Introduction to Nanoscience and Nanotechnology Assignment

Assignment Task

Introduction

The nanoscience and nanotechnology are relatively recent developing trend and showing widespread activities in scientific research. Nanotechnology is the study of controlling the matter on an atom and molecular space. The word ‘NANO’ came from the Greek word ‘Nanos’ which means extremely small [1]. Any engineered object with at least one of its dimensions less than 100nm is called as a nanomaterial. Nanomaterials have gained much attention because they possess excellent and unique mechanical, optical, electrical, magnetic, catalytic, biological properties compared with their bulk counterparts. Top down and bottom- up methods are the two approaches used in nanotechnology and nanofabrication. Bottom- up approach is concerned with combining of various atoms and studying its various properties. The bottom-up approach is more worthwhile than the top down approach because the former has a better chance of producing the nanostructures with less defects, more homogeneous chemical composition, and better short long range ordering.

The main abettor of nanotechnology is carbon nanostructures, through which research has contributed to nanoscale. These carbon nanostructures include: fullerenes, carbon nanotubes and graphene [4]. These are all sp ² hybridized and are basically made up of carbon having examples such as fullerenes; here carbon tubes are made up by folding the graphene. Their properties are similar to graphene such as young modulus. This way the discovery of fullerenes in 1985 [5] had helped in finding the way to the discovery of carbon nanotubes [6] and later the discovery of graphene [4, 7]. Today, carbon nanostructures are a major part of another technological and scientific revolution.

A fullerene is an allotrope of carbon, whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh. The field of molecular electronics abided a revolutionizing change after the discovery of carbon fullerene (C60) in the year 1985 by Kroto and his group [8].

Graphene is an allotrope of carbon in the form of a single layer of atoms in a 2- dimensional hexagonal lattice.

Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. They can be single-walled (SWCNT) with a diameter of less than 1 nanometer (nm) or multi-walled (MWCNT), consisting of several concentrically interlinked nanotubes, with diameters reaching more than 100 nm. Their length can reach several micrometers or even millimeters.

Fig 1 : Schematic representation of Single Walled Carbon Nanotube (SWCNT) and Multi Walled Carbon Nanotube (MWCNT)

It has been found that carbon is not the only element capable of forming nanostructures. As graphene, one of the most popular 2D layered materials has some disadvantages such as toxicity, lacking of an intrinsic band gap and incompatibility with current silicon-based electronic technology. For tackling this issue, several researchers have performed significant efforts to search for other honeycomb-like structures composed of group IV elements such as Silicene (Si) [9-16], Germanene (Ge) [17,18] and Antimonene (Sb) [19,20]. Among the group-IV (Si, Ge, Sn) analogues of graphene, stanene has attracted great interest over the past few years. It exhibits fascinating properties such as Dirac-cone-shaped energy band structure, the ultra-high carrier mobility and gapless nature. Thus, it is of great importance to realize atomically thin group-IV materials with honeycomb like structures. Doped stanene monolayer could act as a potential candidate for a large variety of applications. The possibility of integrating stanene nanostructures with other materials is one of the profound interests in stanene research during the past years. As stanene based nanostructures have garnered immense interest in the last decade, we summarize here the important properties and structure of stanene based nano-materials.

Amalgamation of Stanene (Sn)

Stanene is a single-layer or 2D material and a 2D topological insulator [20-22]. It is composed of tin atoms arranged in a single, hexagonal layer, in a manner similar to graphene. Its name combines stannum (the Latin name for tin) with the suffix -ene used by graphene.

Stanene was theoretically predicted to be a 2D topological insulator in 2011[23] and its functionalized derivations as topological insulators were predicted in 2013[23]. Both may display dissipation-less superconductive currents at their edges near room temperature. The addition of fluorine atoms to the tin lattice could extend the operating temperature up to 100 °C [24]. This would make it practical for use in integrated circuits to make smaller, faster and more energy efficient computers. The synthesis and study of optical properties of stanene was first claimed by researchers at the Indian Institute of Technology Bombay [24].Stanene synthesis was reported by a second group in 2015, using molecular beam epitaxial on a substrate of bismuth telluride [24].Theoretical research suggested that Ag (111) surface may be a good substrate to grow stanene epitaxial [24]. In 2018 the growth of epitaxial 2D stanene on an Ag (111) single crystal template was reported.

Properties of Stanene

Some realistic analysis, techniques and methods with respect to stanene are revived:

Adsorption

Amirali Abbasi investigated the effects of noble metals (Ag, Au, Pd, and Pt) adsorption on the structural and electronic properties of stanene nanosheet. The calculations were calculated using density functional theory and the results suggested that the adsorption of noble metals on the hollow site is more energetically favorable than on the top and valley sites. The band structures represent that the Ag and Au adsorbed stanene monolayers exhibit metallic behavior whereas Pd and Pt adsorbed ones show semiconductor characteristics.

Jingjin Chen et al. investigated the adsorption of transition metal atoms on stanene monolayer using first principles calculations. The results show that the transition metal atoms are energetically favorable at the hollow and top sites of the stanene. So, stanene has a good adsorption capacity to foreign adsorbed atoms and also have stronger than that of phosphorene and graphene.

Amirali Abbasi studied the adsorption of phenol, hydrazine and thiophene molecules on the stanene monolayers using density functional theory. Adsorption energy results indicate that the adsorption of phenol, hydrazine and thiophene molecules on the stanene is energetically favorable.

Sensing

Jaber Jahanbin Sardroodi et al. investigated the electronic properties of the armchair (6, 6) and (8, 8) and zigzag (8, 8) stanene based nanotubes as promising sensing materials for SO₃ molecules. The results depicted that different orientation of the SO₃ molecule towards the nanotube giving rise to the different adsorption configurations. They suggested that the molecular adsorption of SO ₃ on the nanotubes is more energetically favorable than the dissociative adsorption, indicating that SO₃ tends to be molecularly adsorbed on buckled nanotube.

Jaber Jahanbin Sardroodi et al. explored the sensing capabilities and electronic structures of TiO₂ Stanene heterostructures as novel and highly efficient materials for detection of toxic SO_X molecules in the environment. The results found that the gas molecules are chemically adsorbed on the TiO₂ Stanene and the most stable sites for adsorption of SO_X molecule.

Mina Yaghoobi and her team performed density functional theory calculations to investigate the geometrical, electronic and adsorption properties of stanene based nanotubes for fulfilling the gas sensing capabilities of the nanotubes. The results presented a great potential of stanene based nanotube for application as a highly sensitive ozone gas sensor.

Kexin Ma et al. studied the structural, electronic and magnetic properties of TM (TM = Zr, Mo, Nb) absorbed stanene with the adsorption of toxic gas molecules (CO, CO ₂ , NO, NO ₂ , SO ₂ , and NH ₃ ) using the first principles calculations. The calculated results showed that the adsorption of TM induces the magnetic properties of stanene, and the adsorption of gas molecule on TM-stanene can tune the magnetic moment. The TM-stanene is more suitable for gas molecules detection compared with the pristine stanene, and the calculated results suggested Zr-stanene is potential for gas sensing. This paper is expected to provide theoretical guidance for the design of toxic gas sensors.

Doping and Defects

Ling- yan Ai et al. investigated the doping characteristics of the transition metals (Mn) and group III/V elements in the stanene monolayers. The substitutional doping of atoms is based on the electronic band structures and electron density difference plots. The codoping of Mn/Al, Mn/P, Mn/Ga and Mn/As pairs into the structure of stanene nanosheets were explored. Results suggested that all the codoped structures are energetically stable. The single Mn-doped stanene nanosheet represents metallic character, while the pair Mn/P and Mn/As doped systems exhibit semiconductor property. The results obtained in this work would be useful for the design of future nanoelectronic devices.

Bhuvaneswari et al. designed the stanene nanotube and used for the detection of trimethyl amine (TMA) and n-butyl amine (n-BA) vapors, which is investigated using first-principles study. The electronic properties of bare stanene nanotube and the adsorption properties of TMA and n-BA molecules are studied using density functional theory with non-equilibrium green’s function. The variation in the flow of electron is noticed upon adsorption of TMA and n-BA molecules in the transmission spectrum of stanene nanotube. The findings of the study suggested that the stanene nanotube molecular device can be used for the detection of trace levels of TMA and n-BA molecules present in the atmosphere.

Fadaie and his team investigated the structural, electronic and optical properties of armchair stanene nanoribbons (ASNRs) by using the first-principles calculations. The structural investigations showed some differences in bond lengths and angles which are related to the edge atoms. The electronic properties strongly depend on their ribbon width. Within each group, band gap decayed with increasing width.

Li Hongyan et al. studied efficient bandgap opening in single layer stanene via patterened Ga-As codoping. The equilibrium structures and electronic behaviors of the Ga, As and Ga-As codoped stanene nanosheets were scrutinized to fully expedite the advances in the field of semiconducting materials technology. The formation energy calculations indicated that Ga/As doped/codoped stanene monolayers are thermodynamically stable. The results suggested that Ga-As codoped stanene exhibits superior semiconducting behavior compared to the perfect system, and can be applied as a promising material for nanosensors and nanoelectronic devices.

Huaguang Li et al. performed the density functional theory computations to examine the interaction between NO molecule and Ga–As codoped stanene nanosheets. The band structure calculations indicated that the Ga–As codoped stanene acts a semiconductor material with a band gap around the Fermi level. Thus, the NO adsorption mechanism is inspected on the Ga–As codoped stanene systems. The results suggested that the NO binding to the stanene via the N center is stronger than that via the O center. The adsorption on the Ga–As codoped system was found to be more favorable in energy than that on the pure one. Therefore, Ga–As codoped stanene systems can provide most stable adsorption configurations with the adsorbed NO molecule.

Nallin Sharma and his team demonstrated Stanene-oxyboride (SnOB) nanosheet, owing to fluxional bonding of boron and its ability to sustain low energy band π-bonded population with Sn. Heterocatenation between Sn-B is impeccable and speculated to have given rise to the wide visible spectrum photoluminescence (PL).

Wenqi Xiong et al. studied the electronic structures and magnetic properties of stanene nanoribbons (SnNRs) are studied by using first-principles calculations by considering the spin-orbit coupling (SOC) effects and edge passivation. The results showed that all considered armchair SnNRs are nonmagnetic semiconductors with the gap values as a periodic oscillation function of ribbon width. The zigzag SnNRs present the antiferromagnetic ground states with opposite spin order between the two edges, and the gaps decrease as the ribbon widths increase. 

Ji Zhou et al. surveyed, the interaction of various molecules (CO, NO, CO ₂ , NO ₂ , NH ₃ and SO ₂ ) with the pristine and Ti-embedded stanene monolayers employing the first-principles calculations. The results suggested that the Ti-embedded stanene can react with gas molecules more effectively as compared to the pristine one.

Wenqi Xiong et al. proposed asymmetric hydrogenated zigzag stanene nanoribbons (ZSnNRs), named as H1– ZSnNRs–H2, considering the spin–orbit coupling effects. The H1–ZSnNRs–H2 is energetic favorably and has the room-temperature FM ground states.

Chayan Halder and his team applied first principles calculation to systematically investigate the vacancy type defects such as single vacancy and double vacancy on the structural and electronic properties of stanene monolayer. The pristine stanene sheet shows zero band gap features and when SOC is considered, a band gap of about 76.6meV is found which is very promising for the application as topological insulator.

Ishtiaque Ahmed Navid et al. computed the thermal conductivity of carbon doped armchair STNR for different types of doping patterns namely single doping, edge doping and double doping with varying doping concentration. The results declared that the thermal conductivity of carbon doped armchair STNR increases continuously with the increasing carbon doping concentration for all doping patterns.

Conclusion and future scope

Now a day, various types of molecular devices are used in Nanotechnology. Nanocomposite materials have gained much attention recently, as they are novel materials, which combine the benefits of various constituting materials. Among various nanocomposites, stanene nanostructures are being explored due to its exceptional properties like Dirac-cone-shaped energy band structure, the ultra-high carrier mobility and gapless nature, etc. Literature has also proved that the inclusion of bit of tin atoms significantly improve the properties which make stanene nanocomposites a promising new class of materials beneficial for widespread activities. In this way we have analyzed stanene nanostructures for their structural, electrical, electronics and optical properties. Stanene has great potential as a gas sensing device material in its pristine and doped forms as evidenced from the recent first-principles calculations. This room temperature topological insulator is a novel 2D material that can overcome the deficiencies of graphene with its excellent electronic properties. Stanene stands out as the new ‘gas sensing wonder’ with its exceptional gas sensing performance.

Stanene can be used in a wide variety of technical applications such as photocatalysis, energy conversion or storage and nanoelectronics community. Stanene could also show enhanced thermoelectricity, and topological superconductivity which leads to further prospective applications of stanene in spintronics and fault-tolerant quantum computation.

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