GaN Nanotubes Research Articles

GaN Haeckelite Single-Layered Nanostructures: Monolayer and Nanotubes.

Nowadays, III-V semiconductors are interesting candidate materials for the tailoring of two dimensional (2D) graphene-like structures. These new 2D materials have attracted profound interest opening the possibility to find semiconductor materials with unexplored properties. First-principles density functional theory calculations are performed in order to investigate the electronic properties of GaN planar and nanotube morphologies based on Haeckelite structures (containing octagonal and square membered rings). Optimized geometries, band-structures, phonon dispersion, binding energies, transmission electron microscopy images simulations, x-ray diffraction patterns, charge densities, and electronic band gaps are calculated. We demonstrated that GaN Haeckelite structures are stable exhibiting a semiconducting behavior with an indirect band gap. Furthermore, it was found that GaN Haeckelite nanotubes are semiconductor with a band gap nature (direct or indirect) that depends of the nanotube´s chirality and diameter. In addition, it was demonstrated that surface passivation and the interaction with hydrazine, water, ammonia, and carbon monoxide molecules can change the band-gap nature. Our results are compared with the corresponding GaN hexagonal honeycomb structures.

Annular-Shaped Emission from Gallium Nitride Nanotube Lasers

Annular-shaped lasing emission is demonstrated from gallium nitride nanotubes fabricated using a two-step top-down technique. By optically pumping, we observe a clear threshold of 1055 kW/cm2, a narrow spectral linewidth of 0.19 nm, and guided emission from the nanotubes. Lasing is also demonstrated in a liquid environment, with an approximate doubling in threshold observed. The nanotube lasers could be of interest for optical nanofluidic applications or applications benefiting from a hollow beam shape. More generally, the results indicate that cross-sectional shape control can be employed to manipulate the properties of nanolasers.

Structure and electronic properties of GaN tubelike clusters and single-walled GaN nanotubes

Extensive studies of the geometric structures, stabilities and electronic properties of gallium nitride (GaN)n tubelike clusters and single-walled GaN nanotubes (GaNNTs) were carried out using density-functional theory (DFT) calculations. A family of stable tubelike structures with Ga–N alternating arrangement was observed when n≥8 and their structural units (four-membered rings (4MRs) and six-membered rings (6MRs)) obey the general developing formula. The size-dependent properties of the frontier molecular orbital surfaces explain why the long and stable tubelike clusters can be obtained successfully. They also illustrate the reason why GaNNTs can be synthesized experimentally. Our results also reveal that the single-walled GaNNTs, which as semiconductors with a large bandgap, can be prepared by using the proper assembly of tubelike clusters.

Surface-Effect-Induced Optical Bandgap Shrinkage in GaN Nanotubes.

We investigate nontrivial surface effects on the optical properties of self-assembled crystalline GaN nanotubes grown on Si substrates. The excitonic emission is observed to redshift by ∼100 meV with respect to that of bulk GaN. We find that the conduction band edge is mainly dominated by surface atoms, and that a larger number of surface atoms for the tube is likely to increase the bandwidth, thus reducing the optical bandgap. The experimental findings can have important impacts in the understanding of the role of surfaces in nanostructured semiconductors with an enhanced surface/volume ratio.

Elastic moduli of boron nitride, aluminium nitride and gallium nitride nanotubes using second generation reactive empirical bond order potential

Purpose – The purpose of this paper is to study elastic properties of III-V nitride nanotubes (NNTs) using second generation (REBO) potential. Design/methodology/approach – In the present research paper elastic properties of BN, AlN and GaN nanotubes have been investigated, using the second generation REBO potential by Brenner and co-workers, which is a bond order potential earlier used for carbon nanostructures successfully. In the present calculation, the same form of potential is used with adjusted parameters for h-BN, h-AlN and h-GaN. In all these cases the authors have considered graphite like network and strongly polar nature of these atoms so electrostatic forces are expected to play an important role in determining elastic properties of these nanotubes. The authors generate the coordinates of nanotubes of different chirality’s and size. Each and every structure thus generated is allowed to relax till the authors obtain minima of energy. The authors then apply the requisite compressions, elongations and twists to the structures and compute the elastic moduli. Young’s Modulus, Shear Modulus and Poisson’s ratio for single-walled armchair and zigzag tubes of different chirality’s and size have been calculated. The computational results show the variation of Young’s Modulus, Poisson’s ratio and Shear Modulus for these NNTs with nanotube diameter. The results have been compared with available data, experimental as well as theoretical. Findings – The authors have calculated bond length, cohesive energy/bond, Strain energy, Young’s Modulus, Shear Modulus and Poisson’s ratio. Originality/value – To the best of the knowledge this work is the first attempt to study elastic properties of III-V NNTs using second generation REBO potential

Band Gap Analysis of Zigzag Shaped Hydrogen Passivated GaN Nanotubes

Band Gap Analysis of Zigzag Shaped Hydrogen Passivated GaN Nanotubes

Frequency Modes of Gallium Nitride Nanotubes on Graphitic Sheet and Double Walled Gallium Nitride Nanotubes as GHz Oscillator

Frequency Modes of Gallium Nitride Nanotubes on Graphitic Sheet and Double Walled Gallium Nitride Nanotubes as GHz Oscillator

Position-controlled growth of GaN nanowires and nanotubes on diamond by molecular beam epitaxy.

In this work the position-controlled growth of GaN nanowires (NWs) on diamond by means of molecular beam epitaxy is investigated. In terms of growth, diamond can be seen as a model substrate, providing information of systematic relevance also for other substrates. Thin Ti masks are structured by electron beam lithography which allows the fabrication of perfectly homogeneous GaN NW arrays with different diameters and distances. While the wurtzite NWs are found to be Ga-polar, N-polar nucleation leads to the formation of tripod structures with a zinc-blende core which can be efficiently suppressed above a substrate temperature of 870 °C. A variation of the III/V flux ratio reveals that both axial and radial growth rates are N-limited despite the globally N-rich growth conditions, which is explained by the different diffusion behavior of Ga and N atoms. Furthermore, it is shown that the hole arrangement has no effect on the selectivity but can be used to force a transition from nanowire to nanotube growth by employing a highly competitive growth regime.

On the piezoelectric potential of gallium nitride nanotubes

The piezoelectric potential of strained intrinsic gallium nitride (GaN) nanotubes (NTs) has been studied analytically and numerically. The material properties used are obtained from molecular dynamics simulations (MDSs) and found to depend on the temperature and the NT׳s wall thickness. A novel core-surface model is developed to explain the size-dependent phenomenon and also used to predict the material properties for large-scale structures, where MDSs are not feasible. The obtained results show that GaN NTs can generate a much higher piezoelectric potential than their nanowire (NW) counterparts due to distinct material and geometric properties of NTs. This observation is not only limit for the present intrinsic structures but also can be expected for the as-grown structures. The influence of material and geometric properties becomes more significant for NTs with smaller radius or wall thickness-to-radius ratio and may enhance the piezoelectric potential by up to ten times for intrinsic NTs. However, the temperature is found to have no significant influence on the improvement of the piezoelectric potential of NTs. The observed improved piezoelectric potential in GaN NTs together with some other advantages of NTs, such as more efficient surface functionalization, suggests that the GaN NT can be a better candidate for the building blocks in piezotronic nanodevices compared with the most commonly used NWs.

First-principles insights on tuning band structure and transport property of GaN nanotube

The band structure and transport properties of GaN nanotube are explored using density functional theory with substitution impurity and defect in GaN nanostructure. The band structure varies with oxygen substitution and defect in the GaN nanotube. The density of states spectrum provides the insight for the localization of charges in different energy intervals. The electron density is found to be more in nitrogen site than in gallium site across GaN nanotube. The substitution impurity has the influence over electron density along GaN nanotube. The transport properties are discussed in terms of transmission spectrum. The orbital delocalization gives rise to peak maximum in different energy intervals. The substitution effect of oxygen and defect in the structure has much impact in the transmission along the valence band and conduction band. The finding of present work gives the insight to tailor the band structure and enhance the transport property of GaN nanotube with substitution impurity and defect structure.

Electronic Structure Study of Gallium and Indium Doped (4,4) armchair Single-Walled Boron Nitride Nanotubes for Production of Solid-State Devices

The influence of Ga and In doping on the (4,4) armchair boron nitride nanotubes (BNNTs) was studied. Density functional theory calculations were performed to investigate the electronic and structural properties including bond lengths, bond angles, tip diameters, dipole moments, energy gaps, binding energies, quantum molecular descriptors, molecular electrostatic potential, NMR and NQR parameters for pristine, Ga-, and In-doped (4,4) BNNT models by using B3LYP/6-31G* level of theory. The DFT calculation was extended to predict the electronic and structural properties of the nanotube models, which are important for production of solid-state devices and other applications. The chemical reactivity of these compounds was compared using density functional-based descriptors such as global softness, global electrophilicity, electronic chemical potential, global hardness, and electronegativity. The results indicated that the electronic sites of the B and N atoms in the InB model exhibit greater changes than the GaB model with respect to the pristine model and the model is a better candidate from GaB model for production of solid-state devices.

First-Principles Study on Structural, Electronic, and Magnetic Properties of 3d Transition-Metal Nanowires Encapsulated Inside GaN Nanotubes

We have performed the first-principles calculations on the structural, electronic, and magnetic properties of 3d transition-metal nanowires (TMNW4s), Fe4, Co4, and Ni4, encapsulated inside GaN nanotubes (GaNNTs). The results show that, all three types of the TMNW4 encapsulated inside the narrower (6,6) and broader (8,8) GaNNTs are both exothermic. The spin polarization and magnetic moment of the TMNW4@(8,8) systems are larger than those of the TMNW4@(6,6) systems due to more weak restriction of the broader (8,8) GaNNT, but those of these two combined systems are smaller than those of the corresponding freestanding TMNW4. Our results reveal that either the TMNW4@(6,6) or TMNW4@(8,8) systems have high spin polarization and magnetic moment and stably exist in atmosphere for long time and thus can be expected to have potential applications in building nanodevices.

Stability and Bandgap Analysis of Fe Doped GaN Nanotubes

Stability and Bandgap Analysis of Fe Doped GaN Nanotubes

Tensile behavior of single crystalline GaN nanotube bundles: An atomistic-level study

The tensile behavior of single crystalline GaN nanotube bundles was studied using classical molecular dynamics. Stillinger–Weber potential was used to describe the atom–atom interactions. The GaN bundles consisted of several individual GaN nanotubes with {100} side planes. The simulation results show that the nanotube bundles show a brittle to ductile transition (BDT) by changing the temperatures. The fracture of GaN nanotube bundles is ruled by a thermal activated process, higher temperature will lead to the decrease of the critical stress. At high temperatures the individual nanotube in the bundles interact with each other, which induces the increase of the critical stress of bundles.

Electronic structure and magnetic properties of transition-metal (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag and Cd) doped in GaN nanotubes

We have presented calculations on the structural, electronic and magnetic properties of 4d transition-metal (TM) (TM=Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag and Cd) doped in gallium nitride nanotube (GaNNT). The calculations illustrate that there is distortion around 4d transition-metal impurities with respect to the pure GaNNTs. The magnetic moments are not consistent with the predicted value of Hund’s rule. The results show Ru doped GaNNT is non-magnetic metal; whereas Ag, and Cd doped GaNNT are ferromagnetic metal. Moreover Y, Rh, Tc and Nb doped GaNNT system are semiconductors with classic, non-magnetic narrow-band, non-magnetic gapless and magnetic gapless nature, respectively. Also the Nb doped GaNNT system have maximum magnetic moments. Our results suggest that 4d TM-doped nanotubes can be valuable in spintronics devices.

GaN tubes with coaxial non‐ and semipolar GaInN quantum wells

AbstractWe present the position‐controlled growth of GaN nanotubes with coaxial GaInN quantum wells by using ZnO nanowires grown on top of GaN pyramids as templates. High resolution scanning transmission electron microscopy allows us to perform a detailed structural analysis of individual tubes. In particular, we report about structural properties like indium incorporation, thickness, and homogeneity of quantum wells realized on nonpolar m‐plane side facets or on semipolar tips. Additionally, high resolution spatially and spectrally resolved cathodoluminescence spectroscopy performed at low temperature enables us to clearly identify the quantum well luminescence contributions for different kinds of facets on a single tube. The luminescence of the quantum wells deposited at variable temperatures shows a clear spectral shift in the cathodoluminescence signal, yielding an activation energy for the indium desorption from the m‐plane side facets of about 1.6 eV. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Doping Induced Structural Stability and Electronic Properties of GaN Nanotubes

The present paper discusses the effect of manganese doping on the structural stability and electronic band gap of chiral (2, 1), armchair (3, 3), and zigzag ((6, 0) and (10, 0)) single walled GaN nanotube by using density functional theory based Atomistix Toolkit (ATK) Virtual NanoLab (VNL). The structural stability has been analyzed in terms of minimum ground state total energy, binding, and formation energy. As an effect of Mn doping (1–4 atoms), all the GaN nanotubes taken into consideration show semiconducting to metallic transition first and after certain level of Mn doping changes its trend.

Single-crystalline GaN nanotube arrays grown on c-Al2O3 substrates using InN nanorods as templates

Single-crystalline GaN nanotube arrays were grown on c-Al2O3 substrates by metal-organic chemical vapor deposition. InN nanorods with In droplets at the top-ends were used as the templates. After growing GaN over the templates, InN nanorods were thermally removed and GaN nanotubes were obtained. In droplets were considered to be the pathways for the decomposed InN species to escape away and played an important role in the formation of GaN nanotubes. The nanotubes are well-aligned along the c-axis of the wurtzite GaN structure with good crystal quality and morphologies. X-ray diffraction and energy-dispersive X-ray spectrometer studies indicate that the products are absent of template related residues. Our method for fabricating GaN nanotubes can be applied to the formation of nanotube arrays of other materials (such as AlGaN and AlN).

Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

The electronic structure and magnetic properties of the transition-metal (TM) atoms (Sc—Zn, Pt and Au) doped zigzag GaN single-walled nanotubes (NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Co-doped GaN NTs induce the largest local moment of 4μB among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it.

Raman Spectral Mapping of III–V Nitride and Graphene Nanostructures

Among several spectroscopic imaging techniques to visualise the nanostructures, Raman spectral imaging is one of the most indispensible non-destructive tools. We discuss the limitations and the importance of each step involved in the Raman imaging in the visualization of different nanostructures and illustrated with examples. Raman spectroscopic imaging of nanostructures is demonstrated for differentiation of morphology in InN nanorods, crystallographic orientation for single square faceted GaN nanotube and layer thickness of graphene layers. The limitations of the spatial and spectral resolutions of the Raman maps are evaluated in the illustration.