Energy Auger Electron Research Articles

Electronic structure ofMg: From monolayers to bulk

The structure of thin $\mathrm{Mg}$ films epitaxially grown onto a $\mathrm{W}(110)$ crystal was analyzed by low energy electron and Auger electron diffraction verifying a growth of bulk $\mathrm{Mg}$. Normal-emission angle-resolved photoemission spectra of the growing films reveal quantum well states on both sides of a surface state. These states result from electron confinement in the $\mathrm{Mg}$ layer and are used to derive the electronic structure perpendicular to the surface. Off-normal, the electronic structure is dominated by the parabolic dispersion of surface states forming circles around the $\overline{\ensuremath{\Gamma}}$-points and ellipses around the $\overline{\mathrm{M}}$-points in the Fermi surface cuts.

Pulsed laser deposition of hard magnetic films

Pulsed laser deposition from elemental targets was used to prepare highly textured hard magnetic Nd–Fe–B and Fe–Pt films with coercivities of 2 T and 5.2 T, respectively. In situ methods such as reflection high energy electron diffraction and Auger electron spectroscopy were applied to analyse film composition and structure during growth. Optimisation of the hard magnetic properties is discussed together with the specific advantages of pulsed laser deposition.

Formation of ordered arrays of Ag nanowires and nanodots on Si(557) surface

The ordered arrays of Ag nanowires and nanodots have been grown in ultra-high vacuum on the Si(5 5 7) surface containing regular steps of three bilayer height. Formation of Ag nanostructures have been studied by scanning tunneling microscopy, low energy electron diffraction and Auger electron spectroscopy at room temperature. It was shown that a sample exposure in the vacuum before Ag growth affects the shape of the forming Ag islands. This effect is caused by oxygen adsorption on the silicon surface from the residual atmosphere in the vacuum chamber. When Ag is deposited on the clean silicon surface the islands, overlapping several (1 1 1) neighboring terraces, form. The arrays of silver nanowires elongated along steps and silver nanodots, arranged in lines parallel to the steps, can be formed on the Si(5 5 7) surface depending on the amount of adsorbed oxygen.

RHEED study of Pd film growth on Al 2O 3 (111)/NiAl (110)

The palladium (Pd) layer growth on well-ordered γ-Al 2O 3 (111) layer has been studied by means of reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). Epitaxial Al 2O 3 layer of the thickness 7–8 Å was prepared by the oxidation of single-crystalline NiAl (110) surface performed at 1070 K and 1200 L of O 2 under pO 2=6.6×10 −6 Pa. The stepwise Pd deposition has been performed at a substrate temperature of 300 K. Depending on the amount of deposited Pd, two different growth modes were detected. The formation of polycrystalline phase has been found at low Pd coverage, whereas the appearance of preferentially oriented Pd islands has been detected at Pd coverage 0.5 ML. Two populations of Pd islands having (111) epitaxial plane parallel to (111) Al 2O 3 surface were found.

Preparation and properties of clean Si 3N 4 surfaces

In situ chemical methods for preparing atomically-clean surfaces of Si 3N 4 thin films in ultra-high vacuum (UHV) have been studied using X-ray and ultraviolet photoemission, electron energy loss and Auger electron spectroscopies. Prior to the UHV studies, the films (grown ex situ on Si(1 0 0) wafers by low-pressure chemical vapor deposition) were characterized using primarily infrared reflection–absorption spectroscopy. A combination of annealing in NH 3 to remove C and deposition of Si (followed by thermal desorption) to remove O is found to be an effective cleaning procedure. Other potential cleaning methods, such as annealing in UHV without in situ chemical treatment and annealing in a flux of H atoms, were also considered and found to be only partly effective. The clean surfaces are disordered but show no evidence of SiSi bonding (which would indicate N vacancies) in the Si LVV Auger spectrum or in surface-sensitive Si 2p photoemission data. Evidence for surface-related features is seen in the N 1s photoemission and in energy loss spectra in the region of valence excitations; however, no indication of occupied surface states near the valence band maximum is seen in ultraviolet photoemission spectra. Preliminary results for O 2 chemisorption show adsorbate-induced features in the Si 3N 4 band gap and also evidence for changes in surface potential due to adsorption.

A phase diagram of the Sb/Si(001) interfacial system

Abstract The dynamics of adsorption and desorption of Sb on atomically clean dimer reconstructed Si(0 0 1) surface is carefully monitored. Superstructure formation of the Sb/Si(0 0 1)-(2 × 1) system is studied by submonolayer Sb adsorption and in situ characterization in ultra-high vacuum by surface sensitive techniques such as low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS). Sb is adsorbed onto double-domain (DD) (2 × 1)-reconstructed Si(0 0 1) surface at a flux rate of 0.06 ML/min at various substrate temperatures. A complete phase diagram for this Sb/Si(0 0 1)-(2 × 1) system is drawn for the first time by consolidating the results of the adsorption–desorption studies for Sb adsorbed at various substrate temperatures and coverages. The 0.6 ML (8 × 4) surface superstructure shown in the phase diagram was reported earlier by us and the novel 0.25 ML (12 × 2) is reported here for the first time. The results demonstrate the ability of kinetic control in forming several stable novel superstructures, depending on the pathway adopted in the formation of the interface.

Co on Mo(1 1 0) studied by scanning tunneling microscopy

We have studied the interface formation of thin films of Co on a Mo(1 1 0) surface by the use of scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and auger electron spectroscopy (AES). Below a coverage of about 0.4 monolayers (ML) we find that Co grows in small islands which are pesudomorphic with the Mo substrate. At a Co coverage above 0.4 ML, the Co atoms condense into larger islands and forms a close-packed Co layer close to that of the Co(0 0 0 1) plane resulting in a coincidence structure with the underlying Mo(1 1 0) substrate. Increasing the Co coverage, we observe that the film grows in a layer-by-layer fashion up to 2 ML at room temperature, however by annealing such a film to 670 K the Co forms 3D islands. STM images displaying atomic resolution, reveal the atomic arrangement and corrugation of the close-packed Co film formed at Co coverages above 0.4 ML at room temperature. In particular, the STM data directly demonstrate the appearance of the coincidence lattice between the Nishiyama–Wasserman orientated Co film and the Mo(1 1 0) substrate. We show how this appearance may change due to subtle changes of the registry between the Co film and the Mo(1 1 0) surface. This behavior can be explained by partial dislocations relaxing the strained close-packed Co layer by a small rigid translation.

Improving the corrosion resistance of NdFeB magnets: an electrochemical and surface analytical study

This study reports the results of work carried out to improve the corrosion resistance of NdFeB magnets by a direct phosphate treatment of the NdFeB magnet surface. The growth of a phosphate film on a NdFeB based magnet in a solution of 0.15M NaH 2PO 4 acidified to pH 3.8, was followed by electrochemical impedance spectroscopy (EIS) and open circuit potential variation as a function of time. After removal from the phosphating solution, the magnet surface was analysed by Auger electron spectroscopy (AES) and energy dispersive X-ray analysis (EDX). Phosphate formation on the surface was confirmed and a significant variation in the Fe/Nd ratio in the phosphate between the Fe and Nd rich phases of the magnet was found. The corrosion resistance of the phosphated magnets was evaluated in a normal enclosed atmospheric environment and in Na 2SO 4 solution and synthetic saliva by EIS measurements. The corrosion resistance was found to be substantially improved by the presence of a phosphate layer.

Electron beam induced deposition of rhodium from the precursor [RhCl(PF 3) 2] 2: morphology, structure and chemical composition

We have studied the morphology, the structure and the chemical composition of micro- and nano-structures grown by electron beam-induced deposition of [RhCl(PF 3) 2] 2. Transmission electron microscopy revealed that the deposits are made up of face centered cubic crystalline Rh grains (4–6 nm in diameter) immersed in an amorphous matrix. Auger electron spectroscopy and electron energy loss spectroscopy showed that a carbon contamination layer is present at the deposit surface, while the bulk material contains the elements Rh (60 at%), P (20 at%), Cl, O and N (remaining 20 at%). The structure, the chemical composition of the deposits and the size of the Rh nano-crystals are independent of the deposit shape and of the deposition parameters, within the range explored in this work.

Initial stages of thallium electrodeposition on iodine-covered Pt(1 1 1)

The initial stages for Tl electrodeposition on Pt(1 1 1) covered with iodine in ( 7 × 7 )R19.1° or (3 × 3) structures are investigated by cyclic voltammetry, low energy electron diffraction and Auger electron spectroscopy. Estimation of faradaic charges in cyclic voltammetry is facilitated by simultaneous measurement of the double-layer capacitance by ac voltammetry. The first electrodeposition peak corresponds to the deposition of 0.22 ML Tl atoms, independently of the structure of the initial iodine adlayer. However, after the electrodeposition of Tl on Pt(1 1 1) ( 7 × 7 )R19.1°-I, the surface undergoes an irreversible rearrangement to a Pt(1 1 1) [ 4 0 3 6 ] -TlI structure, with two Tl atoms and six I atoms per unit cell. In this rearrangement, thallium and iodine are removed from the surface in a 1:1 ratio.

Determination of Ion Irradiation Influence on π-plasmon Properties of Carbon Nanotubes

AbstractIn this paper, the results of experiments on irradiation of the singlewall (SWNT) and multiwall carbon nanotube (MWNT) samples by argon ions are presented. They were obtained by reflection electron energy loss spectroscopy and Auger electron spectroscopy.Results indicate the π-plasmon energy Eπ and the full width at half maximum (FWHM) of the plasma peak were sensitive to the dose of ion irradiation. In particular, the π-plasmon energy Eπ decreases and the plasma peak broadens with the increase of the dose of Ar+irradiation.The π-plasmon peak broadening is associated with damage of carbon nanotubes under ion irradiation. Possible causes of the carbon nanotubes deformation and influence of deformation on π-band structure of carbon nanotubes are discussed.

Epitaxial α-Be3N3 Films Analyzed In Situ by AES, XPS, and EELS

In situ Auger electron, x-ray photoelectron, and electron energy loss spectroscopic data were obtained on epitaxial α-Be3N2 layers grown on (111) and (100) silicon substrates. Films were grown by laser ablating a beryllium foil in molecular nitrogen ambient at 750 °C. The ultrahigh vacuum laser ablation growth system is attached to an analysis chamber equipped with an e-gun, an x-ray source (dual anode Mn/Al), and an electron analyzer MAC-3, all from CAMECA. The spectra show that the film surface is free of impurities, except for traces, of oxygen. Quantitative XPS analysis for the film yields 61, 35, and 4 at % for beryllium, nitrogen, and oxygen concentrations, respectively.

Compositional analysis of thin SiO xN y:H films by heavy-ion ERDA, standard RBS, EDX and AES: a comparison

The composition of silicon oxynitride (SiO x N y :H) films deposited by electron cyclotron resonance chemical vapour deposition (ECR-CVD) was analysed by ion beam techniques, heavy-ion elastic recoil detection analysis (HI-ERDA) with 150 MeV 86Kr ions and Rutherford backscattering spectroscopy (RBS) with 1.4 MeV 4He ions. The results were compared with energy dispersive X-ray analysis (EDX) and Auger electron spectroscopy (AES). Since HI-ERDA provides absolute atomic concentrations of all film components including hydrogen with a sensitivity of at least 0.005 at% the data from this method were used as a quantitative reference to assess the applicability of RBS, EDX and AES to the analysis of silicon oxynitrides. For each of these techniques the comparison with HI-ERDA allowed a discussion of the different sources of error, especially of those causing systematic deviations of the measured concentration values. A novel approach to determine from RBS spectra also the hydrogen concentrations appeared to be applicable for hydrogen levels exceeding 2 at%. Furthermore, it is shown that the film density can be determined from the HI-ERDA results alone or in combination with single-wavelength ellipsometry.

Formation and annealing effect for close-packed Ge/Cu(111) layers

Growth and annealing effects of Ge/Cu(111) ultrathin films as deposited at ambient temperature have been studied using Auger electron spectroscopy and low-energy electron diffraction techniques. Ge/Cu(111) system shows a 1×1 structure up to 5 monolayers as deposited at 300 K. The kinetic energy of Cu L3M45M45 Auger electrons shifts to a lower value upon deposition of Ge overlayers. This could be explained by the electric charge transfer between Ge and Cu atoms. From the intensity ratio change of Auger signals (IGe/ICu), significant interdiffusion of Ge/Cu(111) films occurs around 375 K. Owing to the formation of a Cu-rich surface layer, the Cu L3M45M45 peak restores to the initial kinetic energy of a clean Cu(111) surface at 500 K.

Titanium nitride diffusion barrier for copper metallization on gallium arsenide

The diffusion properties of Cu, Cu/titanium nitride (TiN) and Cu/TiN/Ti metallization on GaAs, including as-deposited film and others annealed at 350–550 °C, were investigated and compared. Data obtained from X-ray diffractometry, resistivity measurements, scanning electron microscopy, energy dispersive spectrometer and Auger electron spectroscopy indicated that in the as-deposited Cu/GaAs structure, copper diffused into GaAs substrate, and a diffusion barrier was required to block the fast diffusion. For the Cu/TiN/GaAs structure, the columnar grain structure of TiN films provided paths for diffusion at higher temperatures above 450 °C. The Cu/TiN/Ti films on GaAs substrate were very stable up to 550 °C without any interfacial interaction. These results show that a TiN/Ti composite film forms a good diffusion barrier for copper metallization with GaAs.

Heteroepitaxial Film of Monolayer Graphene/Monolayer h-BN onNi(111)

Heteroepitaxial multilayers, consisting of graphene/hexagonal boron nitride (h-BN) films on Ni (111), have been investigated by means of vibrational spectroscopy, low energy electron diffraction and Auger electron spectroscopy. Vibrational spectra of the heteroepitaxial film show the appearance of transverse optical ( TO⊥) modes with out-of-plane polarization at 100 meV of the monolayer h-BN, in contrast to the softening phonon at 90 meV on the pristine system of monolayer h-BN on Ni (111). The findings strongly suggest that the interfacial bonds between h-BN and Ni (111) weaken due to the formation of monolayer graphene.

Phases of Ag-Adsorbed Si Surfaces Studied by Low Energy Electron Diffraction and Auger Electron Spectroscopy

The Ag-adsorbed Si(110)2×16 surfaces were investigated using low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). When Ag was deposited on a Si(110)2×16 surface at room temperature (RT) and annealed at several elevated temperatures, diffuse 1×1, 1×2+streak, 1×2, and (-1, 6)×(-7, 0) structures were observed by LEED. The relative Ag coverage of the reconstructed structures were estimated from Ag(MNN)/Si(LVV) AES intensity ratios and previous results. The structural model of the Ag/Si(110)1×2 surface was proposed from the LEED and AES results.

Heteroepitaxial System of h-BN/Monolayer Graphene on Ni(111)

A heteroepitaxial system of h-BN/monolayer graphene on Ni(111) has been investigated by means of vibrational spectroscopy, accompanied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The system was prepared in an epitaxial manner on a Ni(111) surface by chemical vapor deposition (CVD). We found that phonon peaks in observed spectra showed typical features of Fuchs–Kliewer (FK) phonons. The vibrational spectra of h-BN films ranging in thickness from 0 to 8.7 monolayers have been compared with theoretical spectra based on a dielectric theory. Detailed analysis has revealed new types of phonons, of which the vibrational amplitudes are localized at edges of h-BN nanocrystals. In addition, we have observed subsidence phenomena of the graphene and h-BN layers into Ni substrate at elevated temperatures.

A novel (8 × 4) superstructure as precursor to the c(4 × 4) phase during Sb/Si(0 0 1) desorption

The role of kinetics in the superstructure formation of the Sb/Si(0 0 1) system is studied using in situ surface sensitive techniques such as low energy electron diffraction, Auger electron spectroscopy and electron energy loss spectroscopy. Sb adsorbs epitaxially at room-temperature on a double-domain (DD) 2 × 1 reconstructed Si(0 0 1) surface at a flux rate of 0.06 ML/min. During desorption, multilayer Sb agglomerates on a stable Sb monolayer (ML) in a DD (2 × 1) phase before desorbing. The stable monolayer desorbs in the 600–850 °C temperature range, yielding DD (2 × 1), (8 × 4), c(4 × 4), DD (2 × 1) phases before retrieving the clean Si(0 0 1)-DD (2 × 1) surface. The stable 0.6-ML (8 × 4) phase here is a precursor phase to the recently reported 0.25-ML c(4 × 4) surface phase, and is reported for the first time.

Oxygen adsorption on Cu–9 at. %Al(111) studied by low energy electron diffraction and Auger electron spectroscopy

Cu-based alloys have been used for electric cables for long time. In the field of microelectronics, Al had been used for electrical wiring. However, it became clear that electromigration occurs in Al that causes breaking of wires in minute wirings. Due to this problem, Cu wiring is used in most advanced microprocessors. Cu metal is more corrosive than Al and Cu-based alloys with a small amount of Al is expected to solve problems both on electromigration and corrosion. The initial stage of corrosion is oxygen adsorption. We studied surface segregation of Al on Cu–9% Al(111) and oxygen adsorption on the surface with/without Al segregation in ultrahigh vacuum by low energy electron diffraction (LEED) and Auger electron spectroscopy. It was found that Al segregates on the surface to form (∛×∛)R30° structure and the structure vanishes above 595 K to give (1×1) structure while Al still segregates. The specimen was exposed to oxygen at different temperatures. The amount of oxygen uptake was not structure dependent but temperature dependent. Below 595 K, only a small amount of oxygen adsorbed. Between 595 and 870 K, oxygen adsorbed surface showed amorphous LEED pattern. The specimen was annealed at 1070 K after oxygen exposure. When the specimen was exposed oxygen below 870 K, the oxygen Auger intensity decreased significantly by annealing and the annealed surface showed (∛×∛)R30° structure at room temperature. When the specimen was exposed to oxygen at 870 K, diffused spots developed newly in LEED pattern but the pattern disappeared after 1070 K annealing while oxygen Auger intensity remained almost constant. Exposing the specimen to oxygen at 995 K resulted in clear spots in the LEED pattern, which were attributed to the (7/∛×7∛)R30° structure.