Supplemental Material for Manuscript
Tunable photoluminescence from sheet-like black phosphorus crystal by
electrochemical oxidation
Z. X. Gan,1 L. L.Sun,1 X. L. Wu,1,* M. Meng,1 J. C. Shen,1and Paul K. Chu2,*
1
Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative
Innovation Center of Advanced Microstructures, National Laboratory of Solid State
Microstructures, Nanjing University, Nanjing 210093, P. R. China
2
Department of Physics and Materials Science, City University of Hong Kong, Tat Chee
Avenue, Kowloon, Hong Kong, China
BP
BP oxide
Reflectance (%)
70
60
50
40
250
500
750
1000
1250
1500
Wavelength (nm)
Figure S1. Diffusion reflectance spectra (DRS) acquired on the Shimadzu UV-3600
spectrometer with an integrated sphere attachment.
The detector changes from a visible one
to NIR at around 750 nm resulting in the sharp drop at 750 nm.
that the bandgap does not change significantly.
The similar DRS tend suggests
Figure S2. DFT calculation conducted to theoretically confirm that the splitting of the 𝐴𝑔1
mode arises from surface oxidation. We first obtain structural optimization of the BP with
surface dangling oxygen by calculating the total energy.
(a) with the red ball representing oxygen.
The optimized structure is shown in
In the calculation, the plane wave basis and norm-
conserving pseudo potentials with gradient exchange-correlation potential corrections are
employed.
Using the BFGS minimizer in the CASTEP package with default convergence
tolerances of 1.0×10-5 eV for energy and 0.03 eV/A˚ for maximum displacement, the geometric
structures of all the supercells are optimized to obtain stable structures or polymorphs with
minimized total energy.
Afterwards, the optimized geometrical structure is employed to
construct and diagonalize the Hessian matrix as follows:
′
𝑘,𝑘
𝐷𝛼𝛼
′ =
′
1
′
√𝑀𝑘 𝑀𝑘 ′
𝑘,𝑘
where Φ𝛼𝛼
′ are the matrix force constants.
𝑘,𝑘
⃗⃗⃗⃗𝛼
−𝑖𝑞⃗ .𝑟
∑ Φ𝛼𝛼
′ 𝑒
𝛼
The vibrational frequencies are obtained as the
square roots of the eigenvalues belonging to each mode of the phonon wavevector 𝑞 = 0.
The calculated Raman spectrum in (b) shows clear splitting in BP oxide compared to bulk BP.
(a)
A
B
C
D
Intensity (a.u.)
1200
800
400
0
100
200
300
400
500
-1
Raman shift (cm )
(b) 1400
Intensity (a.u.)
1200
1000
800
600
400
200
0
1000
2000
3000
4000
5000
6000
-1
Raman shift (cm )
Figure S3. (a) Raman spectra acquired from four different sheets after removing the oxidized
surface layers.
No Raman peaks appear below 300 cm-1 and the three sharp peaks
corresponding to the 𝐴𝑔1 , 𝐵𝑔2 , and 𝐴𝑔2 modes confirm that the core of the BP oxide is not
oxidized by the electrochemical treatment.
(b) Long-range Raman spectrum showing no PL
peaks indicating that oxidation occurs mainly occurs on the surface of BP oxide.