Effects of sputter deposition parameters and post-deposition annealing on the electrical characteristics of LaAlO3 dielectric films on Si

The influence of processing parameters on the electrical characteristics of RuO₂/LaAlO₃/Si metal-oxide-semiconductor structures was investigated. In particular, the sputtering regime during deposition of LaAlO₃ on Si and the atmosphere used in the post-deposition annealing step were addressed by determining capacitance-voltage and gate current-voltage characteristics. These results were correlated with compositional information obtained by Rutherford backscattering spectrometry and nuclear reaction analysis. A post-deposition annealing step in oxygen at 600 °C resulted in better electrical characteristics of the final structure as compared to the same treatment performed in nitrogen. This result is explained by oxygen ability to heal oxygen vacancies in the LaAlO₃ film, especially at the dielectric/semiconductor interface region. A thermalized sputtering regime during deposition of LaAlO₃ on Si leads to capacitors with electrical characteristics superior to those deposited in ballistic regime. PACS 77.84.Dy; 81.15.Cd; 81.40.Gh; 73.40.Qv; 82.80.Yc     

The partial hydrogenation of benzene to cyclohexene by nanoscale ruthenium catalysts in imidazolium ionic liquids

The controlled decomposition of an Ru(0) organometallic precursor dispersed in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI.PF(6)), tetrafluoroborate (BMI.BF(4)) or trifluoromethane sulfonate (BMI.CF(3)SO(3)) ionic liquids with H(2) represents a simple and efficient method for the generation of Ru(0) nanoparticles. TEM analysis of these nanoparticles shows the formation of superstructures with diameters of approximately 57 nm that contain dispersed Ru(0) nanoparticles with diameters of 2.6+/-0.4 nm. These nanoparticles dispersed in the ionic liquids are efficient multiphase catalysts for the hydrogenation of alkenes and benzene under mild reaction conditions (4 atm, 75 degrees C). The ternary diagram (benzene/cyclohexene/BMI.PF(6)) indicated a maximum of 1 % cyclohexene concentration in BMI.PF(6), which is attained with 4 % benzene in the ionic phase. This solubility difference in the ionic liquid can be used for the extraction of cyclohexene during benzene hydrogenation by Ru catalysts suspended in BMI.PF(6). Selectivities of up to 39 % in cyclohexene can be attained at very low benzene conversion. Although the maximum yield of 2 % in cyclohexene is too low for technical applications, it represents a rare example of partial hydrogenation of benzene by soluble transition-metal nanoparticles.     

Atomic transport and chemical stability during annealing of ultrathin Al2O3 films on Si

Ultrathin films of Al2O3 deposited on Si were submitted to rapid thermal annealing in vacuum or in oxygen atmosphere, in the temperature range from 600 to 800 degrees C. Nuclear reaction profiling with subnanometric depth resolution evidenced mobility of O, Al, and Si species, and angle-resolved x-ray photoelectron spectroscopy revealed the formation of Si-Al-O compounds in near-surface regions, under oxidizing atmosphere at and above 700 degrees C. Under vacuum annealing all species remained essentially immobile. A model is presented based on diffusion-reaction equations capable of explaining the mobilities and reproducing the obtained profiles.     

Measurement of gamow-teller strength for 176Yb --> 176Lu and the efficiency of a solar neutrino detector

We report a 0 degrees 176Yb(p,n)176Lu measurement at IUCF where we used 120 and 160 MeV protons and the energy dependence method to determine Gamow-Teller (GT) matrix elements relative to the model independent Fermi matrix element. The data show that there is an isolated concentration of GT strength in the low-lying 1(+) states making the proposed Low Energy Neutrino Spectroscopy detector (based on neutrino captures on 176Yb) sensitive to pp and 7Be neutrinos and a promising detector to resolve the solar neutrino problem.     

The diffraction of elastic waves by an imperfect fusion bond

We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material.     

The formation of intermetallic phases by solid-phase reaction of Fe/Al multilayers

Thin film multilayers of Fe and Al with thicknesses ranging from 10 nm/2 nm to 10 nm/420 nm Fe/Al are used as starting structures to produce intermetallic phases by solid-phase reaction during high-vacuum thermal annealings. By measuring the relative concentrations of the reacting Fe and Al species nearby the growing interfaces and using the recently introduced concept of effective heat of mixing of binary thin-film metallic systems, a method is suggested to predict the phases to be obtained from different combinations of initial multilayer thickness and annealing temperature.     

In situ identification of organic components of ink used in books from the 1900s by atmospheric pressure matrix assisted laser desorption ionization mass spectrometry

Transport of N, O, and Ti during dc magnetron sputtering deposition of nanoscopic TiN/Ti and TiN structures on plasma nitrided M2 tool steel, as well as transport of metallic species composing the plasma nitrided steel substrates were investigated. N and O depth distributions were determined with subnanometric resolution using narrow resonant nuclear reaction profiling, whereas Ti was profiled, also with subnanometric depth resolution, by medium energy ion scattering. The surface elementary compositions of the TiN/Ti/nitrided steel and TiN/nitrided steel structures were determined by low energy ion scattering. The chemical compounds formed during deposition were accessed by X-ray photoelectron spectroscopy, indicating the presence of TiN, TiO₂, Ti oxynitrides, as well as other metallic nitrides and oxynitrides, but no metallic Ti was observed. Owing to the observed intensive atom mobility, the compositions of the deposited films on plasma nitrided steel structures varied continuously on a nanoscopic scale, from the core of the steel substrate to the bulk of the stoichiometric TiN films. The Ti interlayer assists interdiffusion of all species, in contrast to the TiN film layer, which is known to be a diffusion barrier. The improved adhesion of TiN hard coatings to plasma nitrided steel under working conditions is discussed in terms of the gradual compositional change around the interfaces and the atomic mobility during their formation.     

Atomic transport during growth of ultrathin dielectrics on silicon

Atomic transport in thermal growth of thin and ultrathin silicon oxide, nitride, and oxynitride films on Si is reviewed. These films constitute the gate dielectrics, the “heart” of silicon metal-oxide-semiconductor field-effect transistor (MOSFET) and dynamic random-access memory (DRAM) devices, which are usually thermally grown on the active region of the semiconductor Si substrate. The drive of ultra-large scale integration towards the 0.18 μm channel length and below requires gate dielectrics with thicknesses of 3–4 nm and less, establishing new and very strict material requirements. Knowledge on an atomic scale of dielectric film growth promoted by thermally activated transport mechanisms is essential to the engineering of this fabrication step. In the case of thermal growth of silicon oxide films on Si in dry O₂, the mobile species is O₂ and growth is essentially a diffusion–reaction phenomenon. The thermal growth of silicon nitride and oxynitride films on Si in NH₃, NO and N₂O, on the other hand, involves catalytic dissociation of the original gas molecules at the surfaces and interfaces and diffusion–reaction of different resulting species, like NH₂, NH, H, N, NO, O, and O₂. Hydrogen transport and incorporation is a crucial, ubiquitous issue in thermally grown dielectric films on Si which is also addressed here. A recall is made of the physico-chemical constitution of the involved surfaces and interfaces for each different dielectric material, as well as complementary studies of the gas, gas-surface, and solid phase chemistry. An outline of the unique tools of isotopic substitution and high resolution depth profiling is included.     

Interdiffusion,reaction, and stability in a thin film iron-aluminium bilayered system

In this work we describe the results of Rutherford backscattering spectrometry, sheet resistivity measurements, X-ray diffractometry and conversion electron Mössbauer spectroscopy performed on thin film Fe-Al bilayered samples submitted to high vacuum furnace annealing. Isothermal anneals were performed at 570 K for time intervals ranging from 60 to 600 min. It is demonstrated that the diffusion of Al into Fe is smaller than the diffusion of Fe into Al for temperatures below 600 K. Sequential isochronous thermal anneals of 60 min were performed at temperatures ranging from 570 to 870 K, in order to study the stability of the formed phases. The stable Fe₂Al₅ intermetallic compound formed at 570 K decomposes at about 650 K, and the FeAl₆ intermetallic compound appears at temperatures around 750 K.Work supported in part by CNPq and FINEP