Epitaxial growth mechanism of high-crystallinity lanthanum hexaboride (001) thin films on silicon (001) by electron beam deposition

Abstract

The growth of high-quality LaB6 thin films on Si(001), by using electron beam deposition, is reported. The films show (001) orientation as confirmed with X-ray diffraction and electron backscattered diffraction (EBSD). The sharp Kikuchi pattern from EBSD evidences a single-crystalline nature of the LaB6(001) films. To accommodate for the lattice mismatch, the LaB6 is azimuthally rotated by 45° with respect to the Si lattice (LaB6[100] ∣∣ Si[110]) and grows in a supercell structure. Early stages of the film growth were clarified using atomic force microscopy, with a unique “directional” and “island-to layer-by-layer” type of growth of this covalently bonded heterosystem.

Optical Properties and Optimization of LaB6 Thin Films for Photothermal Applications

“…Beyond this temperature, the possible interdiffusion of B and Si can degrade the crystallinity of LaB 6 . [26] This also agrees with our experimental results obtained at 800 °C, where a lower FOM can be observed when compared to the films deposited at 770 °C. In addition to E-beam evaporation, we attempted to deposit LaB 6 under similar conditions, except for a slower deposition rate through the pulsed laser deposition (PLD) technique, i.e., ≈0.05 Å s −1 (Figures S2 and S3, Supporting Information).…”

“…A separate crystal growth study indicated that this coherence in the crystal orientation is motivated by epitaxial growth with a magic mismatch of the coincidence lattices of LaB 6 and Si(001) surface, which exhibits an in‐plane azimuthal rotation of 45° with respect to each other (LaB 6 [100]||Si [110]). [ 26 ]…”

“…Acoustic or T 1u modes with a displacement of lanthanum atoms with respect to boron octahedral cages can be observed. [ 26,32,33 ] This mode is originally Raman inactive in bulk, but becomes Raman active herein, probably owing to the deformation and symmetry breaking of the near‐surface lattices or at the grain boundaries. It can be observed that all LaB 6 Raman modes are present in the LaB 6 films deposited at substrate temperatures higher than 400 °C, whereas the film deposited at 300 °C exhibits only a dielectric nature and does not exhibit any LaB 6 Raman modes.…”

“…[20][21][22][23][24][25] It should also be noted that to achieve a high NIR absorbance, a uniform dispersion of LaB 6 nanoparticles in a matrix is required, without which unstable optical performance will most likely occur. [25] Although the high-temperature stability of a LaB 6 crystal/ electronic structure has been well established, there have been few reports focusing on the synthesis of pristine LaB 6 thin films [26][27][28] with specific characteristics such as high crystallinity and low loss, high optical response, thermal stability, and CMOS compatibility for plasmonic device applications. In this study, we demonstrate the synthesis of highly oriented LaB 6 films with low-loss and high optical response, having an optical figure of merit (FOM) closer to that of Au and better than those of W, Mo, and TiN.…”

“…A separate crystal growth study indicated that this coherence in the crystal orientation is motivated by epitaxial growth with a magic mismatch of the coincidence lattices of LaB 6 and Si(001) surface, which exhibits an in-plane azimuthal rotation of 45° with respect to each other (LaB 6 [100]||Si [110]). [26] As mentioned earlier, there have been very few reports on the optimization of pristine LaB 6 films for optical applications. Although the effect of substrate temperature has been investigated, improvement of the optical properties of LaB 6 has focused mainly on doping.…”