The effect of annealing temperature on optical and structural properties of ZnO thin films

Çinko oksit (ZnO) yasak band aralığı yaklaşık 3.3 eV olan ve elektromanyetik spektrumun geniş bir aralığında yüksek geçirgenliğe sahip yarıiletken bir malzemedir. Çinko oksit ucuzluğu, sağlığa zararlı olmaması ve diğer şeffaf iletken malzemelere alternatif olma potansiyelinden dolayı son yıllarda yaygın olarak çalışılmaktadır. Bu çalışmada sol-jel döndürerek kaplama metodu ile Corning 2947 taşıyıcılar üzerine çinko oksit ince filmler hazırlanmıştır. Hazırlanan filmlere 100, 250, 350 ve 550oC’de ısıl işlem uygulamıştır. Farklı ısıl işlem sıcaklıklarının çinko oksit ince filmlerin optik ve yapısal özellikleri üzerine etkisi araştırılmıştır. Optik parametreler NKD spektrofotometresinden elde edilmiştir. Filmlerin kristal yapısı ve yüzey morfolojisi sırasıyla X-Işını Kırınımı (X-Ray Diffraction, XRD) ve Atomik Kuvvet Mikroskobu (Atomic Force Microscopy, AFM) ile analiz edilmiştir. Farklı ısıl işlem uygulanan filmlerin tamamının görünür bölgede oldukça yüksek geçirgenliğe sahip oldukları görülmüştür. 300–400 nm dalgaboyu aralığında ise ısıl işlem sıcaklığının etkisi daha belirgin ortaya çıkmıştır. XRD sonuçlarına göre 100, 250 ve 350oC ısıl işlem sıcaklığına tabi tutulan filmlerin amorf yapıda oldukları; 550oC’de ısıl işlem uygulanan filmin ise kristal yapıda olduğu görülmüştür. AFM resimlerinden elde edilen sonuçlara göre ısıl işlem sıcaklığının artmasıyla filmlerin yüzey morfolojilerinin de önemli ölçüde değiştiği görülmüştür. Hazırlanan ZnO filmlerin tamamı uygulanan bütün ısıl işlem sıcaklıklarında 7.5 nm ve altındaki Rms değerleriyle oldukça pürüzsüz yüzeylere sahiptir. En düşük pürüzlülüğe sahip film 350oC’de elde edilmiştir. Anahtar Kelimeler: Çinko oksit, sol-jel, optik özellikler, yapısal özellikler.Zinc oxide (ZnO) is an n-type semiconducting material with a ~3.3 eV band gap and high transparency over a wide range of the electromagnetic spectrum. Zinc oxide has been studied widely due to its inexpensiveness, non-toxicity and since it is a potential alternative to other transparent conducting materials. ZnO thin films are important due to their potential for applications such as gas sensors, solar cells, optoelectronic devices, transparent conducting electrodes and optical waveguides. ZnO thin films have been prepared by various methods such as chemical vapor deposition, pulsed laser deposition, sputtering, r.f. magnetron sputtering, spray pyrolysis and the sol-gel process. Among them, the sol-gel method is preferred since it has the advantages of easy control of the film composition and easy fabrication of large-area films with low cost. There are many factors that affect the optical and microstructural properties of sol-gel-made films.   Among them are the chemical composition and concentration of the solution, the coating parameters, the thickness of the film, the preheating temperature and time between each layer deposition, and the final annealing temperature. In this study, transparent ZnO thin films were prepared on Corning 2947 substrates by the sol-gel spin coating method. ZnO films were annealed at 100, 250, 350 and 550oC for 1 hour. The effects of annealing temperature on microstructure and optical properties were investigated. The coating solution was prepared by dissolving zinc acetate dihydrate (Zn(CH3COO)2 .2H2O, 98%, Aldrich) in 2-propanol (99.5%, Aldrich) and stirring by a magnetic stirrer at 60oC for 10 min. Diethanolamine (DEA, 99%, Aldrich) was added drop by drop to the solution during stirring. Then, distilled water was slowly added to the solution and stirred 10 min more. Finally, a clear and homogeneous solution was obtained. (DEA:ZnAc=1:1 [mol ratio] and H2O:ZnAc=2:1 [mol ratio]). An amount of ZnO solution was dropped onto Corning 2947 glass substrates on the spin coater, which were rotated at 3000 rpm for 30 s. The films were dried at 100oC for 2 min to evaporate the solvent and remove organic residuals. The coating procedure was repeated six times to reach the desired thickness. Finally, the films were heat treated at 100, 250, 350 and 550oC for 1 hour. All coatings were made at room temperature (~21oC) and ~55% relative humidity. Optical transmittance and reflectance of the ZnO films were measured in the spectral range of 300?1000 nm using an NKD 7000 (Aquila, UK) spectrophotometer. Measurements were made with a beam incidence angle of 30o using s-polarized light. AFM images of the films were obtained using a SPM-9500J3 (Shimadzu, Japan) scanning probe microscope in contact mode. The crystalline structures of the films were analyzed by an X-ray diffractometer (Philips PW3710, CuKα radiation). All the ZnO thin films were highly transparent with a transmittance of ~85% in the visible range. The ZnO thin films annealed at 100, 250, 350 and 550oC had transmittance values of 88.4%, 86%, 87.1%, 86.7% and reflectance values of 10.5%, 13.8%, 12.7%, 13.2% at the wavelength of 550 nm, respectively. The effect of the annealing temperature was significant between the wavelength range of 300?400 nm. The peaks in this range for films annealed at 350 and 550oC are a property of semiconducting materials due to excitonic absorption.  ZnO has a high excitonic binding energy (60 meV) which causes exciton-related emission in the ultraviolet region. The XRD diffraction peaks belonging to the (100), (002), (101), (102) (110), (103) and (112) planes were seen only in ZnO films annealed at 550oC for 1 hour. The film annealed at 550oC was crystalline with hexagonal wurtzite structure. However, there were no peaks for the other films annealed at 100, 250 and 350oC for 1 hour. ZnO thin films had smooth surfaces with RMS values of 7.5, 1.2, 0.5 and 3.3 nm for annealing temperatures of 100, 250, 350 and 550oC, respectively. This study showed that annealing temperature has a considerable effect on the optical and structural properties of ZnO thin films. Keywords: Zinc oxide, sol-gel, optical properties, structural properties

Éléments de réflexion sur le foncier et sa contribution au prix de l’immobilier

Cet article s’intéresse aux différentes sources de dysfonctionnement du marché foncier français et à ses conséquences sur le marché de l’immobilier en termes de prix et d’offre de logements. En France, à l’exception de certaines zones, la rareté du foncier apparaît construite par le jeu des acteurs qui, tout le long de la chaîne, grippe la production de terrains à bâtir. Dans les années 2000, cette insuffisance du foncier, combinée aux règles urbanistiques, s’est traduite par une offre de logements trop faible au regard des besoins. L’article formule plusieurs propositions en vue d’améliorer le fonctionnement du marché foncier français, allant de la simple publication de données sur le foncier à une proposition plus ambitieuse qui assortit la déclaration de constructibilité d’un terrain de l’obligation de construire

Synthesis and some optical results of long chain substituted phthalocyanines

Four metallo (zinc, copper, vanadyl, and indium) phthalocyanine derivatives bearing four aliphatic (hexylthio) groups were prepared from corresponding phthalonitrile compounds. The metallophthalocyanines were characterized with ultraviolet{visible spectroscopy (UV-Vis), proton nuclear magnetic resonance ( 1 H NMR), Fourier transform-infrared spectroscopy (FT-IR), and mass and elemental analyses techniques. Aggregation properties of metallophthalocyanines in solution were studied in varied concentration ranges. Thin lms of metallophthalocyanines were obtained by spin coating technique. Optical measurements showed that transmittance values of metallophthalocyanine thin lms obviously changed with respect to the metal ion in the phthalocyanines. Transmittance spectra of the phthalocyanines synthesized using different metal ions showed a variation of about 8% and 15% in transmittance spectra of the Q band region was obtained by mixing the two metal phthalocyanine (indium and zinc) solutions.Four metallo (zinc, copper, vanadyl, and indium) phthalocyanine derivatives bearing four aliphatic (hexylthio) groups were prepared from corresponding phthalonitrile compounds. The metallophthalocyanines were characterized with ultraviolet{visible spectroscopy (UV-Vis), proton nuclear magnetic resonance ( 1 H NMR), Fourier transform-infrared spectroscopy (FT-IR), and mass and elemental analyses techniques. Aggregation properties of metallophthalocyanines in solution were studied in varied concentration ranges. Thin lms of metallophthalocyanines were obtained by spin coating technique. Optical measurements showed that transmittance values of metallophthalocyanine thin lms obviously changed with respect to the metal ion in the phthalocyanines. Transmittance spectra of the phthalocyanines synthesized using different metal ions showed a variation of about 8% and 15% in transmittance spectra of the Q band region was obtained by mixing the two metal phthalocyanine (indium and zinc) solutions

Optical investigation of palladium(II) phthalocyanine including an aromatic group

Peripherally β-naphthoxy unit substituted palladium(II) phthalocyanine was synthesized from corresponding phthalonitrile compounds. The palladium (II) phthalocyanine was characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform- infrared spectroscopy (FT-IR), mass and elemental analyses techniques. Thin films of palladium (II) phthalocyanine were prepared using different organic solvents by the spin coating technique. Transmittance and absorbance spectra of the thin films were studied in the wavelength range of 200–1000 nm. Optical band gaps of palladium (II) phthalocyanine thin films were also calculated

The effect of polyvinyl alcohol (PVA) on rheological and dielectric properties of kaolinite dispersion

The purpose of this study is to investigate the effect of polyvinyl alcohol (PVA) on rheological and dielectric properties of suspension in the different concentration of PVA prepared by using kaolinite 0.1%. The viscosity values of suspension have been measured and the dependence of viscosity on temperature and concentration have been investigated. The specific viscosity and activation energy have been calculated by using the measured viscosity values. It has been observed that the values of viscosity increase exponantially with the concentration of PVA and decrease with increasing temperature. Dielectric constants of suspensions prepared by using PVA-deionized water and PVA-water-kaolinite have been measured in the temperature range from 0;deg;C to 15;deg;C, and its dependence on concentration and temperature also investigated. It has been observed that dielectric constant slightly increases with PVA concentration, but decreases with increasing temperature.Bu çalışmanın amacı % l kaolin kullanarak değişik PVA konsantrasyonlarında hazırlanmış süspansiyonun reolojik ve dielektrik özellikleri üzerinde polivinil alkol(PVA)ün etkisini araştırmaktır. Süspansiyonun viskozite değerleri ölçülmüş ve viskozitenin sıcaklık ile konsantrasyona bağlılığı incelenmiştir. Ölçülen viskozite değerleri kullanılarak spesifik viskozite ve aktivasyon enerjisi hesaplanmıştır. Viskozite değerlerinin PVA konsantrasyonu ile eksponansiyel olarak arttığı ve artan sıcaklıkla azaldığı gözlenmiştir. PVA-deiyonize su karışımlarının dielektrik sabitleri ve PVA-su-kaolin ile hazırlanan karışımların dielektrik sabitleri 0°C-15°C sıcaklık aralığında ölçülmüş, sıcaklık ve konsantrasyon bağlılıkları incelenmiştir.Dielektrik sabitinin PVA konsantrasyonu ile yavaş artış gösterdiği ve artan sıcaklıkla azaldığı gözlenmiştir

Cycling Durability of Electrochromic W-Ti Oxide Thin Films : Optical Transmittance Data Signal Dual Degradation Modes

Electrochemical degradation of electrochromic W oxide and W–Ti oxide thin films, prepared by reactive DC magnetron sputtering, was studied by voltammetric cycling in potential intervals from 1.5–4.0 to 2.0–4.0 V vs Li/Li+ in an electrolyte of lithium perchlorate in propylene carbonate. Cycling-dependent evolution of the upper and lower limits for the optical modulation range was critically dependent on potential interval. This phenomenon was analyzed through an extension of a previously formulated model for power-law dynamics; it was discovered that the upper and lower limits for the optical modulation range varied in distinctly different ways, and that only data acquired in the interval 2.0–4.0 V vs Li/Li+ could be reconciled with dispersive chemical kinetics. We thus find that our data on optical transmittance degradation lends strong support to the existence of dual degradation modes for electrochromism upon extended electrochemical cycling. This result is of great importance for the development of highly durable electrochromic devices such as smart windows for energy-efficient buildings. The present article is a sequel to a recent publication of ours [J. Electrochem. Soc., 166, H795 (2019)]

Electrochromism of DC magnetron sputtered TiO2 thin films : Role of deposition parameters

We performed a comprehensive study on the electrochromism in TiO2 thin films made by reactive DC magnetron sputtering and elucidated the roles of sputter gas pressure p, O-2/Ar gas ratio gamma and substrate temperature tau(s). Good mid-luminous optical modulation taken to be similar to 50% in similar to 200-nm-thick films was obtained under charge exchange in a Li+ electrolyte for p > 15 mTorr and tau(s) < 100 degrees C, whereas gamma was less important. The deposition rate dropped for increasing p, and hence p approximate to 15 mTorr was optimal. These films were X-ray amorphous and contained some water. The coloration efficiency eta was 25 cm(2)/C, which exceeds data on eta in most prior studies on sputter deposited TiO2 and verifies that such films can display the same values of eta as those of TiO2 films made by several chemical techniques

Electrochromism of W-In oxide thin films : Implications for cycling durability

Electrochromic W oxide and W–In oxide thin films were prepared by dual-target reactive DC magnetron sputtering and were cycled voltammetrically in an electrolyte of lithium perchlorate in propylene carbonate. Film degradation was investigated for up to 500 cycles in the voltage ranges 1.5–4.0, 1.7–4.0 and 2.0–4.0 V vs. Li/Li+, and optical transmittance was recorded concurrently. Indium doping was found to be unambiguously detrimental to electrochromic cycling durability, which resolves an outstanding issue related to recently discovered unprecedented durability of potentiostatically pretreated W oxide films backed by In2O3:Sn and gives strong support in favor of beneficial effects of solid-electrolyte interfacial layers