Jarmila Cervena

Neutron depth profiling study of lithium niobate optical waveguides

Abstract The relation between optical properties and the structure of proton exchanged and annealed proton exchanged optical waveguides in lithium niobate was studied using the mode spectroscopy and neutron depth profiling methods. We have found a close correlation between the lithium depletion and the depth profile of the extraordinary refractive index. The form of the observed dependence between Li depletion and refractive index depends on the fabrication procedure by which the waveguide was prepared but it is highly reproducible for specimens prepared by the same procedure.

Pulse-shape discrimination in neutron depth profiling technique

Abstract Pulse-shape discrimination (PSD) is used for the first time for reduction of unwanted background in analyses of solid surfaces by neutron depth profiling method (NDP) based on the detection of charged particles from the (n, p) and (n, α) nuclear reactions induced by thermal neutrons on some light elements. The experimental PSD arrangement is described and its performance is demonstrated on the measurement of real sample. Background reduction by about two orders of magnitude in the energy region below 1 MeV leads to sensitivity improvement by about one order of magnitude and to extension of measurable depth region for some of light elements like N and Cl.

ON ANOMALOUS CONCENTRATION DEPTH PROFILES OF ATOMS IMPLANTED INTO POLYMERS

Abstract Different polymers were implanted with 50–200 keV heavy ions to fluences of ≥ 1 × 1015cm−2 and the concentration depth profiles of the implanted atoms were measured by standard Rutherford backscattering technique (RBS). The experimental projected ranges were found to be 10–30% lower than those estimated by the TRIM91 code. The measured range stragglings, on the other hand, are by a factor of 1.4–2.4 higher than the calculated ones. The discrepancies are explained by the loss of matter during the implantation process.

LiNbO3 exposed to radio-frequency plasma

Abstract Radio-frequency (27.12 MHz) glow discharge in H 2 and O, have been used for surface modification of LiNbO 3 wafers. The properties of plasma modified surface layers were dependent on the gas pressure and radio frequency (RF) input power. At pressures below 1 Torr of H 2 and input powers of 1–10 W/cm 3 , a low-resistance layer was created with a sheet resistivity of 2.6 mΩ cm. At pressures of several Torrs, an Li density drop up to a depth of 1 μm appeared, accompanied by OH − radical formation. The sample processing in oxygen plasma was aimed at restoring light transparency of the samples, which was lost during hydrogen processing. The restoration is attainable in a short time and at much lower sample temperature than under thermal bleaching. Processing under certain plasma parameters decreased the density of point defects in the material. The methods used for characterizing the plasma-modified layers were neutron depth profiling (NDP) and Rutherford backscattering (RBS), X-ray induced photoelectron spectroscopy (XPS), X-ray diffraction, visible and infrared transmission and reflection spectroscopy. The paper summarizes the results of a four year study and suggests possible applications of the findings.

Features of APE waveguides in different Er:LiNbO3 and (Er + Yb):LiNbO3 cuts: electrooptical coefficient r33

Abstract Our contribution represents a systematic study of optical layers fabricated by the annealed proton exchange (APE) method in various cuts (X, Y, Z) of lithium niobate that was doped in bulk with erbium (500 ppm) and mixture of erbium and ytterbium in weight portion 1:9 (1000 ppm). Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA) and neutron depth profiling (NDP) methods have been used for monitoring a composition of fabricated optical layers, i.e. changes of the concentration of the rare earths (RE), hydrogen and lithium. We have used mode spectroscopy and a Mach–Zehnder interferometer to monitor the relevant properties, i.e. changes in the effective refractive index and the electrooptical coefficient r33. The obtained results show that during the APE process, there is no loss of the rare earths from the substrate and that during the treatment of the as-exchanged samples the hydrogen concentration increases while the lithium concentration decreases. Waveguiding properties and composition of the RE doped waveguides were not substantially changed compared with those fabricated in pristine lithium niobate. The presence of the doping ions decreases the r33, however, a carefully designed APE technology can increase the r33 almost to the value of the pristine LiNbO3. A correlation between the uniform distribution of lithium and high values of the electrooptic coefficient r33 was found. According to our results the proton exchange not necessarily lowers the efficiency of the 1.5 μm emission and certainly does not lower the concentration of the RE.

The possibility of tailoring the ne vs cLi relationship in lithium niobate optical waveguides

Abstract We present results of our study of concentration profiles of lithium ( c Li ) in annealed proton exchanged (APE) waveguiding layers as measured by the neutron depth profiling (NDP) method. This non-destructive method, based on the 6 Li(n,α) 3 H reaction induced by thermal neutrons, allowed easy monitoring of c Li profiles in a large number of samples fabricated under various fabrication conditions. Our systematic study revealed that, though every particular waveguide could be characterised by very similar mirror-shaped extraordinary refractive index ( n e ) as well as c Li depth profiles, in contrast with up to now generally accepted opinion, there was no linear relationship which unambiguously attributed Δn e to Δc Li . The most important fabrication step appeared to be the post-exchange annealing, during which the lithium atoms were transported towards the sample surfaces. The annealing regime pre-destined not only the depth distribution of the lithium atoms but, as a consequence of it, also other properties of the waveguiding region. That knowledge allows us to fabricate the APE waveguides with a priori given properties for a wide range of special applications. We have also formulated the n e vs c Li semi-empirical relationship, which was proved to fit all our fabricated APE waveguides.

Three-dimensional implantation distribution of lithium implanted into pyrographite, as revealed by solid state tomography in combination with neutron depth profiling

Abstract We have studied the three-dimensional distribution of 2.5 MeV Li implanted into pyrographite at room temperature by means of modified tomography in combination with neutron depth profiling. Our new findings essentially reconfirm earlier results (D. Fink et al., J. Appl. Phys. 58 (1985) 668 [1]; Radiat. Eff. and Def. in Solids 114 (1990) 21 [2]) which indicated the presence of some radiation-enhanced mobility of the implanted lithium. This diffusion is anisotropic. It preferentially proceeds into the radial direction.

High fluence boron implantation into polyimide

Abstract 100 keV B+ ions are implanted at high fluences into polyimide and the boron depth distributions are measured by the neutron depth profiling technique. Subsequently the implanted samples are annealed isochronally to determine the diffusional, trapping and detrapping behaviour of the boron atoms. The boron depth profiles of as-implanted samples differ significantly from those predicted by TRIM code. Pronounced inward and outward profile tails point at increased mobility and redistribution of boron atoms after implantation. Thermal annealing to the temperatures below 150°C does not change the total boron content in 1 μm thick surface layer and the boron depth profiles as well. For higher annealing temperatures a continuous desorption and significant redistribution of boron atoms is observed.

Annealing behaviour of boron atoms implanted into polyethyleneterephtalate

Hundred keV B a ions were implanted at high fluences into polyethyleneterephtalate (PET, Mylar) and the boron depth distributions were measured by the neutron depth profiling technique (NDP). Subsequently the implanted samples were annealed isochronally to determine the diAusional, trapping and detrapping behaviour of the boron atoms. The boron depth profiles of as-implanted samples diAer significantly from those predicted by TRIM code. Pronounced inward and outward profile tails point at increased mobility and redistribution of boron atoms during the implantation. Thermal annealing to the temperatures below 100∞C does not change the total boron content in the 1 lm thick surface layer and the boron depth profiles as well. For higher annealing temperatures a significant redistribution of boron atoms is observed. ” 2000 Elsevier Science B.V. All rights reserved.

Multistage Ion Implantation of Polyamide-6 Films

Abstract The radiation defect formation accompanied by the paramagnetic centre creation by multistage boron ion implantation into polyamide-6 (PA) films was studied using the ESR technique. It was found that the multistage implantation with the energy increasing from step to step results in the rearrangement of the polymer layer being accompanied with the compensation of the terminated carbon bonds and strong exchange interaction between π-electrons. By contrast, a decrease of the ion energy from one implantation step to another one leads to the progressive accumulation of the paramagnetic centres in the implanted layers that permits to create highly conductive channels from the surface to the buried conducting carbonaceous layer produced in the polymer film via ion bombardment and to fabricate planar field-effect electronic devices based on ion-implanted polymers.