Most of the applications of the nano structures dependent on the morphology which affects the opto electronics properties. This research article provides a pathway of guiding optical properties like band-gap and fluorescence properties by controlled growth of nano-rods, -flowers, -needles or- tubes without external chemical doping, by simple hydro thermal method by controlling over synthesis parameter, temperature.
In this study, we report the enhancement in field emission (FE) properties of ZnO nanostructure by Ni doping at the base pressure of ~1 x 10-8 mbar, which were grown by the simple wet chemical process. ZnO nanostructure shows single crystalline wurtzite structure up to Ni 10% doping. FESEM represents change in the nanostructure morphology from thick nanoneedles to nanoflakes via thin nanorods with increase in Ni doped ZnO. The turn-on field required to draw a field emission (FE) current density at 1μA/cm2 is found to be 2.5, 2.3, 1.8 and 1.7 V/μm for ZnO(Ni0%), ZnO(Ni5%), ZnO(Ni7.5%) and ZnO(N…
Low-temperature heat capacities (Cp) of nanostructured rock salt (rs-ZnO) and wurtzite (w-ZnO) polymorphs of zinc oxide were measured in the 2-315 K temperature range. No significant influence of nanostructuring on Cp of w-ZnO has been observed. The measured Cp of rock salt ZnO is lower than that of wurtzite ZnO below 100 K and is higher above this temperature. Using available thermodynamic data, we established that the equilibrium pressure between nanocrystalline w-ZnO and rs-ZnO is close to 4.6 GPa at 300 K (half as much as the onset pressure of direct phase transformation) and slightly chan…
ZnO nanostructured films were prepared by chemical bath deposition method on glass substrates without any assistance of either microwave or high pressure autoclaves. The effect of solute concentration on the pure wurtzite ZnO nanostructure morphologies is studied. The controlling of the solute concentration help to control nano-structure in the form of nano-needles, and rods.
This paper deals with the investigations on the nucleation and growth of ZnO nanostructures in a catalyst free synthesis. The ZnO nanostructures have been formed by evaporation of Zn (99.99%) in O_2 and Ar atmosphere in single zone furnace under two temperature regions, region A (~1173-1073K) and region B (~873-773K). Through application of XRD and TEM techniques, it has been shown that first ZnO is formed which changes to ZnOx through creation of oxygen vacancies. The ZnOx acts as self-catalyst and leads to formation of various nanostructures. Those observed in the present investigation are n…
Flower-like nanostructures formed by ZnO nanorods were synthesized and deposited on seeded silicon and glass substrates by a hexamethylenetetramine (HMTA) - assisted hydrothermal method at low temperature (90 oC) with methenamine ((CH3)6N4), as surfactant and catalyst. The substrates were seeded with ZnO nanoparticles. The structure and morphology of the nanostructures were studied by means of x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM) techniques. Influence of the seed nanoparticle on the formation of the flower-lik…
The magnetic transition-metal (TM) @ oxide nanoparticles have been of great interest due to their wide range of applications, from medical sensors in magnetic resonance imaging to photo-catalysis. Although several studies on small clusters of TM@oxide have been reported, the understanding of the physical electronic properties of TMn@(ZnO)42 is far from sufficient. In this work, the electronic, magnetic and optical properties of TMn@(ZnO)42 (TM = Fe, Co and Ni) hetero-nanostructure are investigated using the density functional theory (DFT). It has been found that the core-shell nanostructure Fe…
We have investigated the magnetic properties of non-doped ZnO nanostructures by using {\it ab initio} total energy calculations. Contrary to many proposals that ferromagnetism in non-doped semiconductors should be induced by intrinsic point defects, we show that ferromagnetism in nanostructured materials should be mediated by extended defects such as surfaces and grain boundaries. This kind of defects create delocalized, spin polarized states that should be able to warrant long-range magnetic interactions.
Precise control of morphologies of one-dimensional (1D) or 2D nanostructures during growth has not been easily accessible, usually degrading the device performance and therefore limiting applications to various advanced nanoscale electronics and optoelectronics. Graphene could be a platform to serve as a substrate for both morphology control and direct use of electrodes due to its ideal monolayer flatness with π electrons. Here, we report that by using graphene directly as a substrate, vertically well-aligned ZnO nanowires and nanowalls were obtained systematically by controlling Au catalyst t…
We have studied the influence of intrinsic and extrinsic defects in the magnetic and electrical transport properties of Co-doped ZnO thin films. X ray absorption measurements show that Co substitute Zn in the ZnO structure and it is in the 2+ oxidation state. Magnetization (M) measurements show that doped samples are mainly paramagnetic. From M vs. H loops measured at 5 K we found that the values of the orbital L and spin S numbers are between 1 and 1.3 for L and S = 3/2, in agreement with the representative values for isolated Co 2+. The obtained negative values of the Curie-Weiss temperature…
We report synthesis of Cd substituted ZnO nanostructures (Zn1-xCdxO with x upto \approx .09) by high pressure solution growth method. The synthesized nanostructures comprise of nanocrystals that are both particles (~ 10-15 nm) and rods which grow along (002) direction as established by Transmission electron microscope (TEM) and X-ray diffraction (XRD) analysis. Rietveld analysis of the XRD data shows monotonous increase of the unit cell volume with the increase of Cd concentration. The optical absorption as well as the photoluminescence (PL) shows red shift on Cd substitution. The line width o…
The structure-property relation of nanostructured Al-doped ZnO thin films has been investigated in detail through a systematic variation of structure and morphology, with particular emphasis on how they affect optical and electrical properties. A variety of structures, ranging from compact polycristalline films to mesoporous, hierarchically organized cluster assemblies, are grown by Pulsed Laser Deposition at room temperature at different oxygen pressures. We investigate the dependence of functional properties on structure and morphology and show how the correlation between electrical and opti…
In this work, a reversible control over the visible luminescence of phosphor ZnO is achieved by the application of a few volts (<5V) to nanostructured ZnO film sandwiched between ITO and LiClO4/PEO solid electrolyte. Since ZnO is a good absorbing material but ITO-Glass substrate is transparent in the range of 320-375 nm, the ZnO-ITO interface has been illuminated by a 345 nm light passing through the ITO glass substrate and the emitted light near 545 nm has been collected in reflection mode. When the solid polymer electrolyte is negatively biased, up to 107 percent enhancement in the visible l…
We report that ZnO nanostructures synthesized by chemical route undergo a shape transition at ~ 20 nm from spherical to hexagonal morphology thereby changing the spectral components of the blue-green emission. Spherically shaped nanocrystals (size range 11 -18 nm) show emission in the range of 555-564 nm and the emission shifts to the longer wavelength as the size increases. On the other hand, rods and hexagonal platelets (size range 20-85 nm), which is the equilibrium morphology after the shape transition, show emission near 465-500 nm and it shifts to shorter wavelength as the size increases…
Nanomaterials based on ZnO have been used to build glucose sensors due to its high isoelectric point, which is important when a protein like glucose oxidase (GOx) is attached to a surface. It also creates a biologically friendly environment to preserve the activity of the enzyme. In this work we study the electrical transport properties of ZnO thin films (TFs) and single crystals (SC) in contact with different solutions by using impedance spectroscopy. We have found that the composition of the liquid, by means of the charge of the ions, produces strong changes in the transport properties of th…
We report the growth of Al-catalysed ZnO nanowires (NWs) using a thermal evaporation technique.Before the growth, the substrates were covered with a distribution of Al nano-island that act as seeds. We found that the density of NWs increases as the density of seeds is increased, confirming the catalyst properties of Al. The critical parameters of growth are the substrate temperature, oxygen partial pressure and the thickness of the initial Al layer from which the seeds are formed. The results showed that the oxygen pressure has a strong influence on the structural characteristics: the nanowire…
The origin of room temperature (RT) ferromagnetism (FM) in Ni doped ZnO samples are systematically investigated through physical, optical, and magnetic properties of nanostructure, prepared by simple low-temperature wet chemical method. Reitveld refinement of X-ray diffraction pattern displays an increase in lattice parameters with strain relaxation and contraction in Zn/O occupancy ratio by means of Ni-doping. Similarly scanning electron microscope demonstrates modification in the morphology from nanorods to nanoflakes with Ni doping, suggests incorporation of Ni ions in ZnO. More interesting…
We have characterized the growth of ZnO using sequential infiltration synthesis (SiS) on PS-b-PMMA block copolymers (BCP) of spherical and cylindrical sub-20nm morphologies and studied how the photoluminescence of these nanostructures varies per its seed layer. Investigation of these structures was done using atomic force microscopy (AFM), spectrofluorometry, Raman spectroscopy, and scanning electron microscopy (SEM). We report blue-shifted photoemission at 335 nm (3.70 eV), suggesting quantum confinement effects. This UV-photoluminescence can be translated into emitter sizes of roughly 1.5nm …
The electrochemical deposition of ZnO hierarchical nanostructures directly from PHEMA hydrogel coated electrodes has been successfully demonstrated. A variety of hierarchical ZnO nanostructures, including porous nanoflakes, nanosheets and nanopillar arrays were fabricated directly from the PHEMA hydrogel coated electrodes. Hybrid ZnO-hydrogel composite films were formed with low zinc concentration and short electrodeposition time. A dual-layer structure consisting of a ZnO/polymer and pure ZnO layer was obtained with zinc concentration above 0.01 M. SEM observations and XPS depth profiling wer…
The modification and tailoring the characteristics of nanostructured materials are of great interest due to controllable and unusual inherent properties in such materials. A simple spray pyrolysis technique is used to prepare pure and La-doped ZnO films. The influence of La concentration (0, 0.33, 0.45, 0.66, 0.92 and 1.04 at. %) on the structural, optical, and magnetic properties of ZnO was investigated. The exact nominal compositions of the prepared films were determined from the field emission scanning electron microscope occupied with EDX. X-ray diffraction confirmed that the samples posse…
Present paper reports the effect of ZnO additives on humidity and temperature sensing properties of cuprous oxide. The cuprous oxide powder was mixed with 10% and 25% ZnO by weight and these samples were pelletized by using hydraulic pressing machine. The sensing materials were also investigated by Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD). SEM images show morphology and porosity of material. The average particles size of cuprous oxide was found to be 1.2 micron. The sheet like structures of ZnO is evident in micrographs. From XRD all peaks are well identified and crystall…
An emerging branch of electronics, the optospintronics, would be highly boosted if the control of magnetic order by light is implemented in magnetic semiconductors nanostructures being compatible with the actual technology. Here we show that the ferromagnetic magnetization of low Fe-doped ZnO nanowires prepared by carbothermal process is enhanced under illumination up to temperatures slightly below room temperature. This enhancement is related to the existence of an oxygen vacancy V$_{\rm O}$ in the neighbouring of an antiferromagnetic superexchange Fe$^{3+}$-Fe$^{3+}$ pair. Under illumination…
In this work, nonlinear optical properties of Na: ZnO thin films (Na: ZnO) have been experimentally elaborated. The principal possibility to operate the nonlinear optical features using external laser beams is shown. The Na: ZnO films were synthesized by spray pyrolysis technique at a deposition temperature equal to about 400 C. XRD graph reveals that the grown films were polycrystalline in nature with a dominant peak corresponding to (0 0 2) plane. Despite the difference in the ionic radii of the Na and Zn, an angle shift in the XRD peak was not observed, whereas there was a significant chang…
The synthesis, morphology and magneto-transport properties of nanostructure-engineered charge-ordered Pr0.5Ca0.5MnO3 grown on ZnO nanowires are reported. The stability of the charge-ordering can be tuned, but more interestingly the sign of the magnetoresistance is inverted at low temperatures. Coexistence of ferromagnetic clusters on the surface and antiferromagnetic phase in the core of the grains were considered in order to understand these features. This work suggests that such a process of growing on nanowires network can be readily extended to other transition metal oxides and open doors …
The non-equilibrium boron nitride (BN) phase of zinc oxide (ZnO) has been reported for thin films and nanostructures, however, its properties are not well understood due to a persistent controversy that prevents reconciling experimental and first-principles results for its atomic coordinates. We use first-principles theoretical spectroscopy to accurately compute electronic and optical properties, including single-quasiparticle and excitonic effects: Band structures and densities of states are computed using density functional theory, hybrid functionals, and the $GW$ approximation. Accurate opt…
The structural, electronic, and vibrational thermodynamic properties of the (ZnO)$_n$ (n=2-16) clusters are studied using density functional - full potential computations. The results show, small clusters up to $n=9$ stabilize in the 2D ring shape geometries while the larger clusters prefer the 3D cage like structures. The ring to cage structural cross over in ZnO clusters is studied by investigating the behavior of the Zn-O-Zn bond angle, the Zn-O bond strength, and the number of bonds in the systems. It is argued that 12 is the lowest magic number of ZnO clusters at ground state, while finit…
The fabrication of nanostructures with controlled assembly and architecture is significant for the development of novel nanomaterials-based devices. In this work we demonstrate that laser techniques coupled with low-temperature hydrothermal growth enable complex three-dimensional ZnO nanorods patterning on various types of substrates and geometries. The suggested methodology is based on a procedure involving the 3D scaffold fabrication using Multi-Photon Lithography of a photosensitive material, followed by Zn seeded Aqueous Chemical Growth of ZnO nanorods. 3D, uniformly aligned ZnO nanorods a…
The structural, optical and magnetic properties of nanostructured ZnO films co-doped with cobalt and aluminium have been studied. The nanocrystalline films, with cluster sizes in range 50 - 100 nm, were deposited by pulsed laser ablation in a mixed atmosphere of oxygen and helium. The nanocrystallites have the wurtzite structure and are highly oriented with the c-axis perpendicular to the substrate. Both optical and electron spin resonance (ESR) spectroscopy results show the substitutional incorporation of Co$^{2+}$ ions on the Zn site inside the ZnO nanoclusters. The temperature dependence of…
Dependence of structural parameters on the size of nanoparticles is a topic of general interest where the effect of shape is often neglected. We report a comprehensive study on size dependent structural parameters of ZnO nanostructures (NS) having a wide range of aspect ratios (length/diameter). It reveals that with increase in size, ZnO NS undergo a shape transition from spherical to rod like morphology that induces sudden change in internal parameter (u) which represents relative position of two hexagonal close-packed sublattices. The change in u introduces concomitant changes in anion-catio…
The data of experimental studies of optical characteristics of colloidal solutions, composition and morphology of its dispersed phase, resulting from laser ablation of zinc in aqueous solutions of anionic surfactants --- sodium dodecyl sulfate (SDS), dioctyl sodium sulfosuccinate (AOT) are presented. It is shown that by studying the optical absorption spectra of the colloid, X-ray spectra and AFM-images of extracted from colloid solid phase, it is possible to trace the dynamics of ZnO nanostructures formation from zinc nanoclasters size of several nanometers to ZnO fractal aggregates (FA) size…
The piezoelectric nanomaterial ZnO exhibits an excellent piezoelectric response that can transduce mechanical energy into electrical signals by applying pressure. The piezoelectric behavior of ZnO nanostructures (especially nanorods or microrods) is getting considerable attention in the fabrications of piezo tactile sensors, energy harvesting devices, and other self-powering implantable devices. Especially vertically aligned ZnO nanorods are of high interest due to their higher value of piezoelectric coefficient along the z-direction. In this report, various geometries and alignments of ZnO na…
Engineering nanostructures from the bottom up enables the creation of carefully engineered complex structures that are not accessible via top down fabrication techniques, in particular, complex periodic structures for applications in photonics and sensing. In this work, we propose and demonstrate a bottom up approach that can be adopted and utilized to controllably build diamond nanostructures. A realization of periodic structures and optical wave-guiding is achieved by growing nanoscale single crystal diamond through a defined pattern.
Fundamental theories and practical methods for large-scale electronic structure calculations are given, in which the computational cost is proportional to the system size. Accuracy controlling methods for microscopic freedoms are focused on two practical solver methods, Krylov-subspace method and generalized-Wannier-state method. A general theory called the 'multi-solver' scheme is also formulated, as a hybrid between different solver methods. Practical examples are carried out in several insulating and metallic systems with 10^3-10^5 atoms. All the theories provide general guiding principles …
A series of MnxZn1-xO (x=0.03, 0.05) nanostructures have been grown via the solution based chemical spray pyrolysis technique. Electron beam induced modifications on structural, linear and nonlinear optical and surface morphological properties have been studied and elaborated. GXRD (glancing angle X-ray diffraction) patterns show sharp diffraction peaks matching with the hexagonal wurtzite structure of ZnO thin films. The upsurge in ebeam dosage resulted in the shifting of XRD peaks (101) and (002) towards lower angle side, and increase in FWHM value. Gaussian deconvolution on PL spectra revea…
