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.

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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.

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High-performance top-gated carbon nanotube field-effect transistors (CNT FETs) with a gate length of 5 nanometers can be fabricated that perform better than silicon complementary metal-oxide semiconductor (CMOS) FETs at the same scale. A scaling trend study revealed that the scaled CNT-based devices, which use graphene contacts, can operate much faster and at much lower supply voltage (0.4 versus 0.7 volts) and with much smaller subthreshold slope (typically 73 millivolts per decade). The 5-nanometer CNT FETs approached the quantum limit of FETs by using only one electron per switching operation. In addition, the contact length of the CNT CMOS devices was also scaled down to 25 nanometers, and a CMOS inverter with a total pitch size of 240 nanometers was also demonstrated.