Zn Doping Concentration Research Articles

Conductivity improvement of CuCrO2 nanoparticles by Zn doping and their application in solid-state dye-sensitized solar cells

Undoped and Zn-doped CuCrO2 nanoparticles were synthesized by sol–gel method as promising wide band gap p-type semiconductor materials for solid-state dye-sensitized solar cells (DSSCs). We studied the influence of Zn dopant concentration on structural, electrical and optical properties of CuCrO2 nanoparticles. The X-ray diffraction data indicated that the delafossite-to-spinel ferrite phase transition occurs by increasing the amount of Zn doping. The average nanoparticle size was determined about 40nm. A minimum value of electrical resistivity of 5.7Ωcm was obtained for doping concentration of 5%. Having optimized the Zn-doped CuCrO2 nanoparticles, solid-state DSSCs were fabricated using undoped and Zn-doped CuCrO2 (5%) as solid electrolytes. As the photoanode layer, the vertically aligned TiO2 nanorod arrays were grown on FTO glass using a hydrothermal method. Compared with undoped CuCrO2, the Zn-doped nanoparticles exhibited an improvement in photovoltaic properties. The overall efficiency enhancement of 39% was obtained for the dopant concentration of 5%. The improved power conversion efficiency is attributed to the lowered electrical resistivity and enlarged work function of Zn-doped CuCrO2 nanoparticles.

Structural, Magnetic, and Thermodynamic Evolutions of Zn-Doped Fe3O4 Nanoparticles Synthesized Using a One-Step Solvothermal Method

Zn-doped Fe3O4 magnetic nanoparticles represented as ZnxFe3-xO4 with different Zn contents of x varying from 0.0 to 1.0 were synthesized using a facile one-step solvothermal method. The Zn/Fe ratio in these particles could be accurately controlled using this facile synthesis technique. The ICP-OES and XRD measurements indicated that in the x range from 0 to 0.4 the doped Zn2+ may replace the Fe3+ at the A site and consequently the B-site Fe2+ changed to Fe3+, while above 0.4 the Zn2+ tends to replace the B-site Fe2+. The morphologies and size distributions of these samples characterized from the TEM showed that the nanoparticles appeared to aggregate into magnetic nanocrystal clusters with varying cluster sizes and different Zn doping contents. The magnetic measurement and Mossbauer spectra investigation revealed that the magnetic properties of the ZnxFe3-xO4 would exhibit a sensitive dependence with the doped Zn variations. Most importantly, the heat capacity studies illuminated that, at low temperatures...

Structural and optical properties of Zn-doped SnO2 films prepared by DC and RF magnetron co-sputtering

In the present work, the Zn-doped SnO2 (SnO2:Zn) thin films, with different Zn-doping concentration, were successfully prepared on Si (100) and glass substrates by direct current (DC) and radio frequency (RF) magnetron co-sputtering. The effects of dopant concentration, determined by the sputtering power applied on Zn target, on the structural, photoluminescent and optical performances of Zn-doped SnO2 films were investigated by X-ray diffraction(XRD), scanning electron microscope(SEM), energy dispersive X-ray (EDX),high-resolution transmission electron microscopy(HRTEM) and Ultraviolet–Visible-Near IR spectroscopy. The results show all these films exhibited excellent crystalline quality with tetragonal rutile structure. Two photoluminescence (PL) peaks related to Zn-doping were detected at about 351 nm (3.53 eV) and 369 nm (3.36 eV). Moreover, the average transmittance and the band gap energy of the films continuously decreased from 85% to 75% and from 3.52 eV to 3.34 eV, respectively, with the increase of the doping level. The excellent properties of Zn-doped SnO2 films make them capable for wider applications.

Synthesis of Hierarchical Porous Zn-Doped SnO2 Spheres and Their Photocatalytic Properties

The undoped and Zn-doped SnO2 products have been synthesized by a solvothermal method. With the Zn doping concentration changing from 0 to 20 mol%, the SnO2 morphology evolved from aggregated nanoprisms into hierarchical porous spheres. The products were characterized by x-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, selected area electron diffraction, UV-Vis absorption spectra, and photoluminescence spectra analysis. The results showed that Zn doping concentration significantly influenced on the microstructure, size, morphology, and optical property of the SnO2 products. Furthermore, the influence of the doping effect on the photocatalytic performance of the as-prepared SnO2 products was compared. The results revealed that 20 mol% Zn-doped SnO2 with hierarchical porous spheres exhibited excellent efficiency of photocatalytic activity, which could be attributed to their abundant oxygen vacancies, large specific surface area, and porous structure.

Unexpected observation of splitting of skyrmion phase in Zn doped Cu2OSeO3.

Polycrystalline (Cu1−xZnx)2OSeO3 (0 ≤ x ≤ 0.2) samples were synthesized using solid-state reaction and characterized by X-ray diffraction (XRD). The effect of Zn doping upon saturation magnetization (MS) indicates that the Zn favors to occupying Cu(II) square pyramidal crystallographic site. The AC susceptibility (χ′ac) was measured at various temperatures (χ′ac–T) and magnetic field strengths (χ′ac–H). The Zn doping concentration is found to affect greatly the M-T and χ′ac-T. The skyrmion phase has been inferred from the χ′ac-H data, and then indicated within the H-T phase diagrams for various Zn doping concentrations. The striking and unexpected observation is that the skyrmion phase region becomes split upon Zn doping concentration. Interestingly, second conical boundary accompanied by second skyrmion phase was also observed from dχ′ac/dH vs. H curves. Atomic site disorder created by the chemical doping modulates the delicate magnetic interactions via change in the Dzyaloshinskii-Moriya (DM) vector of distorted Cu(II) square pyramidal, thereby splitting of skyrmion phase might occur. These findings illustrate the potential of using chemical and atomic modification for tuning the temperature and field dependence of skyrmion phase of Cu2OSeO3.

Influence of Zn doping on structural, optical and electrical properties of nanocrystalline CdSe thin films

Nanocrystalline Zn doped CdSe thin films with different Zn contents are prepared by thermal evaporation using the Inert Gas Condensation technique. The prepared samples are characterized by Energy dispersive X-ray spectroscopy (EDX), Scanning electron microscope (SEM), X-ray diffractometer (XRD), UV–Vis-IR spectrophotometer and Photoluminescence (PL) techniques, respectively. SEM investigation reveals uniform distribution of the films over the entire substrate surface. XRD results indicate that Zn doped CdSe thin films grew with the hexagonal phase. The variation of the optical band gap with change in Zn dopant concentration has been studied. PL intensity increases for Zn 5% doped nanocrystalline CdSe thin films as compared to doping with Zn 1%. Electrical investigations have also been made for nanocrystalline Zn 1% and Zn 5% doped CdSe thin films. Hall measurements indicate that Zn 1% and Zn 5% doped CdSe thin films are of n type.

Understanding the role of Zn in improving the phase change behaviors of Sb2Te3 films

The Zn-doped Sb2Te3 films have been investigated systematically during the phase transformation process. It was found that, the increase of crystallization temperature in the Zn-doped Sb2Te3 films leads to its enhanced amorphous stability, and Zn incorporation can increase electrical resistance, widen optical band gap and refine crystalline grain size. The crystallization mechanism can be tuned into nucleation-dominated from growth-dominated type. Moreover, Sb2Te3 film with high Zn-doping concentration such as Zn38.8(Sb2Te3)61.2 film was found to exhibit a higher crystallization temperature (233°C), better data retention ability (keeping the amorphous state at 146.5°C for ten years), and wider band gap (0.839eV). A lower threshold of crystallization (~25ns) can be realized in the Zn38.8(Sb2Te3)61.2 film irradiated at the laser power of 70mW in comparison with that in the conventional Ge2Sb2Te5 film. We confirm that the Zn doping is responsible for a fast switching and the Zn38.8(Sb2Te3)61.2 compound is stable against segregation with cycling.

Investigation on pseudo-binary ZnSb–Sb2Te3 material for phase change memory application

Crystallization process and amorphous state stability of pseudobinary ZnSb–Sb2Te3 materials have been studied for application in phase change memory. The effects of Zn concentration and Sb content on crystalline resistance, crystallization temperature, crystallization activation energy and amorphous state stability of films have been studied. The microstructures of Sb-rich Zn–Sb–Te films were analyzed through X-ray diffraction. Different crystalline phases have been observed in annealed Sb-rich Zn–Sb–Te films. Low Zn-doping concentration Zn–Sb–Te films crystallized into rhombohedral Sb2Te3 phase while high Zn-doping concentration Zn–Sb–Te films crystallized into rhombohedral Sb phase. The crystallization activation energy (Ea) of Zn1.1Sb45.7Te53.2 and Zn5.2Sb46.3Te48.5 films were confirmed to be 2.0 and 2.93eV, while Ea of Zn16.0Sb47.3Te36.7 film increased to 3.2eV and further reached to 3.3eV for Zn19.7Sb48.1Te32.2 film. Zn addition increased the crystallization temperature and crystalline resistance of Zn–Sb–Te films largely, and enhanced the amorphous thermal stability and data retention ability of the films, while high Sb/Te ratio reveals the improvement in crystallization speed and good cycle ability. Therefore, Sb-rich Zn–Sb–Te film seems to be a good way to solve the contradiction between thermal stability and fast crystallization speed.

Phase transformation (cubic to rhombohedral): the effect on the NO2 sensing performance of Zn-doped flower-like In2O3 structures

Cubic In2O3 (bcc-In2O3) was transformed into a mixture of bcc-In2O3 and rhombohedral In2O3 (rh-In2O3) by Zn doping. The Zn-doped flower-like In2O3 structures consisted of many thin sheets with a length of 0.4–1 μm, and cubes with a length of 200 nm, while the size of the microflowers was 1–3.5 μm. The Zn doping concentration significantly affected the phase transformation and the overall morphology of In2O3. Furthermore, the analysis of N2 adsorption–desorption measurements showed that the Zn-doped flower-like In2O3 structures (sample S5) adsorbed the largest amount of N2 and had the biggest surface area (46.41 m2 g−1), which contributed to an improvement in gas sensing performance. Finally, sensors based on the mixture of bcc- and rh-In2O3 structures exhibited a much higher response to NO2 than the pure bcc-In2O3 (sample S1), and the Zn-doped flower-like In2O3 structures (sample S5) exhibited the highest response of 27.4 ± 2.5 for 5 ppm NO2. Thus, the gas sensing performance of In2O3 was enhanced significantly by the phase transformation.

Optical property theoretical study and mild-temperature synthesis of (Ga,Zn)N nanocrystals

Wurtzite GaN and (Ga,Zn)N nanocrystals with the size of 8–20nm were synthesized by the solid-phase thermal decomposition method at mild temperature of 350–650°C. This synthesis method is a simple and low cost method. From the further study on the luminescence mechanism, Zn dopant introduces new energy levels in the band gap of GaN nanocrystals, which effectively induces the fluorescence emission in the visible region. In addition, the VN-H defect significantly affects the optical properties of nanocrystals. Moreover, GaN nanocrystals with a proper Zn-doping concentration will produce a white light.

X-ray photoelectron spectroscopy study and humidity sensing properties of Zn doped SnO2 thin films

Undoped and Zn-doped SnO2 thin films are deposited onto glass substrates by sol–gel spin coating method. All the films are characterized by X-ray photon spectroscopy (XPS) and Fourier transform infra-red spectroscopy (FTIR). XPS shows that Sn presence as valence of Sn4+ in the prepared SnO2 thin films instead of Sn2+. In addition, it also exhibits the amount of Zn in SnO2 thin films, which increases with increasing Zn doping percentage. The Zn (2P3/2) peak is symmetric and centred at around 1,021.73 eV which shifts to the lower binding energy of 1,020.83 eV for 15 at.% Zn doped SnO2 thin film. FTIR study is used to describe the local environment of undoped and Zn-doped SnO2 thin films which also confirms the synthesis of undoped and Zn-doped SnO2 thin films. It is found that the resistance of SnO2 thin films increases as Zn doping concentration increases at room humidity. The resistance of all the samples increases as relative humidity (RH) increases. The sensitivity of SnO2 thin films increases as RH increases while it decreases as Zn doping percentage increases. Response time of SnO2 thin film decreases as Zn doping percentage increases and recovery time slightly increases with doping percentage.

Enhanced thermal stability and electrical behavior of Zn-doped Sb2Te films for phase change memory application

Zn-doped Sb2Te films are proposed to present the feasibility for phase-change memory application. Zn atoms are found to significantly increase crystallization temperature of Znx(Sb2Te)1−x films and be almost linearly with the wide range of Zn-doping concentration from x = 0 to 29.67 at.%. Crystalline resistances are enhanced by Zn-doping, while keeping the large amorphous/crystalline resistance ratio almost constant at ∼105. Especially, the Zn26.07(Sb2Te)73.93 and Zn29.67(Sb2Te)70.33 films exhibit a larger resistance change, faster crystallization speed, and better thermal stability due to the formation of amorphous Zn-Sb and Zn-Te phases as well as uniform distribution of Sb2Te crystalline grains.

The Multiferroic Properties of Zn Doped BiFeO3 Thin Films

BiFe1−x Zn x O3 thin films (x=0, 0.05, 0.1, 0.2, and 0.3) were prepared on LaNiO3 buffered surface oxidized Si substrates using pulsed laser deposition. The effect of Zn dopants on the structural, electrical, magnetic properties, and exchange bias on NiFe layers for BiFeO3 thin films has been systematically investigated. X ray diffraction and Raman spectra show that BiFe1−x Zn x O3 thin films have polycrystalline rhombohedral structure with Zn concentration smaller than 5 %, and a large amount of the impurity phase of Bi2Fe4O9 with further increasing Zn concentration above 10 %. With 5 % Zn doping in BiFeO3, the film quality is improved with larger grain size, better ferroelectricity, and larger magnetization. The exchange bias of BiFe1−x Zn x O3 on a 3.6 nm thick NiFe layer drastically decreases with increasing Zn doping concentration, and totally disappears with the Zn concentration larger than 10 %, indicating that the canted antiferromagnetic spin structure of BiFeO3 was suppressed with increasing the Zn doping concentration.

Synthesis of nonstoichiometric zinc ferrite nanoparticles with extraordinary room temperature magnetism and their diverse applications

A series of nonstoichiometric zinc ferrite (ZndFe3−dO4) nanoparticles with Zn-dopant concentration d ranging from 0 to 0.5 was synthesized via thermal decomposition route employing oleic acid as surfactant. The zinc dopant concentration was controlled by the ratio of Zn/Fe precursors. High room temperature saturation magnetization of 110 emu g−1 was obtained for large Zn ferrite particles (more than 100 nm) with nominal composition of Zn0.468Fe2.532O4. The origin of the extraordinary magnetic property was revealed as the Zn substitution of Fe atoms at the tetrahedral site (A site) in the spinel magnetite phase. It was found that the precursor/surfactant ratio was an important parameter for the control of the shape and size of as-synthesized Zn ferrite particles. The details were investigated through a series of experimental work. Size-dependent applications, such as radar absorption and magnetic fluid hyperthermia, were further studied. Both applications required magnetic particles with high saturation magnetization, hence our samples displayed advantages over Fe3O4 magnetite nanoparticles. Especially for magnetic fluid hyperthermia, 26 nm Zn ferrite nanoparticles coated by P-mPEG polymer showed superior biocompatibility and heating efficiency, implying the potential usefulness to in vivo cancer therapy.

Zn-Doped SnO2 with 3D Cubic Structure for Humidity Sensor

Zinc doped tin oxide (Zn-doped SnO2) with three dimension (3D) cubic structure has been successfully grown on top of ZnO thin film. In this research, ZnO thin films prepared by rf magnetron sputtering and cubic structure of Zn-doped SnO2 developed by immersion method at low temperature are reported. The effects Zn doping concentration at (0 to 5 at.%) on the Zn-doped SnO2 were studied to form cubic structure. The performance of humidity sensor was tested using current-voltage (I-V) measurement (Keithley 2400) in a controlled chamber. The structural characterization was performed using field emission scanning electron microscopy (FESEM). The sensor performance at 5% doping concentration was found to be highly sensitive and can be used as humidity sensor. The size of cubic structure decreases with the increase in doping concentration.

Zn-Doped p-Type Gallium Phosphide Nanowire Photocathodes from a Surfactant-Free Solution Synthesis

Gallium phosphide (GaP) nanowire photocathodes synthesized using a surfactant-free solution-liquid-solid (SLS) method were investigated for their photoelectrochemical evolution of hydrogen. Zinc as a p-type dopant was introduced into the nanowires during synthesis to optimize the photocathode's response. Investigation of the electrical properties of Zn-doped GaP nanowires confirmed their p-type conductivity. After optimization of the nanowire diameter and Zn doping concentration, higher absorbed photon-to-current efficiency (APCE) over the spectrum was achieved. The versatility of the SLS synthesis and the capability to control the electrical properties suggest that our approach could be generalized to other III-V and II-VI semiconductors.

Zn-doped TiO2 electrodes in dye-sensitized solar cells for enhanced photocurrent

Porous nanocrystalline Zn/TiO2 materials were synthesized employing agarose gel as a template, achieving a maximum Zn-doping concentration of around 2 at.%. Low Zn-doping concentrations (e.g. <1 at.%) improved the photocurrent of the dye-sensitized solar cell when these materials were applied as the working electrode, as n-type doping favors electron transportation. Compared to the efficiency of the undoped sample, 6.7%, the 0.5 at.% sample showed a much higher efficiency of 7.6%. Further doping decreases the performance of the device as it introduces deficiencies that act as electron–hole recombination centers.

Crystal structure and electrochemical properties of LiFe1−xZnxPO4 (x ≤ 1.0)

A series of LiFe1−xZnxPO4 (0.0 ≤ x ≤ 1.0) compounds were prepared by solid-state reaction. Effects of the substitution of Zn for Fe on crystal structure and electrochemical properties of LiFe1−xZnxPO4 were investigated. The results show that single-phase regions of LiFe1−xZnxPO4 with orthorhombic (space group Pmna) and monoclinic (Cc) structures were found for the compounds with low Zn (or high Fe) contents of 0.0 ≤ x ≤ 0.30 and high Zn (or low Fe) contents of 0.90 ≤ x ≤ 1.0, respectively. The LiFe1−xZnxPO4 compounds with medium Zn (or Fe) contents of 0.35 ≤ x ≤ 0.80 are two-phase mixtures containing both the orthorhombic and the monoclinic phases. Systematic variations of unit-cell parameters a, b, c, and volume V with the Zn content determined by X-ray diffraction have also been obtained. Our electrochemical study show that the conductivity of LiFe1−xZnxPO4 increases by almost 2 orders of magnitude from 2.13 × 10−9 to 1.27 × 10−7 Scm−1 as the Zn content increasing from x = 0 to 0.3. The initial specific capacity decreases and the cycle performance increase with increasing Zn-doping content in the four orthorhombic LiFe1−xZnxPO4 compounds. Among the four LiFe1−xZnxPO4 compounds, LiFe0.8Zn0.2PO4 has the highest capacity retentions after 6 to 20 cycles and the capacity retention is 93.7% after 20 cycles, even though the initial discharge specific capacity of LiFe0.8Zn0.2PO4 is lower than those of LiFeZnPO4 and LiFe0.9Zn0.1PO4. LiFe0.7Zn0.3PO4 has the highest capacity retention of 97% after 20 cycles.

Suppression of superconductivity in Zn-doped SmFeAsO0.8F0.2 system

A series of SmFe1−xZnxAsO0.8F0.2 samples with x=0, 0.05, 0.1, 0.2 and 0.4 have been successfully synthesized using a solid state method. The lattice parameters are found to increase with increasing Zn doping content. The superconductivity has been definitely suppressed by Zn doping at Fe site with the transition temperature Tc being reduced from 52.5K to 23.3K for the sample of x=0.05, and to 18.2K for the sample of x=0.1. For the samples with x>0.1, the superconducting transition vanishes, and, at the meantime, the spin-density-wave anomaly recovers at 140K. The metal to semiconductor transition is also observed in the SmFe1−xZnxAsO0.8F0.2 system. The behavior of SmFe1−xZnxAsO0.8F0.2 is very different from that of REFeAsO (RE=rare earth metal), which reveals a very strong electron correlation in SmFe1−xZnxAsO0.8F0.2.

Unusual enhancement in electrical conductivity of tin oxide thin films with zinc doping

Electrical conductivity of SnO(2)-based oxides is of great importance for their application as transparent conducting oxides (TCO) and gas sensors. In this paper, for the first time, an unusual enhancement in electrical conductivity was observed for SnO(2) films upon zinc doping. Films with Zn/(Zn + Sn) reaching 0.48 were grown by pulsed spray-evaporation chemical vapor deposition. X-Ray diffraction (XRD) shows that pure and zinc-doped SnO(2) films grow in the tetragonal rutile-type structure. Within the low doping concentration range, Zn leads to a significant decrease of the crystallite size and electrical resistivity. Increasing Zn doping concentration above Zn/(Zn + Sn) = 0.12 leads to an XRD-amorphous film with electrical resistivity below 0.015 Ω cm at room temperature. Optical measurements show transparencies above 80% in the visible spectral range for all films, and doping was shown to be efficient for the band gap tuning.