Plasma-enhanced Hot Filament Chemical Vapor Research Articles

Plasma produced photoluminescent molybdenum sub-oxide nanophase materials

An effective and green synthesis method for building photoluminescent molybdenum sub-oxide nanophase materials is reported. The method is based on plasma-enhanced hot filament chemical vapor deposition with N2 and MoO3 precursors. The microanalysis conformed that the nanomaterials are composed of MoO2 and Mo4O11 phases. Studies on formation mechanism indicate that the formation of different molybdenum oxide phases is the result of MoO3 reduction in different environments. The photoluminescence properties of molybdenum sub-oxide nanophase materials were studied at room temperature. The results reveal photoluminescence emission in a broad range from ultraviolet to infrared. This emission is attributed to electron transitions between the conduction and valence bands, between conduction and localized levels, and plasmon generation. These studies advance the knowledge of structural and optical properties of sub-stoichiometric molybdenum oxide nanomaterials and can contribute to the development of advanced optoelectronic devices.

C and O doped BN nanoflake and nanowire hybrid structures for tuneable photoluminescence

Abstract C and O doped BN nanoflakes and hybrid nanoflake-nanowire structures were synthesized in N2+H2 environment using plasma-enhanced hot filament chemical vapour deposition with solid B4C as boron and carbon precursor. Structure and chemical composition of the C and O doped BN nanoflakes and hybrid nanoflake-nanowire hybrid structures were systemically studied using advanced characterization instruments including high resolution transmission electron microscope, micro-Raman spectroscope, Fourier transform infrared spectroscope, X-ray diffractometer, field emission scanning electron microscope, and X-ray photoelectron spectroscope. The obtained results evidence that the C and O doped BN nanowires nucleate and grow directly on the tops of C and O doped BN nanoflakes due to the presence of dangling bonds on the surfaces of tips of C and O doped BN nanoflakes, which were formed by the ion bombardment in plasma. The photoluminescence (PL) properties of C and O doped BN nanoflakes and C and O doped BN nanoflake-nanowire hybrid structures were studied at room temperature using a micro-Raman system with the 325 nm line of He-Cd laser as the excitation source. The results of PL measurements indicate that the PL properties of C and O doped BN nanoflake-nanowire hybrid structures significantly change with the length of C and O doped BN nanostructures due to the interface zones caused by the nanowire length. Thus, the PL properties can be efficiently tuned by the length of nanowires. These achievements can contribute to the synthesis of novel BN-based hybrid nanostructures and the development of the next generation BN-based optoelectronic nanodevices.

Conversion of vertically-aligned boron nitride nanowalls to photoluminescent CN compound nanorods: Efficient composition and morphology control via plasma technique

Two-dimensional BN/CN nanomaterials of various composition and morphology were synthesized in N2H2 plasma by plasma-enhanced hot filament chemical vapor deposition, with B4C used as precursor. The results of field emission scanning electron microscopy, X-ray diffractometer, transmission electron microscopy, micro-Raman and X-ray photoelectron spectroscopy evidence that the hexagonal boron nitride nanowalls with carbon and oxide phases were synthesized under about 1:1 ratio of H2 to N2, while the CN nanorods with boron and oxide phases are formed under other ratios of H2 to N2, and the nanowires made of oxide phases are grown without the plasma. Efficient control over the nanostructure composition and morphology was demonstrated, thus proposing a cheap and convenient fabrication technique for the advanced composite boron nitride/graphene materials. The photoluminescence properties of the synthesized BN and CN nanomaterials were also studied using the 325 nm line of HeCd laser as the excitation source. The fabricated nanomaterials can generate the ultraviolet, blue and green multi-PL bands, which are associated to the defects formed in these nanomaterials and the carbon clusters, respectively. These outcomes can make a great contribution to the design of functional BN- and CN-nanomaterials of various morphologies and compositions for the applications in various electronic and carbon-based optoelectronic nanodevices.

Structure and photoluminescence of boron and nitrogen co-doped carbon nanorods

Boron and nitrogen doped carbon nanorods (BNCNRs) were synthesized by plasma-enhanced hot filament chemical vapor deposition, where methane, nitrogen and hydrogen were used as the reaction gases and boron carbide was the boron source. The results of scanning electron microscopy, micro-Raman spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy indicate that boron and nitrogen can be used as co-dopants in amorphous carbon nanorods. Combined with the characterization results, the doping mechanism was studied. The mechanism is used to explain the formation of different carbon materials by different methods. The photoluminescence (PL) properties of BNCNRs were studied. The PL results show that the BNCNRs generate strong green PL bands and weak blue PL bands, and the PL intensity lowered due to the doping of boron. The outcomes advance our knowledge on the synthesis and optical properties of carbon-based nanomaterials and contribute to the development of optoelectronic nanodevices based on nano-carbon mateirals.

Structure and photoluminescence properties of carbon nanotip-vertical graphene nanohybrids

We report on the effective enhancement and tuning of photoluminescence (PL) by combining vertical graphene nanoflakes (VGs) and carbon nanotips (CNTPs). The VGs are grown on the vertical CNTPs by hot filament chemical vapor deposition in the methane environment, where the CNTPs are synthesized on silicon substrates by CH4-H2-N2 plasma-enhanced hot filament chemical vapor deposition. The results of field emission scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy indicate that the VGs can be grown on the CNTP and silicon substrate surfaces with the orientation perpendicular to the surfaces of CNTPs and silicon substrates. The PL properties of VG, CNTP, and CNTP-VG structures are studied using a 325 nm line of He-Cd laser as the excitation source. The PL results indicate that the PL of VGs is enhanced by the CNTPs due to the increasing density of PL emitters, while the PL properties of the nanohybrid system can be tuned. Furthermore, the potential applications of CNTP-VG structures in optoelectronic devices are analyzed. These results contribute to the design of functional graphene-based materials and the development of next-generation optoelectronic devices.

Self-organized graphene-like boron nitride containing nanoflakes on copper by low-temperature N2 + H2 plasma

A simple and efficient method for synthesizing complex graphene-inspired BNCO nanoflakes by plasma-enhanced hot filament chemical vapour deposition using B4C as a precursor and N2/H2 reactive gases is reported.

Structure and photoluminescence of films composed of carbon nanoflakes

Carbon nanoflake films (CNFFs) were directly synthesized by plasma-enhanced hot filament chemical vapor deposition. The results of field emission scanning electron microscope, transmission electron microscope, micro-Raman spectroscope, X-ray photoelectron spectroscope and Fourier transform infrared spectroscope indicate that the CNFFs are composed of bending carbon nanoflakes with the hydrocarbon and hydroxyl functional groups, and the carbon nanoflakes become thin in a long deposition time. The structural change of carbon nanoflakes is related to the formation of structural units and the aggregation of hydrocarbon radicals near the carbon nanoflakes. Moreover, the photoluminescence (PL) properties of CNFFs were studied in a Ramalog system and a PL spectroscope. The PL results indicate that the PL intensity of CNFFs is lowered with the increase of thickness of CNFFs. The lowering of PL intensity for the thick CNFFs originates from the effect of more dangling bonds in the CNFFs. In addition, we studied the structural difference of carbon nanoflakes grown by different CVD systems and the PL difference of carbon nanoflakes in different measurement systems. The results achieved here are important to control the growth and structure of graphene-based materials and fabricate the optoelectronic devices related to carbon-based materials.

Plasma effects in aligned carbon nanoflake growth by plasma-enhanced hot filament chemical vapor deposition

Carbon nanofilms are directly grown on silicon substrates by plasma-enhanced hot filament chemical vapor deposition in methane environment. It is shown that the nanofilms are composed of aligned carbon nanoflakes by extensive investigation of experimental results of field emission scanning electron microscopy, micro-Raman spectroscopy and transmission electron microscopy. In comparison with the graphene-like films grown without plasmas, the carbon nanoflakes grow in an alignment mode and the growth rate of the films is increased. The effects of the plasma on the growth of the carbon nanofilms are studied. The plasma plays three main effects of (1) promoting the separation of the carbon nanoflakes from the silicon substrate, (2) accelerating the motion of hydrocarbon radicals, and (3) enhancing the deposition of hydrocarbon ions onto the substrate surface. Due to these plasma-specific effects, the carbon nanofilms can be formed from the aligned carbon nanoflakes with a high rate. These results advance our knowledge on the synthesis, properties and applications of graphene-based materials.

Comparative study of the carbon nanofilm and nanodots grown by plasma-enhanced hot filament chemical vapor deposition

Carbon nanofilm and nanodots were grown by plasma-enhanced hot filament chemical vapor deposition using methane, hydrogen and nitrogen as the reactive gases. The results of field emission scanning electron microscopy, micro-Raman spectroscopy and X-ray photoelectron spectroscopy indicate that the amorphous carbon nanofilm and nanodots are formed without and with nitrogen, respectively. The formation of carbon nanofilm and nanodots is the consequence of different sputtering-etching effects. The photoluminescence (PL) of carbon nanofilm and nanodots was studied in a SPEX 1403 Ramalog system using a 325nm He–Cd laser as an excitation source and the PL spectra show the PL bands centered at about 411 and 513nm for the carbon nanofilm and 405 and 504nm for the carbon nanodots. Simultaneously, the PL results also indicate that the intensity of PL bands of carbon nanofilm is lower than that of carbon nanodots. The generation of different PL bands was interpreted by the transition mechanism. The difference in the intensity of PL bands is related to the size of carbon nanodots. The electron field emission (EFE) characteristics of carbon nanofilm and nanodots were investigated in a high-vacuum system. The results show that Fowler–Nordhelm curves are composed of two or three straight lines and the carbon nanofilm can emit a high current density, which originate from the diversification of carbon nanodots. The difference in the EFE results of carbon nanofilm and nanodots is associated to the size and number of carbon nanodots. These results can enrich our knowledge about carbon-based nanomaterials and are important to fabricate the carbon-based solid nanodevices in the field of optoelectronics.

Catalytic growth mechanism and catalyst effects on electron field emission of nitrogenated carbon nanorods formed by plasma-enhanced hot filament chemical vapor deposition

Nitrogenated carbon nanorods (NCNRs) with different structures were catalytically synthesized on the silicon substrate deposited with gold films in a plasma-enhanced hot filament chemical vapor deposition system, where methane, nitrogen and hydrogen were used as the reactive gases. The structure and composition of synthesized NCNRs were investigated by field emission scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy and X-ray photoelectron spectroscopy, respectively. The results indicate that the gold particles locate at the tops of NCNRs composed of amorphous carbon with nitrogen incorporation and their growth was improved with the increase of nitrogen. According to the theory related to thermodynamics, the catalytic growth mechanism of NCNRs was studied. The electron field emission (EFE) properties of NCNRs were studied in a high-vacuum system of ∼10−6 Pa. The EFE results show that the turn-on field changes from 2.26 to 3.11 V/μm for the NCNRs with different structures and the current density is up to about 2.2 mA/cm2. The EFE results also indicate that the Fowler–Nordheim curves of NCNRs are composed of three straight lines, which are different from the F–N curve of single carbon nanorod reported. In addition, the work function of carbon nanorods was measured by X-ray photoelectron spectroscopy and the results show that the work function is closely correlated with the structure and composition of the synthesized carbon nanorods. Depending on the interface barrier formed between the NCNRs and gold particles, the effects of catalyst on the EFE properties of NCNRs were studied according to the analysis of the change in the slope of F–N curves. These results can enrich our knowledge on the structure and EFE properties of carbon nanomaterials and are highly relevant to fabrication of next generation of optoelectronic devices.

Structure and surface effect of field emission from gallium nitride nanowires

Gallium nitride nanowires (GaN NWs) were synthesized by plasma-enhanced hot filament chemical vapor deposition under different ratios of nitrogen to hydrogen, which the GaN powder and nitrogen gas were used as the Ga and N sources. The characterization results indicate that the GaN NWs are grown in wurtzite crystalline structure with different length, diameters and surface adsorption. The field emission of GaN NWs was measured in the high vacuum condition of ∼10−6Pa, which the results show that the turn-on field of GaN NWs changes from 0.86 to 2.8V/μm depending on their structures and the current density can reach up to 830μA/cm2 at the field of 6V/μm. Combined the characterization results with the work function theory related to field emission, the origin of the field emission enhancement was analyzed, which associates with their surface potential and geometric structure. These results can enrich our knowledge on the field emission of GaN NWs and are highly related to the development of the next-generation of GaN nano-electronic devices.

Comparative study on catalyst-free formation and electron field emission of carbon nanotips and nanotubes grown by chemical vapor deposition

The catalyst-free growth of carbon nanotips and nanotubes on silicon substrate pre-deposited with carbon film was realized under different temperatures in plasma-enhanced hot filament chemical vapor deposition system, in which methane, nitrogen and hydrogen were used as the reactive gases. The structure and composition of synthesized carbon nanotips and nanotubes were investigated using field emission scanning electron microscope, transmission electron microscope and micro-Raman spectroscopy, respectively. The results indicate that the carbon nanotips are formed at about 800°C while the carbon nanotubes are formed about 900°C. According to the ion bombardment effect and the diffusion at different temperatures, the catalyst-free formation of carbon nanotips and nanotubes was comparatively studied. The transformation from carbon film to spherical carbon particles at a high temperature results in the formation of carbon nanotubes depending on the diffusion of carbon. At a low temperature, the carbon film still locates at the substrate and leads to the formation of carbon nanotips relying on the sputtering-etching of etching ions and the deposition of carbonaceous ions. In addition, the electron field emission characteristics of carbon nanotips and nanotubes were investigated. The results indicate that there is much difference in the electron field emission properties for the carbon nanotips and nanotubes. According to the thermal effect produced by Joule heat during electron emission, the difference was interpreted.

Structure and electrical property of gallium nitride nanowires synthesized in plasma-enhanced hot filament chemical vapor deposition system

Aligned gallium nitride (GaN) nanowires were catalytically synthesized in a plasma-enhanced hot filament chemical vapor deposition system, in which GaN powder and nitrogen were used for the gallium and nitrogen sources, respectively. The results of scanning electron microscope, X-ray diffractometer, micro-Raman spectroscopy and transmission electron microscope indicate that the n-type GaN nanowires with different diameters are formed in wurtzite crystal structure. Combined the vapor–liquid–solid growth mechanism with the plasma-related effects, the formation of n-type GaN nanowires with different diameters was analyzed. The electrical property of a single GaN nanowire was measured in transmission electron microscope at room temperature and the result indicates that the current–voltage curve exhibits a nonlinear behavior and a double diode-like characteristic. In particular, the double diode-like characteristic is highly related to the application of GaN nanowires in the area of nano-diode devices such as alternating current limiter.

Growth of carbon nanotubes and nanowires from amorphous carbon films by plasma-enhanced hot filament chemical vapor deposition

Carbon nanowires and nanotubes were directly synthesized from amorphous carbon films deposited on silicon substrate in a plasma-enhanced hot filament chemical vapor deposition system. The morphologies and structures of the synthesized carbon nanowires and nanotubes were studied by field emission scanning electron microscopy, transmission electron microscopy and micro-Raman spectroscopy. According to the characterization results, the formation models of carbon nanowires and nanotubes were suggested. In addition, the characteristic of electron field emission from carbon nanowires and nanotubes was measured in the condition of high vacuum. The result of electron field emission exhibits that the current density is 1.7mA/cm2 at 6.2V/μm. The high current density suggests that they can serve as effective electron field emission sources for numerous applications.

Study on structures and electron field emission of nitrogenated carbon nanotips grown by plasma-enhanced hot filament chemical vapor deposition

Nitrogenated carbon nanotips (NCNTPs) with different structures were synthesized by plasma-enhanced hot filament chemical vapor deposition under different time using methane, nitrogen and hydrogen as the reaction gases. The results of field emission scanning electron microscopy, micro-Raman spectroscopy and X-ray photoelectron spectroscopy indicate that the NCNTPs are amorphous structure and they have significant changes in the morphologies and components with the growth time. The electron field emission (EFE) from NCNTPs was measured and the results show that the current density increases from about 200 to 2800μA/cm2 at the field of 12V/μm depending on their structures and components. According to the growth conditions, the characterization results and the electronic structure of amorphous carbon, the changes in the structures, components and work function of NCNTPs were analyzed. Combined the work function with the characterization results, the EFE properties of NCNTPs were studied.

Study on electron field emission enhancement from nitrogenated carbon nanotips synthesized by plasma-enhanced hot filament chemical vapor deposition

Nitrogenated carbon nanotips (NCNTPs) with different structures were synthesized by plasma-enhanced hot filament chemical vapor deposition using methane, hydrogen and nitrogen as the reactive gases. The structures and compositions of the NCNTPs were studied by field emission scanning electron microscopy (FESEM), micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The XPS spectra reveal that nitrogen is incorporated into the carbon nanotips to form the NCNTPs under plasma condition. The Raman spectra and FESEM images show that the NCNTPs are amorphous structure and their morphologies change with the change in deposition conditions, respectively. The electron field emission (EFE) from the NCNTPs was measured and the EFE results indicate that the NCNTPs with the smooth surfaces and high density can emit a current density of 3 × 103 μA/cm2 at an electric field of 7.2 V/μm, which exhibits better EFE characteristic than the NCNTPs with the carbon nanowires on their surfaces due to small amount of oxygen adsorbed on the smooth surfaces of NCNTPs. According to the possible structures of nitrogen in sp2 cluster in rings, the EFE enhancement of the NCNTPs compared with pure carbon nanotips was studied. The high emission current density (3 × 103 μA/cm2) at low field (7.2 V/μm) suggests that the NCNTPs can serve as effective electron emission sources for numerous applications.

The effect of temperature on the mechanism of photoluminescence from plasma-nucleated, nitrogenated carbon nanotips

Nitrogenated carbon nanotips (NCNTPs) have been synthesized using customized plasma-enhanced hot filament chemical vapor deposition. The morphological, structural, and photoluminescent properties of the NCNTPs are investigated using scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. The photoluminescence measurements show that the NCNTPs predominantly emit a green band at room temperature while strong blue emission is generated at 77K. It is shown that these very different emission behaviors are related to the change of the optical band-gap and the concentration of the paramagnetic defects of the carbon nanotips. The studies shed light on the controversies on the photoluminescence mechanisms of carbon-based amorphous films measured at different temperatures. The relevance of the results to the use of nitrogenated carbon nanotips in light-emitting optoelectronic devices is discussed.

Enhanced electron field emission from plasma-nitrogenated carbon nanotips

Nitrogenated carbon nanotips (NCNTPs) are synthesized by plasma-enhanced hot filament chemical vapor deposition from the hydrogen, methane, and nitrogen gas mixtures with different flow rate ratios of hydrogen to nitrogen. The morphological, structural, compositional, and electron field emission (EFE) properties of the NCNTPs were investigated by field emission scanning electron microscopy, Raman spectroscopy, x ray photoelectron spectroscopy, and EFE high-vacuum system. It is shown that the NCNTPs deposited at an intermediate flow rate ratio of hydrogen to nitrogen feature the best size/shape and pattern uniformity, the highest nanotip density, the highest nitrogen concentration, as well as the best electron field emission performance. Several factors that come into play along with the nitrogen incorporation, such as the combined effect of the plasma sputtering and etching, the transition of sp3 carbon clusters to sp2 carbon clusters, the increase of the size of the sp2 clusters, as well as the reduction of the work function, have been examined to interpret these experimental findings. Our results are highly relevant to the development of the next generation electron field emitters, flat panel displays, atomic force microscope probes, and several other advanced applications.

非晶碳氮纳米尖端的微结构和发光机理

Carbon nitride nanotips were prepared on silicon substrate in plasma-enhanced hot filament chemical vapor deposition system,in which methane,hydrogen and nitrogen were used as the reaction gases.The carbon nitride nanotips were characterized by scanning electron microscopy and micro-Raman spectroscopy.The photoluminescence of the carbon nitride nanotips was measured at room temperature and the photoluminescence spectrum shows two emission bands at 406 and 506 nm.Combined with the Raman spectrum,the microstructure of the carbon nitride was analyzed.According to the structure and photoluminescence mechanism of amorphous carbon nitride films,the photoluminescence of carbon nitride nanotips was studied.

Carbon fractals grown from carbon nanotips by plasma-enhanced hot filament chemical vapor deposition

Carbon nanomaterials with different structures were prepared in a custom-designed plasma-enhanced hot filament chemical vapor deposition system using methane, hydrogen and nitrogen. They were investigated by scanning electron microscopy (SEM) and micro-Raman spectroscopy. The SEM images show that the smooth carbon nanotips are formed under a high bias current and the carbon fractals can grow from the tips of the carbon nanotips under a low bias current. The results of micro-Raman spectroscopy indicate that the graphitization of the carbon nanomaterials was improved by ion bombardment. Combined the ion bombardment, electric field enhancement and electron emission mechanisms, the formation model of the carbon fractals was suggested.