Ferromagnetic materials are important for modern technology; their applications range from distribution of power to high-speed computers and electronic devices of all kinds. Considerable attention has been paid in recent years to the development of ferromagnetic nanocomposites, such as ferromagnetic metals confined within nanostructures, for their potential use in spintronics, for example magnetoresistive random access memory, anisotropic magnetic response, lowthreshold-voltage electron emitters, and magnetic recording media with high storage densities.[1±5] In particular, extensive investigations [6±14] have been carried out to fill carbon nanotubes (CNTs) with metallic elements or compounds. Here we report an investigation of the possible use of a CNT/Fe nanocomposite as a high-loss material, for example as an electromagnetic shielding material or a high-performance radar-absorbent material (RAM). We will show that Fe can be filled into CNTs by a simple catalytic pyrolysis routine, and that both the shape and phase of the filler Fe, which has a profound effect on the microwave absorption properties and the complex permittivity and permeability of the CNT/Fe nanocomposite, can be controlled. Our CNT samples were prepared by the chemical vapor deposition (CVD) method [15] (see also the Experimental section). The samples used for electromagnetic measurements were prepared by dispersing the CNT/Fe nanocomposite into epoxy resin with a weight ratio of 1:5. In order to measure the reflection loss of the sample, a portion of the sample was coated onto an aluminum substrate (180 mm 180 mm) with a thickness of 1.2 mm. The remaining sample was molded into the hollow pipe of a rectangular waveguide cavity for complex permittivity and permeability measurements; the cavity has a dimension of 10.2 mm 2.9 mm 1.2 mm. For comparison we also prepared a flat sheet of soft Fe 1.2 mm thick (sample F). The complex relative permittivity e r = e¢ ± je² r , permeability lr = l¢ ± jl² r , and reflection loss were measured using a HP8510C vector network analyzer working at the 2±18 GHz band.Comprehensive structural characterizations of the samples were carried out.[15] Three transmission electron microscope (TEM) images of samples A±C are shown in Figures 1a±c, respectively, and Figure 1d shows a high-resolution TEM (HRTEM) image of sample E. These TEM images and the corresponding electron diffraction (ED) patterns (Figs. 1g,h) and element maps (Figs. 1e,f) show that sample A is composed of mainly multiwalled CNTs (MWCNTs; Fig. 1a), sample B is composed of mainly particle-like Fe encapsulated within carbon nanocages (Fig. 1b), and sample C is composed of mainly Fe nanowires encapsulated within MWCNTs (Fig. 1c). Detailed electron energy loss spectroscopy (EELS) and elemental mapping studies showed that the filler Fe is pure Fe rather than its oxide (see Fig. 1c and especially the iron and oxygen maps, Figs.

We present the results of a thorough study of wet chemical methods for transferring chemical vapor deposition grown graphene from the metal growth substrate to a device-compatible substrate. On the basis of these results, we have developed a "modified RCA clean" transfer method that has much better control of both contamination and crack formation and does not degrade the quality of the transferred graphene. Using this transfer method, high device yields, up to 97%, with a narrow device performance metrics distribution were achieved. This demonstration addresses an important step toward large-scale graphene-based electronic device applications.

A metal‐semiconductor‐metal (M‐S‐M) model for quantitative analysis of current–voltage (I–V) characteristics of semiconducting nanowires is described and applied to fit experimental I–V curves of Bi2S3 nanowire transistors. The I–V characteristics of semiconducting nanowires are found to depend sensitively on the contacts, in particular on the Schottky barrier height and contact area, and the M‐S‐M model is shown to be able to reproduce all experimentally observed I–V characteristics using only few fitting variables. A procedure for decoupling contact effects from that of the intrinsic parameters of the semiconducting nanowires, such as conductivity, carrier mobility and doping concentration is proposed, demonstrated using experimental I–V curves obtained from Bi2S3 nanowires and compared with the field‐effect based method.

We have fabricated ballistic n-type carbon nanotube (CNT)-based field-effect transistors (FETs) by contacting semiconducting single wall CNTs using Sc. Together with the demonstrated ballistic p-type CNT FETs using Pd contacts, our work closes the gap for doping-free fabrication of CNT-based ballistic complementary metal-oxide semiconductor (CMOS) devices and circuits. We demonstrated the feasibility of this dopingfree CMOS technology by fabricating a simple CMOS inverter on a SiO 2 /Si substrate using the back-gate geometry, but in principle much more complicated CMOS circuits may be integrated on a CNT on any suitable insulator substrate using the top-gate geometry and high-K dielectrics. This CNT-based CMOS technology only requires the patterning of arrays of parallel semiconducting CNTs with moderately narrow diameter range, for example, 1.6−2.4 nm, which is within the reach of current nanotechnology. This may lead to the integration of CNT-based CMOS devices with increasing complexity and possibly find its way into the computers brain: the logic circuit.