Edge Passivation Research Articles

Investigation of transport in edge passivated armchair silicene nanoribbon field effect transistor by ab-initio based Wannierised tight binding

In this work, comparative analysis of hydrogen(H), hydroxyl (OH), fluorine (F) and chlorine (Cl) edge passivated silicene nanoribbon (SiNR) field effect transistors (FETs) having nanoribbon width of 7 dimers along the armchair direction has been carried out. The ab-initio tight binding simulations of SiNR with different edge passivation uses the multi-scale approach which consists of density functional theory , Wannier function based tight binding and the non-equilibrium Green's Function formalism. It has been found that, the band gap of hydrogen passivated SiNR is comparatively larger than the other edge passivated SiNRs. To choose the optimum number of Wannier functions for tight binding approximations, the contribution of orbitals has also been analyzed. It has been found that, in transport characteristics of X-edge passivated SiNR FETs (X is H, F, Cl and OH), the H-edge passivated SiNR FET shows improved transfer characteristics in comparison to OH, Cl and F–edge passivated SiNR FETs. • Performance analysis of various edge passivated Silicene armchair nanoribbon. • Bandgap of H-passivated SiNR is higher than OH, Cl and F–edge passivated SiNR. • Use of projected density of states to choose the optimum number of Wannier function. • Higher I ON / I OFF in case of H-passivated SiNR FET in comparison other–edge passivated SiNR FET. • Performance of H-passivated SiNR FET is superior among other–edge passivated SiNR FET.

Increasing stability of MoS2 nanoribbons by edge engineering

The effect of edge passivation with non-metallic atoms was evaluated on some structural and electronic properties of MoS2 nanoribbons. It was observed that at Na = 12 and above, the band gap is less oscillating and converges to 0.58 eV. By reducing the dimensionality, the band gap value changed dramatically. We found that d orbital of Mo atom greatly affects the density of states. All passivation processes were performed with H and X atoms, where X is a non-metallic atom. The hybridization of p and s orbitals of X and Mo atoms plays an important role in changing the electronic properties of AMoS2NR. It was found that after passivation the largest band gap change is related to the most stable structure. Our studies suggest that the band gap of AMoS2NR-H-X depends on two factors: the nanoribbon width and the hybridization of Mo-X orbitals.

Detection of DNA Bases via Field Effect Transistor of Graphene Nanoribbon With a Nanopore: Semi-Empirical Modeling.

DNA sequencing techniques are critical in order to investigate genes' functions. Obtaining fast, accurate, and affordable DNA bases detection makes it possible to acquire personalized medicine. In this article, a semi-empirical technique is used to calculate the electron transport characteristics of the developed z-shaped graphene device to detect the DNA bases. The z-shaped transistor consists of a pair of zigzag graphene nanoribbon (ZGNR) connected through an armchair graphene nanoribbon (AGNR) channel with a nanopore where the DNA nucleobases are positioned. Non-equilibrium Green's function (NEGF) integrated with semi-empirical methodologies are employed to analyze the different electronic transport characteristics. The semi-empirical approach applied is an extension of the extended Hückel (EH) method integrated with self-consistent (SC) Hartree potential. By employing the NEGF+SC-EH, it is proved that each one of the four DNA nucleobases positioned within the nanopore, with the hydrogen passivated edge carbon atoms, results in a unique electrical signature. Both electrical current signal and transmission spectrum measurements of DNA nucleobases inside the device's pore are studied for the different bases with modification of their orientation and lateral translation. Moreover, the electronic noise effect of various factors is studied. The sensor sensitivity is improved by using nitrogen instead of hydrogen to passivate the nanopore and by adding a dual gate to surround the central semiconducting channel of the z-shaped graphene nanoribbon.

Thermoelectric properties study on the BN nanoribbons via BoltzTrap first-principles

Thermoelectric materials have attracted the attention of scientists because they directly convert waste heat of electric energy into valuable electrical energy. In recent years, the boron nitride structure has attracted much attention due to its thermoelectric properties and environmental friendliness. In this paper, the thermoelectric properties of boron nitride nanoribbons were simulated and analyzed, discovering that the figure-of-merit (ZT) value of armchair boron nitride nanoribbons is much better than that of zigzag boron nitride nanoribbons. Subsequently, we discuss the bandwidth effects and edge chirality on two important thermoelectric properties, Seebeck coefficient and ZT. Although edge passivation has been carried out, different edge chiralities still have a significant impact on carrier transport. The development of boron nitride-based materials will clarify their potential for developing high performance next generation thermoelectric devices.

Structural & electronic properties of zigzag silicene nanoribbons with symmetric/asymmetric edge passivations via fluorine and hydrogen

The intriguing properties of silicene nanoribbons indicate potential applications in nanoelectronic devices. The first-principles calculation based on density functional theory has been performed to investigate the structural, electronic and magnetic properties of asymmetric (sp3-sp2) and symmetric (sp3-sp3) edge functionalized zigzag silicene nanoribbons (ZSiNR). The structural analysis reveals that fully fluorinated ZSiNR for both asymmetric and symmetric edge functionalized ZSiNRs are energetically more stable irrespective of ribbon width. For selective structures, the magnetic ground state is found to be robust against thermal excitations at room temperature (25 meV) indicating their potential for practical applications. Moreover, bipolar magnetic semiconductor and half-metallic behavior have been observed in spin-based band structure calculations. Further, the spin-dependent transport properties of ZSiNR have been performed using the two-terminal device model which produces negative differential resistance (NDR) behavior due to spin-down current. This investigation reveals the immense capabilities of fluorine symmetric and asymmetric termination to modulate the electronic and spintronic properties of ZSiNR. Thus, the present work can pave the way for futuristic electronics and spintronics nanodevices.

Effect of single-hydrogen-induced out-of-plane passivation on plasmon excitation in nanostructured graphene

We investigate the effect of excess hydrogen adsorption on plasmon excitation in nanostructured graphene with in-plane (IP) and out-of-plane (OP) hydrogen passivation. On the basis of the results for the considered geometric structures of (hexagonal, triangular, and rectangular) nanographene, we observe that OP passivation even with a single hydrogen atom can have an obvious impact on plasmon excitation. The plasmon excitation intensity in the high energy region (~5.0 eV) is greatly weakened after hydrogen adsorption in both edge and center OP passivation, and peak splitting occurs in hexagonal and rectangular nanographene. Analysis of the induced charge density distribution at the corresponding plasmon peaks shows that OP passivation, caused by a single hydrogen atom, will also greatly affect the distribution of hot carriers and plasmon-induced electric near-field. Additionally, we note that this phenomenon is still observable for bulk plasmon even for hexagonal nanographene with a size of 2.0 nm.

Tunable Electronic Properties of Lateral Monolayer Transition Metal Dichalcogenide Superlattice Nanoribbons.

The structural stability and structural and electronic properties of lateral monolayer transition metal chalcogenide superlattice zigzag and armchair nanoribbons have been studied by employing a first-principles method based on the density functional theory. The main focus is to study the effects of varying the width and periodicity of nanoribbon, varying cationic and anionic elements of superlattice parent compounds, biaxial strain, and nanoribbon edge passivation with different elements. The band gap opens up when the (MoS2)3/(WS2)3 and (MoS2)3/(MoTe2)3 armchair nanoribbons are passivated by H, S and O atoms. The H and O co-passivated (MoS2)3/(WS2)3 armchair nanoribbon exhibits higher energy band gap. The band gap with the edge S vacancy connecting to the W atom is much smaller than the S vacancy connecting to the Mo atom. Small band gaps are obtained for both edge and inside Mo vacancies. There is a clear difference in the band gap states between inside and edge Mo vacancies for symmetric nanoribbon structure, while there is only a slight difference for asymmetric structure. The electronic orbitals of atoms around Mo vacancy play an important role in determining the valence band maximum, conduction band minimum, and impurity level in the band gap.

Stability, edge passivation effect, electronic and transport properties of POPGraphene nanoribbons.

POPGraphene is a theoretically predicted 2D carbon allotrope which presents a unit cell with 5-8-5 carbon rings. It presents metallic behavior and has a low diffusion energy barrier, which suggests applications as an anode material in batteries. Motivated by the fact that nanoribbons present different properties to their 2D counterparts, in this work two kinds of POPGraphene nanoribbons were proposed, with (POPGNRH) and without (POPGNR) hydrogen edge passivation, and their electronic and transport properties were investigated, in order to characterize them and verify the influence of hydrogen edge passivation. Density functional theory was employed for structure optimization and combined with the Non-Equilibrium Green's Function to obtain the electronic transport properties. We predict that both nanoribbons are stable and can be obtained experimentally. Furthermore, hydrogen passivation reduces the bands around the Fermi level and shift them toward the region of negative energies, which can be seen from the presence of NDR in the transport properties of the hydrogenated device. The electronic transport properties suggest that POPGNR shows Field effect transistor behavior in the analyzed range and POPGNRH shows the same behavior, but in the range of -0.70 V to 0.70 V. Also, due to the presence of NDR, POPGNRH presents Resonant Tunneling Diode behavior in the range of ±0.70 V to ±1.00 V. Therefore, the results suggest applications for both nanoribbons in the field of molecular electronics.

First-Principle Analysis of Transition Metal Edge-Passivated Armchair Graphene Nanoribbons for Nanoscale Interconnects

In this article, the importance of edge-passivation with transition metals (TM) in armchair graphene nanoribbons (AGNRs) is described for interconnect applications. The electronic and transport properties of TM edge-passivated AGNRs structure is found to be exceptional in comparison to hydrogen edge-passivated AGNRs. Detailed analysis of binding energy, E- k diagram, density of states (DOS), transmission spectrum, current-voltage characteristics and number of conduction channels of TM edge-passivated AGNRs configuration has been performed using density functional theory and non-equilibrium Green function technique. The significant interconnect performance metrics such as delay, energy-delay-product (EDP) have also been evaluated to justify the importance of projected work. The TMs considered in this work are Palladium (Pd), Platinum (Pt), Rhodium (Rh) and Ruthenium (Ru). It is observed that both-side edge-passivation provides better results as compared to single-side. Ru is the potential TM that provides higher currents among all when used in both-edge passivated AGNRs. Ru-AGNR-Ru shows a 10.6x lesser delay and 9.2x lesser EDP as compared to H-AGNR-H interconnects. Therefore, taking all the results into account, both edge Ru-passivated AGNRs i.e., Ru-AGNR-Ru, with the most stable structure in both side TM edge passivation, proves to be the best contender for future interconnect applications.

The effect of edge passivation with different atoms on ZrSe2 nanoribbons

In recent years, several two-dimensional (2D) materials with semiconducting electronic properties have been introduced. The ZrSe2 (Zirconium diselenide) is one of the best materials to replace the silicon in nanoelectronics due to its proper bandgap. In this research, we study the electronic properties of the armchair and zigzag ZrSe2 nanoribbons (AZSNRs and ZZSNRs). Moreover, we have investigated the effect of edge passivation of two 3AZSNR and 3ZZSNR (the ribbon width is 3) structures with hydrogen (H) and oxygen (O) atoms and also both of them (H/O) concurrently. By calculating the cohesive energy of all structures, we deduce that all zigzag and armchair structures with different edge passivations are stable and energy favorable. Also the edge passivation with H–O atoms can change the electronic properties of 3ZZSNR structure significantly, and the structure behavior changes from semiconductor to metallic. In the case of the armchair structures, the edge passivated structure with O atoms (3AZSNR-O) is the most stable and feasible to fabricate in nanoscale experiments. These results show that the ZrSe2 nanoribbons with different edge passivations have potential applications in nanoelectronics.

Effect of pore-size disorder on the electronic properties of semiconducting graphene nanomeshes

Graphene nanomeshes (GNMs) are novel materials that recently raised a lot of interest. They are fabricated by forming a lattice of pores in graphene. Depending on the pore size and pore lattice constant, GNMs can be either semimetallic or semiconducting with a gap large enough (∼ 0.5 eV) to be considered for transistor applications. The fabrication process is bound to produce some structural disorder due to variations in pore size. Recent electronic transport measurements in GNM devices (ACS Appl. Mater. Interfaces 10, 10 362, 2018) show a degradation of their bandgap in devices having pore-size disorder. It is therefore important to understand the effect of such variability on the electronic properties of semiconducting GNMs. In this work we use the density functional-based tight binding formalism to calculate the electronic properties of GNM structures with different pore sizes, pore densities, and with hydrogen and oxygen pore edge passivations. We find that structural disorder reduces the electronic gap and the carrier group velocity, which may interpret recent transport measurements in GNM devices. Furthermore, the trend of the bandgap with structural disorder is not significantly affected by the change in pore edge passivation. Our results show that even with structural disorder, GNMs are still attractive from a transistor device perspective.

Stabilization of metallic phases through formation of metallic/semiconducting lateral heterostructures.

In this study, we develop a new approach for stabilization of metallic phases of monolayer MoS2 through the formation of lateral heterostructures composed of semiconducting/metallic MoS2. The structure of metallic (a mixture of T and T') and semiconducting (2H) phases was unambiguously characterized by Raman spectroscopy, x-ray photoelectron spectroscopy, photoluminescence imaging, and transmission electron microscope observations. The amount of NaCl, reaction temperature, reaction time, and locations of substrates are essential for controlling the percentage of metallic/semiconducting phases in lateral heterostructures; loading a large amount of NaCl at low temperatures with short reaction times prefers metallic phases. The existence of the semiconducting phase in MoS2 lateral heterostructures significantly enhances the stability of the metallic phases through passivation of reactive edges. The same approach can be applied to other transition metal dichalcogenides (TMDs), such as WS2, leading to boosting of basic research and application of TMDs in metallic phases.

Edge passivation control of graphene nanoribbons for robust pure spin current generation with photogalvanic effect

Photogalvanic effect has been demonstrated to induce pure spin current in several spin polarized systems, but limited to specific photon energy or specific polarization/helicity angles of the incident light in any of the reported systems. The requirement of such a precise tuning to the specific photon energy or polarization/helicity angles makes it extremely difficult to achieve pure spin current practically. In this work, we propose a realization scheme with zigzag-edged graphene nanoribbons (ZGNRs) by edge passivation control. In detail, we divide a ZGNR into two halves, with one half monohydrogenated at the upper edge and dihydrogenerated at the lower edge, while the other half hydrogenated oppositely. By extensive first principles calculations, we show that pure spin current can always be generated, neither dependent of the photon energy and polarization/helicit angle, nor dependent of whether it is linearly, circularly or elliptically polarized. Such a robustness in pure spin current generation is found to originate from the inversion symmetry in the geometry structure and the spin semiconducting feature of the ZGNRs. This suggests a fantastic scheme for practically generating pure spin current with photogalvanic effect in graphene and will be of great significance in spintronics.

Tuning electronic transport properties of wide antimonene nanoribbon via edge hydrogenation and oxidation

In this paper, we study the electronic structures and electronic transport properties of wide buckled and puckered antimonene nanoribbions (SbNRs) via edge hydrogenation and oxidation by using a first principle method. The calculated results show that the edge passivations play an important role in the band structures of wide buckled and puckered SbNRs. The current-voltage characteristics of buckled and puckered SbNRs consistent with their band structures. The currents of buckled and puckered SbNR devices via edge hydrogenation are nearly zero at low bias region, but the edge oxidation can enlarge the device’s conductance obviously. More importantly, the tunable negative differential resistance behavior can be found in the buckled and puckered SbNR devices via edge oxidation. Our researches are of great significance for the subsequent application of SbNR devices.

Adsorption of single alkali-metal atoms (Li, Na, K) over the edge-passivated zigzag blue phosphorene nanoribbons

In the wake of blue phosphorene’s theoretical prediction and experimental synthesis, it has emerged as an excellent candidate for anode materials in alkali-metal-ion batteries due to its outstanding electrochemical performance. In the work, we have addressed the impact of edge passivation by both hydrogen (H) and oxygen (O) atoms on single adsorption of different alkali-metal atoms (Li, Na, K) over zigzag blue phosphorene nanoribbons (ZBPNRs) using first-principles calculations. Our results unravel that in the presence of edge H-passivation, the nanoribbon binds alkali-metal atoms inferior to the pristine blue phosphorene with binding energies varying from −1.53 to −1.90eV. A complete suppression of binding even occurs at the passivated edge. By contrast, the binding of adatoms is substantially enhanced by passivating the edge of the nanoribbon with O atom. The enhancement in binding not only appears at the edge but also extends across the entire nanoribbon under study. More importantly, the edge of O-passivation binds alkali-metal atoms most strongly amongst all sites, with adsorption energies between −3.93 and −4.83eV. These observations show that the edge O-passivation is highly important to make the adsorption of alkali-metal atoms over ZBPNRs more stable thermodynamically, which can be used to further tailor the nanoribbon’s electronic and magnetic properties. Overall, strengthening of the binding of these alkali-metal atoms to the ZBPNRs of edge O-passivation has clear technological implications for the design and development of electrochemical energy storage devices.

Negative differential resistance effect in different structures of armchair graphene nanoribbon

Graphene is a one-atom-thick stable covalently bonded carbon layer ordered in a honeycomb lattice. Single layer graphene of nanoscale width (including a few numbers of atoms across the width) is known as Graphene Nanoribbon, GNR. Armchair chirality of GNR provides appropriate value of band gap (in the range of that of common semiconductors), whereas its bandgap is tunable by only changing the width of ribbon. These two properties in addition to availability in two-dimension and very high carrier mobility made GNR a unique semiconductor substance in recent years. Therefore, in the past few years it has gained lots of attention for its interesting properties and applications such as: sensors, filters, detectors and switches. On the other hand, passivation of edges of GNR plays a fantastic role in its electrical behavior, where by implementing some special configuration for passivation Negative-Differential-Resistance (NDR) can be created. Graphene-based NDR behavior creates a great potential for providing some new devices in electronics. This work is focused on armchair graphene nanoribbons (AGNR) for its semiconducting behavior, where the edges of ribbon have significant effects on the current-voltage characteristic of the device. We report a theoretical investigation and numerical simulation of the effect of passivating the edges on the carrier transport in AGNRs. The number of carbon atoms across the ribbon width is an important parameter that we selected ten atoms to have a suitable size for simulation and appropriate band gap energy as a semiconductor material. Calculations are done based on density functional theory (DFT) and using Green's function of atomic structure of the device. Four types of edge terminations as: H-edged-AGNR, O-edged-AGNR, homo H-O-edged-AGNR and hetero H-O-edged-AGNR terminations are investigated in detail. It is shown that the edge termination of graphene nanoribbons by a special arrangement of both hydrogen and oxygen atoms causes NDR behavior which can have interesting applications in nanoelectronics and nanosensors. In addition, the oxygen atoms edge termination demonstrates NDR behavior, while such a behavior is not observed by only hydrogen atoms edge termination.

Sculpting Artificial Edges in Monolayer MoS2 for Controlled Formation of Surface-Enhanced Raman Hotspots.

Hotspot engineering has the potential to transform the field of surface-enhanced Raman spectroscopy (SERS) by enabling ultrasensitive and reproducible detection of analytes. However, the ability to controllably generate SERS hotspots, with desired location and geometry, over large-area substrates, has remained elusive. In this study, we sculpt artificial edges in monolayer molybdenum disulfide (MoS2) by low-power focused laser-cutting. We find that when gold nanoparticles (AuNPs) are deposited on MoS2 by drop-casting, the AuNPs tend to accumulate predominantly along the artificial edges. First-principles density functional theory (DFT) calculations indicate strong binding of AuNPs with the artificial edges due to dangling bonds that are ubiquitous on the unpassivated (laser-cut) edges. The dense accumulation of AuNPs along the artificial edges intensifies plasmonic effects in these regions, creating hotspots exclusively along the artificial edges. DFT further indicates that adsorption of AuNPs along the artificial edges prompts a transition from semiconducting to metallic behavior, which can further intensify the plasmonic effect along the artificial edges. These effects are observed exclusively for the sculpted (i.e., cut) edges and not observed for the MoS2 surface (away from the cut edges) or along the natural (passivated) edges of the MoS2 sheet. To demonstrate the practical utility of this concept, we use our substrate to detect Rhodamine B (RhB) with a large SERS enhancement (∼104) at the hotspots for RhB concentrations as low as ∼10-10 M. The single-step laser-etching process reported here can be used to controllably generate arrays of SERS hotspots. As such, this concept offers several advantages over previously reported SERS substrates that rely on electrochemical deposition, e-beam lithography, nanoimprinting, or photolithography. Whereas we have focused our study on MoS2, this concept could, in principle, be extended to a variety of 2D material platforms.

Influence of edge passivation on the transport properties of the zigzag phosphorene nanoribbons

By using first-principles calculation based on density functional theory and non-equilibrium Green's function method, we investigate the transport properties of zigzag phosphorene nanoribbons (ZPNRs). The edges of the ZPNRs can be passivated in three ways named W1, W2, W3. These calculated results show that the electronic transport properties of the ZPNRs can be seriously influenced by the edge passivation ways, and the transport is determined by both the two edges and the interaction between them. Moreover, we find the width of the ZPNR can switch on or switch off the transport channel of the W3-type ZPNR. Furthermore, we present the transmission spectra, the band structures of both left and right electrodes, the molecular energy levels, and transmission eigenstates of the H-S-passivated W3-type ZPNRs to uncover the transport mechanism. This study provides a theoretical support for designing the related nanodevices by changing the passivation ways, which is an effective route for tuning the electronic structures and the transport properties of the phosphorene nanoribbons.

Influence of edge functionalization on electronic and optical properties of armchair phosphorene nanoribbons: a first-principles study

In this work, we present a systematic first-principles density-functional theory based study of geometry, electronic structure, and optical properties of armchair phosphorene nanoribbons (APNRs), with the aim of understanding the influence of edge passivation. Ribbons of width ranging from 0.33 nm to 3.8 nm were considered, with their edges functionalized with the groups H, OH, F, Cl, S, and Se. The geometries of various APNRs were optimized, and the stability was checked by calculating their formation energies. Using the relaxed geometries, calculations of their band structure and optical properties were performed. Pristine APNRs, as expected, exhibit significant edge reconstruction, rendering them indirect band gap semiconductors, except for one width (N = 5, where N is the width parameter) for which a direct band gap is observed. The edge passivated APNRs are found to be direct band gap semiconductors, with the band gap at the Γ-point, for all the functional groups considered in this work. To obtain accurate estimates of band gaps, calculations were also performed using HSE06 hybrid functional for several APNRs. Our calculations reveal that functional groups have significant influence on the band gaps and optical properties of narrower APNRs. For wider passivated ribbons, with the increasing ribbon widths, the gaps converge to almost the same value, irrespective of the group. We also performed calculations including the spin–orbit coupling (SOC) for hydrogen passivated APNRs with N = 5 and 11. We found that SOC has no significant influence on the band structure of the studied APNRs. However, for the broader APNR, a lowering of peak intensities was observed in the optical absorption spectrum beyond 5 eV.

Orientation and edge passivation modulated magnetism in phosphorene nanoribbons

We have investigated the magnetic properties of phosphorene nanoribbons (PNRs) using the first-principles calculations within density functional theory. Our results suggest that the magnetism can be modulated by fabrication of nanoribbons with certain orientation in PNRs. The stable magnetic ground states were found in the O-terminated PNRs with (0, 1), (1, 1), (1, 2), (3, 1) edges. The (1, 1) and (1, 2) edges prefer the intra-edge ferromagnetic (FM) and inter-edge antiferromagnetic (AFM) order, but the (0, 1) and (3, 1) edges are stabilized as intra- and inter-edge AFM order. Moreover, the magnetism arising from the edge states is highly sensitive to the terminating functionalized atoms. The H-termination suppresses the magnetization of the edges due to the formation of saturated bonds with the edge P atoms.