Low-temperature fabrication of sol–gel NiO film for optoelectronic devices based on the ‘fuel’ of urea

In this work, NiO coating is fabricated by a low temperature ‘combustion process’ driven by ‘chemical oven’ on quartz and indium tin oxide (ITO) substrates followed by an annealing process in air at 225 °C for 2 h. The NiO coating is analyzed by means of thermalgravimetric differential thermal analysis (TG-DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electric microscopy (SEM), atomic force microscope (AFM), and UV–visible spectrometer. A prelimilary photovoltaic performance measurement of the fabricated device (ITO/NiO/poly-TPD/PC₇₁BM/Al) shows a short circuit current density (J_sc) of 5.28 mA cm⁻² and power conversion efficiency (PCE) of 1.56% under an illumination of 100 mW cm⁻². The PCE of device with combustion NiO HTLs is almost 10-fold higher than those of the devices based on common NiO HTLs. The combustion fabricated NiO coating may provide an effective approach to fabricate other NiO-based optoelectrical devices at relative low temperature.     

Control of refractive index by annealing to achieve high figure of merit for TiO2/Ag/TiO2 multilayer films

We modified the refractive index (n) of TiO₂ by annealing at various temperatures to obtain a high figure of merit (FOM) for TiO₂/Ag/TiO₂ (45 nm/17 nm/45 nm) multilayer films deposited on glass substrates. Unlike the as-deposited and 300 °C-annealed TiO₂ films, the 600 °C-annealed sample was crystallized in the anatase phase. The as-deposited TiO₂/Ag/as-deposited TiO₂ multilayer film exhibited a transmittance of 94.6% at 550 nm, whereas that of the as-deposited TiO₂/Ag/600 °C-annealed TiO₂ (lower) multilayer film was 96.6%. At 550 nm, n increased from 2.293 to 2.336 with increasing temperature. The carrier concentration, mobility, and sheet resistance varied with increasing annealing temperature. The samples exhibited smooth surfaces with a root-mean-square roughness of 0.37–1.09 nm. The 600 °C-annealed multilayer yielded the highest Haacke's FOM of 193.9×10⁻³ Ω⁻¹.     

Heteroepitaxial growth of Cu2O films on Nb-SrTiO3 substrates and their photovoltaic properties

In this paper, p-type Cu₂O thin films have been epitaxially grown on n-type semiconducting (001) oriented Nb-SrTiO₃ (NSTO) substrates with different Nb doping concentration by pulsed laser deposition technique. X-ray diffraction and high resolution transmission electron microscopy reveal a cube-on-cube epitaxial relationship between Cu₂O and NSTO. It is found that the deposition temperature, the thickness of Cu₂O films and the Nb doping concentration of NSTO substrates have critical impact on the photovoltaic (PV) properties of the Cu₂O/NSTO heterojunction devices. A maximum PV performance is observed in ITO/Cu₂O/NSTO device when the deposition temperature, film thickness and Nb doping concentration of NSTO are 550 °C, 76 nm, and 0.7 wt% NSTO, respectively. The optimized PV output corresponds to the open circuit voltage, short-circuit current density, fill factor and photovoltaic conversion efficiency about 0.45 V, 1.1 mA/cm², 46% and 0.23%,respectively. This work offers an insight into the strategy for developing and designing novel optoelectronics of NSTO-based oxide heterostructures.     

Characterization of luminescent properties of ZnO:Er thin films prepared by rf magnetron sputtering

ZnO:Er thin films were deposited on c-plane sapphire substrates by rf magnetron sputtering and annealed at 700 °C under air and H₂ atmospheres for the luminescent improvement. The effects of sputtering parameters and the annealing conditions on visible and 1.54 μm IR emissions were investigated. Structural and luminescent properties strongly depended on the deposition conditions and annealing atmospheres. By tuning the excitation wavelength, ZnO:Er thin films exhibited a strong emission band at around 465 nm and a weak emission at 525 nm originated from the energy transition of ⁴I_15/2–⁴F_5/2 and ⁴I_15/2–²H_11/2, respectively, while 1.54 μm IR emissions due to ⁴I_15/2–⁴I_13/2 transition.     

Annealing effect on temperature coefficient of resistivity in La1−xSrxMnO3 ceramics

We investigated annealing effects of La_1?xSr_xMnO₃ (x = 0–0.6) on electrical resistivity and the temperature coefficient of resistivity (TCR). The annealed samples’ resistivity was lower than those of non-annealed samples. For example, annealing changed the resistivity of x = 0.3 at 25 °C from 4.50 × 10^?5 to 3.71 × 10^?5 Ω m. Remarkable difference in TCR was observed after annealing, for x = 0.3, 0.45, and 0.5. For x = 0.3, the TCR after annealing was 4000 ppm/°C, which was 1250 ppm/°C greater than that before annealing. We investigated (1) crystal phase, (2) Mn average valence, (3) Mott insulator–metal transition temperature, and (4) microstructure. The microstructure was remarkably varied for annealed x = 0.3 and 0.5. The average grain size of the x = 0.3 increased from 1.60 up to 2.38 μm. Results show that annealing affects resistivity and TCR because of grain growth during annealing.     

Annealing induced discoloration of transparent YAG ceramics using divalent additives in solid-state reaction sintering

Tetraethyl orthosilicate (TEOS) was commonly served as a sintering additive to promote the densification of transparent Y₃Al₅O₁₂ (YAG) ceramics. However, Si⁴⁺ that decomposed from TEOS would restrain the conversion of dopants into a higher valence state (e.g., Cr³⁺ → Cr⁴⁺). In this study, by using divalent sintering additives (CaO and MgO), the colorless and highly transparent YAG ceramics (T = 84.6%, at 1064 nm) were obtained after vacuum sintering at 1840 °C for 8 h and without subsequent annealing in air. An absorption peak centered at ∼320 nm was observed before annealing, and it extended to ∼550 nm after annealing at 1450 °C for 10 h in air. A discoloration phenomenon occurred and more scattering centers were observed with the formation of new [Mg/Ca²⁺F⁺] color centers. Air annealing did not improve the optical quality of the as-fabricated YAG ceramics with divalent dopants as sintering additives, owing to the formation of scattering centers.     

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.     

Low-temperature fabrication of Ba1−xSrxTiO3 thin films with good dielectric properties on platinized silicon substrates

Ba_0.7Sr_0.3TiO₃ (BST) thin films 500 nm in thickness were prepared on technologically desirable Pt/TiO₂/SiO₂/Si(1 0 0) substrates by ion beam sputtering (IBS) and post-deposition annealing method. The effect of annealing temperature on the structural and dielectric properties of BST thin films was systematically investigated. A sharp transition in their tunable dielectric behaviours was observed in good agreement with the evolution of crystal structure from amorphous to crystalline phase. It was demonstrated that the perovskite phase could crystallize in BST films at a very low temperature, around 450 °C. The lowering of perovskite crystallization temperature in the BST films was explained in terms of the high energetic process nature of IBS technique. A high dielectric tunability of 42% at E (electric field intensity) = 500 kV/cm and a low loss tangent of 0.013 at zero bias were both obtained in the 450 °C-annealed film, thereby resulting in the highest figure-of-merit factor among all the different temperature annealed films. Moreover, the 450 °C-annealed film showed superior leakage current characteristics with a low leakage current density of about 10^?4 A/cm² at E = 800 kV/cm.     

Lead zirconium titanate thin films prepared by thermal annealing of multilayer structures composed of PbO,ZrO2 and TiO2

Lead zirconium titanate [Pb(Zr_xTi_1?x)O₃ or PZT] thin films were prepared by the thermal annealing of multilayer films composed of binary oxide layers of PbO, ZrO₂ and TiO₂. The binary oxides were deposited by metal organic chemical vapor deposition. An interdiffusion reaction for perovskite PZT thin films was initiated at approximately 550 °C and nearly completed at 750 °C for 1 h under O₂ annealing atmosphere. The composition of Pb/Zr/Ti in perovskite PZT could be controlled by the thickness ratio of PbO/ZrO₂/TiO₂ where the contribution of each binary oxide at the same thickness was 1:0.55:0.94. The electrical properties of PZT (Zr/Ti = 40/60, 300 nm) prepared on a Pt-coated substrate included a dielectric constant ?_r of 475, a coercive field E_c of 320 kV/cm, and remnant polarization P_r of 11 μC/cm² at an applied voltage of 18 V.     

Synthesis and characterization of the crystalline powders on the basis of Lu2O3:Eu3+spherical submicron-sized particles

This study is devoted to the preparation of the crystalline powders on the basis of non-agglomerated monodisperse Lu₂O₃:Eu³⁺ spherical particles with the diameters in the range of 50–250 nm by the soft chemistry co-precipitation route. The influence of the synthesis parameters on control morphology, particles size and agglomeration in the final Lu₂O₃:Eu³⁺ powder was considered. Lu₂O₃:Eu³⁺ crystalline powders were characterized by means of electron microscopy methods (TEM, SEM), FT-IR spectroscopy, thermal analysis (TG-DTA) and X-ray diffractometry. The mechanisms of the precursor decomposition and crystallization at the temperatures ranging from 60 to 900 °C were discussed. It was shown that the powders obtained were characterized by the effective luminescence under X-ray excitation in λ = 575–725 nm spectral region corresponding to ⁵D₀ → ⁷F_J transitions (J = 0–4) of Eu³⁺ ions with a maximum at 612 nm and the luminescence intensity strongly depends on annealing temperature. The relative densities of the green-bodies on the basis of Lu₂O₃:Eu³⁺ powders were estimated and the sintering of compacts at the temperatures up to 1500 °C was studied.     

Synthesis and photovoltaic characterization of D/A structure compound based on N-substituted phenothiazine and benzothiadiazole

In this study, poly [(N-10′-dodecyl-phenothizin-3,7-ylene)-alt-(2,2′-bithiophen-5-yl)] (P1) and poly [(N-10′-dodecyl-phenothiazin-3,7-ylene)-alt-(5′,6′-dioctyloxy-benzothiadiazole-bithiophene)] (P2) were synthesized by Suzuki coupling reaction. Optical and electrochemical characteristics of the synthesized polymers, P1 and P2, were then analyzed, indicating that their wavelength of maximum absorption was 453 nm and 533 nm, respectively, and their band-gap was 1.93 eV and 1.74 eV, respectively. The maximum power conversion efficiency (PCE) of organic photovoltaic cells created by using P1 and P2 were 0.74% (P1:PC₇₁BM = 1:4,w/w) and 1.00% (P2:PC₇₁BM = 1:3,w/w), respectively, and the short circuit current density (J_SC), fill factor (FF), and open circuit voltage (V_OC) of the device were 3.5 mA/cm², 31.8%, and 0.68 V, respectively, for P1 and 3.9 mA/cm², 32.7%, and 0.78 V, respectively, for P2.     

Effects of annealing temperature on the microstructure,ferroelectric and dielectric properties of W-doped Na0.5Bi0.5TiO3 thin films

The effects of annealing temperature on the structure, morphology, ferroelectric and dielectric properties of Na_0.5Bi_0.5Ti_0.99W_0.01O_3+δ (NBTW) thin films are reported in detail. The films are deposited on indium tin oxide/glass substrates by a sol-gel method and the annealing temperature adopted is in the range of 560–620 °C. All the films can be well crystallized into phase-pure perovskite structures and show smooth surfaces without any cracks. Particularly, the NBTW thin film annealed at 600 °C exhibits a relatively large remanent polarization (P_r) of 20 μC/cm² measured at 750 kV/cm. Additionally, it shows a high dielectric constant of 608 and a low dielectric loss of 0.094 as well as a large dielectric tunability of 62%, making NBTW thin film ideal in the room-temperature tunable device applications.     

Nucleation and growth surface conductivity of H-terminated diamond films prepared by DC arc jet CVD

High-quality polycrystalline diamond film has been extremely attractive to many researchers, since the maximum transition frequency (f_T) and the maximum frequency of oscillation (f_max) of polycrystalline diamond electronic devices are comparable to those of single crystalline diamond devices. Besides large deposition area, DC arc jet CVD diamond films with high deposition rate and high quality are one choice for electronic device industrialization. Four inch free-standing diamond films were obtained by DC arc jet CVD using gas recycling mode with deposition rate of 14 μm/h. After treatment in hydrogen plasma under the same conditions for both the nucleation and growth sides, the conductivity difference between them was analyzed and clarified by characterizing the grain size, surface profile, crystalline quality and impurity content. The roughness of growth surface with the grain size about 400 nm increased from 0.869 nm to 8.406 nm after hydrogen plasma etching. As for the nucleation surface, the grain size was about 100 nm and the roughness increased from 0.31 nm to 3.739 nm. The XPS results showed that H-termination had been formed and energy band bent upwards. The nucleation and growth surfaces displayed the same magnitude of square resistance (R_s). The mobility and the sheet carrier concentration of the nucleation surface were 0.898 cm/V s and 10¹³/cm² order of magnitude, respectively; while for growth surface, they were 20.2 cm/V s and 9.97 × 10¹¹/cm², respectively. The small grain size and much non-diamond carbon at grain boundary resulted in lower carrier mobility on the nucleation surface. The high concentration of impurity nitrogen may explain the low sheet carrier concentration on the growth surface. The maximum drain current density and the maximum transconductance (g_m) for MESFET with gate length L_G of 2 μm on H-terminated diamond growth surface was 22.5 mA/mm and 4 mS/mm, respectively. The device performance can be further improved by using diamond films with larger grains and optimizing device fabrication techniques.     

Optical and mechanical properties of amorphous bulk and eutectic ceramics in the HfO2–Al2O3–Y2O3 system

Bulk glasses containing HfO₂ nano-crystallites of 20–50 nm were prepared by hot-pressing of HfO₂–Al₂O₃–Y₂O₃ glass microspheres at 915 °C for 10 min. By annealing at temperatures below 1200 °C, the bulk glasses were converted into transparent glass-ceramics with HfO₂ nano-crystallites of 100–200 nm, which showed the maximum transmittance of ～70% in the infrared region. An increase of annealing temperature (>1300 °C) resulted in opaque YAG/HfO₂/Al₂O₃ eutectic ceramics. The eutectic ceramics contained fine Al₂O₃ crystallites and showed a high hardness of 19.8 GPa. The fracture toughness of the eutectic ceramics increased with increasing annealing temperature, and reached the maximum of 4.0 MPa m^1/2.     

The effect of annealing on electrical properties of fluorinated amorphous carbon films

Fluorinated amorphous carbon (a–C:F) films have been deposited by electron cyclotron resonance chemical vapor deposition (ECR–CVD) at room temperature using C₄F₈ and CH₄ as precursor gases. The chemical compositions and electrical properties of a–C:F films have been studied by X-ray photoelectron spectroscopy (XPS), capacitance–voltage (C–V) and current-voltage (I–V) measurements. The results show that C–CF_x and C–C species of a–C:F films increase and fluorine content decreases after annealing. The dielectric constant of the annealed a–C:F films increases as a result of enhancement of film density and reduction of electronic polarization. The densities of fixed charges and interface states decrease from 1.6 × 10¹⁰ cm^− 2 and (5–9) × 10¹¹ eV^− 1 cm^− 2 to 3.2 × 10⁹ cm^− 2 and (4–6) × 10¹¹ eV^− 1 cm^− 2 respectively when a–C:F films are annealed at 300 °C. The magnitude of C–V hysteresis decreases due to reduced dangling bonds at the a–C:F/Si interfaces after heat treatment. The conduction of a–C:F films shows ohmic behavior at lower electric fields and is explained by Poole–Frankel (PF) mechanism at higher electric fields. The PF current increases indicative of reduced trap energy when a–C:F films are subjected to higher annealing temperatures.     

Synthesis and chemosensory properties of terpyridine-containing diblock polycarbazole through RAFT polymerization

This paper describes the synthesis of a terpyridine-containing diblock copolymer, poly(N-vinylcarbazole)-block-poly[4′-((4-vinylphenyl) phenyl)-2,2′:6′,2″- terpyridine] (poly(VK₁₅-b-TPY₄)), using the macro-chain transfer agent VK macro-CTA, and employing two-step reverse addition-fragmentation transfer (RAFT) polymerization. We examined the effect of terpyridine units on sensory characteristics of fluorescent chemosensors. VK macro-CTA and diblock copolymer poly(VK₁₅-b-TPY₄) both exhibited moderate thermal stability, with thermal decomposition temperatures of 5% weight losses at approximately 307 °C and 378 °C, respectively, suggesting that the enhancement of thermal stability was attributed to the incorporation of terpyridine segments into the block copolymer. Poly(VK₁₅-b-TPY₄) exhibited higher sensitivities to Ni^2 + and Mn^2 + ions, with Stern–Volmer constants (K_sv) of 2.58 × 10⁵ M^− 1 and 2.57 × 10⁵ M^− 1, respectively. Adding a Zn^2 + ion not only caused partial fluorescence enhancement (3.2-fold quantum efficiency) but also induced a bathochromic shift of emission peak by approximately 56 nm (from 429 nm to 485 nm), indicating that the Zn^2 +-terpyridine complex reduced the twist and vibration of the C–C polymer backbone and enhanced the charge transfer from donors to acceptors because of the more planar and rigid structure. Our results suggest that poly(VK₁₅-b-TPY₄) is a promising material for chemosensory applications.     

Annealing-induced structural changes of carbon onions: High-resolution transmission electron microscopy and Raman studies

The first- and second-order Raman spectra of carbon nano-onions (CNOs), produced via annealing of detonation nanodiamonds with a mean grain size of ∼5 nm in the argon ambience at the maximal temperature of annealing process (T_MAX) varying from 1500 to 2150 °C, are analyzed together with the high-resolution transmission electron microscopy (HRTEM) images. The combined analysis provides a deep insight into the annealing-induced atomic-scale structural modifications of the CNO nanoparticles. The Raman and HRTEM data unambiguously demonstrate the reduction in the number of defects in the CNO structure, as well as indicate the conversion from the diamond sp³-bonded carbon phase to the sp²-bonded carbon phase with increasing T_MAX and its almost full completion for T_MAX = 1600 °C.     

PNBE-supported metallopolymer-type hybrid materials through grafting of Ln3-benzimidazole-arrayed (Ln = Nd,Yb or Er) complex monomers with efficient NIR luminescence

Through the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) with each of the obtained allyl-containing complex monomers {[Ln₃(L)₄Cl₄(MeOH)₂]·Cl} (Ln = La, 1; Nd, 2; Yb, 3; Er, 4 or Gd, 5; HL = 4-allyl-2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol), a series of metallopolymers Poly({[Ln₃(L)₄Cl₄(MeOH)₂]·Cl}-co-NBE) were obtained, respectively. Especially for Poly(NBE-co-2) and Poly(NBE-co-3), covalently-bonded grafting endows significantly improved physical properties including efficient NIR luminescence (Φ_Nd^L = 0.58% and Φ_Yb^L = 0.88%) in solid state.     

Orientation control and electrical properties of PZT/LNO capacitor through chemical solution deposition

This paper describes the deposition of PZT/lanthanum nickel oxide (LNO) electrode thin-film capacitor on a Si(1 0 0) substrate with a chemical solution deposition (CSD). Highly (1 0 0)-oriented LNO film with a perovskite structure was deposited by annealing at 700 °C from a precursor solution of La(NO₃)₃ and Ni(CH₃COO)₂. In addition, highly (1 0 0)&(0 0 1)-oriented PZT/LNO capacitor was deposited on LNO/Si substrate by annealing at 600 °C, showing P_r = 18 μC/cm² and E_c = 36 kV/cm. Furthermore, the resultant PZT/LNO thin-film capacitor exhibited no fatigue up to 10⁸ switching cycles.     

Carbons with narrow pore size distribution prepared by simultaneous carbonization and self-activation of tobacco stems and their application to supercapacitors

Highly microporous carbons with narrow pore size distribution have been prepared by simultaneous carbonization and self-activation of tobacco wastes at temperatures ranging from 600 to 1000 °C. The efficiency of porosity development, without pores broadening, is attributed to well-distributed alkalis at the molecular level in the tobacco precursor. With Burley tobacco, the BET specific surface area and average micropore size L₀ increased up to 800 °C (Burley 800), where the values reached maxima of 1749 m² g⁻¹ and 1.2 nm, respectively. At temperatures higher than 800 °C, annealing of the materials dominates and provokes a decrease of S_BET and L₀. Burley carbons were implemented in supercapacitors using 1 mol L⁻¹ aqueous Li₂SO₄ or 1 mol L⁻¹ TEABF₄ in acetonitrile. In both electrolytes, the capacitance of Burley carbons followed the same trend as S_BET and L₀. Burley 800 demonstrated outstanding capacitance values of 167 F g⁻¹ (at 0.8 V limit) and 141 F g⁻¹ (at 2.3 V limit) in 1 mol L⁻¹ aqueous Li₂SO₄ and 1 mol L⁻¹ TEABF₄, respectively. Such values, about 50% higher as compared to commercially available carbons, are attributed to the narrow pore size distribution of this carbon with a maximum of pores around 1.2 nm close to the size of solvated ions in these electrolytes.