## 3 Results
\begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Sample No.**} & \multirow{2}{*}{**Carrier Type**} & \multirow{2}{*}{\begin{tabular}{c} **R\({}_{\text{sheet}}\)** \\ **(\(\mathbf{\Omega}\)/\(\mathbf{\Sigma}\))** \\ \end{tabular} } & **Thickness** & \multirow{2}{*}{\
\begin{tabular}{c} **Carrier** \\ **(nm)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **\(\mathbf{\mu}\)** \\ **(\(\mathbf{\Omega}\)/cm\({}^{3}\))** \\ \end{tabular} } & **Resistances** \\  & & & & & **(\(\mathbf{\Omega}\)/cm\({}^{3}\))** & **(cm\({}^{2}\)/V\(\cdot\)s)** & **(f\(\mathbf{\Omega}\))** \\ \hline A-1 & \(\backslash\) & \(\backslash\) & 57.81 ± 4.38 & \(\backslash\) & \(\backslash\) & Insulating \\ A-2 & \(p\) & 75.04 & 32.01 ± 2.08 & 2.23 ± 1020 & 74.62 & 21.85/12.23 \\ B-1 & \(p\) & 147.1 & \(\approx\)15 & 4.39 ± 1020 & 64.44 & 39.81/26.08 \\ \hline \end{tabular}
\end{table} 
Table 2: Electrical properties of sample A-1, A-2, and B-1 resistances are measured from two orthogonal directions of a square-shaped sample. (the blue curves), when growth temperature increases, the total crystalline content on the sapphire surface decreases in the growth window until zero. It is worth mentioning that all of the XRD scans are symmetric scans on the sapphire (0001) so only the crystal planes that are parallel to the surface can be measured. This means the total crystalline content is underestimated and the detected signals indicate the coherence of the crystals that are likely to have been epitaxially grown on the substrate. We also introduce an effective adsorption coefficient to describe the adsorption process of Sb\({}_{4}\) molecules on c-plane sapphire, as shown in Figure 3c (the red curve). The effective adsorption coefficient is calculated while using the ratio of the effective thickness at all growth temperatures (Table 1) and the effective thickness of 150 \({}^{\circ}\)C. We assume that, under 150 \({}^{\circ}\)C, the effective adsorption coefficient is 1, because of the low vapor pressure and high sticking coefficient of Sb at this temperature [36]. Calculation details can be found in the Supplementary Materials. We tried to fit the Sb (003) peak and Sb (012) peak using a multi-order Gauss function to further determine the antimonene percentage more quantitatively in the grown samples. Subsequently, we calculated the integrated area of each peak and got the ratio of Sb (012)/[Sb (003) + Sb (012)] to estimate the antimonene percentage in the crystalline contents. Based on this calculation, we draw the phase diagram of antimonene formation and crystalline content as a function of the growth temperature on c-plane sapphire, as shown in Figure 3d. We can see that, when the growth temperature is between 220 \({}^{\circ}\)C-260 \({}^{\circ}\)C, there is a clear trend showing the antimonene content increases, which exceeds 50 percent. However, during the same temperature region, the total crystalline content decreases, which indicates that the reduction of effective adsorption limits the yield of crystal growth. This competing mechanism makes the preferential growth of antimonene very difficult. When the growth temperature is either between 200 \({}^{\circ}\)C-220 \({}^{\circ}\)C or 260 \({}^{\circ}\)C-270 \({}^{\circ}\)C, the antimonene content becomes  
Figure 2: (**a**–**h**) AFM images of a c-plane sapphire substrate and sample A-1 to A-7, showing the surface morphology change due to the temperature increment. (**i**) Raman spectra of all the group A (Sb\({}_{4}\)) samples. Peaks at 350 cm\({}^{-1}\) to 450 cm\({}^{-1}\) are from the c-plane sapphire, 110 cm\({}^{-1}\) and 150 cm\({}^{-1}\) are the two signature vibrational modes of antimony. (**j**,**k**) AFM images of antimonene, being characterized immediately after the sample is taken out of the vacuum and one year later. lower than 50 percent. When it is below 200 \({}^{\circ}\)C, the deposited antimony on sapphire is amorphous and, when it is higher than 270 \({}^{\circ}\)C, no growth is observed, which is mainly due to the low sticking coefficient.