Yoshihiro Momose

Ar, O2 and CF4 plasma treatment of poly-(vinylidene fluoride), polyimide and polyamidoimide and its relationship to wettability

Abstract The surface modification of polymers by exposure to plasma has been investigated. Poly-(vinylidene fluoride) (PVdF), Kapton polyimide (PI) and polyamidoimide (PAI) were used. Ar or O2 plasma treatment incorporated oxygen to a considerable extent onto the surfaces of all the types of polymers and gave a highly enhanced hydrophilic nature. With PVdF samples subjected to CF4 plasma treatment various types of fluorine-containing groups were incorporated, accompanied by a little increase in O content, the surface thus having a greatly enhanced hydrophobic nature. The surface layer was quite stable to water. With PI and PAI samples exposed to CF4 plasma the hydrophobic nature of the surfaces was highly increased, but the adhesion between the fluorine-containing surface layer and the substrate was poor.

Temperature-programmed photoelectron emission technique for metal surface analysis

To characterize easily the state of real metal surfaces in ambient environments, we have developed an extremely sensitive technique for surface analysis using photoelectron emission phenomena as a function of temperature. We will call this method temperature-programmed photoelectron emission (TPPE). The emitted electrons are detected by a gas-flow Geiger counter with Q gas. The TPPE measurement is performed by scanning the wavelength of incident UV light at different temperatures in the temperature-increase and subsequent temperature-decrease process between 25 and 350°C. A photoelectron emission (PE) spectrum representing the curve of PE intensity vs wavelength is obtained at each temperature. The number of emitted electrons in a PE spectrum is termed PE total count. The PE total count as a function of the measurement temperature was investigated for 17 kinds of commercial rolled metal sheets. The metals were distinctly classified into two main groups A and B, the former indicating a temperature-dependent PE total count and the latter a virtually temperature-independent PE total count. Group A included Al, Pt, Pb, Cu, Ag, Au and Ni; group B included Ta, Ti, Mo, Pd, W, Fe, Co, Zn, Nb and Sn. With group A, the greater amount of adsorbed oxygen present at the initial surface was found by XPS to change to the oxide oxygen after TPPE measurement. This chemical change is suggested to play a substantial role in the temperature dependence of the PE total count.

Temperature dependence of the photoelectron emission from intentionally oxidized copper

Abstract The characteristics of the photoelectron emission (PE), measured by varying the wavelength of incident light, form copper subjected to oxidation treatment in air have been investigated as a function of the measurement temperature between 25 and 300°C using a gas-flow counter. The intensity of PE at a certain measurement temperature decreased with increasing oxidation temperature (100 to 800°C) and the intensity of PE for a given oxidation temperature increased with decreasing measurement temperature. The PE behavior was correlated to the chemical and electrical nature of the surfaces analyzed by X-ray photoelectron spectroscopy and surface potential measurement. A mechanism is proposed for the PE of the untreated sample which exhibited a completely different PE behavior.

Plasma oxidation of Cu, Ti and Ni and the photoelectrochemical properties of the oxide layers formed

Abstract Plasma oxidation of Ti, Cu and Ni was carried out using a conventional diode-type glow discharge system. Structural and photoelectrochemical properties of the oxide layers formed were examined. Electron diffraction confirmed the formation of a TiO2, Cu2O/CuO, and NiO layer on the Ti, Cu, and Ni surfaces, respectively, after the plasma oxidation. Photoelectrochemical solar cells were fabricated using the oxide layers formed as a semiconductor electrode. The TiO2 electrodes showed moderate photoresponse under anodic potentials in a methanol aqueous solution, while the Cu2O/CuO and NiO electrodes showed a weak photoresponse under cathodic potentials. In conclusion, the TiO2 layers prepared by plasma oxidation work well as a semiconductor electrode for a photoelectrochemical cell and are stable in methanol solution.

Thermally stimulated exoelectron emission from silicon subjected to argon plasma treatment

We have investigated the thermally stimulated exoelectron emission (TSEE) from Ar plasma‐treated Si by x‐ray photoelectron spectroscopy and by employing a theoretical equation. The sample surfaces were exposed to ambient air after the plasma treatment. The TSEE glow curve (298–623 K) exhibited broad emission peaks at ∼373 and ∼473 K, and an increase in the intensity above 573 K. A theoretical analysis revealed that the glow curves were composed of four peaks except for the increase above 573 K, where each peak had a different trap depth, but almost the same electron affinity. The resolved two peaks in the lower temperature region increased compared to those in the higher temperature region with an increase in the O1s/Si2p ratio and also in the Si2p (oxide)/Si2p (substrate) ratio. The relationship of the surface chemical structure to the resolved four peaks is considered.

Lithium insertion into (V1−yMoy)2O5

The effects of structural modification caused by substitution of Mo for a part of V in V 2 O 2 on structural changes upon lithium insertion were investigated. For this purpose (V 1-y Mo y ) 2 O 5 (y = 0.25) was synthesized, and its insertion behavior and structural changes upon lithium insertion were analyzed by XRD and ESR methods. In (V 0.75 Mo 0.25 ) 2 O 5 , the phases except for the starting material were not observed upon lithium insertion, and no phase transformation characteristics of V 2 O 5 occurred. From ESR measurement, a broad singlet signal of V(IV) was found, but those of Mo(V) were not detected. The line width of the signal V(IV) increased steeply at 0.7 < x < 1. The open circuit potentials became less noble with increasing x, and dropped steeply at 0.7 < x < 1. These dependencies closely correlate with structural changes estimated from results of ESR and XRD analyses. At 2.7 < x, ω-phase oxide was formed.

Cyclic voltammetric study of the corrosion protection of metal surfaces by plasma-polymerized coatings

The corrosion-protective performance of plasma-polymerized (PP) films on metal substrates has been investigated by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and surface potential measurements. A PP film from cyclohexane was deposited on Fe, Ni, and Cu substrates using a radiofrequency generator. A PP film-coated metal substrate was employed as the working electrode in aerated NaCl aqueous solution and the cyclic voltammogram was measured repeatedly ten times upon application of a triangular potential between -1 and 1 V vs. the initial corrosion potential of the sample. The cyclic voltammogram depended strongly on the metal substrate: with Fe and Ni, only an anodic current was observed; with Cu, an anodic and subsequently a cathodic current appeared. For all the metals, the anodic current level in the voltammograms at the same potential sweep number decreased with increasing film deposition time. The anodic current level for Fe and Cu increased with increasing potential sweep number, but that for Ni exhibited a maximum, followed by a decrease. The anodic current level for the metal substrates decreased in the order Fe > Ni > Cu. The cathodic current for Cu decreased with an increase in the deposition time and increased with an increase in the potential sweep number. The dependence of the cyclic voltammogram on the metal substrate is discussed in terms of the PP film thickness and the positive charge on the film surface, as well as the standard reduction potential of the metal. The corrosion potential for PP film-coated metal substrates also changed with the deposition time; this change is suggested to be related to the increase in the positive charge on the surfaces.

Reaction of argon plasma-treated teflon PFA with aminopropyltriethoxysilane in its n-hexane solution

Aspects of argon plasma treatment of tetrafluoroethylene-perfluoropropylvinylether copolymer (PFA) films, followed by air exposure and its subsequent reaction with 3-aminopropyltriethoxy silane (3-APS) have been investigated using XPS and electron spin resonance (ESR) to gain a better understanding about the surface bonding between the modified PFA and 3-APS. The plasma treatment was performed under varying parameters such as radiofrequency power, gas pressure and treatment time. A good correlation was found between the atomic ratios of O/F and Si/F for PFA before and after the reaction with 3-APS. The amount of peroxy radicals before the reaction with 3-APS was also closely related with the atomic ratio of Si/F. By the derivatization reaction of plasma-treated PFA with NaOH it was confirmed that -C(O)OH groups exist on the treated PFA surfaces. These observations revealed that the oxygen incorporated at the surface leading to -C(O)OH groups plays a substantial role as the reaction site for 3-APS. A similar trend was found between the atomic ratios of Na/F and Si/F after the reactions with NaOH and 3-APS. Based on this observation it is proposed that the surface bonding of 3-APS to the -C(O)OH group at the surface occurs through its -NH 2 group. The analysis of the atomic ratios of O/F, N/F and Si/F after the reaction with 3-APS revealed that a polyaminosiloxane oligomer with a stoichiometry different from that expected for the original 3-APS is formed. The wettability of 3-APS-bound PFA was found to become much greater than that of PFA plasma treated alone. The ageing effect of the wettability of 3-APS-bound PFA was observed, whereas the Si atomic concentration at the surface remained nearly unchanged during ageing.

Surface fluorination of electrophotographic photoreceptors by plasma treatment for contact charging with a wet polymer roller

Abstract In order to increase the hydrophobicity of an organic photoreceptor (OPC) surface for contact charging with a wet polymer roller, surface fluorination treatment was carried out on OPC drums using CF4 rf plasma, and the charging characteristics and surface properties were examined. The hydrophobicity of the plasma-treated OPC drum surface was evaluated by measuring the water contact angle and the water extinction time due to evaporation. It was confirmed that the hydrophobicity of the OPC drum surface was improved considerably by the plasma treatment with little influence on the contact charging characteristics. XPS analysis indicated that fluorine was introduced into the OPC surface by the plasma treatment and its fraction increased with an increase in the treatment time. Further, the XPS spectra suggested that CF, CF2 and CF3 bonds existed on the plasma-treated OPC surface.

Spectral analysis of thermally stimulated exoelectron emission from glass deposited on metal by argon plasma treatment

Abstract Glow curves of thermally stimulated exoelectron emission (TSEE) originating from silicon oxide deposited on Au surfaces by argon plasma treatment are spectrally analyzed. The analysis shows that the variation of the TSEE glow curves due to the conditions of the plasma is ascribed to the growth of the deposited layer.