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.

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.

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 demonstrate a graphene-based electro-absorption modulator achieving extraordinary control of terahertz reflectance. By concentrating the electric field intensity in an active layer of graphene, an extraordinary modulation depth of 64% is achieved while simultaneously exhibiting low insertion loss (∼2 dB), which is remarkable since the active region of the device is atomically thin. This modulator performance, among the best reported to date, indicates the enormous potential of graphene for terahertz reconfigurable optoelectronic devices.

Electrical transport measurements were conducted on semiconducting nanowires and three distinct current-voltage (I-V) characteristics were observed, i.e., almost symmetric, almost rectifying, and almost linear. These I-V characteristics were modeled by treating the transport in the nanowire as in a metal-semiconductor-metal structure involving two Schottky barriers and a resistor in between these barriers, and the transport is shown to be dominated by the reverse-biased Schottky barrier under low bias and by the semiconducting nanowire at large bias. In contrast to the conventional Schottky diode, the reverse current in the nano-Schottky barrier structure is not negligible and the current is largely tunneling rather than thermionic. Experimental I-V curves are reproduced very well using our model, and a method for extracting nanowire resistance, electron density, and mobility is proposed and applied to ZnO, CdS, and Bi2S3 nanowires.

Near ballistic n-type single-walled carbon nanotube field-effect transistors (SWCNT FETs) have been fabricated with a novel self-aligned gate structure and a channel length of about 120 nm on a SWCNT with a diameter of 1.5 nm. The device shows excellent on- and off-state performance, including high transconductance of up to 25 microS, small subthreshold swing of 100 mV/dec, and gate delay time of 0.86 ps, suggesting that the device can potentially work at THz regime. Quantitative analysis on the electrical characteristics of a long channel device fabricated on the same SWCNT reveals that the SWCNT has a mean-free-path of 191 nm, and the electron mobility of the device reaches 4650 cm(2)/Vs. When benchmarked by the metric CV/ I vs Ion/Ioff, the n-type SWCNT FETs show significantly better off-state leakage than that of the Si-based n-type FETs with similar channel length. An important advantage of this self-aligned gate structure is that any suitable gate materials can be used, and in particular it is shown that the threshold voltage of the self-aligned n-type FETs can be adjusted by selecting gate metals with different work functions.

We determined the band alignment of a graphene-insulator-semiconductor structure using internal photoemission spectroscopy. From the flatband voltage and Dirac voltage, we infer a 4:6 Â 10 11 cm À2 negative extrinsic charge present on the graphene surface. Also, we extract the graphene work function to be 4.56 eV, in excellent agreement with theoretical and experimental values in literature. Electron and hole injection from heavily doped p-type silicon (Si) are both observed. The barrier height from the top of the valence band of Si to the bottom of the conduction band of silicon dioxide (SiO 2) is found to be 4.3 eV. The small optical absorption in graphene makes it a good transparent contact to enable the direct observation of hole injection from Si to graphene. The barrier height for holes escaping from the bottom of Si conduction band to the top of SiO 2 valence band is found to be 4.6 eV. V