Synthesis And Physical Property Studies Of1D Light-element (B/C/N) Nanomaterials

Light-element nanomaterials are expected to be broadly applicated innanoelectronics owing to their special structure and unique properties. In this thesis,we have studied the synthesis and physical properties of four novel one-dimensional（1D） light-element nanomaterials: the controlable synthesis and application onresistance-based strain sensing of horizontally aligned ultralong single-walledcarbon nanotube （SWCNT） arrays; the controlable synthesis and physical propertiesstudies of horizontally aligned ultralong boron and nitrogen co-doped SWCNT（B_xC_yN_z-SWNT） arrays; the controlable synthesis and physical properties studies ofnitrogen doped SWCNTs （N-doped SWCNTs）; the large-scale controlable synthesisand physical properties studies of hexagonal boron nitride nanoribbons （BNNRs）.Firstly, we successfully synthesised the diameter and density controlled parallelaligned ultralong SWCNT arrays on SiO₂/Si substrates and slit substrates viacontrolling the gas flow state by small quartz tube during chemical vapor deposition（CVD） growing by tuning the diameter and density of catalyst nanoparticles. Thecharacterized results of scanning electron microscope （SEM）, atomic forcemicroscope （AFM）, transmission electron microscope （TEM） and Raman spectrumindicated that the as-grown ultralong SWCNT arrays had well horizontal alignment,the length of the tubes in the arrays riched several centimeters, and achievedultralong growth. And the tubes in the arrays are all single-walled with perfectstructure, the diameter of the tubes and the tube density of the arrays are wellcontrolled via tuning the diameter and density of catalyst nanoparticles. We presentthe―convection model‖growth mechanism of by research the growing process.Secondly, based on―convection model‖growth mechanism, we invented a gasflow oriented CVD method to growing parallel aligned ultralong SWCNT arrays onany thermostable substrates by using ethanol as carbon source and the strips withself-assemnled metal nanopartcles pattern arrays as catalysts. We directly grewparallel aligned ultralong SWCNT arrays on transparent flexible fluorphlogopitemica （F-mica） substrates successfully, and the as-grown samples are still transparentand flexible. Based on the parallel aligned ultralong SWCNT arrays on F-mica, wefrabricated high sensitive macro-scale resistance-based strain sensors, which can beeasily fabriathed and integrated. The sensor devices have high working current,excellent and sensitive sensing property and fairly repeatability with the gage factorabout27. After reseach the working mechanism of the SWCNT-array-based strainsensor, we present a―shunt resistance‖model of the ultralong SWCNT arrayresistance-based strain sensors, which considered that the strain sensing ability mainly came from the qusi-metallic SWCNTs of the nanotube arrays. Besides theapplication on strain sensing, The large-area growth of aligned ultralong SWCNTarrays on F-mica substrates is a promising technique for scalable and high-throughput fabrication of nanodevices for flexible and transparent electronics.Thirdly, we invented a gas flow oriented CVD method to growing parallelaligned ultralong B_xC_yN_z-SWNT arrays, and successfully synthesised the diameterand density controlled purely semiconductiong parallel aligned ultralongB_xC_yN_z-SWNT arrays on SiO₂/Si substrates, and fabricated back gate field effecttransistor （FET） devices on the nanotube arrays. And the FET devices have highon-off ratio, more than105, large working current and can be depleted completely,the ultralong B_xC_yN_z-SWNT arrays behave p-type semiconducting transportproperty. The Raman specturm researches indicated that the boron and nitrogendoping （BN-doping） renormalized the energy of electrons and phonons of SWCNTs,up-shifted the frequency of Raman G-band and2D-band phonons, that meansBN-doping is a p-type doping, induced hole-injection. In this thesis, we use ab initiodensity functional theory （DFT） method calculating the electron energy bandstructure, electron density of states, electron densities and difference electrondensities of B_xC_yN_z-SWNTs. The results of calculations indicated that thenon-localized electrons of carbon atoms are localized by BN-doping inducedAnderson localization, which induced Anderson metal-semiconducting transition,made the metallic SWCNTs opened a band-gap and transformed to besemiconducting B_xC_yN_z-SWNTs. The capability of CVD growing ultralong alignedand purely semiconducting B_xC_yN_z-SWNTs allows for large-scale integration ofaddressable FET devices and therefore provides a realistic pathway to thedevelopment of nanotube-based electronics.And we also developped a sample CVD method to growing N-doped SWCNTsby using magnesium oxide supported iron-molybdenum alloy nanoparticle catalystpowder（Fe-Mo/MgO） as catalysts, employing methane （CH4） and ammonia （NH3）gas as carbon and azotic feedback, respectively. We successfully synthesised aseries of N-doped SWCNTs with different N concentration. The Raman specturmresearches indicated that N-doping also renormalized the energy of electrons andphonons of SWCNTs, which blue-shifted the frequency of Raman G-band andred-shifted the frequency of Raman2D-band phonons, that means N-doping is an-type doping, induced electron-injection. The results of calculations also indicatedthat some non-localized electrons of nitrogen atoms transferred to all carbon atoms,and induced electron-injection in SWCNTs, as well as induced the polarization ofthe electron destribution arround all carbon atoms and formed electric dipole moment. The N-doping induced impurity band covered the band-gap ofsemiconducting SWCNTs and made them transformed to be metallic N-dopedSWCNTs.Finally, we invented a sample method to large-scale synthesizing edge, lengthand width controlled BNNRs by using accessible hexagonal boron nitride （h-BN） asraw materials, and the metal nanoparticles supported on h-BN as catalysts. We firstsuccessfully synthesised edge, length and width controlled BNNRs with orderly andclean edges. The magnetic properties testing results indicated that the as-grownBNNRs are ferrimagnetic soft magnetic materials. Using a sample theoretical modelcan find out that the magnetism of BNNRs mainly came from the edges ofzigzag-edged BNNRs, and the conducting edge electron states made zigzag-edgedBNNRs formed half-metal electron band structure. The zigzag-edged BNNRs arehalf-metal materials with spin polarized. Furthermore, the conducting edge electronstates are protected by the topological order of the h-BN lattice in BNNRs, sozigzag-edged BNNRs are also two dimensional topological insulators. Thecapability of large-scale synthesizing BNNRs provides a realistic pathway to thewidely application in nanoelectronics and spintronics.