Superhydrophobic surfaces via controlling the morphology of ZnO micro/nano complex structure

ZnO micro/nano complex structure films, including reticulate papillary nodes, petal-like and flake-hole, have been self-assembled by a hydrothermal technique at different temperatures without metal catalysts. The wettability of the above film surfaces was modified with a simple coating of heptadecafluorodecyltrimethoxy-silane in toluene. After modifying, the surface of ZnO film grown at 50~${^\circ}$C was converted from superhydrophilic with a water contact angle lower than 5$^{\circ}$ to superhydrophobic with a water contact angle of 165$^{\circ}$. Additionally, the surface of reticulate papillary nodes ZnO film grown at 100~${^\circ}$C had excellent superhydrophobicity, with a water contact angle of 173$^{\circ}$ and a sliding angle lower than 2$^{\circ}$. Furthermore, the water contact angle on the surface of petal-like and flake-hole ZnO films grown at 150~${^\circ}$C and 200~${^\circ}$C were found to be 140$^{\circ}$ and 120$^{\circ}$, respectively. The wettability for the samples was found to depend strongly on the surface morphology which results from the growth temperature.     

Graphitic nanofilms as precursors to wurtzite films: theory

Periodic ab initio density functional calculations on ultrathin films of AlN, BeO, GaN, SiC, ZnO, and ZnS demonstrate the stabilization of thicker films terminating with the polar {0001} surface via charge transfer and metallization of the surface layers. In contrast thinner films remove the dipole by adopting a graphiticlike structure in which the atoms are threefold coordinate. This structure is thermodynamically the most favorable for these thinner films. Implications for the crystal growth of wurtzite materials are discussed.     

Microstructural study of MBE-grown ZnO film on GaN/sapphire (0001) substrate

Single crystalline ZnO film is grown on GaN/sapphire (0001) substrate by molecular beam epitaxy. Ga₂O₃ is introduced into the ZnO/GaN heterostructure intentionally by oxygen-plasma pre-exposure on the GaN surface prior to ZnO growth. The crystalline orientation and interfacial microstructure are characterized by X-ray diffraction and transmission electron microscopy. X-ray diffraction analysis shows strong c-axis preferred orientation of the ZnO film. Cross-sectional transmission electron microscope images reveal that an additional phase is formed at the interface of ZnO/GaN. Through a comparison of diffraction patterns, we confirm that the interface layer is monoclinic Ga₂O₃ and the main epitaxial relationship should be and .      

Surface origin of high conductivities in undoped In2O3 thin films

The microscopic cause of conductivity in transparent conducting oxides like ZnO, In{2}O{3}, and SnO{2} is generally considered to be a point defect mechanism in the bulk, involving intrinsic lattice defects, extrinsic dopants, or unintentional impurities like hydrogen. We confirm here that the defect theory for O-vacancies can quantitatively account for the rather moderate conductivity and off-stoichiometry observed in bulk In{2}O{3} samples under high-temperature equilibrium conditions. However, nominally undoped thin-films of In{2}O{3} can exhibit surprisingly high conductivities exceeding by 4-5 orders of magnitude that of bulk samples under identical conditions (temperature and O{2} partial pressure). Employing surface calculations and thickness-dependent Hall measurements, we demonstrate that surface donors rather than bulk defects dominate the conductivity of In{2}O{3} thin films.     

Ordering mechanisms in epitaxial SiGe nanoislands

We investigate and elucidate the surprising observation of atomically ordered domains in dome-shaped SiGe nanoislands. We show, through atomistic Monte Carlo simulations, that this ordering is a surface-related phenomenon, and that is driven by surface equilibrium rather than by surface kinetics. The ordering depends on facet orientation. The main source of ordering is the {15 3 23} facet, while the {105} and {113} facets contribute less. Subsurface ordered configurations self-organize under this facet and are frozen-in and buried during island growth, giving rise to the ordered domains. Ordering mechanisms based on constrained surface kinetics, requiring step-mediated segregation at the island facets, are shown to be much less likely.     

Magnetic properties of Mn-doped ZnO diluted magnetic semiconductors

A series of Mn-doped ZnO films have been prepared in different sputtering plasmas by using the inductively coupled plasma enhanced physical vapour deposition. The films show paramagnetic behaviour when they are deposited in an argon plasma. The Hall measurement indicates that ferromagnetism cannot be realized by increasing the electron concentration. However, the room-temperature ferromagnetism is obtained when the films are deposited in a mixed argon-nitrogen plasma. The first-principles calculations reveal that antiferromagnetic ordering is favoured in the case of the substitution of Mn^2＋ for Zn^2＋ without additional acceptor doping. The substitution of N for O （NO^-） is necessary to induce ferromagnetic couplings in the Zn-Mn-O system. The hybridization between N 2p and Mn 3d provides an empty orbit around the Fermi level. The hopping of Mn 3d electrons through the empty orbit can induce the ferromagnetic coupling. The ferromagnetism in the N-doped Zn-Mn-O system possibly originates from the charge transfer between Mn^2＋ and Mn^3＋ via NO^-, The key factor is the empty orbit provided by substituting N for O, rather than the conductivity type or the carrier concentration.     

Tunable anharmonicity versus high-performance thermoelectrics and permeation in multilayer (GaN)1-x(ZnO)x

Nonisovalent (GaN)$_{1-x}$(ZnO)$_x$ alloys are more technologically promising than their binary counterparts because of the abruptly reduced band gap. Unfortunately, the lack of two-dimensional (2D) configurations as well as complete stoichiometries hinders to further explore the thermal transport, thermoelectrics, and adsorption/permeation. We identify that multilayer (GaN)$_{1-x}$(ZnO)$_x$ stabilize as wurtzite-like $Pm$-(GaN)$_3$(ZnO)$_1$, $Pmc2_1$-(GaN)$_1$(ZnO)$_1$, $P3m1$-(GaN)$_1$(ZnO)$_2$, and haeckelite $C2/m$-(GaN)$_1$(ZnO)$_3$ via structural searches. $P3m1$-(GaN)$_1$(ZnO)$_2$ shares the excellent thermoelectrics with the figure of merit $ZT$ as high as 3.08 at 900 K for the p-type doping due to the ultralow lattice thermal conductivity, which mainly arises from the strong anharmonicity by the interlayer asymmetrical charge distributions. The $p$-$d$ coupling is prohibited from the group theory in $C2/m$-(GaN)$_1$(ZnO)$_3$, which thereby results in the anomalous band structure versus ZnO composition. To unveil the adsorption/permeation of H$^+$, Na$^+$, and OH$^-$ ions in $AA$-stacking configurations, the potential wells and barriers are explored from the Coulomb interaction and the ionic size. Our work is helpful in experimental fabrication of novel optoelectronic and thermoelectric devices by 2D (GaN)$_{1-x}$(ZnO)$_x$ alloys.     

First-principles study on the structural and electronic properties of ultrathin ZnO nanofilms

Using first-principles density-functional calculations, we have studied the structural and electronic properties of ultrathin ZnO {0001} nanofilms. The structural parameters, the charge densities, band structures and density of states have been investigated. The results show that there are remarkable charge transfers from Zn to O atoms in the ZnO nanofilms. All the ZnO nanofilms exhibit direct wide band gaps compared with bulk counterpart, and the gap decreases with increased thickness of the nanofilms. The decreased band gap is associated with the weaker ionic bonding within layers and the less localization of electrons in thicker films. A staircase-like density of states occurs at the bottom of conduction band, indicating the two-dimensional quantum effects in ZnO nanofilms.     

A fabrication and magnetic properties study on Al doped Zn0.99Co0.01O dilution ferromagnetic semiconductors

This paper reports that a chemical method is employed to synthesize Co and Al co-doped ZnO,namely,Zn0.99 x Co0.01 Al x O dilution semiconductors with the nominal composition of x = 0,0.005 and 0.02.Structural,magnetic and optical properties of the produced samples are studied.The results indicate that samples sintered in air under the temperatures of 500 C show a single wurtzite ZnO structure and the ferromagnetism decreases with the increase of Al.Photoluminescence spectra of different Al-doped samples indicate that increasing Al concentration in Zn0.99 x Co0.01 Al x O results in a decrease of Zn i,which resembles the trend of the ferromagnetic property of the corresponding samples.Therefore,it is deduced that the ferromagnetism observed in the studied samples originates from the interstitial defect of zinc(Zni) in the lattice of Co-doped ZnO.     

Study on the design of ZnO/PANI composites and the mechanism of enhanced humidity sensing properties

ZnO/PANI composite humidity sensor was prepared by hydrothermal method. The first principles of density functional theory study the sensing mechanism. The calculation shows that the oxygen vacancy on ZnO surface is beneficial to the adsorption of water molecules. The {0 0 0‾1} crystal plane with the largest lattice oxygen number in ZnO has a strong adsorption capacity for water molecules, which is also conducive to improving the humidity sensitivity. PANI is easy to be combined on {0 1‾1 0} plane of ZnO, and it indirectly promotes the growth of {0 0 0‾1} plane, increasing the adsorption of water molecules and the proportion of H⁺ and H₃O⁺ ions. In addition, the N–H group in ZnO/PANI enhances the H⁺ conduction, which further improves the performance of the sensor. The results concluded that the proportion of lattice oxygen in humidity sensor is an important factor of humidity sensor sensitive detection.     

单原子Pt吸附于不同原子暴露终端BiOBr{001}面的第一性原理研究

基于密度泛函理论(density functional theory, DFT)的第一性原理方法研究了暴露不同原子终端的BiOBr{001}表面以及单原子Pt吸附于BiOBr{001}-BiO不同位置的几何构型、电子结构、光学性质和电荷转移.计算结果表明:BiOBr{001}面BiO终端暴露可诱导产生表面态且价带和导带能级向低能方向移动,光氧化性增强,尤其导带下方出现的表面态能级有助于光生电子-空穴对的分离和迁移,光吸收显著增强,且BiOBr{001}面BiO终端的功函数远低于贵金属Pt,有利于电荷定向转移.其次,单原子Pt吸附于BiOBr{001}-BiO为基底的表面,在禁带中间诱导产生杂质能级, Pt吸附于穴位时吸附能最小,光响应能力最好且电荷转移量最大,吸附于顶位和桥位时,形成开放性的贫电子区域,因此可预测穴位为Pt原子的吸附位点,预示其良好的降解有机污染物效果, Pt吸附于BiOBr{001}-BiO的顶位和桥位,具有潜在的CO_2还原或固氮等领域应用.     

Non-equilibrium plasma production by pulsed laser ablation of gold

A gold target has been irradiated with a Q-switched Nd:Yag laser having 1064\,\hbox{nm} wavelength, 9\,\hbox{ns} pulse width, 900\,\hbox{mJ} maximum pulse energy and a maximum power density of the order of 10^{10}\,\hbox{W}/\hbox{cm}^2 . The laser-target interaction produces a strong gold etching with a production of a plasma in front of the target. The plasma contains neutrals and ions having high charge state. Time-of-flight measurements are presented for the analysis of the ion production and ion velocity. A cylindrical electrostatic deflection ion analyzer permits to measure the yield of the emitted ions, their charge state and their ion energy distribution. Measurements indicate that the ion charge state reaches 6^+ and 10^+ at a laser fluence of 100\,\rm{J/cm}^2 and 160\,\rm{J/cm}^2 , respectively. The maximum ion energy reaches about 2\,\hbox{keV} and 8\,\hbox{keV} at these low and at high laser fluence, respectively. Experimental ion energy distributions are given as a function of the ion charge state. Obtained results indicate that electrical fields, produced in the plume, along the normal to the plane of the target surface, exist in the unstable plasma. The electrical fields induce ion acceleration away from the target with a final velocity dependent on the ion charge state. The ion velocity distributions follow a "shifted Maxwellian distribution", which the authors have corrected for the Coulomb interactions occurring inside the plasma.     

Segregations at antiphase boundaries in hexagonal close-packed superstructures. II

As was shown in the first part of this study [1], slip occurs in polycrystalline ordered Mg₃Cd, which has a DO₁₉ superstructure, along the {0001} basis planes, {1010} prismatic planes, and {1011} and {1012} pyramidal planes [2,3]. The formation of segregations at antiphase boundaries (APB's) in the {0001} basis and {1011} pyramidal planes was also examined there [1]. Segregations at APB's in planes are treated in this second part of the study. A zero-energy APB may form in the prismatic plane [4]. Segregation of atoms, on the other hand, is not allowed at such an APB according to the Gorskii-Bragg-Williams theory if correlation and interaction in the second and higher coordination spheres are not taken into account.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 5, pp. 62–70, May, 1969.The authors thank N. S. Golosov and N. V. Kozhemyakin for discussion of this study and valuable advice.     

Probe for the strong parity violation effects at RHIC with three particle correlations

In non-central relativistic heavy ion collisions, P\mathcal{P}-odd domains, which might be created in the process of the collision, are predicted to lead to charge separation along the system orbital momentum [1]. An observable, P\mathcal{P}-even, but directly sensitive to the charge separation effect, has been proposed in Ref. [2] and is based on 3-particle mixed harmonics azimuthal correlations. We report the STAR measurements using this observable for Au+Au and Cu+Cu collisions at ?{s_NN }\sqrt {s_{NN} } = 200 and 62 GeV. The results are reported as function of collision centrality, particle separation in rapidity, and particle transverse momentum. Effects that are not related to parity violation but might contribute to the signal are discussed.     

Improved growth of solution‐deposited thin films on polycrystalline Cu(In,Ga)Se2

CdS and Zn(O,S) grown by chemical bath deposition (CBD) are well established buffer materials for Cu(In,Ga)Se₂ (CIGS) solar cells. As recently reported, a non‐contiguous coverage of CBD buffers on CIGS grains with {112} surfaces can be detected, which was explained in terms of low surface energies of the {112} facets, leading to deteriorated wetting of the chemical solution on the CIGS surface. In the present contribution, we report on the effect of air annealing of CIGS thin films prior to the CBD of CdS and Zn(O,S) layers. In contrast to the growth on the as‐grown CIGS layers, these buffer lay‐ ers grow densely on the annealed CIGS layer, even on grains with {112} surfaces. We explain the different growth behavior by increased surface energies of CIGS grains due to the annealing step, i.e., due to oxidation of the CIGS surface. Reference solar cells were processed and completed by i‐ZnO/ZnO:Al layers for CdS and by (Zn,Mg)O/ZnO:Al for Zn(O,S) buffers. For solar cells with both, CdS and Zn(O,S) buffers, air‐annealed CIGS films with improved buffer coverage resulted in higher power‐conversion efficiencies, as compared with the devices containing as‐grown CIGS layers. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Synthesis of dimension-tunable ZnO nanostructures via the design of zinc hydroxide precursors

A facile synthesis route is presented to achieve dimension-tunable ZnO nanostructures by the design of zinc hydroxide precursors under the surfactant-free condition. From three types of zinc hydroxide precursors, namely, crystalline Zn(OH)(NO₃)(H₂O) nanobelts, amorphous zinc hydroxides microparticles and soluble Zn(OH)^2-₄\mathrm{Zn}(\mathrm{OH})^{2-}_{4} species, the porous ZnO nanosheets, ZnO nanoparticles and ZnO nanowires can be achieved, respectively. The porous ZnO nanosheets exhibit large polar surface area. Thermal analysis indicates that the crystalline Zn(OH)(NO₃)(H₂O) nanobelts were converted to the porous ZnO nanosheets by in situ lattice reconstruction, which was attributed to the unique fibrous structure of Zn(OH)(NO₃)(H₂O) nanobelts. The as-prepared dimension-tunable ZnO nanostructures have potential applications in solar cells, photocatalysis, novel chemical and biological sensors, etc.     

Surface phase transition in H/W(110) induced by tuning the fermi surface nesting vector by hydrogen loading

At a hydrogen coverage of one monolayer, W(110) is known to exhibit a Fermi nesting in its electronic surface states with a nesting vector q{N} of 0.9 A{-1} along [001]. Here we show that additional H adsorption allows a controlled tuning of q{N}. As q{N} approaches the commensurate value of 1.0 A{-1}, its signature in inelastic He-atom scattering becomes more pronounced, finally disappearing as a surface charge density wave (CDW) develops and the surface symmetry changes from c(2 x 2) to a p(8 x 2) superstructure. The gradual change in q{N} is attributed to an energetic shift of the spin-polarized electronic surface states that eventually form the surface CDW.     

First-principles calculations for titanium monoxide clusters TinO （n=1-9）

Based on the density-functional theory, this paper studies the geometric and magnetic properties of TinO （n=1-9） clusters. The resulting geometries show that the oxygen atom remains on the surface of clusters and does not change the geometry of Tin significantly. The binding energy, second-order energy differences with the size of clusters show that Ti7O cluster is endowed with special stability. The stability of TinO clusters is validated by the recent time-of-flight mass spectra. The total magnetic moments for TinO clusters with n=1-4, 8-9 are constant with 2 and drop to zero at n=5-7. The local magnetic moment and charge partition of each atom, and the density of states are discussed. The magnetic moment of the TinO is clearly dominated by the localized 3d electrons of Ti atoms while the oxygen atom contributes a very small amount of spin in TinO clusters.     

Crystal orientation control of polycrystalline TiN thin films using ZnO under layers deposited by magnetron sputtering

The effect of ZnO under layers on crystal growth of TiN thin films was investigated. TiN single layers and double-layered ZnO/TiN thin films were deposited on soda-lime-silicate glass substrates by magnetron sputtering. XRD analysis indicated that TiN single layers exhibited {1 1 1} preferred orientation on glass substrates; on the other hand, the TiN thin films with {1 0 0} preferred orientation were obtained using ZnO under layers and crystallized better than the TiN single layers. This crystal orientation change of TiN thin films should come from heteroepitaxial-like growth because the TiN{1 0 0} and ZnO{0 0 1} crystal lattice planes have similar atomic arrangements. Besides, the possible mismatch between TiN and ZnO atomic arrangements was estimated to be 7.8%. Furthermore, the resistivity and optical absorbance of TiN thin films decreased when they were deposited on ZnO under layers. It can be considered that electrical and optical properties should be improved due to the well-crystallization of TiN thin films using ZnO under layers.     

Improved performance of MoS2 FET by in situ NH3 doping in ALD Al2O3 dielectric

Since defects such as traps and oxygen vacancies exist in dielectrics, it is difficult to fabricate a high-performance MoS$_{2}$ field-effect transistor (FET) using atomic layer deposition (ALD) Al$_{2}$O$_{3}$ as the gate dielectric layer. In this paper, NH$_{3}$ in situ doping, a process treatment approach during ALD growth of Al$_{2}$O$_{3}$, is used to decrease these defects for better device characteristics. MoS$_{2}$ FET has been well fabricated with this technique and the effect of different NH$_{3}$ in situ doping sequences in the growth cycle has been investigated in detail. Compared with counterparts, those devices with NH$_{3}$ in situ doping demonstrate obvious performance enhancements: $I_{\rm on}/I_{\rm off}$ is improved by one order of magnitude, from $1.33\times 10^{5}$ to $3.56\times 10^{6}$, the threshold voltage shifts from $-0.74 $ V to $-0.12$ V and a small subthreshold swing of 105 mV/dec is achieved. The improved MoS$_{2}$ FET performance is attributed to nitrogen doping by the introduction of NH$_{3}$ during the Al$_{2}$O$_{3}$ ALD growth process, which leads to a reduction in the surface roughness of the dielectric layer and the repair of oxygen vacancies in the Al$_{2}$O$_{3}$ layer. Furthermore, the MoS$_{2}$ FET processed by in situ NH$_{3}$ doping after the Al and O precursor filling cycles demonstrates the best performance; this may be because the final NH$_{3}$ doping after film growth restores more oxygen vacancies to screen more charge scattering in the MoS$_{2}$ channel. The reported method provides a promising way to reduce charge scattering in carrier transport for high-performance MoS$_{2 }$ devices.