Raman studies on the effect of multiple-energy ion implantation on single-crystal hexagonal boron nitride

Abstract

Single energy ion implantation of hexagonal boron nitride (h-BN) at various fluences and keV energies has shown that there is a change in the local symmetry of the crystal from hexagonal to the cubic (c-BN) symmetry. These conclusions have been primarily based on Raman scattering (RS) and Fourier transform infrared spectroscopy. Transmission electron microscopy (TEM) analyses have been a challenge because the sample preparation for cross-sectional study of both the polycrystalline substrates and single-crystal material used in the study presented problems that were difficult to circumvent. A multiple-energy implant with different fluence fractions has been used to create a uniform implanted layer in the material from the surface to the end of range of the implant in this study. We report on the initial RS studies on these samples.

Allotrope conversion and surface hardness increase in ion implanted boron nitride

“…Hardness testing of the implanted BN samples was carried out using the FM-700 micro- Cubic BN with nanoscale particles tends to show the LO phonon modes [4,[7][8], shifted to lower energies, as we see here after implantation as broad peaks around 1300 cm -1 ; this peak indicates a phase change to cubic-BN, as reported in detail before [1][2][3][4][5].…”

“…Cubic BN is synthesized in industrial quantities under pressure, but it has been shown that the implantation of light ions into h-BN can trigger a phase change to c-BN, which forms a thin layer of nanoparticles (9nm) within the implanted region. From Raman, X-ray and infrared analyses [1][2][3][4][5] there is an optimum ion fluence for He + , Li + , B + and N + which decreases as the ion mass increases. The creation of interstitial defects is thought to tip the structure from hexagonal layers to the tetrahedral cubic form.…”

“…Raman spectroscopy was used to analyse the samples to confirm any ion induced phase change reported in [1][2][3][4][5]. This was done by taking Raman measurements (the 514.5nm…”

Cross-sectional transmission electron microscopy studies of boron ion implantation in hexagonal boron nitride

“…In this work we use moderate energy B ion implantation as a technique to promote h-BN to c-BN nucleation and characterize samples using TEM. stretching within the basal plane [36], [43]. Figure 3 (b) represents the Raman spectrum for the sample implanted with 150 keV B to a fluence of 1.5×10 15 ions/cm 2 .…”

“…Cubic BN with size >500 nm showstwo phonon modes: the Transverse Optical (TO) line which occurs at ~1057 cm -1 and the Longitudinal Optical (LO) line which occurs at ~1305 cm -1 [45].If the c-BN contains micron and nano-size crystals, the Raman spectrum will display a TO mode at 1057 cm -1 and LO modes at 1305 cm -1 with an unstructured broad feature located near the LO phonon mode centred around 1290 cm -1 . When the specimen is made of nanocrystals (<100nm) the TO mode for c-BN disappears, while the LO mode peak broadens and shifts to a frequency of about 1290 cm -1 .The experimental measurements and analyses for the changes in c-BN Raman lineshape for c-BN with various particle sizes have been carried out and discussed in previous work [36]. Parayanthal et al [46]using the Spatial Correlation Model (SCM) explained the effect of particle size on the changes in the Raman lineshape broadening and symmetry.…”