Graphene-like ZnO Research Articles

Tuning the Magnetism by CO Adsorption in Graphene-Like ZnO with Defect

The present work investigates the effect of adsorbate CO molecule on magnetism in the imperfect graphene-like ZnO through first-principles calculations. It is found that the magnetism in an undoped...

Design of half-metallic properties induced by 2p impurities in ZnO nanosheet

We perform first-principles study on the electronic and magnetic properties of X-doped (X=Be, B, C, N) graphene-like ZnO nanosheet (NS). When one oxygen is substituted by X atom in ZnONS, X-induced spin polarizations led to transition from the semiconducting to half-metallic properties, with magnetic moments of 2.0, 1.0, 2.0, and 1.0 μ{sub B} per Be, B, C, and N dopant, respectively. The local magnetic moments are found to equal to unpaired electrons in the 2p spin states of the doping X atoms. While two oxygen atoms are substituted by X in ZnONS, the formation energy analysis indicates that X ions have a clear clustering tendency. Depending on distance between two X dopants, the ferromagnetic, antiferromagnetic or nonmagnetic states are all found in X-doped ZnONSs. More interestingly, for C and N doped cases, the half-metallic properties are robust independent on the doping concentrations, while Be or B doped systems would result in half-metallic to magnetic state transition as the doping concentrations increase. - Graphical abstract: Structure of ZnO NS employed to define various configurations of X-doped, as well as spin-density distribution of one Be-doped system. Highlights: ► X-induced spin polarizations result in half-metallicity. ► The local moments equal to unpaired electronsmore » in 2p spin states of X atom. ► The FM, AFM, and NM states are all found in X-doped ZnONSs. ► The half-metallicity in C and N doped cases are robust.« less

Surface effects on the optical and photocatalytic properties of graphene-like ZnO:Eu3+ nanosheets

The graphene-like ZnO:Eu3+ (ZEO) nanosheets with different Eu3+ doping concentrations are synthesized successfully by a simple hydrothermal method. We utilize the native surface effect in the ZEO nanosheets for the first time to certify the resonant energy transfer mechanism from the ZnO host to the Eu3+ ions by means of the power-dependent photoluminescence technique. Meanwhile, to further explore the functional applications of the graphene-like ZEO, we also characterize their photocatalytic activity on the Rhodamine B dye and reveal that both the higher specific surface area and Eu3+ doping lead to the higher degradation efficiency of ZEO nanosheets.

The electronic and magnetic properties with intrinsic defects in ZnO nanosheets: First-principles prediction

Using full-potential linearized augmented plane wave (FLAPW) method, we investigated the effects of intrinsic vacancies on electronic and magnetic properties in graphene-like ZnO nanosheets. The results show that the oxygen vacancy (VO) has no influence on magnetism in ZnO nanosheet, whereas the Zn vacancy (VZn) lead to spin polarization of the nanostructures with a total magnetic moment of 2.0μB due to O-2p and Zn-3d hybridization. When the distance of two VZn defects increases to 6.499 Å, the system shows an intriguing half-metallic character with 100% spin-polarized carriers due to O(2p)–Zn(3d)–O(2p) coupling chain between two VZn defects.

Tunable Magnetism in a Nonmetal-Substituted ZnO Monolayer: A First-Principles Study

We have studied structural, electronic, and magnetic properties of the graphene-like ZnO monolayer doped with nonmetal species using the first-principles calculations. Particular attention has been placed on the ZnO monolayer with one or two oxygen atoms per supercell substituted by carbon, boron, or nitrogen atoms. We find that the ZnO monolayer with one oxygen atom per supercell substituted by a carbon or boron atom is ferromagnetic (FM) half metal (HM), while that with a nitrogen atom per supercell is a FM semiconductor. Upon the ZnO monolayer with two oxygen atoms per supercell substituted by carbon or boron, the magnetic properties vary, depending on the distance between two impurities. Two neighboring carbon or boron atoms in the ZnO monolayer form dimer pairs, which convert the ZnO monolayer into an n-type semiconductor with a nonmagnetic (NM) ground state. As the distance between two carbon or boron atoms increases, the doped ZnO monolayer undergoes both NM–AFM–FM and semiconductor–HM transitions. However, the ZnO monolayer with two N atoms per supercell is a p-type semiconductor with the antiferromagnetic (AFM) ground state, regardless of the distance between N atoms. The negligible energy difference between AFM and FM states of the N-doped ZnO monolayer implies it exhibits paramagnetic behavior at room temperature. Our study demonstrates that nonmetal-doped ZnO monolayers possess tunable magnetic and electronic properties, suitable for applications in electronics and spintronics at nanoscale.

Tuning the electronic and magnetic properties of carbon-doped ZnO nanosheets: First-principles prediction

Using the full-potential linearized augmented plane wave (FLAPW) method, we study the electronic and magnetic properties of C-doped graphene-like ZnO nanosheets (NSs). The results show that in a specimen with isolated C-doping, there is a spontaneous polarization with a magnetic moment 2.0μB/C. In two C-doped systems the antiferromagnetic (AFM) coupling is more favorable in energy and C ions tend to form a cluster, while the metastable states are ferromagnetic (FM) order with a magnetic moment about 4.0μB/2 C. More importantly, the long-range FM order appears due to a p-p coupling interaction and p-d exchange hybridization, and the p-p coupling is the dominant mechanism.

Self‐Assembly of Graphenelike ZnO Superstructured Nanosheets and Their Application in Hybrid Photoconductors

Photoconductors require high charge-carrier mobilities, sensitivity over a wide range of light levels, and good stability. Combining an organic semiconductor with environmentally benign inorganic nanoparticles is a rational means to develop photoconductors with such properties. However, an inhomogeneous distribution of nanoparticles in the active layer restricts both charge-carrier mobility and charge collection at an electrode. In this paper, ultrathin ZnO superstructured nanosheets are successfully synthesized by a solvothermal method. Time-dependent investigations show that the superstructured nanosheets assemble in solution during the growth process. Given that high-quality ZnO nanosheets are obtained, a hybrid photoconductor device with P3HT is fabricated and investigated. Sensitivity above 200% under simulated sunlight is obtained with good air stability. This study demonstrates a general approach to design photoconductors using hybrid nanomaterials.

First principles investigation of oxygen adsorptions on hydrogen–terminated ZnO graphene-like nanosheets

The structures of ZnO graphene-like nanosheets (ZnOGLNS), i.e., ZnO aromatic-like (AL-ZnONS), naphthalene-like (NLL-ZnONS), pyrene-like (PRL-ZnONS), coronene-like (CNL-ZnONS) and circumcoronene-like (CCL-ZnONS) and their oxygen adsorptions were obtained using the B3LYP/LanL2DZ method. Adsorption energies of O(2) on AL-ZnONS, NLL-ZnONS, PRL-ZnONS, CNL-ZnONS and CCL-ZnONS are reported. The bond strengths of the most inner Zn-O bonds of ZnOGLNSs are in order: CCL-ZnONS > CNL-ZnONS > PRL-ZnONS. It was found that chemisorptions of O(2) occur on the hydride atoms of zinc-hydride in the ZnOGLNSs. Physisorptions of O(2) only occurring over the plane of ZnOGLNS were found. All the ZnOGLNSs are oxygen sensitive materials and would be developed to be oxygen sensor based on electrical conductivity.

Prediction for room-temperature half-metallic ferromagnetism in the half-fluorinated single layers of BN and ZnO

On the basis of density functional calculations we explored the possibility that BN and ZnO single layers can become ferromagnetic at room temperature and half-metallic upon fluorine adsorption. Fluorine atoms form stable bonds only with the B and Zn atoms on the graphenelike BN and ZnO single layers, respectively, and the resulting fluorinated BN and ZnO single layers are expected to become ferromagnetic half metals with Curie temperatures around room temperature. The fluorination of semiconductor single layers can lead to interesting spintronics and functional applications.

Ferromagnetic coupling in a Co-doped graphenelike ZnO sheet

Using first-principles calculations it is demonstrated that Co doped graphenelike ZnO sheet presents ferromagnetic coupling. The Co atoms are energetically barrierless absorbed in the Zn sites, suffering a Jahn-Teller distortion. The results reveal that the origin of the ferromagnetic coupling, different from the bulk 3D ZnO stacking, is mainly guided by a direct exchange interaction without any additional defect. This ferromagnetic coupling is due to the system topology, namely, it is a direct consequence of the two-dimensional character of the ZnO monolayer within graphenelike structure. Increasing the number of ZnO layers the ferromagnetic coupling vanishes.