De-Quan Yang

Preparation and characterization of nanostructured silver thin films deposited by radio frequency magnetron sputtering

Nanostructured silver thin films were prepared by radio frequency magnetron sputtering at room and liquid nitrogen substrate temperatures. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were employed to study the topography and chemical composition, respectively, of the thin films. The AFM results indicate a significant difference in the morphology of the thin films when argon or nitrogen ions were used as sputtering ions. For argon ion sputtering, a difference also exists in the microstructure and topography of the thin films for ambient and liquid nitrogen substrate temperatures. The XPS results show a high purity of nanostructured silver thin films for sputtering by both argon ions and nitrogen ions, but with some oxygen and carbon contamination. For argon ion sputtering, the content of oxygen and carbon is less than 6.9% and 4.5%, and for nitrogen ion sputtering, less than 4.7% and 3.6%.

Sizes correction on AFM images of nanometer spherical particles

Atomic Force Microscopy (AFM) is widely used in morphology characterization of materials on nanometer and sub-micron scales. However, distortions universally exist in AFM images due to geometrical interaction between the sample surface and the limited size tip. Correction factors for AFM images are given in the paper based on a simple mathematical model. The results reveal that the correction factors are related with the distribution of the particles (compacted or dispersed). The distortions can cause bigger images than the real sizes using commercial pyramidal tips and the distortions are deflation under certain conditions as well. The distortions of the images are affected by the shape of the AFM tip and circumstance of the particles. The results are compared the experimental data.

Preparation and structural characterization of nanostructured iron oxide thin films

Abstract Nanostructured iron oxide thin films were prepared using a dip-coating technique by forced hydrolysis of a FeCl3 solution with 2% gelatin at 60°C. The structural properties were characterized by X-ray diffractometer (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV–Vis absorption measurements. XRD analysis revealed that the iron oxide in the films consisted of α-Fe2O3, AFM showed that the Fe2O3 particles in the films were relatively uniform in size and XPS showed that there was little carbon on the surface and that the Fe2O3 fully covered the Si substrate. The particle sizes can be easily controlled through the pH of the solution.

X-ray photoelectron spectroscopy of nickel dithiolene complex Langmuir-Blodgett films

Abstract The chemical states, composition, and structures of monolayer and multilayer Langmuir–Blodgett (LB) films of a nickel dithiolene (BDN) complex and stearyl alcohol (SA), and BDN powder were characterized using X-ray photoelectron spectroscopy (XPS). The results indicate that Ni atoms mainly exist as Ni2+ in the LB films, while those exist in both Ni2+ and Ni0 states in pure BDN powder. S–O and Ni–O bonds are more apparent in the XPS spectra of the LB films sample. The study of the peak features of S2p and Ni2p3/2 with various thickness on silicon (with little silicon oxide surface) substrate indicates that chemisorption occurs in BDN molecules on a Si substrate. The electrical conductivity of BDN bulk and LB films and its relationship with the chemical state were also discussed.

Study of the environment effect on the properties of BDN-SA Langmuir–Blodgett films

The chemical and electrical properties of BDN-SA Langmuir–Blodgett films in air and N2H4 gas respectively, were studied using X-ray Photoelectron Spectroscopy (XPS) and the electrical resistance measurement. The results indicate that the oxidation effect caused by air leads to the lost of N and partial oxidation of Ni and S in the LB films; while the reduction effect induced by N2H4 gas decreases the amount of O in the LB films. The electrical resistance of LB film decreases dramatically after the film being exposed to N2H4 gas while increases with the exposure time in air.

Study on nucleation and growth of Ag nanoparticles prepared by radio-frequency sputtering on highly oriented pyrolytic graphite and amorphous carbon

The initial growth process of silver nanoparticles on highly oriented pyrolytic graphite (HOPG) and amorphous carbon (a-C) was studied. Scanning tunneling microscopy was used for analysis of the nanoparticles formed on HOPG. Transmission electron microscopy was employed to study the growth procedure on a-C. The number densities (Dn) of silver nanoparticles on both HOPG and a-C remain constant at a very early stage, then both decrease with deposition time and have a saturated value. The Dn decrease suggests migration followed by impingement. We found evidence of migration of 5 nm particles on a-C. Interpretations are given to explain the impingement and shape change of the silver nanoparticles.

N2H4 gas detection using Langmuir-Blodgett films of a dithiolene complex on chemiresistor sensors

A device based on a mono or multilayers films of a nickel dithiolene-stearyl alcohol complex built with the Langmuir- Blodgett (LB) technique has been investigated as a N2H4 gas detector. The films deposited on an aluminum electrode and the changes in the electrical properties of the film when exposed to the N2H4 gas were tested. It was found that there still a well response when the device exposed 0.5 ppm N2H4 gas at the room temperature, and the changes of electrical conductive of the film is roughly linear with N2H4 gas concentration in the lower concentration. The experimental results indicated the response time and recovery time of the sensor are less than 30 seconds.

Electrical properties of bis(4-diethyannodithiobenzil) nickel and stearyl alcohol mixed Langmuir-Blodgett films

Abstract Direct current (d.c.) electrical properties of bis(4-diethyannodithiobenzil)nickel and stearyl alcohol mixed Langmuir–Blodgett films (BDN-SA LB films) were measured using multilayer LB films deposited on planar interdigital electrodes under various pressure and temperature conditions. The results show that the conductivity of the LB films is strongly influenced by the pressure and temperature. The activation energy is estimated to be approximately 0.56 eV, close to the 0.50 eV value of the bulk material. The correlation between the electrical conductivity of the LB films with atmosphere pressure is discussed.

Attenuation Lengths of Photoelectrons in BDN-SA Langmuir-Blodgett Films

Abstract Based on the X-ray photoelectron spectroscopy(XPS) of monolayer and multilayer dithiolene(BDN) stearyl alcohol(SA) complex Langmuir-Blodgett films on silicon and gold substrate, respectively, we measured the attenuation lengths(ALs) of photoelectrons in BDN-SA LB films. Combined with the Atomic Force Microscopy(AFM) investigations, the results are discussed.

Structural characterization of BDN-SOH LB films using small angle XRD and Fourier transform IR spectroscopy

We investigated the structure of BDN(bis(4-diethylaminodithiobenzil) Nickel)-SOH(Stearyl alcohol) Langmuir-Blodgett films using small angle X-ray diffraction and polarized FTIR spectroscopy. The results show that the microcrystal domains formed on the surface of LB film resemble a well-laminated periodic structure with a molecular spacing of 2.56 nm. Meanwhile, the tilted angles of the molecules of SOH and BDN are about 30°, referring to the normal direction of the sample surface, as determined by our XRD and FTIR studies.