Microstructure and optical properties of Ag/ITO/Ag multilayer films

Transflective and highly conductive Ag/ITO/Ag multilayer films were prepared by magnetron sputtering on glass substrates. The microstructure and optical properties of Ag/ITO/Ag multilayer films were systematically investigated by X-ray diffraction, scanning electron microscopy, and ultraviolet-visible spectroscopy. The optical properties of the multilayer films were significantly influenced by the thickness of the Ag surface layer from 3.0 to 12.6 nm. The multilayer film of Ag9.3nm/ITO142nm/Ag9.3nm shows the best comprehensive property. It could satisfy the requirement for transflective LCD.     

Influence of Ag incorporation on the structural,optical and electrical properties of ITO/Ag/ITO multilayers for inorganic all-solid-state electrochromic devices

Indium tin oxide/silver/indium tin oxide (ITO/Ag/ITO, IAI) multilayer structures were prepared by DC magnetron sputtering as a conductive transparent electrode for inorganic all-solid-state electrochromic devices. A thin layer of silver (Ag) with various thicknesses was inserted between two layers of ITO films. The XRD and SEM results revealed that the microscopic morphology of Ag film was closely related to the thickness. Besides, the electrical and optical properties of the IAI multilayers were significantly influenced by the Ag layer thickness. The optimized IAI multilayers demonstrated the best combination of electrical and optical properties with a figure of merit of 54.05 (sheet resistance of 6.14 Ω/cm²and optical transmittance of 90.83%) when the Ag film was 10 nm thick. In order to evaluate the IAI multilayers as a transparent electrode for electrochromic applications, two ECDs with the structures of ITO/NiO_x/LiPON/WO₃/ITO and ITO/NiO_x/LiPON/WO₃/IAI were prepared, and their electro-optical properties were characterized by cyclic voltammetry (CV), chronoamperometry (CA) and spectroscopic measurements. Compared with ECD the pure ITO top electrode (ITO/NiO_x/LiPON/WO₃/ITO), the ECD with the IAI top electrode (ITO/NiO_x/LiPON/WO₃/IAI) presented a slightly smaller optical modulation amplitude, but a faster switching speed. All our findings indicate that the IAI multilayer structure is a promising alternative to the ITO thin film for inorganic all-solid state electrochromic applications.     

ITO薄膜的研究进展

ITO是锡掺杂氧化铟薄膜的简称,属于透明导电氧化物材料。常规沉积方法制备的ITO薄膜通常为非晶态或体心立方晶系晶体,为n型半导体材料,其载流子为自由电子,主要来源于沉积过程中薄膜化学计量比偏离或阳离子掺杂形成的施主杂质。ITO薄膜是当前研究和使用最为广泛的透明导电氧化物薄膜材料,由于具有低电阻率、高可见光透过率、高红外反射率等独特物理特性而被大量应用于平板显示器、太阳能电池、发光二极管、气体传感器、飞机风挡玻璃除霜器等领域。此外,ITO薄膜对微波还具有高达85%的衰减作用,因而在电磁屏蔽等军用领域显示出巨大的潜在应用价值。过去几十年里,针对ITO薄膜的研究工作主要聚焦于薄膜的光电性能上。当前,伴随着ITO薄膜的应用范围在航空航天和军用武器装备等领域的拓展,ITO薄膜在恶劣力学环境中的使用日渐增多。因此,除光电性能外,ITO薄膜的力学性能也开始受到研究者越来越多的关注,人们对薄膜器件在各类恶劣使用环境中的稳定性及耐久性提出了更高的要求,这一要求使得对ITO薄膜力学性能的深入研究分析有了重要的理论及实际意义。本文综述了近年来ITO薄膜在微结构特性、能带结构、光电性能及力学性能等方面的研究进展,简略探讨了ITO薄膜的研究发展方向。     

Influence of an In2O3 buffer layer on the properties of ITO thin films

In the present study, an indium oxide (In₂O₃) thin film was deposited as a buffer layer between ITO (indium tin oxide) and PES (polyestersulfone) by RF (radio frequency) magnetron sputtering at room temperature, and X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were conducted to characterise the structural variation. The random texture of the ITO/In₂O₃ multilayered film favoured the (2 2 2) crystallographic plane rather than the (4 0 0) plane, which was favoured in single-layer ITO films. Transmission electron microscopy (TEM) observations further indicated that the buffer layer of In₂O₃ film was amorphous, while the ITO film was characterised by a columnar structure that was oriented perpendicular to the substrate surface. The electrical and optical properties of ITO/In₂O₃ multilayered films were enhanced due to the superior crystallinity and larger grain size of the material, as observed by XRD and FESEM. The multilayered film presented an electrical resistivity of 3.1 × 10⁻⁴ Ω cm, which is significantly better than that of a single-layer ITO film without an In₂O₃ buffer layer (4.7 × 10⁻⁴ Ω cm). In addition, optical transmission through the multilayered film increased by 2-4% due to the widening of the band gap by 0.2 eV, which was attributed to a Burstin-Moss shift.     

Ferroelectric and dielectric properties of manganese-doped Na0.5Bi0.5TiO3 nanocrystalline thin films prepared by metal organic decomposition: A single-layer thickness-dependent study

2 at% Manganese-doped Na_0.5Bi_0.5TiO₃ (NBTMn) thin films with single-layer thicknesses ranging from 15 to 45 nm/l were deposited on the indium tin oxide/glass substrates by a metal organic decomposition process and spin coating technique. The influence of single-layer thickness on the crystal structure, surface morphology, insulating ability, ferroelectric and dielectric properties was mainly investigated. Compared with the other films, NBTMn film with a single-layer thickness of 30 nm/l exhibits the (110)-preferred orientation and dense structure. Also, it shows the enhanced ferroelectricity with a large remanent polarization (P_r) of 38 μC/cm² due to the preferred orientation and low leakage current density. Meanwhile, a high dielectric tunability of 39% for NBTMn with 30 nm/l can be observed by varying the measuring applied voltage and frequency. These results indicate that the suitable layer thickness is beneficial to improve the electrical performances of NBTMn thin film.     

Layer-by-layer assembly of graphene/polyaniline multilayer films and their application for electrochromic devices

Graphene/polyaniline (PANI) multilayer films were prepared via alternate deposition of negatively charged graphene oxide (GO) and positively charged PANI upon electrostatic interaction, followed by the reduction of their GO components with hydroiodic acid. The thickness of the multilayer film increased linearly with the number of its bilayers and that of each bilayer was measured to be about 3 nm. Cyclic voltammetry studies indicated that these thin composite films were electroactive, and their redox reactions were related to the insertion-extraction of counter ions in PANI layers. Furthermore, the composite films were tested to be promising electrode materials for electrochromic devices even without using the conventional indium tin oxide (ITO) electrodes.     

On the determination of the film hardness in hard film/substrate composites using depth-sensing indentation

The main difficulty in the mechanical characterisation of thin films using depth-sensing indentation is the determination of the relative substrate and film contributions to the measured properties of the film/substrate composite. In this study, a three-dimensional numerical simulation of the Vickers hardness test is used to study the influence of the substrate and film mechanical properties on the composite's behaviour under depth-sensing indentation. The particular case of hard films on soft substrates is analysed. In order to understand the behaviour of the composite, a study of the plastic strain distribution under indentation of several composites is performed. A methodology to determine the relative film hardness, i.e. H_F/H_S ratio, is proposed. The methodology is successfully verified using fictitious and real composite materials.     

Large enhancement of energy storage density in (Pb0.92La0.08)(Zr0.65Ti0.35)O3/PbZrO3 multilayer thin film

(Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ (PLZT), PbZrO₃ (PZO) films, and type A and type B PLZT/PZO multilayer thin films were deposited on Pt(111)/TiO_x/SiO₂/Si substrates by sol-gel method, where type A and type B films stand for PLZT/PZO/PLZT/PZO/PLZT/PZO and PLZT/PZO/PLZT/PLZT/PZO/PLZT multilayer thin film, respectively. Compared to the PLZT and PZO film, enhanced breakdown field strength and improved energy storage density were obtained in type A and B multilayer thin films. A superior energy storage density of 29.7 J/cm³ with the energy storage efficiency of 50.8% was achieved in type B multilayer thin film, corresponding to 81% enhancement compared with the energy storage density of PLZT films (16.4 J/cm³). Additionally, the type B multilayer thin film exhibits a good thermal stability up to 160 °C and excellent fatigue endurance after 10⁷ charging-discharging cycles. The enhanced energy storage performance of type B multilayer thin film shows promise and may stimulate further researches on energy storage applications of multilayer dielectric thin films.     

Enhanced multiferroic properties of Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 layered composite thin films

In this work, Bi₄Ti_3-xCo_xO₁₂/La_0.67Sr_0.33MnO₃ (BITC_x/LSMO, x = 0.025, 0.05, 0.10 and 0.15) layered magnetoelectric (ME) composite thin films were successfully synthesized by chemical solution deposition, and the effect of Co²⁺ doping content on the microstructure, leakage, dielectric property, ferroelectricity, ferromagnetism and ME coupling performance of BITC_x/LSMO composite thin films was investigated. Co²⁺ doping induces improved ferroelectricity and weak ferromagnetism for the BITC_x phase. Especially, the single-phase BITC_0.05 film exhibits a maximum ME voltage coefficient (α_E) of 0.445 mV/cm·Oe at room temperature, suggesting excellent single-phase multiferroic properties. The BITC_0.05/LSMO composite thin film possesses the lowest leakage current density, maximum ?_r, minimum tanδ, highest remnant polarization of 24.2 μC/cm², lowest coercive field of 137 kV/cm and improved saturation magnetization along with a maximum a_E value of 27.3 V/cm·Oe. Based on these findings, Co²⁺-doped Bi₄Ti₃O₁₂ has excellent single-phase multiferroic properties, and the incorporation of magnetic ion-doped Bi₄Ti₃O₁₂ with ferromagnetic oxides benefits the improvement of ME composite thin films.     

Highly ordered columnar ITO thin film with enhanced thermoelectric and mechanical performance over wide temperature range

Indium tin oxide (ITO) based thin films offer the possibility to improve the performance of high-temperature thermocouples by providing good sensitivity and reliability over a wide temperature range. In this study, a thin but robust ITO-based thin-film thermocouple, with a low-crystallised highly ordered columnar structure, was fabricated. The electrical conductivity exhibited a high temperature-dependent sensitivity owing to the increasing density with increasing temperature. The nano-hardness and interfacial robustness were evaluated and found to exhibit excellent service reliability at high temperatures because of the low thermal stress. Furthermore, the similar mechanical and electrical performances of the thin films, after annealing at 600 and 800 °C, demonstrated that the enhanced performance was mainly determined by the orientation of the ITO thin films. An enhanced Seebeck coefficient (～100 μV K^?1) was obtained for the ITO thin film after annealing at 1000 °C, resulting in a special structure with profuse nanoholes. These results highlight the good mechanical performance and stability of the thermoelectric properties of highly ordered columnar thin films over a wide temperature range, and can serve as a guide for the preparation of thin but robust functional ceramic-based materials.     

Effect of (Zn,Mn) co-doping on the structure and ferroelectric properties of BiFeO3 thin films

BiFe_1-2xZn_xMn_xO₃ (BFZMO, with x = 0–0.05) thin films were synthesized via sol–gel method. Effects of (Zn, Mn) co-doping on the structure, ferroelectric, dielectric, and optical properties of BiFeO₃ (BFO) films were investigated. BFZMO thin films exhibit rhombohedral structure. Scanning electron microscopy (SEM) images indicate that co-doping leads to a decrease in grain size and number of defects. Leakage current density (4.60 × 10^?6 A/cm²) of BFZMO film with x = 0.02 was found to be two orders of magnitude lower than that of pristine BFO film. Owing to decreased leakage current density, saturated P–E curves were obtained. Maximum double remnant polarization of 413.2 μC/cm² was observed for BFZMO thin film with x = 0.02, while that for the BFO film was found to be 199.68 μC/cm². The reason for improved ferroelectric properties is partial substitution of Fe ions with Zn and Mn ions, which resulted in a reduction in the effect of oxygen vacancy defects. In addition, co-doping was found to decrease optical bandgap of BFO film, opening several possible routes for novel applications of these (Zn, Mn) co-doped BFO thin films.     

Rapid thermal annealing effect of transparent ITO source and drain electrode for transparent thin film transistors

We investigated the rapid thermal annealing (RTA) sequence effect on the electrical, optical, morphological, and structural properties of transparent thin film transistors (TTFTs) with an indium gallium zinc oxide (IGZO) channel and an indium tin oxide (ITO) source/drain. The electrical and optical properties of the IGZO channel and the ITO source/drain electrodes were compared as a function of RTA temperature in ambient air. The performance of a TTFT with only an RTA-processed IGZO channel was compared with that of a TTFT with an RTA-processed IGZO channel and ITO source/drain electrodes. Using the circular transmission line measurement (CTLM) method, we suggest a possible mechanism that explains the effect of the RTA process on the performance of the TTFT with only an annealed IGZO channel vs. that with an annealed IGZO/ITO multilayer. The TTFT with an RTA-processed IGZO/ITO multilayer showed a threshold voltage shift, an improved on/off ratio of 3.54 × 10¹¹, a subthreshold swing of 0.33 V/decade, and a high mobility of 8.69 cm²/V·s. This indicates that simultaneous RTA processing for an IGZO channel and an ITO electrode is beneficial for the fabrication of high-performance TTFTs.     

Essential Macleod Program (EMP) simulated fabrication of high quality Zn:SnO2/Ag/Zn:SnO2 multilayer transparent conducting electrode on flexible substrates

In the quest of promising Indium free amorphous transparent conducting oxide (TCO), Zn-doped SnO₂/Ag/Zn-doped SnO₂ (OMO) multilayer films were prepared on flexible polyethylene terephthalate (PET) substrates by RF sputtering at room temperature (RT). Growth parameters were optimized by varying sputtering power and working pressure, to have high electrical conductivity and optical transmittance. Optimization of the thickness of each layer was done by Essential Macleod Program (EMP) simulation to get the higher transmission through OMO multilayer. The sheet resistance and transmittance of 3 at% Zn-doped SnO₂ thin film (30 nm) were 2.23 kΩ/□, (ρ ~ 8.92×10⁻³ Ω∙cm) and 81.3% (at λ ~ 550 nm), respectively. By using optimized thicknesses of Zn-doped SnO₂ (30 nm) and Ag (12 nm) and optimized growth condition Zn-doped SnO₂/Ag/Zn-doped SnO₂ multilayer thin films were deposited. The low sheet resistance of 7.2 Ω/□ and high optical transmittance of 85.1% in the 550 nm wavelength region was achieved with 72 nm multilayer film.     

Relationship between mechanical properties and coefficient of friction of sputtered a-C/Cu composite thin films

The article reports on properties of a-C films containing different amount of Cu. Films were sputtered by unbalanced magnetron from a graphite target with Cu fixing ring in argon under different deposition conditions. Relationships between the structure, mechanical properties, macrostress σ and coefficient of friction (CoF) μ of a-C/Cu films sputtered on Si substrates were investigated in detail. Besides, a special attention was concentrated on investigation of the effect of a deposition rate a_D of the a-C/Cu film on its hardness H and macrostress σ. Four main issues were found: (1) the addition of Cu into a-C film strongly influences its structure and mechanical properties, i.e. the hardness H, effective Young's modulus E⁎ macrostress σ and CoF, and makes it possible to form electrically conductive films; here E⁎ =  E / (1 − ν²), E is the Young's modulus, and ν is the Poisson's ratio, (2) the hardness H and compressive macrostress σ of the a-C/Cu film decrease with increasing a_D due to decreasing of total energy E_T delivered to the film during its growth, (3) hard a-C/Cu films with low value of CoF (μ ≈ 0.1) can be sputtered at high deposition rates a_D ranging from ~ 10 to ~ 80 nm/min, and (4) CoF decreases with increasing (i) hardness H and (ii) resistance of film to plastic deformation characterized by the ratio H³/E⁎² but only in the case when compressive macrostress σ is low.     

Fabrication of highly efficient TiO2/Ag/TiO2 multilayer transparent conducting electrode with N ion implantation for optoelectronic applications

Fabrication of highly conductive and transparent TiO₂/Ag/TiO₂ (referred hereafter as TAT) multilayer films with nitrogen implantation is reported. In the present work, TAT films were fabricated with a total thickness of 100 nm by sputtering on glass substrates at room temperature. The as-deposited films were implanted with 40 keV N ions for different fluences (1×10¹⁴, 5×10¹⁴, 1×10¹⁵, 5×10¹⁵ and 1×10¹⁶ ions/cm²). The objective of this study was to investigate the effect of N⁺ implantation on the optical and electrical properties of TAT multilayer films. X-ray diffraction of TAT films shows an amorphous TiO₂ film with a crystalline peak assigned to Ag (111) diffraction plane. The surface morphology studied by atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) revealed smooth and uniform top layer of the sandwich structure. The surface roughness of pristine film was 1.7 nm which increases to 2.34 nm on implantation for 1×10¹⁴ ions/cm² fluence. Beyond this fluence, the roughness decreases. The oxide/metal/oxide structure exhibits an average transmittance ~80% for pristine and ~70% for the implanted film at fluence of 1×10¹⁶ ions/cm² in the visible region. The electrical resistivity of the pristine sample was obtained as 2.04×10⁻⁴ Ω cm which is minimized to 9.62×10⁻⁵ Ω cm at highest fluence. Sheet resistance of TAT films decreased from 20.4 to 9.62 Ω/□ with an increase in fluence. Electrical and optical parameters such as carrier concentration, carrier mobility, absorption coefficient, band gap, refractive index and extinction coefficient have been calculated for the pristine and implanted films to assess the performance of films. The TAT multilayer film with fluence of 1×10¹⁶ ions/cm² showed maximum Haacke figure of merit (FOM) of 5.7×10⁻³ Ω⁻¹. X-ray photoelectron spectroscopy (XPS) analysis of N 1s and Ti 2p spectra revealed that substitutional implantation of nitrogen into the TiO₂ lattice added new electronic states just above the valence band which is responsible for the narrowing of band gap resulting in the enhancement in electrical conductivity. This study reports that fabrication of multilayer transparent conducting electrode with nitrogen implantation that exhibits superior electrical and optical properties and hence can be an alternative to indium tin oxide (ITO) for futuristic TCE applications in optoelectronic devices.     

Excellent antimicrobial properties of mesoporous anatase TiO2 and Ag/TiO2 composite films

Optically transparent, crack-free, mesoporous anatase TiO₂ thin films were fabricated. The Ag/TiO₂ composite films were prepared by incorporating Ag in the pores of TiO₂ films with an impregnation method via photoreduction. The as-prepared composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectronic spectra (XPS) and N₂ adsorption. The release behavior of silver ions in the mesoporous composite film was also studied. Moreover, the antimicrobial behaviors of the mesoporous film were also investigated by confocal laser scanning microscopy. The antibacterial activities of the composite films were studied by a fluorescence label method using Escherichia coli (E. coli) as a model. The as-prepared mesoporous TiO₂ films showed much higher antimicrobial efficiency than that of glass and commercial P25 TiO₂ spinning film. The facts would result from the high surface area, small crystal size and more active sites for the mesoporous catalysis. After the doping of Ag, a significant improvement for the antimicrobial ability was obtained. To elucidate the roles of the membrane photocatalyst and the doped silver in the antimicrobial activity, cells from a silver-resistant E. coli were used. These results indicated that Ag nanoparticles in the mesoporous were not only an antimicrobial but also an intensifier for photocatalysis. The as-prepared mesoporous composite film is promising in application of photocatalysis, antimicrobial and self-clean technologies.     

Multiferroic and magnetoelectric properties of lead-free Ba0.8Sr0.2Ti0.9Zr0.1O3-Ni0.8Zn0.2Fe2O4 composite films with different deposition sequence

Ba_0.8Sr_0.2Ti_0.9Zr_0.1O₃/Ni_0.8Zn_0.2Fe₂O₄(BN) and Ni_0.8Zn_0.2Fe₂O₄/Ba_0.8Sr_0.2Ti_0.9Zr_0.1O₃ (NB) composite film were deposited on Pt/Ti/SiO₂/Si substrates by the sol-gel method and spin-coating method. The results show that the deposition sequences of the composite films have significant influence on the ferroelectric, ferromagnetic and magnetoelectric properties of the composite films. Two composite films possess not only good ferroelectric and ferromagnetic properties but good magnetoelectric properties as well. The NB composite film has clear interface between the ferroelectric film and ferromagnetic film and possesses greater magnetoelectric coupling effect than the BN composite film under the same H_bias. The maximum value of α_E is 70.14?mV?cm^?1 Oe^?1 was obtained in the NB composite film when H_bias is 638?Oe.     

Preparation of diamond like carbon thin films above room temperature and their properties

Diamond like carbon (DLC) thin films were deposited on p-type silicon (p-Si), quartz and ITO substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) at different substrate temperatures (RT ∼ 300 °C). Argon (Ar: 200 sccm) was used as carrier gas while acetylene (C₂H₂: 20 sccm) and nitrogen (N: 5 sccm) were used as plasma source. Analytical methods such as X-ray photoelectron spectroscopy (XPS), FT-IR and UV–visible spectroscopy were employed to investigate the structural and optical properties of the DLC thin films respectively. FT-IR spectra show the structural modification of the DLC thin films with substrate temperatures showing the distinct peak around 3350 cm^− 1 wave number; which may corresponds to the sp² C–H bond. Tauc optical gap and film thickness both decreased with increasing substrate temperature. The peaks of XPS core level C 1 s spectra of the DLC thin films shifted towards lower binding energy with substrate temperature. We also got the small photoconductivity action of the film deposited at 300 °C on ITO substrate.     

A leaf-like structured ITO conductive transparent thin film from visible to near-infrared region with enhanced stability

ITO thin films as the optical and electrical windows to transform photons and charges have been applied in many areas. Here, a leaf-like structured particle is composed of small particles growing along three different orientations leading to low thermal stress accompanied by well transmittance (85%) in a wide wavelength range from visible to near-infrared region and a narrowed band gap 3.07 eV. The evolution of structure and electronic performance was studied to obtain the low resistivity (12 μΩ m) and enhanced stability of the film (1000 °C). The leaf-like structure can be maintained under 600 ℃ and the electrical properties can be modified in He and N₂ atmosphere, owing to the reduced defects, increased concentration of Sn and carrier mobility. Although the structure has changed after being annealed at 1000 °C in N₂, the thin film performs excellent electrical properties (?3.44 × 10²⁰ cm^?3 and 28 cm² V^?1 s^?1).     

ITO electrode modified by self-assembling multilayer film of polyoxometallate on poly(vinyl alcohol) nanofibers and its electrocatalytic behavior

Poly(vinyl alcohol) (PVA) nanofiber mats were collected on indium tin oxide (ITO) substrate by electrospinning method. A multilayer film composed of α-[P₂W₁₈O₆₂]⁶⁻ (abbr. P₂W₁₈), a polyoxometallate (POM) anion, and poly(diallymethylammonium chloride) (abbr. PDDA) was fabricated by layer-by-layer (LBL) self-assembly technique on the PVA/ITO electrode. The PDDA/P₂W₁₈ multilayer film could be unselectively or selectively deposited on the PVA/ITO electrode via changing the amount of PVA nanofibers on the ITO substrate. The scanning electron microscope (SEM) images showed that when the electrospun time was short the PDDA/P₂W₁₈ multilayer film was unselectively deposited on PVA nanofiber mats because the amount of PVA nanofibers was too little to cover most of the ITO substrate. However, when the electrospun time was long enough, the PDDA/P₂W₁₈ multilayer film was selectively deposited on PVA nanofiber mats because of the larger surface area and higher surface energy of PVA nanofibers in comparison with the flat ITO substrate. Growth process of the multilayer film was determined by cyclic voltammetry (CV). Electrocatalytic effects of the PDDA/P₂W₁₈ multilayer film unselectively and selectively deposited on the PVA/ITO electrode on NO₂⁻ were observed.