Functionalized few-layer silicene nanosheets: density functional theory on stability, structural, and electronic properties

Using density functional theory calculations, we investigated the properties of few-layer silicene nanosheets, namely bilayers and trilayers, functionalized with group-III or group-V atoms of the periodic table. We considered the Si$_2$X$_2$ bilayers and the Si$_2$X$_4$ trilayers, X = B, N, Al, P. We computed the structural, energetic, dynamic, elastic, and electronic properties of those systems in several stacking configurations, labeled as AA$'$, AB, AA$'$A$''$, and ABC. The results revealed that AA$'$-Si$_2$N$_2$, AB-Si$_2$N$_2$, AA$'$-Si$_2$P$_2$, AB-Si$_2$P$_2$, ABC-Si$_4$B$_2$, ABC-Si$_4$Al$_2$, AA$'$A$''$-Si$_4$P$_2$, and ABC-Si$_4$P$_2$ nanosheets are all dynamically stable, according to their respective phonon dispersion spectra. Additionally, by comparing the standard enthalpies of formation of doped few-layer silicene systems with the ones of the pristine silicene monolayer, bilayer, and trilayer nanosheets, we found that those structures could be experimentally accessed. Exploring the electronic properties of those stable systems, we discovered that the silicene bilayers and trilayers functionalized with N or P atoms change from a metallic to a semiconducting behavior. However, the metallic behavior is kept when the nanosheets are functionalized with B or Al atoms. Finally, by placing our results within the context of silicon-based systems previous investigations, we could envision potential applications for those nanosheets in van der Waals heterostructures, alkali-metal ion batteries, UV-light devices, and thermoelectric materials.