**2. Experiment**

Nanowires, planar nanometric thin films and nanocolumns of Fe/MgO/Fe were synthesized using magnetron DC/RF sputtering, AXXIS sputtering tool from Kurt J. Lesker Company. Fe target of purity 99.9% and MgO of purity 99.95% were sputtered using high-purity Ar. Nanowires were synthesized by magnetron DC and RF sputtering in the interior cylindrical space of carbon nanotubes by magnetron DC and RF sputtering.

Thermal chemical vapor deposition method (TCVD) was used to grow vertically aligned CNTs on the SiO<sup>2</sup> substrate thus filled with Fe/MgO/Fe in this experiment [11]. TCVD involves exposing silica structures to a mixture of ferrocene and xylene at 770°C for 600 s. In TCVD, the furnace is pumped down to about 200 mTorr in an argon bleed, and then, the temperature is raised to 770°C. The solution of ferrocene dissolved in xylene of concentration about 0.01 g/ ml and was preheated in a bubbler to 175°C and then passed through the tube furnace. The furnace is cooled down to room temperature, and tips of the CNTs were exposed to plasma to open the nanotubes for the next procedure. The open-ended CNT tips were filled with Fe/ MgO/Fe using DC magnetron for the Fe and RF sputtering method for the insulator (MgO) at a substrate temperature of 100°C. This substrate temperature, 100°C, yielded in planar samples the highest value of coercive field compared to several other synthesis substrate temperatures [12].

Nanowires of Fe/MgO/Fe Encapsulated in Carbon Nanotubes http://dx.doi.org/10.5772/intechopen.79819 7

**Figure 3.** Schematic of planar TMR and array of TMR structure.

anisotropy sufficient to overcome the demagnetizing field. This feature makes it important for high-density magnetic media, highly sensitive sensors and parts for a quantum computer. This system in addition to its enormous potential for technological applications is an attractive

Samples were prepared in the form of nanometric thin films and nanocolumns as shown in **Figure 2**. Nanocolumn arrays were fabricated with different shapes and in-plane orientations by glancing angle deposition (GLAD). This will provide shape anisotropy, which will compete with surface and volume anisotropy. Many unique and fascinating properties have already been demonstrated by nanocolumns synthesized using GLAD, such as superior mechanical toughness, higher luminescence efficiency, enhancement of thermoelectric figure of merit and lowered lasing threshold. Homogeneous nanowires and nanowire networks have been previously used as chemical sensors, field-effect transistors and inverters, photodetectors, light-emitting diodes, lasers and logic gates. Very recently, by altering the compositions of the nanostructures during fabrication, super-lattice nanowire has been demonstrated, which can greatly increase the versatility and application of these building blocks in nanoscale electronic, photonic, and biological applications. Fe nanocolumns were used to synthesize metal-assisted protein crystallization [10]. Possible applications, including thermoelectrics, nanobarcodes, injection lasers and one-dimensional waveguides, could be implemented through these super-lattice nanostructure building blocks. One very important issue associated with these studies is how to assemble one-dimensional nanostructures in an effective and controllable way. GLAD produces columnar structures through the effect of shadowing

during film growth, while the substrate rotation controls the shape of the columns.

space of carbon nanotubes by magnetron DC and RF sputtering.

Nanowires, planar nanometric thin films and nanocolumns of Fe/MgO/Fe were synthesized using magnetron DC/RF sputtering, AXXIS sputtering tool from Kurt J. Lesker Company. Fe target of purity 99.9% and MgO of purity 99.95% were sputtered using high-purity Ar. Nanowires were synthesized by magnetron DC and RF sputtering in the interior cylindrical

Thermal chemical vapor deposition method (TCVD) was used to grow vertically aligned

exposing silica structures to a mixture of ferrocene and xylene at 770°C for 600 s. In TCVD, the furnace is pumped down to about 200 mTorr in an argon bleed, and then, the temperature is raised to 770°C. The solution of ferrocene dissolved in xylene of concentration about 0.01 g/ ml and was preheated in a bubbler to 175°C and then passed through the tube furnace. The furnace is cooled down to room temperature, and tips of the CNTs were exposed to plasma to open the nanotubes for the next procedure. The open-ended CNT tips were filled with Fe/ MgO/Fe using DC magnetron for the Fe and RF sputtering method for the insulator (MgO) at a substrate temperature of 100°C. This substrate temperature, 100°C, yielded in planar samples the highest value of coercive field compared to several other synthesis substrate tem-

substrate thus filled with Fe/MgO/Fe in this experiment [11]. TCVD involves

research object in nanomagnetism.

6 Nanowires - Synthesis, Properties and Applications

**2. Experiment**

CNTs on the SiO<sup>2</sup>

peratures [12].

Nanowires were synthesized by magnetron DC and RF sputtering in the nanometric interior cylindrical volume of carbon nanotubes at a substrate temperature of 100°C.

Nanometric thin films were epitaxially grown on the MgO (100) substrate of dimensions 5 mm × 5 mm × 0.5 mm using magnetron DC and RF sputtering at several temperatures. All substrates were degassed at 350°C in vacuum of 0.1 μTorr for 1800 s, and samples were pre- and postannealed at a preselected deposition temperature for 1800 s in vacuum. The source substrate distance was kept fixed at 30 cm, and the substrate surface normal was kept at 45° with a line connecting the center of the sample to the center of the target, while being rotated at a constant rate of 20 rpm for uniform deposition. Under these conditions, epitaxial Fe grows on MgO (100) due to a good lattice match of MgO and Fe, and weak interface interaction [13, 14] free standing Fe is formed. The deposition rate for Fe was 0.17 nm/s as calibrated by the deposition time versus thickness measurements for Fe films several hundred nm thick. In my previous research on thin films of Fe/MgO/Fe, several planar samples were synthesized at several substrate temperatures [12]. The film synthesized at 100°C has the highest saturation magnetization.

Nanocolumns of Fe/MgO/Fe were synthesized at a glancing angle of 70°, and other parameters remained the same as in the synthesis of thin film (**Figure 3**).

All sets of samples were grown using the same magnetron sputtering deposition tool. The planar films established initial growth conditions for the arrays of nanowires and nanocolumns.
