We investigate the time-dependent electronic transport in single-walled carbon nanotubes (SWCNTs) functionalized with Au clusters on CO gas exposure. Using a tight-binding Hamiltonian and the nonequilibrium Green's function (NEGF) formalism the time-dependent zeroth and first order contributions to the current are calculated. The zeroth order contribution is identified as the time-dependent Landauer formula in terms of the slow time variable, whereas the first order contribution is found to be small. The Green's function for the SWCNT is derived using the equation of motion and Dyson equation technique. The conductance is explicitly evaluated by considering a form for the hopping integral which accounts for the effect of dopants on the charge distribution of the carbon atoms and the nearest-neighbor distance. The effect of dopants is also studied in terms of fluctuations by calculating the autocorrelation function for the experimental and theoretical data. These calculations allow direct comparison with the experiment and demonstrate how the presence of dopants modifies the conductance of the SWCNT measured experimentally and provide the only study of fluctuations in the sensor response in terms of the autocorrelation function.
Scanning tunneling microscopy (STM) gives us the opportunity to map the surface of functionalized carbon nanotubes in an energy resolved manner and with atomic precision. But this potential is largely untapped, mainly due to sample stability issues which inhibit reliable measurements. Here we present a simple and straightforward solution that makes away with this difficulty, by incorporating the functionalized multiwalled carbon nanotubes (MWCNT) into a few layer graphene - nanotube composite. This enabled us to measure energy resolved tunneling conductance maps on the nanotubes, which shed li…
In terms of lattice dynamics theory, we study the vibrational properties of the oxygen-functionalized single wall carbon nanotubes (O-SWCNs). Due to the C-O and O-O interactions, many degenerate phonon modes are split and even some new phonon modes are obtained, different from the bare SWCNs. A distinct Raman shift is found in both the radial breathing mode and G modes, depending not only on the tube diameter and chirality but also on oxygen coverage and adsorption configurations. With the oxygen coverage increasing, interesting, a nonmonotonic up- and down-shift is observed in G modes, which …
Carbon nanotubes are of central importance for applications in nano-electronics thanks to their exceptional transport properties. They can be used as sensors, for example in biological applications, provided that they are functionalized to detect specific molecules. Due to their one-dimensional geometry the carbon nanotubes are very sensitive to the phenomenon of Anderson localization and it is therefore essential to know how the functionalization modifies their conduction properties and if they remain good conductors. Here we present a study of the quantum localization induced by functionaliz…
We report optically induced aggregation and subsequent separation of selective single-walled carbon nanotubes (SWNT) functionalized with bacteriorhodopsin in the aqueous solution. Well-dispersed, aqueous solutions of hydrophobic pristine SWNT were prepared using a biocompatible surfactant. Dispersed SWNTs were then functionalized with biologically synthesized, optically active purple membrane from Halobacterium salinarium S9. Bacteriorhodopsin is the optically active protein of the purple membrane. Charge transfer and interactions between an optically active purple membrane (PM) and nanotubes …
We investigate the electronic structure of carbon nanotubes functionalized by adsorbates anchored with single C-C covalent bonds. We find that, despite the particular adsorbate, a spin moment with a universal value of 1.0 $μ_B$ per molecule is induced at low coverage. Therefore, we propose a mechanism of bonding-induced magnetism at the carbon surface. The adsorption of a single molecule creates a dispersionless defect state at the Fermi energy, which is mainly localized in the carbon wall and presents a small contribution from the adsorbate. This universal spin moment is fairly independent of…
First-principles density functional theory (DFT) is employed to investigate the interactions of CO2 gas molecules with pristine and lithium-functionalized germanene. It is discovered that although a single CO2 molecule is weakly physisorbed on pristine germanene, a significant improvement on its adsorption energy is found by utilizing Li-functionalized germanene as the adsorbent. However, the moderate adsorption energy at high CO2 coverage predicts an easy release step. More excitingly, the structure of Li-functionalized germanene can be fully recovered after removal of CO2 gas molecules. Our …
Annotation A carbon nanotubes (CNT) filled polymer nanocomposites with their unique physical, mechanical and electro-optical properties has repeatedly discussed in the literature. The main part of this problem is to obtain high quality dispersion of CNTs. If for water-soluble polymers this problem can be considered as solved, it is not so for hydrophobic polymers, and PVC is an important example of this kind. This paper describes the methods of dispersion of SWNTs bundles in PVC, both by the use of specially synthesized surfactants, and by means of chemical surface modification of CNTs. The ma…
We study the effects of covalent functionalization of single wall carbon nanotubes (CNT) on their elastic properties. We consider simple organic molecules -NH, -NH2, -CH2, -CH3, -OH attached to CNTs' surface at various densities. The studies are based on the first principles calculations in the framework of density functional theory. We have determined the changes in the geometry and the elastic moduli of the functionalized CNTs as a function of the density of adsorbed molecules. It turns out that elastic moduli diminish with increasing concentration of adsorbands, however, the functionalized …
The controlled introduction of covalent sp$^{3}$ defects into semiconducting single-walled carbon nanotubes (SWCNTs) gives rise to exciton localization and red-shifted near-infrared luminescence. The single-photon emission characteristics of these functionalized SWCNTs make them interesting candidates for electrically driven quantum light sources. However, the impact of sp$^{3}$ defects on the carrier dynamics and charge transport in carbon nanotubes remains an open question. Here, we use ultrafast, time-resolved optical-pump terahertz-probe spectroscopy as a direct and quantitative technique …
We use DFT to study the effect of molecular adsorbates on the conductance of metallic carbon nanotubes. The five molecules considered (NO2, NH2, H, COOH, OH) lead to similar scattering of the electrons. The adsorption of a single molecule suppresses one of the two available channels of the CNT at low bias conductance. If more molecules are adsorbed on the same sublattice, the remaining open channel can be blocked or not, depending on the relative position of the adsorbates. If a simple geometric condition is fulfilled this channel is still open, even after adsorbing an arbitrary number of mole…
We present a first-principles study of the electronic transport properties of micrometer long semiconducting CNTs randomly covered with carbene functional groups. Whereas prior studies suggested that metallic tubes are hardly affected by such addends, we show here that the conductance of semiconducting tubes with standard diameter is on the contrary severely damaged. The configurational averaged conductance as a function of tube diameter and with a coverage of up to one hundred functional groups is extracted. Our results indicate that the search for a conductance-preserving covalent functional…
High spin polarization materials or spin filters are key components in spintronics, a niche subfield of electronics where carrier spins play a functional role. Carrier transmission through these materials is "spin selective" i.e. these materials are able to discriminate between "up" and "down" spins. Common spin filters include transition metal ferromagnets and their alloys, with typical spin selectivity (or, polarization) ~50% or less. Here we consider carrier transport in an archetypical one-dimensional molecular hybrid in which a single wall carbon nanotube (SWCNT) is wrapped around by sing…
We investigate through non-equilibrium Molecular Dynamics simulations the structure and flow of fluids in functionalized nanopores. The nanopores are modeled as cylindrical structures with solvophilic and solvophobic sites. Two fluids are modeled. The first is a standard Lennard Jones fluid. The second one is modeled with a isotropic two-length scale potential, which exhibits in bulk water-like anomalies. Our results indicates distinct dependence of the overall mass flux for each species of fluid with the number of solvophilic sites for different nanotubes radii. Also, the density and fluid st…
We developed a scalable, label-free all-electronic sensor for D-glucose based on a carbon nanotube transistor functionalized with pyrene-1-boronic acid. This sensor responds to glucose in the range 1 uM - 100 mM, which includes typical glucose concentrations in human blood and saliva. Control experiments establish that functionalization with the boronic acid provides high sensitivity and selectivity for glucose. The devices show better sensitivity than commercial blood glucose meters and could represent a general strategy to bloodless glucose monitoring by detecting low concentrations of gluco…
Using first-principles calculations, we investigate the electronic structures and binding properties of nicotine and caffeine adsorbed on single-walled carbon nanotubes to determine whether CNTs are appropriate for filtering or sensing nicotine and caffeine molecules. We find that caffeine adsorbs more strongly than nicotine. The different binding characteristics are discussed by analyzing the modification of the electronic structure of the molecule-adsorbed CNTs. We also calculate the quantum conductance of the CNTs in the presence of nicotine or caffeine adsorbates and demonstrate that the i…
Attraction between the polycyclic aromatic surface elements of carbon nanotubes (CNT) and the aromatic nucleotides of deoxyribonucleic acid (DNA) leads to reversible adsorption (physisorption) between the two, a phenomenon related to hybridization. We propose a Hamiltonian formulation for the zipper model that accounts for the DNA-CNT interactions and allows for the processing of experimental data, which has awaited an available theory for a decade.
A suspended carbon nanotube can act as a nanoscale resonator with remarkable electromechanical properties and the ability to detect adsorption on its surface at the level of single atoms. Understanding adsorption on nanotubes and other graphitic materials is key to many sensing and storage applications. Here we show that nanotube resonators offer a powerful new means of investigating fundamental aspects of adsorption on carbon, including the collective behaviour of adsorbed matter and its coupling to the substrate electrons. By monitoring the vibrational resonance frequency in the presence of …
In the last decade, solid state nanopores nanogaps have attracted significant interest in the rapid detection of DNA nucleotides. However, reducing the noise through the controlled translocating of the DNA nucleobases is a central issue for the developing nanogap nanopore based DNA sequencing to achieve single nucleobase resolution. Furthermore, the high reactivity of the graphene pores gaps exhibits clogging of the pore gap, leading to the blockage of the pores gaps, yielding sticking, and irreversible pore closure. To address the prospective of functionalization of carbon nanostructure and f…
The recent experimental synthesis of the two-dimensional (2D)boron-graphdiyne (BGDY) nanosheet has motivated us to investigate its structural, electronic,and energy storage properties. BGDY is a particularly attractive candidate for this purpose due to uniformly distributed pores which can bind the light-metal atoms. Our DFTcalculations reveal that BGDY can accommodate multiple light-metal dopants (Li, Na, K, Ca)with significantly high binding energies. The stabilities of metal functionalized BGDY monolayers have been confirmed through ab initio molecular dynamics simulations. Furthermore, sig…
In their tubelike phase, nanowire-adsorbed polymers exhibit strong structural similarities to morphologies known from single-walled carbon (hexagonal) and boron (triangular) nanotubes. Since boron/boron nitride tubes require some disorder for stability the triangular polymer tubes provide a closer analog to the carbon tubes. By means of computer simulations of both two and three dimensional versions of a coarse-grained bead-spring model for the polymers, we investigate their structural properties and make a detailed comparison with structures of carbon nanotubes.
With a view towards optimizing gas storage and separation in crystalline and disordered nanoporous carbon-based materials, we use ab initio density functional theory calculations to explore the effect of chemical functionalization on gas binding to exposed edges within model carbon nanostructures. We test the geometry, energetics, and charge distribution of in-plane and out-of-plane binding of CO2 and CH4 to model zigzag graphene nanoribbons edge-functionalized with COOH, OH, NH2, H2PO3, NO2, and CH3. Although different choices for the exchange-correlation functional lead to a spread of values…
The thermodynamics of adsorption of light alkanes and alkenes (CH4, C2H6, C2H4, C3H8, and C3H6) in single-walled carbon nanotube bundles is studied by configurational-bias grand canonical Monte Carlo simulation. The bundles consist of uniform nanotubes with diameters in the range 11.0 < D (A) < 18.1, arranged in the usual close-packed hexagonal lattice. The phase space is systematically analyzed with calculations for adsorption at room temperature and reduced pressure range of 8.7 x 10-9 < (p/p0) < 0.9. The simulation results are interpreted in terms of the molecular nature of the adsorbate an…
First-principles calculations have been performed to study the effects of adsorbates (CO molecules and O atoms) and defects on electronic structures and transport properties of Au nanotubes (Au(5, 3) and Au(5, 5)). For CO adsorption, various adsorption sites of CO on the Au tubes were considered. The vibrational frequency of the CO molecule was found to be very different for two nearly degenerate stable adsorption configurations of Au(5, 3), implying the possibility of distinguishing these two configurations via measuring the vibrational frequency of CO in experiments. After CO adsorption, the…
Detecting dopamine is of great biological importance because the molecule plays many roles in the human body. For instance, the lack of dopamine release is the cause of Parkinson's disease. Although many researchers have carried out experiments on dopamine detection using carbon nanotubes (CNTs), there are only a few theoretical studies on this topic. We study the adsorption properties of dopamine and its derivatives, L-DOPA and dopamine o-quinone, adsorbed on a semiconducting (10, 0) CNT, using density functional theory calculations. Our computational simulations reveal that localized states …
The normal paper used in any printer is among the cheapest flexible organic materials that exist. We demonstrate that we can print on paper high-frequency circuits tunable with an applied dc voltage. This is possible with the help of an ink containing functionalized carbon nanotubes and water. After the water is evaporated from the paper, the nanotubes remain steadily imprinted on paper, showing a semiconducting behaviour and tunable electrical properties.
Diazonium reactions with carbon nanotubes form optical $sp^3$ defects that can be used in optical and electrical circuits. We investigate a direct on-device reaction supported by confined laser irradiation and present a technique where an arbitrary carbon nanotube can be preferentially functionalized within a device by matching the light frequency with its transition energy. An exemplary reaction was carried out between (9,7) nanotube and 4-bromobenzenediazonium tetrafluoroborate. The substrate supported nanotubes of multiple semiconducting chiralities were locally exposed to laser light while…
We demonstrate wafer-scale integration of single electron memories based on carbon nanotube field effect transistors (cnfets) by a complete self assembly process. First, a dry self assembly based on a Hot Filament assisted Chemical Vapor Deposition technique allows both localized growth and in situ electrical connection of carbon nanotubes on predefined catalytic electrodes. The semiconducting carbon nanotubes integration yield can exceed 50% for a batch. Secondly, a wet self-assembly attaches single 30 nm-diameter gold bead in the nanotube vicinity via chemical functionalization. The bead act…
The adsorption of two different organic molecules cyanidin glucoside (C$_{21}$O$_{11}$H$_{20}$) and TA-St-CA on anatase (101) and (001) nanowires have been investigated using the standard and the range separated hybrid density functional theory calculations. The electronic structures and optical spectra of resulting dye--nanowire combined systems show distinct features for these types of photochromophores. The lowest unoccupied molecular orbital of the natural dye cyanidin glucoside is located below the conduction band of the semiconductor while, in the case of TA-St-CA, it resonates with the …
Vapor sensors based on functionalized carbon nanotubes (NTs) have shown great promise, with high sensitivity conferred by the reduced dimensionality and exceptional electronic properties of the NT. Critical challenges in the development of NT-based sensor arrays for chemical detection include the demonstration of reproducible fabrication methods and functionalization schemes that provide high chemical diversity to the resulting sensors. Here, we outline a scalable approach to fabricating arrays of vapor sensors consisting of NT field effect transistors functionalized with single-stranded DNA (…
Applications based on Single Walled Carbon Nanotube (SWNT) are good example of the great need to continuously develop metrology methods in the field of nanotechnology. Contact and interface properties are key parameters that determine the efficiency of SWNT functionalized nanomaterials and nanodevices. In this work we have taken advantage of a good control of the SWNT growth processes at an atomic force microscope (AFM) tip apex and the use of a low noise (1E-13 m/rtHz) AFM to investigate the mechanical behavior of a SWNT touching a surface. By simultaneously recording static and dynamic prope…
Covalent functionalization of semiconducting single-wall carbon nanotubes (CNT) introduces new photoluminescent emitting states. Theses states are spatially localized at around functionalization sites and strongly red-shifted relative to the emission commonly observed from the nanotube band-edge exciton state. A particularly important feature of these localized exciton states is that, because the exciton is no longer free to diffusively sample photoluminescent quenching sites along the CNT length, its lifetime is significantly extended. We have recently demonstrated that an important relaxatio…
A theoretical understanding of the experimental electronic transport phenomena in gas sensors based on DNA functionalized graphene is presented by quantitatively investigating the time-dependent electronic transport in these devices using the nonequilibrium Green's function (NEGF) formalism and tight-binding approximation. The time-dependent zeroth and first order contributions to the current are calculated with derivations of the equation of motion and Dyson equation. The zeroth order contribution is identified as the time-dependent Landauer formula in terms of the slow time variable and the …
We demonstrate a "bottom up" approach to the computational design of a multifunctional chemical sensor. General techniques are employed for describing the adsorption coverage and resistance properties of the sensor based on density functional theory (DFT) and non-equilibrium Green's function methodologies (NEGF), respectively. Specifically, we show how Ni and Cu doped metallic (6,6) single-walled carbon nanotubes (SWNTs) may work as effective multifunctional sensors for both CO and NH3.
We explore the electric-field effect of carbon nanotubes (NTs) in electrolytes. Due to the large gate capacitance, Fermi energy shifts of order +/- 1 V can be induced, enabling to tune NTs from p to n-type. Consequently, large resistance changes are measured. At zero gate voltage the NTs are hole doped in air with E_F ? 0.3-0.5 eV, corresponding to a doping level of ? 10^{13} cm^{-2}. Hole-doping increases in the electrolyte. This hole doping (oxidation) is most likely caused by the adsorption of oxygen in air and cations in the electrolyte.
We investigate adsorption effects of copper phthalocyanine molecules on excitons and trions in air-suspended carbon nanotubes. Using photoluminescence excitation spectroscopy, we observe that exciton energy redshifts gradually with the molecular deposition thickness. The trion emission is also observed at large deposition amounts, which indicates charge transfer between the phthalocyanine molecules and carbon nanotubes. Analysis of the spectra for individual tubes reveal a correlation between the exciton-trion energy separation and the exciton emission energy, showing that the many-body intera…
We use the non-interacting tight-binding model to study the effect of isolated hydrogen adsorbates on the quasiparticle spectra of single-layer graphene. Using the Green's function approach, we obtain analytic expressions for the local density of states and the spectral function of hydrogen-doped graphene, which are also numerically evaluated and plotted. Our results are relevant for the interpretation of scanning tunneling microscopy and angle-resolved photoemission spectroscopy data of functionalized graphene.
Photoluminescence spectroscopy measurements are performed on suspended carbon nanotubes in a field-effect configuration, and the gate voltage dependence of photoluminescence spectra are compared for the pristine and the molecularly adsorbed states of the nanotubes. We quantify the molecular screening effect on the trion binding energies by determining the energy separation between the bright exciton and the trion emission energies for the two states. The voltage dependence shows narrower voltage regions of constant photoluminescence intensity for the adsorbed states, consistent with a reductio…
We use computational screening to systematically investigate the use of transition metal doped carbon nanotubes for chemical gas sensing. For a set of relevant target molecules (CO, NH3, H2S) and the main components of air (N2, O2, H2O), we calculate the binding energy and change in conductance upon adsorption on a metal atom occupying a vacancy of a (6,6) carbon nanotube. Based on these descriptors, we identify the most promising dopant candidates for detection of a given target molecule. From the fractional coverage of the metal sites in thermal equilibrium with air, we estimate the change i…
Electrical resistivity and magnetoresistance(MR) in polyaniline(PANI) with carbon nanotube(CNT) and functionalized carbon nanotube(fCNT) composites have been studied for different weight percentage down to the temperature 4.2K and up to magnetic field 5T. Resistivity increases significantly in composite at low temperature due to functionalization of CNT compare to only CNT. Interestingly transition from negative to positive magnetoresistance has been observed for 10wt% of composite as the effect of disorder is more in fCNT/PANI. This result depicts that the MR has strong dependency on disorder…
The conductivity of carbon nanotube (CNT) networks can be improved markedly by doping with nitric acid. In the present work, CNTs and junctions of CNTs functionalized with NO$_3$ molecules are investigated to understand the microscopic mechanism of nitric acid doping. According to our density functional theory band structure calculations, there is charge transfer from the CNT to adsorbed molecules indicating p-type doping. The average doping efficiency of the NO$_3$ molecules is higher if the NO$_3$ molecules form complexes with water molecules. In addition to electron transport along individu…
We present results of extensive theoretical studies concerning stability, morphology, and band structure of single wall carbon nanotubes (CNTs) covalently functionalized by -CHn(for n=2,3,4),-NHn(for n=1,2,3,4),-COOH and -OH groups. Our studies are based on ab initio calculations in the framework of the density functional theory. We determine the dependence of the binding energies on the concentration of the adsorbed molecules, critical densities of adsorbed molecules, global and local changes in the morphology, and electronic structure paying particular attention to the functionalization indu…
We measure the resistance and frequency-dependent gate capacitance of carbon nanotube (CNT) thin films in ambient, vacuum, and under low-pressure (10E-6 torr) analyte environments. We model the CNT film as an RC transmission line and show that changes in the measured capacitance as a function of gate bias and analyte pressure are consistent with changes in the transmission line impedance due to changes in the CNT film resistivity alone; the electrostatic gate capacitance of the CNT film does not depend on gate voltage or chemical analyte adsorption. However, the CNT film resistance is enormous…
