SupplementaryMaterial

Synthesis of largemonolayer single crystal MoS2nanosheetswith

uniformsizethrough adouble-tube technology

Synthesis

Monolayer MoS2 grains were grown on SiO2(300 nm)/Si substrate using

chemical vapor deposition(CVD) method and a double-tube system. The system

consisted of a 2-inch-diameter quartztube furnace and a one-side sealed inner tube,

which was placed at the high-temperature area.Substrates were cleaned in acetone,

alcohol and deionized water with ultrasonic cleaning for 15 minutes respectively. The

quartz boat containing 15 mg MoO3 (>99.9%, Alfa Aesar) wasplaced at the bottom of

inner tube and another boat containing 0.6 g S waslocated in the entrance of the 2-

inch-diameter outer tube, whilethe substratewas placed between the quartz boats. The

growth was carried out at atmospheric pressure with an argon flow of 150 sccm. The

furnace was heated from room temperature to 850 °C at a speed of 40 °C/min. After

keeping at 850°C for 10 minutes, the furnace cooled to room temperature

naturally.Figure S1(a) shows the PL spectrum of monolayer MoS2. The excited laser

wavelength is 532 nm.

Figure S1(b) shows the Ramanspectracorresponding with Figure 2(b).

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Numerical Simulation

The concentration distribution of the sources is simulated by a diffusion

equation. The equation is as followed:

dcdt

=D（ d2 cd x2 +

d2 cd y2 ）+R

Where c is the concentration, D is the diffusion coefficient, and R is the source

term or the concentration at the source. A convection-diffusion equation should be

more accurate for the simulation since the material is transported by Arflow. But the

velocity of Arflow, 0.03 cm/s (150 sccm) is much smaller than the diffusion velocity

calculated below, the convection term can be ignored. The equation is solved using

finite element methods (FEM).

The diffusion coefficient is estimated by the Lennard-Jones potential function:1

D=1.8583 ×10−7 √T3( 1M 1

+ 1M 2

)

pσ122 Ω

Where T is the absolute temperature, p is the pressure,M is the molar mass,1 and

2 index the two kinds of molecules present in the gaseous mixture,σ 12 is the average

collision diameter, of order 10, andΩis the collision integral, oforder 1.The diffusion

coefficients of MoO3 and S are estimated as 1.5 cm2/s based on the parameters in our

experiment.

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As for the concentration at source, we assume the MoO3 and S precursors are

sublimated at a constant speed. From the diffusion coefficient we can derive the space

occupied by the sublimated precursors per unit time. The concentration at source then

can be estimated as the ratio of the sublimated amount of substance per unit time

divided by the space occupied, i.e. C source=m

t ∙ S. The concentration at source is

2.6 ×10−9 mol/cm3 for MoO3 and 2.6×10−6 mol/cm3 for S. Parameters used in our

calculation are listed below:

TABLE SI. Coefficients used in the calculation.

T (K)

P (atm

)

Mass of MoO3(mg)

Mass of S(mg)

Time of reaction (min)

Diameter of outer tube

(mm)

Diameter of inner tube

(mm)

1123 1 2.5 600 30 44 21

1 Yogesh Jaluria Wilson K. S. Chiu, Numerical Heat Transfer, Part A: Applications 37, 113 (2000).

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FIG. S1. (a) PL spectrum of monolayer MoS2. (b) Raman spectra of MoS2 on the nine parts.

FIG. S2. The optical images of products at A, B and C of Figure 3(c).

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FIG. S3. Raman spectrum of MoO3-x.

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FIG. S4. Concentration distributions of MoO3 and S in (a) double-tube system (left side of the inner

tube is sealed); (b) an inner tube with both sides opened and covered by an outer tube; (c) outer tube.

Except for the set-ups, other parameters are the same.

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FIG. S5. Characterization of MoOS2: (a) SEM photo; (b) SAED pattern; (c) EDS spectrum of MoOS2.

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