^{1}and Guojun Jin

^{1,a)}

### Abstract

We investigate the uniaxial strain modulated electronic structure and optical absorption of a triangular zigzag graphene quantum dot within the tight-binding approach. According to the symmetry analysis, the electronic structure and optical absorption can be correctly characterized before and after the strain is applied. The redshift or blueshift of the absorption peaks can be observed in the optical spectrum by uniaxial tensile or compressive strain, indicating that the strained triangular zigzag graphene quantum dot can be used as a strain sensor. The influence of dot sizes on the sensor sensitivity is also considered. Furthermore, the robustness of such a function against a single vacancy defect is confirmed. On the other hand, by applying a gate voltage on the strained dot, the Fermi energy is shifted away from zero, obvious far-infrared absorption peaks can appear in the optical spectrum, which means it is possible to realize far-infrared photodetectors based on strained graphene quantum dots.

This work was supported by the State Key Program for Basic Research of China (Grant Nos. 2009CB929504 and 2011CB922102), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and the National Natural Science Foundation of China (Grant Nos. 60876065 and 11074108).

I. INTRODUCTION

II. MODEL AND FORMALISM

III. GROUP THEORY ANALYSIS

IV. STRAIN SENSOR

V. FAR-INFRARED ABSORPTION

VI. SUMMARY

### Key Topics

- Absorption spectra
- 27.0
- Graphene
- 24.0
- Optical absorption
- 20.0
- Blue shift
- 15.0
- Quantum dots
- 15.0

## Figures

Structure of a TZGQD. (i = 1, 2, 3) indicate the lattice vectors. Solid and open circles distinguish the two sublattices in the honeycomb lattice. Here, Nz equals 6. A denotes one of the edge atoms.

Structure of a TZGQD. (i = 1, 2, 3) indicate the lattice vectors. Solid and open circles distinguish the two sublattices in the honeycomb lattice. Here, Nz equals 6. A denotes one of the edge atoms.

(a)–(c) are the energy level diagrams of the TZGQD with for the uniaxial strain , the uniaxial strain along the zigzag direction and the uniaxial strain along the armchair direction, respectively. The irreducible representations of the levels are labeled in the figures. (d) and (e) plot the jointed density of state and the optical absorption spectrum of the unstrained TZGQD. (f)–(h) plot the jointed density of state, the optical absorption spectrum and of the TZGQD for the strain along the zigzag direction. (i), (j), and (k) are the same as (f), (g), and (h), but for the strain along the armchair direction. Here, we use a Lorentz function with a broadening factor of 0.05 eV. To be clear, some levels are plotted with the dashed lines.

(a)–(c) are the energy level diagrams of the TZGQD with for the uniaxial strain , the uniaxial strain along the zigzag direction and the uniaxial strain along the armchair direction, respectively. The irreducible representations of the levels are labeled in the figures. (d) and (e) plot the jointed density of state and the optical absorption spectrum of the unstrained TZGQD. (f)–(h) plot the jointed density of state, the optical absorption spectrum and of the TZGQD for the strain along the zigzag direction. (i), (j), and (k) are the same as (f), (g), and (h), but for the strain along the armchair direction. Here, we use a Lorentz function with a broadening factor of 0.05 eV. To be clear, some levels are plotted with the dashed lines.

Energy spectra of the TZGQD with as functions of the uniaxial strain η along the zigzag direction in (a) and along the armchair direction in (c). (b) and (d), respectively, plot the band gaps of (a) and (c) versus η.

Energy spectra of the TZGQD with as functions of the uniaxial strain η along the zigzag direction in (a) and along the armchair direction in (c). (b) and (d), respectively, plot the band gaps of (a) and (c) versus η.

(a)–(c), respectively, plot the joint density of states, the optical absorption spectra and of the TZGQD with for the different strains η along the zigzag direction. (d), (e), and (f) are the same as (a), (b), and (c), but when the uniaxial strain is along the armchair direction. In (b), (c), (e), and (f), the redshift can be observed with the tensile strain increasing and the blueshift can be observed with the compressive strain increasing. The baseline of each curve in the figures is shifted vertically.

(a)–(c), respectively, plot the joint density of states, the optical absorption spectra and of the TZGQD with for the different strains η along the zigzag direction. (d), (e), and (f) are the same as (a), (b), and (c), but when the uniaxial strain is along the armchair direction. In (b), (c), (e), and (f), the redshift can be observed with the tensile strain increasing and the blueshift can be observed with the compressive strain increasing. The baseline of each curve in the figures is shifted vertically.

Optical absorption spectra of the TZGQD with in (a) and (b), in (c) and (d), and in (e) and (f). Thereinto, (a), (c), (e) are for and (b), (d), (f) are for . Here, the strain is along the armchair direction. (g) and (h), respectively, plot the peak shifts and versus the strain applied along the armchair direction, reflecting the sensitivity of the TZGQD strain sensor for four different sizes.

Optical absorption spectra of the TZGQD with in (a) and (b), in (c) and (d), and in (e) and (f). Thereinto, (a), (c), (e) are for and (b), (d), (f) are for . Here, the strain is along the armchair direction. (g) and (h), respectively, plot the peak shifts and versus the strain applied along the armchair direction, reflecting the sensitivity of the TZGQD strain sensor for four different sizes.

(a) and (b) are the optical absorption spectra and of a TZGQD with the size introduced a vacancy defect at site A, as shown in Fig. 1 , when the strain is along the armchair direction. The redshift and the blueshift effects of the main absorption peaks can be still observed clearly.

(a) and (b) are the optical absorption spectra and of a TZGQD with the size introduced a vacancy defect at site A, as shown in Fig. 1 , when the strain is along the armchair direction. The redshift and the blueshift effects of the main absorption peaks can be still observed clearly.

The optical absorption spectra of the TZGQD with are, respectively, plotted (a) for no strain and , (b) for a uniaxial tensile strain along the armchair direction and , (c) for a uniaxial tensile strain along the armchair direction and . The energy spectrum (d), (e), and (f), respectively, correspond to (a), (b), and (c). The irreducible representations of the levels are labeled in the figures. The dashed line in (f) indicates the position of the Fermi energy.

The optical absorption spectra of the TZGQD with are, respectively, plotted (a) for no strain and , (b) for a uniaxial tensile strain along the armchair direction and , (c) for a uniaxial tensile strain along the armchair direction and . The energy spectrum (d), (e), and (f), respectively, correspond to (a), (b), and (c). The irreducible representations of the levels are labeled in the figures. The dashed line in (f) indicates the position of the Fermi energy.

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