Additions and Corrections - Vapor Pressures of the Methylamine-Boranes and Ammonia-Triborane.

Alton, Earl Robert.; Brown, R. S.; Carter, J.; Taylor, R. C.

doi:10.1021/ja01509a612

Cited by 3 publications

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“…As compared to AB, TMAB has a lower melting temperature due to the presence of the alkyl groups. 44,45 Therefore, the growth of the h-BN films can be realized by sublimating TMAB at a relatively lower sublimation temperature (T s ). Figure 1b shows the thermogravimetric 47,48 Further intermolecular reactions of this compound through dehydrocoupling form cyclic chains with the framework of h-BN, 47,48 and 2D h-BN film will be produced by further crosslinking of these chains at above 1000 °C.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…As shown in the DTA spectrum of TMAB (Figure 1b), the decomposition/ melting of the precursor will occur at a faster rate when a higher temperature is used. 45 This results in the increase of volatile dehydrogenated products transported to the Cu substrate within a shorter time. We propose that the formation of BCN film is associated with the increased flow rate of the dehydrogenated derivatives and during the cross-linking process to form cyclic chains of h-BN, the methyl group may have played a more active role which forms chemical bonds within the h-BN structure, resulting in an increased density of N−C bonds.…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

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Trimethylamine Borane: A New Single-Source Precursor for Monolayer h-BN Single Crystals and h-BCN Thin Films

Tay

Tsang³

et al. 2016

Chem. Mater.

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Due to their exceptional chemical and thermal stabilities as well as electrically insulating property, atomically thin hexagonal boron nitride (h-BN) films have been identified as a promising class of dielectric substrate and encapsulation material for high-performance two-dimensional (2D) heterostructure devices. Herein, we report a facile chemical vapor deposition synthesis of large-area atomically thin h-BN including monolayer single crystals and C-doped h-BN (h-BCN) films utilizing a relatively low-cost, commercially available trimethylamine borane (TMAB) as a single-source precursor. Importantly, pristine 2D h-BN films with a wide band gap of ∼6.1 eV can be achieved by limiting the sublimation temperature of TMAB at 40 °C, while C dopants are introduced to the h-BN films when the sublimation temperature is further increased. The h-BCN thin films displayed band gap narrowing effects as identified by an additional shoulder at 205 nm observed in their absorbance spectra. Presence of N−C bonds in the h-BCN structures with a doping concentration of ∼2 to 5% is confirmed by X-ray photoelectron spectroscopy. The inclusion of low C doping in the h-BN films is expected to result in constructive enhancement to its mechanical properties without significant alteration to its electrically insulating nature. This study provides new insights into the design and fabrication of large-area atomically thin h-BN/h-BCN films toward practical applications and suggests that the range of precursors can be potentially extended to other anime borane complexes as well.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Chemistry Of Materialsmentioning

confidence: 99%

Trimethylamine Borane: A New Single-Source Precursor for Monolayer h-BN Single Crystals and h-BCN Thin Films

Tay

Tsang³

et al. 2016

Chem. Mater.

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“…12,15,16,18,21,[32][33][34][35][36][37][38] High purity ammonia-borane shows no decomposition over two months at room temperature, 39 and its vapor pressure has been estimated to be ~10 -4 Torr at room temperature. 40,41 Heating ammonia-borane generates hydrogen and volatile B-and N-containing species that enable h-BN growth; the generated precursor H3N-BH3 (Aldrich) is transferred under N2 into a stainless steel ampoule, minimizing water exposure of the hygroscopic H3N-BH3. To transport the precursor into the furnace, the ampoule is heated to ~95 °C, and volatilized material is swept into the furnace by a 4:1 Ar/H2 carrier.…”

Section: Introductionmentioning

confidence: 99%

“…12,15,16,18,21,32−38 High purity ammonia-borane shows no decomposition over two months at room temperature, 39 and its vapor pressure has been estimated to be ∼10 −4 Torr at room temperature. 40,41 Heating ammonia-borane generates hydrogen and volatile B-and N-containing species that enable h-BN growth; the generated species include monomeric aminoborane (H 2 N=BH 2 ), borazine, and small amounts of diborane. 34,42 However, the growth of h-BN from ammonia-borane, typically carried out in the presence of H 2 , gives variable results depending on the growth temperature, 43 substrate roughness, 44,45 substrate structure, 46 position of the growth substrate relative to the precursor source, 35,36,43 and precursor flux.…”

Section: ■ Introductionmentioning

confidence: 99%

Role of Pressure in the Growth of Hexagonal Boron Nitride Thin Films from Ammonia-Borane

et al. 2016

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We analyze the optical, chemical, and electrical properties of chemical vapor deposition (CVD) grown hexagonal boron nitride (h-BN) using the precursor ammonia-borane (H3N-BH3) as a function of Ar/H2 background pressure (PTOT). Films grown at PTOT ≤ 2.0 Torr are uniform in thickness, highly crystalline, and consist solely of h-BN. At larger PTOT, with constant precursor flow, the growth rate increases, but the resulting h-BN is more amorphous, disordered, and sp 3 bonded. We attribute these changes in h-BN grown at high pressure to incomplete thermolysis of the H3N-BH3 precursor from a passivated Cu catalyst. A similar increase in h-BN growth rate and amorphization is observed even at low PTOT if the H3N-BH3 partial pressure is initially greater than the background pressure PTOT at the beginning of growth. h-BN growth using the H3N-BH3 precursor reproducibly can give large-area, crystalline h-BN thin films, provided that the total pressure is under 2.0 Torr and the precursor flux is well-controlled.* Correspondence should be addressed to lyding@illinois.edu, jkoepkeuiuc@gmail.com, and joshua.wood@northwestern.edu. Films of h-BN have been used as insulating spacers, 1 encapsulants, 2 substrates for electronic devices, 3, 4 corrosion and oxidation-resistant coatings, 5, 6 and surfaces for growth of other 2D nanomaterials such as graphene 7 and WS2. 8 Most of these studies employed small-area (~100 µm 2 ) h-BN pieces exfoliated from sintered h-BN crystals, 9 limiting technological use of h-BN films. Additionally, unlike graphene, h-BN is difficult to prepare in monolayer form by exfoliation. The electronegativity difference between B and N and the reduced resonance stabilization relative to graphene results in electrostatic attractions between layers and in-plane. Consequently, it is more challenging to control h-BN grain size and layer number. Furthermore, partially ionic B-N bonds can form between neighboring BN layers, serving to "spot weld" such layers together. 10 Several groups have sought to overcome these limitations by using chemical vapor deposition (CVD) to grow large-area, monolayer h-BN films. [11][12][13][14][15][16][17][18][19][20][21][22] CVD growth of h-BN has been accomplished using various precursors (e.g., ammonia borane, borazine, and diborane) on transition metal substrates (e.g., Cu, Ni, 23 Fe, 24 Ru, 25, 26 etc.). Of these h-BN growth substrates, we focus on Cu, as Cu has a high catalytic activity, 27 is inexpensive, and is the typical growth substrate 28 for conventional graphene CVD.Regarding h-BN growth precursors, volatile borazine-B3N3H6, isoelectronic with benzene-is far from an ideal choice, as borazine is hazardous and decomposes quickly even at room temperature. While borazine can pyrolyze and dehydrogenate 23, 25,29,30 to generate h-BN films, 13,17,19,20,22,31 partial dehydrogenation is common, [30] resulting in oligomeric BN compounds and aperiodic h-BN grain boundaries. 13,17 Finally, thin films of h-BN can also be grown from mixtures of diborane (B2H6) and ammonia (NH3...

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“…The results show the reaction c-N 2 B 2 H 4 Me 4 + 2 H 2 → 2 Me 2 NHBH 3 to be 24.3 kcal/mol endothermic in the gas phase. We use this value along with the heats of sublimation reported by Burg , and Alton , to calculate the thermochemistry of the reaction in the condensed phase (1 atm, 298 K standard states). As shown in Figure , enthalpy of the condensed-phase hydrogenation reaction is estimated to be 2.9 kcal/mol endothermic.…”

Section: Resultsmentioning

confidence: 99%

Raman Spectroscopy, X-ray Diffraction, and Hydrogenation Thermochemistry of N,N,N,N-Tetramethylcyclotriborazane under Pressure

et al. 2014

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The novel hydrogen-rich BN materials Me2NHBH3 and c-N2B2H4Me4 have been studied by a combination of vibrational spectroscopy and single crystal X-ray diffraction over the pressure range 0–40 GPa. Assignments of Raman-active vibrational modes were made for c-N2B2H4Me4 on the basis of a combination of gas-phase predictions and previous assignments for similar compounds. The Raman spectrum of single crystals were found to have excellent signal-to-noise for pressures over the 0–40 GPa range, making it an ideal method for in situ analysis of high pressure reactions involving c-N2B2H4Me4. The enthalpy of the reaction c-N2B2H4Me4 + 2 H2 → 2 Me2NHBH3 was estimated to be 2.9 kcal/mol endothermic at ambient pressure. The corresponding pressure dependence of ΔG rxn was estimated from the P–V equations of state (EOS) measured for Me2NHBH3, c-N2B2H4Me4, and H2 over the 0–12 GPa range. Using the EOS for fluid hydrogen, the reaction is estimated to have a favorable ΔΔG rxn of 10 kcal/mol over the 0–2 GPa pressure range. Above 2 GPa, a positive pressure dependence of ΔG rxn is observed. On the basis of these experimental observations, we estimate the reaction thermochemistry to approach a thermoneutral equilibrium over the 0–2 GPa range. Above 2 GPa, the reaction volume becomes positive, causing this hydrogenation pathway to remain unfavorable over a pressure range extending to greater than 100 GPa at 298 K.

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Additions and Corrections - Vapor Pressures of the Methylamine-Boranes and Ammonia-Triborane.

Cited by 3 publications

References 0 publications

Trimethylamine Borane: A New Single-Source Precursor for Monolayer h-BN Single Crystals and h-BCN Thin Films

Trimethylamine Borane: A New Single-Source Precursor for Monolayer h-BN Single Crystals and h-BCN Thin Films

Role of Pressure in the Growth of Hexagonal Boron Nitride Thin Films from Ammonia-Borane

Raman Spectroscopy, X-ray Diffraction, and Hydrogenation Thermochemistry of N,N,N,N-Tetramethylcyclotriborazane under Pressure

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