Gd-doped ZnO Research Articles

Modified Ultrasonic Technique to Study Gd-Doped ZnO Films

Normal ultrasonic transducers of 0.5, 1, and 2 MHz are modified using delay lines which are made of Quartz. Such modification is to ameliorate the capability of the transducer to investigate Gd-doped ZnO thin films whose thickness is too thin. The normal transducers cannot test materials that have too thin thickness due to the near fields of these transducers. The near field is considered as blind area of the transducer. Therefore, the specimen under test must have thickness bigger than the near field of the used transducer, or instead delay lines can be used. Samples of Gd-doped ZnO thin films are prepared using sol gel technique. The ultrasonic pulse echo method is used at room temperature. Flaws are found in different prepared specimens. Results show that such delay lines are suitable to ameliorate the ultrasonic transducer to test Gd-doped ZnO thin films.

Investigations on structural, magnetic and electronic structure of Gd-doped ZnO nanostructures synthesized using sol–gel technique

GdxZn1−xO (x = 0, 0.02, 0.04 and 0.06) nanostructures have been synthesized using sol–gel technique and characterized to understand their structural and magnetic properties. X-ray diffraction (XRD) results show that Gd (0, 2, 4 and 6 %)-doped ZnO nanostructures crystallized in the wurtzite structure having space group C3v (P63mc). Photoluminescence and Raman studies of Gd-doped ZnO powder show the formation of singly ionized oxygen vacancies. X-ray absorption spectroscopy reveals that Gd replaces the Zn atoms in the host lattice and maintains the crystal symmetry with slight lattice distortion. Gd L3-edge spectra reveal charge transfer between Zn and Gd dopant ions. O K-edge spectra also depict the charge transfer through the oxygen bridge (Gd–O–Zn). Weak magnetic ordering is observed in all Gd-doped ZnO samples.

Identifying the influence of the intrinsic defects in Gd-doped ZnO thin-films

Gd-doped ZnO thin films were prepared using pulsed laser deposition at different oxygen pressures and varied Gd concentrations. The effects of oxygen deficiency-related defects on the Gd incorporation, optical and structural properties, were explored by studying the impact of oxygen pressure during deposition and post-growth thermal annealing in vacuum. Rutherford Backscattering Spectrometry revealed that the Gd concentration increases with increasing oxygen pressure for samples grown with the same Gd-doped ZnO target. Unexpectedly, the c-lattice parameter of the samples tends to decrease with increasing Gd concentration, suggesting that Gd-defect complexes play an important role in the structural properties. Using low-temperature photoluminescence (PL), Raman measurements and density functional theory calculations, we identified oxygen vacancies as the dominant intrinsic point defects. PL spectra show a defect band related to oxygen vacancies for samples grown at oxygen deficiency.

Structural and Dielectric Studies of Gd Doped ZnO Nanocrystals at Room Temperature

Gadolinium doped Zinc oxide (Zn1–xGdxO) nanocrystals with different percentage of Gd content (x = 0, 0.2, 0.4, 0.6, 0.8) have been prepared by the solid state reaction method. The structural, mor-phological and chemical studies of the samples were performed by X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy dispersive X-ray (EDX) analysis. The XRD spectra confirm that all the samples have hexagonal wurtzite structure. Decrease in average crystallite size with an increase in Gd concentration is observed in XRD. SEM images show that the grain size of undoped ZnO is larger than the Gd doped ZnO, specifying the hindrance of grain growth upon Gd doping. The chemical composition of the samples was confirmed using Energy dispersive X-ray (EDX) analysis. The variation of dielectric constant (εr), dielectric loss (tan δ) and AC conductivity as a function of frequency is studied at room temperature in a frequency which ranges from 100 Hz - 4.5 MHz by using LCR Hi TESTER. All the samples exhibit the normal dielectric behavior, i.e. decreases with increase in frequency which has been explained in the light of Maxwell-Wagner model. The dielectric constant and dielectric loss can be varied intensely by tuning Gd concentration in Zn1–xGdxO compounds.

Investigation of the Structural, Optical and Electrical Properties of Gadolinium-Doped Zinc Oxide Films Prepared by Sol-Gel Method

Thin films of undoped and gadolinium-doped zinc oxide (Gd-doped ZnO) with different Gd concentration (1-8 at. %) were deposited onto a glass substrate by sol–gel spin-coating technique. X-ray diffraction (XRD, Bruker D8 Advance) studies confirmed the nature of the films as polycrystalline, with typical hexagonal wurtzite structure. The film also showed variation in crystallite size and change in relative intensities, upon different Gd concentrations. Besides, the influence of Gd concentration on the optical transmittance of ZnO films was studied using ultraviolet-visible spectrophotometer (UV-Vis, Shimadzu UV 1800) in the wavelength range 300-800 nm. The optical transmittance of all films is higher than ~95% in the visible region, and doped films become more transparent. The electrical resistance was measured by two point probe (Keithley-2400). The resistance decrease with increasing Gd concentration up to 2 at.% and it increased for further increase Gd concentrations.

Effect of Crystallite Size on the Optical and Structural Properties of Gadolinium-Doped Zinc Oxide

Rare earth Gd-doped ZnO thin films were prepared by a simple sol-gel spin coating method in order to search for a new functional diluted magnetic semiconductor for potential application in spintronics. The thin films were deposited onto glass substrates with zinc acetate dehydrate, monoethanolamine and 2-methoxyethanol as a starting material, stabilizer and solvent, respectively. The dopant percentage was increased up to 8%. Optical investigation showed that the crystallinity of the thin films was changing due to the increase of the Gd concentrations and optical band gap energy (Eg) value was estimated to be around 3.12 ~ 3.28 eV using Tauc's model. The crystallite size determined from XRD spectra and the results was found that the value is in the range of 14.42 ~ 21.98 nm.

Effect of Rare-Earth Gd Incorporation on the Characteristics of ZnO Thin Film.

The doping of oxide-based semiconductors with rare-earth ions may serve as an alternative to transition metal doping with the possibility of room-temperature ferromagnetism. Here, highly transparent thin films of ZnO doped with a rare-earth element, Gd, were prepared via a sol-gel-derived precursor. A series of Gd-doped ZnO films with different Gd concentrations (0 to 8 at.%) were deposited onto glass substrates. XRD analysis revealed that the FWHM of the diffraction peaks increased with the increase of Gd composition which may indicate that the Gd incorporation decreased the crystallinity. However no new peaks associated with the formation of secondary phases such as GdO and Gd metal clusters were detected. The MFM images were seen to be more pronounced with the incorporation of Gd ions where we could clearly observe the magnetic signals at room temperature especially for the samples with higher Gd doping of 4 and 8 at.% Gd. Evidently, the magnetic domain size exhibited a significant increase with the increase of Gd composition in contrast to the undoped sample.

Synthesis and Characterization of Gd-Doped ZnO Nanopencils for Acetone Sensing Application

Synthesis and Characterization of Gd-Doped ZnO Nanopencils for Acetone Sensing Application

The effect of Gd doping on the electrical and photoelectrical properties of Gd:ZnO/p-Si heterojunctions

Undoped ZnO thin films, as well as 1%, 3% and 5% Gd-doped ZnO films, were deposited on p-type Si using spin coating. The structural properties of these thin films were analysed using X-ray diffraction, and the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the Gd:ZnO/p-Si heterojunctions were compared with those of the undoped ZnO/p-Si heterojunctions. We found that Gd doping had a strong effect on the performance of the devices, and that the Gd:ZnO/p-Si heterojunctions formed with 1% Gd-doped ZnO were the most strongly rectifying, and had the highest barrier height and the lowest series resistance. Furthermore, the I–V measurements of the 1% Gd-doped ZnO/p-Si heterojunction exhibited the strongest response to light.

Fabrication and photocatalytic properties of Gd-doped ZnO nanoparticle-assembled nanorods

Gd-doped ZnO nanorods composed of nanoparticles were synthesized via an electrospinning combined with calcination route. It is revealed that the Gd-doped ZnO catalyst calcined at 500°C for a time of 7h shows the best photodegradation activity. A short calcination time of 1h gives rise to large amounts of residual carbon and low crystallinity of ZnO, which are adverse for charge separation. Increasing calcination time to 3h or 5h, suitable amounts of residual carbon that favors charge transfer plays a greater role than crystallinity. When the calcination time is further prolonged to 9h, a growth of nanoparticle size leads to a decreased photocatalytic performance. Thus, the efficiency for degradation activity is determined by the combinational effects of residual carbon, crystallinity and nanoparticle size.

Obtaining strong ferromagnetism in diluted Gd-doped ZnO thin films through controlled Gd-defect complexes

We demonstrate the fabrication of reproducible long-range ferromagnetism (FM) in highly crystalline GdxZn1−xO thin films by controlling the defects. Films are grown on lattice-matched substrates by pulsed laser deposition at low oxygen pressures (≤25 mTorr) and low Gd concentrations (x ≤ 0.009). These films feature strong FM (10 μB per Gd atom) at room temperature. While films deposited at higher oxygen pressure do not exhibit FM, FM is recovered by post-annealing these films under vacuum. These findings reveal the contribution of oxygen deficiency defects to the long-range FM. We demonstrate the possible FM mechanisms, which are confirmed by density functional theory study, and show that Gd dopants are essential for establishing FM that is induced by intrinsic defects in these films.

Defect-band mediated ferromagnetism in Gd-doped ZnO thin films

Gd-doped ZnO thin films prepared by pulsed laser deposition with Gd concentrations varying from 0.02–0.45 atomic percent (at. %) showed deposition oxygen pressure controlled ferromagnetism. Thin films prepared with Gd dopant levels (<Gd 0.112 at. %) at low oxygen deposition pressure (<25 mTorr) were ferromagnetic at room temperature. Negative magnetoresistance, electric transport properties showed that the ferromagnetic exchange is mediated by a spin-split defect band formed due to oxygen deficiency related defect complexes. Mott's theory of variable range of hopping conduction confirms the formation of the impurity/defect band near the Fermi level.

Synthesis, Characterization and Photocatalytic Application of Gd Doped ZnO Nanoparticles

Synthesis, Characterization and Photocatalytic Application of Gd Doped ZnO Nanoparticles

Magnetic coupling properties of Gd-doped ZnO nanowires studied by first-principles calculations

Magnetic coupling properties of Gd-doped ZnO nanowires are studied theoretically by using first-principles calculations. Several positions of Zn atoms that may be substituted by Gd atoms in ZnO nanowires are discussed. Numerical results show that the magnetic coupling is ferromagnetic when the two Gd atoms doped in ZnO nanowires are near each other. Injection of suitable amount of electrons can enforce these ferromagnetic properties in Gd-doped ZnO nanowires. It is also found that s-f coupling becomes remarkable when the Gd atoms are doped in ZnO nanowires, making the ferromagnetic coupling state more stable than the anti-ferromagnetic coupling state, and this is also the mechanism to elucidate the origination of ferromagnetic state in Gd-doped ZnO nanowires in experiments. These results will give a theoretical support for those who found experimentally that Gd-doped ZnO nanowires show ferromagnetic properties.

Ferromagnetism in Gd doped ZnO nanowires: A first principles study

In several experimental studies, room temperature ferromagnetism in Gd-doped ZnO nanostructures has been achieved. However, the mechanism and the origin of the ferromagnetism remain controversial. We investigate the structural, magnetic, and electronic properties of Zn48O48 nanowires doped with Gd, using density functional theory. Our findings indicate that substitutionally incorporated Gd atoms prefer occupying the surface Zn sites. Moreover, the formation energy increases with the distance between Gd atoms, signifying that no Gd-Gd segregation occurs in the nanowires within the concentration limit of ≤2%. Gd induces ferromagnetism in ZnO nanowires with magnetic coupling energy up to 21 meV in the neutral state, which increases with additional electron and O vacancy, revealing the role of carriers in magnetic exchange. The potential for achieving room temperature ferromagnetism and high TC in ZnO:Gd nanowires is evident from the large ferromagnetic coupling energy (200 meV) obtained with the O vacancy. Density of states shows that Fermi level overlaps with Gd f states with the introduction of O vacancy, indicating the possibility of s-f coupling. These results will assist in understanding experimental findings in Gd-doped ZnO nanowires.

Structural and magnetic properties of Gd-doped ZnO

We use density functional theory to investigate structural and magnetic properties of Gd doped ZnO, accounting for the impurity 4f states using the GGA + U method. (i) We calculate the binding energy of forming [Gd–Gd] dimers, [VO − GdZn] and [VZn − GdZn] complexes and find that while the formation of [VZn − GdZn] is favourable, [GdZn − GdZn] and [VO − GdZn] complexes are less likely to form. Next, (ii) we investigate the spacial arrangement of two (and three) GdZn impurities in a 3 × 3 × 2 supercell and find that the magnetic impurities are energetically favourable when occupying distant lattice sites. Finally, we study the nature of interactions between the magnetic impurities (iii) for Gd in nearest-neighbour and non-nearest-neighbour Zn sites, (iv) in the presence of Zn or O vacancies, and (v) with and without additional charge carriers. Our results show mainly paramagnetic behaviour. In a few cases, e.g. magnetic impurities occupying in-plane nearest-neighbour zinc sites with n-type carrier doping, weak ferromagnetic coupling is observed. This magnetic ordering is of the order of a few meV and can be easily destroyed by thermal fluctuations. We thus expect Gd:ZnO to show paramagnetic behaviour at temperatures approaching room temperature.

Sonocatalytic degradation of a textile dye over Gd-doped ZnO nanoparticles synthesized through sonochemical process

The present study was performed to sonochemically synthesize GdxZn1−xO (x=0–0.1) nanoparticles for sonocatalysis of Acid Orange 7 (AO7) in an aqueous medium. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis confirmed proper synthesis of Gd-doped sonocatalyst. 5% Gd-doped ZnO nanoparticles with band gap of 2.8eV exhibited the highest sonocatalytic decolorization efficiency of 90% at reaction time of 90min. The effects of initial dye concentration and sonocatalyst dosage on decolorization efficiency were evaluated. In the presence of sodium sulfate, sodium carbonate and sodium chloride the decolorization efficiency decreased from 90 to 78, 65 and 56%, respectively. Among various enhancers, the addition of potassium periodate improved the decolorization efficiency from 90 to 100%. The highest decolorization efficiency was obtained at pH value of 6.34 (90%). The decolorization efficiency decreased only 6% after 4 repeated runs. Therefore, Gd-doped ZnO nanoparticles can be used as a promising catalyst for degradation of organic pollutants with great reusability potential.

Spectroscopic and fiber optic ethanol sensing properties Gd doped ZnO nanoparticles

We report the structural, optical and gas sensing properties of prepared pure and Gd doped ZnO nanoparticles through solgel method at moderate temperature. Structural studies are carried out by X-ray diffraction method confirms hexagonal wurtzite structure and doping induced changes in lattice parameters is observed. Optical absorption spectral studies shows red shift in the absorption peak corresponds to band-gap from 3.42eV to 3.05eV and broad absorption in the visible range after Gd doping is observed. Scanning electron microscopic studies shows increase in particle size where the particle diameters increase from few nm to micrometers after Gd doping. The clad modified ethanol fiber-optic sensor studies for ethanol sensing exhibits best sensitivity for the 3% Gd doped ZnO nanoparticles and the sensitivity get lowered incase of higher percentage of Gd doped ZnO sample.

Structural and magnetic analysis of epitaxial films of Gd-doped ZnO

Zn${}_{(1\ensuremath{-}x)}$Gd${}_{x}$O epitaxial films prepared by reactive magnetron sputtering were studied using a combination of synchrotron based x-ray absorption spectroscopies, x-ray diffraction, and classical magnetometry. With nominal Gd concentrations of up to 16$%$ only paramagnetism is found. Reducing the oxygen content in the sputter gas provokes phase separation, however, the samples remain paramagnetic. The experimental findings are corroborated by first-principles density-functional theory calculations. In all cases a paramagnetic behavior is found with Gd atomic moments comparable to the experiment. The structural degradation with increasing Gd concentration is consistently found by experiment as well as theory.

Fluorescence-enhanced gadolinium-doped zinc oxide quantum dots for magnetic resonance and fluorescence imaging

We report here the development of Gd-doped ZnO quantum dots (QDs) as dual modal fluorescence and magnetic resonance imaging nanoprobes. They are fabricated in a simple, versatile and environmentally friendly method, not only decreasing the difficulty and complexity, but also avoiding the increase of particle’s size brought about by silica coating procedure in the synthesis of nanoprobes reported previously. These nanoprobes, with exceptionally small size and enhanced fluorescence resulting from the Gd doping, can label successfully the HeLa cells in short time and present no evidence of toxicity or adverse affect on cell growth even at the concentration up to 1 m m. These results show that such nanoprobes have low toxicity, especially in comparison with the traditional PEGylated CdSe/ZnS or CdSe/CdS QDs. In MRI studies, they exert strong positive contrast effect with a large longitudinal relaxivity (r 1) of water proton of 16 m m −1 s −1. Their capability of imaging HeLa cells with MRI implies that they have great potential as MRI contrast agents. Combining the high sensitivity of fluorescence imaging with high spatial resolution of MRI, We expect that the as-prepared Gd-doped Zn o QDs can provide a better reliability of the collected data and find promising applications in biological, medical and other fields.