Study of graphene device electronic properties with horizontal and vertical double vacancy defects

Abstract

Graphene device electronic properties with double vacancy (DV) defects for two cases, along the direction and perpendicular to the current pathways graphene device, were investigated by using the first principles calculations in combination with density functional theory. The bond lengths, density of states, transmission probability, and current-voltage curves are computed. For relaxed pristine graphene the bond length is around 1.43?Å. However, the bond lengths near the defects for relaxed graphene for DV case are modified to 1.40-1.49?Å. It is also observed that I???V graph is nonlinear based on the current-voltage curve of graphene device which contain DV defects. Furthermore, it has been shown that having the DV defects lead to reduce the current relative to the case of perfect graphene device. Moreover, we noted that when the voltage is increased from zero to one volt new peaks are created near Fermi level in the transmission spectrum graphs. In addition, we noted that the current for the vertical DV defect is smaller than the pristine and horizontal DV device because the number of blocked electrons current pathways in vertical DV defect is larger than the two other cases, namely the pristine and horizontal DV defect cases The obtained results can be useful for the construction of new nanoelectronic devices and may have practical applications.     

Structural and electronic properties of Ti-nanowires/C-single wall nanotubes composites by density functional theory calculations

Structural and electronic properties of composite Ti-nanowires/single wall carbon nanotubes ((6,0) and (10,0)) (SWNT) were evaluated by means of density functional theory computations. We considered the cases of monoatomic (MNW), BCC (β-NW) and HCP (α-NW) nanowires that were either inserted or deposited in/on the SWNTs. In all cases the NWs turn the cylindrical SWNTs’ shape to ellipsoid, an effect that is closely related to charge transfer from Ti toward C neighboring atoms. We found that the wires inside the SWNT appear to be more stable compared to the outside cases, while all NWs contribute with new energy states at the Fermi level, transforming the semiconducting (10,0) to a conducting composite. In addition, we found spin up–down differences in the β-NW_on case and electronic charge redistributions e.g. in α-NW_in (charge accumulation internally along the tube's axis) or in α-NW_on (superficial charge accumulation in the vicinity of the NW), accompanied by manifestation of electric dipole moment that reaches the value of 10 Debye in a-NW_on. These results may be of use in the design of new C-based nanocomposite systems suitable for applications in microelectronics, sensors and catalysis.     

Encapsulation of cellulose chain into carbon nanotubes and boron nitride nanotubes

Encapsulation of cellulose chain into carbon nanotubes and boron nitride nanotubes was investigated to find out the possibility of band gap engineering in these nanotubes. The structural stability and the electronic properties of the zigzag carbon nanotubes and boron nitride nanotubes filled with cellulose chain were studied using density functional theory. It was found that encapsulation of cellulose chain into nanotubes was an exothermic process. The metallic properties of the carbon nanotubes did not change by cellulose encapsulation. The semiconductor and insulator nanotubes filled with cellulose were shown semiconducting properties. The energy band gap of these tubes was decreased by cellulose encapsulation. The results demonstrated the ability of band gap engineering through the encapsulation of cellulose chain into carbon nanotubes and boron nitride nanotubes.     

Structural and electronic properties of C and BN nanotubes based on periodic fullerenes: A density functional theory study

The structural and electronic properties of C and BN nanotubes based on periodic fullerenes were studied using density functional theory. It was shown that these tubular structures are stable. The electronic band structures and density of states indicated that the C nanotubes based on periodic fullerenes are metals. The energy band gap was appeared by substitution of C atoms with B and N atoms. The BN nanotubes based on periodic fullerenes show semiconducting properties. Our results suggest that the nanotubes based on periodic fullerenes can be used to design of nanoelectronic devices.     

Selective adsorption of cations on single-walled carbon nanotubes: A density functional theory study

The selective adsorption of cation on single-walled carbon nanotubes (SWNTs) is systemically studied by using density functional theory calculations. It is found that the adsorption energy of cations on SWNTs depends on the concentration of cations and the diameter and the electronic structure of SWNTs. The binding strength of on each SWNT increases monotonically as the concentration of decreases, undergoing a change from endothermic to exothermic reaction. Generally speaking, the binding of on SWNTs becomes weaker as the diameter increases. In the medium-diameter region (9 < d < 11 Å), prefers to interact with metallic SWNTs (m-SWNTs) rather than semiconducting SWNTs (s-SWNTs) at the same concentration of . In the small-diameter region (d < 9 Å), the binding of is nearly independent of metallicity, but it is stronger than that of on the medium-diameter s-SWNTs. In the large-diameter region (d > 11 Å), the dependence of adsorption on the electronic structure is complicated, but the binding of is weaker than that on the medium-diameter s-SWNTs. Our results are in agreement with the experimental report that the small-diameter m- and s-SWNTs and the medium-diameter m-SWNTs are etched away by while the medium-diameter s-SWNTs and the large-diameter m- and s-SWNTs are intact.     

Strain-tunable electronic and transport properties of MoS2 nanotubes

Using density functional theory calculations, we have investigated the mechanical properties and strain effects on the electronic structure and transport properties of molybdenum disulfide （MoS2） nanotubes. At a similar diameter, an armchair nanotube has a higher Young＇s modulus and Poisson ratio than its zigzag counterpart due to the different orientations of Mo-S bond topologies. An increase in axial tensile strain leads to a progressive decrease in the band gap for both armchair and zigzag nanotubes. For armchair nanotube, however, there is a semiconductor-to-metal transition at the tensile strain of about 8%. For both armchair and zigzag nanotubes, the effective mass of a hole is uniformly larger than its electron counterpart, and is more sensitive to strain. Based on deformation potential theory, we have calculated the carrier mobilities of MoS2 nanotubes. It is found that the hole mobility is higher than its electron counterpart for armchair （6, 6） nanotube while the electron mobility is higher than its hole counterpart for zigzag （10, 0） nanotube. Our results highlight the tunable electronic properties of MoS2 nanotubes, promising for interesting applications in nanodevices, such as opto-electronics, photoluminescence, electronic switch and nanoscale strain sensor.     

真空度对纳米碳管场发射性能的影响

研究了单壁纳米碳管(SWNTs)、双壁纳米碳管(DWNTs)和多壁纳米碳管(MWNTs)在不同真空度下的场发射性能。在超高真空条件下(2.0×10-7Pa),以上三种材料均表现出良好的稳定性;而在高真空条件下(1.0×10-4Pa),三种材料的场发射稳定性有不同程度的下降。通过控制系统真空度在2.0×10-7Pa～1.3×10-3Pa范围内逐渐变化,考察了真空度对纳米碳管场发射性能的影响及其机制,提出适合于SWNTs、DWNTs和MWNTs场发射性能测试和应用的真空度下限分别为6.0×10-5Pa、1.0×10-4Pa和5.7×10-4Pa。     

氧气与水对碳纳米管纤维电子特性的影响

由于碳纳米管特殊的中空结构及高的比表面积,其对气体与液体的吸附有极大的先天优势。研究了不同环境下碳纳米管纤维对氧气与水分的吸附与解吸过程中其电子特性变化。电弧实验表明,碳纳米管纤维在较低电压(≤30V)与相应电流下(2A)可以产生强烈电弧,同时局部产生高温;高温易使纤维对氧气产生解吸,从而引起纤维电阻增大。室温条件下碳纳米管纤维对空气中水分子的吸附较对氧分子要强,水分子吸附增加了其表面羟基基团,使得其内部空穴数量减少,导电性降低,纤维电阻增大。     

Theoretical analysis on electronic properties of zigzag-type single-walled carbon nanotubes under radial deformation

Carbon nanotubes (CNTs) have been attracting attention because they have characteristic mechanical and electronic properties. It has been reported that single-walled CNTs can induce large deformation without bond breaking. Therefore, it is of interest to elucidate the electronic properties of CNTs under large deformation. We investigate the deformation behavior and the change in the electronic properties of zigzag-type single-walled CNTs with chiral vectors of (8,0), (12,0) and (14,0) under radial compression with semi-empirical band calculations based on the tight-binding method. The resistance against the deformation increases with the deformation, and its behavior depends on the diameter of the CNTs. The CNTs, which have band gap energy at the initial state, become metallic by the compression.     

Effects of functional group of carbon nanotubes on mechanical properties of carbon fibers

The effects of surface functionalization of carbon nanotubes (CNTs) on the mechanical properties of carbon fibers (CFs) have been investigated. The surface functionalization of CNTs was carried out with a diazonium reagent. Compared to pure PAN, only the fluoro phenyl functionalized CNTs (F-Ph-CNT) incorporated PAN composites showed a significant increase up to 22 °C of T_g and displayed the second peak due to the interfacial interaction between F-Ph-CNT and PAN. Among the samples, 0.5wt% of F-Ph-CNT reinforced CFs exhibited a 46% increase in tensile strength (4.1 GPa) and a 37% increase in modulus (302 GPa), respectively compared to that of pure CFs.     

添加纳米碳管对高密度聚乙烯力学行为和结晶过程的影响

利用熔融法制备了一系列具有不同纳米碳管含量的纳米碳管(Q盯)／高密度聚乙烯(HDPE)复合材料。对其拉伸性能的研究结果表明，添加质量分数分别为2％，5％和10％的纳米碳管使HDPE的拉伸模量分别提高了7．4％，27．0％和28．6％，屈服强度分别提高了3．3％，14．4％和18．5％，但是会降低HDPE的断裂强度和断裂伸长率。同时，对复合材料中HDPE结晶过程的研究表明，纳米碳管可以提高HDPE的开始结晶温度，降低结晶活化能，但是会使HDPE的结晶速率下降，结晶度降低。     

Hierarchical composites of carbon nanotubes on carbon fiber: Influence of growth condition on fiber tensile properties

Growing carbon nanotubes (CNT) on the surface of high performance carbon fibers (CF) provides a means to tailor the thermal, electrical and mechanical properties of the fiber–resin interface of a composite. However, many CNT growth processes require pretreatment of the fiber, deposition of an intermediate layer, or harsh growth conditions which can degrade tensile properties and limit the conduction between the fiber and the nanotubes. In this study, high density multi-wall carbon nanotubes were grown directly on two different polyacrylonitrile (PAN)-based carbon fibers (T650 and IM-7) using thermal Chemical Vapor Deposition (CVD). The influence of CVD growth conditions on the single-fiber tensile properties and CNT morphology was investigated. The mechanical properties of the resultant hybrid fibers were shown to depend on the carbon fiber used, the presence of a sizing (coating), the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. The CNT density and alignment morphology was varied with growth temperature and precursor flow rate. Overall, it was concluded that a hybrid fiber with a well-adhered array of dense MWCNTs could be grown on the unsized T650 fiber with no significant degradation in tensile properties.     

Dispersion of metal nanoparticles on carbon nanotubes with few surface oxygen functional groups

Homogeneous dispersion of metal oxide nanoparticles was achieved on carbon nanotubes (CNTs) even with a very small amount of surface oxygen functional groups (SOFGs) aided by using ethylene glycol (EG) and sodium hydroxide during the process. Similar particle size distributions were obtained for iron deposited on CNTs containing various amounts of SOFGs. We proposed that formation of hydrogen bonds between EG on the CNT surface and sodium hydroxide is likely responsible, which creates precipitating sites for iron ions on the CNT surface. This facile method is expected to find applications not only for catalysis but also in the fields such as sensors and magnetic materials in particular where a perfect sp² hybridized carbon structure is preferred.     

Nd掺杂对ITO粉体性能的影响

研究了掺杂稀土元素Nd对ITO粉末粒径大小、电学及光学性能的影响.实验结果表明,掺入Nd后在形貌上表现为随着掺杂量的增加,ITO粉末的粒径变小;在光学性能上表现为ITO粉末位于500-1000 cm-1的红外吸收峰向短波方向发生蓝移;在电学性能上表现为随着掺杂量的增加,ITO粉末的电阻率逐渐增加.     

B/N/Si掺杂的(9,0)型碳纳米管电子结构第一性原理研究

基于密度泛函理论(DFT)的DMol3软件包,研究了(9,0)型碳纳米管(CNT)顶端掺杂B/N/Si等元素对其几何结构及电子结构的影响.结果表明,掺杂原子对非掺杂区几何结构影响微弱;加电场后,各种掺杂CNT顶端局域态密度(LDOS)峰位向价带移动;B/N/Si掺杂不仅引起CNT费米能级(Ef)处LDOS增大,而且最低空轨道与最高占有轨道的差值(LUMO-HOMO)降低.由此可预期CNT顶端掺B/N/Si均有利于场致电子发射,且改善幅度依次增强.     

Effects of vacancies on electronic and optical properties of GaN nanosheet: A density functional study

In this work, electronic and linear optical properties of GaN nanosheet are investigated through density functional theory and the dielectric tensor is derived within the random phase approximation (RPA). Electronic band structure calculations indicate that Ga atom vacancies in the 2D GaN system leads to n-type semiconductor, whereas the N atom vacancies change the electronic structure to a p-type semiconductor. Dielectric function, absorption coefficient, optical conductivity, extinction index, reflectivity, loss function and the refraction index of the GaN nanosheet and the Ga-defected or N-defected GaN systems are studied for both parallel (E∥x) and perpendicular (E∥z) applied electric field polarizations. Our results confirm that GaN nanosheet is a semiconductor which is sensitive to the type of vacancies and shows optical anisotropy at both polarizations states.