Carbon, with its variety of allotropes and forms, is the most versatile material, and virtually any combination of mechanical, optical, electrical, and chemical properties can be achieved with carbon by controlling its structure and surface chemistry. The goal of this article is to help readers appreciate the variety of carbon nanomaterials and to describe some engineering applications of the most important of these. Many different materials are needed to meet a variety of performance requirements, but they can all be built of carbon. Considering the example of supercapacitor electrodes, zero- and one-dimensional nanoparticles, such as carbon onions and nanotubes, respectively, deliver very high power because of fast ion sorption/desorption on their outer surfaces. Two-dimensional (2D) graphene offers higher charge/discharge rates than porous carbons and a high volumetric energy density. Three-dimensional porous activated, carbide-derived, and templated carbon networks, with high surface areas and porosities in the angstrom or nanometer range, can provide high energy densities if the pore size is matched with the electrolyte ion size. Finally, carbon-based nanostructures further expand the range of available nanomaterials: Recently discovered 2D transition-metal carbides (MXenes) have already grown into a family with close to 20 members in about four years and challenge graphene in some applications.

Epitaxial graphene and carbon nanotubes (CNTs) grown on SiC have shown big potential in electronics. The motivation to produce faster and smaller electronic devices using less power opened the way to a study of how to produce controlled epitaxial graphene and CNTs on SiC. Since defects are among the important tools to control the properties of materials, the effects of defects on the carbon formation on SiC have been analyzed. In this study, the effects of defects on the carbon formation on SiC have been analyzed. We produced carbon films on the surface of four different SiC materials (polycrystalline sintered SiC disks, single crystalline SiC wafers, SiC whiskers, and nanowhiskers) by chlorination and vacuum annealing with the goal to understand the effects of surface defects on the carbon structure and the SiC decomposition rate. We have shown that grain boundaries, dislocations, scratches, surface steps, and external surfaces may greatly enhance the reaction rate and affect the final structure of carbon derived from SiC.

Recently, we reported on the facile synthesis of a number of two-dimensional early transition metal carbides and nitrides, derived from the MAX phases, that we labeled MXenes. Herein, we report on the electronic and elastic properties—investigated by first principles calculations utilizing the generalized gradient approximation within the density functional theory—of the following two-dimensional transition metal carbides: Ti2C, Ti3C2, Ti4C3, V2C, Cr2C, Zr2C, Hf2C, and Ta2C, Ta3C2, and Ta4C3. Similar to the MAX phases, the MXenes are found to be metallic and possess high elastic moduli when stretched along the basal planes.

We report on the synthesis of unique tetragonal nanostructures from porous anodic aluminum oxide that enables geometrical three-dimensional (3D) microdesign of the porous surfaces. Scanning electron microscopy study revealed self-organization of hollow oxide nanostructures into hierarchical arrays. The formation of these structures has a localized nature and is associated with local electrical break-down during hard anodization of aluminum in oxalic acid solution. Moreover, in this communication we propose the mechanism of the nucleation and growth of complex 3D structures from porous anodic alumina.

Capacitive energy storage mechanisms in nanoporous carbon supercapacitors hinge on endohedral interactions in carbon materials with macro-, meso-, and micropores that have negative surface curvature. In this article, we show that because of the positive curvature found in zero-dimensional carbon onions or one-dimensional carbon nanotube arrays, exohedral interactions cause the normalized capacitance to increase with decreasing particle size or tube diameter, in sharp contrast to the behavior of nanoporous carbon materials. This finding is in good agreement with the trend of recent experimental data. Our analysis suggests that electrical energy storage can be improved by exploiting the highly curved surfaces of carbon nanotube arrays with diameters on the order of 1 nm.

Multi-walled carbon nanotube (MWCNT) grafting onto electrospun poly(acrylonitrile) (PAN) nanofibers yields a layer by layer deposition of self assembled (LBL-SA) nanotube filaments or nanowires. PAN fibers were first functionalized with carboxylic groups through a sodium hydroxide treatment. Then, poly(diallyldimethylammonium chloride) (PDDAC), a positively charged polyelectrolyte was adsorbed onto the fibers via electrostatic interaction. When placed in contact with the modified fibers, acid treated MWCNT (ac-MWCNT) self-assemble, producing a dense and continuous layer onto the polymer nanofibers, while the inherent structure and morphology of the polymer nanofibers are retained. This method is being investigated as a universal approach applicable to a variety of materials. By producing layers of nanotubes, the electrical conductivity of polymers may be improved due to formation of a continuous MWCNT monolayer on the surface as opposed to traditional incorporation of large amounts of nanotubes into the bulk of the polymer. This method can further be implemented on polymer systems that promote a positively charged surface for COOH functionalized MWCNT to attach. Polyamides offer a perfect scenario in which they do not need to be modified to allow hydrogen bonding between the polymer and the ac-MWCNTs. Electrospun polyamide 11 (PA 11) provides a network of 100 nm and greater, fibers for deposition of ac-MWCNTs. These MWCNT coated nanofibers possess high electrical conductivity, about 0.1 S/cm, resulting from a dense coverage of MWCNTs on the polymer surface.

High temperature annealing in vacuum, air, hydrogen, chlorine, and ammonia are described as a means to change surface chemistry and phase composition of nanodiamond powders of three different grades, which have different sp2/sp3 carbon ratios. The changes in surface chemistry and phase composition of the powders are analyzed using Raman spectroscopy and Fourier Transform Infra Red (FTIR) spectroscopy. Advantages and limitation of high-temperature treatment techniques as well as potential applications of the gas-treated nanodiamond powders are discussed.

Multi-atom vacancies and pores in diamond-structured carbon phases play an important role in carbon sieves and carbon based storage. The size and shape of pores have a profound effect on the energetics of adsorptive storage. We are modeling large numbers of vacancy configurations with a combination of ab initio density functional theory (DFT), tight binding DFT and simpler methods based on Brenner-potentials and modified Brenner potentials. The more accurate calculations serve as the basis of the parametrization which is then used in lattice Monte Carlo simulations on more complex vacancies. The results will be put in the context of SiC-derived porous carbon materials with the purpose to explore basic questions of energetics in porous carbons.

Unloading rate and maximum load have been previously shown to affect the response of silicon to sharp indentation, but no such study exists for spherical indentation. In this work, a statistical analysis of over 1900 indentations made with a 13.5-μm radius spherical indenter on a single-crystal silicon wafer over a range of loads (25–700 mN) and loading/unloading rates (1–30 mN/s) is presented. The location of “pop-in” and “pop-out” events, most likely due to pressure-induced phase transformations, is noted, as well as pressures at which they occur. Multiple occurrences of pop-in and pop-out events are reported. Raman micro-spectroscopy shows a higher intensity of metastable silicon phases at some depth under the surface of the residual impression, where the highest shear stresses are present. A stability range for Si-II is demonstrated and compared with previous results for Berkovich indentation.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Early exposure of Nanoscale Science, Engineering and Technology (NSET) to undergraduate students is anticipated to play a pivotal role in recruiting highly qualified professionals for industry and in preparing future faculty and researchers for graduate education. Focusing on early undergraduate education in NSET, the newly launched Drexel Nano Engineering Track (DNET) program at Drexel University addresses the urgent need for early NSET education at the University level. The primary objective of the DNET program is to expose freshmen and sophomores in Drexel's College of Engineering to basic concepts in NSET. It is envisioned that the career decisions of a large fraction of students will be directed as they learn the vocabulary of NSET and see potential engineering applications. The current DNET program activities include (1) updating/modifying a series of freshmen/sophomore courses / laboratories to infuse NSET into early undergraduate curriculum. Because of the size of the established tDEC program, this initiative has been able to reach a remarkably large body of students immediately. Over 700 students are enrolled in NSET-revised freshmen courses, and they will progress to NSET-revised sophomore courses the next year. (2) developing a number of modules for NSET education and (3) launching/maintaining a DNET web for information dissemination, performance assessment and outreach activities. The DNET program, together with the existing Nanotechnology Institute and Drexel/Upenn IGERT program that focus on the NSET research and graduate education, offer a stream of NSET education from college to graduate school at Drexel University.