AlN Nanotubes Research Articles

Electronic sensor for sulfide dioxide based on AlN nanotubes: a computational study

Single-walled aluminum nitride nanotubes (AlNNTs) are introduced as an electronic sensor for detection of sulfur dioxide (SO₂) molecules based on density functional theory calculations. The proposed sensor benefits from several advantages including high sensitivity: HOMO-LUMO energy gap of the AlNNT is appreciably sensitive toward the presence of SO₂ so that it decreases from 4.11 eV in the pristine tube to 1.01 eV in the SO₂-adsorbed form, pristine application: this nanotube can detect the SO₂ molecule in its pristine type without manipulating its structure through doping, chemical functionalization, making defect, etc., short recovery time: the adsorption energy of SO₂ molecule is not so large to hinder the recovery of AlNNTs and therefore the sensor will possess short recovery times, and good selectivity: the tube can selectively detect the SO₂ molecule in the presence of several molecules such as H₂O, CO, NH₃, HCOH, CO₂, N₂, and H₂.

A first-principles study of H2S adsorption and dissociation on the AlN nanotube

Adsorption of hydrogen sulfide (H2S) onto AlN nanotube surface was investigated using density functional theory. It was found that the molecule is either physically adsorbed on the surface of the tube or chemically dissociated into –H or –SH fragments. The physical adsorptions are barrierless, while the dissociations have to overcome small activation energies of 2.2–3.1kcal/mol, suggesting that the tube might be a potential catalyst for dehydrogenation of the H2S molecule. All the adsorptions are electronically harmless processes and have negligible effects on the electronic properties especially on the HOMO/LUMO energy gap of the AlN nanotube.

AlN nanotube as a potential electronic sensor for nitrogen dioxide

Equilibrium geometries, stabilities, and electronic properties of nitrogen dioxide (NO2) molecule adsorption on the exterior surface of single-walled aluminum nitride nanotubes (AlNNTs) have been investigated through density functional calculations for exploring their potential usage as nanosensors. The NO2 molecule is chemisorbed on the surface of AlNNTs with adsorption energies in the range −0.10 to −0.80eV. It has been revealed that electron transport through AlNNTs is significantly increased in the presence of the NO2 molecule due to the reduced HOMO–LUMO energy gap. Based on the obtained results, it is expected that AlNNTs can be a promising candidate in gas sensor devices for detecting the NO2 molecule. The results also show that the AlNNTs benefit from fairly short recovery time and high sensitivity.

Theoretical study of CO adsorption on the surface of BN, AlN, BP and AlP nanotubes

Behavior of CO adsorption on the surface of BN, AlN, BP, and AlP nanotubes was investigated using density functional theory calculations, by means of B3LYP and B97D functionals. It was found that energetic feasibility of this process depends on several factors including LUMO energy level of tubes, electron density, and length of the surrounding bonds of adsorbing atoms plus their hybridization. These factors compete against each other to specify the adsorption behavior of the tubes. Frontier molecular orbital theory (FMO) and structural analyses show that high energy level of LUMO and short bond lengths of the tube surfaces prevent the adsorption of CO on BN nanotubes. The results suggest that the AlN nanotubes are energetically the most favorable cases toward the CO adsorption. It was found that B97D functional changes the absolute energy values of B3LYP results, but it doesn't change their relative-order of magnitudes.

Preparation of Al2O3 and AlN Nanotubes by Atomic Layer Deposition

ABSTRACTAl2O3 and AlN nanotubes were fabricated by depositing conformal thin films via atomic layer deposition (ALD) on electrospun nylon 66 (PA66) nanofiber templates. Depositions were carried out at 200°C, using trimethylaluminum (TMAl), water (H2O), and ammonia (NH3) as the aluminum, oxygen, and nitrogen precursors, respectively. Deposition rates of Al2O3 and AlN at this temperature were ∼1.05 and 0.86 Å/cycle. After the depositions, Al2O3- and AlN-coated nanofibers were calcinated at 500°C for 2 h in order to remove organic components. Nanotubes were characterized by using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). AlN nanotubes were polycrystalline as determined by high resolution TEM (HR-TEM) and selected area electron diffraction (SAED). TEM images of all the samples reported in this study indicated uniform wall thicknesses.

Computational studies on aluminum nitride and aluminum phosphide nanotubes: density functional calculations of 27Al electric field gradient tensors

Nuclear quadrupole resonance (NQR) parameters including the nuclear quadrupole coupling constant (C Q) and asymmetry parameter (η Q) at the sites of various 27Al nuclei on (6,0) zigzag and (4,4) armchair AlN and AlP nanotubes (NTs) were calculated by using the density functional theory (DFT) method to study the properties of the electronic structures of the nanotubes. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using the Gaussian 03 suite of programs. The calculated electric field gradient tensors were converted to the nuclear quadrupole resonance parameters, C Q constant, and η Q parameter. The quadrupole resonance parameters in each of the structures were divided into four layers with equivalent electric field gradient tensor eigenvalues in each layer. The results show that, in AlN and AlP nanotubes, the Al atoms at the edges of the nanotubes play dominant roles in determining the electronic behavior of the nanotubes and important roles in growth and synthesis processes of the nanotubes. Also the average values of C Q(27Al) for the AlNNT models were higher in comparison with the AlPNT models, while variations of C Q(27Al) in AlPNTs were greater in comparison with in AlNNTs. .

The H2 dissociation on the BN, AlN, BP and AlP nanotubes: a comparative study

The thermodynamic and kinetic feasibility of H(2) dissociation on the BN, AlN, BP and AlP zigzag nanotubes has been investigated theoretically by calculating the dissociation and activation energies. We determined the BN and AlP tubes to be inert toward H(2) dissociation, both thermodynamically and kinetically. The reactions are endothermic by 5.8 and 3 kcal mol(-1), exhibiting high activation energies of 38.8 and 30.6 kcal mol(-1), respectively. Our results indicated that H(2) dissociation is thermodynamically favorable on both PB and AlN nanotubes. However, in spite of the thermodynamic feasibility of H(2) dissociation on PB types, this process is kinetically unfavorable due to partly high activation energy. Generally, we concluded that among the four studied tubes, the AlN nanotube may be an appropriate model for H(2) dissociation process, from a thermodynamic and kinetic stand point. We also indicated that H(2) dissociation is not homolytic, rather it takes place via a heterolytic bond cleavage. In addition, a comparative study has been performed on the electrical and geometrical properties of the tubes. Our analysis showed that the electrical conductivity of tubes is as follows: BP>AlP>BN>AlN depending on how to combine the electron rich and electron poor atoms.

Stability and electronic properties of AlN nanotubes under the influence of external electric field

Zigzag and armchair single-walled aluminum nitride nanotubes, with diameters ranging from 5 A to 15 A, under the influence of perpendicular external electric fields, are studied using first-principle calculations. Through the analysis of the formation energy it is observed that tubes with larger diameters are energetically favored when compared to smaller ones. Also, it is shown that the electric fields up to 0.5 V/A have little influence on the stability of aluminum nitride nanotubes. Regarding the electronic structure, it was found that the larger the diameter of the tubes the greater the response to the electric field application, with a significant bandgap reduction up to 2.5 eV.

Formation of crystalline AlN nanotubes by a roll-up approach

In this study, aluminum nitride (h-AlN) nanotubes with high crystallinity and yield have been prepared by AlP and NaN3 in a stainless steel autoclave at 350°C. The samples were studied by powder X-ray diffraction pattern (XRD), transmission electron microscopy (TEM) and HRTEM in detail. The lengths of the AlN nanotubes are about 1μm with most of the tube ends are open. The AlN nanotube preferentially grow along the [001] direction. The results demonstrate that the bending and roll-up of a thin layer to form tubular nanoscrolls is a thermally driven process. One-dimensional preferential growth was explained in terms of the crystallographic feature of hexagonal AlN.

Structural, electronic and magnetic properties of the 3d transition-metal-doped AlN nanotubes

We have performed the first-principles calculations onto the structural, electronic and magnetic properties of seven 3d transition-metal (TM) impurities (V, Cr, Mn, Fe, Co, Ni and Cu) doped armchair (5,5) and zigzag (8,0) aluminum nitride nanotubes (AlNNTs). The results show that, there exists a structural distortion around 3d TM impurities with respect to the pristine AlNNTs. The magnetic moment increases for V-, Cr- and Mn-doped AlNNTs successively and reaches maximum for Fe-doped AlNNTs, and then decreases for Co-, Ni- and Cu-doped AlNNTs successively, consistent with the predicted trend of the Hund's rule to maximize the magnetic moments of the doped TM ions. However, the values of the magnetic moments are smaller than the predicted values of Hund's rule due to strong hybridization between p orbitals of near N and Al atoms of AlNNTs and d orbitals of the TM ions. Furthermore, the V- and Ni-doped (5,5) and (8,0) AlNNTs with half-metal and thus 100% spin-polarization characters seem to be good candidates for spintronic applications.

DFT study on influence of Si and Ge doping on the chemical shielding tensors in the armchair AlN nanotubes

To investigate the influence of Si and Ge doping on electrostatic structure properties, we considered an armchair model of (4, 4) aluminum nitride nanotubes (AlNNTs) of 1 nm length, consisting of 32 Al and 32 N atoms. The mouths of the nanotubes are capped by hydrogen atoms in order to saturate the dangling bonds of the boundaries, to simulate a longer tube and to decrease calculation time. The calculated chemical shielding (CS) tensors are converted to isotropic and anisotropic CS. The results show that in both models of Si- and Ge-doped AlNNTs, among all N atoms those that are directly connected to Si and Ge atoms have the smallest isotropic and anisotropic chemical shielding. The calculations are performed at the level of the density functional theory (DFT) using a Gaussian 03 package of program.

Self filling of Ni nanoparticles in amorphous AlN nanotubes and its field emission property

Unique aluminum nitride amorphous nanotubes filled with Ni nanoparticles have been successfully synthesized through the reaction of NH 3 over Ni–Al thin film at 1000 °C, which is similar to the extended vapor–liquid–solid technique. The X-ray diffraction and high-resolution transmission electron microscopic results are in good agreement with the amorphous nature of AlN nanotubes and crystallinity of Ni nanoparticles. The AlN nanotubes were having average diameter 35 nm and length ∼4 μm, whereas the Ni nanoparticles were having 5 nm in diameter. The unique structure showed excellent field emission property and high electrical conductivity ∼0.43 kmho/m at room temperature. The mechanism of good field emission property has been explained in detail.

Synthesis of an AlN Polycrystalline Bulk Layer and Nanotubes by Using NH3and Bi

A bulk layer of aluminum nitride (AIN) polycrystals was synthesized on a boron nitride crucible surface by heating Al chunks with 5 mol% of bismuth at 1273 K for 3 h under NH 3 gas flow. The fragments of the layer were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The platelet grains of AlN with a size of 0.1-1.0 μm and having preferred orientation of the c-axis perpendicular to the layer were formed at the crucible side. Nanotubes 6-15 μm long and about 20-100 nm thick grew on the gas phase side of the layer.

A DFT study of the nuclear magnetic response of the zigzag AlN–BN and BN–AlN nanotube junctions

The chemical shielding (CS) tensors of 15N, 27Al and 11B nuclei are calculated for the first time. The calculations were done on zigzag single-walled models of aluminum nitride–boron nitride (AlN–BN) and boron nitride–aluminum nitride (BN–AlN) nanotube (NT) junctions using B3LYP method and Gaussian 03 program. The computed CS tensors are converted to isotropic (ICS) and anisotropic chemical shielding (ACS). Our calculations show that there are significant changes in the NMR values for the N atoms as compared to such values for the Al and B atoms within AlN–BN and BN–AlN nanotubes.

Potential of AlN Nanostructures as Hydrogen Storage Materials

The capability of AlN nanostructures (nanocages, nanocones, nanotubes, and nanowires) to store hydrogen has been studied using gradient-corrected density functional theory. In contrast to bulk AlN, which has the wurtzite structure and four-fold coordination, the Al sites in AlN nanostructures are unsaturated and have two- and three-fold coordination. Each Al atom is capable of binding one H(2) molecule in quasi-molecular form, leading to 4.7 wt % hydrogen, irrespective of the topology of the nanostructures. With the exception of AlN nanotubes, energetics does not support the adsorption of additional hydrogen. The binding energies of hydrogen to these unsaturated metal sites lie in the range of 0.1-0.2 eV/H(2) and are ideal for applications under ambient thermodynamic conditions. Furthermore, these materials do not suffer from the clustering problem that often plagues metal-coated carbon nanostructures.

Elastic moduli of faceted aluminum nitride nanotubes measured by contact resonanceatomic force microscopy

A new methodology for determining the radial elastic modulus of a one-dimensionalnanostructure laid on a substrate has been developed. The methodology consists of thecombination of contact resonance atomic force microscopy (AFM) with finite elementanalysis, and we illustrate it for the case of faceted AlN nanotubes with triangularcross-sections. By making precision measurements of the resonance frequencies of the AFMcantilever-probe first in air and then in contact with the AlN nanotubes, we determine thecontact stiffness at different locations on the nanotubes, i.e. on edges, inner surfaces,and outer facets. From the contact stiffness we have extracted the indentationmodulus and found that this modulus depends strongly on the apex angle of thenanotube, varying from 250 to 400 GPa for indentation on the edges of the nanotubesinvestigated.

Density Functional Calculations of 27Al, 11B,and 14N and NQR Parameters in the (6, 0) BN_AlN Nanotube Junction

Density Functional Calculations of 27Al, 11B,and 14N and NQR Parameters in the (6, 0) BN_AlN Nanotube Junction

Ab initio study of confinement and surface effects in hexagonal AlN nanotubes

Abstract Thickness dependence of electronic and optical properties of AlN nanotubes is studied using density functional theory. It is found that the surface atoms induce their electronic states near the upper valence band edge as well as the lower conduction band edge. Moreover, the absorption spectrum of AlN nanotubes is shown to be dependent on the ratio of surface to bulk atoms. The effect of piezoelectric field on the optical properties of AlN nanotubes is also computed. We showed that in addition to the shifts towards higher energies, as it is usual in bulk AlN, one can also obtain shifts towards lower energies according to frequencies.

Thickness-dependent electronic and optical properties of faceted hexagonal aluminum nitride nanotubes

Electronic and optical properties of aluminum nitride nanotubes are studied in the framework of density-functional theory. It is found that the surface atoms attribute their electronic states near the upper valence band edge as well as the lower conduction band edge as defect states. Moreover, the absorption spectrum of a AlN nanotube is shown to be correlated with the ratios of the surface atoms to the bulk atoms. As tube thickness increases, a AlN tube is observed to have an increased tendency to show an optical absorption of bulk wurtzite AlN. Therefore, we predict that for realistic AlN nanotubes with large thicknesses (30–80 nm), the absorption spectra are most probably originating from the electronic states arising from the bulk portion.

First-principles calculation of electronic polarization of III-V nanotubes

A first-principles study of the electronic polarization of BN and AlN nanotubes and their graphitic sheets under an external electric field has been performed. We found that the polarization per atom of zigzag nanotubes increases with decreasing diameter while that of armchair nanotubes decreases. The variation of the polarization is related to the exterior angle of the bonds around the B or Al atoms rather than that around the N atoms. The increase in the polarization of the zigzag nanotubes with decreasing diameter is caused by the large variation of the exterior angle when they are wrapped into the tubular form. On the other hand, the decrease in the bond length results in the weak polarization of thin armchair nanotubes.