X-ray Photoelectron Spectroscopy Peak Research Articles

Role of magnesium doping for ultrafast room temperature crystallization and improved photocatalytic behavior of TiO2 nanotubes

In this work, a simple and cost effective two step anodization method is used to prepare Magnesium doped TiO2 nanotubes (Mg-TONTs) which demonstrate superior photocatalytic performance. Room temperature (28 °C) crystallization of well alligned TONTs is achieved by Mg doping within a record time of 10 s whereas undoped samples prepared at 28 °C are amorphous. Mg-TONTs possess a photocatalytic degradation rate of 0.006/min which is 5 times higher than that by undoped amorphous TONT (0.0015/min) for the degradation of the organic pollutant methylene blue. The samples are morphologically, structurally, compositionally as well as optically characterised by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectrometer (DRS). FESEM reveal perfect tubular structure even after Mg doping with no Mg overlayer at the top of the tube. XRD and TEM confirm the polycrystalline nature of the tube and attainment of room temperature crystallization with a prominent peak at 25.100 and 47.80° in the former. XPS peak at ∼1303.5 eV corresponding to Mg1s confirms the formation of Mg bonding in the compound. The optical study indicates a decrease in the band gap of the doped sample that enables visible photon absorption that contributes to the enhanced photocatalytic activity.

Effects of Plasma Treatment on the Composition and Phase Changes of Sputter-Deposited SnOx Thin Films.

This study examined the effects of the plasma treatment of CF₄ or SF6 on the properties of tin oxide (SnOx) thin films prepared at room temperature using a radio frequency sputtering technique. The properties of the samples were characterized by dynamic-secondary ion mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Hall Effect measurements. All untreated samples showed Sn4+ and Sn2+ XPS peak area percentages of 57.6 and 34.6%, respectively, indicating a larger amount of SnO₂ phase in the samples than SnO. The samples treated with CF₄ plasma exhibited the maximum and minimum Sn4+ and Sn2+ peak areas, respectively, at a treatment time of 35 s. This was attributed to the maximum oxygen atomic percentage at 35 s and the injection of additional carbon and fluorine into the sample with increasing treatment time. On the other hand, in the case of samples treated with SF6 plasma, the Sn4+ peak area increased with increasing treatment time while the Sn2+ peak area decreased. This suggests that SnO₂ is a stronger phase for samples treated with SF6 plasma for a longer duration. Furthermore, the changes in the Sn4+ and Sn2+ peak areas of the samples treated with CF₄ plasma were much larger than those of the samples treated with SF6 plasma, which indicates that CF₄ plasma has a larger impact on the properties of the samples. This difference in impact showed a correlation with the sharper decrease in the number of oxygen vacancies for CF₄ plasma-treated samples. These results were attributed to the introduction of additional fluorine and carbon into CF₄ plasma-treated samples compared to the SF6 plasma-treated ones. In addition, XRD showed that the plasma treatment did not affect the amorphous phase in the samples.

Identifying a perovskite phase in rare-earth nickelates using X-ray photoelectron spectroscopy

We demonstrate a practical way to identify the presence of a perovskite phase in rare-earth nickelates (RNiO3) using X-ray photoelectron spectroscopy (XPS). By varying the calcination temperature, we prepared RNiO3 powders with different degrees of chemical reaction. We found that perovskite RNiO3 becomes predominant after high-temperature calcination (≥1,000 °C) in X-ray diffraction and XPS (at Ni 3p and O 1s edges) measurements. While the observed spectra at the Ni 3p edge are similar for all powders, a sizable difference was observed in the O 1s-edge spectra depending on the calcination temperature. With the formation of a perovskite phase with a trivalent Ni3+ state, an XPS peak corresponding to oxygen ions in the perovskite lattice distinctly emerges. Our work shows that the Ni3+ state cannot be determined by analyzing the Ni 3p edge solely and rather, the O 1s edge should be simultaneously monitored for explicit identification.

Investigation on Surface Properties of Mn-Doped CdSe Quantum Dots Studied by X-ray Photoelectron Spectroscopy

In this work, we report on the effects of incorporating manganese (Mn) dopant into different sizes of cadmium selenide (CdSe) quantum dots (QDs), which improves the electronic and optical properties of the QDs for multiple applications such as light-emitting diodes, lasers, and biological labels. Furthermore, the greener inverse Micelle method was implemented using organic ligand, which is oleic acid. This binding of the surface enhanced the QDs’ surface trap passivation of Mn-doped CdSe, which then increased the quantity of the output. In addition, the inverse Micelle technique was used successfully to dope Mn into CdSe QDs without the risk of Mn dopants being self-purified as experienced by wurtzite CdSe QDs. Also, we report the X-ray photoelectron spectroscopy (XPS) results and analysis of zinc blended manganese-doped cadmium selenide quantum dots (Mn-doped CdSe QDs), which were synthesized with physical sizes that varied from 3 to 14 nm using the inverse Micelle method. The XPS scans traced the existence of the Se 3d and Cd 3d band of CdSe crystals with a 54.1 and 404.5 eV binding energy. The traced 640.7 eV XPS peak is proof that Mn was integrated into the lattice of CdSe QDs. The binding energy of the QDs was related to the increase in the size of the QDs.

Photoluminescence and cathodoluminescence of spin coated ZnO films with different concentration of Eu3+ ions

ZnO thin films doped with Eu3+ up to 4 mol% were successfully prepared using a sol-gel spin coating technique. The structure, morphology, chemical analysis and luminescence of the films were studied. X-ray photoelectron spectroscopy (XPS) analysis for the Eu 3d core shells confirmed the presence of divalent (Eu2+) and trivalent (Eu3+) states. Time of flight secondary ion mass spectroscopy showed that the Eu3+ions were homogeneously distributed throughout the thin film with Eu2+ mainly only in the surface region of the thin films. The films exhibited ZnO exciton emission around 376 nm, broad defect related emission and the Eu3+ characteristic emission simultaneously when excited at 325 nm. For the excitation at 464 nm, the doped samples exhibited only the characteristic emissions of Eu3+ which were attributed to the 5D0-7FJ (J = 0, 1, 2, 3, 4) transitions, respectively. The film with a 3 mol% of Eu3+ has emitted the highest photo/cathodoluminescence (PL/CL) emission. Therefore, it was subjected to electron beam irradiation in vacuum for about 22 h to establish the effect of the electron beam on the film's surface state, chemical and luminescence stability. Minor surface modification during electron beam irradiation was observed. The O 1s XPS peak revealed the creation of new defects associated with oxygen deficiencies due to the irradiation. Surface modification and creation of defects were identified as the major mechanisms for the initial decrease in the CL intensity. This film was very stable during prolonged electron beam irradiation.

Hydrophilic Food-Borne Nanoparticles from Beef Broth as Novel Nanocarriers for Zinc

Food-borne nanoparticles (FNs) may be used as nanocarriers for metal ion chelation in micronutrient supplements. In this paper, the preparation and characterization of hydrophilic FNs were reported from beef broth cooked with a pressure cooker at 117 °C for different periods (30, 50, and 70 min) and their potential application as nanocarriers for zinc was investigated. The broth FNs are quasi-spherical with good water solubility and ultrasmall size, which can emit a strong sapphire color under 365 nm ultraviolet irradiation. X-ray photoelectron spectroscopy (XPS) analysis showed that there are carboxyl, amino, and hydroxyl groups on the FNs, which are useful for Zn(II) chelation. The vibration band of C═O at 1688 cm-1 in the infrared spectrum of FNs shifted to 1718 cm-1 after binding with Zn(II) ions, suggesting the participation of the carbonyl group in Zn(II) ion chelation. The appearance of Zn2p XPS peaks, at 1021.6 and 1045 eV for Zn(II)-FNs, clearly demonstrated the formation of Zn-O between the FNs and zinc ions. Biodistribution of FNs and the Zn(II)-FN complex in normal rat kidney cells demonstrated that they could easily enter normal rat kidney cells. A downfield was found for the signals of Zn(II)-FNs in 1H nuclear magnetic resonance spectroscopy and strongly suggested the binding of Zn(II) ions to FNs through carboxylic acid, hydroxyl, and amine groups. In addition, no obvious cytotoxicity was found for Zn(II)-FNs compared to zinc (ZnSO4) and commercial zinc gluconate. The results revealed that the FNs from beef broth may have a potential as nanocarriers for zinc chelation.

On the presence of Ga2O sub-oxide in high-pressure water vapor annealed AlGaN surface by combined XPS and first-principles methods

We conducted X-ray photoelectron spectroscopy (XPS) and first-principles calculations based on density functional theory (DFT) to confirm the presence of Ga2O sub-oxide in high-pressure water vapor annealed AlGaN surface. We note that the Ga 3d XPS peak broadens and shifts towards higher binding energies, which suggests surface oxide formation. Deconvoluted Ga 3d XPS profiles between HPWVA-treated and reference samples reveal reasonable inclusion of Ga2O peak, suggesting formation of Ga2O sub-oxide. To theoretically confirm the presence of Ga2O, we calculated the Ga 3d core-level shift using initial state approximation. We obtained a 0.74 eV shift, in reasonable agreement with that of Ga2O. Moreover, based on the calculation of net charge on Ga using DFT, we also obtained a +1 oxidation state for Ga, indicating its existence in Ga2O form. By combining theory and experiment, therefore, we have explored the possibility of the formation of Ga2O sub-oxide, which may provide new avenues for obtaining highly stable operation in GaN-based devices.

Effects of the Process Parameters on the Properties of Sputter-Deposited Tin Oxide Thin Films.

This study examined the effects of the oxygen partial pressure on the properties of tin oxide (SnOx) thin films deposited by radio frequency magnetron sputtering using a SnO target. The properties of the samples were characterized by Hall Effect measurements, dynamic-secondary ion mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and atomic force microscopy. All the samples exhibited dominant Sn2+ XPS peaks, indicating that SnO with p-type conductivity was the main composition regardless of the oxygen partial pressure. The samples deposited with an oxygen partial pressure of 12% showed the best p-type characteristics, which included a maximum hole mobility of 1.94 cm²/Vs, carrier concentration of 3.83×1017/cm³, Sn2+ peak area percentage of 91.34%, Sn4+ peak area percentage of 2.35%, and Sn0 peak area percentage of 6.31%. As the oxygen partial pressure was increased to more than 12%, the Sn2+ peak area percentage decreased while the Sn4+ peak area percentage increased. This was attributed to the reduction of the SnO phase and the growth of the SnO₂ phase in the samples due to the incorporation of more oxygen. These results are expected to contribute to the development of p-type SnO-based TFTs with good performance.

Effects of Oxygen Ratio on the Properties of Tin Oxide Thin Films Doped with Bismuth

This study examins the effects of the oxygen ratio on the properties of bismuth (Bi)‐doped tin oxide (Bi‐SnOx) films deposited by radio frequency magnetron sputtering using a SnO (90 at%)‐Bi (10 at%) ceramic target. The properties of the samples are characterized by X‐ray photoelectron spectroscopy (XPS), Hall effect measurements, dynamic‐secondary ion mass spectrometry (D‐SIMS), and X‐ray diffraction (XRD). The samples deposited without oxygen gas exhibit Sn4+ and Sn2+ XPS peak areas of 44.7 and 41.1%, respectively. The Sn4+ area increases to 64.1% with increasing oxygen ratio up to 20% with a concomitant decrease of the Sn2+ area to 26%, indicating that SnO2 with n‐type conductivity is the dominant phase under a higher oxygen partial pressure. XPS shows that with increasing oxygen ratio, the chemical state of Bi changes from metallic Bi (Bi0) to Bi3+. Furthermore, with increasing oxygen ratio, the Bi content in the samples increases because of the increase in Bi2O3 formation, which causes a decrease in the number of oxygen vacancies in the samples. These results suggest that the oxygen ratio is useful for controlling Bi doping in SnOx films. Therefore, Bi doping is valuable for suppressing the formation of oxygen vacancies and improving the properties of SnOx films.

Enhancing oxygen vacancy photocatalytic efficiency of bismuth tungstate using In-doped W site

Pure and In-doped orthorhombic Bi<sub>2</sub>WO<sub>6</sub> are synthesized by sol-gel method through using raw materials Bi(NO<sub>3</sub>)<sub>3</sub>·5H<sub>2</sub>O, In(NO<sub>3</sub>)<sub>3</sub>·6H<sub>2</sub>O, (NH<sub>4</sub>)<sub>2</sub>WO<sub>4</sub> and surfactants citric acid, polyethylene glycol. All samples are in pure phase without impurity phase as indicated by X-ray diffraction characterization. The In-doped sample degradation efficiency for rhodamine B is higher than that for pure phase with the optimal content 7% mole ratio. Because indium impurity adhering to Bi<sub>2</sub>WO<sub>6</sub> nucleus surface may affect the crystallization range, the sample morphology gradually becomes fluffy and regular, which is reveled through scanning electron microscopy analysis. This morphology change plays an important role in electron-hole transport process as well as contact area of carrier and organic molecule. Using X-ray photoelectron spectroscopy (XPS) characterization and Gaussian fitting, it is found that the O 1s XPS peak of pure and In-doped sample each contain three peak sites. The low energy peak around 530 eV originates from W—O and Bi—O bond. The high peak is ascribed to lattice oxygen defect and its intensity is enhanced gradually with the increase of In content. Thus the increase of oxygen vacancies is the main reason for this photocatalytic performance improvement. Comparing with the impurity-free sample, the visible absorption of In-doped Bi<sub>2</sub>WO<sub>6</sub> is enhanced and the corresponding band gap slightly decreases, which is indicated by diffraction reflection spectroscopy measurement. The reduction of forbidden band width further enhances the photocatalytic performance. After configuration relaxation and self-consistence calculation, the formation energy obtained from a single oxygen vacancy model is less than those from the Bi1<sub>In</sub> + V<sub>O</sub> and the Bi2<sub>In</sub> + V<sub>O</sub> co-doping models, and greater than the W<sub>In</sub> + V<sub>O</sub> formation energy. This result indicates that indium replacing W site can promote the generating of oxygen vacancies. The calculation of the 18%-hybridization function electronic structure shows that the Bi<sub>2</sub>WO<sub>6</sub> has indirect band gap semi-conduction with energy gap 2.76 eV, which is consistent with the experimental value 2.79 eV. A series of new local states appears in the band gap and near conduction band bottom based on the oxygen vacancy model. These local states promote light absorption and enhance photocatalytic performance. In conclusion, the enhanced photocatalytic performance of Bi<sub>2</sub>WO<sub>6</sub> is attributed to the indium entering into the tungsten site rather than the bismuth site as indicated by the experimental and theoretical result.

Accurate chemical analysis of oxygenated graphene-based materials using X-ray photoelectron spectroscopy

A simple, fast and general protocol for quantitative analysis of X-ray photoelectron spectroscopy (XPS) data provides accurate estimations of chemical species in graphene and related materials (GRMs). XPS data are commonly used to estimate the quality of and defects in graphene and graphene oxide (GO), by comparing carbon and oxygen 1s XPS peaks, obtaining an O/C ratio. This approach, however, cannot be used in the presence of extraneous oxygen contamination.The protocol, based on quantitative line-shape analysis of C 1s signals, uses asymmetric pseudo-Voigt line-shapes (APV), in contrast to Gaussian-based approaches conventionally used in fitting XPS spectra, thus allowing better accuracy in quantifying C 1s contributions from graphitic carbon (sp2), defects (sp3 carbon), carbons bonded to hydroxyl and epoxy groups, and from carbonyl and carboxyl groups. The APV protocol was evaluated on GRMs with O/C ratios ranging from 0.02 to 0.30 with film thicknesses from monolayers to bulk-like (>30 nm) layers and also applied to previously published data, showing better results compared to those from conventional XPS fitting protocols.Based uniquely on C 1s data, the APV protocol can quantify O/C ratio and the presence of specific functional groups in GRMs even on SiOx, substrates, or in samples containing water.

Aging Properties of Phenol-Formaldehyde Resin Modified by Bio-Oil Using UV Weathering.

The aging properties of phenol-formaldehyde resin modified by bio-oil (BPF) were analyzed using ultraviolet (UV) weathering. The variations on bonding strength of BPF were measured, and the changes on microstructure, atomic composition and chemical structure of BPF were characterized by using a scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR), respectively. With the increase of aging time, the bonding strength decreased gradually, the resin surface became rougher and the O/C radio of resin surface increased. However, the loss rate of bonding strength of BPFs was 9.6–23.0% lower than that of phenol-formaldehyde resin (PF) after aging 960 h. The aging degree of BPF surfaces was smaller in comparison to PF at the same aging time. These results showed that the bio-oil had a positive effect on the anti-aging property. Analytical results revealed that with increasing the aging time, the XPS peak area of C–C/C–H decreased, while that of C=O and O–C=O increased. The intensity of methylene and ether bridges in NMR analysis decreased along with increasing the intensity of aldehydes, ketones, acids and esters. These results indicated that the aging mechanism of BPF was a process of the breakage of molecular chains and formation of oxygen-containing compounds.

Wet Pretreatment-Induced Modification of Cu(In,Ga)Se2/Cd-Free ZnTiO Buffer Interface.

We report a novel Cd-free ZnTiO buffer layer deposited by atomic layer deposition for Cu(In,Ga)Se2 (CIGS) solar cells. Wet pretreatments of the CIGS absorbers with NH4OH, H2O, and/or aqueous solution of Cd2+ ions were explored to improve the quality of the CIGS/ZnTiO interface, and their effects on the chemical state of the absorber and the final performance of Cd-free CIGS devices were investigated. X-ray photoelectron spectroscopy (XPS) analysis revealed that the aqueous solution etched away sodium compounds accumulated on the CIGS surface, which was found to be detrimental for solar cell operation. Wet treatment with NH4OH solution led to a reduced photocurrent, which was attributed to the thinning (or removal) of an ordered vacancy compound (OVC) layer on the CIGS surface as evidenced by an increased Cu XPS peak intensity after the NH4OH treatment. However, the addition of Cd2+ ions to the NH4OH aqueous solution suppressed the etching of the OVC by NH4OH, explaining why such a negative effect of NH4OH is not present in the conventional chemical bath deposition of CdS. The band alignment at the CIGS/ZnTiO interface was quantified using XPS depth profile measurements. A small cliff-like conduction band offset of -0.11 eV was identified at the interface, which indicates room for further improvement of efficiency of the CIGS/ZnTiO solar cells once the band alignment is altered to a slight spike by inserting a passivation layer with a higher conduction band edge than ZnTiO. Combination of the small cliff conduction band offset at the interface, removal of the Na compound via water, and surface doping by Cd ions allowed the application of ZnTiO buffer to CIGS treated with Cd solutions, exhibiting an efficiency of 80% compared to that of a reference CIGS solar cell treated with the CdS.

The Gaussian-Lorentzian Sum, Product, and Convolution (Voigt) functions in the context of peak fitting X-ray photoelectron spectroscopy (XPS) narrow scans

X-ray photoelectron spectroscopy (XPS) is arguably the most important vacuum technique for surface chemical analysis, and peak fitting is an indispensable part of XPS data analysis. Functions that have been widely explored and used in XPS peak fitting include the Gaussian, Lorentzian, Gaussian-Lorentzian sum (GLS), Gaussian-Lorentzian product (GLP), and Voigt functions, where the Voigt function is a convolution of a Gaussian and a Lorentzian function. In this article we discuss these functions from a graphical perspective. Arguments based on convolution and the Central Limit Theorem are made to justify the use of functions that are intermediate between pure Gaussians and pure Lorentzians in XPS peak fitting. Mathematical forms for the GLS and GLP functions are presented with a mixing parameter m. Plots are shown for GLS and GLP functions with mixing parameters ranging from 0 to 1. There are fundamental differences between the GLS and GLP functions. The GLS function better follows the ‘wings’ of the Lorentzian, while these ‘wings’ are suppressed in the GLP. That is, these two functions are not interchangeable. The GLS and GLP functions are compared to the Voigt function, where the GLS is shown to be a decent approximation of it. Practically, both the GLS and the GLP functions can be useful for XPS peak fitting. Examples of the uses of these functions are provided herein.

Surface and interface properties of polar thin films on a ferroelectric substrate: ZnO on LiNbO3 (0001) and (0001¯)

The impact of ferroelectric polarization on film growth has been studied through the deposition of polar ZnO thin films on ferroelectric LiNbO3 (0001) and (0001¯) surfaces. The growth was monitored by reflection high energy electron diffraction and characterized by x-ray photoelectron spectroscopy (XPS), x-ray diffraction, and x-ray reflectivity. The evolution of the XPS peak intensities and x-ray reflectivity data suggest that the growth was Stranski–Krastanov with a two-dimensional to three-dimensional transition and a small degree of roughness at the interface. The film maintained the substrate surface crystallography initially, then transitioned to an ordered ZnO (0001) phase after passing through a disordered regime. Higher Zn 2p XPS core level binding energies were observed on positively poled LiNbO3 and were attributed to the negative compensating charges at the positive surface n doping the ZnO film, thereby the Fermi level is pinned at the bottom of the ZnO conduction band. In addition, the reaction of 2-propanol was used as a probe to identify the polarity of thick ZnO films. The results indicate that ZnO films grown on either LiNbO3 (0001) or (0001¯) polar surfaces ultimately develop a negative polarization. Therefore, it is concluded that the LiNbO3 polar substrate has a more obvious impact over a short range near the ZnO/LiNbO3 interface but this does not translate into directing the polarization direction of thicker ZnO films.

Thiophene Derivatives on Gold and Molecular Dissociation Processes

We report a systematic study of thiophene derivatives on gold surfaces. These molecules are of interest in molecular electronics, and the characracteristics of the thiophene–electrode interface in devices needs to be understood as it affects electron transport characteristics. Some experiments indicated S–C bond scission in contact with metals resulting in disruption of the π-electron system that affects charge transport, which would also be affected by presence of split-off chemisorbed sulfur. We explored this dissociation aspect by photoemission for the case of monocrystalline Au(111) surfaces and Au films grown on mica for a series of polythiophenes molecules (nT, n = 1–4, 6) as well as for α,ω-diquaterthiophene (DH4T) and dihexylsexithiophene (DH6T). The S 2p X-ray photoelectron spectroscopy peaks are found to have complex line shapes corresponding to S atoms with different core level binding energies (CLBE). Density functional theory calculations of adsorption energies and CLBEs were performed for va...

Effects of Mn Ion Implantation on XPS Spectroscopy of GaN Thin Films

Gallium nitride (GaN) thin film was deposited onto a sapphire substrate and then implanted with 250 keV Mn ions at two different doses of 2 × 1016 ions/cm2 and 5 × 1016 ions/cm2. The as-grown and post-implantation-thermally-annealed samples were studied in detail using x-ray photoelectron spectroscopy (XPS). The XPS peaks of Ga 3d, Ga 2p, N 1s, Mn 2p and C 1s were recorded in addition to a full survey of the samples. The doublet peaks of Ga 2p for pure GaN were observed blue-shifted when compared with elemental Ga, and appeared further shifted to higher energies for the implanted samples. These observations point to changes in the bonds and the chemical environment of the host as a result of ion implantation. The results revealed broadening of the N 1s peak after implantation, which is interpreted in terms of the presence of N-Mn bonds in addition to N-Ga bonds. The XPS spectra of Mn 2p recorded for ion-implanted samples indicated splitting of Mn 2p 1/2 and Mn 2p 3/2 peaks higher than that for metallic Mn, which helps rule out the possibility of clustering and points to substitutional doping of Mn. These observations provide a framework that sheds light on the local environment of the material for understanding the mechanism of magnetic exchange interactions in Mn:GaN based diluted magnetic semiconductors.

High performance PtxEu alloys as effective electrocatalysts for ammonia electro-oxidation

Pt-rare-earth alloys are rarely studied as electrocatalysts for direct ammonia fuel cells. Thus, their electrocatalytic performance of ammonia electro-oxidation is worth studying, especially for PtxEu alloys. Herein, a series of PtxEu/C (x = 1, 3 and 5) electrocatalysts has been prepared using polyol reduction method. Among them, PtEu/C is found to be a promising candidate for ammonia electro-oxidation. Physical characterizations show that PtEu/C has a small lattice parameter and narrow size distribution. X-ray photoelectron spectroscopy peak shifts of PtEu/C indicate the electron transfer from Eu to Pt. Electrochemical measurement results indicate that PtEu/C is highly active. Particularly, it has a higher current density, lower activity loss and apparent activation energy toward ammonia electro-oxidation compared to Pt/C catalyst.

Carbonization of Silicon Nanoparticles via Ablation Induced by Femtosecond Laser Pulses in Hexane

Silicon carbide (SiC) has been widely used in various technological applications, including power devices, light-receiving devices, and light-emitting devices. Several methods for fabricating SiC particles with nanometer dimensions have been reported, including carbo-thermal reduction of silica, chemical vapor deposition, laser pyrolysis, and microwave irradiation. To develop a new and simple method for fabricating SiC nanoparticles, we investigated the possibility of using femtosecond-laser ablation. In this paper, we report the formation of SiC nanoparticles by femtosecond-laser ablation on silicon immersed in hexane. By using a high-peak-power laser that can achieve extremely high temperatures and pressures on the silicon surface, SiC nanoparticles were successfully fabricated via ablation in hexane. In our experiments, femtosecond pulses from a Yb-fiber laser were used to irradiate to silicon single crystal. The laser was focused onto a spot on the silicon surface. After ablation, we evaluated the particles on the target substrate and particles in the irradiated hexane. Scanning electron microscopy revealed that the particles range in size from 100 to 400 nm. X-ray diffraction analysis indicated that the nanoparticles might be SiC. The characteristic X-ray photoelectron spectroscopy peaks of nanoparticles were Si-2p (100.1 eV) and C-1s (282.9 eV), which are identical to the characteristic peaks of SiC (John et al. in Handbook of X-ray photoelectron spectroscopy, Physical Electronics, Eden Prairie, 1995; Hijikata et al. in Appl Surf Sci 184:161–166, 2001; Shen et al. in Chem Phys Lett 375:177–184, 2003). We also used transmission electron microscopy and electron energy-loss spectroscopy to evaluate particles from the irradiated hexane. Such a simple method of fabricating SiC nanoparticles by femtosecond-laser ablation may open new possibilities in the development of growth techniques for SiC.

Effect of PLD growth atmosphere on the physical properties of ZnO:Zn thin films

Highly preferential c-axis (002) orientated ZnO:Zn films were successfully prepared in different growth atmospheres using the pulsed laser deposition technique. The stress parameters in the films were determined as −2.81 GPa, −1.03 GPa and −0.08 GPa for the thin films deposited in O2, Ar and vacuum, respectively. X-ray photoelectron spectroscopy (XPS) high resolution spectra of the Zn-2p peak confirmed that Zn atoms were in a doubly ionized state, and the deconvolution of the O-1s XPS peak showed the presence of oxygen related defects in the films. The surface of the film prepared in Ar was the most rough, while the surface of the films deposited in vacuum and O2 were relatively smooth. All the films exhibited ultraviolet emission around 378 nm with different intensities. The film prepared in Ar showed a weak deep level emission around 550 nm which was an indication of the low defect concentration in the film. The film prepared in O2 exhibited yellow emission centered at 600 nm, which XPS results showed to be due to the oxygen related defects. The film obtained in vacuum had a blue and green emission at 405 nm and 512 nm, respectively. The formation of the defects-related visible emission in the different atmosphere was discussed. A good agreement with the theoretical results was obtained, oxygen interstitial and oxygen vacancies were the defects that were responsible for the visible emission around 600 nm and 500 nm–550 nm, respectively. Different from previous papers is the fact that the defects and therefor the defect emission in the thin films could be controlled by using different growth atmospheres to prepare the thin films.