Time dependent decomposition of ammonia borane for the controlled production of 2D hexagonal boron nitride.

Ammonia borane (AB) is among the most promising precursors for the large-scale synthesis of hexagonal boron nitride (h-BN) by chemical vapour deposition (CVD). Its non-toxic and non-flammable properties make AB particularly attractive for industry. AB decomposition under CVD conditions, however, is complex and hence has hindered tailored h-BN production and its exploitation. To overcome this challenge, we report in-depth decomposition studies of AB under industrially safe growth conditions. In situ mass spectrometry revealed a time and temperature-dependent release of a plethora of NxBy-containing species and, as a result, significant changes of the N:B ratio during h-BN synthesis. Such fluctuations strongly influence the formation and morphology of 2D h-BN. By means of in situ gas monitoring and regulating the precursor temperature over time we achieve uniform release of volatile chemical species over many hours for the first time, paving the way towards the controlled, industrially viable production of h-BN

Making and manipulating nanowires inside carbon nanotubes

This thesis summaries the study of various aspects related to the growth of multi-wall carbon nanotubes (MWCNTs) filled with metals and their post-synthesis processing to form macroscopic papers, known as buckypapers (BPs). Fe-filled MWCNTs (Fe@MWCNTs) and Fe/Co-filled MWCNTs (Fe/Co@MWCNTs) were produced by chemical vapour deposition (CVD), with the objective of growing sufficient quantities of these materials, whilst retaining their quality. A systematic study was carried out to investigate the effects of changing the synthesis parameters (sublimation and pyrolysis temperature, furnace gap and Ar flow) on the quality of Fe@MWCNTs produced. Crucially, this systematic study revealed the conditions to produce Fe@MWCNTs of high enough quality and quantity for post-synthesis processing. In situ residual gas analysis (RGA) revealed that regardless of pyrolysis temperature, the detected high mass fragments were broken down over the course of the reaction to ethene and methane, which continued to break down and release H2 even after exhaustion of ferrocene. In situ TEM studied passing current through a Co- NP decorated Fe@MWCNT and emphasised the importance of discerning the affects of current on the structure of the metal filling before utilising them in electrical applications. Fe@MWCNTs were processed to form BPs (4 cm diameter), constructed by depositing layers of Fe@MWCNTs and conventional MWCNTs. Strips of these BPs were successfully prototyped as the moving component in a non-metallic electromechanical relay. I/V measurements showed these ferromagnetic BPs were capable of consistently carrying the same current at a given voltage, up to 3 V, for a minimum of 50 cycles. Selectively depositing the Fe@MWCNTs produced BPs which responded in pre-selected regions to external magnetic stimuli. Tensile tests performed on BPs formed of conventional and N-doped MWCNTs, of two different lengths each, revealed that CNT length and type influence different aspects of the BP’s mechanical properties

Making and manipulating nanowires inside carbon nanotubes

This thesis summaries the study of various aspects related to the growth of multi-wall carbon nanotubes (MWCNTs) filled with metals and their post-synthesis processing to form macroscopic papers, known as buckypapers (BPs). Fe-filled MWCNTs (Fe@MWCNTs) and Fe/Co-filled MWCNTs (Fe/Co@MWCNTs) were produced by chemical vapour deposition (CVD), with the objective of growing sufficient quantities of these materials, whilst retaining their quality. A systematic study was carried out to investigate the effects of changing the synthesis parameters (sublimation and pyrolysis temperature, furnace gap and Ar flow) on the quality of Fe@MWCNTs produced. Crucially, this systematic study revealed the conditions to produce Fe@MWCNTs of high enough quality and quantity for post-synthesis processing. In situ residual gas analysis (RGA) revealed that regardless of pyrolysis temperature, the detected high mass fragments were broken down over the course of the reaction to ethene and methane, which continued to break down and release H2 even after exhaustion of ferrocene. In situ TEM studied passing current through a Co- NP decorated Fe@MWCNT and emphasised the importance of discerning the affects of current on the structure of the metal filling before utilising them in electrical applications. Fe@MWCNTs were processed to form BPs (4 cm diameter), constructed by depositing layers of Fe@MWCNTs and conventional MWCNTs. Strips of these BPs were successfully prototyped as the moving component in a non-metallic electromechanical relay. I/V measurements showed these ferromagnetic BPs were capable of consistently carrying the same current at a given voltage, up to 3 V, for a minimum of 50 cycles. Selectively depositing the Fe@MWCNTs produced BPs which responded in pre-selected regions to external magnetic stimuli. Tensile tests performed on BPs formed of conventional and N-doped MWCNTs, of two different lengths each, revealed that CNT length and type influence different aspects of the BP’s mechanical properties.</p

Making and manipulating nanowires inside carbon nanotubes

This thesis summaries the study of various aspects related to the growth of multi-wall carbon nanotubes (MWCNTs) filled with metals and their post-synthesis processing to form macroscopic papers, known as buckypapers (BPs). Fe-filled MWCNTs (Fe@MWCNTs) and Fe/Co-filled MWCNTs (Fe/Co@MWCNTs) were produced by chemical vapour deposition (CVD), with the objective of growing sufficient quantities of these materials, whilst retaining their quality. A systematic study was carried out to investigate the effects of changing the synthesis parameters (sublimation and pyrolysis temperature, furnace gap and Ar flow) on the quality of Fe@MWCNTs produced. Crucially, this systematic study revealed the conditions to produce Fe@MWCNTs of high enough quality and quantity for post-synthesis processing. In situ residual gas analysis (RGA) revealed that regardless of pyrolysis temperature, the detected high mass fragments were broken down over the course of the reaction to ethene and methane, which continued to break down and release H2 even after exhaustion of ferrocene. In situ TEM studied passing current through a Co- NP decorated Fe@MWCNT and emphasised the importance of discerning the affects of current on the structure of the metal filling before utilising them in electrical applications. Fe@MWCNTs were processed to form BPs (4 cm diameter), constructed by depositing layers of Fe@MWCNTs and conventional MWCNTs. Strips of these BPs were successfully prototyped as the moving component in a non-metallic electromechanical relay. I/V measurements showed these ferromagnetic BPs were capable of consistently carrying the same current at a given voltage, up to 3 V, for a minimum of 50 cycles. Selectively depositing the Fe@MWCNTs produced BPs which responded in pre-selected regions to external magnetic stimuli. Tensile tests performed on BPs formed of conventional and N-doped MWCNTs, of two different lengths each, revealed that CNT length and type influence different aspects of the BPâs mechanical properties.</p

Bismuth zinc vanadate, BiZn2VO6: New crystal structure type and electronic structure

We report a combined experimental and computational study of the crystal structure and electronic properties of bismuth zinc vanadate, BiZn2VO6, known for its visible light photocatalytic activity. The crystal structure has been solved from laboratory powder X-ray diffraction data using the repeated minimisations from random starting values method. BiZn2VO6 adopts a new structure type, based on the following building blocks: corner- and edge-sharing ZnO4 tetrahedra, ZnO6 octahedra and VO4 tetrahedra, and Bi2O12 dimers. It is the only known member of the BiM2AO6 (M=Pb, Ca, Cd, Mn, Zn, Mg, Cu; A=V, P, As) family which does not appear to be structurally closely related to others. The electronic structure of BiZn2VO6, calculated by DFT methods, shows that it is an indirect gap semiconductor with a calculated band gap of 1.6 eV, which compares favourably to the experimentally measured value of 2.4 eV