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The hexagonal boron nitride nanosheets (BNNSs) are one of the 2-dimensional(2D) materials, and have been explored for their applications in nanoelectronics etc, owing to their unique properties. Here, BNNSs are utilized to develop a high-performance hybrid piezo/triboelectric nanogenerator (PTEG). BNNSs of a few percentages in weight are incorporated into polydimethylsiloxane (PDMS) to form composites that are able to produce piezoelectric voltages up to ~ 5.4 V with d 33 ~ 12 pC/N. A PTEG composed of BNNS-PDMS and polyamide-6 (PA6) membranes ( 20 × 20 mm 2 ) demonstrates a current density of ~ 230 mA m − 2 , an output voltage of ~ 1870 V and a maximum power density of ~ 103.7 W m − 2 , more than three times higher than those of the control PDMS/PA6 nanogenerator. Electric polarization of the BNNS-PDMS membranes can further enhance the output of PTEGs. Detailed investigation reveals that the dramatically enhanced performance originates from the synergy of piezoelectric effect of BNNSs and increased electron affinity of BNNS-PDMS membranes, demonstrates the excellent potential of BNNS-based PTEGs.

The authors demonstrate that the residual compressive stress in cubic boron nitride films could be relaxed by 1500 K post annealing in H2 atmosphere. According to the IR peak shifting, approximately 4.5 GPa stress was relaxed after 4 hours annealing. Thus film adhesion was improved significantly, cubic boron nitride films with a cubic phase concentration of 90% (vol%) and a thickness of more than 200 nm showed excellent stability and no delaminations were observed even after annealing for over 30 months in the open air, while films without annealing delaminated from substrates within 1 week. Moreover, the relaxation of the compressive stress is accompanied with cubic boron nitride d (111) interplanar distance broadening and corresponding IR peak intensities increasing.

Boron nitride (BN) thin films were deposited on silicon and sapphire substrates by an inductively coupled plasma chemical vapor deposition technique with time-dependent control of the substrate dc bias (Vdc). Turbostratic BN films were deposited on sapphire when the bias reduction rate, ·Vdc, was optimized specifically for cBN growth on silicon. This difference depending on the substrates was explained by a potential drop in the dielectric substrate. By reducing ·Vdc at the early stage of deposition, the cBN phase was successfully deposited on both substrates. We also found that the chemical composition of BN varied from B/(B + N) = 0.48 to 0.57 upon changing the gas ratio of diborane to nitrogen. The gas ratio for film nonstoichiometry resulted in a thicker initial layer, i.e., the delayed nucleation of cBN.

Electronic properties of cubic boron nitride (c-BN) doped with group IIA elements were systematically investigated using the first principle calculation based on density functional theory. The electronic bandgap of c-BN was found to be narrowed when the impurity atom substituted either the B (IIA→B) or the N (IIA→N) atom. For IIA→B, a shallow accept level degenerated into valence band (VB); while for IIA→N, a shallow donor level degenerated conduction band (CB). In the cases of IIBe→N and IIMg→N, deep donor levels were also induced. Moreover, a zigzag bandgap narrowing pattern was found, which is in consistent with the variation pattern of dopants’ radius of electron occupied outer s-orbital. From the view of formation energy, the substitution of B atom under N-rich conditions and the substitution of N atom under B-rich conditions were energetically favored. Our simulation results suggested that Mg and Ca are good candidates for p-type dopants, and Ca is the best candidate for n-type dopant.

Two kinds of turbostratic boron nitride (tBN) thin films were deposited by sputtering with pure Ar or N2 plasma in an ultraclean vacuum chamber. Current–voltage (I–V) characteristics of Ti/tBN/Ti structures revealed that films deposited in Ar showed at least three-orders higher conductivity with strong temperature and electric field dependence compared with those deposited in pure N2. The origin of the higher conductivity was confirmed to be the nonstoichiometry and higher defect density of the tBN films. On the other hand, films deposited in pure N2 plasma showed the characteristics of intrinsic insulator even though the basal plane of tBN was oriented normal to the substrate, namely, parallel to the direction of electronic conduction.

Two kinds of boron nitride thin films, cubic boron nitride film with a layered structure, and turbostratic boron nitride film with a c-axis parallel to the substrate surface, were prepared by inductively coupled plasma-enhanced chemical vapor deposition. Nanoindentation tests revealed that the hardness and elastic modulus of cubic boron nitride films increased with cubic phase content and approached approximately 50 and 250 GPa, respectively, for the case of 96% cubic phase, while those of turbostratic boron nitride films were load and loading rate dependent and as low as 1.5 and 30 GPa, respectively. Moreover, the hysteretic recovery of turbostratic boron nitride after indentation was confirmed, and approximately 50% of the energy dissipated during indentation was found to be released within 1 min.

Nanocrystalline p -type cubic boron nitride/ n -type silicon diodes with three different interfaces were fabricated by plasma chemical vapor deposition and ultrahigh-vacuum bias sputter deposition. When the interface contained a t-BN layer of 25 nm thickness or less, rectification ratios as high as 4×10 4 at room temperature and 10 at 570 K were observed. Even when the interface contained a 1–2-nm-thick insulating layer, diode characteristics were also observed but with a lower rectification ratio of 5×10 2 . The carrier conduction at the interface was characterized primarily by thermal excitation, where barrier height altered with bias voltage similar to the case of an ideal n -Si/ p -c-BN heterojunction in the temperature range of 300–570 K.

The deformation behavior of a textured turbostratic boron nitride thin film of 120 nm in thickness, with its c -axis parallel to the film surface, was investigated under nanoindentation. The load displacement response of the textured turbostratic boron nitride film was revealed to be loading rate dependent, and a creep-like phenomenon was observed under constant load. Moreover, the textured turbostratic boron nitride film was found to be able to recover with hysteresis, even when pressed to the maximum depth of approximately 20% of the film thickness. The apparent hardness and Young's modulus were estimated to be 1.5 and 30 GPa, respectively. The reversible hysteretic deformation, similar to that of a viscoelastic body, is clearly controlled by the bending of the sp 2 -bonded turbostratic boron nitride basal planes.

We could determine the substrate pretreatment conditions required for the deposition of cubic boron nitride films without an interfacial amorphous layer by investigating nanostructures, chemical composition, and bonding states of the amorphous layer, which inevitably grew prior to the growth of cubic BN in ion-assisted chemical vapor deposition. The amorphous layer was composed of a native Si oxide layer and a complex oxide layer consisting of B, N, Si, and 10–20 at. % oxygen. However, by the substrate pretreatment, 1200 K heating in 20 mTorr H2 atmosphere for 120 min, the crystallinity of the Si substrate surface could be retained throughout the removal of the native oxide layer, and turbostratic BN was revealed to grow directly on the Si substrate. In addition, we could reduce the thickness of the turbostratic BN layer to less than 3 nm, and increase the adhesion strength markedly. The formation of the amorphous layer was found to be caused by two factors: the native oxide layer and the ion bombardment effects.

Chemical species in plasma are crucial for understanding the mechanism of cubic boron nitride film vapor phase deposition and controlling the film structure. In this study, the plasma condition for cubic boron nitride deposition by low-pressure inductively coupled plasma-enhanced chemical vapor deposition using B2H6, N2, and Ar as reactant gases has been diagnosed by a quadrupole mass spectrometer with an ion energy analyzer. The ionization potentials of BXHY (X=1–2, Y=0–6) decomposed from B2H6 have been measured to be between 11.6 and 18.9 eV. B2H6 was totally ionized to B+ together with small amounts of BH+, BH2+ and B2HY+ in plasma above the 2 kW input power. N2 was only partially ionized, and the degree of ionization increased with increasing Ar partial pressure. Neutral species under the present plasma environment were N2, Ar and He, but N and H were not detected even by appearance mass spectrometry. Our results demonstrate that the main sources for cubic boron nitride formation are ions produced in plasma. The interaction between N2 and the growth surface suppresses the cubic boron nitride formation by enhancing the tBN growth, and this surface interference can be reduced by introducing Ar into the system.

Inductively coupled plasma-enhanced chemical vapor deposition with a time-dependent biasing technique was applied for cubic boron nitride (c-BN) deposition on a Si substrate, and the growth mode of the transition layer was investigated by high-resolution transmission electron microscopy. It was found that elimination of either an amorphous layer or a turbostratic BN (t-BN) layer was possible, and the two-layered structure, namely, direct growth of a c-BN layer on an amorphous layer or a t-BN layer on a Si substrate, was realized by pre-treatment conditions of positive bias.

Cubic boron nitride thin films were deposited on silicon substrates by plasma chemical vapor deposition, and the nanostructure of the interface between the film and substrate was investigated by cross-sectional high-resolution transmission electron microscopy. Cubic boron nitride was found to nucleate directly on the properly pretreated silicon substrates in some local areas; in particular, cBN nuclei with a size of approximately 3 nm are nucleated on (111)–(100) step surfaces with an epitaxial relationship. This suggests the possibility of direct growth of cubic boron nitride in special surface environments of silicon substrates.

With the aim of developing a nanostructure, we produced an sp 2 -bonded boron nitride nanoarray (BNNA), and observed its dynamic deformation behavior using high-resolution transmission electron microscopy with a piezoceramic tube for three-axis positioning of an indenter. The BNNA has remarkable flexibility and resiliency, such that no permanent deformation occurred when it was bent repeatedly to the minimum radius of curvature of about 4 nm. Even in repeated bends to the minimum radius of curvature of about 0.3 nm, the BNNA underwent no catastrophic failure.

Cubic boron nitride (cBN) thin films were deposited on silicon wafers by low-pressure inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD). By using special substrate pre-treatment processes including positive biasing treatment in H2 plasma or 1200 K pre-heating in H2 atmosphere followed by an N2 plasma treatment, turbostratic BN (tBN) intermediate layer was revealed to directly grow on Si substrates without an initial amorphous layer. The thickness of the tBN transition layer can be reduced to less than 3 nm.

Structural and electronic properties of Zn-doped cubic boron nitride (cBN) were investigated via first principle calculation based on density functional theory. Our simulation suggests that Zn can substitute for both B (ZnB) and N (ZnN) atom; ZnB is energetically favorable, and ZnN can only be prepared under B-rich conditions. ZnB induced a shallow acceptor level; however, the large difference in electronegativity between Zn and N makes the acceptor level strongly localized, which reduces effective carrier density. In the case of ZnN, both deep acceptor levels within band gap and shallow acceptor levels at the top of valence band were induced, which produced more free carriers than ZnB. The calculated results account for experimental results of enhanced electric conductivity of Zn-doped cBN films prepared under B-rich conditions.

Theoretical and experimental investigations on the dependence of the intensity of infrared (IR) absorption of polycrystalline cubic boron nitride thin films under the residual compressive stress conditions have been performed. Our results indicate that the intensity of the IR absorption is proportional to the total degree of freedom of all the ions in the ordered regions. The reduction of interstitial Ar atom concentration, which causes the increase in the ordered regions of cubic boron nitride (cBN) crystallites, could be one cause for the increase in the intensity of IR absorption after residual compressive stress relaxation. Theoretical derivation is in good agreement with the experimental results concerning the IR absorption intensity and the Ar interstitial atom concentration in cubic boron nitride films measured by energy dispersion X-ray spectroscopy. Our results also suggest that the interstitial Ar is the origin of residual compressive stress accumulation in plasma enhanced cBN film deposition.

The effects of compressive stress on the TO phonon frequencies of hexagonal boron nitride (hBN) in cubic BN (cBN) films were investigated using infrared absorption spectroscopy, showing that the B–N stretching vibration of hBN at 1380 cm−1 shifted to high wavenumbers under biaxial compressive stress with the rate 2.65 cm−1 per GPa, while the B–N–B bending vibration near 780 cm−1 shifted to low wavenumbers with the rate −3.45 cm−1/GPa. The density functional perturbation theoretical calculation was carried out to check the above phonon frequencies under stress for two typical orientations of hBN crystallite. The results are shown to be in fair agreement with the experimental data. Our results suggest that the residual compressive stress accumulated in cBN films can be evaluated from the IR peak position near 780 cm−1.

Cubic BN films with a pure cubic phase upper layer were prepared by plasma-enhanced chemical vapor deposition. Infrared spectroscopy was applied to analyze the content of initial sp2-bonded BN layer in cubic BN thin films under compressive stress. It was found that the peak intensity near 1380cm−1 attributed to the B–N stretching vibration of sp2-bonded BN was suppressed by the compressive stress in cubic BN films. The deviation between the measured and calculated peak intensities was found to be linear with the compressive stress when the upper layer of the film is a pure cubic phase layer.

Chemical species in the low-pressure inductively coupled plasma for cubic boron nitride (cBN) film deposition using B 2 H 6 , N 2 , He and Ar as reactant gases were investigated by quadrupole mass spectrometry. B 2 H 6 was found to be ionized totally, while N 2 was only partially ionized. The species in plasma were Ar, He, N 2 molecules and Ar + , He + , N + , N + 2 , B + , B x H + y , H + and H + 2 ions, no H and N radical was detected by appearance potential mass spectrometry. The introduction of H 2 and N 2 gases into the deposition system was found to produce a large mount of H radicals and excited N * 2 molecules, which suppressed the cBN formation by reacting with the growth surface. The etching and sputtering of cBN and turbostraotic boron nitrde (tBN) by H 2 and Ar plasmas were also evaluated, and we did not find that the tBN is selectively etched or sputtered. Moreover, high-resolution transmission electron microscopy of as-deposited cBN on the edge of ultrathin silicon flake substrate showed that the surface of as-deposited cBN film was composed of cBN {111} nanofacets, and no thin sp 2 -bonded boron nitride surface layer was observed. Our results suggest that cBN nucleates and then grows on the top surface in chemical vapor deposition systems, and the processes of cBN surface nucleation and growth in the present system was also discussed simply.

Nanostructures of the turbo-stratic boron nitride (tBN) transition layer in cubic BN (cBN) thin films deposited on silicon substrates by low-pressure inductively coupled plasma-enhanced chemical vapor deposition have been studied by means of cross-sectional high-resolution transmission electron microscopy. The variation of tBN (0002) basal plane orientation at different growth stages, from random to texture and then random again, was observed. Quantitative analysis of tBN orientation revealed that cBN nucleation occurred when approximately 64% of the tBN c axis oriented parallel to the substrate surface in the angle ±10° and the distribution function drawn in a polar diagram was approximated by the function: cos6 (θ). At the interface between tBN and cBN, both hexagonal and rhombohedral configurations were observed, and both were found to act as structural precursors and/or deposition sites for cubic boron nitride nucleation. In addition, the compressed tBN configuration accompanied by d spacing contracti...