Chemical changes induced on a TiO2 surface by electron bombardment

We study the TiO₂ (Ti⁴⁺) chemical reduction induced by electron bombardment using Auger electron spectroscopy and factor analysis. We show that the electron irradiation of a TiO₂ sample is characterized by the appearance of a lower Ti oxidation state, Ti₂O₃ (Ti³⁺), followed by a further deposition of carbon, which is present inevitably in the environment even under ultra-high vacuum conditions. The appearance of C over the surface is found to be a complex mechanism which affects the reduction process through passivation of the electron-induced oxygen desorption and formation of titanium carbide. For very high irradiation doses, we also found that the chemical changes on the surface are stopped due to the deposition of carbon in a graphitic form.     

Kinetics of cuprous oxide etching with β-diketones in Supercritical CO2

Cuprous oxide films (Cu₂O) supported on Cu or on SiO₂ were etched using solutions of β-diketones including 1,1,1,5,5,5-hexafluoroacetylacetone, 2,2,6,6-tetramethyl-3,5-heptanedione and 2,2,7-trimethyl-3,5-octanedione (TMOD) in supercritical carbon dioxide at temperatures between 80 and 150 °C and pressures between 20 and 27.5 MPa. The films and etched substrates were analyzed by X-ray photoelectron spectroscopy depth profiling, field emission scanning electron microscopy and spectroscopic ellipsometry. Each of the etching agents was effective. Etching kinetics using TMOD were measured at 100, 125 and 150 °C. At 150 °C the etch rate was 1.5 nm/min. Based on the activation energy obtained from the studies (66 kJ/mol), etching rates of greater than 10.0 nm/min can be obtained at 200 °C.     

Surface reactions between CO2 and H over K-modified Cu(0 0 1)

Low temperature (115-160 K) adsorption of CO on clean Cu(0 0 1), CO₂ on potassium modified Cu(0 0 1) and surface reactions between H₂ and CO₂ were studied. Pre-adsorption of K leads to strong interaction of the interface with arriving carbon dioxide molecules and linear CO₂(phys), bent , CO and are observed as adsorbed species. Annealing of the CO₂/K/Cu(0 0 1) interface causes, successively, desorption of the reaction products. Pre-adsorbed hydrogen on the alkali-modified substrate changes the surface reaction channels, mainly with no presence of CO and creation of surface formate species. Details of surface reactions are compared with results for thick potassium film on a copper substrate.     

Irradiation-induced gold silicide formation and stoichiometry effects in ion beam-mixed layer

The irradiation-induced silicide formation in ion beam-mixed layer of Au/Si(1 0 0) system was investigated by using 200 keV Kr⁺ and 350 keV Xe⁺ ions to fluences ranging from 8×10¹⁴ to 1×10¹⁶ ions/cm² at room temperature. The thickness of Au layer evaporated on Si substrate was ∼500 Å. Rutherford backscattering spectrometry (RBS) experiments were carried out to study the irradiation effects on the mixed layers. We observed that at the fluence of 1×10¹⁶ Kr⁺/cm² and starting from the fluence of 8×10¹⁴ Xe⁺/cm², a total mixing of the deposited Au layer with Si was obtained. RBS data corresponding to the fluences of 1×10¹⁶ Kr⁺/cm² and 8×10¹⁴ Xe⁺/cm² clearly showed mixed layers with homogenous concentrations of Au and Si atoms which can be attributed to gold silicides.The samples irradiated to fluences of 1×10¹⁶ Kr⁺/cm² and 1×10¹⁶ Xe⁺/cm² were also analyzed by X-ray photoelectron spectroscopy (XPS). The observed chemical shift of Au 4f and Si 2p lines confirmed the formation of gold silicides at the surface of the mixed layers. Au₂Si phase is obtained with Kr⁺ irradiation whereas the formed phase with Xe⁺ ions is more enriched in Si atoms.     

Influence of incorporated non-metallic impurities on electromigration in copper damascene interconnect lines

Low electromigration in Cu interconnect lines represents one of the major challenges for a good performance of semiconductor devices. Referring to this, experiments were carried out to study the influence of non-metallic impurities like Cl, S, and C incorporated in Cu during the electrochemical deposition. In the case of a lower impurity content a higher resistance against electromigration was verified. The electromigration activation energy for metallizations with small contaminations was found to be (1.00 ± 0.06) eV whereas Cu interconnect lines with high non-metallic impurities revealed an activation energy of (0.65 ± 0.03) eV. The electromigration induced degradation by void formation starts at the top interface between Cu and dielectric cap layer. Probably, this results from high mechanical stresses due to differences in material properties or due to an interface weakening by the segregation of S and C impurities.     

Cu surface segregation in Ni/Cu system

We report experimental evidence of Cu surface segregation in Ni/Cu system, during deposition of Ni film onto Cu substrate at room temperature and during heat treatment in vacuum. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) by Tougaard's analysis results show that surface segregation defeats in competition with increase in Ni thickness and terminates when thickness of Ni increase to more than 4 nm. Surface energy and concentration were calculated using contact angle measurements and the results confirm that segregation reduces the surface energy. Surface segregation during heat treatment at 150-220 °C range as a function of time initially shows linear mass transfer. By solving Fick's equation and taking empirical diffusion coefficient, 125 ± 20 kJ/mol is obtained for activation enthalpy of effective diffusion.     

Influence of hydrogen annealing on the properties of hafnium oxide thin films

Thin films of hafnium oxide were deposited by electron beam evaporation, and were subsequently annealed in hydrogen. X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, photoluminescence, spectrophotometry, and current–voltage measurements were performed to investigate the structural, chemical, optical, and electrical properties of the films. As-deposited films were amorphous and nearly stoichiometric. Annealing led to crystallization of the films, and reduction of stoichiometry. Photoluminescence measurements revealed the presence of oxygen-related defects. Optically, the films were transparent with a wide band gap, and this was not affected by hydrogen annealing. Moreover, the films were suitable as anti-reflection coatings on silicon. The electrical resistivity of the films was significantly reduced as a result of annealing.     

Spontaneous oxide reduction in metal stacks

Aluminum and copper interconnects are widely used for microelectronic applications. A problem can arise when interfacial oxides are present. Such oxides can significantly degrade device performance by increasing electrical resistance. This paper describes analyses of interfacial oxide layers found in Al/Ta and Ta/Cu metal stacks. The analyses were performed through transmission electron microscopy (TEM). The data indicated that the interfacial oxides resulted from spontaneous reductions; that is, Al spontaneously reduced Ta₂O₅ to form Al₂O₃, while Ta spontaneously reduced Cu oxide to form Ta₂O₅.     

The effect of dopant-induced electron traps on spectrum evolution of doped organic light-emitting devices

A prototype of light emitting device with two symmetrically located Al/LiF electrodes is fabricated to study the voltage dependence of emission spectra. 4-(dicyanomethylene)-2-methyl-6- (pdimethylaminostyryl)-4H-pyran doped tris-(8-hydroxy-quinolinato) aluminum thin film is the emitting layer of the device. Experiments show that with increasing applied voltage the emission intensity of the device decreases, of which the dopant emission intensity decreases more steeply than that of the host. Based on the theory of space-charge-limited current in insulator with a single shallow trap level it is deduced that the photoluminescence intensity of the dopant emission decreases linearly with applied voltage, in good agreement with experimental measurements. The evolution of the emission spectra can be well explained by the suggested mechanism that the electrons are trapped in the dopant molecules, which blocks the energy transfer from the host, and leads to more excitons in the host to emit light.     

Improved performances in a top-emitting green organic light-emitting device with light magnification

A top-emitting organic light-emitting device (TOLED) with an architecture of Si/SiO₂/Ag (100 nm)/Ag₂O (UV ozone treatment for 30 s)/ 4′,4?-tris(3-methylphenylphenylamino)triphenylamine (45 nm)/4,4′-bis [N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl (5 nm)/tris-(8-hydroxyquinoline) aluminum (Alq₃):10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]-pyrano[6,7,8-ij]quinolizin-11-one (C545T) (1: 0.5 weight %, 20 nm)/Alq₃ (30 nm)/LiF(1 nm)/Al (0.5 nm)/Ag(30 nm) is designed with a resonance wavelength in the TOLED corresponding to the peak wavelength of C545T. With this enhanced cavity structure, light magnification with a coefficient of ∼ 19 (forward direction) is observed, leading to significantly improved performances with brightness of 80215 cd/m² at 9 V, luminous efficiency of 32.7 cd/A at 6 V, external quantum efficiency of 8.9% at 7.5 V, and low turn-on voltage of 2.5 V.     

Exact Analysis of a One-Dimensional Attractive δ-Function Fermi Gas with Arbitrary Spin Polarization

We study a one-dimensional integrable system of N spin-1/2 fermions with attractive δ-function interaction at zero temperature. The Gaudin integral equation describing the ground state with arbitrary spin polarization is solved in the form of power series. We also study the ground state energy as a function of the coupling constant and the polarization.     

Generation of nitrogen beams with very high N/N2 ratio using hollow cathode discharge

Nitrogen beams with very high N⁺/N₂⁺ ratio were generated using hollow-cathode discharge. The dependence of N⁺/N₂⁺ ratio in the extracted beams on the discharge parameters was studied by mass spectroscopy. Very high N⁺ fractions (up to 90% and the maximum is about 98%) can be easily achieved without mass separation under typical operating conditions. The extracted beams with discharges using mixture precursors, such as N₂/NH₃, or N₂/Ar were also investigated.     

Oxidation resistance of thin boron carbo-nitride films on Ge(100) and Ge nanowires

Chemical vapor deposition of thin (< 10 nm) films of amorphous boron carbo-nitride (BC_0.7N_0.08, or BCN) on Ge(100) and Ge nanowire (GeNW) surfaces was studied to determine the ability of BCN to prevent oxidation of Ge. X-ray photoelectron spectroscopy was used to track Ge oxidation of BCN-covered Ge(100) upon exposure to ambient, 50 °C deionized water, and a 250 °C atomic layer deposition HfO₂ process. BCN overlayers incorporate O immediately upon ambient or water exposure, but it is limited to 15% O uptake. If the BCN layer is continuous, the underlying Ge(100) surface is not oxidized despite the incorporation of O into BCN. The minimum continuous BCN film thickness that prevents Ge(100) oxidation is ~ 4 nm. Thinner films (≤ 3.2 nm) permitted Ge(100) oxidation in each of the oxidizing environments studied. GeNWs with a 5.7 nm BCN coating were resistant to oxidation for at least 5 months of ambient exposure. High resolution transmission electron microscopy images of HfO₂/BCN/Ge(100) cross-sections and BCN-coated GeNWs reveal clean, abrupt BCN-Ge(100) interfaces.     

Auger electron spectroscopy analysis of SiC layers formed by carbon ion implantation into silicon

Analysis of Si LVV and CKLL Auger spectra combined with Auger in-depth profiles were carried out for SiC layers formed by the implantation of carbon into silicon. It was found that in layers which were implanted with carbon ions to appropriate doses SiC-like bonds were formed at room temperature, although the crystal perfection was not pronounced. When these layers were annealed above 1100°C, their Auger spectra were in good agreement with those of β-SiC. In layers which were implanted with carbon ions much above a critical dose and annealed at 1200°C, however, CKLL Auger spectra showed the presence of graphite-like carbon. This result was consistent with the IR analysis and the transmission electron microscopy or electron diffraction observations reported in our previous papers, and it suggested the formation of carbon clusters. The Auger spectra also showed the advantages of hot implantation over room temperature implantation.     

Low-loss electron beam transport in a high-power, electrostatic free-electron maser

At the FOM Institute for Plasma Physics “Rijnhuizen”, The Netherlands, the commissioning of a high-power, electrostatic free-electron maser is in progress. The design target is the generation of 1 MW microwave power in the frequency range 130–260 GHz. The foreseen application of this kind of device is as a power source for electron cyclotron applications on magnetically confined plasmas.

The device is driven by a high-power electron beam. For long-pulse operation a low loss current is essential. A 3-A electron beam has been accelerated to energies ranging from 1.35 to 1.7 MeV and transported through the undulator at current losses below 0.02%. Further, it was shown that the beam line accepts an electron energy variation of 5% with fixed beam optics. This is essential for rapid tuning of the microwave frequency, over 10%.

Electron beam simulations have shown to be remarkably accurate both for the prediction of the lens settings and for the intercepted current. The operational settings of the beam line which give the highest current transmission are within a few percent of the simulated values.     

Preparation and characterization of indium zinc oxide thin films by electron beam evaporation technique

In this work, the preparation of In₂O₃-ZnO thin films by electron beam evaporation technique on glass substrates is reported. Optical and electrical properties of these films were investigated. The effect of dopant amount and annealing temperature on the optical and electrical properties of In₂O₃-ZnO thin films was also studied. Different amount of ZnO was used as dopant and the films were annealed at different temperature. The results showed that the most crystalline, transparent and uniform films with lowest resistivity were obtained using 25 wt% of ZnO annealed at 500 °C.     

Molecular pumping properties of the LHC arc beam pipe and effective secondary electron emission from Cu surface with artificial roughness

A simplified 2D method of angular coefficients is applied to calculations of the molecular pumping properties of complex vacuum systems. An optimization of geometry for the cold LHC beam vacuum chamber with electron shields is performed.An additional interesting application of the angular coefficients method is the estimation of the effective secondary electron emission from surface with artificial roughness. This method allows to take into account re-reflection of electrons using experimental data of the secondary electron energy distributions and surface reflectivity. The suppression efficiency of the secondary electron emission from Cu as a function of roughness parameter is presented. This result is a good input for designing future accelerators and storage rings with potential electron-cloud problems.     

Ion etching methods for depth profiling of complex three-dimensional samples in combination with scanning Auger electron microscopy

Ion etching of surfaces combined with detection of secondary events (particles or radiation emitted) are used for depth profiling of samples with interesting features at-, near-, or somewhat below the surface. These methods are destructive and relatively slow, and compete with non-destructive methods like Rutherford backscattering spectroscopy, energy-dispersive X-ray spectroscopy in the scanning electron microscope or angle-resolved photoemission spectroscopy, which are non-destructive and relatively faster methods. In this work we have concentrated on the use of noble gas ion sputtering with low-energy beams in combination with electron excited Auger electron spectroscopy and imaging for analysis of nanostructured and microstructured samples. No attempt will be made here to justify this method over the other methods, as their relative merits depend on the nature of the sample and the problem at hand. We have thus chosen to study samples and problems for which this technique would be obvious to use. This work is also aimed at providing practical standards and guidelines (“metrology”) for the use of the technique in the context of industrial nanotechnology. The use of Auger electron spectroscopy instead of photoemission spectroscopy is preferred for laterally non-uniform samples due to the presently better resolution capabilities of electron beams and narrower information depths of typical Auger electron transitions. The use of Auger electrons for concentration sampling, and low-energy beams of noble gas ions for sputtering, reduces the adverse influence of atomic mixing. In this report two systems are intensively studied with sputter profiling in combination with Auger electron spectroscopy and scanning electron imaging: a hard disk and a surface of a stainless-steel sample.     

Concentration profiles of Zn ions implanted with 60 keV for nanoparticle formation in silica glass

Surface recession due to sputtering under low-energy and high-fluence heavy-ion implantation makes shallower and broader depth profile of implanted ions than those calculated by conventional ion-range simulation-codes such as SRIM. Depth profiles of Zn atoms in silica glasses (SiO₂) implanted with Zn⁺ ions of 60 keV up to 1.0×10¹⁷ ions/cm² were evaluated using both experimental methods as Rutherford backscattering spectrometry (RBS), sputtering depth-profiling by X-ray photoelectron spectroscopy (XPS), and an advanced numerical simulation code TRIDYN, which includes the sputtering loss effects. The TRIDYN code predicts the shallowing of the projectile range from ∼46 to ∼27 nm with increasing the fluence up to 1×10¹⁷ ions/cm², and very high-concentration (∼20 at%) of Zn atoms close to the surface. However, RBS and XPS results exclude such high concentration close to the surface. These results suggest remarkable redistribution of Zn atoms from the nearer surface to the deeper region during the implantation. In fact, Zn-atom concentration near the surface and that near the projectile range are, respectively, lower and higher than those by the SRIM code predictions.