Supporting information for:
Low temperature electrical and photo-responsive properties of MoSe2
1. SEM and TEM images
2. Optical photography of the device
3. Photo-responsive phenomenon
4. Experimental details
5. Process of device fabrication
1. SEM AND TEM IMAGES
Figure S1| (a) Typical SEM image of the as prepared MoSe2. (b) Topography taken on
the edge of the as prepared MoSe2, scanned by TEM. (c) HR-TEM image of marked
circular area.
Fig. S1 shows typical SEM and TEM images of the as prepared MoSe2. The as
prepared MoSe2 were assembled with Nanosheets and formed MoSe2 flower-like
nanostructure. The average diameter of the as prepared MoSe2 is about 500 nm. The
fringes of the as prepared crimped and the detail HR-TEM image is shown in Fig. S1c.
the planes of crystal lattices are obviously observed and the distance between two
(002) planes is 0.689 nm, as labeled in Fig. S1c.
2. OPTICAL PHOTOGRAPHY OF THE DEVICE
Figure S2| Top view optical photography of the fabricated device with the as prepared
MoSe2
The top view optical photography of the device is presented in Figure S2. White parts
of two sides in Figure S2 are ITO and the middle part is the as prepared MoSe2. The
distance of the gap between two sides is about 121 μm.
3. PR PHENOMENON
Figure S3| (a) I-T curve measured using red illumination wavelengths of 650 nm at
different temperatures from 300 to 43 K. (b) PR curves under red illumination
repeatedly turned on and off.
Single cycle and sum of cycles are shown in Figure S3a and S3b. Electrical
conductivity reduced as temperatures went down and the shapes of PR current became
different at temperatures below 183K.
4. EXPERIMENT DETAILS
The method to fabricated MoSe2 were described in our previous work and crystalline
structure of the as prepared products was characterized by powder X-ray diffraction
(XRD) with 2θ ranging from 10° to 70° at room temperature, using Cu Ka radiation(λ
= 0.15406 nm). The surface morphologies and element content of the products was
detected by scanning electron microscopy (SEM), energy dispersive X-ray
spectroscopy (EDX) and high resolution transmission electron microscope (HR-TEM).
A Raman spectrum was measured from 100 to 400 cm-1 using a He-Ne laser with a
532 nm wavelength. Ultraviolet visible (UV-Vis) absorption spectroscopy was tested
with AvaSpec 2048 UV-VIS-NIR spectrophotometer.
First-principles calculations are performed using the Vienna ab initio simulation
package (VASP) on
the basis
of density-functional
theory (DFT). The
exchange-correction interaction is treated by the generalized gradient approximation
(GGA) with Perdew-Burke-Ernzerhof (PBE) functional. The cutoff energy is set to be
500 eV. The Monkhorst-Pack grids of 12121 and 12126 are used for monolayer
and bulk MoSe2, respectively. In order to eliminate the interaction between two
adjacent monolayer of MoSe2, a vacuum layer larger than 12 Å is adopted. The
geometric structures are fully relaxed until the Hellmann-Feynman force on each
atom is less than 0.02 eV/Å. In the calculations, the experimental lattice constants of
bulk MoSe2 (a=3.288Å, c=12.900Å).
5. PROCESS OF DEVICE FABRICATION
Figure S4| Diagram of the fabrication process of device with the as prepared MoSe2.
Figure S4 shows a diagram of device fabrication with the as prepared MoSe2. The as
prepared MoSe2 were firstly re-dispersed in ethanol by ultrasonic for 30min. The
drips containing the as prepared MoSe2 were dropped onto the gap between two ITO
electrodes, and then the device was dried in vacuum at 60ºC for 10 minutes. The two
steps were repeated for several times. Two copper leads were adhered with silver glue
on surfaces of two ITO electrodes.