Rapid formation of transparent CuAlO2 thin film by thermal annealing of Cu on Al2O3

Abstract

An 850-nm-thick CuAlO₂ film was formed by solid state reaction of evaporated thin film Cu on c-cut Al₂O₃ (sapphire) at 1200 °C for reaction times as short as 10 min. X-ray diffractogram confirms the formation of (0 0 l) CuAlO₂, indicating oriented growth of CuAlO₂ on c-cut Al₂O₃. Fourier transformation infra-red (FTIR) spectra showed peaks corresponding to Cu–O, Al–O and O–Cu–O bonds, confirming further the CuAlO₂ phase formation. UV–visible spectrum measurement showed high transparency of the film in the visible region with a direct band gap of 3.25 eV. The mechanism of the formation of the film is discussed.

Keywords

• CuAlO₂;
• Solid-state reaction;
• P-type;
• Transparent conducting oxides

Solar Energy Materials and Solar Cells

Volume 93, Issue 8, August 2009, Pages 1383–1387

Characterization of anodic SiO2 films on P-type 4H-SiC

Abstract

The physical and electronic properties of 100–120-nm thick anodic silicon dioxide film grown on p-type 4H-SiC wafer and annealed at different temperatures (500, 600, 700, and 800 °C) have been investigated and reported. Chemical bonding of the films has been analyzed by Fourier transform infra red spectroscopy. Smooth and defect-free film surface has been revealed under field emission scanning electron microscope. Atomic force microscope has been used to study topography and surface roughness of the films. Electronic properties of the film have been investigated by high frequency capacitance–voltage and current–voltage measurements. As the annealing temperature increased, refractive index, dielectric constant, film density, SiC surface roughness, effective oxide charge, and leakage current density have been reduced until 700 °C. An increment of these parameters has been observed after this temperature. However, a reversed trend has been demonstrated in porosity of the film and barrier height between conduction band edge of SiO₂ and SiC.

Keyword

• Anodic oxidation;
• Atomic force microscope;
• Annealing;
• Silicon carbide

Thin Solid Films

Volume 517, Issue 8, 27 February 2009, Pages 2808–2812

Oxide-assisted growth of silicon nanowires by carbothermal evaporation

Abstract

Silicon nanowires (SiNWs) have successfully been synthesized by carbothermal evaporation method. By ramping-up the furnace system at 20 °C min⁻¹ to 1100 °C for 6 h, the vertically aligned coexist with crooked SiNWs were achieved on the silicon substrate located at 12 cm from source material. The processing parameters such as temperature, heating rate, duration, substrate position and location are very important to produce SiNWs. Morphology and chemical composition of deposited products were investigated by field-emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray analysis (EDX). The existence of small sphere silicon oxide capped nanowires suggested that the formation of SiNWs was governed by oxide-assisted growth (OAG) mechanism.

Keywords

• Evaporation and sublimation;
• Silicon;
• Carbon;
• Silicon oxides;
• Nanostructures

Applied Surface Science

Volume 254, Issue 2, 15 November 2007, Pages 633–637

Microstructure and dielectric properties of CaCu3Ti4O12 ceramic

Abstract

CaCu₃Ti₄O₁₂ (CCTO) was prepared by the solid state technique. The sample was calcined at 900 °C/12 h and sintered at 1050 °C/24 h, then subjected to XRD to ensure CCTO formation. The microstructure was observed by SEM. XRD results identified both samples as single phase CCTO, whereas the microstructure shows abnormal grain growth and large pores. Sintering was studied in the temperature range of 950–1050 °C for 3–12 h. Increasing sintering temperature enhances the density and secondary formation of Cu₂O. A clear grain boundary and dense microstructure were observed. The results show that the sample sintered at 1040 °C/10 h yields a clearly uniform grain size with the highest ε_r (33,210).

Keywords

• Sintering;
• Microstructure;
• Dielectric;
• CCTO

Materials Letters

Volume 61, Issues 8–9, April 2007, Pages 1835–1838

Fabrication of BaTiO3 thin films through ink-jet printing

Abstract

BaTiO₃ thin films were prepared by ink-jet printing aqueous solutions of TiO₂ sol and soluble Ba salts. Higher pH values (pH > 13) as well as higher than stoichiometric Ba (Ba:Ti = 1.1:1) salt additions were required to compensate for the different aqueous solubilities of the Ba and the Ti. Impedance spectroscopy of the samples shows the thin film samples to have similar activation energy with bulk samples prepared through low temperature aqueous synthesis. The relative permittivity of the thin films (∼ 280) was lower than the bulk pellets (∼ 2750) which was attributed to the lower temperature heat treatment for the thin films.

Keywords

• Sol–gel preparation;
• Dielectrics;
• Thin films

Materials Letters

Volume 61, Issues 23–24, September 2007, Pages 4536–4539

Microwave assisted sintering of CaCu3Ti4O12

Abstract

CaCu₃Ti₄O₁₂ electroceramic was prepared by a microwave assisted solid-state reaction technique from CaCO₃, CuO and TiO₂ powders. Processing involved the preparation of raw material, mixing and milling, calcination, pellet forming and sintering processes. Conventional furnace and microwave assisted sintering processes were employed in order to improve phase structures, morphology and dielectric properties of CaCu₃Ti₄O₁₂ ceramics. Surface and fracture FESEM analysis showed that the microwave assisted sintered CaCu₃Ti₄O₁₂ produced better densification and more uniform grain size compared to the conventional sintered sample.

Keywords

• A. Microwave processing;
• B. Grain boundaries;
• C. Dielectric properties;
• D. Perovskites

Ceramics International

Volume 34, Issue 4, May 2008, Pages 939–942

The role of tin oxide addition on the properties of microwave treated CaCu3Ti4O12

Abstract

A microwave (MW) irradiation process was performed to pre-sintered CaCu₃Ti₄O₁₂. A conventional furnace was used for calcination as well as for the sintering processes, whilst a domestic microwave oven was employed for MW irradiation in order to produce better morphology, improved phase structures and dielectric properties of CaCu₃Ti₄O₁₂ products. SEM analysis shows that the microstructures of MW irradiated samples are denser, with larger grain size if compared to the untreated samples. Dielectric properties also have been improved by MW treatment with higher dielectric constant and lower dielectric loss. Meanwhile, the addition of tin oxide (SnO₂) to CaCu₃Ti₄O₁₂ provides strong effects on the dielectric constant of both without and with MW irradiated samples. It was found that the dielectric constant of CaCu₃Ti₄O₁₂ decreases exponentially with mole percentages of SnO₂. However, the addition of SnO₂ shows better dielectric loss properties of CaCu₃Ti₄O₁₂.

Keywords

• Ceramics;
• Heat treatment;
• Electron microscopy;
• Dielectric properties

Materials Chemistry and Physics

Volume 112, Issue 1, 15 November 2008, Pages 83–87

Dielectric properties of Nb-doped CaCu3Ti4O12 electroceramics measured at high frequencies

Abstract

In this work, Nb dopant was introduced into CaCu₃Ti₄O₁₂ (CCTO) electroceramic in order to improve the dielectric properties. The CCTO electroceramic was prepared using the solid state reaction method. An X-ray diffractometer (XRD) analysis proved the formation of a single CCTO phase after sintering at 1040 °C for 10 h. Abnormal grain growth was observed in undoped CCTO and 1 mol% Nb-doped CCTO. Normal grain growth was produced at Nb dopant levels higher than 3 mol%. Dielectric properties were measured at a frequency range of 1 MHz to 1 GHz. It was found that CCTO doped with 1 mol% Nb gave the highest dielectric constant of 18,000 at 1 MHz. Meanwhile, the lowest dielectric loss (0.31) at 1 MHz was given by CCTO doped with 10 mol% Nb. The dielectric constant between 10 MHz and 1 GHz was almost stable with values at around 500.

Keywords

• Ceramics;
• Solid state reaction;
• Sintering;
• Dielectric response;
• Scanning electron microscopy;
• X-ray diffraction

Journal of Alloys and Compounds

Volume 493, Issues 1–2, 18 March 2010, Pages 486–492

Improvement in dielectric properties of Zn-doped CaCu3Ti4O12

Abstract

A single-phase of calcium copper titanate (CaCu₃Ti₄O₁₂) was produced at lower temperature and shorter calcination time via a combination of solid state reaction and mechanical alloying techniques. The raw materials mixture was subjected to fast ball-milling for 5 h. The mixture was calcined at 750 °C for 9 h to form a single-phase CaCu₃Ti₄O₁₂. Effect of zinc dopant to the dielectric properties of CaCu₃Ti₄O₁₂ had been studied. At lower frequencies, it was found that the dielectric constants had a minimum value at 1.5 mol% Zn. The minimum dielectric loss was observed at 5 mol% Zn. At 1 kHz, the dielectric loss decreases from 30% (undoped) to a minimum value of 18% at 5 mol% Zn dopant. This result indicates that certain Zn dopant can be used to improve the dielectric loss properties of CaCu₃Ti₄O₁₂.

Keywords

• Ceramics;
• Mechanical alloying;
• Dielectric response;
• Microstructure;
• Scanning electron microscopy

Journal of Alloys and Compounds

Volume 476, Issues 1–2, 12 May 2009, Pages 477–481

Electromagnetic interference shielding properties of sintered cement-based ceramics

Abstract

Cement-based ceramic pellets were prepared and their properties were studied for electromagnetic interference (EMI) shielding applications. The shielding materials were made of Portland cement with the addition of different concentrations of manganese oxide (MnO₂) up to 10 wt%. The pellets were sintered at 850 °C for 5 h and then polished prior to characterizations of density, porosity, microstructures, dielectric properties, and EMI shielding effectiveness (SE). Results show that the MnO₂–cement pellets have good dielectric properties, i.e. high dielectric constant (∼300) and low dielectric loss (<0 .3="" constant="" dielectric="" increased="" increasing="" mno="" sub="" the="" with="">2

content in the cement matrix. The SE values of the MnO₂–cements fluctuated between 2 dB and 9 dB in the frequency range of 8–13 GHz. The sample with 10 wt% MnO₂ additive had SE values of up to 9 dB. Most of the samples with high additive concentrations produced SE exceeding 7 dB.

Keywords

• A. Sintering;
• B. Composites;
• C. Dielectric properties;
• E. Functional applications;
• Electromagnetic interference shielding;
• Manganese oxide

Ceramics International

Volume 38, Issue 1, January 2012, Pages 671–678

High frequency response to the impedance complex properties of Nb-doped CaCu3Ti4O12 electroceramics

Abstract

Impedance analyses was performed on undoped and Nb-doped CaCu₃Ti₄O₁₂ (CaCu₃Ti_4−xNb_xO_12+x/2; x = 0, 0.01, 0.03, 0.05, 0.1) to investigate their electrical properties. The pellet samples were prepared using the solid state reaction method. Silver electrode was deposited on both pellets’ surfaces for electrical measurement. The thermally etched samples showed tiny bumped domains within the grains. The existence of both domain and grain boundaries are believed to strongly influence the dielectric constant of CaCu₃Ti₄O₁₂ (CCTO). Undoped CCTO showed two arcs of impedance complex plane while Nb-doped samples have three arcs. Each arc represents the constituent elements of the CCTO. The highest frequency arc is evidence that CCTO consists of conductive domains which measure about 1 Ω and are insulated by two types of barriers, i.e. domain boundary and grain boundary.

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Highlights

► The thermally etched samples show tiny bumped domains within grain. ► The existence of both domain and grain boundaries are believed to strongly influence the dielectric constant of CCTO. ► Nb-doped CCTO give three arcs of impedance complex plane measured in the range frequency of 1 Hz to 1 GHz. ► Each arc represents the constituent elements of the CCTO. ► The highest frequency arc is evidence that CCTO consists of conductive domains which about 1 Ω and are insulated by two types of barrier, i.e. domain boundary and grain boundary.

Keywords

• Powders-solid state reaction;
• Grain boundaries;
• Dielectric properties;
• Impedance;
• Perovskites

Journal of Alloys and Compounds

Volume 509, Issue 18, 5 May 2011, Pages 5701–5707

Influence of sintering parameters on melting CuO phase in CaCu3Ti4O12

Abstract

Dielectric material CaCu₃Ti₄O₁₂ (CCTO) was prepared by solid state technique. CaCO₃, TiO_2, and CuO powders were mixed thoroughly in a ball mill for an hour and were calcined at 900 °C for 12 h. This is followed by sintering at a defined standard temperature for this work (1050 °C for 24 h). Other samples were prepared in a similar manner but with different sintering durations. Each of the sample’s microstructure was observed by a Scanning Electron Microscope (SEM). Meanwhile, Energy-dispersive X-ray Spectroscopy (EDX) analysis was done on fracture surfaces in order to examine the elements present at grain boundaries. Microstructure observations show the melting and abnormal grain growth with large pores. The solidified liquid at grain boundaries was verified as Cu rich region, as confirmed by EDX analysis. By using the SEM, microstructure of small grains with clear grain boundaries were obtained when sintering was done at temperatures lower than 1050 °C. The microstructure of CCTO was very sensitive to sintering parameters.

Keywords

• CuO melt phase;
• Microstructure;
• CCTO

Journal of King Saud University - Engineering Sciences

Volume 25, Issue 1, January 2013, Pages 35–39

The sensing mechanism and detection of low concentration acetone using chitosan-based sensors

 

Abstract

This paper aims to discuss the usage of chitosan film sensors to detect acetone concentrations in human breath, in order to precisely diagnose diabetes mellitus in patients. Acetone concentration in the breath varies from 0.3 to 0.9 ppm in healthy people to more than 1.8 ppm for diabetics. This makes acetone a suitable chemical marker for diabetes diagnosis. Therefore, the preliminary study on the electrical laboratory testing of the chitosan film sensor properties to acetone vapor-contaminated air in range of 0.1–100 ppm was carried out at room temperature (∼25–30 °C) in normal air. Our results suggested that the proposed acetone-based gas sensor can operate at room temperature with a high performance demonstrated by good response, recovery, stability and repeatability. This trouble free, painless and steadfast technique will improve the current gold standard in diagnosing diabetes, enabling quick and early detection.

Keywords

• Chitosan-based acetone sensor;
• Diabetes mellitus;
• Acetone vapor;
• Electrical properties;
• Electrochemical deposition

Sensors and Actuators B: Chemical

Volume 177, February 2013, Pages 522–52

A novel 5.8 GHz quasi-lumped element resonator antenna

 

Abstract

In this paper, a novel quasi-lumped element resonator antenna is presented. The proposed antenna consists of the interdigital capacitor in parallel with a straight line inductor and is fabricated on Duroid RC4003C circuit board. The entire arrangement was fed by a coaxial feed at a frequency of 5.8 GHz. The size, bandwidth and radiation patterns were studied. The proposed antenna exhibits better impedance bandwidth and significant size reduction in comparison with similar results obtained from the conventional microstrip patch antenna with similar feeding technique and resonant frequency. The size of the proposed antenna structure is 5.8 × 5.6 mm² and experimental results are shown to be in good agreement with the design simulation.

Keywords

• Quasi-lumped element;
• Patch antenna;
• Coaxial feed;
• Resonator;
• Antenna real estate

AEU - International Journal of Electronics and Communications

Volume 67, Issue 7, July 2013, Pages 557–563