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MPhil Thesis Presentation 
Chemical Vapor Deposition Growth of Three-Dimension Topological Insulator $Bi_2(Se_xTe_{1-x})_3$
Speaker Mr Huanwen Wang
Department of Physics, The Hong Kong University of Science and Technology
Date 6 June 2017 (Tuesday)
Time 10:00 - 11:00
Venue Room 4472 (Lifts 25-26), HKUST
Binary topological insulator $Bi_2X_3$ ($X=Te, \ Se$) nanoplates have been synthesised via catalyst free chemical vapor deposition method. A silicon nitride protecting layer was deposited to measure the Raman spectra for those nanoplates without introducing damage to the sample surface. Temperature dependent nonresonant Raman spectra at the excitation of $512.5 \ \text{nm}$ show rather small first-order temperature coefficients for all Raman modes in $Bi_2Te_3$ and $Bi_2Se_3$ nanoplates compared to the reported value in bulk single crystal. Besides, the $A_{1g2}$ mode shows electronic resonant enhancement in the Raman spectra at the excitation of $633 \ \text{nm}$, which gives a similar small first-order temperature coefficient as the non-resonant one. Magnetotransport measurement for grown $Bi_2Se_3$ nanoplate shows pronounced weak anti-localization effect in the low field region, linear magnetoresistance in the perpendicular high field and a weak negative magnetoresistance in the in-plane direction. All the magnetotransport signatures are expected to originate from the topological surface states.
Ternary compound $Bi_2Te_{1.7}Se_{1.3}$, $Bi_2TeSe_2$ and $Bi_{2.1}Te_{1.4}Se_{1.5}$ nanoplates have been deposited on $SiO_2$/$Si$ substrates via catalyst free chemical vapor deposition method. The evolution of Raman spectra for $Bi_2(Te_{1-x}Se_x)_3$ has been studied, which shows blue shift in $A_{1g1}$, $E_{g2}$ and $A_{1g2}$ mode when increase the atomic ratio of Se. A new Raman mode (V) appears in the ternary compound compared to the binary compound, we attempt to attribute this new mode to the Te1-Se2 anti-sites in $Bi_2(Te_{1-x}Se_x)_3$