Mo-doped ZnO Research Articles

Impact of Mo doping on photo-sensing properties of ZnO thin films for advanced photodetection applications

This work explored the impact of Mo-doping on the structural, optical, photophysical, and electrical characteristics of ZnO thin films and their potential application to the UV light detection properties was investigated. The hexagonal structure of the films without any impurities or extra phases was confirmed by X-ray diffraction and FT-Raman spectroscopy. The crystallite size reduced from 36 nm to 25 nm with the addition of 3 wt% of Mo in ZnO. The EDX/SEM e-mapping verified the elemental composition and uniform Mo doping throughout the films. The FESEM images revealed spherical nanoparticles with smaller grains size for higher Mo-doping levels. The absorption spectra were recorded from UV to NIR range, and the bandgap was observed to increase from 3.25 eV for pure ZnO to 3.42 for 3% Mo-doped ZnO sample. The Mo-doped ZnO film showed PL quenching, which indicates charge transfer and suppression of defect sates in the ZnO films via Mo-doping. The time-resolved fluorescence spectra (TRFS) of these films revealed that the carrier lifetime increased from 80 ps for pure ZnO to 144 ps for 3% Mo-doped ZnO thin film. The electrical parameters including resistivity, carrier mobility, concentrations, and sheet resistance of fabricated films were evaluated by Hall-effect measurement. The resistivity and mobility were observed to decrease from 9.33×104 Ω.cm, 55.1 cm2/V.s to 2.03×103 Ω.cm 15.4 cm2/V.s for 3% Mo-doped ZnO thin film, while carrier density increased. The photodetection study demonstrated that the responsivity, detectivity, external quantum efficiency and response time of devices were significantly enhanced with Mo idoping.

Doping zinc oxide (ZnO) nanoparticles with molybdenum boosts photocatalytic degradation of Rhodamine b (RhB): Particle characterization, degradation kinetics and aquatic toxicity testing

Undoped and Mo-doped ZnO photocatalysts were synthesized by hydrothermal method and characterized by field emission scanning electron microscopy coupled to energy dispersive- X ray spectroscopy (FESEM- EDAX), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) and thermogravimetric analysis (TGA) analyses. The photocatalytic activity of the photocatalysts and the kinetic of the reaction was assessed by degrading Rhodamine B under UV and sun light irradiation under variable conditions. Eventually the acute toxicity of undoped and doped nanophotocatalysts, RhB and the consequences of photocatalytic treatment were assessed using zebrafish (Danio rerio). The analytical results showed that Mo doping increased catalysts specific surface area and thermal stability. The results of photocatalytic degradation demonstrated that Mo doping has increased the photocatalytic activity under both UV and sunlight irradiation with 95 % RhB degradation efficiency and 41 % TOC removal efficiency over 30 min. The reusability of photocatalysts showed constant degradation efficiency over multiple cycles. The 96 h LC50 of undoped ZnO, Mo doped ZnO and RhB were 482.71 and 459.05 and 20.38 mg/L, respectively. Moreover, a lower toxicity was observed for the treated compared to untreated dye solution. This study indicates a promising potential of Mo-doped ZnO nanophotocatalysts for wastewater treatment and warrants further studies in this direction.

Compositional mapping of Mo-doped ZnO thin films: Mechanical, nano-surface and ToF-SIMS analyses

ZnO and Mo-doped ZnO thin films were grown using the spray pyrolysis process with variations in Mo doping concentrations. The films were characterized with a comprehensive compositional analysis, including electron dispersive X-ray (EDX), X-rays photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS), along with grazing incidence X-ray diffraction(GIXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV–Vis spectroscopy to investigate their structural, morphological, optical and chemical compositions. Micro-hardness analysis was performed on films as a function of the Mo content. GIXRD analysis detected the presence of characteristic peaks of ZnO along the (100), (002) and (101) planes. The presence of Zn, O, and Mo in the synthesized samples was revealed by EDX, XPS, and ToF-SIMS results, which matched the experimental values of a pure and Mo:ZnO-x composition. XPS analysis revealed the Mo6+ oxidation state of molybdenum present in Mo:ZnO films. From UV–Vis absorption spectroscopy, the bang gap was observed to increase with Mo content, up 5 at.%, and located in the 3.18 – 3.24 eV interval. These results will be helpful in the synthesis of Mo:ZnO films for relevant applications, including sensing, optoelectronics and antimicrobial.

Green synthesis and characterizations of bi-functional Mo-doped ZnO nanostructures for antimicrobial and photocatalytic applications

The preparation of effective and excellent antimicrobial agent is becoming a severe issue from last few decades against human tested bacteria. Also, the polluted wastewater from industries severely required a sophisticated photocatalyst. Beside of all other semiconductor oxides, ZnO gained the great attention because of its unique and versatile antimicrobial and photocatalytic properties. In this work, its antimicrobial and photocatalytic nature is improved by preparing using green synthesis approach i.e extract of moringa oleifera seeds as these are naturally anti-oxidizing and antimicrobial agents. The XRD spectroscopic tool was used to reveal the structural properties of as prepared samples. SEM and HRTEM techniques were employed for in depth morphological study. EDX analysis tool was employed to check the purity and for compositional analysis of samples. For further structural study, SAED technique was also employed. UV–vis and PL tools were used to investigate the optical properties and recombination rates of charge carriers. The as developed nanostructures possessing much reduced grain sizes have significantly improved the antibacterial and photocatalytic performance of ZnO based samples by offering much enhanced active surface area and active sites for their working. The charge carriers’ dynamics was evaluated by studying EIS and photocurrent intensity response by as prepared samples. The green synthesized Mo doped ZnO has exhibited a reduced band gap i.e 3.11 eV than 3.25 eV offered by pure ZnO. The antimicrobial activity against B. subtilis and E. coli bacteria explored that the as green synthesized Mo doped ZnO nanomaterial was very competent for the inhibition of bacterial growth. Moreover, this green Mo-doped ZnO sample has also exhibited its excellent photocatalytic nature against a well-known rhodamine-B water pollutant by degrading its 89.6% just after 180 min. Also, this sample has shown good catalytic stability i.e 81 %. The reproducibility of the samples was made sure by preparing batches of three samples and taking the best out of them showing very small performance error. These superior antimicrobial and photocatalytic properties shown by green synthesized Mo-doped ZnO have opened new platform for bacteria inhibition and water purification applications.

Precursor Molarity Influence on Sprayed Mo-doped ZnO Films for solar cells

Objectives: Current research focuses on the role of precursor molarity effect on sprayed Mo-doped ZnO films and their suitability as window layers in solar cells. Methods: Molybdenum (Mo) doped zinc oxide (MZO) thin films were deposited by the technique of spray pyrolysis, varying the Zn molarity in the range, of 0.01 M to 0.20 M at a constant substrate temperature of 400 ◦C. The Mo doping concentration was constant at 2 at. %. Findings: The XPS studies witnessed the presence of Mo and Zn in +6 and +2 state respectively. The XRD pattern showed both (111) and (002) as strong peaks, confirming the hexagonal wurtzite crystal structure. The optical investigations showed that the MZO films with Zn molarity 0.10 M exhibited high optical transmittance having a wide energy band gap. Films with zinc molarity of 0.10 M showed low resistivity and high mobility. The prepared CTS/MZO hetero junction solar cells performance was studied by evaluating parameters such as open circuit voltage (Voc) of 0.14 V, short circuit current density (Jsc) of 6.46 mA cm-2, a fill factor (FF) of 0.27, and a conversion efficiency of 0.25 %. Novelty: Studies on the physical properties of Mo:ZnO layers such as Ritveld refinement analysis and Haze were reported first time. CTS/MZO hetero junction solar cells have not yet been published. The observed results are analogous to improve the efficiency of solar cells using environmentally benign materials. Keywords: Spray pyrolysis; Thin films; XRD; Optical properties; Haze; Hall measurements

Effects of coexistence of Mo and Zn vacancies with different valence states and interstitial H on the magneto-optical properties of ZnO: First-principles calculations

Research progress has been achieved on the influence of transition metal Mo doping and Zn vacancy coexistence on the magnetic and optical properties of ZnO. However, the interstitial H impurity in the Mo-doped ZnO system has been neglected. In this work, first principles were used to calculate the effects of the coexistence of different valence states of Mo and Zn vacancies and interstitial H on the magneto-optical properties of ZnO under the framework of density functional theory. Magnetic results showed that when Mo and Zn vacancies have +6 and 0 valences, respectively, the Zn22Mo6+O24(VZn0) system without interstitial H shows the largest magnetic moment and strongest magnetism. In the doped system, the local electrons of the spin-polarized O-2p orbital behave as acceptors near the valence band maximum, and the itinerant electrons behave as donors near the conduction band minimum. The itinerant electrons of the O-2p orbital adjacent to the Zn vacancy mainly contribute to the magnetic properties of the Zn22Mo6+O24(VZn0) system, and they are most beneficial to the design and preparation of new ZnO-based dilute magnetic semiconductors. Analysis of optical properties found that the Zn22Mo6+HiO24(VZn0) system with interstitial H have the easiest separation of electron–hole pairs, the highest mobility, the longest relaxation time, and the strongest built-in electric field when the Mo and Zn vacancies have +6 and 0 valences, respectively. Therefore, this system has the longest carrier lifetime and best activity. In addition, the absorption spectrum of the Zn22Mo6+HiO24(VZn0) system shows the most remarkable red shift in the visible and near-infrared regions. When pH = 0/7, the Zn22Mo6+HiO24(VZn0) system shows the strongest photocatalytic reduction ability. Given its carrier lifetime and activity, absorption spectrum, and redox ability, the Zn22Mo6+HiO24(VZn0) system is relatively the best for the design and preparation of new ZnO-based photocatalysts.

Free-Standing ZnO:Mo Nanorods Exposed to Hydrogen or Oxygen Plasma: Influence on the Intrinsic and Extrinsic Defect States.

Cationic doping of ZnO nanorods has gained increased interest as it can lead to the production of materials with improved luminescent properties, electrical conductivity and stability. We report on various Mo-doped ZnO powders of nanorods synthesized by the hydrothermal growth method. Further annealing or/and cold hydrogen or oxygen plasma modification was applied. The atomic structure of the as-grown and plasma-modified rods was characterized by X-ray diffraction. To identify any possible changes in morphology, scanning electron microscopy was used. Paramagnetic point defects were investigated by electron paramagnetic resonance. In particular, two new types of defects were initiated by the plasma treatment. Their appearance was explained, and corresponding mechanisms were proposed. The changes in the luminescence and scintillation properties were characterized by photo- and radioluminescence, respectively. Charge trapping phenomena were studied by thermally stimulated luminescence. Cold plasma treatment influenced the luminescence properties of ZnO:Mo structures. The contact with hydrogen lead to an approximately threefold increase in intensity of the ultraviolet exciton-related band peaking at ~3.24 eV, whereas the red band attributed to zinc vacancies (~1.97 eV) was suppressed compared to the as-grown samples. The exciton- and defect-related emission subsided after the treatment in oxygen plasma.

First principle study of electronic structure and optical properties of Mo doped ZnO with different concentrations

The technology of doping molybdenum into zinc oxide (ZnO) is an effective method to increase the electron concentration. In this presentation, Mo-doped ZnO (MZO) models with different Mo doping concentrations are constructed to systematically reveal the effect of Mo doping concentration on the photoelectric performance of ZnO. Moreover, the photoelectric performances, such as band structure, electronic conductivity, absorption, reflectivity and transmittance, have been investigated by means of the first-principles method based on density functional theory (DFT). The results indicated that MZO materials are all n-type semiconductors. Both the band gaps and electric conductivities were grown as the Mo doping concentration increased. Furthermore, the absorption and reflectance of the MZO increased, and the transmittance decreased with the increase of Mo doping concentration. Moreover, when the MZO materials are performed as the thin films, the light transmittance of MZO increased as the thickness of the thin films decreased. Especially, in the range of yellow light to red light, the transmittance of MZO was obviously greater than that of ZnO. Accordingly, the conductivity and optical performance of MZO materials are extreme sensitivity to the Mo doping concentration and thin film thickness, and should be optimized. This result provided theoretical guidance for the preparation of Mo-doped ZnO transparent conductive films.

Effects of different valence states of Mo and point vacancies on magneto-optical properties of ZnO

Experimental studies have been conducted to characterize the physical properties of Mo-doped ZnO. However, they have not considered the effects of different valence states and point vacancies on the magneto-optical performance of the system. The present study adopted the plane-wave ultrasoft pseudopotential + U method within the framework of spin density functional theory. The formation energy, electronic structure, and optical properties of ZnO systems with coexisting different valence states of Mo and point vacancies were calculated. Results showed that the formation energy of all doping systems was negative under Zn-rich and O-rich conditions, but the formation energy was relatively lower under O-rich conditions than under Zn-rich conditions. Compared with Mo6+ and Mo5+ when the concentration of O vacancies or Zn vacancies was the same, Mo6+-doped ZnO had the lowest formation energy, was the easiest to dope, and had the most stable system structure. Zn34Mo5+O36 and Zn34Mo6+O36 systems exhibited ferromagnetism, and their Curie temperature was above room temperature. The Zn34Mo6+O36 system had the largest magnetic moment, which is beneficial for designing and preparing new types of diluted magnetic semiconductors. The band gap widths of the Zn34Mo5+O36 (3.04 eV) and Zn34Mo6+O36 (2.92 eV) systems were both narrower than that of the pure ZnO system. By comparison, the band gap widths of the Zn35Mo5+O35 and Zn35Mo6+O35 systems were 4.07 and 3.94 eV, respectively. Although the band gap width widened, under light excitation conditions, the valence band electrons could absorb the photons of lower energy to transition to the impurity energy level, and then transition further from the impurity energy level to the conduction band. During the hierarchical transition, visible light and infrared light effects still occurred. The range of photon energy response of all doping systems expanded, and the absorption spectrum red-shifted in the light-absorption edge within the low-energy (0–3.2 eV) range. In particular, the Zn35Mo6+O35 system exhibited the strongest polarization ability, photoelectric field strength, and charge-binding ability in the low-energy region. Moreover, the dielectric and absorption peaks of the imaginary part of the dielectric function were relatively large, and the red-shift of the absorption spectrum was relatively substantial. Therefore, the Zn35Mo6+O35 system is useful in designing and preparing novel ZnO-based photocatalysts.

Structural and Dielectric Properties of Zn1-xMoxO Nanoparticles

Abstract: In this work, samples of zinc oxide nanoparticles doped by molybdenum (Zn1-xMoxO with 0 ≤ x ≤ 0.1) were prepared by using the wet co-precipitation method. The characterization of the prepared samples was carried out by means of X-ray powder diffraction (XRD). The samples reserved their hexagonal wurtzite structure with Mo doping and showed a decrease in the crystallite size up to x = 0.04 followed by a further increase. On the other hand, dielectric measurements were performed using an LCR meter. The effect of frequency and temperature on the dielectric properties such as the real and imaginary parts of dielectric constant (ε^' and ε'', respectively), dielectric loss (tanδ) and ac-conductivity (σ_ac) of Mo-doped zinc oxide samples, was studied in the frequency range (100 Hz - 1 MHz) and at temperatures (300 - 773 K). The values of room temperature dielectric parameters were found to be strongly dependent on the Mo-doping. However, the increase in temperature caused an enhancement in the values of the dielectric parameters, particularly at 773 K. Keywords: Zinc oxide, XRD, Dielectric constants, Ac-conductivity.

Optoelectronic properties and anisotropic stress of Mo:ZnO thin films deposited on flexible substrates by radio frequency magnetron sputtering.

This research investigated the optoelectronic properties and anisotropic stress of Mo-doped ZnO (MZO) films, which were deposited on polyethylene terephthalate and polycarbonate flexible substrates with radio frequency magnetron sputtering. The optical properties, x-ray diffraction (XRD) spectra, Hall effect measurements, and self-made phase-shift shadow moiré interferometer readings were utilized to evaluate the performances of the MZO films. Based on the results, the transmittance and (002) peak size of the XRD spectra decreased when the substrate temperature increased. However, this took place especially when the oxygen flow was on the increase. Also, carrier mobility, carrier concentration, and anisotropic stresses increased at higher substrate temperatures, but this was not the case when the oxygen flow increased. The energy gap (Eg) of the MZO films showed a blueshift with an increase in the substrate temperatures, but this rather changed to a redshift when the oxygen flow was observed to be on the rise.

First-principles analysis of ferromagnetic properties of molybdenum-doped wide-band-gap oxides

ABSTRACTThe possibility of ferromagnetic ordering in four different Mo-doped oxide semiconductors has been studied theoretically using density functional theory. All four systems, namely Mo-doped TiO2, SnO2, MgO and ZnO, show energetically stable ferromagnetic ordering. In addition, the Mo-doped MgO system shows half-metallic ferromagnetism. From magnetic density calculations, it has been found that for all systems, the 4d electrons of the dopant Mo atoms are the main source of magnetism. Bader analysis shows a higher positive charge on Mo in the case of TiO2 and SnO2 compared to MgO and ZnO.

Mo-doped ZnO nanoflakes on Ni-foam for asymmetric supercapacitor applications.

A single-step hydrothermal route for synthesizing molybdenum doped zinc oxide nanoflakes was employed to accomplish superior electrochemical characteristics, such as a specific capacitance of 2296 F g−1 at current density of 1 A g−1 and negligible loss in specific capacitance of 0.01025 F g−1 after each charge–discharge cycle (up to 8000 cycles). An assembled asymmetric supercapacitor (Mo:ZnO@NF//AC@NF) also exhibited a maximum energy density and power density of 39.06 W h/kg and 7425 W kg−1, respectively. Furthermore, it demonstrated a specific capacitance of 123 F g−1 at 1 A g−1 and retained about 75.6% of its initial capacitance after 8000 cycles. These superior electrochemical characteristics indicate the potential of this supercapacitor for next-generation energy storage devices.

Electrical and Photoluminescence Properties of Mo-doped ZnO Films Deposited by Spray Pyrolysis

Spray deposited Mo-doped zinc oxide (MZO) films were grown on glass substrates at different substrate temperatures (Ts)that varied in the range of 300°C-450 °C at aconstant Mo-doping concentration of 2 at. %.XRD spectra revealed better crystallinity of films prepared atTs400 °C. FTIR spectra showed the vibrational modes related toZn–O bonding.Photoluminescence spectra of MZO films showed a peakrelated toviolet emissionsbetween 400 nm and 420 nm. Electrical analysis showed n type semiconducting nature of the films and the films grown at Ts= 400 °C hadlow resistivity and high mobility.Adetailed analysis on theeffect of substrate temperatureon photoluminescence and electrical propertiesof MZO films wasdiscussed and reported.

A critical study of the optical and electrical properties of transparent and conductive Mo-doped ZnO films by adjustment of Mo concentration

Mo-doped zinc oxide (ZnO: Mo) transparent conductive thin films were prepared on the glass substrates using simple chemical spray pyrolysis technique by varying the Mo doping concentration in the range, 0–5 at.% at a constant substrate temperature, 400 °C. The effect of Mo-doping concentration on the physical behavior of ZnO films was investigated. The X-ray Photoelectron Spectroscopy (XPS) analysis confirmed the presence of Zn, O, and Mo in the layers with Mo in +6 state. The X-ray diffraction (XRD) patterns exhibited hexagonal wurtzite crystal structure without any secondary phases. The microstructural analysis revealed the spherical nut-shaped grains over the substrate surface. The optical studies revealed that the films with Mo-doping concentration of 2 at.% showed high optical transmittance and a wide band gap than pure and highly Mo-doped ZnO films. From the optical transmittance versus wavelength data, the refractive index, extinction coefficient, dispersion constants were evaluated. In addition, other optical parameters such as the optical conductivity, dielectric constants, dissipation factor, electron energy loss functions and Haze were also calculated. The FTIR studies revealed the presence of modes related to ZnO. Finally the electrical parameters such as resistivity, charge carrier mobility and density of ZnO: Mo films were also analyzed and presented.

The Optical and Electrical Properties of MZO Transparent Conductive Thin Films on Flexible Substrate

In this paper the optical and electrical properties of Mo doped ZnO (MZO) thin films on flexible substrate made by DC sputtering was investigated. The electrical, optical and micro-structural characteristics of MZO thin films made using different deposition parameters was also studied. XRD analysis showed that all the films exhibited strong (0 0 2) MZO preferential orientation. It was found that the average visible light transmittance of all the MZO thin films was about 70%. The resistivity was 6.02 × 10−3 Ω-cm and electron mobility, from the Hall effect, was 39 cm2/Vs.

Effect of Mo doping concentration on the physical properties of ZnO studied by first principles

The experimental results of red-shift and blue-shift in absorption spectrum of Mo-doped ZnO are in mutual contradiction, and this phenomenon has not been explained rationally so far. For explaining this phenomenon, we analyze the energy band structure, state density, and absorption-spectrum distributions for each of Zn0.9583Mo0.0417O, Zn0.9375Mo0.0625O and Zn14Mo2O by first-principles calculation. The results show that within a limited doping amount range of 2.08 at%-3.13 at%, the higher Mo doping amount results in higher doping system volume, higher formation energy, lower system stability, and more difficult to dope. Meanwhile, all doping systems are converted into n-type degenerate semiconductors. Compared with the band gap of pure ZnO, the band gap of each doping system becomes narrow and the absorption spectrum shows red-shift. The higher the Mo doping amount, the weaker the narrowing of band gap becomes and the weaker the red-shift in absorption spectrum as well as the lower the electronic effective mass and the lower the electronic concentration; the lower the electronic mobility, the lower the electronic conductivity is; the lower the electronic magnetic moment is. The Curie temperature of doping system can reach a temperature higher than room temperature.

Effect of substrate temperature on the structure, electrical and optical properties of Mo doped ZnO films

Mo-doped ZnO (MZO) transparent conductive thin films were prepared on glass substrate under various substrate temperature from 50°C to 200°C. The microstructural, electrical and optical properties of the MZO films were investigated by X-ray diffraction (XRD), Hall effect and UV–vis spectrophotometer. Based on XRD measurements, all films are polycrystalline with preferential c-axis growth. The lowest resistivity was obtained to be 2.8×10−3Ω·cm. According to X-ray photoelectron spectroscopy (XPS) measurement, the valence of the Mo ions in the ZnO matrix is a mixture of +5 and +6. In addition, the transmittance of the film is ∼80% throughout the visible light region. Our results indicate that the MZO films are suitable for potential transparent optoelectronic applications.

Effect of growth rate on the structure and physical properties of Mo doped ZnO films

In this work, Mo-doped ZnO (MZO) films were prepared on glass substrate via magnetron co-sputtering of ZnO and Mo targets. Based on the x-ray diffraction (XRD) measurements, all films are crystallized into wurtzite ZnO structure with its c-axis perpendicular to the substrates. Higher growth rate leads to slightly decrease of the optical energy gap from 3.35 eV to 3.25 eV. Hall effect measurements were carried out which suggested the lowest resistivity of 2.8 × 10−3 Ω cm. In addition, UV–vis measurement shows that the transmittance in the visible light region is ∼80%, which indicates that MZO film is suitable for potential transparent optoelectronic applications.

전기방사방법에 의해 합성된 ZnO 중공 나노섬유의 trimethylamine 가스 감응 특성

Abstract Pure and Mo-doped ZnO hollow nanofibers were prepared by single capillary electrospinning and their gas sensing characteristicstoward 5 ppm ethanol, trimethylamine (TMA), CO and H 2 were investigated. The gas responses and responding kinetics were depen-dent upon sensing temperature and Mo doping. Mo-doped ZnO hollow nanofibers showed high response to 5 ppm TMA ( R a /R g = 111.7,R a : resistance in air, R g : resistance in gas) at 400 o C, while the responses of pure ZnO hollow nanofibers was low (R a /R g = 47.1). In addi-tion, the doping of Mo enhanced selectivity toward TMA. The enhancement of gas response and selectivity to TMA by Mo dopingto ZnO nanofibers was discussed in relation to the interaction between basic analyte gas and acidic additive materials. Keywords: ZnO nanofiber, Molybdenum, Gas sensor, Oxide semiconductor, Electrospinning 1. 서론 폭발성가스, 환경가스, 독성가스, 농수산물에서 발생되는 가스등의 미량검지를 위해서 감도 및 선택성이 우수한 가스센서가요구되고 있다. 산화물 반도체형 가스센서는 감응물질의 표면과피검 가스의 반응에 의한 저항 변화를 이용하여 가스를 검출한다[1]. 가스 감응물질로 SnO