92 research outputs found
Anomalous Increase in Carbon Capacitance at Pore Sizes Less Than 1 Nanometer
Carbon supercapacitors, which are energy storage devices that use ion adsorption on the surface of highly porous materials to store charge, have numerous advantages over other power-source technologies, but could realize further gains if their electrodes were properly optimized. Studying
the effect of the pore size on capacitance could potentially improve performance by maximizing the
electrode surface area accessible to electrolyte ions, but until recently, no studies had addressed the lower size limit of accessible pores. Using carbide-derived carbon, we generated pores with average sizes from 0.6 to 2.25 nanometer and studied double-layer capacitance in an organic
electrolyte. The results challenge the long-held axiom that pores smaller than the size of solvated electrolyte ions are incapable of contributing to charge storage
Phonon Confinement Effects in the Raman Spectrum of Nanodiamond
Nanodiamonds (ND) exhibit unique properties due to their small size and high surface-to-volume ratio compared to bulk diamonds. A reduction in crystal size also affects ND Raman spectra. The confinement of optical phonons in nanocrystals (\u3c10 nm) results in asymmetrically broadened Raman lines, which are shifted toward lower wavenumbers. The phonon confinement model (PCM) relates the observed changes in the Raman spectra to the crystal size and can be used for size characterization at the nanoscale. While the PCM was successfully applied to a variety of materials including Si and BN, results remained unsatisfactory in the case of ND. In order to improve the agreement between the predictions of the model and experimental Raman spectra of ND, effects such as crystal size distribution, lattice defects, and the energy dispersion of the phonon modes were taken into consideration and incorporated into the PCM. This work has shown that phonon wave vectors from small vibrational domains lead to a broad shoulder peak at ~1250 cm-1, that is often observed in the Raman spectrum of ND
Separation and Liquid Chromatography Using a Single Carbon Nanotube
Use of a single template-grown carbon nanotube as a separation column to separate attoliter volumes of binary mixtures of fluorescent dyes has been demonstrated. The cylindrical nanotube walls are used as stationary phase and the surface area is increased by growing smaller multi-walled carbon nanotubes within the larger nanotube column. Liquid-liquid extraction is performed to separate selectively soluble solutes in a solvent, and chromatographic separation is demonstrated using thin, long nanotubes coated inside with iron oxide nanoparticles. The setup is also used to determine the diffusion coefficient of a solute at the sub-micrometer scale. This study opens avenues for analytical chemistry in attoliter volumes of fluids for various applications and cellular analysis at the single cell level
Boron Nitride Colloidal Solutions, Ultralight Aerogels and Freestanding Membranes through One-Step Exfoliation and Functionalization
Manufacturing of aerogels and membranes from hexagonal boron nitride (h-BN) is much more difficult than from graphene or graphene oxides because of the poor dispersibility of h-BN in water, which limits its exfoliation and preparation of colloidal solutions. Here, a simple, one-step mechano-chemical process to exfoliate and functionalize h-BN into highly water-dispersible, few-layer h-BN containing amino groups is presented. The colloidal solutions of few-layer h-BN can have unprecedentedly high concentrations, up to 30 mg ml-1, and are stable for up to several months. They can be used to produce ultralight aerogels with a density of 1.4 mg cm-3, which is ~1,500 times less than bulk h-BN, and freestanding membranes simply by cryodrying and filtration, respectively. The material shows strong blue light emission under ultraviolet excitation, in both dispersed and dry state
Formation of porous SiC ceramics by pyrolysis of wood impregnated with silica
International Journal of Applied Ceramic Technology, 3(6): pp. 485-490.Biomorphous β-SiC ceramics were produced at 1400°C from pine wood impregnated with
silica. This one-step carbothermal reduction process decreases the cost of manufacturing of
SiC ceramics compared to siliconization of carbonized wood in silicon vapor. The
synthesized sample exhibits 14 m2/g surface area and has a hybrid pore structure with large 5-
20 μm tubular macropores and small (< 50 nm) slit shaped mesopores. SiC whiskers of 20-
400 nm in diameter and 5-20 μm in length formed within the tubular pores. These whiskers
are expected to improve the filtration by removing dust particles that could otherwise
penetrate through large pores. After ultrasonic milling, the powdered sample showed an
average particle size of ~30 nm. The SiC nanopowder produced in this process may be used
for manufacturing SiC ceramics for structural, tribological, and other applications
Carbon Nanopipettes Characterize Calcium Release Pathways in Breast Cancer Cells
Carbon-based nanoprobes are attractive for minimally-invasive cell interrogation but their application in cell physiology has thus far been limited. We have developed carbon nanopipettes (CNPs) with nanoscopic tips and used them to inject calcium-mobilizing messengers into cells without compromising cell viability. We identify pathways sensitive to cyclic adenosine diphosphate ribose (cADPr) and nicotinic acid adenine dinucleotide phosphate (NAADP) in breast carcinoma cells. Our findings demonstrate the superior utility of CNPs for intracellular delivery of impermeant molecules and, more generally, for cell physiology studies. The CNPs do not appear to cause any lasting damage to cells. Their advantages over the commonly used glass pipettes include smaller size, breakage and clogging resistance, and potential for multifunctionality such as concurrent injection and electrical measurements
Carbide-derived carbons designed for efficient hydrogen storage
Carbide-derived carbons (CDCs) with specific surface area (SSA) ~ 2000 m2/g and open pore volume up to 80% are produced by chlorine etching of metal carbides. Tuning the pore size distribution by carbide precursor selection and etching temperature yields enhanced hydrogen storage capacity at both ambient and elevated pressure. Our goal is to establish the fundamental relation between capacity and SSA, pore size and pore volume
Intercalation and Delamination of Layered Carbides and Carbonitrides
Intercalation and delamination of two-dimensional solids in many cases is a requisite step for exploiting their unique properties. Herein we report on the intercalation of two-dimensional Ti3C2, Ti3 CN and TiNbC - so called MXenes. Intercalation of hydrazine, and its co-intercalation with N,N-dimethylformamide, resulted in increases of the c-lattice parameters of surface functionalized f-Ti3C2, from 19.5 to 25.48 and 26.8 Ã…, respectively. Urea is also intercalated into f-Ti3C2. Molecular dynamics simulations suggest that a hydrazine monolayer intercalates between f-Ti3C2 layers. Hydrazine is also intercalated into f-Ti3 CN and f-TiNbC. When dimethyl sulphoxide is intercalated into f-Ti3C2, followed by sonication in water, the f-Ti3C2 is delaminated forming a stable colloidal solution that is in turn filtered to produce MXene \u27paper\u27. The latter shows excellent Li-ion capacity at extremely high charging rates
Numerical derivative analysis of load-displacement curves in depth-sensing indentation
Materials Research Society Symposium Proceedings, 791: pp. 191-202. Retrieved September 19, 2006 from http://nano.materials.drexel.edu/Papers/NumericalDerivativeAnal.pdf.We have investigated strain fields around GaN nanoindentations. Stress relaxation around the edges
of the nanoindentation was evident in atomic force microscopy images. More detailed information
on the strain fields was obtained from Raman scattering, which has been used to analyze the shape
of the strain field around the indentation. We find that the Berkovich tip giving a triangular imprint
on the sample generates a strain field, which represents a hexagonal pattern. Negative values of the
strain indicate that the residual stress is compressive. Strain is larger in the center of the indentation
than outside. Analysis of the ratio of the frequency shift of the E2 and A1sLOd modes suggests that
the residual strains are close to biaxial state outside the indentation contact zone, and mostly
hydrostatic within the indentation center
Magnetically assembled carbon nanotube tipped pipettes
Applied Physics Letters, 90: pp. 103108-1 - 103108-3.The authors have developed a biological probe at the nanoscale with a magnetic carbon nanotube
mCNT tip that has the ability to transfer fluids. Fabrication is performed by injection of mCNTs
into micropipettes, which are then positioned as probe tips via magnetophoresis, and affixed with
polymeric adhesive. In this letter the authors discuss the magnetic fabrication process and
demonstrate the versatility of this probe
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