Papers by Keyword: X-Ray Photoelectron Spectroscopy (XPS)

Abstract: The aim of this work is to investigate specific properties of tin-doped magnesium phthalocyanine (Sn-doped MgPc) thin films grown by thermal co-evaporation. Morphological, optical and chemical properties of the doped-films were characterized by atomic force microscopy (AFM), UV-Visible spectroscopy and X-ray photoelectron spectroscopy (XPS). Furthermore, electrical properties of ITO/Sn-doped-MgPc/Al devices such as carrier mobility and carrier concentration were extracted from current-voltage and capacitance-voltage measurements. Morphology of the doped films shows strong dependence on the existence of Sn in the doped films as clearly observed by changing of features of the film surface e.g. surface grain size and roughness. Optical absorption spectra of all conditions provide regular three dominant beta-phase peaks at 352, 640 and 691 nm corresponding to absorption from B-band and Q-band, respectively. The electrical properties obtained from ITO/Sn-doped MgPc/Al device suggest that the enhancement of the current flow in the doped device is a result from the increase of both carrier mobility and carrier concentration. Moreover, photoelectron analysis reveals two formations of Sn dopant in MgPc those are tin metal and derivative of tin oxide.

Abstract: Wet and N₂O oxidized SiO₂/SiC for C-face substrates were comprehensively investigated to clarify the origin of oxide defects which affect channel mobility and threshold voltage stability by using leakage-current analysis. The estimated defects are identified by cathode luminescence, X-ray photoelectron spectroscopy, and high-resolution Rutherford backscattering spectroscopy. The origin of the observed oxide defects might be complex defect of O vacancy defects and/or C related defects including N.

Abstract: In this paper, the interface between Al₂O₃ and p-type 4H-SiC is evaluated using x-ray photoelectron spectroscopy (XPS) measurements. These studies are made on dielectric-semiconductor test structures with Al₂O₃ as dielectric with different pre-and post-deposition treatments. XPS measurements on the as-deposited samples with two different pre-surface cleaning have shown no formation of a SiO₂ interlayer. However, after the post deposition rapid thermal annealing (RTA) at 1100 °C in N₂O for 60s, a SiO₂ interlayer is formed. The surface band bending was determined from Si 2p core level peak shifts measured using XPS. These results suggest that Al₂O₃ deposited on the p-type 4H-SiC have a net positive oxide charge which is complementary to that of n-type 4H-SiC. From these shifts it was found that the as-deposited RCA cleaned sample had an oxide charge of 5.6×10¹³ q/cm^-2, as compared to standard cleaned samples, having 4.6×10¹³ q/cm^-2. A further reduction in oxide charge was observed after annealing at 1100 °C in N₂O, down to a value of 4×10¹³ q/cm^-2.

Abstract: Bismuth-doped copper phthalocyanine (Bi-doped CuPc) thin films were grown by organic-source thermal co-evaporation under five different deposition rates. Morphological, optical and chemical properties of the doped-films were characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), UV-Visible spectroscopy and X-ray photoelectron spectroscopy (XPS). Furthermore, electrical properties of ITO/Bi-doped-CuPc/Al devices i.e. carrier mobility and carrier concentration were characterized by current-voltage and capacitance-voltage measurements. Morphology of the doped films shows strong dependence on preparation conditions, as clearly observed by features of film surface i.e surface grain size and roughness. Optical absorption spectra of all doping conditions provide regular three dominant α-phase peaks at 339, 620 and 695 nm corresponding to absorption from B-band and Q-band, respectively. Electrical properties exhibit the enhancement of the film conductivity due to increase of both carrier mobility and carrier concentration with higher Bi-doping level. Moreover, photoelectron analysis reveals chemical information of the metal dopant in the host material.

Abstract: This research is related to growth and characterizations of indium-doped pentacene thin films as a novel hybrid material. Doped films were prepared by thermal co-evaporation under high vacuum. The doping concentration was varied from 0% to 50% by controlling the different deposition rate between these two materials while the total thickness was fixed at 100 nm. The hybrid thin films were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and UV-Visible spectroscopy to reveal the physical and optical properties. Moreover, the electrical properties of ITO/indium-doped-pentacene/Al devices i.e. charge mobility and carrier concentration were determined by considering the relationship between current-voltage and capacitance-voltage. AFM results identify that doping of indium into pentacene has an effect on surface properties of doped films i.e. the increase of surface grain size. XRD results indicate that doping of metal into pentacene has an effect on preferential orientation of pentacene’s crystalline domains. UV-Vis spectroscopy results show evolution of absorbance at photon energy higher than 2.7 eV corresponding to absorption from oxide of indium formed in the films. Electrical measurements exhibit higher conductivity in doped films resulting from increment of both charge carrier mobility and carrier concentration. Furthermore, chemical interactions taken place inside the doped films were investigated by x-ray photoelectron spectroscopy (XPS) in order to complete the remaining questions i.e. how do indium atoms interact with the neighbor molecules, what is the origin of the absorption at E > 2.7 eV Further results and discussions will be presented in the publication.

Abstract: Tin-doped nickel phthalocyanine thin films (Sn-doped NiPc) were deposited by thermal co-evaporation method. Doping concentration of tin in NiPc was controlled via different deposition rates between metal dopent and host organic material. Properties of the thin films doped by tin in the range of 3 to 15% were characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), UV-Visible spectroscopy and X-ray photoelectron spectroscopy (XPS). Furthermore, electrical properties of Al/Sn-doped-NiPc/ITO devices i.e. charge carrier concentration and carrier mobility were characterized by current-voltage and capacitance-voltage measurements. Microscopic results show clear evidence of the morphological transition from granular structure in undoped-film to rod-liked structure in the films doped more than 5%. Moreover, surface grain size exhibits the tendency to decrease with the increase of doping concentration. Optical properties reveal that the packing of NiPc molecules in all doping conditions is the combination of α-phase (majority) and β-phase (minority). However, evolution of β-phase NiPc is observed with the increase of doping concentration. Photoelectron analyses indicate shift of binding energy in both Ni2p and Sn3d levels corresponding to charge transfer between nickel-core and tin dopant. In addition, the electrical properties show the enhancement of the film’s conductivity due to the increase of charge carrier concentration with the higher Sn-doping level.

Abstract: This paper introduces the X-ray photoelectron spectroscopy (XPS) technique, well applicable for the analysis of the interfacial layer between polyvinyl alcohol and monocalcium aluminate in macro defect-free (MDF) cement. The experimental results explain the chemical reaction mechanism during the mechanochemical process, which is crucial for the formation of those non-traditional polymercement composite materials.

Abstract: Mechanical alloying (MA) is an established way to prepare nanocrystalline materials and metastable solutions of materials, which normally have no mutual solubility. This is also the case for oxide dispersion strengthened (ODS) steels with improved mechanical properties at elevated temperatures. It is known that a small addition of yttria (Y₂O₃) has a beneficial effect on high temperature strength and reduces the creep rate in mechanically alloyed ferritic steels by about six orders of magnitude. In this work we present an experimental study using atom probe tomography, X-ray photoelectron spectroscopy, and positron annihilation spectroscopy combined with first principles modeling focusing on the distribution and behavior of yttria in pure iron prepared by mechanical alloying. Atom probe tomography and X-ray photoelectron spectroscopy measurements as well as positron annihilation spectroscopy conducted on powder particles directly after milling have revealed that a predominantly fraction of the yttria powder dissolves in the iron matrix and Y atoms occupy convenient positions, such as vacancies or dislocations. This is supported by ab initio calculations demonstrating that the formation energy for Y substitutional defects in bcc-Fe is significantly lower in the close neighborhood of vacancies.

Abstract: Zinc Oxide (ZnO) films were deposited by Atomic Layer Deposition (ALD) using Diethylzinc and a combination of Water and Ozone as the precursores. Electrical conductivity of ALD grown ZnO films, under low field, were studied with varied partial pressure of the constituent reactants. Supressing the oxygen vacancy by introducing O₃ during the reaction increase the resistivity of the films by couple of orders of magnitude. UV-Vis spectroscopy measurement showed the films to be transparent giving a room for its application as a TCO in solar cell.

Abstract: This study presents the variation of the thermal resistance of a system Cu/Ceramic in relation with the parameters of the development process. More particularly, a thermal treatment is applied to this system with the aim of improving heat transfer both within the film and at the film/substrate interface. The obtained results show a very significant decrease of the effective thermal resistance with a thermal treatment at 300 °C during one hour. These effects on heat transfer were highlighted with the study of the chemical composition within the interface by using depth profiles carried out by X-ray photoelectron spectroscopy (XPS). The deconvolution of the system shows that the interface thickness initially of roughly 20 nm reaches 50 nm after treatment. All these results are discussed in relation with the adhesion force, the porosity and the nucleation phenomena in the film.