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Layer‐Dependent Nonlinear Optical Properties and Stability of Non‐Centrosymmetric Modification in Few‐Layer GaSe Sheets

Abstract

Gallium selenide, an important second‐order nonlinear semiconductor, has received much scientific interest. However, the nonlinear properties in its two‐dimensional (2D) form are still unknown. A strong second harmonic generation (SHG) in bilayer and multilayer GaSe sheets is reported. This is also the first observation of SHG on 2D GaSe thin layers. The SHG of multilayer GaSe above five layers shows a quadratic dependence on the thickness; while that of a sheet thinner than five layers shows a cubic dependence. The discrepancy between the two SHG responses is attributed to the weakened stability of non‐centrosymmetric GaSe in the atomically thin flakes where a layer–layer stacking order tends to favor centrosymmetric modification. Importantly, two‐photon excited fluorescence has also been observed in the GaSe sheets. Our free‐energy calculations based on first‐principles methods support the observed nonlinear optical phenomena of the atomically thin layers.

2D‐Materialien: Eine schichtabhängige optische Nichtlinearität zweiter Ordnung wurde in mehrlagigen GaSe‐Blättern beobachtet. Dies ist die erste Beobachtung einer Frequenzverdopplung (SHG; siehe Bild) in GaSe‐Nanoblättern, verursacht durch die Abwesenheit eines Inversionssymmetriezentrums in ε‐GaSe. Das Material zeigt außerdem Zweiphotonen‐angeregte Fluoreszenz.

Authors:   Wenjing Jie, Xi Chen, Dian Li, Lu Xie, Yeung Yu Hui, Shu Ping Lau, Xiaodong Cui, Jianhua Hao
Journal:   Angewandte Chemie
Year:   2014
Pages:   n/a
DOI:   10.1002/ange.201409837
Publication date:   02-Dec-2014
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