Meng-Chi Li

Low-temperature synthesis of graphene on Cu using plasma-assisted thermal chemical vapor deposition

Plasma-assisted thermal chemical vapor deposition (CVD) was carried out to synthesize high-quality graphene film at a low temperature of 600°C. Monolayer graphene films were thus synthesized on Cu foil using various ratios of hydrogen and methane in a gaseous mixture. The in situ plasma emission spectrum was measured to elucidate the mechanism of graphene growth in a plasma-assisted thermal CVD system. According to this process, a distance must be maintained between the plasma initial stage and the deposition stage to allow the plasma to diffuse to the substrate. Raman spectra revealed that a higher hydrogen concentration promoted the synthesis of a high-quality graphene film. The results demonstrate that plasma-assisted thermal CVD is a low-cost and effective way to synthesis high-quality graphene films at low temperature for graphene-based applications.

The effect of annealing on nanothick indium tin oxide transparent conductive films for touch sensors

This study aims to discuss the sheet resistance of ultrathin indium tin oxide (ITO) transparent conductive films during the postannealing treatment. The thickness of the ultrathin ITO films is 20 nm. They are prepared on B270 glass substrates at room temperature by a direct-current pulsed magnetron sputtering system. Ultrathin ITO films with high sheet resistance are commonly used for touch panel applications. As the annealing temperature is increased, the structure of the ultrathin ITO film changes from amorphous to polycrystalline. The crystalline of ultrathin ITO films becomes stronger with an increase of annealing temperature, which further leads to the effect of enhanced Hall mobility. A postannealing treatment in an atmosphere can enhance the optical transmittance owing to the filling of oxygen vacancies, but the sheet resistance rises sharply. However, a higher annealing temperature, above 250°C, results in a decrease in the sheet resistance of ultrathin ITO films, because more Sn ions become an effective dopant. An optimum sheet resistance of 336Ω/sqr was obtained for ultrathin ITO films at 400°C with an average optical transmittance of 86.8% for touch sensor applications.

Influence of hydrogen on the properties of Al and Ga-doped ZnO films at room temperature

Low resistivity and high transmittance of Al-doped ZnO (AZO) and Ga-doped ZnO (GZO) transparent conductive thin films have been achieved by use of pulsed dc magnetron sputtering in a hydrogen environment at room temperature. The addition of hydrogen to the sputtering gas can reduce the resistivity of the films and improve their electrical properties compared to those prepared without H2, because the hydrogen acts a shallow donor. The average transmittance was over 85% in the visible region, and the lowest resistivity of the AZO and GZO films was 4.01×10(-4) (Ω-cm) and 4.39×10(-4) (Ω-cm), respectively.

Application of white-light scanning interferometer on transparent thin-film measurement

A method to measure thin-film thickness, refractive index, and dispersion constants based on white-light interferometry is described. The thin-film property is retrieved from the Fourier amplitude of the white-light correlogram. The sources of errors in Fourier amplitude, which include the accuracy of wave number, light source variation in time, and illumination nonuniformity, are investigated. With all these errors reduced, the film thicknesses and refractive indices of four samples measured by white-light interferometry are within 1% of the ellipsometry results.

Transparent Conductive Distributed Bragg Reflectors Composed of High and Low Refractive Index Transparent Conductive Films

This article has shown that the co-sputtering method and post-annealing treatment have successfully fabricated the transparent conductive distributed Bragg reflectors (TCDBR). The transparent conducting film, anatase Nb-doped TiO2 (TNO), which has a high refractive index can be combined with Al-doped ZnO (AZO) low refractive index transparent conducting films to make a TCDBR capable of transferring the current from electrode to semiconductor while still maintaining the advantage for the micro resonant cavity. The eight-period stack of AZO/TNO achieves a reflectivity of up to 90% centered at 550 nm and a resistivity of 1.88×10-3 Ω cm.

Optical and electric properties of aluminum-gallium doped zinc oxide for transparent conducting film

The well-known indium-tin-oxide is not suitable for solar cell, because of the chemical reduction, even without any hydrogen dilution. The inexpensive and non-toxic of transparent conducting Aluminum and Gallium doped ZnO (AZO and GZO) thin films have been investigated for the substitutes for the indium-tin-oxide thin films. AZO performs high transmittance at visible region, however, higher resistance than GZO. In this study, AZO and GZO composed film (GAZO) will be fabricated using DC magnetron co-sputtering deposition system to achieve lower resistance than AZO and higher transmittance than GZO. The optical and electric properties of different thickness of GAZO such as transmittance, reflection, carrier concentration, Hall mobility, and resistivity will be measured and analyzed.

Preparation of Low Resistivity Transparent Conductive Nb-Doped TiO2 Films by the Co-sputtering Method

Low resistivity Nb-doped TiO2 transparent conducting oxide (TNO) thin films have been achieved by a pulsed dc magnetron co-sputtering at room temperature and the annealing treatment. Pulsed dc power provides the stabilization of reactive sputtering. The dc power of Nb target is controlled to find the optimum Nb content in TNO films. The carrier concentration is linearly proportional to Nb content in TNO films. The lowest resistivity was measured as 4.55×10-4 Ω cm at 24 W dc power of Nb and the average absorbance in the visible light region was smaller than 8% for different dc powers. The results of contact angle revealed that TNO films still keep the surface hydrophilicity and have the characteristic of photo-catalyst.

The deviation of growth model for transparent conductive graphene.

An approximate growth model was employed to predict the time required to grow a graphene film by chemical vapor deposition (CVD). Monolayer graphene films were synthesized on Cu foil at various hydrogen flow rates from 10 to 50 sccm. The sheet resistance of the graphene film was 310Ω/□ and the optical transmittance was 97.7%. The Raman intensity ratio of the G-peak to the 2D peak of the graphene film was as high as ~4 when the hydrogen flow rate was 30 sccm. The fitting curve obtained by the deviation equation of growth model closely matches the data. We believe that under the same conditions and with the same setup, the presented growth model can help manufacturers and academics to predict graphene growth time more accurately.

The Influence of Hydrogen on the Properties of Al and Ga Doped ZnO Films at Low Temperature

Low resistivity and high transmittance of Al-doped ZnO and Ga-doped ZnO transparent conductive thin films have been achieved by a pulsed DC magnetron sputtering in various hydrogen ambient at low temperature.

Monitoring the narrow-band pass filter deposition by calculating refractive index in real-time

Optical monitoring plays an important role in film deposition. In this study, an optical monitoring method which can work out the refractive index of material in real-time improves the quality of narrow-band pass filter effectively.