Nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) were synthesized using a floating catalyst aerosol chemical vapor deposition method, with carbon monoxide as carbon source, ammonia as nitrogen source, and iron particles derived from evaporated iron as catalyst. The material was deposited as grown directly from the gas phase as films on various substrates, and subsequently characterized by Raman and optical absorption spectroscopies, sheet resistance measurements, electron microscopy and energy-loss spectroscopy, and X-ray photoelectron spectroscopy. The sheet resistance measurements revealed that the doped films had unexpectedly high resistances. This stands in contrast to the case of N-MWCNT films, where decreased resistance has been reported with N-doping. To understand this effect, we developed a resistor network model, which allowed us to disentangle the contribution of bundle-bundle contacts when combined with data on undoped films. Assuming doping does not significantly change the contacts, the increased resistances of the doped films are likely due to enhanced carrier scattering by defect sites in the nanotubes. This work represents the first experimental report on macroscopic N-SWCNT thin films.

Catalysis over metal nanoparticles is essential for the growth of carbon nanotubes and all the properties of the resulting nanotube, such as diameter and chirality, are affected by the metal particle. Thus, it is very important to understand the carbon chemistry taking place on nanometer size metal particles. Here we present the fi rst ab initio computational study of chemical reactions on a nanosized iron cluster. The clusters have reaction sites, such as edges and vertexes between the facets, Which have not been studied before. First principles electronic structure calculations, fully incorporating the effects of spin polarization and non-collinear magnetic moments, have been used to investigate CO disproportionation on an isolated Fe 55 cluster. After CO dissociation, O atoms remain on the surface while C atoms move into the cluster, presumably as the initial step toward carbide formation. Here we show that the lowest CO dissociation barrier found on the cluster (0.77 eV) is lower than on most previously studied Fe surfaces. This dissociation occurs on a vertex between the facets. Several possible paths for CO 2 formation were identifi ed. The calculated lowest reaction barrier is 1.08 eV, which is comparable to the barrier of 0.65 eV obtained by experiment. KEYWORDSNanoparticle, density functional theory (DFT), mechanism, synthesis Since their discovery, carbon nanotubes (CNTs) have been the object of very intensive research. CNTs are of great interest since they exhibit unique and useful chemical and physical properties related to toughness, electrical/thermal conductivity, and magnetism [1]. Several different techniques have been introduced to synthesize CNTs [2 5] but among the various routes, carbon vapor deposition (CVD) methods have attracted widespread interest since they open a way to highly controlled and continuous CNT production on designed architectures [5 9]. In these processes, metal nanoparticles are produced in a mixed flow of carbon precursors and other gases (e.g., hydrogen) and the growth process is driven by cleaving the carbon atoms from the precursors and these atoms then form carbon structures on the surface of the nanoparticles. The metal catalyst nanoparticle is essential for CNT growth. All properties, like diameter and chirality, of the nanotube are determined by the metal particle. The ability to control the properties of CNTs is essential for their use in technological applications [10]. Thus, it Nano Research 661 Nano Res (2009) 2: 660 670 is very important to understand the carbon chemistry taking place on the nanometer size metal particles. I n a d d i t i o n t o t h e C N T s y n t h e s i s , m e t a l nanoclusters with a size less than 10 nm have attracted a great deal of attention due to their applications in magnetism [11], electronics [12], and catalysis [13]. Often the good catalytic activity can be related to catalytic sites, like atomic size steps, on the cluster. Due to the high curvature of the clusters, the special site density and distribution are much hi...

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Recent years have witnessed an ever growing interest in theoretically studying chemical processes at surfaces. Apart from the interest in catalysis, electrochemistry, hydrogen economy, green chemistry, atmospheric and interstellar chemistry, theoretical understanding of the molecule-surface chemical bonding and of the microscopic dynamics of adsorption and reaction of adsorbates are of fundamental importance for modeling known processes, understanding new experimental data, predicting new phenomena, controlling reaction pathways. In this work, we review the efforts we have made in the last few years in this exciting field. We first consider the energetics and the structural properties of some adsorbates on metal surfaces, as deduced by converged, first-principles, plane-wave calculations within the slab-supercell approach. These studies comprise water adsorption on Ru(0001), a subject of very intense debate in the past few years, and oxygen adsorption on aluminum, the prototypical example of metal passivation. Next, we address dynamical processes at surfaces with classical and quantum methods. Here the main interest is in hydrogen dynamics on metallic and semi-metallic surfaces, because of its importance for hydrogen storage and interstellar chem- istry. Hydrogen sticking is studied with classical and quasi-classical means, with particular emphasis on the relaxation of hot-atoms following dissociative chemisorption. Hot atoms dynamics on metal surfaces is investigated in the reverse, hydrogen recombination process and compared to Eley-Rideal dynamics. Finally, Eley-Rideal, collision-induced desorption, and adsorbate-induced trapping are studied quantum mechanically on a graphite surface, and unexpected quantum effects are observed.

First-principles electronic structure calculations, fully incorporating the effects of spin polarization and noncollinear magnetic moments, have been used to investigate CO disproportionation on an isolated Fe cluster. After CO dissociation, which occurs on a vertex between the facets, O atoms remain on the surface while C atoms move into the cluster as the initial step toward carbide formation. The lowest CO dissociation barrier found (0.77 eV) is lower than that on most of the studied Fe surfaces. Several possible paths for CO 2 formation were identified. The lowest reaction barrier was 1.08 eV.The carbon nanotubes (CNTs) are of great interest since they exhibit unique and useful chemical and physical properties related to toughness, electrical/thermal conductivity, and magnetism.1 The chemical vapor deposition (CVD) methods are widely used as a CNTs synthesis method since they open a way to highly controlled and continuous CNT production. [2][3][4][5] In these processes, metal nanoparticles are produced in a mixed flow of carbon precursors and other gases (e.g., hydrogen), and the growth process is driven by cleaving the carbon atoms from the precursors, and these atoms will form carbon structures on the nanoparticles' surface. All properties, like diameter and chirality, of the nanotube are determined by the metal particle. In addition to the CNT synthesis, the metal nanoclusters with a size of less than 10 nm have attracted a great deal of attention due to their applications in magnetism, 6 electronics, 7 and catalysts. 8 The metal nanoparticles are widely used in several real-world catalytic applications, including the car exhaust catalysts, where reactions happen on 3-8 nm size Pt group metal particles. Often, the good catalytic activity can be related to catalytic sites, like atomic size steps, on the cluster. Due to the high curvature of the clusters, the special site density and distribution is much higher than that on almost flat surfaces. Furthermore, the real nanoclusters have several unique active sites like facets and vertexes between the facets, which can have catalytic properties that differ drastically from the ones of almost flat surfaces. The research related to the active sites is mainly limited to atomic steps, and the nanosized clusters have received much less attention.9 Experimentally, many investigators have studied metal nanostructures using a wide range of surface science techniques, but these studies were done with rather a arbitrary size of clusters because it is very difficult to prepare fixed size clusters. 9 If we want to understand the active sites on clusters, we have to know which cluster we are studying. Even then, each cluster has several different active sites, and it is very difficult to know which of them is the most active one. For this reason, the computational approach, where precise sites can be studied, is very attractive.The present study is addressing the CO disproportionation CO (g) + CO (g) h CO 2(g) + C (s) on an iron nanocluster during the CVD method for the sy...