This PDF file contains the front matter associated with SPIE Proceedings Volume 8462, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

A preliminary study on reduced temperature chemical vapor deposition of graphene on copper substrates was performed. Graphene's exceptional mechanical strength, very high electrical and thermal conductivity, and stability at atomic layer thicknesses, generates potential for a broad range of applications, from nanodevices to transparent conductor to chemical sensor. Of the techniques demonstrated for graphene formation, chemical vapor deposition is the sole process suitable for manufacturing large area films. While large area film deposition of graphene has been shown on metal substrates, this process has been limited to high temperatures, 900-1000C, which increases the cost of production and limits methods of integrating the graphene with other material structures. In this work, CVD of graphene on copper foil was attempted over a range of temperatures (650 - 950C) on substrates as large as 5 x 15 cm in a horizontal tube reactor. Depositions were performed using both CVD and upstream Plasma-Enhanced CVD (PECVD), and the results are compared for both techniques. Quality of graphene films deposited with and without plasma enhancement was characterized by micro Raman spectroscopy.

In this paper we have demonstrated successfully for the first time, a simple but efficient and reliable approach for the growth of multi walled carbon nanotubes (MWCNTs) with high degree of crystallinity, purity and density under a wide range of growth parameters. Multi-walled carbon nanotubes (MWCNTs) were synthesized at 800 - 950°C by thermal chemical vapor deposition (TCVD) method using a thin nickel film as catalyst and methane gas as carbon source. In this process, two substrates were placed in a long alumina boat inside a double-heater TCVD. One of the substrates was covered with a short upside down alumina boat. The prepared nanotubes were characterized by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) and it was found that, CNT growth on the covered substrate was improved in terms of quality and density compared to the other uncovered substrate. In addition, the nanotube diameter is reduced more than half. Results also revealed that the temperature gradient played a key factor for growth efficiency and purity of nanotubes. In addition, the diameter of CNT can be influenced by growth temperature too. The catalyst thickness and gas flow rate were found to influence the diameter and density of tubes, whereas the effect of synthesis time was on the CNT length. This growth technique is unique because of its simplicity, high efficiency and its ability to yield CNTs of high purity and density. This finding is supported by Raman spectrometry analysis.

The role of the nickel catalyst size and its chemical and structural evolution during the early stages of carbon nanopearl nucleation and growth, by chemical vapor deposition from acetylene/argon mixture, was investigated and correlated with the resulting nanopearls morphological and structural properties. Carbon nanopearls were grown using Ni nanoparticles that were 20 nm and 100 nm in size, at a growth temperature of 850 °C, for the following growth times: 10sec, 30 sec, 60 sec, 90 sec, 120 sec and 300 sec. X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy were performed on the carbon nanopearl samples. The X-ray diffraction and X-ray photoelectron spectra showed the following chemical constituents were present during the growth of carbon nanopearls: NiO, Ni₂O₃, Ni₃C, Ni, CO and C (both amorphous and graphite). Transmission electron microscopy showed an increase in carbon nanopearl size with larger Ni nanoparticles. Finally, the results showed that the 20 nm Ni nanoparticles chemically reacted sooner than the 100 nm Ni nanoparticles.

In this paper we first present a new fabrication process of downscaled graphene nanodevices based on direct milling of graphene using an atomic-size helium ion beam. We address the issue of contamination caused by the electron-beam lithography process to pattern the contact metals prior to the ultrafine milling process in the helium ion microscope (HIM). We then present our recent experimental study of the effects of the helium ion exposure on the carrier transport properties. By varying the time of helium ion bombardment onto a bilayer graphene nanoribbon transistor, the change in the transfer characteristics is investigated along with underlying carrier scattering mechanisms. Finally we study the effects of various single defects introduced into extremely-scaled armchair graphene nanoribbons on the carrier transport properties using ab initio simulation.

A key limitation to graphene based electronics is graphene’s interaction with dielectric interfaces. SiO₂ and various high-k gate dielectrics can introduce scattering from charged surface states, impurities, and surface optical phonons; degrading the transport properties of graphene. Hexagonal boron nitride (h-BN) exhibits an atomically smooth surface that is expected to be free of dangling bonds, leading to an interface that is relatively free of surface charge traps and adsorbed impurities. Additionally, the decreased surface optical phonon interaction from h-BN is expected to further reduce scattering. While h-BN gated graphene FETs have been demonstrated on a small scale utilizing CVD grown or exfoliated graphene, integrating quasi-freestanding epitaxial graphene (QFEG) with h-BN gate dielectrics on a wafer scale has not been explored. We present results from the first large scale CVD growth of h-BN and its subsequent transfer to a 75mm QFEG wafer. The effects of growth conditions on the thickness and quality of the h-BN film and its potential and limitations as a gate dielectric to QFEG are discussed. The introduction of charged impurities during the transfer process resulted in an average degradation in mobility of only 9%. Despite the slight degradation, we show that h-BN is highly beneficial compared to high-k dielectrics when the charged impurity concentration of QFEG is below 5x10¹²cm^-2. Here we show improvements in mobility of >3x and intrinsic cutoff frequency of >2x compared to HfO₂.

In this paper we report the use of graphene for microwave integrated circuit transmission lines. Multi-layered graphene films were grown on Si wafers coated with SiO₂ and Ni using chemical vapour deposition. A modified procedure to etch graphene used in our work involved the use of Au on top of graphene which formed defects by breaking bonds of the underlying graphene, but our modified procedure enabled the etching process to be performed with the presence of PMMA masking layer. The etchant was made of 3HCl:HNO₃:8H₂O. Co-planar transmission lines of various widths and lengths were constructed on graphene to ensure compatibility with microwave wafer probes used in the measurements. The lines and the underlying SiO₂ layer were modeled using CST Microwave Studio electromagnetic simulator. The centre conductor width was 30 μm, while the spacing varied from 30 to 100 μm. The graphene parameters were subsequently subtracted out from measurements by curve-fitting the experimental results with simulation. Low frequency I-V measurements revealed conductivity of the order of 2.89 × 10⁷ S/m, but scattering parameter measurements of the samples conducted over 1 to 20 GHz revealed much lower conductivity, an effect which we think was the result of poor quality thermally grown SiO₂ substrates used in this experiment.

We use 3D FEM simulation to study electrically-short carbon-nanotube-based antennas and their application to wireless on-chip communication. We first expose our model for single-wall carbon nanotubes and our simulation technique. This is then used to study extensively the various parameters involved in the design of a planar dipole antenna made of carbon nanotubes aligned over a quartz substrate. From this study, an appropriate design is selected and studied in an antenna-to-antenna transmission link.

The electrical properties of carbon nanostructures have been greatly stimulating to use in the nanotechnology for electronic components. In this paper, we study the AC and DC electrical conductivity responses of multi-walled carbon nanotube films, prepared by the vacuum filtration methods, with noncontact terahertz time-domain spectroscopy (THz- TDS) approach utilizing the extrapolation analysis as well as probe-in line technique.

Terahertz (THz) electromagnetic signals will certainly push the border in nanotechnology due to higher optoelectronic performance. The main purpose of this work is to analyze and study the coherent terahertz time-domain spectroscopy (THz-TDS) signals which provide a precise approach to achieve the electromagnetic absorption and dispersion responses of uniform and flat parallel face carbon nanostructures thin-films deposited on the transparent quartz substrate in the THz regime. We employ the THz differential analysis without concerning the complex iteration algorithm to extract the optical properties parameters of multi-walled carbon nanotubes (MWNTs) thin-films.

We report transmission spectroscopy results from the mid- to far-infrared on graphene, grown by chemical vapor deposition (CVD) on Cu. Similar results have been reported by several groups and their substrates of choice were thermal Si dioxide, quartz, or SiC, where strong phonon absorption results in transmission blocking bands in midinfrared. Silicon wafers (thickness ~ 500 μm), on the other hand, have transmission extending out to about 100 cm-1 when the doping level is low. Therefore, we choose to use Si wafers as the carrier substrates for transferred CVD graphene. The complex refractive index of the Si substrate is measured by infrared spectroscopic ellipsometry. As a result, continuous spectra (without blocking bands) in the range of 400 to 4000 cm-1 are obtained and they are modeled by free carrier absorption (the Drude model) and interband transitions (considering the Pauli blocking.) From these, the carrier density, carrier mobility, sheet resistivity, intraband scattering rate, and graphene layer number can be inferred. In the far-infrared range, the absorption is dominated by the intraband free carrier absorption and it mainly results from the interband transition in the mid-infrared range. Having continuous spectra using the Si substrates gives us the advantage to model the whole spectral region (from far-infrared to mid-infrared) accurately.

In this study, an apertureless near-field scanning optical microscope-Raman spectroscopy system is constructed and the topography and Raman scattering image of carbon nano-materials are simultaneously measured with high spatial resolution by using a sharp Au tip. The Rayleigh scattering image, and Raman scattering image of the carbon nanotubes showed improved spatial resolution and enhanced scattering intensity owing to the optical antenna effect of Au tip.

Using single-molecule confocal imaging techniques combined with time-correlated single-photon counting we investigated the electron transfer (ET) rates to the single-walled carbon nanotubes from various types of semiconductor hetero-nanocrystals of type-I or type-II band alignment. We observed significantly larger ET rate for type-II ZnSe/CdS dot-in-rod nanostructures as compared to type-I spherical CdSe/ZnS core/shell quantum-dots, and to CdSe/CdS dot-in-rod structures. We demonstrated that such rapid ET dynamics can compete with both Auger and radiative recombination processes, leading to potentially more effective photovoltaic operation. In another work, we used aligned single-walled carbon nanotubes as saturable absorbers for ps laser pulse generation. Using the vertical evaporation technique we fabricated saturable absorbers by transferring the water-soluble single wall carbon nanotubes onto a hydrophilic quartz substrate. The fast recovery times of the absorber were measured to be 136 fs and 790 fs. The modulation depth of the absorber was about 1.5%. Passive mode-locked Nd: GdVO4 laser using such an absorber was demonstrated. The continuous wave mode-locked pulses with the pulse duration of 12.4 ps and the repetition of 120 MHz were achieved. The maximum average output power of the mode-locked laser is 2.4 W at the pump power of 13 W. Such a kind of absorbers has potential to be put into practical use.

Graphene possesses unique physical properties, due to its specific energy bands configuration, substantially different from that of materials traditionally employed in solid-state optoelectronics. Among the variety of remarkable properties, strong field effect, high transparency in the visible-light range and low resistivity of graphene sheets are the most attractive ones for optoelectronic applications. Zero-dimensional colloidal semiconductor nanocrystals, known as quantum dots (QDs), attract immense attention in the field of photonics due to their size-dependent tunable optical properties. By combining these two types of nanomaterials together, we demonstrate the role of graphene as an efficient charge transfer medium from- and to II-VI quantum dots. The optical excitation of II-VI quantum dots dispersed on single layer graphene results in an electron transfer from the nanocrystals to graphene. This is evidenced from photoluminescence imaging and confirmed by the electrical measurements on QDs-decorated single layer graphene field effect transistors (SLG-FET). In the second part of this paper we demonstrate an efficient hole injection from graphene into QDs-layered nanocrystalline structures and the operation of the corresponding graphene-based quantum dot light emitting diodes (QD-LED). We also benchmark graphene vs. indium-tin-oxide (ITO) based QD-LEDs in terms of device electroluminescence intensity performance. Our experimental results show better hole injection efficiency for graphenebased electrode at current densities as high as 200 mA/cm² and suggest single layer graphene as a strong candidate to replace ITO in QD-LED technology.

Here we present our on-going efforts toward the development of stable ballasted carbon nanotube-based field emitters employing hydrothermally synthesized zinc oxide nanowires and thin film silicon-on-insulator substrates. The semiconducting channel in each controllably limits the emission current thereby preventing detrimental burn-out of individual emitters that occurs due to unavoidable statistical variability in emitter characteristics, particularly in their length. Fabrication details and emitter characterization are discussed in addition to their field emission performance. The development of a beam steerable triode electron emitter formed from hexagonal carbon nanotube arrays with central focusing nanotube electrodes, is also described. Numerical ab-initio simulations are presented to account for the empirical emission characteristics. Our engineered ballasted emitters have shown some of the lowest reported lifetime variations (< 0.7%) with on-times of < 1 ms, making them ideally-suited for next-generation displays, environmental lighting and portable x-rays sources.

Nanomedicine is the science of fabricating smart devices able to diagnose and treat diseases more efficiently than conventional medicine while minimizing costs, complexity and adverse effects. Carbon nanotubes (CNTs) are receiving considerable attention for biomedical applications due to their extraordinary properties. In particular, their chemical nature and high aspect ratio (ratio between the length and the diameter) make them ideal carriers to achieve delivery of high doses of therapeutic and imaging cargo to a specific site of interest. A major obstacle to the use of pristine (unmodified) CNTs in biological systems is their complete aqueous insolubility and low biocompatibility and toxicity profiles. To endow CNTs with solubility in a biological milieu, several non-covalent and covalent modification methods have been explored. Suitably modified CNTs have shown increased solubility under physiological conditions, improved biocompatibility profiles and lack of toxicity after injection in living animals. Additionally, after being loaded with cargo (small molecules, proteins, peptides or nucleic acids) they have been successfully evaluated as pharmaceutical, therapeutic and diagnostic tools.

We propose a new type of dye-sensitized solar cell (DSC) using carbon nanotubes (CNTs). Recently, global warming due to CO₂ generated from power plants, cars, and so on has received much attention. Therefore, clean power, e.g., solar power, is gaining in importance. In this study, we focused on a DSC that uses CNTs. Generally, sensitized dyes on semiconducting and metallic electrodes are used for constructing DSCs. In contrast, CNTs have many excellent properties. In particular, they have metallic and semiconducting properties that are used for the electrodes of DSCs. Therefore, we applied CNTs for fabricating a new “painting-type” DSC with semiconducting and metallic electrodes. CNTs are dispersed in water with surfactant to prepare CNT-paste for painting. This resulting CNT-paste has the same properties as a normal CNT. A DSC is comprised of two electrodes. One is a semiconducting electrode with a sensitized dye and another is a metallic one, as mentioned above. We fabricated the two electrodes by painting the CNT-paste onto substrates. Thus, this type of DSC can be applied to various objects, for example, the wall and car and housetop. An electrolyte is required and must be put between the electrodes. The method for fabricating a painting type DSC is very simple. First, two versions of the paste are used. One is a semiconducting CNT-paste that adsorbs a dye and the other is a CNT-paste without a dye. Second, we paint each paste onto two substrates. Finally, the two substrates are stacked. We drip about 10μl of an electrolyte onto the stacked substrates and irradiate them with solar light (1300 W/m²). An electromotive force (EMF) is generated by excited electrons from the dye, which are adsorbed on the semiconducting electrode. The maximum EMF reached about 250 mV and the current reached about 10 μA. These results indicate that the proposed painting-type DSC can be used a new type of solar cell.

This study investigated the application of single-wall carbon nanotubes( SWCNTs) on transparent conducting film. The SWCNTs films deposited on the flexible substrate using dip-coating. The major issue was studying the time and temperature of sulfuric acid effect on the pretreatment of SWCNTs. The post-treatment of etching dispersion and how to affect the optical and sheet resistance were always considered. The results showed that the sheet resistance of SWCNTs under 12 hrs pretreatment was higher than that without pretreatment, but over 12hrs the sheet resistance was lower than that without pretreatment. The sheet resistance of SWCNTs over 120°C pretreatment temperature was higher than that of pristine, but the sheet resistance of SWCNTs below 120°C pretreatment temperature was lower than that of pristine. Simultaneously, the dispersion combined with the functional group consisting of acetic acid (-OOH) could make SWCNTs to be more dispersion than before. Pretreatment of sulfuric acid at temperature of 120°C and time of 24 hrs had the good performance on optical and electricity for SWCNTs film. And the sheet resistance of SWCNTs film could reach 781 Ω/sq at transmittance of 70%. This study investigated the mechanism of the pretreatment of the dispersing and acid destroying for SWCNTs. An optimized acid pretreatment was used to improve the transparent and electricity on the flexible substrate with SWCNTs.