Zn LMM Research Articles

Zinc sulfide chemical vapor deposition optical ceramic analyzed by XPS

Commercially available zinc sulfide (ZnS) ceramics, synthesized using chemical vapor deposition and subsequently hot isostatically pressed, are optically transparent as compared to other zinc sulfide chemical vapor deposited films and ceramics. The unique optical transparency along with the hardness and chemical resistance of ZnS makes it an important material for infrared transmission applications. X-ray photoelectron spectroscopy and x-ray induced Auger electron spectroscopy were performed on an optically transparent ZnS ceramic. This report includes charge corrected scans for the survey along with S 2s, S 2p, S LMM, Zn 2p, Zn 2s, Zn 3d, Zn 3p, Zn 3s, Zn LMM, O 1s, and C 1s surface photoelectron signals. The scans provide photoelectron spectroscopy investigation data to help with the identification of metal sulfide compounds.

Propane Dehydrogenation on Single-Site [PtZn4] Intermetallic Catalysts

Summary Propane dehydrogenation (PDH) is a commercial propylene production technology that has received much attention, but high reaction temperatures result in a decrease of propylene selectivity and catalyst stability. This paper describes a single-site [PtZn4] catalyst by assembling atomically ordered intermetallic alloy (IMA) as a selective and ultrastable PDH catalyst. The catalyst enables more than 95% of propylene selectivity from 520°C to 620°C. No obvious deactivation is observed within the 160-h test, superior to PtSn/Al2O3 and state-of-the-art Pt-based catalysts. Based on in situ X-ray absorption fine structure, X-ray photoelectron spectroscopy measurements, and density functional theory calculations, we reveal that the surface [PtZn4] ensembles in PtZn IMAs serve as the key active site structures, wherein the geometry-isolated and electron-rich Pt1 site in [PtZn4] ensembles readily promotes the first and second C–H cleavage of propane but inhibits further dehydrogenation of surface-bounded propylene. This significantly improves the selectivity and stability by prohibiting coke side reactions.

Polarization dependence of ZnO Schottky barriers revealed by photoelectron spectroscopy

In order to answer the question of whether Schottky barriers on polar ZnO surfaces are different at Zn- and O-terminated surfaces, the interface formation of $n$-type ZnO and different high work function metals and metal oxides (Pt, ${\mathrm{PtO}}_{x}$, and ${\mathrm{RuO}}_{2}$) with Schottky barrier heights of up to 1.5 eV has been studied using photoelectron spectroscopy with in situ sample preparation. The experiments are designed to exclude the effects of substrate reduction and consequent Fermi level pinning by high concentrations of oxygen vacancies. Moreover, by including the Zn LMM Auger emission in the analysis, it is demonstrated that an accurate extraction of barrier heights needs to take into account that the screening of the photoelectron core hole can change in the course of contact formation. The polarization dependence of Schottky barriers, which is important for piezotronic applications, is in most cases dominated by the influence of defects. Reducing the influence of defects, up to $\ensuremath{\sim}240$ meV higher Schottky barriers are revealed on oxygen-terminated surfaces. This is opposite to what has been reported in the literature but agrees with the dependence of barrier heights expected for an incomplete screening of the polarization of ZnO by the electrode as for ferroelectric materials.

Zinc selenide analyzed by XPS

Zinc selenide (ZnSe) was analyzed using x-ray photoelectron spectroscopy (XPS). A small notched rod was fractured in the XPS vacuum system at 6 × 10−4 Pa to create an oxygen-free surface for analysis. Spectral regions for Zn 2p, Zn 3d, Zn LMM, O 1s, C 1s, Se 3d, Se 3p, and Se LMM and valence band regions were acquired. The presence of carbon could not be confirmed due to interferences between C 1s and Se LMM and between C KLL and Zn 3s. It is believed that any carbon present is very low.

ZnO-based nanocomposites prepared by a vapor phase route, investigated by XPS

Nanostructured materials based on ZnO, eventually functionalized with titanium oxide (TiO2) or tungsten oxide (WO3), were fabricated on fluorine-doped tin oxide-coated glass substrates by a combined chemical vapor deposition/radio frequency-sputtering route. In particular, the present work focuses on the use of x-ray photoelectron and x-ray excited Auger electron spectroscopies for a detailed investigation of the system O 1s, Zn 2p3/2, Zn 3p, and Zn LMM core levels, as well as Ti 2p and W 4f photoelectron peaks. In a nutshell, the results of these analyses highlight the obtainment of pure ZnO nanodeposits, as well as of ZnO-TiO2 and ZnO-WO3 composites, in which the identity of each component is preserved, and the occurrence of an electronic interplay between ZnO and WO3 phases in the latter system.

XPS resolved surface states analysis of ZnO and Ni doped ZnO films for quantum well applications

ZnO and Ni doped ZnO (NiZnO) thin films were fabricated on c-plane sapphire substrate using Pulsed Laser Deposition (PLD) Technique. The surface states of the deposited thin films were analyzed using X-Ray Photoelectron spectroscopy (XPS) technique. The Zn LMM Auger transitions during XPS were examined in detail to identify the doping induced structural transformations in ZnO films. Hall effect and UV-Visible spectroscopic measurements were carried out on the prepared samples to estimate the electronic and optical properties. The obtained results favor the utilization of NiZnO as active well layer and ZnO as barrier layer in NiZnO/ZnO based Quantum Well structure fabrication.

Transition Metal Manganites Prepared by a Green and Low-Temperature Wet Chemistry Route, Investigated by XPS

In the present contribution, three transition metal manganites, namely the copper manganite CuMnO2 and the zinc manganites ZnMnO3 and ZnMn2O4, were investigated through X-ray photoelectron spectroscopy (XPS). The chosen synthesis route involved the combination of coprecipitation of oxalates from an aqueous solution and hydrothermal processing at a mild temperature (180 °C). The precipitates were then separated and dried for 4 h at 80 °C, yielding crystalline nanostructured powders without the need for calcination. Along with survey scans of the analyzed samples, detailed spectra of the C 1s, O1s, Mn 2p, Mn 3p, Mn LMM as well as Cu 2p, Cu 3p, Cu LMM, Zn 2p and Zn LMM (depending on the sample in question) were collected. The data obtained from these analyses is discussed.

ZnO/ZnAl2O4Nanocomposite Films Studied by X-Ray Diffraction, FTIR, and X-Ray Photoelectron Spectroscopy

ZnO/ZnAl2O4nanocomposite films were synthesised by ultrasonic spray pyrolysis (USP) by extracting Al2O(SO4)2oxide with zinc chloride hydrate in deionised water. The sample was then subjected to heat treatment at 650°C and 700°C for 1 h, which led to the formation of the spinel oxide (ZnAl2O4) and wurtzite (ZnO) phases. Al2(SO4)3·18H2O salt was transformed into aluminum oxide sulfate Al2O(SO4)2, which is an intermediary decomposition product, by calcination at 795°C for 3 h. The structures of the synthesised ZnO/ZnAl2O4films were confirmed by XRD, FTIR, and X-ray photoelectron spectroscopy (XPS). XPS spectra of the major Zn, Al, and O photoelectron lines and the major X-ray induced Zn LMM Auger lines for ZnO/ZnAl2O4are presented.

X-ray photoelectron spectroscopic study on interface bonding between Pt and Zn- and O-terminated ZnO

Interface bonding between Pt and Zn- and O-terminated ZnO surfaces was investigated by precise analysis of x-ray photoelectron spectra. The interfaces were formed by vapor depositing Pt onto the ZnO surfaces in ultrahigh vacuum. The changes in the Zn 2p3/2, O 1s, Zn LMM Auger, and Pt 4f7/2 spectra upon Pt deposition were observed. The changes in the shape of the Zn LMM spectra and the shifts in the binding energy of Zn 2p3/2 and O 1s revealed that there was a metallic Zn component in the Zn LMM and Zn 2p3/2 spectra for Zn-terminated ZnO and a Pt-O component in the O 1s spectra for both Zn- and O-terminated ZnO. Peaks were fitted with multiple components accordingly. The binding energy shifts of Zn 2p3/2 and O 1s for the ZnO component were almost the same, which confirmed that the fitting was reasonable. From the fitting results, the interface bonding was concluded to be O-terminated, i.e., Zn-O-Pt bond formation occurred at the interface for both Zn- and O-terminated ZnO. This clearly demonstrated that the stable interface bonding occurring between Pt and ZnO is Zn-O-Pt bonding whether the ZnO substrate is initially Zn-terminated or O-terminated.

Ferromagnetism in Li doped ZnO nanoparticles: The role of interstitial Li

ZnO nanoparticles doped with Li (Zn1−yLiyO, y ≤ 0.1) have been investigated with emphasis on the correlation between their magnetic, electronic, and structural properties. In particular, defects such as interstitial Li and Zn atoms, substitutional Li atoms, and oxygen vacancies have been identified by X-ray photoelectron spectroscopy (XPS) and their respective roles in stabilization of the magnetic moment are discussed. X-ray diffraction (XRD) and XPS give clear evidence of Li presence at both substitutional and interstitial sites. XPS studies further show that the amount of substitutional Li defects (Lizn) and interstitial Li defects (Lii) vary non-monotonically with the Li concentration, with the Lii defects being noticeably high for the y = 0.02, 0.08, and 0.10 concentrations, in agreement with the XRD results. Magnetization studies show room temperature ferromagnetism in these nanoparticles with the moment being largest for the particles with high concentration of interstitial lithium and vice versa. Both interstitial Zn (Zni) defects and Zn-O bonds were determined from the Zn LMM Auger peaks; however, the variation of these with Li concentrations was not large. Oxygen vacancies (Vo) concentrations are estimated to be relatively constant over the entire Li concentration range. We relate the Lii and Zni defects to the formation and stabilization of Zn vacancies and thus stabilizing the p-type ferromagnetism predicted for cation (zinc) vacancy in the ZnO type oxides.

Oxide-state evaluation of the zinc and aluminium in metallic thin films using Auger-electron-spectroscopy depth profiles

Two different, commercial, thin, metallic layers, one with a submicron thickness, containing Zn and Al as the main constituents, were depth profiled using Auger electron spectroscopy (AES). Large, oxidation-state-dependent, kinetic-energy shifts of the Al KLL and Zn LMM peaks were used to evaluate the oxide state of the elements inside the layers. An attempt was also made to use the peak shapes of the respective peaks by fitting measured peaks using linear combinations of the peaks corresponding to the oxide and metallic states.

Effect of Interface Reaction between ZnO:Al and Amorphous Silicon on Silicon Heterojunction Solar Cells

Silicon heterojunction solar cells have been studied by many research groups. In this work, silicon heterojunction solar cells having a simple structure of Ag/ZnO:Al/n type a-Si:H/p type c-Si/Al were fabricated. Samples were fabricated to investigate the effect of transparent conductive oxide growth conditions on the interface between ZnO:Al layer and a-Si:H layer. One sample was deposited by ZnO:Al at low working pressure. The other sample was deposited by ZnO:Al at alternating high working pressure and low working pressure. Electrical properties and chemical properties were investigated by light I-V characteristics and AES method, respectively. The light I-V characteristics showed better efficiency on sample deposited by ZnO:Al by alternating high working pressure and low working pressure. Atomic concentrations and relative oxidation states of Si, O, and Zn were analyzed by AES method. For poor efficiency samples, Si was diffused into ZnO:Al layer and O was diffused at the interface of ZnO:Al and Si. Differentiated O KLL spectra, Zn LMM spectra, and Si KLL spectra were used for interface reaction and oxidation state. According to AES spectra, sample deposited by high working pressure was effective at reducing the interface reaction and the Si diffusion. Consequently, the efficiency was improved by suppressing the SiOx formation at the interface.

Structure and optical properties of Al xZn 1− xO alloys by sol–gel technique

Al x Zn 1− x O ( x = 0–0.5) thin films were prepared on quartz glass substrates by sol–gel technique. X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) were employed for microstructure characterization of these thin films. In films with up to 20 at.% Al incorporation, compound nano-crystal phase was observed while wurtzite structure disappeared. Zn3d electron binding energy and Zn LMM‘s chemical shift were both increased by more than 0.4 eV. Transmittance spectra revealed that these films possessed high transmittance in the visible region, and the end of UV absorption edge shifted to less than 300 nm when Al content exceeds 20 at.% due to quantum confinement effect.

Optical and electronic properties of native zinc oxide films on polycrystalline Zn

The oxide layer spontaneously formed on zinc and an "electrochemically reduced" oxide has been characterised by a combination of X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). The onset of the main electronic absorption, which is directly related to the bandgap, is extracted from the SE measurements. The SE results are compared with simulations on the basis of zinc and bulk zinc oxide optical constant data. Measurements in the ultraviolet and visible (UV-vis) spectral range show the presence of an absorption at ∼1.8 eV (680 nm) which is unaccounted for from the bulk data, and is likely to originate from intragap energy levels, implicating the presence of surface defects in the layers. Analysis of the Zn LMM Auger peaks in XPS data show the presence of Zn different from bulk zinc and bulk ZnO, attributed to excess Zn in the oxide films. Mid-infrared (IR) ellipsometry shows two peaks around 0.12 and 0.15 eV (1000 and 1200 cm(-1)), which strengthen the assumption of the presence of a locally distorted structure in the oxide layers. Electrochemically reduced samples show a much thinner oxide layer and higher Zn-doping concentration films than samples purely dipped in NaOH solution. Using a self-contained multiple sample SE analysis, estimates of the refractive index and absorption coefficient (i.e., the optical constants) of the oxide films are presented from 1.5-4.4 eV (280 to 810 nm).

ZnO Nanoplatelets Obtained by Chemical Vapor Deposition, Studied by XPS

Zinc oxide nanoplatelets have been successfully grown on Si(l00) by a catalyst-free Chemical Vapor Deposition (CVD) route starting from a second-generation Zn(II) molecular precursor, Zn(hfa)2?TMEDA (Hhfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedione; TMEDA=N,N,N′,N′-tetramethylethylenediamine). The syntheses were performed under a nitrogen+wet oxygen atmosphere and the best results were obtained at deposition temperatures of 350 and 400 °C. The obtained samples were thoroughly characterized by several techniques, namely Glancing-Incidence X-ray Diffraction (GIXRD), Atomic Force Microscopy (AFM), Field Emission-Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray Spectroscopy (EDXS), X-ray Photoelectron (XPS) and X-ray Excited Auger Electron (XE-AES) Spectroscopies. Finally, the photocatalytic performances of ZnO nanoplatelets in the decomposition of the azo-dye Orange II were also evaluated. The present contribution is specifically dedicated to the XPS and XE-AES characterization of a representative ZnO nanoplatelet sample deposited at 350 °C. Beside the wide scan spectrum, detailed spectra for the Zn 2p3/2, Zn 3p, Zn LMM, O 1s, and C 1s are also presented. The obtained results evidenced the formation of pure zinc oxide systems under the adopted synthetic conditions.

Analysis of Nanocrystalline ZnS Thin Films by XPS

Nanocrystalline ZnS thin films were synthesized by chemical vapor deposition (CVD) using Zn(O-iPrXan) 2 [O-iPrXan=S2COCH(CH3) 2] as a single-source precursor compound. The coatings were deposited on silica substrates in N2 atmosphere at temperatures between 200 and 450 °C and subsequently characterized by glancing-incidence x-ray diffraction (GIXRD), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM), UV-Vis absorption spectroscopy, x-ray photoelectron (XPS), and x-ray excited auger electron (XE-AES) spectroscopies. This work is dedicated to the XPS and XE-AES characterization of a representative zinc sulfide thin film. Besides the wide scan spectrum, detailed spectra for the Zn 2p3/2, Zn 3p, Zn LMM, S 2p,O 1s, and C 1s regions and related data are presented and discussed. Both the S/Zn atomic ratio and the evaluation of the Auger parameter point out to the formation of stoichiometric zinc sulfide. Moreover, oxygen and carbon contamination were merely limited to the outermost sample layers.

Zinc Aluminate (ZnAl2O4) by XPS

Zinc aluminate (ZnAl4O4, also known as zinc aluminum oxide) is a material that has applications as a catalyst and catalyst support. This paper presents the XPS spectra of the major Zn, Al, and O photoelectron lines, and the major x-ray induced Zn LMM Auger lines for ZnAl2O4.

A study of the oxygen adsorption and initial oxidation on polycrystalline zinc by AES line shapes and EELS

The adsorption and initial oxidation on polycrystalline zinc have been studied by EELS and AES line shape techniques. During oxygen exposure, two zinc species which are related to pure zinc and ZnO have been detected by the Zn LMM and Zn MNN line shape. Using the O KLL line shape, it is possible to distinguish the adsorbed oxygen from reacted oxygen during oxygen exposure. From the AES and EELS investigations, we can conclude that the ZnO film which is formed during oxygen adsorption and initial oxidation exists in isolated islands. The surface structure and properties of ZnO films is different from that of pure bulk ZnO.