TY - JOUR
T1 - Surface optical phonon modes in hexagonal shaped Al0.97Ga0.03N nanostructures
AU - Sivadasan, A. K.
AU - Singha, Chirantan
AU - Raghavendra, K. G.
AU - Amirthapandian, S.
AU - Bhattacharyya, A.
AU - Dasgupta, Arup
AU - Dhara, Sandip
N1 - Funding Information:
We thank S. Parida of SND and N. Meher of Materials Physics Division, IGCAR for their valuable suggestions and help in theoretical simulations. We also extend our thanks to UGC-DAE-CSR for FESEM and TEM facility. One of us (CS) also acknowledges Department of Science and Technology (DST) INSPIRE Fellowship for funding his research. The work at the University of Calcutta work was partially funded by the Department of Information Technology (12(3)/2011-PDD), Government of India and the MHRD, Government of India.
Publisher Copyright:
© 2017, Springer-Verlag GmbH Germany.
PY - 2017/8/1
Y1 - 2017/8/1
N2 - Raman modes of plasma assisted molecular beam epitaxy grown, c-plane oriented and hexagonal shaped cylindrical Al0.97Ga0.03N nanostructures are reported. Apart from the group theoretically allowed optical phonons at zone center (wave vector, q = 0), two additional phonon modes around 763 and 846 cm−1 are observed in between the reported values of longitudinal optical (LOq=0) and transverse optical (TOq=0) phonon modes. The observed phonon mode frequencies are matched with the simulated dispersion curve for the surface optical (SO) phonon modes and subsequently assigned as SO(A1) and SO(E1) with A1 and E1 symmetries, respectively. A change in the dielectric constant of the surrounding medium using CCl4 is demonstrated to show a significant red shift of the additional modes with respect to those in air, and they show good agreement with the calculated SO phonon frequencies. The origin of SO phonon modes are attributed to the relaxation of Raman selection rules away from the Brillouin zone centre because of the presence of periodic surface modulations of sharp edges at the corners of well-faceted Al0.97Ga0.03N hexagonal crystallites in the sample. An appropriate quantification is also made in this regard to find out the Fourier component of the surface potential responsible for activating the SO mode.
AB - Raman modes of plasma assisted molecular beam epitaxy grown, c-plane oriented and hexagonal shaped cylindrical Al0.97Ga0.03N nanostructures are reported. Apart from the group theoretically allowed optical phonons at zone center (wave vector, q = 0), two additional phonon modes around 763 and 846 cm−1 are observed in between the reported values of longitudinal optical (LOq=0) and transverse optical (TOq=0) phonon modes. The observed phonon mode frequencies are matched with the simulated dispersion curve for the surface optical (SO) phonon modes and subsequently assigned as SO(A1) and SO(E1) with A1 and E1 symmetries, respectively. A change in the dielectric constant of the surrounding medium using CCl4 is demonstrated to show a significant red shift of the additional modes with respect to those in air, and they show good agreement with the calculated SO phonon frequencies. The origin of SO phonon modes are attributed to the relaxation of Raman selection rules away from the Brillouin zone centre because of the presence of periodic surface modulations of sharp edges at the corners of well-faceted Al0.97Ga0.03N hexagonal crystallites in the sample. An appropriate quantification is also made in this regard to find out the Fourier component of the surface potential responsible for activating the SO mode.
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U2 - 10.1007/s00339-017-1139-3
DO - 10.1007/s00339-017-1139-3
M3 - Article
AN - SCOPUS:85025150314
SN - 0947-8396
VL - 123
JO - Applied Physics A: Materials Science and Processing
JF - Applied Physics A: Materials Science and Processing
IS - 8
M1 - 527
ER -