Surface treatments of indium tin oxide films by using high density plasma

We investigated the effects of various surface treatments on the work function and chemical composition of an indium tin oxide (ITO) surface. Ultraviolet photoelectron spectroscopy (UPS) was used to measure the work function of ITO. X-ray photoelectron spectroscopy (XPS) was used to study the electron structures of ITO surface. We performed surface treatments on ITO using O₂ plasma and HCl solution. Our UPS/XPS analysis indicates increases in the work functions by O₂ plasma treatments. It is known that the Fermi energy level is controlled by the donor concentration, and thus the Fermi energy level is shifted toward the valence band minimum.     

Formation of Hf- and Ta-aluminates by reactive ion beam mixing of X/Al interfaces (X = Hf or Ta)

Hf- and Ta-aluminates have been grown by 3 keV O₂⁺ reactive ion beam mixing (IBM) of X/Al interfaces (X = Hf or Ta). The kinetics of growth, composition and electronic structure of the films formed have been studied using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and factor analysis. A reactive IBM kinetics of two stages has been found by means of factor analysis. In a first stage, HfO₂ or a mixture of Ta suboxides and Ta₂O₅ species are formed for the Hf/Al or Ta/Al interface, respectively. Ta suboxide species are subsequently transformed into Ta₂O₅ species at the beginning of the second stage. In a second stage, HfO₂ or Ta₂O₅ species are transformed progressively into Hf-O-Al or Ta-O-Al species, respectively, leading to the synthesis of custom designed Hf- and Ta-aluminates. The evolution of the Auger parameters and UPS valence band spectra shows that this transformation is accompanied by changes in the electronic structure of the oxide films formed.     

On the structure and surface chemical composition of indium-tin oxide films prepared by long-throw magnetron sputtering

Structures and surface chemical composition of indium tin oxide (ITO) thin films prepared by long-throw radio-frequency magnetron sputtering technique have been investigated. The ITO films were deposited on glass substrates using a 20 cm target-to-substrate distance in a pure argon sputtering environment. X-ray diffraction results showed that an increase in substrate temperature resulted in ITO structure evolution from amorphous to polycrystalline. Field-emission scanning electron microscopy micrographs suggested that the ITO films were free of bombardment of energetic particles since the microstructures of the films exhibited a smaller grain size and no sub-grain boundary could be observed. The surface composition of the ITO films was characterized by X-ray photoelectron spectroscopy (XPS). Oxygen atoms in both amorphous and crystalline ITO structures were observed from O 1 s XPS spectra. However, the peak of the oxygen atoms in amorphous ITO phase could only be found in samples prepared at low substrate temperatures. Its relative peak area decreased drastically when substrate temperatures were larger than 200 °C. In addition, a composition analysis from the XPS results revealed that the films deposited at low substrate temperatures contained high concentration of oxygen at the film surfaces. The oxygen-rich surfaces can be attributed to hydrolysis reactions of indium oxides, especially when large amount of the amorphous ITO were developed near the film surfaces.     

Electronic structure and chemical properties of Pd films supported by MgO

Pd films were deposited on MgO-covered Mg substrate by the thermal evaporation method under high vacuum conditions. The electronic and chemical properties of Pd structures with different Pd thicknesses were studied using X-ray photoelectron spectroscopy (XPS) and field emission-scanning electron microscopy (FE-SEM). For relatively low Pd thicknesses (<1 nm), separate Pd particles could be observed. At higher Pd thicknesses, continuous Pd thin films formed by agglomeration of Pd nanoparticles were found. With decreasing Pd thickness, a chemical state with a higher-binding-energy became more pronounced in the Pd core level spectra, demonstrating the electron-deficient nature of Pd atoms in contact with MgO substrate. Very small Pd particles with a pronounced core level shift were shown to be less active toward CO oxidation than thicker Pd films.     

X-ray photoelectron spectroscopy analyses of titanium oxynitride films prepared by magnetron sputtering using air/Ar mixtures

X-ray photoelectron spectroscopy (XPS) has been employed to investigate titanium oxynitride (TiN_xO_y) films prepared by d.c. magnetron sputtering using air/Ar mixtures, which allows one to perform the deposition at a high base pressure (1.3 × 10^− 2 Pa) and can reduce substantially the processing time. XPS analyses revealed that all the prepared TiN_xO_y films comprised Ti-N, Ti-N-O, and Ti-O chemical states. When the air/Ar ratio was below 0.3, nitrogen-rich TiN_xO_y films were obtained. As the air/Ar ratio was above 0.4, oxygen-rich TiN_xO_y films were formed. XPS depth profile analyses were also performed in selected specimens. It has been found that at relatively low air/Ar ratios, such as 0.5, the oxygen content of the films increased toward the film/substrate interface and when the air/Ar ratio was higher, TiN_xO_y films with large oxygen content with uniform concentrations were then formed.     

Complex investigation of electronic structure transformations in Lead Sulphide nanoparticles using a set of electron spectroscopy techniques

It has been reported recently that kinetic energy of photoelectrons emitted from core levels decreases with decreasing of the nanocrystal size. This phenomenon is called the size shift. The size shift value is the same for donor and acceptor in the compound. The present work is aimed on the explanation of this phenomenon. Crystals of lead sulfide PbS with different size from 50 to 350 nm were grown by chemical bath deposition (CBD) technique from alkaline solution onto Si and GaAs substrates. The morphology and size of crystals were analyzed by high resolution scanning electron microscopy (HRSEM). Complex electron spectroscopy investigations of electronic structure were carried out. In recent experiments X-ray photoelectron spectroscopy (XPS) was used for determination of Pb 4f, and S 2p electronic level positions and their size shifts. To explain the observed dependences in this work, we applied the following methods: analysis of PbS valence band (VB) and Pb 5d electronic level structure in the range ∼0-30 eV by XPS, high resolution electron energy losses spectroscopy (HREELS) for analysis of band gap transformations and work function measurements by Kelvin probe microscopy for the contact potential difference (CPD). The influence of work function increasing, widening of the band gap, transformations in VB and inter-level energy distances with decreasing of nanocrystal size on the size shift function ΔE(R) is discussed.     

Titanium monoxide ultra-thin coatings evaporated onto polycrystalline copper films

We evaporated polycrystalline copper thin films of thickness between 10 and 100 nm on silicon substrates with their native oxide under ultra-high-vacuum conditions. Some of them were exposed to air for a period ranging from 1 day to 2 weeks. X-ray photoelectron spectroscopy (XPS) revealed a clean copper surface with a trace of oxygen. These films that were exposed to air presented oxides in the state Cu(II), the amount of CuO depended on the time that the film was exposed to air. Subsequently, we deposited TiO ultra-thin films on polycrystalline copper substrates. Both these thin films were formed by electron beam evaporation. XPS spectra showed that the surface of the titanium monoxide (TiO) films was contamination-free. An evaporation of 0.3 nm of TiO reduced the native oxide of the copper substrates from Cu(II) to Cu(I) or Cu(0) and transformed the TiO into TiO₂ at the interface. Low-energy ion spectroscopy showed that the complete coverage of the substrates depends on the thickness of the copper films. For 10 nm copper thin films the complete coverage occurred at 1.5 nm of TiO, and for 100 nm it occurred at 2.0 nm of TiO. In samples exposed to air, the complete coverage occurred at a film thickness slightly higher than those treated under ultra-high-vacuum conditions.     

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiO_x nanocomposite films have been fabricated by co-sputtering Au wires and SiO₂ target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiO_x films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiO_x films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiO_x films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiO_x NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.     

Properties of ZrNx films with x > 1 deposited by reactive radiofrequency magnetron sputtering

Thin ZrN_x films have been prepared by reactive radiofrequency magnetron sputtering varying the nitrogen partial pressure in the range 0-3.26 Pa. The films have been analyzed by X-ray photoelectron spectroscopy (XPS) and by optical characterization in the UV-Vis-IR range. The cross-section and surface morphology of the samples were examined by means of field emission gun-scanning electron microscopy. The effects of the nitrogen partial pressure on the ZrN_x films stoichiometry have been studied correlating the N 1s photoelectron peaks with different bounding states for the zirconium nitride. The XPS depth profile analysis has revealed the presence of metastable phases (ZrN₂, Zr₃N₄) that vanishes when lowering the nitrogen partial pressure. The optical analysis has permitted to distinguish two different behaviours of the deposited samples in the visible range: semi-transparent and absorbent. Drude-Lorentz model fitted the behaviour of absorbent films, while the O'Leary model was applied to the semi-transparent ones. The semi-transparent films had a band gap varying between 2.36 and 2.42 eV, typical values of N-rich zirconium nitride films. Morphological analysis showed a compact and dense columnar structure for all the samples. A simple growth model explains the presence of the different nitride phases considering implantation and re-sputtering effects.     

Poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate): Correlation between colloidal particles and thin films

We deal with correlation between sizes of colloidal particles and minimum thickness of spin-coated thin films of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) studied by a dynamic light scattering (DLS), a scanning transmission electron microscopy coupled with an energy dispersive X-ray spectroscopy (STEM-EDX), C₆₀-sputtering X-ray photoelectron spectroscopy (XPS), and an atomic force microscopy. Based on the various measurements, it was pointed out that, PEDOT/PSS colloidal dispersion contained majority of primary nanoparticles with mean diameter of 41 nm and 16 nm for BAYTRON P AG (denote P grade) or BAYTRON PH500 (denote PH grade) solutions, respectively, and small amount of clusters aggregated by the primary particles, based on the DLS measurement and STEM observation. On the other hand, PEDOT/PSS thin films with thickness of 44 nm and 16 nm were easily prepared by spin-coating on silicon wafers from the P and PH grade solutions, respectively. Results of STEM-EDX, DLS, and XPS measurements suggested that the PEDOT/PSS thin films consist of the randomly packed primary nanoparticle-“monolayer”.     

Preparation of highly transparent conductive Al-doped ZnO thin films and annealing effects on properties

Aluminum-doped ZnO (ZAO) thin films were deposited on fused quartz substrates by radio frequency sputtering in pure argon ambient at 450 °C. Effects of in situ annealing temperature and annealing atmosphere on microstructure, electrical and optical properties of ZAO films have been investigated. Results showed that as-grown film without annealing treatments attained lowest resistivity of 1.1 × 10⁻⁴Ω cm. And all films performed high average transmittance greater than 90% in visible region. X-Ray diffraction (XRD), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) were utilized to characterize the microstructure properties of films. XRD results indicated that as-grown film had higher crystalline quality and larger grain size than annealed films. Al atoms replaced Zn efficiently to provide electrons stable in all samples. PL spectra revealed that high annealing temperature and oxygen atmosphere would generate more Zn vacancy (V_Zn) and oxide antisite defect (O_Zn), respectively and composition content results from XPS provided supports to this.     

Synthesis of type-II textured tungsten disulfide thin films with bismuth interfacial layer as a texture promoter

Highly textured tungsten disulfide (WS₂) thin films have been obtained by sulfurization of tungsten trioxide. The properties of WS₂ thin films prepared with bismuth interfacial layer as texture promoter has been studied. The WS₂ thin films were found to have predominant type-II orientation. The stacking of 2H-WS₂ crystallites observed with scanning electron microscopy was not reported hitherto. The films can be pictured as an assembly of WS₂ hexagonal crystallites. The energy dispersive X-ray analysis and X-ray photoelectron spectroscopy (XPS) studies confirm that the films are stoichiometric. The XPS analysis described the local environment of the tungsten atoms and the formal oxidation states of the tungsten and sulfur atoms were + 4 and − 2. Together with the high degree of crystallinity and excellent texture of the film, a relatively smooth morphology, on submicron scale, is revealed through atomic force microscopy study. The conditions for the desired textured growth with the van der Waals planes parallel to the substrate surface are reported.     

Influence of thermal annealing on microstructural,morphological, optical properties and surface electronic structure of copper oxide thin films

In this study, effect of the post-deposition thermal annealing on copper oxide thin films has been systemically investigated. The copper oxide thin films were chemically deposited on glass substrates by spin-coating. Samples were annealed in air at atmospheric pressure and at different temperatures ranging from 200 to 600°C. The microstructural, morphological, optical properties and surface electronic structure of the thin films have been studied by diagnostic techniques such as X-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV–VIS) absorption spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The thickness of the films was about 520 nm. Crystallinity and grain size was found to improve with annealing temperature. The optical bandgap of the samples was found to be in between 1.93 and 2.08 eV. Cupric oxide (CuO), cuprous oxide (Cu₂O) and copper hydroxide (Cu(OH)₂) phases were observed on the surface of as-deposited and 600 °C annealed thin films and relative concentrations of these three phases were found to depend on annealing temperature. A complete characterization reported herein allowed us to better understand the surface properties of copper oxide thin films which could then be used as active layers in optoelectronic devices such as solar cells and photodetectors.     

Functionalized interfaces by plasma treatments on silicon and silicon dioxide substrates

Plasma-enhanced chemical vapour deposition has been applied to the fabrication of high-quality SiO₂/Si interfaces and to the functionalization of the silicon dioxide surfaces for organic thin film transistor applications. The advantage of the method herein reported resides in the possibility of activating the substrate, depositing and functionalizing high-quality SiO₂ films in a single-run process, at low temperature. The structural properties of silicon dioxide samples have been studied by infrared spectroscopy, angle resolved and depth profiling X-ray photoelectron spectroscopy. The electronic properties have been retrieved from the leakage current values and the Fowler-Nordheim current plots.     

Irradiation induced effects on Ni3N/Si bilayer system

The irradiation effect in Ni₃N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10¹⁴ ions/cm² was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni₂Si and Si₃N₄ phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni₃N thin films. It was observed that after irradiation (Ni 2p_3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10⁻⁴ torr, were examined using Au ions. In-situ I–V measurements on Ni₃N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.     

Surface studies of crystalline and amorphous Zn-In-Sn-O transparent conducting oxides

X-ray and ultraviolet photoelectron spectroscopy (UPS) studies were made of in situ RF magnetron-sputtered crystalline (c) and amorphous (a) Zn-In-Sn-O (ZITO) thin films, ex situ pulsed laser deposited c- and a-ZITO thin films, and bulk ZITO ceramics. Cosubstitution of Zn and Sn for In results in an increase of the In core level binding energy at a given Fermi level compared to that measured in undoped and Sn-doped In₂O₃ (ITO). In plots of work function vs. Fermi level, in situ c-ZITO and a-ZITO films have low ionization potentials (7.0-7.7 eV) that are similar to undoped In₂O₃. In contrast, dry-air-annealed in situ films, ex situ films, and bulk ceramics have higher ionization potentials (7.7-8.1 eV) that are more similar to ITO and match well with previous work on air-exposed surfaces. Kelvin Probe measurements were made of select a-ZITO films exposed to air and ultraviolet/ozone-treated so as to measure work functions under conditions commonly employed for device fabrication. Results (4.8-5.3 eV) were in good agreement with the UPS work functions of oxygen-exposed materials and with literature values. Lastly, a parallelogram plot of work function vs. Fermi level shows that a wider range of work functions is achievable in ZITO materials as compared to other transparent conducting oxides (Sb-doped SnO₂, Al-doped ZnO, Sn-doped In₂O₃), making ZITO more versatile for applications.     

HOMO–HOMO Electron Transfer: An Elegant Strategy for p-Type Doping of Polymer Semiconductors toward Thermoelectric Applications

Unlike the conventional p-doping of organic semiconductors (OSCs) using acceptors, here, an efficient doping concept for diketopyrrolopyrrole-based polymer PDPP[T]₂-EDOT (OSC-1) is presented using an oxidized p-type semiconductor, Spiro-OMeTAD(TFSI)₂ (OSC-2), exploiting electron transfer from HOMO_OSC-1 to HOMO_OSC-2. A shift of work function toward the HOMO_OSC-1 upon doping is confirmed by ultraviolet photoelectron spectroscopy (UPS). Detailed X-ray photoelectron spectroscopy (XPS) and UV–vis–NIR absorption studies confirm HOMO_OSC-1 to HOMO_OSC-2 electron transfer. The reduction products of Spiro-OMeTAD(TFSI)₂ to Spiro-OMeTAD(TFSI) and Spiro-OMeTAD is also confirmed and their relative amounts in doped samples is determined. Mott–Schottky analysis shows two orders of magnitude increase in free charge carrier density and one order of magnitude increase in the charge carrier mobility. The conductivity increases considerably by four orders of magnitude to a maximum of 10 S m⁻¹ for a very low doping ratio of 8 mol%. The doped polymer films exhibit high thermal and ambient stability resulting in a maximum power factor of 0.07  µ W m⁻¹ K⁻² at a Seebeck coefficient of 140 µ V K⁻¹ for a very low doping ratio of 4 mol%. Also, the concept of HOMO_OSC-1 to HOMO_OSC-2 electron transfer is a highly efficient, stable and generic way to p-dope other conjugated polymers.     

On work function and characteristics of anomalous electrodeposited nickel-cobalt films

The anomalous cobalt content in the electrodeposited nickel-cobalt (Ni-Co) alloy films significantly influenced by the current density was related to the variation of morphology and electron work function (EWF) of the films. The characteristics and EWF of Ni-Co films were investigated by scanning electron microscope with an attached energy dispersive X-ray spectrometer, X-ray diffraction, ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe technique, respectively. As the current density increased from 1 to 20 ampere per square decimeter (A/dm²), the Co atomic concentration (at.%) in Ni-Co greatly decreased from 22.5 at.% to 13.2 at.% correspondingly. The surface morphology of film obtained at low current density became smoother than that at high current density. Both UPS and Kelvin probe results showed the same trend of EWF variation which increased with increasing current density from 1 to 10 A/dm² and kept nearly unchanged at 10-20 A/dm². The smooth Ni-Co film with low EWF could be achieved at low current density. In comparison, Kelvin probe operated at atmosphere ambient could be a good candidate for EWF measurement because of the lower cost and easier operation than UPS at ultra high vacuum.     

Characterization of the protective surface films formed on molten magnesium in air/HFC-134a atmospheres

The surface films formed on molten magnesium in an air/HFC-134a gas mixture at 700 °C were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Auger electron spectroscopy (AES). The results showed that there was a protective film on molten magnesium surface, which can prevent molten magnesium from oxidation and ignition. The surface film contained primarily four elements: magnesium, fluorine, oxygen and carbon, and was composed of MgF₂, MgO and C. The film properties depended on the HFC-134a concentration in the gaseous mixture and exposure time. The thickness of the film formed after exposure to air containing 0.5% HFC-134a for 10 min was about 1–2 μm.     

二极溅射沉积Fe-N-O薄膜的形貌与结构分析

利用二极溅射的方法在不同衬底上沉积了Fe N O薄膜。通过扫描电子显微镜(SEM)、光电子能谱(XPS)和透射电子显微镜(TEM)等先进实验分析手段对二极溅射沉积Fe N O薄膜的形貌与结构进行了分析。XPS和TEM的结果表明,薄膜的主要成分为FeO和少量的Fe16N2多晶体组成,生长上存在择优取向;表面均匀、致密、平整,晶粒大小在50nm左右。