Cadmium-tin Oxide Films Research Articles

Cadmium Stannate Films for Immobilization of Phospholipid Bilayers

Cadmium tin oxide (CTO) films on glass substrates were synthesized and functionalized by octadecyltrichlorosilane (OTS). CTO films were transparent with the bandgap of 2.92 eV. They exhibited n-type conductivity and carrier concentration of (3.31 ± 0.38) · 1019 cm−3. Weak temperature dependence points out to a nearly degenerative state of the carriers in the CTO films. Silanization by OTS yielded hydrophobic surface with the contact angle values reaching 103 ± 12 degrees. Silanization of films was followed by a significant reduction of the interfacial capacitance, which upon completion of the functionalization reached levels below 3 μF cm−2. The value of the electric capacitance as well as data of ATIR absorption, hints at sparse and disordered coverage of the CTO surface by octadecylalkylsilane molecules. Such organic layer, however, was able to trigger phospholipid (60% dioleoylphosphocholine and 40% cholesterol) vesicle rupture and the formation of a secondary layer of phospholipid, thus rendering hybrid bilayer surface construct. Such hybrid constructs may be useful in applications where electrode coupling to a model biological membranes and membrane bound proteins is required, such as biosensing and photovoltaics.

Investigation of hexadecanethiol self-assembled monolayers on cadmium tin oxide thin films

This study reports the use of variable angle reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy to investigate the formation of a 1-hexadecanethiol adlayer on cadmium tin oxide (CTO) thin film surfaces. These adlayers appear to be robust, ordered monolayers. The optical and electronic properties of CTO thin films chemically vapor deposited onto glass substrates were also investigated. The reflectance of the CTO films was dependent upon the incident angle of the impinging radiation and revealed a reflectance decrease indicative of a plasma frequency in the mid-IR using p-polarized radiation.

Transparent conducting oxide thin films of Cd 2SnO 4 prepared by RF magnetron co-sputtering of the constituent binary oxides

Thin films of cadmium tin oxide (Cd 2SnO 4) have been deposited on glass substrates by RF magnetron co-sputtering from cadmium oxide (CdO) and tin oxide (SnO 2) targets in an Argon ambient. Co-sputtering offers a means to control the atomic stoichiometry of Cd 2SnO 4, which influences the material's electro-optical and structural properties. The Cd 2SnO 4 films were deposited at room temperature and subsequently subjected to a heat treatment in inert or reducing (H 2) ambient. The as-deposited films were amorphous, and became polycrystalline after annealing at high temperatures. Using this method, Cd 2SnO 4 films with a Hall mobility of 32.3 cm 2 V −1 s −1 and a carrier concentration of 7.40×10 20 cm −3 corresponding to a resistivity of 2.07×10 −4 Ω cm have been prepared. The films exhibited average optical total transmission in excess of 90% in the visible region. The optical bandgap was found to be in the range of 2.97–3.18 eV, depending on post deposition treatment.

Properties of R.F. magnetron sputtered cadmium–tin–oxide and indium–tin–oxide thin films

The electrical, optical, structural, chemical, and etch properties of r.f. magnetron, sputter-deposited thin films of indium–tin–oxide (ITO) and cadmium–tin–oxide (CTO) are presented. Polycrystalline thin films of CTO and ITO with distinct diffraction peaks corresponding to the (220), (222), and (400) crystal planes and with an overall preferential 〈111〉 orientation were obtained at elevated deposition temperatures. The lattice parameter of these films was determined to be 0.948 and 1.026 nm for CTO and ITO, respectively. These thin films possess low resistivities in the 10 −4 Ω cm range, Hall mobilities up to 30 cm 2/V s, and carrier concentrations in the 10 20 cm −3 range. In excess of 85% of the perpendicularly incident optical radiation, in the 0.85 to 1.55 μm wavelength range, and up to 50% of the incident radiation at a wavelength of 365 nm was transmitted through the CTO and ITO conductors. A variety of wet and dry etching techniques were investigated in order to delineate features in the thin films. From investigations concerned with the Schottky and ohmic contact characteristics of CTO and ITO films deposited on undoped AlGaAs and InAlAs, ideality factors ranging from 1.1 to 1.2 and Schottky barrier heights ranging from 0.67 to 1.05 eV were obtained.

Measurement of the Effective Mass of Transparent Conducting films of Cadmium Tin Oxide

ABSTRACTWe have prepared transparent conducting films of cadmium stannate (Cd2SnO4 with resistivity as low as 1.5×10-4 Ω cm. The resistivity of these films is low because of their surprisingly high mobility (60 cm2 V-1 sec-1) at high carrier concentration (7×1020cm-3). We conducted an investigation to determine whether the high mobility is due to unusually low carrier effective mass or to a long carrier relaxation time. The conductivity effective mass and relaxation time were estimated by Drude free-electron modeling of reflectance and transmittance spectroscopie measurements. The Drude model appears to represent the behavior of cadmium tin oxide very well. The optical effective mass of the electrons in cadmium stannate is about 0.35 mo, which is similar to that of other transparent conducting oxides. By varying the doping level, we were able to fabricate films with various levels of degeneracy, but these showed no significant difference in effective mass.We were also able to determine the carrier effective mass and the relaxation time by measuring four separate electron transport coefficients: conductivity, Hall, Seebeck, and transverse Nernst-Ettingshausen (Nernst). The Fermi level was found to vary from 0.31 to 0.83 eV above the conduction band minimum, and the conduction band was very close to parabolic in this range, with m* ∼ 0.33 mo, in good agreement with the optical result. We conclude that the effective mass of electrons in cadmium stannate is similar to electrons in other transparent conducting oxides and that high mobility results from a relatively long carrier relaxation time.

INVESTIGATION ON THE PHYSICAL PROPERTIES AND DEFECTS OF Cd2SnO4 FILMS DEPOSITED BY RF REACTIVE SPUTTERING

Transparent conductiong films of cadmium-tin oxide were prepared by rf reactive sputtering from a Cd-Sn alloy target in an Ar-O2 atmosphere. The structure of the films was examined by X-ray diffraction. The electrical and optical properties of the films were found to depend on the oxygen concentration in the gas mixture and the substrate temperature as well as the post-deposition heat treatment. The lowest resistivity obtained was 1.74×10-6Ω·cm and the highest optical transmission was 95% over the visible region. For the films deposited at substrate temperature of 400℃ in an Ar-O2 atmosphere of 6% O2, heat treatment increased the optical gap energy from 2.37eV to 2.64eV.

Cadmium-tin oxide films deposited by rf sputtering from a CdO-SnO2 target

Cadmium-tin oxide (CTO) films with high conductivity and high transparency were prepared by rf sputtering from a CdO-SnO2 target in an Ar or Ar-O2 atmosphere. The resistivity of CTO films was 6.5×10−4 Ω in the film thickness range of 2500–15000 Å, and the average transmission was 90% over the visible region.

Transparent electrode properties of CdSn oxide films by dc reactive sputtering

Films of cadmium-tin oxide were prepared by dc reactive sputtering of alloy target in ArO 2 mixtures. The lowest resistivity obtained was 4 × 10 −4 Ω cm and the average optical transmission was 90% in the visible region. The films were annealed at temperatures up to 400°C. The optical and electrical properties of the films were examined as a function of annealing conditions, such as atmosphere, temperature, and time. These properties of the films are believed to be related to the amount of oxygen deficiency of the films.