<p>The primary goals of this study were to demonstrate and fully characterize a microscale ionization source (i.e. micro-ion source) and to determine the validity of impact ionization theory for microscale devices and pressures up to 100 mTorr. The field emission properties of carbon nanotubes (CNTs) along with Micro-Electro-Mechanical Systems (MEMS) design processes were used to achieve these goals. Microwave Plasma-enhanced CVD was used to grow vertically aligned Multi-Walled Carbon Nanotubes (MWNTs) on the microscale devices. A 4-dimensional parametric study focusing on CNT growth parameters confirmed that Fe catalyst thickness had a strong effect on MWNT diameter. The MWNT growth rate was seen to be a strong function of the methane-to-ammonia gas ratio during MWNT growth. A high methane-to-ammonia gas ratio was selected for MWNT growth on the MEMS devices in order to minimize growth time and ensure that the thermal budget of those devices was met. </p><p>A CNT-enabled microtriode device was fabricated and characterized. A new aspect of this device was the inclusion of a 10 micron-thick silicon dioxide electrical isolation layer. This thick oxide layer enabled anode current saturation and performance improvements such as an increase in dc amplification factor from 27 to 600. The same 3-panel device was also used as an ionization source. Ion currents were measured in the 3-panel micro-ion source for helium, argon, nitrogen and xenon in the 0.1 to 100 mTorr pressure range. A linear increase in ion current was observed for an increase in pressure. However, simulations indicated that the 3-panel design could be modified to improve performance as well as better understand device behavior. Thus, simulations and literature reports on electron impact ionization sources were used to design a new 4-panel micro-ion source. The 4-panel micro-ion source showed an approximate 10-fold performance improvement compared to the 3-panel ion source device. The improvement was attributed to the increased electron current and improved ion collection efficiency of the 4-panel device. Further, the same device was also operated in a 3-panel mode and showed superior performance compared to the original 3-panel device, mainly because of increased ion collection efficiency. </p><p>The effect of voltages applied to the different electrodes in the 4-panel micro-ion source on ion source performance was studied to better understand device behavior. The validity of the ion current equation (which was developed for macroscale ion sources operating at low pressures) in the 4-panel micro-ion source was studied. Experimental ion currents were measured for helium, argon and xenon in the 3 to 100 mTorr pressure range. For comparison, theoretical ion currents were calculated using the ion current equation for the 4-panel micro-ion source utilizing values calculated from SIMION simulations and measured electron currents. The measured ion current values in the 3 to 20 mTorr pressure range followed the calculated ion currents quite closely. A significant deviation was observed in the 20-100 mTorr pressure range. The experimental ion current values were used to develop a corrected empirical model for the 4-panel micro-ion source in this high pressure range (i.e., 3 to 100 mTorr). The role of secondary electrons and electron path lengths at higher pressures is discussed.</p> / Dissertation

<p>Carbon nanomaterials have a wide range of promising and exciting applications. One of the most heavily investigated carbon nanomaterial in recent history has been the carbon nanotube. The intense interest in carbon nanotubes can be attributed to the many exceptional characteristics which give them great potential to revolutionize modern mechanical, optical and electronic technologies. However, controlling these characteristics in a scalable fashion has been extremely difficult. Although some progress has been made in controlling the quality, diameter distribution and other characteristics of carbon nanotube samples, several issues still remain. The two major challenges which have stood in the way of their mainstream application are controlling their orientation and their electronic characteristics. Developing and understanding a Chemical Vapor Deposition based carbon nanotube synthesis method has been the major focus of the research presented here. Although several methods were investigated, including the so-called "fast-heating, slow-cooling" and large feeding gas flowrate methods, it was ultimately found that high-quality, perfectly aligned carbon nanotubes from a variety of metal catalysts could be grown on quartz substrates. Furthermore, it was found that using MeOH could selectively etch small-diameter metallic carbon nanotubes, which ultimately led to the productions of perfectly aligned single-walled carbon nanotube samples consisting almost entirely of semiconducting carbon nanotubes. Thiophene was utilized to investigate and support the hypothesized role of MeOH in producing these selectively gown semiconducting carbon nanotube samples. Additionally, this sulfur-containing compound was used for the first time to demonstrate a two-fold density enhancement in surface grown carbon nanotube samples. This method for selectively producing perfectly aligned semiconducting carbon nanotubes represents a major step towards the integration of carbon nanotubes into mainstream applications.</p><p>Although extremely useful in a variety of technologies, carbon nanotubes have proven impractical for use in H₂ storage applications. As such, microporous carbons have been heavily investigated for such ends. Microporous carbons have distinguished themselves as excellent candidates for H₂ storage media. They are lightweight and have a net-capacity of almost 100%, meaning that nearly all of the H₂ stored in these materials is easily recoverable for use in devices. However, developing a microporous carbon with the appropriately small pore diameters (~1nm), large pore volumes (>1cm<super>3</super>) and large surface areas (&#8805;3000m<super>2</super>/g) has proven exceedingly difficult. Furthermore, maintaining the ideal graphitic pore structure has also been an unresolved issue in many production means. Several microporous carbon synthesis methods were investigated herein, including inorganic and organically templated production schemes. Ultimately, thermally treating poly (etherether ketone) in CO₂ and steam environments was found to produce large surface area porous carbons (&#8805;3000m<super>2</super>/g) with the appropriately small pore diameters (<3nm) and large pore volumes (>1cm<super>3</super>) necessary for optimized storage of H2. Furthermore, the surface chemistry of these pores was found to be graphitic. As a result of these ideal conditions, these porous carbons were found to store ~5.8wt.% H₂ at 77K and 40bar. This represents one of the most promising materials presently under investigation by the United States Department of Energy H₂ Sorption Center of Excellence. </p><p>The success of both of these materials demonstrates the diversity and promise of carbon nanomaterials. It is hoped that these materials will be further developed and will continue to revolutionize a variety of vital technologies.</p> / Dissertation

The primary goal of this research was to develop the laser chemical vapor deposition (LCVD) process to be able to directly deposit carbon nanotubes onto substrates selectively. LCVD has traditionally been used to directly deposit complex geometries of other materials, including many metals and ceramics. Carbon nanotube deposits were formed using codeposition and other techniques. Multiwall carbon nanotubes as small as 7 nm were synthesized. Utilizing electron microscopy, deposits were characterized to determine the effects of laser power, catalyst and hydrocarbon concentration, time, pressure, and other variables on the number of nanotubes formed, their size, and their spatial location. The most important variables were shown to be hydrocarbon and catalyst concentration and laser power. These results were analyzed and statistics based models were developed to express these trends. Additionally, the process was also used successfully to deposit linear patterns of carbon nanotubes. Carbon nanotube deposits were also carried out in the presence of an electric field. It was demonstrated that a field of sufficient strength could be used to orient tube growth. LCVD is a thermally driven process and a thermal feedback and control system is typically employed to allow for real time control of the reaction zone temperatures. The current thermal imaging system installed on the LCVD reactor is limited to operation at temperatures above which nanotube deposition occurs. A heat and mass transport model was therefore developed to simulate deposition temperatures and provide an estimate of the desired laser power needed to achieve a desired reaction temperature. This model included all significant modes of heat transport including conduction, natural convection and radiation. Temperature dependant material properties were also employed to help achieve greater accuracy. Additionally, the model was designed to be able to simulate a scanning laser beam which was used to deposit linear patterns of carbon nanotubes. Modeling calculations of laser heating compared favorably with experimental data. The results of this work show that LCVD has potential for use in the commercial market for selective direct deposition of patterns of aligned carbon nanotubes on multiple substrate materials.

Disinfectants, such as chlorine, are widely used in water treatment plants to ensure the safety and quality of drinking water. However, these disinfectants easily react with some natural or man-made organic compounds in raw water and form disinfection by-products (DBPs). For example, halogenated acetic acid (HAAs) and trihalomethanes (THMs) are two main components of DBPs. These DBPs contained in drinking water will increase the risk of cancer in human body. Therefore, researches on halogenated acetic acid¡¦s potential of causing cancer have increased currently. Organic acids are usually the reactants which proceed in chlorination reaction into products of disinfection by-products in water treatment plant. The purpose of this study is to investigate adsorption characteristics in solution by using tests of kinetics and equilibrium adsorptions and kinetic model evaluations of selected fulvic acids (FA) extracted from raw water. Therefore, we use commercial single-walled carbon nanotube (SWCNT) for the adsorbents, and calculate thermodynamic parameters (£GG, £GS and £GH) in order to further understand the adsorption mechanism of CNTs. The maximum adsorbed amounts of FA onto SWCNTs was calculated by the Langmuir model at 25¢J, reaching 61.88mg / g which were much higher than that onto commercially available granular activated carbon (10.69 mg/g). The adsorption capacity of FA onto CNTs increased with decreasing outer diameter of CNTs (dp), molecular weight of FA, trmperature and pH value in all texts. In the condition of constant temperature 25¢J, we analyzed HAAFP after the test of equilibrium adsorption and that the removal efficiency of HAAFP could reach 40.76%. The best selection in kinetic models evaluation, fitting models such as Modified Freundlich equation, Pseudo-1st-order equation and Pesudo-2nd-oder equation, is Modified Freundlch equation model. In addition, intraparticle diffusion equation model was fitted well and showed adsorption process was controlled by pore diffusion. We calculated the activation energy of carbon nanotube adsorption of FA and found that film diffusion was the main factor for controlling reaction rate. According to results of thermodynamic parameters indicated that the adsorption was spontaneously and an exothermic reaction. It is obvious that the adsorption capacity as well as the reaction rate of CNTs are superior to that of granular activated carbon in raw water. These results suggest that CNTs possess highly potential applications in environmental protection. In the future, if we can combine nanotube technology with disinfection technology and apply such technique on the end of processing unit for design of either the domestic treatment facilities or small simple water treatment in drinking water. Thus it will enhance the new treatment technology of drinking water and the safety of the public health. Another possibility will be to promote the opportunity of marketing development in drinking water.

Polymer light emitting diodes (PLED) were using a heterocyclic aromatic rigid-rod polymer poly-p-phenylene-benzobisoxazole (PBO) as an opto-electronically active layer; and poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) as a hole transporting layer. Aluminum (Al) and indium tin oxide (ITO) were served as device cathode and anode, respectively. [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) or derivatized multi-wall carbon nano-tube (MWCNT-C18), with great electron transporting ability, was doped into PBO to enhance the performance of PLED devices as well as the thin-film electrical conductivity. The optical length was changed by using different spin coating speeds and durations. From the research, the £fmax of electroluminescence (EL) was blue-shifted as PEDOT:PSS spin coating speed increased for a thinner layer. Once using a higher spin coating speed repeatedly to coat PEDOT:PSS, the £fmax of electroluminescence was red-shifted. If the PEDOT:PSS film thicknesses were similar, the EL spectra were almost the same, independent of device processing scheme. The injection current and EL intensity were enhanced by doping PC61BM or MWCNT- C18. The electric conductivity parallel to film surface (£m¡ü) was increased as the doping concentration increased. Because of the extremely different aspect ratio, the MWCNT-C18 had a lower percolation threshold concentration. Therefore, at a low MWCNT-C18 doping concentration, the injection current and the EL intensity were enhanced compared with those of PC61BM.

We comprehensively investigated the concentration effect of dispersed single-walled carbon nanotubes (SWCNTs) in polymer films for being a saturable absorber (SA) to stabilize the mode locking performance of the Erbium-doped fiber laser (EDFL) pulse through the diagnosis of its nonlinear properties of SA. The measured modulation depth was 1 to 4.5% as the thickness increased from 18 to 265 £gm. We obtained the stable pulse of the mode-locked EDFL (MLEDFL) when the full-width half-maximum (FWHM) decreased from 3.43 to 2.02 ps as the concentrations of SWCNTs SA increased from 0.125 to 0.5 wt%. At constant concentration of 0.125 wt%, the similar pulse shortening effect of the MLEDFL was also observed when the FWHM decreased from 3.43 to 1.85 ps was the thickness of SWCNTs SA increased from 8 to 100 £gm. In EDFL system, we vary group-velocity dispersion (GVD) with different cavity length to achieve optical pulse compression. We got the shortest pulsewidth was 713 fs, and the time-bandwidth product (TBP) was 0.345. An in-depth study on the stable mode-locked pulse formation employing SWCNTs SA, it is possible to fabricate the SWCNT films for use in high performance MLEDFL and utilization of many other low-cost nanodevices.

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In this study, we used the Density functional theory (DFT) to obtain the relationship between mechanical property and electronic property of Boron nitride nanotubes (BNNTs) under the uni-axial strain. Moreover, we also investigated one CO molecule adsorbed on the BNNTs under the uni-axial strain. We also use the molecular dynamics to introduce the mechanical property and dynamic behavior of (8,8)BNNT under the uni-axial strain. There were three parts in this study: The first part: The effect of uni-axial strain on the electronic properties of (5,5) and (8,0)boron nitride nanotubes were obtained by DFT calculation. We used the HOMO-LUMO Gap¡Bbond angle¡Bbond length and radial buckling to analyze the electronic properties and mechanical properties. The stress-strain profiles indicated that different BNNTs types displayed very similar mechanical properties, but there were variations in HOMO-LUMO gaps at different strains, indicating that the electronic properties of BNNTs not only depend on uni-axial strain, but on BNNT type. In addition, the variations in nanotube geometries, partial density of states (PDOS) and charges of boron and nitride atoms were also discussed for (8,0) and (5,5) BNNTs at different strains. The second part: The DFT was used to investigate electronic properties of CO molecule adsorbed on BNNT under the uni-axial strain. The stress-strain profiles indicated that the CO molecule adsorption on BNNT leaded only to a local mechanical deformation. The strength of BNNT could not be affected when the CO molecule adsorbed on that. Moreover, we obtained that the charge of CO will slightly transfer to the adsorbed atom of BNNT when strain increased. Hence, the adsorption energy increased slightly under the uni-axial strain. The third part: The molecular dynamics simulations were performed to investigate deformation behaviors of (8,8)BN nanotubes under axial tensile strains at 300k. Variations with the tensile strain in the axial stress, bond lengths, bond angles, radial buckling, and slip vectors were all examined. The axial, radial, and tangential components of the slip vector were also employed to monitor, respectively, the local elongation, necking, and twisting deformation near the failure of the nanotube. The components of the slip vector grew rapidly and abruptly after the failure strain, especially for the axial component. This implies that the local elongation dominates the failure of the loaded BN nanotube and finally results in a chain-like tensile failure mode.

In this study, we employed density functional theory (DFT) and molecular dynamics (MD) to investigate the mechanical and electronic properties of one-dimensional zinc oxide nanostructure. This study can be arranged into two parts: In part I: We investigated the mechanical and electronic properties of one-dimensional zinc oxide nanostructure under axial mechanical deformations by density functional theory. In this case, we could find both the highest occupied molecular orbital and the lowest unoccupied molecular orbital gap (HOMO-LUMO gap) and value of radial buckling will decrease linearly with the increase of axial strain. The changes of bond lengths and bond angles show the variation of nanostructure dependence to the increase of axial strain. This study also used partial density of state (PDOS), bond order (BO) and deformation density to analyse the differences of the electronic properties between the zinc oxide nanotubes under axial strain. In part II: This study, which employed molecular dynamics combines Buckingham and Core-Shell potentials, shows the different physical parameters, such as yield stress, young¡¦s modulus and slip vector to research the mechanical behavior and variation of structure of nanotube under axial strain.

The dependence of thickness and concentration product (TCP) of single-wall carbon nanotubes saturable absorber (SWCNTs SA) on stabilizing and shortening pulse width in passively mode-locked erbium-doped fiber ring laser (MLEDFL) was investigated and measured. The TCP represented the amounts of SWCNTs, which the optical beam encountered when passing through the SWCNTs SA. If the TCP was smaller than 8.25 (£gm x wt%), the spectral bandwidth was below 2 nm. The pulse shaping was dominated by its own self amplitude modulation (SAM) of SWCNTs SA. With further increasing TCP, the soliton-like ML operation was achieved and the spectral bandwidth was expanded to 6 nm. For soliton-like mode locking (ML) operation, the area theorem dominated the pulse shaping. Through area theorem analysis, the estimation of SPM increased as the TCP increased. The adequate enhanced SPM for balancing the slight negative GVD was provided to generate soliton-like ML pulses shorten the pulse width. However, as the TCP increased, the soliton pulse energy decreased. The decreasing soliton pulse energy restricted the further pulse shortening. The results showed that the dependence of the pulse energy and nonlinear self phase modulation (SPM) on TCP enabled to determine the shortest pulse width in MLEDFL based on the area theorem. At optimized TCP of 70.93 (£gm x wt%), it was found that the shortest pulse width of 418 fs. In addition, based on the estimated SPM from area theorem, the nonlinear refractive index n2 was calculated at the level of 0.4 - 1 x 10^-15 m^2/W that was close to the literature values of 10^-15 - 10^-16 m2/W. It provides another way to estimate the nonlinear refractive index except for the Z-scan measurement. We could also estimate the SPM if an active Z-scan measurement was taken to obtain the nonlinear refractive index of the sample. We realized the trend of pulse energy through few samples in MLEDFL, the behavior of pulse width could be theoretically simulated based on area theorem. Hence, with the area theorem analysis, the optimized TCP of SWCNTs SA could be simulated and estimated to generate the shortest pulse width from the trends of pulse energy and estimated SPM. The significant effect of TCP on pulse energy, SPM, pulse width, and spectral bandwidth of MLFLs suggests that the TCP represents the total amount of SWCNTs in SA, which can be used as one of key parameters for characterizing the passive MLFL pulse width. Through the study of the dependence of TCP on ML pulses in MLEDFL, it may provide a guideline to fabricate an effective SWCNTs SA to generate the shortest pulse width of the MLEDFL.