight into the nucleation and growth process. Strong enhancement and orientation independent growth due to plasma formed SiH3 and SiH2 species (Fig.1) show the vapor-liquid incorporation step and not the liquid-solid crystallization step is rate-limited mechanism. • Plasma excitation enables efficient low temperature nucleation required for NW growth (Fig.2) due to higher chemical potential.• A two-step process is demonstrated to enable lower temperature Si NW synthesis for creating nanowire heterostructures

Fig. 2 SEM of low temperature Si NWs showing little nucleation of seeds by thermal and extensive growth by plasma

Fig. 1 NW growth rate vs. reciprocal temperature without (thermal) and with plasma excitation for [110] & [111] NWs

Research in Engineering and Applied Sciences

Each fall semester at Arizona State University, graduate students in the Fulton School of Engineering are offered an excellent opportunity to present their innovative, exciting research in Engineering and Applied Sciences at the Research in Engineering and Applied Sciences Symposium (REAS).  The event serves to bring together student researchers in a professional supportive conference atmosphere for discussions and potential collaborations on their work. Annually over 40 students participate, 300 students/faculty attend, and a keynote address from a local industry leader finishes out the day-long symposium.

Hosted by the Fulton School of Engineering Graduate Student Association (FGSA), this symposium takes a broad interdisciplinary view of the different engineering disciplines at ASU, including the newly formed School of Materials at ASU.

Graduate students in the Picraux group have presented group research every year and have participated in the running the REAS symposia. Post docs and Picraux have routinely served as judges.

Annual REAS Symposium: Providing professional experience to graduate students

S. Tom Picraux, DMR0413523

Arizona State University