Alkylboranes, such as trimethylboron (TMB) and triethylboron (TEB), are promising alternative precursors in lowtemperature chemical vapor deposition (CVD) of boron-containing thin films. In this study, CVD growth of B−C films using TMB and quantum-chemical calculations to elucidate a gas phase chemical mechanism were undertaken. Dense, amorphous, boron-rich (B/C = 1.5−3) films were deposited at 1000 °C in both dihydrogen and argon ambients, while films with crystalline B 4 C and B 25 C inclusions were deposited at 1100 °C in dihydrogen. A script-based automatization scheme was implemented for the quantum-chemical computations to enable time efficient screening of thousands of possible gas phase CVD reactions. The quantum-chemical calculations suggest TMB is mainly decomposed by an unimolecular α-H elimination of methane, which is complemented by dihydrogen-assisted elimination of methane in dihydrogen.

Epitaxial rhombohedral boron nitride films were deposited on α-Al2O3(001) substrates by chemical vapor deposition, using trimethylboron, ammonia, and with a low concentration of silane in the growth flux. The depositions were performed at temperatures from 1200 to 1485 °C, pressures from 30 to 90 mbar and N/B ratios from 321 to 1286. The most favorable conditions for epitaxy were: a temperature of 1400 °C, N/B around 964, and pressures below 40 mbar. Analysis by thin film X-ray diffraction showed that most deposited films were polytype-pure epitaxial r-BN with an out-of-plane epitaxial relationship of r-BN[001] ∥ w-AlN[001] ∥ α-Al2O3[001] and with two in-plane relationships of r-BN[110] ∥ w-AlN[110] ∥ α-Al2O3[100] and r-BN[110] ∥ w-AlN[110] ∥ α-Al2O3[1 � 00] due to twinning.

The elongation transition thickness (hElong) is a central concept in the theoretical description of thin-film growth dynamics on weakly interacting substrates via scaling relations of hElong with respect to rates of key atomistic film-forming processes. To date, these scaling laws have only been confirmed quantitatively by simulations, while experimental proof has been left ambiguous as it has not been possible to measure hElong. Here, we present a method for determining experimentally hElong for Ag films growing on amorphous SiO2: an archetypical weakly interacting film/substrate system. Our results confirm the theoretically predicted hElong scaling behavior, which then allow us to calculate the rates of adatom diffusion and island coalescence completion, in good agreement with the literature. The methodology presented herein casts the foundation for studying growth dynamics and cataloging atomistic-process rates for a wide range of weakly interacting film/substrate systems. This may provide insights into directed growth of metal films with a well-controlled morphology and interfacial structure on 2D crystals-including graphene and MoS2-for catalytic and nanoelectronic applications. Published by AIP Publishing.

Funding Agencies|Linkoping University (LiU) [Dnr-LiU-2015-01510]; Swedish research council [VR-2011-5312, VR-2015-04630]; Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC)

We use the ability to control surface chemistry in chemical vapor deposition (CVD) to deposit boron−carbon films into pores with an aspect ratio of 60:1 without clogging the opening, and into lateral trenches with ratios of up to 2000:1. In contrast to many other surface-controlled CVD processes, operating at low temperatures (100−250 °C) and pressures (10−1000 Pa), we use trimethylboron at a higher temperature (700 °C) and pressure (5000 Pa), affording a surface-inhibited CVD process in hydrogen ambient. We show that the deposition rate is highly dependent on the partial pressure of hydrogen; decreasing proportionally to the logarithm of the partial pressure. The surface-controlled effect is not encountered in argon ambient. We propose that this is explained by a competitive adsorption of growth species and inhibiting dihydrogen or atomic hydrogen species following a Temkin isotherm.

Boron nitride (BN) layers with sp2 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 5.45 eV, and it intercalates between the two recombination bands typical of rBN at 5.35 eV (strong intensity) and 5.55 eV(weaker intensity). The analogs of the high intensity band at 5.35 eV in rBN sit at 5.47 eV for hBN and at 5.54 eV for bBN.