Improving optical and electrical performances of aluminum-doped zinc oxide thin films with laser-etched grating structures

A laser etching method was performed to achieve the dual purpose of fabricating grating structures and laser annealing on aluminum-doped zinc oxide (AZO) thin films, and thus improve the film photoelectric performances. Different line spacings and laser fluences were adopted to systematically explore the optimal laser etching condition. Too narrow line spacings or too high laser fluences led to light reflections at the grating external surface to cause more light dissipation, and too wide line spacings or too low laser fluences resulted in relatively small total grating lateral areas being detrimental to multiple internal light reflections. Moreover, too narrow line spacings brought about laser-caused lattice disorder and too high laser fluences produced laser-ablated spots or overburned traces. Therefore, using the medium line spacing and laser fluence, e.g. 40 μm and 0.6 J/cm² in the present work, was more suitable for synchronously realizing grating structure fabrication and laser annealing. The corresponding AZO film exhibited the maximum figure of merit of 2.89 × 10^?2 Ω^?1, which was 1.6 times that of the untreated AZO film. This study is expected to expand performance improvement methods of TCO films and promote the application of laser-etched grating structures.     

Room temperature sputtering deposition of high-haze Ga-doped ZnO transparent conductive thin films on self-textured bio-based poly(ethylene 2, 5-furandicarboxylate) substrates

In this work, bio-based poly(ethylene 2,5-furandicarboxylate) (PEF) films were prepared by drop-casting method and used as substrates for depositing Ga-doped ZnO (GZO) transparent conductive thin films. Results showed that the 300-nm GZO thin films deposited on PEF substrates exhibited haze values above 65% at 550 nm without post-treatment. The high haze value was because of the large surface roughness of PEF films. The total optical transmittance and electrical properties of GZO thin films on PEF were comparable to those of GZO thin films on PET. The present study provides a simple way for the sputtering deposition of high-haze transparent conductive thin films on flexible substrates.     

Optimization of the sputtering process parameters of GZO films using the Grey–Taguchi method

This paper examines the optimization of the process parameters of GZO films deposited on polyethylene terephthalate substrates by R.F. magnetron sputtering using the Taguchi method, aiming to obtain highly transparent and conductive films. The influences of the various sputtering factors (R.F. power, sputtering pressure, deposition time, substrate temperature and post-annealing temperature) on electrical resistivity and structural, morphological and optical transmittance of GZO films are analyzed. The electrical resistivity and the optical transmittance of GZO films were improved by post-annealing the substrate during the deposition process. Experimental results indicate the optimal process parameters in GZO films deposited on polyethylene terephthalate substrates can be determined effectively. The electrical resistivity of GZO films is decreased from 1.194 × 10⁻³ Ω cm to 8.627 × 10⁻⁴ Ω cm and the optical transmittance is increased from 86.148% to 90%, leading to multiple performance characteristics in deposition qualities through the Grey–Taguchi method.     

Formation of nanometer-size high-density pits on epitaxial diamond (100) films

We report the formation of pits having widths of approximately 10 nm and a density of 2.5 × 10¹¹/cm² on epitaxial diamond (100) films. The pits are formed by etching the films using atomic hydrogen at a substrate temperature of approximately 500 °C. Exposure to oxygen followed by etching with atomic hydrogen forms additional pits. We propose that the high-density pits are formed due to etching that occurs both perpendicular and parallel to the surface.     

Surface composition,bonding, and morphology in the nucleation and growth of ultra-thin,high quality nanocrystalline diamond films

The morphology, composition, and bonding character (carbon hybridization state) of continuous, ultra-thin (thickness ∼ 60 nm) nanocrystalline diamond (NCD) membranes are reported. NCD films were deposited on a silicon substrate that was pretreated using an optimized, two-step seeding process. The surface after each of the two steps, the as-grown NCD topside and the NCD underside (revealed by etching away the silicon substrate) is examined by X-ray PhotoElectron Emission spectroMicroscopy (X-PEEM) combined with X-ray absorption near edge structure (XANES) spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The first step in the seeding process, a short exposure to a hydrocarbon plasma, induces the formation of SiC at the diamond/Si interface along with a thin, uniform layer of hydrogenated, amorphous carbon on top. This amorphous carbon layer allows for a uniform, dense layer of nanodiamond seed particles to be spread over the substrate in the second step. This facilitates the growth of a homogeneous, continuous, smooth, and highly sp³-bonded NCD film. We show for the first time that the underside of this film possesses atomic-scale smoothness (RMS roughness: 0.3 nm) and > 98% diamond content, demonstrating the effectiveness of the two-step seeding method for diamond film nucleation.     

Lightwave irradiation-assisted low-temperature solution synthesis of indium-tin-oxide transparent conductive films

Transparent conductive oxide (TCO) films have important applications in many areas. Unfortunately, TCOs are usually fabricated using vacuum and high-temperature methods, preventing them from applications in low-cost flexible devices. In this paper, facile low-temperature sol-gel method is described that can be used to fabricate high-quality TCO films. This study uses lightwave (LW) irradiation (at ～280 °C) with indium-tin-oxide (ITO) as a typical example. Both structure and key properties of ITO films are investigated for different LW irradiation conditions. ITO can be formed via LW irradiation after a period as short as 5 min. Furthermore, it is found that LW irradiation can promote the formation of M ? O framework, effectively remove Cl impurities, and facilitate the elimination of hydroxyl oxygen defects - even at temperatures as low as ～280 °C. The optimal ITO films show excellent electronic properties, including low sheet-resistance (14.5 Ω·sq^?1) and high conductivity (1.7 × 10³ S cm^?1). Moreover, ITO films also show high transmittance (above 87%). Overall, our ITO films have a figure of merit (FOM) of 1.72 × 10^?2 Ω^?1, which is comparable to (or higher than) those of previous ITO films that were produced using conventional vacuum and high-temperature methods. Our LW irradiation method provides facile and effective approach to produce high-performance TCO films at remarkably low cost. This means these films could be used in affordable flexible large-area devices.     

Room temperature preparation of high performance AZO films by MF sputtering

Aluminum-doped zinc oxide (AZO) thin films have been deposited by MF magnetron sputtering from a ceramic oxide target without heating the substrates. This study has investigated effects of sputtering power on the structural, electrical and optical properties of the AZO films. The films delivered a hexagonal wurtzite structure with (002) preferential orientation and uniform surface morphology with 27–33 nm grain size. The results indicate that residual stress and grain size of the AZO films are dependent on sputtering power. The minimum resistivity of 7.56×10^?4 Ω cm combined with high transmittance of 83% were obtained at deposited power of 1600 W. The films delivered the advantages of a high deposition rate at low substrate temperature and should be suitable for the fabrication of low-cost transparent conductive oxide layer.     

Dielectric behavior and magnetical response for porous BFO thin films with various thicknesses over Pt/Ti/SiO2/Si substrate

A novel sol–gel method has been developed to deposit multiferroic nanocrystalline bismuth ferrite (BFO) thin films over Pt/Ti/SiO₂/Si substrate by spin-coating technique with various thicknesses. It is found that the deposition parameters significantly influence the quality and the thickness of BiFeO₃ films. The films are all uniform and adherent to Pt/Ti/SiO₂/Si substrate. The spin-coated films are characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Atomic force microscope (AFM), photoluminescence spectroscopy (PL) and Fourier transform infrared spectroscopy (FTIR). Rhombohedral structure of BFO is confirmed from the XRD and FT-IR studies. The SEM image shows a porous structure formation of BFO over Pt/Ti/SiO₂/Si substrate. The surface outgrowth for the films at various thicknesses is measured from root mean square (RMS) and surface roughness through AFM. The step height and the RMS are found to be high for the film at 500 nm in comparison with thickness of 200 nm. The influence of the dielectric properties of the porous BFO at different thicknesses is studied using LCRQ meter. Finally, the magnetic behavior of film is compared with M–H hysteresis loop and Magnetoresistance (MR) studies.     

Sol–Gel‐Derived High‐Performance Stacked Transparent Conductive Oxide Thin Films

Single‐ and multi‐layer transparent conductive oxide (TCO) thin films exhibiting high performance, good packing density and low surface/interface roughness are deposited on silica glass substrates by the sol–gel method. The crystal and microstructural properties of the TCO thin films are evaluated as an alternate to films prepared by ultra‐high vacuum deposition. Tin‐doped indium oxide (ITO) thin films produced using a two‐step drying process showed low surface roughness because of dense packing structure not only horizontal but also vertical directions. As a result, electrical conductivity, carrier concentration, carrier mobility, and optical transmittance of 2.3 × 10³ S/cm, 8 × 10²⁰ cm^?3, 18 cm²/Vs, and over 98% at 500 nm, respectively, were achieved. A multilayer ZnO/ITO stacked structure was also fabricated using the sol–gel process. Our findings suggest that solution‐based methods show promise as an alternative to existing ultra‐high vacuum methods to fabricate TCO thin films.     

Fabrication of oxide-based near infrared-shielding coatings for a smart window to prevent infrared-induced photoaging in human skin

Oxide-based near infrared (IR)-shielding coatings consisting of quarter‐wave stacks of oxygen-deficient tantalum oxide (Ta₂O_5?x) and silicon oxide (SiO₂) multilayers and tin-doped indium oxide (In₂O₃) (ITO) films with the thicknesses of 200–600 nm can block the passage of IR-A (wavelength: 760–1400 nm) and IR-B (wavelength: 1400–3000 nm) radiation, respectively. In this study, the optical properties and microstructure of these oxide-based IR-shielding coatings were investigated. Transmission electron microscopy images indicated that amorphous Ta₂O_5?x/amorphous SiO₂ multilayers were uniform and dense. ITO films were found to be highly crystalline and show carrier concentrations of up to 7.1 × 10²⁰ cm^?3, resulting in the strong IR-B optical absorption due to the plasma excitation of the free carriers. Oxide-based IR-shielding coatings with an ITO thickness of 420 nm were found to have near-IR shielding rates of >90% and an average visible light transmittance of >70%. The effects of IR on human keratinocytes were studied to evaluate the IR-induced photoaging in human skin. It was found that the downregulation of cellular proliferation and the enhancement of senescence-associated β-galactosidase activity induced by IR irradiation were significantly inhibited by oxide-based IR-shielding coatings. Thus, this study provides a facile method for the development of coatings for smart windows with high IR-shielding ability and high visible light transmittance.     

Performance optimization of fluorine-doped tin oxide thin films by introducing ultrasonic vibration during laser annealing

Commercial fluorine-doped tin oxide (FTO) thin films were subjected to laser annealing coupled with ultrasonic vibration (48 kHz and 350 W). The effects of ultrasonic vibration, laser fluence and defocusing amount were systematically studied. Laser annealing could result in grain growth or damage of the FTO layer, and introducing ultrasonic vibration during laser annealing could effectively enhance the film compactness, decrease the film thickness and refine the grains in the film. As a result, the optical and electrical properties of the ultrasonic-vibration-assisted laser-annealed FTO films were significantly improved by using low laser fluences and high defocusing amounts, and were slightly deteriorated when high laser fluences and low defocusing amounts were adopted. The results indicated that the film obtained by ultrasonic-vibration-assisted laser annealing using a laser fluence of 0.6 J/cm² and a defocusing amount of 2.0 mm had the best overall photoelectric property with an average transmittance of 84.1%, a sheet resistance of 8.9 Ω/sq and a figure of merit of 1.99×10^–2 Ω^–1, outperforming that of the film obtained by pure laser annealing using the same experimental parameters. The present study confirms the efficacy of ultrasonic-vibration-assisted laser annealing in optimizing performance of FTO films.     

Highly transparent,UV-B protective Al–Zn–O films with potential application in greenhouse screen systems

Extremely thin, Al–Zn–O composite films (21 ± 6 nm) are deposited on fused silica substrates under various percentages of oxygen in the oxygen/argon gas mixture (3%, 4.5%, 6%, and 7.5%). The films are prepared by a cylindrical DC magnetron sputtering system, utilizing a single compound target. The effects of the oxygen percentage on the compositional, morphological, and optical properties of the films are investigated by energy-dispersive X-ray spectroscopy, scanning electron microscopy, UV-visible spectrophotometry, and atomic force microscopy. The chemical composition of the films is Al₁ Zn_1+X O with 0.2 < X < 1. The average visible transmittance of 93.6% with a high level of uniformity is obtained when the sputtering deposition performs under the oxygen percentage of 6%. It is found that the optical band gap of the films can be tailored toward higher energy by increasing oxygen percentage; however, the adjustable range is not so significant. The results offer cost-efficient films with high, uniform transmittance in the visible region and with an ability to attenuate more than 10% of incident UV-B radiation (280-315 nm). This type of films can potentially be included in greenhouse screen systems to effectively protect the plants from the elevated UV-B radiation without altering natural conditions.     

Influence of a Ni interlayer on the optical and electrical properties of trilayer GZO/Ni/GZO films

Trilayer GZO/Ni/GZO films were deposited onto polycarbonate (PC) substrates with RF and DC magnetron sputtering, and then the influence of a Ni interlayer on the optical and electrical properties of the films was investigated. A 2-nm-thick Ni interlayer decreased the resistivity to 6.4×10⁻⁴ Ω cm and influenced the optical transmittance.Although optical transmittance deteriorated with Ni insertion, the films showed a relatively high optical transmittance of 74.5% in the visible wavelength region. The figure of merit (FOM) of a GZO single layer film was 1.2×10⁻⁴ Ω⁻¹, while that of the GZO/Ni/GZO films reached a maximum of 8.2×10⁻⁴ Ω⁻¹.Since a higher FOM results in higher quality transparent-conductive oxide (TCO) films, it is concluded that GZO films with a 2 nm Ni interlayer have better optoelectrical performance than single-layer GZO films.     

富马酸交联PVA/ZIF-8新型复合薄膜的制备及性能研究

采用流延法制备了一系列富马酸交联的聚乙烯醇(PVA)/沸石咪唑酯骨架材料(ZIF-8)新型复合薄膜,通过接触角、溶胀度、拉伸强度、透光率和雾度、透湿性能和傅里叶变换红外光谱等测试对复合薄膜进行了性能表征,研究了ZIF-8含量对PVA复合薄膜的亲水性、力学性能、渗透性、透光性能的影响。结果表明,随着ZIF-8含量的增加,复合薄膜的耐水性明显提高,接触角上升了20.01 °,透湿性能提高了7.12×10?13 g·cm/cm2·s·Pa,但薄膜的拉伸强度下降了71.52 MPa,透光率下降了33.43 %。     

Adhesion improvement of diamond coatings on cemented carbide with high cobalt content using PVD interlayer

At present, diamond coating is usually deposited on cemented carbide (WC-Co) tool with low Co content (Co ≤ 6 wt.%). It is more difficult to deposit diamond coating on WC-Co with high Co content because of the strong catalytic effect of Co. However, WC-Co tools with high Co content (Co ≥ 6 wt.%) are more widely used in difficult-to-cut materials machining because of their higher strength and better ductility. In this paper, the research was carried out on the adhesion performance of diamond coating on WC-Co (Co 10 wt.%). The deposition of diamond coating was conducted in hot filament chemical vapor deposition (HFCVD) system with the presence of the strong carbon-forming metallic interlayer (Nb, Cr or Ta), which was prepared using physical vapor deposition (PVD) on WC-Co substrate after chemical etching through a two-step process (Murakami solution and Caro's acid), which is a general way to treat the WC-Co substrate before growth of diamond coating. The results showed that the diamond films grown on the above treated WC-Co substrate have higher nucleation density, purity and adhesion strength than those on WC-Co substrates pretreated only using PVD interlayer or chemical etching. The PVD interlayer restrains the diffusion of Co as a result of high substrate temperature during the diamond film deposition, and consequently prevents the formation of the loosened layer induced by the removal of Co binder phase in the WC-Co substrate. The results also indicated that Nb interlayer leads to the most adhesion improvement of diamond films on the WC-Co inserts among the Nb, Ta and Cr interlayers.     

Tailored biodegradable films via extrusion blow molding using PBS,PBAT, and TPS

Research to replace synthetic polymers with biodegradable polymers is on the rise because common plastics have generated serious ecosystem problems. Films with thermoplastic starch (TPS), poly(butylene succinate) (PBS), poly(butylene adipate-co-butylene terephthalate (PBAT), and citric acid (CA) were produced by blown extrusion. They were characterized by blow-up ratio (BUR), water vapor permeability (WVP), soluble ratio (SR), water sorption isotherm, and thermogravimetric (TG) techniques. Films were uniform and showed BUR > 205%. The different proportions of PBS and PBAT significantly influenced the WVP of the films. All samples had WVP with an order of magnitude similar to other blends with high starch content (10⁻⁶ g m⁻¹ day⁻¹ Pa⁻¹). CA efficiently decreased the WVP of the PBS/PBAT/TPS formulations (15/15/70% and 20/10/70% by mass) by 25.2% and 24.7% compared to the acid-free formulations. There was no significant difference in SR (19.0%–20.1%). These materials were sensitive to moisture since the equilibrium moisture content increased pronouncedly from water activity of 0.5. Films showed good thermal stability, with a maximum decomposition temperature close to pure polyesters. CA did not increase the thermal stability of blends, probably because of the low content used (0.1%). Given the outcomes of this study, these films could be deemed appropriate for applications in food packaging.     

Transparent and high infrared reflection film having sandwich structure of SiO2/Al:ZnO/SiO2

New transparent and high infrared reflection films having the sandwich structure of SiO₂/Al:ZnO(AZO)/SiO₂ were deposited on the soda-lime silicate glass at room temperature by radio frequency (R.F.) magnetron sputtering. The optical and electrical properties of SiO₂ (110 nm)/AZO (860 nm)/SiO₂ (110 nm) sandwich films were compared with those of single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. The results show that these sandwich films exhibit high transmittance of over 85% in the visible light range (380–760 nm), and low reflection rate of below 4.5% in the wavelength range of 350–525 nm, which is not shown in the conventional single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. Further these sandwich films display a low sheet resistance of 20 Ω/sq by sheet resistance formula and high infrared reflection rate of above 80% in the wavelength range of 15–25 μm. In addition, the infrared reflection property of these sandwich films is determined mainly by the AZO film. The outer SiO₂ film can diminish the interference coloring and increase transparency; the inner SiO₂ film improves the adhesion of the coating to the glass substrate and prevents Ca²⁺ and Na⁺ in the glass substrate from entering the AZO film.     

The preparation of high quality oriented diamond thin films via low temperature and hydrogen ion etched nucleation

A three-step process was used to prepare high quality [001]-oriented diamond films. First, diamond crystallites were nucleated for 20 min on Si(001) at a temperature around 740 °C by bias-enhance method, during this step the portion of [001]-oriented diamond nuclei was increased in comparison with the nuclei deposited by a two-step method. Then hydrogen ion etching was performed for 30 min by setting an electric potential of −140 V. After the etching step most of the crystallites were [001]-oriented and twinned crystallites disappeared. Finally, diamond thin films were deposited under conventional conditions for [001]-textured growth. SEM was used to analyse the morphology of diamond crystallites and films. The results indicate that large area, uniform and [001]-oriented diamond thin films can be prepared by three-step growth. The films show good Raman characteristics and higher thermal conductivity than those deposited by a two-step process.     

Multifunctional ZnO/Fe-O and graphene oxide nanocomposites: Enhancement of optical and magnetic properties

ZnO is a semiconductor with a great interest, but it has several deficiencies which limit its use in technologic applications. One important limitation is having the band gap in the UV which reduces its use in optical devices. To solve this problem, in this work, composites based in ZnO with goethite and graphene oxide (GO) by sol-gel are prepared. The obtained samples (powders and thin films) were characterized microstructurally (DTA, XRD, micro-Raman, FE-SEM), optically (transmittance and photoluminescence) and magnetically (SQUID). The ZnO band gap of multifunctional composites shows a red-shift towards visible range (E_g ∼3.01 eV) with high transmittance ∼85% (thickness of 362 nm) over the visible wavelength range. A long-range magnetic order at room temperature appears in these nanocomposites (Ms = 1.60·10⁻² emu/g). The combination of both dopants allows modifying the functional properties of ZnO, opening a great field of applications in ZnO composites, such as spintronic and optoelectronic devices.     

Transparent conductive oxide films mixed with gallium oxide nanoparticle/single-walled carbon nanotube layer for deep ultraviolet light-emitting diodes

We propose a transparent conductive oxide electrode scheme of gallium oxide nanoparticle mixed with a single-walled carbon nanotube (Ga₂O₃ NP/SWNT) layer for deep ultraviolet light-emitting diodes using spin and dipping methods. We investigated the electrical, optical and morphological properties of the Ga₂O₃ NP/SWNT layers by increasing the thickness of SWNTs via multiple dipping processes. Compared with the undoped Ga₂O₃ films (current level 9.9 × 10^-9 A @ 1 V, transmittance 68% @ 280 nm), the current level flowing in the Ga₂O₃ NP/SWNT increased by approximately 4 × 10⁵ times and the transmittance improved by 9% after 15 times dip-coating (current level 4 × 10^-4 A at 1 V; transmittance 77.0% at 280 nm). These improvements result from both native high transparency of Ga₂O₃ NPs and high conductivity and effective current spreading of SWNTs.