Fabrication of Multilayer ZnO/TiO2/ZnO Thin Films with Enhancement of Optical Properties by Atomic Layer Deposition (ALD)
TL;DR: In this paper, the optical and electrical properties of multilayer ZnO/TiO2/ZnO films were investigated using X-ray diffraction (XRD), atomic force microscope (AFM) and scanning electron microscope (SEM).
Abstract: Atomic layer deposition (ALD) is a precision growth technique that is able to deposit either amorphous or epitaxial layer on a wide range of substrates. Multilayer thin films have been widely studied because their properties are different from those of bulk materials constituents owing to the two-dimensional films and high density of interfaces. Multilayer nanostructured thin films were fabricated on silicon and glass substrates by ALD. The optical and electrical of multilayer ZnO/TiO2/ZnO films were investigated. The microstructure compositions and surface morphology of these multilayer films were analyzed by X-ray diffraction (XRD), Atomic force microscope (AFM) and Scanning electron microscope (SEM). The optical properties were characterized using photoluminescence (PL) and UV-VIS spectroscopy. XRD patterns confirmed that ZnO with wutrtize crystal structure and TiO2 with anatase structure were presented. The degree of crystallinity of multilayer thin films has been improved through the deposition of ZnO. The intensity of UV luminescence of the multilayer has increased as compared to the single layer TiO2 and bilayer ZnO/TiO2. The multilayer ZnO/TiO2/ZnO has high transmittance (above 80%) in visible region. All the result suggested that the use of multilayer thin films effectively enhanced the quality of films crystallinity and optical properties as compared to single layer ZnO and bilayer ZnO/TiO2.
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TL;DR: In this article, the structural, morphological and electrical properties of multilayer ZnO/TiO 2 thin films deposited by sol-gel technique on a glass substrate were investigated.
Abstract: Investigations of the structural, morphological and electrical properties of multilayer ZnO/TiO 2 thin films deposited by sol–gel technique on glass substrate. Sol–gel is a technique in which compound is dissolved in a liquid in order to bring it back as a solid in a controlled manner. TiO 2 solution was obtained by dissolving 0.4 g of TiO 2 nano powder in 5 ml ethanol and 5 ml diethylene glycol. ZnO solution was obtained by dissolving 0.88 g zinc acetate in 20 ml of 2-methoxyethanol. X-ray diffraction (XRD) (PW 3050/60 PANalytical X’Pert PRO diffractometer) results showed that the crystallinity is improved when the number of ZnO/TiO 2 layers increased. Also it shows the three phases (rutile, anatase and brookite) of TiO 2 . Surface morphology measured by scanning electron microscopy (SEM) (Quanta 250 fei) revealed that Crakes are present on the surface of ZnO/TiO 2 thin films which are decreased when the number of ZnO/TiO 2 layers increased. Four point probe (KIETHLEY instrument) technique used to investigate the electrical properties of ZnO/TiO 2 showed the average resistivity decreased by increasing the number of ZnO/TiO 2 layers. These results indicated that the multilayer thin films improved the quality of film crystallinity and electrical properties as compared to single layer.
67 citations
TL;DR: In this paper, a multilayer of 2% Cu doped TiO2 thin films have been grown by sol-gel spin coating on glass substrate in the form of three, five and seven layers.
Abstract: Multilayer of 2% Cu doped TiO2 thin films have been grown by sol–gel spin coating on glass substrate in the form of three, five and seven layers. X-ray diffractrometer (XRD) confirms the doping of Cu into TiO2. Scanning electron microscopy (SEM) confirms the formation of nano particles with average size of 19, 25 and 35 nm for three, five and seven layers of thin films, respectively. The electrical resistivity of these multilayer films is found as 2.19 × 107, 1.20 × 107 and 1.11 × 107 ohm-m respectively. UV–vis shows that the films have 80% transmittance in the visible region which is good for solar spectrum. The optical band gap energy decreases with an increase in the number of layers as 3.778, 3.768 and 3.736 eV respectively for 3, 5 and 7 layered thin films. This work provides an environment friendly and low cost use of an abundant material for optoelectronic devices.
24 citations
Cites background from "Fabrication of Multilayer ZnO/TiO2/..."
...In our work we can interpret that nanostructure multilayer thin films are attributed to the change in particle shape that in turn improves the crystallinity related properties of the material [26]....
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...The distribution of particle size is highly sensitive to the deposition temperature and impurities/defects that usually segregate at the grain boundaries [26]....
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TL;DR: In this article, an S-ALD system with modular injectors is introduced for fabricating binary oxides and their nanolaminates, and the as-deposited ZnO film has high carrier mobility and the TiO2 film shows suitable optical transmittance and band gap.
Abstract: Spatial atomic layer deposition (S-ALD) is a potential high-throughput manufacturing technique offering fast and large scale ultrathin films deposition. Here, an S-ALD system with modular injectors is introduced for fabricating binary oxides and their nanolaminates. By optimizing the deposition conditions, both ZnO and TiO2 films demonstrate linear growth and desired surface morphology. The as-deposited ZnO film has high carrier mobility, and the TiO2 film shows suitable optical transmittance and band gap. The ZnO/TiO2 nanolaminates are fabricated by alternating substrate movement between each S-ALD modular units of ZnO and TiO2. The grazing incidence x-ray diffraction spectra of nanolaminates demonstrating the signature peaks are weaker for the same thickness nanolaminates with more bilayers, suggesting tuning nanolaminates from crystalline to amorphous. Optical transmittances of ZnO/TiO2 laminates are enhanced with the increase of the bilayers' number in the visible range. Refractive indices of nanolaminates increase with the thickness of each bilayer decreasing, which demonstrates the feasibility of obtaining desired refractive indices by controlling the bilayer number. The electronic properties, including mobility, carrier concentration, and conductivity, are also tunable with different bilayers.
12 citations
01 Jan 2015
TL;DR: In this article, the authors demonstrated a self-limiting of 0.017 - 0.024 nm/cycle growth of the TiO2 thin films using TTIP and H2O, at deposition temperatures ranging from 100°C to 300°C.
Abstract: The thin films ceramic oxide can be fabricated by ALD because this technique promises to control the deposition on an
atomic scale by sequentially dosing the surface with appropriate chemical precursors, and by promoting surface chemical
reactions that are inherently self-limiting. TiO2 has been widely used in photocatalysts, due to its photosensitivity and
thermal stability. TiO2 also has strong absorption in the UV range, at around 3.3 eV. ALD deposition cycle and
temperature would determine the surface morphology of TiO2 thin films from a very smooth surface to a rough surface,
which is important for their functional applications. The combined results of XRD and AFM show that the deposition
temperature played an important role in the growth of TiO2 thin films and the phase transition from amorphous to anatase.
These results demonstrated a self-limiting of 0.017 - 0.024 nm/cycle growth of the TiO2 thin films using TTIP and H2O, at
deposition temperatures ranging from 100°C to 300°C. The optical properties of TiO2 thin films were also influenced by
the deposition temperature. In addition, UV luminescence (at 353 nm) was present in the TiO2 thin films deposited at
200°C whereas there was no UV luminescence for pure bulk TiO2.
10 citations
Cites methods from "Fabrication of Multilayer ZnO/TiO2/..."
...ALD (Atomic Layer Deposition) is an ideal technique for the deposition of nanostructured scale thin films in single layer (Hussin et al., 2012) and multilayer (Hussin et al., 2014)....
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06 Feb 2019
TL;DR: In this article, a double layer of ZnO and TiO2 is used to enhance photocatalytic activity using the different deposition temperature between the layer, which can enhance the surface state and surface atomic mobility.
Abstract: ZnO/TiO2 thin films have some advantages such as can enhance the surface state and surface atomic mobility which are useful for improving the photocatalytic activity. The motivation to used double layer of ZnO and TiO2 is to enhance photocatalytic activity using the different deposition temperature between the layer. The structural properties and photocatalytic activity of ZnO/TiO2 thin films with calcination temperature as parameter were studied. It is found that ZnO (600 °C)/TiO2 (500 °C) thin film consists of ZnO with zincite structure and TiO2 with anatase structure while the other ZnO/TiO2 thin films only exhibit TiO2 with anatase structure. The X-Ray Diffraction (XRD) patterns become more intense and sharper when the calcination temperature increases. Field Emission Scanning Electron Microscope (FESEM) was used to determine the surface morphology of ZnO/TiO2 thin films. The results showed that surface morphology of ZnO/TiO2 thin film becomes rougher but homogeneous. Size of particles also becomes smaller when the calcination temperature increases. The photocatalytic activity of ZnO/TiO2 thin films was analyzed using photodegradation of methylene blue (MB) solution. A higher calcination temperature of ZnO buffer layer leads to enhance the degradation efficiency of MB dye using ZnO/TiO2 thin films as photocatalysts. It is proposed that the ZnO/TiO2 thin film with higher calcination temperature can be an efficient photocatalyst under UV irradiation.ZnO/TiO2 thin films have some advantages such as can enhance the surface state and surface atomic mobility which are useful for improving the photocatalytic activity. The motivation to used double layer of ZnO and TiO2 is to enhance photocatalytic activity using the different deposition temperature between the layer. The structural properties and photocatalytic activity of ZnO/TiO2 thin films with calcination temperature as parameter were studied. It is found that ZnO (600 °C)/TiO2 (500 °C) thin film consists of ZnO with zincite structure and TiO2 with anatase structure while the other ZnO/TiO2 thin films only exhibit TiO2 with anatase structure. The X-Ray Diffraction (XRD) patterns become more intense and sharper when the calcination temperature increases. Field Emission Scanning Electron Microscope (FESEM) was used to determine the surface morphology of ZnO/TiO2 thin films. The results showed that surface morphology of ZnO/TiO2 thin film becomes rougher but homogeneous. Size of particles also becomes sm...
7 citations
References
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TL;DR: The present status and prospects for further development of polycrystalline or amorphous transparent conducting oxide (TCO) semiconductors used for practical thin-film transparent electrode applications are presented in this paper.
Abstract: The present status and prospects for further development of polycrystalline or amorphous transparent conducting oxide (TCO) semiconductors used for practical thin-film transparent electrode applications are presented in this paper. The important TCO semiconductors are impurity-doped ZnO, In2O3 and SnO2 as well as multicomponent oxides consisting of combinations of ZnO, In2O3 and SnO2, including some ternary compounds existing in their systems. Development of these and other TCO semiconductors is important because the expanding need for transparent electrodes for optoelectronic device applications is jeopardizing the availability of indium-tin-oxide (ITO), whose main constituent, indium, is a very expensive and scarce material. Al- and Ga-doped ZnO (AZO and GZO) semiconductors are promising as alternatives to ITO for thin-film transparent electrode applications. In particular, AZO thin films, with a low resistivity of the order of 10−5 Ω cm and source materials that are inexpensive and non-toxic, are the best candidates. However, further development of the deposition techniques, such as magnetron sputtering or vacuum arc plasma evaporation, as well as of the targets is required to enable the preparation of AZO and GZO films on large area substrates with a high deposition rate.
1,959 citations
TL;DR: The high sensitivity and dynamic repeatability observed in these sensors reveal that the core-shell nanofibers are promising as sensitive and reliable chemical sensors.
Abstract: SnO2–ZnO core–shell nanofibers were synthesized via a novel two-step process. First, SnO2 nanofibers were synthesized by electrospinning. In sequence, ZnO shell layers were deposited using atomic layer deposition on the electrospinning synthesized SnO2 nanofibers. To demonstrate the practical applications of the synthesized core–shell nanofibers, we investigated their sensing properties to O2 and NO2. The high sensitivity and dynamic repeatability observed in these sensors reveal that the core–shell nanofibers are promising as sensitive and reliable chemical sensors.
242 citations
"Fabrication of Multilayer ZnO/TiO2/..." refers background in this paper
...Zinc Oxide (ZnO) based nanostructured composites become more attractive when being simply assemble together with other metallic oxide[2]....
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TL;DR: In this paper, a high electron mobility of 30 cm 2 /V·s was obtained for undoped ZnO films with the thickness of only 220 nm and a resistivity of 7.5×10 −4 Ω cm.
232 citations
"Fabrication of Multilayer ZnO/TiO2/..." refers background in this paper
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187 citations
"Fabrication of Multilayer ZnO/TiO2/..." refers background in this paper
...Multilayer thin films consist of alternating layer of two different materials which may contain several repeated thin films layer in range of nano or micro scale [1] ....
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TL;DR: The first example of atomic layer-controlled growth or atomic layer epitaxy on a polymer substrate was reported in this article, where the growth was accomplished by separating the CVD reaction, Zn(CH 2 CH 3 ) 2 ǫ+H 2 Oǫ→ ZnO+2CH 3 CH 3, into the following half reactions: (A) Zn−OH * ǒ + Zn+Zn−Oǫ + CH 3 CH3 ) 2ǫ → Zn-O + CH 2 CH3 + CH3 CH
159 citations