Preface

Nanowires are attracting wide scientific interest due to the unique properties associated with their one-dimensional geometry. Nanowires, with diameters reaching the quantum re‐ gime, have been the focus of research for several decades and remain at the forefront of both scientific research and developing nanotechnology applications. The benefits of 1D proper‐ ties lie in various applications for future quantum devices, nanoelectronics, nanophotonics, nanobiointerfaces, and energy harvesting. Developments in the understanding of the funda‐ mental principles of nanowire growth mechanisms and mastering functionalization provide tools to control crystal structure, morphology, and interactions at the material interface, and create characteristics that are superior to those of planar geometries. This book provides a comprehensive overview of the most important developments in the field of nanowires, from their synthesis, to their properties, to their nanowire applications.

The book consists of two parts: the first is devoted to the synthesis of nanowires and charac‐ terization, and the second investigates the properties of nanowires and their applications in future devices.

The synthesis and characterization section starts with Chapter 1 dealing with nanowires of tunneling magnetoresistance (TMR) synthesis and characterization. Nanowires of Fe/MgO/Fe encapsulated in carbon nanotubes were synthesized using glancing angle depo‐ sition. Nanowires of TMR were synthesized using magnetron DC/RF sputtering by filling Fe/MgO/Fe inside vertically grown and substrate-supported carbon nanotubes. TMR is a macroscopic quantum phenomenon that allows electrical current to flow across an insulator between two electrodes with the application of an external magnetic field. The coherent TMR effect is paramount in making spintronic devices. Changing the geometry from planar trilayer nanometric thin film to a nanowire with cylindrical geometry of nanometric diame‐ ter introduces shape anisotropy, which can play an important role in coherence.

A review of diamond nanowire (DNW) synthesis methods is given in Chapter 2. Due to su‐ perior hardness, Young's modulus, and biocompatibility, optical and fluorescence nanodia‐ mond seems to be outstanding among carbon nanomaterials. The development of DNW is known to be a significantly innovative field due to its diverse applications such as sensors, semiconductors, and electrochemical utilities. However, DNW synthesis in a reproducible way is still a challenging task. Detailed studies on DNW structures may help researchers to use them in diverse applications. In this chapter , up-to-date applications of DNW along with its synthesis, structures, and properties are presented.

Chapter 3 is dedicated to the synthesis of LiMn2O4 nanowires and their application as a bat‐ tery cathode material. Nanowires offer the following advantages: large surface-to-volume ratio, efficient electron conducting pathways, and facile strain relaxation. To enhance activi‐ ty and stability, flexible spinel nanowires were synthesized via an α-MnO2 nanowire precur‐ sor method. Ultrathin LiMn2O4 nanowires with cubic spinel structures were synthesized by using a solvothermal reaction to produce α-MnO2 nanowires followed by solid-state lithia‐ tion. The LiMn2O4 nanowires are used as a stabilizing support during electrochemical redox processes. The unique nanoporous material effectively accommodates structural transforma‐ tion during Li+ ion insertion and effectively reduces Li+ diffusion distances. Electrochemical and spectrochemical interrogation techniques have demonstrated that LiMn2O4 nanowires are promising cathode materials for lithium ion batteries as opposed to LiMn2O4 powders.

Section 2 is devoted to nanowire applications. The section starts with Chapter 4, dealing with nanowires for room-temperature mid-infrared emission. This chapter reviews InAsbased nanowire crystal structures for faceted quantum wells along with an analysis of their optical emission characteristics, which show quantum confinement and localization of the carriers on the quantum well nanostructure. This enables tuning of the emission wavelength and enhanced emission intensity up to the technologically important room-temperature op‐ eration point. The chapter details the growth development of advanced faceted multiquan‐ tum well structures within InAs nanowires using molecular beam epitaxy.

Application in future electronics is investigated in Chapter 5, which is dedicated to the ef‐ fects of the parasitic capacitances on scaling lateral nanowires beyond 7 nm node dimen‐ sions targeting 5 nm node technology. The gate-all-around silicon nanowire transistor has manifested itself as one of the most fortunate candidates for advanced node integrated cir‐ cuits. The presence of a vast metal line forms a strong parasitic capacitance. While scaling down sub-7 nm node dimensions, these capacitances strongly influence overall device per‐ formance. In this chapter, the effects of various parasitic capacitances on scaling device di‐ mensions are discussed, including performance at high-frequency operations.

The book ends with Chapter 6, dedicated to the original work for characterization of LSMO nanowire networks, prepared by electrospinning techniques, concentrating on the parame‐ ters influencing magnetoresistance and morphology. The nanowires form a nonwoven fab‐ ric-like arrangement, allowing the attachment of electric contacts for magnetoresistance measurements. Magnetization measurements reveal the soft magnetic character of the sam‐ ples. A thorough analysis of the microstructure of these nanowire networks is performed, including scanning electron microscopy and transmission electron microscopy.

> **Dr. Simas Rackauskas** Chief Researcher Kaunas University of Technology Institute of Materials Science Kaunas, Lithuania

**Section 1**

**Synthesis and Characterization**

**Synthesis and Characterization**

ty and stability, flexible spinel nanowires were synthesized via an α-MnO<sup>2</sup> nanowire precur‐ sor method. Ultrathin LiMn2O<sup>4</sup> nanowires with cubic spinel structures were synthesized by using a solvothermal reaction to produce α-MnO<sup>2</sup> nanowires followed by solid-state lithia‐ tion. The LiMn2O4 nanowires are used as a stabilizing support during electrochemical redox processes. The unique nanoporous material effectively accommodates structural transforma‐ tion during Li+ ion insertion and effectively reduces Li+ diffusion distances. Electrochemical and spectrochemical interrogation techniques have demonstrated that LiMn2O<sup>4</sup> nanowires are promising cathode materials for lithium ion batteries as opposed to LiMn2O4 powders. Section 2 is devoted to nanowire applications. The section starts with Chapter 4, dealing with nanowires for room-temperature mid-infrared emission. This chapter reviews InAsbased nanowire crystal structures for faceted quantum wells along with an analysis of their optical emission characteristics, which show quantum confinement and localization of the carriers on the quantum well nanostructure. This enables tuning of the emission wavelength and enhanced emission intensity up to the technologically important room-temperature op‐ eration point. The chapter details the growth development of advanced faceted multiquan‐

Application in future electronics is investigated in Chapter 5, which is dedicated to the ef‐ fects of the parasitic capacitances on scaling lateral nanowires beyond 7 nm node dimen‐ sions targeting 5 nm node technology. The gate-all-around silicon nanowire transistor has manifested itself as one of the most fortunate candidates for advanced node integrated cir‐ cuits. The presence of a vast metal line forms a strong parasitic capacitance. While scaling down sub-7 nm node dimensions, these capacitances strongly influence overall device per‐ formance. In this chapter, the effects of various parasitic capacitances on scaling device di‐

The book ends with Chapter 6, dedicated to the original work for characterization of LSMO nanowire networks, prepared by electrospinning techniques, concentrating on the parame‐ ters influencing magnetoresistance and morphology. The nanowires form a nonwoven fab‐ ric-like arrangement, allowing the attachment of electric contacts for magnetoresistance measurements. Magnetization measurements reveal the soft magnetic character of the sam‐ ples. A thorough analysis of the microstructure of these nanowire networks is performed,

> **Dr. Simas Rackauskas** Chief Researcher

> > Kaunas, Lithuania

Kaunas University of Technology Institute of Materials Science

tum well structures within InAs nanowires using molecular beam epitaxy.

VIII Preface

mensions are discussed, including performance at high-frequency operations.

including scanning electron microscopy and transmission electron microscopy.

**Chapter 1**

**Provisional chapter**

**Nanowires of Fe/MgO/Fe Encapsulated in Carbon**

**Nanowires of Fe/MgO/Fe Encapsulated in Carbon**

DOI: 10.5772/intechopen.79819

Nanowires of tunneling magnetoresistance (TMR) were synthesized using magnetron DC/RF sputtering by filling Fe/MgO/Fe inside vertically grown and substrate-supported carbon nanotubes. Nanocolumns of Fe/MgO/Fe TMR were synthesized using glancing angle deposition. The magnetic properties of nanowires, nanocolumns and planar nanometric thin films of Fe/MgO/Fe showed similarities including twofold magnetic symmetry. Nanowires of Fe/MgO/Fe showed improved magnetic properties, in particular its coercive field, which is 754% higher than planar thin films of Fe/MgO/Fe. A macroscopic phenomenon that can be explained only by quantum mechanics is TMR, where electrical current can flow across a nanometric thin insulator layer between two electrodes when an external magnetic field is applied parallel to the trilayer system. Coherence in the TMR effect is paramount to make spintronic devices. Nanowires possess shape anisotropy,

**Keywords:** nanowires, Fe/MgO/Fe, magnetoresistance, anisotropy, sputtering

In TMR, electrical current flows across a barrier of nanometric thin insulator layer between two ferromagnetic metal electrodes when an external magnetic field is applied parallel to the trilayer surface. TMR is one of the few examples of macroscopic quantum mechanical phenomena that have no classical explanation. TMR has a wide array of applications including magnetic random access memory for futuristic quantum computer and ultrasensitive sensors [1]. TMR is the basic building block of magnetic tunnel junctions (MTJs); specifically Fe/MgO/Fe TMR having one of the highest magnetoresistance (MR) ratio is of current interest as evidenced by

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

which can play an important role in coherence.

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79819

**Nanotubes**

**Nanotubes**

Dereje Seifu

Dereje Seifu

**Abstract**

**1. Introduction**

#### **Nanowires of Fe/MgO/Fe Encapsulated in Carbon Nanotubes Nanowires of Fe/MgO/Fe Encapsulated in Carbon Nanotubes**

DOI: 10.5772/intechopen.79819

#### Dereje Seifu Dereje Seifu

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79819

#### **Abstract**

Nanowires of tunneling magnetoresistance (TMR) were synthesized using magnetron DC/RF sputtering by filling Fe/MgO/Fe inside vertically grown and substrate-supported carbon nanotubes. Nanocolumns of Fe/MgO/Fe TMR were synthesized using glancing angle deposition. The magnetic properties of nanowires, nanocolumns and planar nanometric thin films of Fe/MgO/Fe showed similarities including twofold magnetic symmetry. Nanowires of Fe/MgO/Fe showed improved magnetic properties, in particular its coercive field, which is 754% higher than planar thin films of Fe/MgO/Fe. A macroscopic phenomenon that can be explained only by quantum mechanics is TMR, where electrical current can flow across a nanometric thin insulator layer between two electrodes when an external magnetic field is applied parallel to the trilayer system. Coherence in the TMR effect is paramount to make spintronic devices. Nanowires possess shape anisotropy, which can play an important role in coherence.

**Keywords:** nanowires, Fe/MgO/Fe, magnetoresistance, anisotropy, sputtering
