Thermomechanical Response of Supported Hexagonal Boron
Nitride Sheets of Various Thicknesses
Lambros Seremetis
Emmanuel N. Koukaras
Sotiria Alexandri
Antonis Michail
George Kalosakas
John Parthenios
Costas Galiotis
Sotirios Tsirkas
Spyridon Grammatikopoulos
Konstantinos Papagelis
10.1021/acs.jpcc.0c01029.s001
https://acs.figshare.com/articles/journal_contribution/Thermomechanical_Response_of_Supported_Hexagonal_Boron_Nitride_Sheets_of_Various_Thicknesses/12361025
Raman
spectroscopy is employed to investigate the temperature dependence
of the E<sub>2g</sub> phonon mode of single-layer, few-layer (FL),
and bulk hexagonal boron nitride (hBN) sheets, situated over Si/SiO<sub>2</sub> (90 nm). Depending on the sample, two temperature regimes
are recorded. In the low to mid range of the examined temperatures,
the monolayer and FL samples exhibit significantly higher slopes compared
to the thicker ones because of the thermal expansion of the underlying
substrate. In the high-temperature region, all the examined samples
show almost the same temperature slope, indicating slippage of the
hBN sheets relative to the substrate and providing strong evidence
that the slopes of the monolayer, FL, and bulk hBN are quite similar
of about −0.020 cm<sup>–1</sup>/K. This is further justified
from the full width at half-maximum versus <i>T</i> of the
studied samples and the observed similarities of the thermal expansion
coefficient (TEC) of one to three layers and bulk hBN, revealing a
comparable level of anharmonicity for the E<sub>2g</sub> mode from
the monolayer up to bulk hBN. Moreover, using a finite element method,
we have determined the TEC of the underling substrate and the strain
induced by TEC mismatch between the single-layer hBN and the substrate.
Consequently, the intrinsic frequency shift of the E<sub>2g</sub> mode
for the monolayer hBN upon temperature change is extracted. Finally,
the vibrational response of monolayer hBN upon temperature is also
examined by means of computational simulations, and satisfactory agreement
with the experiment is obtained.
2020-05-22 22:30:20
Various Thicknesses Raman spectroscopy
monolayer hBN
substrate
FL samples exhibit
Hexagonal Boron Nitride Sheets
TEC
E 2 g mode
E 2 g phonon mode
bulk hBN