AlN Nanoribbons Research Articles

Thermal transport properties of hexagonal monolayer group-III nitride nanoribbons

In this study, the thermal transport properties of hexagonal monolayer BN, AlN, and GaN nanoribbons are systematically investigated using non-equilibrium molecular dynamics simulations. Firstly, the effect of length, width, and temperature on the lattice thermal conductivities of these ribbons are explored. It is observed that increases in sample geometry lengths of simulations and decreases in temperature lead to an increase in the thermal conductivity of all three materials. Secondly, thermal rectification coefficients of ribbons are calculated by creating asymmetric thermal contacts through non-equilibrium molecular dynamics simulations. Thus, it is shown that thermal rectification factors of up to 20% can be achieved by manipulating the thermal asymmetry ratio in pristine structures without asymmetry of group-III nitride nanoribbons. These results imply that group-III nitride nanoribbons may be considered as an alternative option to control the heat flow in thermal management and thermoelectric device applications.

Electronic and Optical Properties of Zigzag BN/AlN Nanoribbons with Misfit Dislocations: First-Principles Calculations

Misfit dislocations (MDs), existing in a broad family of materials, are known to exhibit unique and remarkable properties that are an important factor in the performance of certain devices. Here we report the first-principles investigation of one-dimensional MDs in a zigzag heterojunction between BN and AlN nanoribbons (BN/AlN). Our results show that MDs enable robust stability and versatile properties. The band gaps and even the nature of the indirect/direct band gap can be tuned by altering the bond types at the interface. Specifically, the band gaps can be reduced to much smaller than those of zigzag AlN nanoribbons by regulation of MDs. Moreover, the formation of interfaces broadens the absorption and reflection ranges considerably. These findings will not only enrich our understanding of MDs, but also provide new opportunities for the manipulation of two-dimensional materials in electronic and photoelectronic applications.

First-Principle Study of Cl Functionalized Zigzag AlN Nanoribbons

We employed density functional theory (DFT)-based first-principle calculations to reveal the structural stability and electronic properties of zigzag AlN nanoribbons (ZAlNNR) functionalized with Cl. Considered structures were found to be energetically feasible. A pure metallic character has been observed for one edge Cl functionalization, whereas for rest of the others, the band gap varies from 2.2 eV to 3.9 eV. Interestingly, a transition from indirect to direct band gap has been obtained for semiconducting ribbons due to Cl functionalization. Present findings show that Cl functionalization could be useful for the band gap engineering and absolute shifting of Fermi level in ZAlNNR.

First-principles study of sensing SO2 adsorption on III–V nitride nanoribbons

The design of efficient, low dimensional sensors is an active topic of research and development. Here, we study the adsorption of SO2 molecules on the edges of III–V nitride nanoribbons to explore their sensing potentials. Zigzag nanoribbons (ZXNNR) and armchair nanoribbons (AXNNR), X = B,Al,Ga, have been investigated. It was noticed that the adsorption of SO2 is mediated via formation of chemical bonds. The calculated adsorption energy varies from -1.09 eV to -4.89 eV for ZXNNR and -0.42 eV to -4.61 eV for AXNNR which ensures the structural stability of considered configurations against thermal excitations. Moreover, for all ZXNNR, a semiconducting to metallic transition has been observed whereas the band gaps in AXNNR are subjected to the adsorption configuration. Further, the selectivity of SO2 with all considered configurations with respect to O2 and N2 is also studied. It is revealed that the selectivity of SO2 with respect to N2 is more suitable as compared to O2. The analysis of recovery time indicates an excellent reversible characteristics in BN nanoribbons irrespective of their edge geometries. GaN nanoribbons could be reversible only for zigzag edges whereas unusually long recovery time in AlN nanoribbons presents them as a disposable sensing material. Present analysis portrays a detailed comparison of zigzag and armchair III–V nanoribbons towards their potential for designing futuristic nano-sensor devices.

Adsorption of CO gas molecules on zigzag BN/AlN nanoribbons for nano sensor applications

First-principle calculations have been performed to study the sensing of CO gas in various considered configurations. The adsorption of CO on zigzag BN nanoribbon (ZBNNR) and zigzag AlN nanoribbon (ZAlNNR) was modelled in five different possibilities. The effect of CO adsorption is to reduce the band gap in both types (BN/AlN) of the nanoribbons. Interestingly, a finite magnetic moment (0.96 μB for ZBNNR and 0.69 μB for ZAlNNR) has been obtained which depends upon the adsorption configuration of CO. Half-metallicity was also observed upon selective CO adsorption on ZAlNNR irrespective of the ribbon width. Present findings suggest that CO gas molecules could be detected through adsorption on BN/AlN nanoribbons via changes in electronic and/or magnetic properties.

Generating Tunable Magnetism in AlN Nanoribbons Using Anion/Cation Vacancies:a First-Principles Prediction

Using first-principles approach, we theoretically study the effect of anion/cation vacancies on structural and electro-magnetic properties of zigzag AlN nanoribbons (ZAlNNRs). Calculations were performed using a full spin-polarized method within the density functional theory (DFT). Our findings shed light on how the edge states combined with vacancy engineering can affect electro-magnetic properties of ZAlNNRs. We found that depending on the nature and number of vacancies, ZAlNNRs can design as half-metal or semiconductor. Our results reveal a significant amount of spin magnetic moment for ZAlNNR with Al vacancies (VAl). These results may open new applications of AlN nano-materials in spintronics.

Adsorption of gas molecules on armchair AlN nanoribbons with a dangling bond defect by using density functional theory

In this paper, the adsorption of gas molecules (CO, NO, O2, CO2, and NO2) on armchair aluminum nitride nanoribbons (AAlNNRs) with a dangling bond defect has been investigated by density functional theory. For all the studied systems, the adsorption geometries, adsorption energies, charge transfer, and electronic structures are discussed. The adsorption energies of O2, NO2, and CO2 are -1.53, -2.24, and -2.88 eV, respectively, corresponding to strong chemisorption. While for CO and NO, the adsorptions are between weak chemisorption and strong physisorption. Moreover, the magnetic property of defective AAlNNR are sensitive to the adsorption of NO2. Therefore, based on the obtained results, AAlNNRs with a dangling bond defect is promising for using in gas sensor devices to detect NO2.

Adjustable localized states in perfect and single C-chain doped zigzag AlN nanoribbons

The localized feature of electronic states is often related to some interesting electronic properties in graphite-like materials. We use the first principles calculations to investigate two important localized states, that is, flat-band states and border states, in zigzag AlN nanoribbons (zAlNNRs). Our results indicate that both localized states can exist in zAlNNRs and the border states have a close relationship with electrical conductivity. It is found that the flat-band states of perfect zAlNNRs result from edge N-pz orbitals, while the border states of doped zAlNNRs are due to π/π* orbitals of C and Al/N atoms. These findings enrich our understanding on localized states in zAlNNRs, showing a potential application in functional nanodevices.

C-chain-doping induced band-state transition in armchair AlN nanoribbons (Phys. Status Solidi B 8/2016)

C-chain-doping induced band-state transition in armchair AlN nanoribbons (Phys. Status Solidi B 8/2016)

Half-metallic ferromagnetism in Mn-doped zigzag AlN nanoribbon from first-principles

Based on first-principles calculations, we investigate the effect of Mn impurity on the electronic and magnetic properties of H-terminated zigzag AlN nanoribbons (ZAlNNRs), using the band structure results obtained through the full potential linearized augmented plane wave method within the density functional theory. The calculated results show that the H-terminated ZAlNNR is semiconducting and non magnetic material with a direct band gap of about 2.78eV. Density of state analyses shows that the top of the valence band is mainly contributed by N atoms, while just beside the conduction band the whole DOS is mainly contributed by Al atoms. The main result is a transition from non-magnetic semiconducting character to half-metallic features upon doping. The Mn-doped ZAlNNR shows complete (100%) spin polarization at the Fermi level and the charge transport is totally originated from Manganese spin up electrons in the nanoribbon. These results propose potential application for the development of AlN nanoribbon-based in magneto-electronic devices.

C-chain-doping induced band-state transition in armchair AlN nanoribbons

Little is known about the band states of armchair AlN nanoribbons (aAlNNRs), so we investigated their band states of perfect and single C-chain-doped aAlNNRs by first-principles calculations. For aAlNNRs with a width N < 12, the nonedge C-chain doping can lead to the distribution of the conduction-band minimum (CBM) electrons transferring from the central part of the ribbon to the C–N–Al ring. One representative model for aAlNNRs with a width of 8 ([aAlNNR]8) was mainly studied. In contrast to a h-AlN monolayer, we find a second degenerate state (above the Fermi level) in perfect [aAlNNR]8, which stems from the Al-s py and hybridized N-s pz orbitals. However, both degenerate states are suppressed by single C-chain doping. For N ≥ 12, wherever a C-chain locates, the CBM always displays similarly delocalized characteristics. Our study can not only show that single C-chain doping can significantly modify the band states, but also can enrich the understanding of aAlNNRs.

Enhanced piezoelectricity and half-metallicity of fluorinated AlN nanosheets and nanoribbons: a first-principles study

Fluorinated AlN nanosheets present an enhanced piezoelectric performance and the corresponding nanoribbons can exhibit a half-metallic behaviour.

Electronic and optical properties of the O-terminated AlN nanoribbons: First-principles study

We perform first-principles calculations based on density functional theory to study the electronic and optical properties of the O-terminated AlN nanoribbons (AlNNR) with both zigzag and armchair edges (ZAlNNR and AAlNNR) of different widths. The results show that ZAlNNR with six zigzag chains across the ribbon width (6-ZAlNNR) presents metallic properties and AAlNNR with sixteen dimer lines across the ribbon width (16- AAlNNR) is semimetallic because of the terminated O atoms. The dielectric function of 6- and 12-ZAlNNR or 7- and 16-AAlNNR is similar independent of the nanoribbon width if they have the same edge shape, but the wider one has a weak red shift and in the visible range (1.6–3.0 eV) the systems can be seen as optically transparent materials. The peaks of the energy loss correspond to the trailing edges in the reflection spectra.

A first-principles study of a single C-chain doped AlN nanoribbons

Under the generalized gradient approximation (GGA), the structural and electronic properties are studied for both zigzag (ZAlNNRs) and armchair (AAlNNRs) AlN nanoribbons terminated with H atoms at both edges by using the first-principles projector-augmented wave (PAW) potential within the density function theory (DFT) framework. The results show that the Al–N, Al–C and Al–H bonds are ionic bonds while the C–C and C–H bonds are typical covalent bonds, and the N–C and N–H bonds have a degree covalent character. The systems of both perfect 7-ZAlNNR and perfect 7-AAlNNR with a single C-chain doped are still nonmagnetic semiconductors, and the C-chain reduces the band gap. The C-chain can change the band gap of 7-ZAlNNR from direct to indirect independent of the position of the C-chain, which is important in the practical application as light emitting devices. For NZ-ZAlNNR-C(n) with NZ=3, 5, 6, 10, the band gap decrease successively for C-chain position n from 2 to 3, 5, 6, 7 and 10, respectively. For NA-AAlNNR-C(n) of arbitrary width NA, except NA-AAlNNR-C(1) and NA-AAlNNR-C(n=NA) have a larger band gap, the band gap of the rest of the NA-AAlNNR-C(n) are about 2.0eV. Furthermore, the maximum band gap gradually decrease with the increase of the width NA. The C-chain substituting Al–N chain process is endothermic for both 7-ZAlNNR and 7-AAlNNR.

Electronic and magnetic properties of Cd-doped zigzag AlN nanoribbons from first principles

The effect of Cd impurity on the electronic structure and magnetic properties of hydrogen-terminated AlN nanoribbons with zigzag edges (ZAlNNRs) was investigate using the band structure results obtained through the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT). The exchange correlation potential was treated by the generalized gradient approximation within the Perdew scheme. The calculated results show that the H-terminated zigzag AlN nanoribbon is semiconducting and nonmagnetic material with a direct band gap of about 2.78 eV, while the Cd-doped H-terminated ZAlNNR structures show complete (100 %) spin polarization very close to the Fermi level, which will result in spin-anisotropic transport. The charge transport is totally dominated by Cd spin down electrons in the H-terminated ZAlNNR. These results suggest potential applications for the development of using the AlN nanoribbons in nanoelectronics and magnetoelectronic devices as a base.

Structural and electronic properties of a single Si chain doped zigzag AlN nanoribbon

The first-principles projector-augmented wave (PAW) potentials within the density function theory (DFT) framework have been used to determine the geometry structures and electronic properties of the zigzag edge AlN nanoribbons (ZAlNNRs) doped with a single Si chain under generalized gradient approximation (GGA). The average Al–Si, Si–Si, Al–N, Si–N, Al–H and N–H bond lengths are 2.39, 2.16, 1.83, 1.74, 1.59 and 1.03Å, respectively. Pure 7-ZAlNNR is an indirect semiconductor with a large band gap of 2.235eV, while a semiconductor to metal transformation is taken place after a single Si chain substituting for a single Al–N chain at various positions. In pure 7-ZAlNNR, the HVB and LCB are mainly attributed to the edge N and Al atoms, respectively, while in a single Si chain substituting doped 7-ZAlNNR, the HVB and LCB are mainly attributed to the Si atoms. The Al–N, Al–H and Al–Si bonds are ionic bond, the Si–Si and Si–H bonds are covalent bond, the N–H and N–Si bonds are covalent bond modified ionic bond.

Exploring electronic transport properties of AlN nanoribbon molecular device – A first-principles investigation

The novel AlN nanoribbon molecular device is investigated using density functional theory for different voltage bias. The electronic transport properties of AlN nanoribbon are discussed in terms of device density of states, electron density, transmission spectrum and transmission pathways. It is evident that increasing the bias voltage leads to transition of electrons from the valence band to the conduction band across AlN nanoribbon. The electron density is found to be more along nitrogen sites. The transmission increases with the increase in bias voltage. The transmission can be fine-tuned at different energy intervals by varying the bias potential. The transmission pathways provide the insight for transmission of electrons along AlN nanoribbon. Mostly, the transmission is observed along the top and bottom regions of AlN nanoribbon. The results of the present work will give a clear picture to improve the electronic transport property along AlN nanoribbon.

The Effects of Dangling Bonds on AlN Nanoribbons: A First-Principles Study

The effects of dangling bonds on electronic and magnetic properties for both zigzag AlN nanoribbons (ZAlNNRs) and armchair AlN nanoribbons (AAlNNRs) are studied by using first-principles calculations. Though ZAlNNRs or AAlNNRs terminated with H at both edges are nonmagnetic semiconductors, the results show that no H at the left side and no H at both edges cause magnetic metal for ZAlNNRs, but magnetic semimetal for ZAlNNRs with no H terminated at the right side, which open a way to design magnetic nanodevices based on AlNNRs. The AAlNNRs with unilateral hydrogen passivation or no H at both edges are still nonmagnetic semiconductors. ZAlNNRs with no H at the right side have a spin polarization value of 100 %, indicating these systems can be used to construct efficient spin-polarized transport devices.

Structural, electronic and magnetic properties of the Si chains doped zigzag AlN nanoribbons

The structural, electronic and magnetic properties of the zigzag Si chains substituting for zigzag Al–N chains in hydrogen terminated hexagonally AlN nanoribbon with 7 zigzag Al–N chains across the ribbon width (7-ZAlNNR) have been investigated systematically using the first-principles calculations. The longer Si–Si bond length leads to a decrease (increase) in armchair (zigzag) Al–N bond length. The pure 7-ZAlNNR is a non-magnetic indirect semiconductor with a large indirect band gap of 2.979eV. The Si chains doped 7-ZAlNNR is always metallic regardless of the Si chains doping concentrations, while the induced magnetic moment depends on the Si chains doping concentrations, increasing from 0.11μB for Si2–7-ZAlNNR to 0.45μB for pure 7-ZSiNR. The very low Si chains doping concentration makes the Si1–7-ZAlNNR a zero magnetic moment. Compared with the total DOS of the pure 7-ZAlNNR, the total DOS of the Si chains doped 7-ZAlNNR is not only broadened and shifted towards the low energy region but also transformed to metal. The magnetic moments of the Si chains doped 7-ZAlNNR are resulted from the zigzag Si chains but are not from zigzag Al–N chains because the Si–Si bond is a covalent σ bond with nonbonding π electrons while the Al–N bond is an ionic bond. Furthermore, on zigzag Si chains, the magnetic moments are mainly localized on the edge Si atoms decaying parallel (antiparallel) to the same (different) inner sub-lattices. With increasing Si chains doping concentration, both spin channels enlarge their distribution regions and thus magnetic moments.

First-principles study of a single Fe-chain doped zigzag AlN nanoribbons

The effects of a single Fe-chain on the structural, electronic and magnetic properties of the H terminated zigzag AlN nanoribbons (ZAlNNRs) have been investigated systemically by using the first-principles methods. The results show that the valence charge density decreases for N, H, Fe and Al atom successively is related to their successively decreasing electronegativity. And no charge accumulated on Al atoms implies a significant charge transfer to N, Fe and H atoms from their nearest Al atom. In addition, the AlN nanoribbons change from nonmagnetic semiconductor to magnetic conductor after doping a single Fe chain, and the spin polarization and magnetic moment change suddenly after doping a single Fe-chain.