Thermal ammonia nitridation on HfO2 and hafnium silicates thin films

17th International Conference on Ion Beam Analysis, Seville, SPAIN, JUN 26-JUL 01, 2005International audienceIn this paper we use isotopic tracing experiments with (NH3)-N-15 and (NH3)-N-14 to investigate the nitridation mechanisms on both hafnium silicates films (40-175 angstrom) and HfO2 (50 angstrom) films deposited by MOCVD on silicon substrate covered by a 10-15 angstrom interfacial SiO2 layer. Nitrogen profiles in the films were obtained through nuclear resonance profiling (NRP) with the N-15(p,alpha gamma)C-12 resonance at 429 keV and the total amounts of atomic species and the overall stoichiometry were obtained by RBS and NRA. In the silicate films, nitrogen is incorporated both into surface and bulk regions. For HfO2, lowering the ammonia pressure favors the fixation of nitrogen in the near surface region of film. This phenomenon is not observed in the case of silicate films. The pressure dependence of near surface nitrogen incorporation in HfO2 films could be related to the formation of oxygen vacancies and opens a way to control the diffusion barrier needed in the gate dielectric. (c) 2006 Elsevier B.V. All rights reserved

Size-dependent thermo-optical properties of embedded Bi nanostructures

International audienceThe thermally induced optical transmission changes upon melting and solidification of Bi nanostructures embedded in amorphous Al(2)O(3) thin films have been studied as a function of characteristic sizes in the range 7-35 nm. The results show a repeatable optical transmission-temperature hysteresis loop with sharp changes at the melting and solidification temperatures. Both temperatures decrease linearly when the mean size of the nanostructures decreases and they are respectively higher and lower than that of the bulk melting temperature of Bi. The optical transmission shows a significant contrast that increases up to 16% as the mean size of the nanostructures increases. The results show that in addition to the usual decrease of melting temperature as the size of the nanostructures decreases, the melting temperatures for all samples are higher than that of the bulk. This unexpected result is associated to the contraction of Bi upon melting and to matrix effects related to the balance of surface energies between the solid and liquid Bi and the matrix. The solidification process shows a weaker dependence on the nanostructure size, and thus it is consistent with a mainly volume controlled process. It is shown that by controlling the characteristic dimensions of the Bi nanostructures the temperature operability of the Bi nanostructures embedded in amorphous Al(2)O(3) as a thermally driven optical switch can be tuned over 73 K

Size-dependent thermo-optical properties of embedded Bi nanostructures

The thermally induced optical transmission changes upon melting and solidification of Bi nanostructures embedded in amorphous Al2O 3 thin films have been studied as a function of characteristic sizes in the range 7-35 nm. The results show a repeatable optical transmission- temperature hysteresis loop with sharp changes at the melting and solidification temperatures. Both temperatures decrease linearly when the mean size of the nanostructures decreases and they are respectively higher and lower than that of the bulk melting temperature of Bi. The optical transmission shows a significant contrast that increases up to 16% as the mean size of the nanostructures increases. The results show that in addition to the usual decrease of melting temperature as the size of the nanostructures decreases, the melting temperatures for all samples are higher than that of the bulk. This unexpected result is associated to the contraction of Bi upon melting and to matrix effects related to the balance of surface energies between the solid and liquid Bi and the matrix. The solidification process shows a weaker dependence on the nanostructure size, and thus it is consistent with a mainly volume controlled process. It is shown that by controlling the characteristic dimensions of the Bi nanostructures the temperature operability of the Bi nanostructures embedded in amorphous Al2O3 as a thermally driven optical switch can be tuned over 73 K. © IOP Publishing Ltd.This work was partially supported by TEC 2006-04538 and MAT2005-06508- C02-01, MEC (Spain).Peer Reviewe

Soft x-ray optical constants of sputtered chromium thin films with improved accuracy in the L and M absorption edge regions

In this study, we determine with improved accuracy the complex index of refraction n = 1 - δ + iβ of sputtered chromium thin films for photon energies ranging from 25 eV to 813 eV. These data include the first absolute measurements of the absorption fine structure near the Cr-L edge. First, we verified by combining Rutherford Backscattering Spectrometry and grazing-incidence x-ray reflectometry that the sputtered thin films were pure Cr with a density consistent with tabulated values. Then, we demonstrated that the Cr surface oxide layer remains stable when the samples are exposed to air for up to 4 years. The Cr absorption coefficient β was determined from the transmittance of freestanding Cr thin films with various thicknesses, measured at the ALS synchrotron radiation source. A model is proposed to correct the transmittance data from the spectral contamination of the source. Finally, we used the new β values, combined with theoretical and tabulated data from the literature, in order to calculate the δ values by the Kramers-Kronig relation. The improvement in the accuracy of β values is demonstrated by the f-sum rule. An additional validation of the new Cr optical constants (δ, β) is performed by comparing the simulated and experimental reflectance of a Cr/B4C multilayer mirror near the Cr-L2,3 edge

Tracer study of pore initiation in anodic alumina formed in phosphoric acid

AbstractArsenic species are utilized as tracers in a study of pore initiation in anodic films that were formed at constant potentials on aluminium in phosphoric acid. The films were grown first in sodium arsenate solution and then in phosphoric acid, and examined using ion beam analysis and scanning and transmission electron microscopies. The analysis of the arsenic content of specimens indicates that the growth mechanisms of incipient and major pores involve mainly field-assisted dissolution and field-assisted flow of the alumina, respectively. The transition between incipient and major pore formation is suggested to be initiated by preferential growth of certain incipient pores, leading to a locally increased current density at the pore bases. The major pores subsequently develop by the flow oxide away from the pore bases, which is evident from the behaviour of the arsenic tracer. The results suggest that the flow is associated with the non-uniform distribution of ionic current and a relatively low volume of formed film material compared with the volume of oxidized aluminium

Status of the problem of nuclear cross section data for IBA

18th International Conference on Ion Beam Analysis, Univ Hyderabad, Sch Phys, Hyderabad, INDIA, SEP 23-28, 2007International audienceThe progress achieved in an IAEA Coordinated Research Project (CRP) to improve the cross section data for IBA is reported. The objective of the CRP, started in 2005, is to create a nuclear cross section database for IBA that contains reliable and usable data freely available to the entire IBA community. The major results achieved so far by the CRP participants are discussed. The results include compilation and assessment of the existing cross sections, new experimental data and evaluation of the most wanted cross sections. The experimental results are incorporated into the IBANDL database (www-nds.iaea.org/ibandl/) and evaluated data are presented at the SigmaCalc cross section calculator (www-nds.iaea.org/sigmacalc/). (c) 2007 Elsevier B.V. All rights reserved

Oxygen incorporated during deposition determines the crystallinity of magnetron-sputtered Ta3N5 films

International audienceTa3N5 belongs to the group of transition metal nitrides with the cation in a high oxidation state. These are typically challenging to synthesize owing to the low reactivity of nitrogen. This applies similarly to Ta3N5 that crystallizes only in the presence of oxygen during synthesis. Typical preparation methods are ammonolysis of oxidized Ta or magnetron sputtering of a Ta target in an atmosphere of Ar, N2 and O2. However, the material typically obtained by either synthesis method is of varying degrees of crystallinity and the key parameter affecting the crystallinity remains elusive. In this study, we examine the role of oxygen for the crystallinity of Ta3N5 samples by studying. Thin film samples prepared by magnetron sputtering reveal that oxygen is indeed the central driver for Ta3N5 crystallinity. While little oxygen in the films yields the metallic δ-TaN phase, excess oxygen results in low crystallinity Ta3N5 or Ta-O-N films. Ta3N5 samples with a high degree of crystallinity are obtained by limiting the oxygen supply to the sample during the deposition. A comparison with other studies suggests a fundamental oxygen incorporation limit above which the crystallinity of Ta3N5 is compromised. The most crystalline sample from this study contains 4.4 at.% of oxygen. It is grown onto a Si(100) substrate, covered with a 30 nm-thick metallic diffusion layer. For this sample, we observe Ta3N5 grains between 80 and 120 nm in size