Search

Boron nitride (BN) layers with sp(2) bonding have been grown by metal organic chemical vapor deposition on AlN underlayers, which are deposited on c-plane sapphire substrates. Two different boron precursors were employed-trimethylboron and triethylboron-while ammonia was used as the nitrogen precursor. The BN obtained epitaxial BN films contain ordered rhombohedral (rBN) and partially ordered turbostratic (tBN) stackings as evidenced by x-ray diffraction analysis. We discriminatively identify the PL signatures of the rBN and tBN from those typical of the hexagonal (hBN) and Bernal stackings (bBN). The optical signature of tBN appears at 5.45eV, and it intercalates between the two recombination bands typical of rBN at 5.35eV (strong intensity) and 5.55eV(weaker intensity). The analogs of the high intensity band at 5.35eV in rBN sit at 5.47eV for hBN and at 5.54eV for bBN., Funding Agencies|network GaNeX [ANR-11-LABX-424 0014]; BONASPES project [ANR-19-CE30 0007]; ZEOLIGHT project [ANR-19-CE08-0016]; Universite de Montpellier; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2017-04164]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [IS14-0027]; Carl Tryggers Foundation for Scientific Research [CTS 14:189]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [2009-00971]; Office of Naval ResearchOffice of Naval Research [N00014-20-1-2474, 428]; National Science FoundationNational Science Foundation (NSF) [CMMI 429, 1538127]

The use of novel organosilica materials embedding π-conjugated moieties as semiconductor into field-effect transistors is demonstrated. The chosen π-conjugated core is a [1]benzothieno[3,2-b][1]benzothiophene that is modified with hydrolyzable and crosslinkable triethoxysilyl moieties. After polycondensation, this compound forms a hybrid material composed of charge transport pathways as well as insulating sublayers made of silicon oxide (SiOx). The hybrid material behaves as a semiconductor and is subsequently integrated as active layer into field-effect transistors. These precursors show J-type aggregation that evolves toward H-type aggregates during the sol–gel process, which improve charge transport. Taking advantage of the sol–gel chemistry involved here, hybrid field-effect transistors that are fully crosslinked with covalent bonds are built. Molecules are crosslinked to each other, covalently bonded to the silicon oxide dielectric, and also covalently bonded to the gold electrodes, thanks to the use of an appropriate additional interfacial monolayer. This is the first report of fully covalent transistors. Those devices with modest mobilities show impressive resilience against polar, aliphatic, and aromatics solvents even under sonication. This study opens the route toward a new class of hybrid materials to create highly robust electronic applications., SCOPUS: ar.j, info:eu-repo/semantics/published

We address the intrinsic optical properties of hexagonal boron nitride in deep ultraviolet. We show that the fine structure of the phonon replicas arises from overtones involving up to six low-energy interlayer shear modes. These lattice vibrations are specific to layered compounds since they correspond to the shear rigid motion between adjacent layers, with a characteristic energy of about 6-7 meV. We obtain a quantitative interpretation of the multiplet observed in each phonon replica under the assumption of a cumulative Gaussian broadening as a function of the overtone index, and with a phenomenological line broadening taken identical for all phonon types. We show from our quantitative interpretation of the full emission spectrum above 5.7 eV that the energy of the involved phonon mode is 6.8±0.5 meV, in excellent agreement with temperature-dependent Raman measurements of the low-energy interlayer shear mode in hexagonal boron nitride. We highlight the unusual properties of this material where the optical response is tailored by the phonon group velocities in the middle of the Brillouin zone. © 2017 American Physical Society.