An important factor in the Accelerator Laboratory activity has been the extent of outside funding which we have been able to maintain at the level of 1996. A direct consequence has been an increase in the number of postgraduate students compared to previous years. The laboratory's research programme has concentrated on materials science and several new domestic and international co-operation projects have been launched during 1997. Further nuclear, applied, laser and molecular physics have been well represented.
The development of the Accelerator Mass Spectrometry (AMS) project has continued and will be in flight in 1998. The main technical developments have been the finalizing of the isotope separator upgrade and the planning and starting the installation of a helium ion source for the EGP-10-II accelerator. The technical projects have been realized by outside funding and by the laboratory's own investments.
1.2. LABORATORY OPERATION AND DEVELOPMENT
Armas Fontell, Raimo Ingren, Heikki Sepponen, Birger Ståhlberg and Kim Wahlström
During the period covered by this annual report the 5 MV EGP-10-II tandem accelerator and the 2.5 MV VdG accelerator completed their 15th and 40th year in service, respectively. Both accelerators operated reliably.
The EGP maintenance has required no essential shutdown. During the late February service of the duoplasmatron ion source was carried out. In the early March service of the sputtering ion source was necessary. The EGP pressure tank was not opened during the year. The VdG required 14 days of maintenance. Service of the beam line valves, the vacuum system and drying of the accelerator were carried out. The scattering chamber was repaired. The VdG pressure tank was opened twice for service of the ion source. Each of these shut-downs, the first one in May and the second one in October, lasted for four days.
The EGP and the VdG provided total beam line of 1826 h and 1894 h, respectively. In July the EGP was shut down due to the annual vacations of the personnel. At the VdG protons were accelerated for 47%, deuterium for 1% and 4He+ for 52% of the total beam time.
Most of the technical improments were directed to the upgrading of the laboratory's isotope separator. Our separator completed its 33th year in service. The following improvements to the old design were completed: - All high voltage and low voltage power supplies were renewed. - A motor generator for the ion source power supply was installed. - Three turbo vacuum pumps were installed. - Most of the old vacuum gate valves were replaced by new pneumatically operated gate valves. - The vacuum measuring equipments were renewed. - Operation safety was improved by installation of an automatic earthing system. - Computer control and construction of its peripheral devices were completed.
In the sample production the isotope separator ion collection energy was varied from low energies up to 120 keV. Altogether 243 samples were produced from 26 different isotopes.
Sisko Vikberg, Kai Arstila, Jura Tarus, Marcus Gustafsson, Antti Kuronen and Kim Wahlström
During the year, major revisions were made to the laboratory computer system. These include the installment of a new 100Base-T network and two optically interconnected Advance Stack Hubs as well as the acquiring of four dual-Pentium Pros.
Although some of the machines in our laboratory can be booted to run DOS/Windows and to connect to the Novell servers at the University, all of them are configured to work as client machines running our primary OS, the freely distributable Linux operating system (currently Red Hat 4.2).
Most of the client machines (14 PC's ranging from 80MHz 486:s to a 200 MHz Pentium) are connected through a 100 Mb/s network connection to our Linux-server (200 MHz dual-Pentium Pro) and also to three separate workstations (200 MHz dual-Pentium Pros) devoted only to heavy numerical simulations and capable of making use of parallell programming.
Most of the application software is free and collected from the Internet. The word-processing is done by using the TeX/LaTeX program. Commercial software includes programs such as Mathematica, Matlab and MicroStation. The main programming languages used are C, Fortran and different script-languages.
The network connections allow us to use the computer resources at the Physics Computation Unit (their DAT-drive is used for making the system backup), the Computer Center of the University and the Center of Scientific Computing of Finland. The machines use ssh (Secure Shell) for secure communication.
Our website is here .
The accelerator's control system has its own separate ethernet network. In the first phase the system controls the 120 kV isotope separator. The system handles automatically routine tasks like analysing magnet control, target venting, implantation dose calculation, implantation report printing etc.
The control system back bone consists of two Windows-NT based operator consoles and one Windows 3.11 based I/O-server. The graphical operator interface is Wonderware InTouch.
PUBLIC RELATIONS ACTIVITY
Birger Ståhlberg, Marcus Gustafsson and Olli J. Marttila
The Department of Physics has continued the policy to invite students leaving the upper secondary school to visit the laboratories of the Department. In addition, an opportunity to get acquinted with working in a research institute has been offered to a few interested students in the last form of lower secondary schools.
In 1997 the Kumpula premises of the Accelerator laboratory were visited by 29 groups, 500 guests in all. 18 groups were from higher or lower secondary schools, and 5 groups from technical colleges, 2 groups from University of Helsinki and 2 groups from two national universities.
1.3 NUCLEAR PHYSICS
LIFETIMES OF 32S LEVELS
Aki Kangasmäki, Pertti Tikkanen, Juhani Keinonen, W.E. Ormand*, S. Raman**, Zs. Fuelöp, A.Z. Kiss*** and E. Somorjai***
The study on the properties of excited states in 32S has been completed . Mean lifetimes of 20 out of 31 bound levels in 32S below an excitation en-ergy of 8.0 MeV are deduced from the Doppler-broadened gamma-ray line shapes produced in the reactions 2H(31P,ngamma) 32S, 28Si(6Li,pn gamma)32S, and 31P(p,gamma) 32S. Of the 20 levels, lifetimes for 4 are reported for the first time. The low-lying portion of the level scheme, level lifetimes, gamma-ray branchings, E2/M1 mixing ratios, and reduced transition probabilities are compared with shell-model calculations. The overall agreement is good. A one-to-one correspondence between 33 experimental and predicted states is established up to 8.2 MeV for both positive- and negative-parity states.
1. A. Kangasmäki et al., submitted to Phys. Rev. C
* Department of Physics and Astronomy, Louisiana State University, Baton
Rouge, LA 70803-4001
** Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
*** Institute of Nuclear Research of the Hungarian Academy of Sciences, P.O. Box 51, H-4001 Debrecen, Hungary
1.4 MATERIALS PHYSICS
ISLAND GROWTH IN ION-BEAM ASSISTED METAL-ON-METAL DEPOSITION MODELLED BY RATE EQUATIONS
Jussi Sillanpää and Ismo Koponen*
Island growth in ion beam assisted deposition (IBAD) is modelled by rate equations, where deposition, diffusion driven aggregation, defect and target adatom production and island fragmentation are taken into account. It is shown that compared with results obtained for a thermal deposition, deposition with ion bombardment induced island fragmentation causes the total island density to increase and average island size to decrease. The observed behaviour is in qualitative agreement with experimental findings. A more detailed study of the island size distributions revealed that the scaled form of distributions depends crucially on the fragmentation process, but is relatively unaffected by diffusion. By increasing fragmentation distributions can be changed gradually and the form of the distributions can be controlled by tuning the magnitude of diffusion in relation to fragmentation. The sensitivity of the form of the distributions to the fragmentation process offers a possibility to test the model experimentally.
* Helsinki Institute of Physics
ION-BEAM MODIFICATIONS OF alpha-SiO2 AND Ni/SiO2 LAYERS
M. Schwickert*, W. Bolse*, Marcus Gustafsson, Juhani Keinonen and K.P. Lieb*
Modifications of thermally grown alpha-SiO2 layers and Ni/SiO2 bilayers after irradiations with 350 keV Xe ions and subsequent isochronal thermal annealings in vacuum at 298-1173 K have been investigated. The analyses were performed by means of Rutherford backscattering spectroscopy (RBS) and surface profilometry. The homogeneity of the Ni films was also controlled by optical and scanning electron microscopy. We here report on the ion-induced surface roughening and sputtering, the athermal ion-beam mixing at the Ni/SiO2 interface and the swelling of the bulks. A low interface mixing rate in agreement with the ballistic model was found . Very little Xe precipitation, which would indicate the presence of end-of-range spikes , was observed to occur at the interface. The rate of Xe loss during annealings was found to strongly depend on the implanted fluence.
* Zweites Physikalisches Institut, Univ. Göttingen, Bunsenstr. 7-9, D-37073 Göttingen, Germany
1. P. Sigmund, A. Gras-Marti, Nucl. Instr. Meth. 182/183 (1981) 25 2. W. Bolse, T. Weber, Nucl. Instr. Meth. B 85 (1994) 188
OXYGEN EFFECT ON THE RECRYSTALLIZATION OF Li-IMPLANTED a-SiO2
F. Roccaforte*, Marcus Gustafsson, L. Ziegler*, W. Bolse* and Juhani Keinonen
SiO2 is broadly used in opto-electronics, high temperature and high speed device technology, and there is a large interest in the damage accumulation and amorphization of crystalline SiO2(alpha-quartz) .
15 keV Li+ ions were used to irradiated quartz samples by ion beam implantation to a fluence of 2.5.1016 ions/cm2. The amorphized samples were thermally annealed in air or vacuum at 300-700°C, and thereafter analysed by means of Rutherford backscattering spectrometry in channeling geometry (RBS-C). The results showed different defect recovery and degree of recrystallization depending on the annealing ambient.
This effect was believed to be caused by the pres-ence of oxygen in air. New samples were prepared that were annealed in 18O in order to be able to distinguish between the oxygen in the quartz and the oxygen incorporation resulting from the annealing. These samples were measured by time-of-flight elastic recoil detection analysis (TOF-ERDA), and based on these results in combination with the channeling spectra, conclusions on the role of oxygen in the recrystallization process could be done.
* Zweites Physikalisches Institut, Univ. Göttingen, Bunsenstr. 7-9, D-37073 Göttingen, Germany
1. "Solid Phase Epitaxial Regrowth of Ion Beam Amorphized a-quartz", F. Roccaforte, W. Bolse and K.P. Lieb, to be published
FULLY ATOMISTIC ANALYSIS OF DIFFUSE X-RAY SCATTERING SPECTRA OF SILICON DEFECTS
Kai Nordlund*,**, P. Partyka**, I. K. Robinson**, P. Ehrhardt*** and R. S. Averback**
Diffuse X-ray scattering (DXS) at glancing incidence is a potentially powerful means for elucidat-ing damage structures in solids. The analysis of diffuse X-ray scattering spectra requires knowledge of the atomic displacement field around defects. The usefulness of the method has been restricted in part by the difficulty of calculating the strain fields of complex defects. Traditionally the form of the displacement field has been estimated analytically in terms of elastic continuum theory.
We present a method for predicting the diffuse scattering line shape by calculating the displacement field around a defect using fully atomistic simulations. We relax a sufficiently large (of the order of 1 - 100 million) number of atoms around a defect using a conjugate gradient method, fully linear algorithms and realistic interatomic potentials. From the relaxed atom positions we obtain the shape of the displacement field and hence the diffuse scattering directly, without the need for continuum approximations.
The method is applied to calculate the diffuse X-ray scattering from various defect configurations in silicon. The calculations are used to interpret experimental DXS results. Comparison with in situ He and Ga irradiation of Si at temperatures of 100 - 300 K indicate that the Si self-interstitial becomes mobile around 150 K. Surprisingly, the He and Ga line profiles look quite similar despite the large mass difference of the projectiles. This suggests that amorphous pockets produced during Ga irradiation at least partially anneal out even at low temperatures, and that amorphization of silicon by at least low- and medium-heavy projectiles occurs homogeneously through buildup of interstitial clusters.
* Accelerator Laboratory, P.O. Box 43, 00014 University of Helsinki,
** Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA
*** IFF, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany
TOF-ERDA SPECTROMETRY APPLIED FOR THE ANALYSIS OF SEMICONDUCTOR MATERIALS AND THIN FILMS
Timo Sajavaara, Janne Jokinen, Kai Arstila and Juhani Keinonen
The migration of ion-implanted Be in (100) GaAs has been studied with Time-of-Flight Elastic Re-coil Detection Analysis (TOF-ERDA) spectrome-try. Migration of Be was observed at 300°C. At 600°C Be had migrated to the surface. The damage in the crystalline structure of the implanted samples was determined with RBS-channeling measurements and the recovery was observed to begin at 3000°C and the structure was recovered at 6000°C. To improve the analysis of ERDA measurements, Monte Carlo simulation method was introduced. Multiple and plural scattering effects were well reproduced with this method.
The collaboration with Helsinki University De-partment of Chemistry and Planar International Ltd has continued during 1997. The aim of the project is to grow thin films with atomic layer epitaxy (ALE) for electroluminescent displays. TOF-ERDA was used for the depth profiling of different samples containing ALE grown layers and impurities.
DEFECT PRODUCTION ON THE Si(100)-(2x1) SURFACE BY 4.5 keV He ATOMS: A MOLECULAR DYNAMICS SIMULATION
Jura Tarus, Kai Nordlund and Juhani Keinonen
We have studied the point defect production in the topmost layers of the 2 x 1 terminated Si(100) surface under 4.5 keV He atom bombardment. The aim of the work is to get data of the early stages of the bombardment. This data will later be used in an experimental study of vacancy and interstitial diffusion in Si by scanning tunneling microscope detection of bulk defect migration to the surface.
The study was done by applying the classical molecular dynamics simulation technique. The Si-Si interactions were modelled by the Tersoff III potential with a corrected repulsive part. The forces between He-Si pairs were evaluated from a repulsive potential calculated with the DMol program package. The simulation box consisted of 2048 Si atoms with periodic xy boundary conditions and a fixed bottom layer. The initial temperature of the box was set to 100 K. The incident angle of the impinging He atom was 25° off-surface (65° off-normal), with a random twist angle.
It was found that the probability of events leading to near surface defects is very low, as most of the He atoms go through the surface layers without experiencing any strong interactions. The probability of one He atom to produce one or more adatom is 0.05±0.01 with an overall adatom production probability of 0.12±0.03 adatoms/He atom. The corresponding numbers for surface layer vacancy production are 0.07±0.01 and 0.126±0.015, respectively. Nevertheless, near-surface explosions were also found to take place where up to 9 adatoms and 8 surface layer vacancies were produced, thus leaving experimentally visible craters.
IDENTIFICATION OF SILICON INTERSTITIALS IN ION IMPLANTED GaAs
The lattice location and diffusion of silicon has been studied in <100> GaAs implanted with 1016 40-keV 30Si+ ions/cm2. The identification of silicon interstitials was made by fitting a concentration dependent diffusion model to the annealed silicon depth profiles measured with secondary ion mass spectrometry. In the diffusion model presented, in addition to silicon located on Ga and As sites and SiGa+ - SiAs pairs, also interstitial silicon is taken into account for the first time. The charge state of the silicon interstitial was calculated to be +1 in order to best fit the experimental profiles.
HYDROGEN MIGRATION IN DIAMONDLIKE CARBON FILMS
Elizaveta Vainonen, J. Likonen*, Tommy Ahlgren, Pekka Haussalo, Juhani Keinonen and C.H. Wu**
Properties of physical vapor deposited diamond like carbon (DLC)films and the migration of hydrogen in H+ and 4He+ ion implanted and hydrogen co-deposited DLC films have been studied. Measurements utilizing Rutherford Backscattering Spec-trometry showed that the films studied have an average mass density of 2.6±0.1 g/cm3. The bonding ratio sp3/sp2 is typically 70% measured with the Electron-Spectroscopy for Chemical Analysis technique. Impurities and their depth distributions were deduced from the Particle Induced X-ray Emission and Secondary Ion Mass Spectrometry (SIMS) measurements. Distributions of implanted and co-deposited hydrogen were measured by the nuclear resonance reaction 1H(15N,alpha gamma)12C and SIMS. It was found that annealing behavior of implanted H in DLC has a diffusion like character. The obtained diffusion coefficients resulted in the activation energy of 2.0±0.1 eV. It was observed that in H co-deposited DLC films the temperature of H release varied between 950°C and 1070°C depending on the H concentration.
* Technical Research Centre of Finland, Chemical Technology, P.O.Box
1404, FIN-02044 VTT
** The NET Team, Max-Planck-Institut für Plasmaphysik, Boltzmannstrasse 2, D-85748 Garching bei München, Germany
ELASTIC SCATTERING CROSS SECTION DETERMINATIONS
Arto Nurmela, Eero Rauhala and Jyrki Räisänen
Elastic scattering cross sections for protons scattering from 4He have been determined at several scattering angles. The scattering cross sections for hydrogen analysis by 4He ion Elastic Recoil Detection were calculated by kinematically reversing the reaction. This study has been brought to conclusion.
The study of proton elastic scattering cross sections by Cu, Mo, Ag and Sn near the Coulomb barrier has been also completed. The measure-ments were performed in the energy region of 2.3 to 6.5 MeV at laboratory scattering angles of 135° and 165°. The threshold energies of deviation from Rutherford scattering were determined.
Elastic scattering cross sections of 6Li ions by natural aluminium, silicon and titanium were measured in the energy range 0.4 - 11.5 MeV at typical backscattering angles of 140° and 170°. The obtained results will be compared with corresponding data measured for 7Li scattering.
STOPPING POWERS OF 0.5-10.5 MeV 7Li IONS FOR POLYIMIDE, VYNS, FORMVAR, POLYSULFONE AND SOLID H, O AND Cl
Kyösti Väkeväinen, Jyrki Räisänen, F. Munnik* and U. Wätjen**
Accurate stopping powers of 0.5-10.5 MeV 7Li ions for polyimide (H10 C22 N2 O5), vyns (H33C22O2C19), formvar (H6.95C5.02O2) and polysulfone (H22 C27O4S) have been determined by the transmission technique. The estimated uncertainty in the stopping power values is 2.5%. The data have been parametrized and compared with predictions based on various models found in the literature. Significant deviations have been observed at the stopping power curve maximum. Based on the present and earlier polymer stopping powers and relevant carbon literature data the elemental stopping cross sections of hydrogen, oxygen and chlorine for 1.7-10.5 MeV 7Li ions have been calculated. The validity of the cores-and-bonds (CAB) model has been investigated, no clear support for the CAB model was found.
* BV Cyclotron, VU, de Boelelaan 1085C, 1081 HV Amsterdam, The Netherlands
** Institute for Reference Materials and Measure-ments (IRMM), European Commission-Joint Research Centre, Retieseweg, B-2440 Geel, Belgium
EFFECTS OF SUBSTRATE TEMPERATURE IN THE DEPOSITION OF HYDROGENATED AMORPHOUS CARBON BY PACVD AT LOW FREQUENCY
R. Gago*, O. Sanchez-Garrido*, A. Climent-Font**, J.M. Albella*, E. Roman*, Jyrki Räisänen and Eero Rauhala
Hydrogenated amorphous carbon films were deposited using a 35 kHz rf-plasma chemical vapor deposition (rf-PACVD) system in the temperature range of 100 to 300°C starting from CH4 and H2 gas mixtures. The films were characterized using ellipsometry, electrical measurements and Raman, Auger Electron, Electron Energy Loss, Rutherford Backscattering and Elastic Recoil Detection spectroscopies. A comparative study of the properties of the films prepared at different deposition temperatures has been made. The results are compared with charateristics of films prepared with a conven-tional 13.56 MHz plasma system.
* Instituto Ciencia de Materiales de Madrid, 28049 Cantoblanco, Madrid,
** Dto. de Fisica Aplicada, Facultad de Ciencias C-XII, U.A.M., 28049 Cantoblanco, Madrid, Spain
AMORPHOUS DIAMOND FILM DEPOSITION
Asko Anttila, Reijo Lappalainen, Marko Hakovirta, Harri Heinonen, Panu Pekko, Jouko Salo and Veli-Matti Tiainen
Amorphous diamond films (sp3 bonding fraction 78%) have been deposited using plasma accelerator methods. Superior attachment of AD coatings on any solid substrate material has been achieved with a new set-up based on the use of simultaneous deposition with two pulsed arc discharge units. Films have been deposited for tribological laboratory tests and industrial applications. Promising results with the amorphous diamond coatings have been achieved, e.g. in medical implants and cutting tools. By using AD coating, the amount of corrosion of conventional medical implant materials has been decreased by a factor of 10000-15000. The steady state wear rate of the coated material is practically zero and at least three orders of magnitude lower than the wear rate of the best conventional implant materials. The optimum conditions and multilayer structures to achieve perfect corrosion and wear resistance for any metal are developed and used for long-term corrosion and wear testing.
GROWTH AND MODIFICATION OF LUMINESCENT THIN FILMS USED IN FULL-COLOR ELECTROLUMINESCENT DISPLAYS BY USING ION BEAM METHODS
Reijo Lappalainen, Juhani Keinonen, M. Leskelä*, M. Ritala* , W.-M. Li*, Timo Sajavaara
SrS:Ce3+ is a promising candidate for the blue phosphor in full-color thin film electroluminescent displays. At present the blue colour is achieved using a filter with the sacrifice of the luminescence intensity. Large efforts have been devoted to improve the luminescence efficiency and chromacity of SrS:Ce films prepared by various deposition techniques. An important, though not thoroughly understood factor in respect of the EL properties of SrS:Ce is the effect of impurities.
In order to get a basis for future studies on the rela-tionships between the impurities and the lumines-cent properties, we have analysed in detail all the relevant impurities such as carbon and oxygen in the state-of-the-art SrS:Ce and SrS:Cu films prepared with different techniques using several nuclear methods. In addition, we have used ion im-plantation to add dopants and impurities in the EL structure in a well-controlled way. The implanted ions include F, Na, Al, P, Cl, K, Cu, Ga and Ce. We have found out that e.g. by optimised F- or K-implantation photoluminescence intensity of the EL structure didn't decrease significantly but the spectrum shifts towards blue. It should be emphasised that even this small blue shift (about 10 nm) is very significant if that can be reproduced in a real EL device.
* Department of Chemistry, P.O. Box 55, University of Helsinki, FIN-00014 Helsinki, Finland
1.5 APPLIED PHYSICS
DETERMINATION OF LATTICE LOCATION OF IMPURITIES IN COMPOUND SEMICONDUCTOR MATERIALS BY PIXE/CHANNELING*
Reeta Salonen, Anni Seppälä, Tommy Ahlgren, Eero Rauhala and Jyrki Räisänen
Rutherford backscattering combined with ion channeling (RBS/C) is a widely used method in determining crystal perfection or lattice location of impurity atoms. However, RBS is not suitable for detecting neighbouring elements or light elements in heavier matrix. With particle induced X-ray emission (PIXE) it is possible to detect successive elements of the periodic table, for example Zn and Ga.
Lattice location studies require a comparison of yields from impurity and host atoms at the same depth. Unfortunately PIXE shows one difficulty; concentration depth information is difficult to obtain. Thus, only a few studies employing X-rays have been published.
We have studied the use of PIXE/channeling for lattice location determination in a ZnSe compound semiconductor material. The undoped ZnSe samples were grown at Tampere University of Technology by molecular beam epitaxy on epitaxial GaAs buffer layers (on bulk GaAs). The layer thicknesses were 130 - 1900 nm.
The effect of the ZnSe layer thickness on the PIXE minimum yield was investigated. The minimum yield increases as a function of layer thickness due to dechanneling. With higher ion beam energies (>2 MeV) the dependence is not significant, because ions with high energy channel better in the crystal. If the distribution of the impurity atoms does not cover the whole matrix layer the minimum yields from host and impurity atoms cannot be directly compared. The measured minimum yields have to be corrected with the known layer thickness dependence. The present results give valuable information in combining different ion beam methods for lattice location determination. We have taken advantage of these results, for ex-ample, in determining the lattice location of implanted titanium in ZnSe.
* This work is part of the EPI2 project funded by the Academy of Finland.
DIFFUSION OF Pt IN MBE-GROWN ZnSe
Jonatan Slotte, Reeta Salonen, Tommy Ahlgren, Jyrki Räisänen, Eero Rauhala and P. Uusimaa*
Diffusion of platinum in zinc selenide has been studied by the use of 4He and 12C ion backscattering technique. The samples were thin films grown by molecular beam epitaxy on GaAs (100) epitaxial layers followed by evaporation of platinum and annealing in the temperature range 550°C - 800°C. The diffusion coefficients were determined by the fitting of a concentration independent solution of the diffusion equation to the experimental depth profiles. The activation energy and the pre-exponential factor of the diffusion process were found to be 1.7 eV and 6.4.106 cm2/s, respectively.
* Tampere University of Technology
AMORPHOUS OR NANOCRYSTALLINE THIN FILMS AND MULTILAYERS
Pauli Torri, Reijo Lappalainen and Juha-Pekka Hirvonen*
We have studied nanocrystalline ceramics in the form of thin films consisting of homogeneously mixed components or multilayers. The materials include Me-MeOx, SiC-Si3N4 and Me-Si-(C,N) ceramics prepared by sputtering or pulsed arc discharge. These methods provide a powder free route for the preparation of specimens with a homogeneous distribution of constituents and give flexibility in the choice of the chemical composition. By the control of crystallization and microstructure it is possible to achieve materials with superior proper-ties compared to normal bulk materials.
We have continued the studies of new multilay-ered MoSi2/SiC, MoSi2N3/SiC, MoSi2/MoSi2N3/SiC/MoSi2N3 and MoSi2-N samples for oxidation, stress relaxation and diffusion studies. We have shown that layer thicknesses and microstructure determined by deposition parameters and heat treatment has an important role in oxidation behaviour, thermal stability and mechanical strength. We have found excellent stability in thin film structures stabilized with nitrogen. This same concept has been tested with amorphous diamond coatings doped with nitrogen and boron.
* European Commission, Joint Research Centre, Institute of Advanced Materials, I-2120 Ispra, Italy
DIFFUSION AND CRYSTALLIZATION STUDIES OF ION IMPLANTED SrS THIN FILMS
Reijo Lappalainen, Milja Karjalainen, Sanna Sevanto, Ritva Serimaa and M. Leskelä*
Strontium sulfide is a promising blue phosphor material for full-color thin film electroluminescent displays. It has been observed that implantation of proper impurity elements, e.g. F and K enhances photoluminescence characteristics. Because heat treatment is necessary to restore the crystallinity and luminescence after implantation, diffusion of implants or impurities and crystallization are relevant issues.
The diffusion of the implanted Ce, F and Na atoms was studied using nuclear resonance broadening and Rutherford backscattering techniques as a function of temperature. The recrystallization of the SrS-based films was observed using x-ray diffraction method. It turned out that annealing at about 700°C for 2 h was sufficient to recrystallise implanted SrS and all the implanted ions mentioned above were diffusing significantly at this temperature.
* Department of Chemistry, P.O. Box 55, University of Helsinki, FIN-00014 Helsinki, Finland.
MECHANICAL TESTING AND EVALUATION OF MATERIALS USED IN ORTHOPAEDIC SURGERY
Reijo Lappalainen, Y.T. Konttinen*, Harri Heinonen, S. Santavirta** and Asko Anttila
Both artificial and natural materials are commonly used in orthopaedic surgery. Especially in the case of lead-bearing applications, e.g. in the spine and neck, mechanical strength is a very relevant issue. Recently, the failure of commercial bonegrafts used in neck surgery has resulted in quadriplegia (paralysis of all four limbs) of a few patients in Finland. Therefore, mechanical characterisation and evaluation of different types of materials is essential.
We have tested mechanical properties of several types of biomaterials such as graphite, bonegrafts and bone cement using tensile and compressive testers. It has turned out that the commercial bonegrafts used for the patients mentioned above are significantly weaker than the manufacturer claims and they especially lose their mechanical strength when they come into contact with body fluids. Therefore, new substitutes for commercial bonegrafts are under study.
* Department of Anatomy, P.O. Box 9, University of Helsinki, FIN-00014
** Department of Orthopaedics and Traumatology, Helsinki University Central Hospital, Topeliuksenkatu 5, FIN-00260 Helsinki
EFFECTS OF PROTON, LITHIUM AND ELECTRON IRRADIATION ON SULFONATION OF POLY (VINYL FLUORIDE)
M. Paronen*, F. Sundholm*, Eero Rauhala, T. Lehtinen** and S. Hietala**
Polymer electrolyte membrane fuel cells are of considerable interest as potential sources of small scale energy production, e.g., in vehicles. In the fuel cells, the polymer membranes are used as proton-conducting matrixes. High chemical stability and ion conductivity, as well as good barrier properties against the permeation of fuel and oxygen are required. At present, the possible membrane materials are subject to intense investigation.
In this study we use proton, lithium and electron beams to irradiate poly(vinyl fluoride) thin films to examine the fabrication processes of the fuel cell membranes, in particular, the irradiation induced effects on the sulfonation of the material . The heavy particle beams used in the irradiation were obtained from the VdG and EGP accelerators at the Accelerator Laboratory of the University of Helsinki.
The direct sulfonation of the thin film material subsequent to ion irradiation was shown to produce proton conducting channels in the material. Among others, the ion exchange capacity, sulfonation efficiency and ion conductivity were analyzed. Increase of the absorbed dose and the linear energy transfer was found to promote the effect on the sulfonation rate and sulfonic acid content. High ion-exchange capacities were obtained in comparison to commercial materials.
* Laboratory of Polymer Chemistry, P.O. Box 55, FIN-00014 University
** Laboratory of Physical Chemistry and Electro-chemistry, Helsinki University of Technology, P.O. Box 6100, FIN-02015 Espoo
1. M. Paronen, F. Sundholm, E. Rauhala, T. Lehti-nen and S. Hietala: Effects of irradiation on sul-fonation of poly (vinyl fluoride), J. Mater. Chem. 7(12) (1977) 2401-2406
1.6 LASER PHYSICS
We have continued to investigate lasers and to perform laser spectroscopy. Mainly we have utilized diode lasers in the red wavelength range. During the autumn Dr. Åsa M. Lindberg returned from her post-doc position in Huygens Laboratory, University of Leiden, The Netherlands. In our group her return created an interest in basic laser physical phenomena, examples of which are given in the descriptions given below. Similarly to the previous years the laboratory facilities and equipments have been utilized for educational demonstrations to groups visiting the laboratory.
SATURATION SPECTROSCOPY OF 127I AT 637 nm
Stefan Eriksson and Birger Ståhlberg
We have continued to investigate a single mode extended-cavity diode laser interaction with iodine. In our experiment we have employed two probe beams. The chopped pump beam overlapped one of the probe beams over a distance of approximately 2 cm. The iodine cell length is about 8 cm and its diameter is 1 cm. We have used pump beam powers of 0.5 - 2 mW and probe beam powers of a few tens of µW. The data collection is based on lock-in techniques. We obtain spectra of excellent signal-to-noise ratios of several transitions around the wavelength 637 nm. One conclusion our measurements give is that to ensure interaction with a selected transition, a wavementer featuring better than a gigahertz accuracy is needed. If the iodine transitions around 637 nm are going to be used for diode laser based realization of the meter, a precise and reliable wavelength reproducibility of the laser has to be developed.
ZERO-FIELD LEVEL-CROSSING OF THE NEON 2p3 - 3s2 TRANSITION
Stefan Eriksson, Birger Ståhlberg and Åsa M. Lindberg
Magneto-optical methods are very useful in inves-tigations of atomic properties. We have employed the magnetic zero-field level-crossing method to investigate the 2p3(J=0)-3s2(J=1) transtion in 20Ne. A single mode extended-cavity diode laser (l = 635.2 nm) traverses a 40 cm long neon discharge. With laser powers above 2 mW and neon pressures below 100 Pa we obtain acceptable interaction signals which are measured as a function of the longitudinal magnetic field strength. The 2p3 - 3s2 transition shows very strong interaction strength dependance on the discharge current. Optimum signal-to-noise ratios are recorded with discharge currents of a few tens of mA. A motivation to this investigation is measurements of the upper level 3s2 (J=1) Zeeman tuning properties. This level is the upper laser level for several He-Ne lasers and there is quite little experimental data on it. Be-cause this level interacts with He-Ne lasers a combination of them with diode lasers make three-level investigations possible with inexpensive laser equipments.
MEASUREMENTS OF THE STABILITY OF THE POLARIZATION STABILIZED He-Ne LASERS INCORPORATED IN THE ABSOLUTE GRAVIMETERS OF THE FINNISH GEODETIC INSTITUTE
Birger Ståhlberg and Jaakko Mäkinen*
Polarization stabilized two-mode He-Ne lasers are utilized as light sources in many gravimeters. We have continued to measure the stability of two such lasers incorporated in the gravimeters FGI and FGII. We have done the measurements four times with a few months intervals during the year. The measurements have been carried out by heterodyning the polarization stabilized lasers against an iodine stabilized He-Ne meter laser. Similarly to the previous years the results show a few MHz (i.e. a few parts in 109) differences between the measurements.
* The Finnish Geodetic Institute, Masala
HIGHER-ORDER TRANSVERSE MODES OF AN UNSTABLE-CAVITY LASER
M.A. van Eijkelenborg*, Åsa M. Lindberg, K. Joosten*, G. Nienhuis*, M.S. Thijssen* and J.P. Woerdman*
The transverse modes of an unstable cavity are rather different from the well known (Hermite-Gaussian) transverse modes of a stable cavity. A well known difference is that they have generally larger extent, so that unstable-cavity modes are often used in high-power laser applications because of the more efficient use of the gain volume. We present measurements of the higher-order transverse modes of an unstable-cavity HeXe gas laser . We have studied the one-dimensional strip-resonator modes, and the two-dimensional square- and circular-resonator modes. The experimental intensity profiles showed generally good agreement with theoretical profiles based upon virtual-source diffraction theory. We also measured the quantum-limited linewidths and excess-noise factors of several of these modes.
* Huygens Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
1. M.A. van Eijkelenborg, Å.M. Lindberg, K. Joosten, G. Nienhuis, M.S. Thijssen and J.P. Woerdman, submitted to IEEE J. Quantum Electron. 1997
OBSERVATION OF EXCESS QUANTUM NOISE IN A GEOMETRICALLY STABLE LASER
Åsa M. Lindberg, M.A. van Eijkelenborg*, K. Joosten*, G. Nienhuis* and J.P. Woerdman*
We have observed excess-quantum noise in a geometrically stable HeXe laser . This was achieved by insertion of an aperture in front of one of the laser mirrors, the aperture diameter being considerably smaller than the beam waist of the lowest-loss Gaussian mode. The measured excess-noise is as large as a factor of 15 for the smallest aperture. A simple model is introduced to calculate the transverse excess-noise factor using a far-field approximation. We have studied the square and circularly shaped aperture case, both theoretically and experimentally. Our experimental data demonstrate that the overall excess-noise factor is given by the product of the transverse and longitudinal excess-noise factors, except for the smallest circular apertures, where the results suggest that possible effects of gain- and wave-guiding need to be considered.
* Huygens Laboratory, Leiden University, P.O.Box 9504, 2300 RA Leiden, The Netherlands
1. Å.M. Lindberg, M.A. van Eijkelenborg, K. Joos-ten, G. Nienhuis, and J.P. Woerdman, to appear in Phys. Rev. A (April 1998)
MODE-CROSSING INTERPRETATION OF RESONANCES IN THE TRANSVERSE EXCESS NOISE FACTOR
Åsa M. Lindberg, G.P. Karman*, K. Joosten*, G. Nienhuis* and J.P. Woerdman*
In recent years much attention has been given to the phenomenon of excess quantum noise. The source for excess quantum noise lies in the spatial (longitudinal and transverse) nonorthogonality of modes. This gives rise to an enhancement of the noise, relative to having "one quantum-noise photon in the laser mode", by a factor K. It has been shown that the transverse K-factor can become very large for the case of a hard-edged unstable-cavity laser; in particular, the excess noise factor K of an unstable-cavity laser shows very pronounced peaks at values of the equivalent Fresnel number for which the losses of the two lowest-loss modes become equal. This makes it natural to explore the validity of a two-mode description of K. We report that the qualitative features of K are indeed revealed by a two-mode formalism . In a quantitative sense, however, the mode-crossing interpretation fails badly.
* Huygens Laboratory, Leiden University, P.O.Box 9504, 2300 RA Leiden, The Netherlands
1. Å.M. Lindberg, G.P. Karman, K. Joosten, G. Nienhuis and J.P. Woerdman, manuscript
MODE FREQUENCY PULLING IN He-Ne LASERS
Åsa M. Lindberg
Many educational institutions have access to He-Ne lasers of which most are used as good light sources in demonstrations and laboratory training. However, quite often complains by physics teachers are presented on the lack of experiments which would demonstrate features of the physics in these very common devices. In the study , it is described how to monitor and how to detect the variation of the frequency difference between two oscillating axial modes of an internal mirror helium-neon laser with the positions of the two modes under the effective gain profile. The observed phenomena, frequency pulling of the modes, is explained in a simple way by introducing the variation of the refractive index near a resonance transition. A modern student laboratory of today should have the possibilities to perform this experiment within the regular scheme of student laboratory training.
1. Å.M. Lindberg, submitted to Am. J. of Phys.
1.7. MOLECULAR PHYSICS
The Molecular Physics Laboratory, historically, has evolved around the Raman spectrometer. At present there are three research groups active in the laboratory, headed by Ass. Prof. Folke Stenman, doc. Niklas Meinander, and Dr. Berit Mannfors. The research interests of doc. Tom Sundius closely associates him with the laboratory. Dr. Sisko Maria Eskola, doc. Kim Palmö (U. of Michigan) and doc. Lars-Olof Pietilä (VTT), who did their PhD-theses in this laboratory, are also actively engaged in the research projects of the laboratory. Graduate students working in the laboratory are Lic. Phil. Stefan Söderholm, Lic. Phil. Olli-Pekka Sievänen, Lic. Phil. Jere Koskinen, M. Sc. Johanna Blomqvist, M. Sc. Leena Wallenius and Ms. Virpi Korpelainen. Two Master's theses were completed in the laboratory during 1997. Several collaborative projects with research groups both in Finland and abroad are going on.
A 2 h/week course presenting the research being done in the laboratory was offered for the second time during the autumn term. Courses on molecular physics, molecular spectroscopy, spectroscopy of liquids, intermolecular forces, molecular modeling, optics and digital spectral analysis are given at more or less regular intervals as part of the senior undergraduate and graduate program of the department.
In the following a brief summary of the current research projects is given.
BINARY INTERACTIONS IN DILUTE GASES
The focus of this work is on the empirical interac-tion energy function and polarizability function of interacting pairs of small symmetric molecules. Experimental data utilized are mainly the interaction-induced light scattering (CILS) spectrum of the gas, the refractivity of the gas, equation of state data and transport properties, such as the viscosity. The molecules under investigation have been the noble gases, mercury, and molecules with tetrahedral and octahedral symmetry, such as CH4 and SF6. The ongoing work has been reported at our national meeting .
1. N. Meinander, The interaction-induced light scattering spectrum of mercury vapour, XXXI An-nual Meeting of the Finnish Physical Society, Hel-sinki, March 13-15, 1997
TWO-DIMENSIONAL POTENTIAL ENERGY SURFACES FOR LOW FREQUENCY LARGE AMPLITUDE VIBRATIONS OF SMALL RING MOLECULES
Two-dimensional polynomial expansions of poten-tial energy surfaces for the large amplitude low frequency ring vibrations of small ring molecules of the form are optimized to the observed IR- and Raman-transitions between the vibrational levels of these coupled large amplitude vibrational modes. The potential energy surface determines the equilibrium conformation of the molecule. This is a collaboration with prof. J. Laane at the Department of Chemistry of Texas A & M University, where the experimental work is carried out.
In a paper  on the ring vibrations of phtalan, submitted in 1997, it was shown that the unusual energy level pattern observed is due to the kinetic coupling of the ring bending and flapping motions of the molecule. This was the first time such large kinetic effects have been observed in the vibra-tional energy level pattern of a molecule. A paper  on the vibrations of tetrahydrofuran-3-one was also completed last year and has been submitted to JCP. The main problem encountered here was the assignment of the observed transitions. One paper  appeared during 1997. The ongoing work has been presented at several conferences during 1997 [4-7]. 1. S. Sakurai, N. Meinander and J. Laane, Two-dimensional vibrational potential energy surface for phtalan: The effect of large coupling on vibrational quantum states, J. Chem. Phys., in press
2. SooNo Lee, N. Meinander, P. Sagear, Deb N. Nath and J. Laane, Far-infrared spectra and two-dimensional potential energy surfaces for the out-of-plane ring vibrations of tetrahydrofuran-3-one in its S0 and S1(n,p*) electronic states, submitted to J. Chem. Phys.
3. J. Choo, N. Meinander, J. R. Villarreal, and J. Laane, Far-infrared spectra and the two-dimensional potential energy surface for 5,6-dihydro-4H-thiopyran, Microchim. Acta [Suppl.] 14 (1997) 497-499
4. S. Sakurai, N. Meinander, J. Laane, and T. Klots, Infrared spectra, Out-of-Plane Ring Modes, and Potential Energy Surface for Phtalan. A case of Strong Vibrational Coupling. Proc. from the 52nd Ohio State University International Symposium on Molecular Spectroscopy, June 16-20, 1997, p. 236
5. S.-N. Lee, N. Meinander, P. Sagear and J. Laane, Far-Infrared Spectra and Two-Dimensional Potential Energy Surfaces for the Out-of-Plane Ring Vibrations of Tetrahydrofuran-3-one in its S0 and S1(n,p*) Electronic States. Proceedings from the 52nd Ohio State University International Sym-posium on Molecular Spectroscopy, June 16-20, 1997, p. 237
6. The same as 5. Abstract 139, 213th ACS Na-tional Meeting, American Chemical Society, San Francisco, CA, USA, April 13-17, 1997
7. The same as 5. Presented at the meeting Struc-tural and Mechanistic Organic Chemistry, An In-ternational Conf. in Honor of Professor Norman L. Allinger, June 3-7, 1997, Athens, Georgia, USA
GAS PHASE ANALYTICS WITH FTIR SPECTROSCOPY
Niklas Meinander and Stefan Söderholm
The possibility to use the FTIR gas analyser, GASMET, manufactured by Temet Instruments OY, for precise (better than 10-4 relative accuracy) determinations of the carbon isotopic composition in atmospheric CO2 has been investigated. This work, which involved development of the data analysis and the elimination of various instabilities of the instrumentation, has been carried out by M. Sc. Stefan Söderholm in the laboratory of prof. Jyrki Kauppinen at the Department of Applied Physics at the University of Turku. By improving the numerical data treatment it was possible to increase the precision of the determination by two orders of magnitude to about 0.07 percent in the isotopic ratio. Further improvements of the method are possible but will require modifications in the hardware. The results have been presented in the Licentiate thesis of Stefan Söderholm,  which was accepted by the Faculty of Science of the University of Turku in 1997, and at a conference. 
1. Stefan Söderholm, Utveckling av analysmetod för bestämning av 13C/12C isotopförhållandet i CO2 med FTIR spektroskopi, Licentiate thesis, University of Turku, 1997
2. S. Söderholm, N. Meinander, and J. Kauppinen, The 13C/12CIsotopic Ratio Determined by FTIR Spectroscopy, 11th International Conference on Fourier Transform Spectroscopy, Athens, Georgia, USA, Aug. 10-15, 1997, p. M 9
RAMAN SPECTROSCOPIC STUDY OF AMORPHOUS SUGARS
Niklas Meinander and Stefan Söderholm
A study of phase transitions in amorphous sugars using Raman spectroscopy was started in 1996. During 1997 measurements of Raman spectra of suchrose, fructose and glucose at different tem-peratures and with varying amounts of water have been made. The sample preparation methods have been developed and various sample holders constructed. Measurements have been done mainly with the FT-Raman equipment at the Department of Physical Chemistry, Åbo Akademi and partly with the Raman spectrometer at the Accelerator Laboratory, Department of Physics at the University of Helsinki. This is a collaboration with Dr. Yrjö Roos at the Department of Food Technology, University of Helsinki (Elintarviketeknologian laitos). The project is part of a large collaboration financed by EU which aims at understanding the rôle of sugar as a food preservative. M. Sc. Stefan Söderholm will write his PhD-thesis on the results of this project. The project has been presented at various conferences during 1997. [1-3]
1. S. Söderholm, Y. H. Roos, and N. Meinander, Characterization of Biomaterials using FT-Raman Spectroscopy, 11th International Conference on Fourier Transform Spectroscopy, Athens, Georgia, USA, Aug. 10-15, 1997, p. W 26
2. S. Söderholm, Characterization of biomaterials using Raman spectroscopy, 7th European Confer-ence on Spectroscopy of Biological Molecules, 7-12 September 1997, Madrid, Spain
3. S. Söderholm, N. Meinander, and Y. Roos, Molecular Mobility in Biopolymers Determined Using Raman Spectroscopy, XXXI Annual Conf. of the Finnish Physical Soc., Helsinki March 13-15, 1997
STUDIES OF STRUCTURE BASED PROPERTIES OF LARGE MOLECULES
Johanna Blomqvist, Virpi Korpelainen, Jere Koskinen, Berit Mannfors and Tom Sundius
In this project atomistic simulations (quantum mechanics and force field methods) are used for prediction of molecular properties based on structure in different types of molecular systems. The results obtained are also utilized in the investigation and development of (spectroscopic and molecular mechanics) force field methods. The research, described below, is divided between two research groups.
FORCE FIELD BASED MODELLING
Johanna Blomqvist, Virpi Korpelainen, Jere Koskinen and Berit Mannfors
This project aims at the construction of realistic potential energy functions for force field based simulations of polymers, catalysts, drugs, and biologically active species. The computational methods used are based on quantum mechanics, molecular mechanics, molecular dynamics, and the rotational isomeric state (RIS) model. Experimental data consist of Raman and infrared vibrational spectra and structure determinations by X-ray crystallography. Major applications are various polymer based materials, protein and drug design. Theoretical calculations have been performed using the facilities at the Center for Scientific Computing (CSC-Tieteellinen laskenta Oy, Espoo, Finland) and the Physics Computation Unit, University of Helsinki.
The research is performed in collaboration with prof. Samuel Krimm (University of Michigan, USA, molecular mechanics and dynamics, proteins), prof. Jacques Weber (University of Geneva, Switzerland, quantum mechanics, organometallics), and the modelling group at VTT Chemical Technology (Dr. Lars-Olof Pietilä, molecular mechanics and RIS simulations, polymers). The experimental part of the research has been done in collaboration with Dr. Ilpo Mutikainen at the Laboratory for Inorganic Chemistry (Department of Chemistry, University of Helsinki, X-ray crystallography).
During 1997 papers dealing with the application of different quantum chemical ab initio and density functional methods to reproduce molecular conformational properties of some conjugated systems containing heteroatoms were published [1,2]. Quantum chemical studies on pharmacologically significant molecular and ionic systems were also published or accepted for publication [2-5]. A molecular mechanics study on the reliability of simulated vibrational spectra of simple aliphatic and conjugated molecules was published . Quantum chemical and force field studies on organometallics and their substitution reactions have been continued during 1997, and manuscripts are in preparation.
Studies on crystal and molecular structures have also been continued [3,7], the most recent com-pounds studied being quinones.
The main focus of the research during 1997 has, however, been in RIS Metropolis Monte Carlo (RMMC) simulations on polymer chains containing ester groups [8-10]. The performance of the pcff-force field, generally used to generate the conformational states of polymer chains in the RMMC method, has been investigated and modified with aid of quantum chemical simulations for selected esters. The improved force field has been utilized for the prediction of various properties of polymer chains, and the results have been in excellent agreement with the experimental ones.
Molecular mechanics studies on olefins and conjugated molecules with polar bonds are in progress in collaboration with the group at the University of Michigan.
1. B. Mannfors, J. T. Koskinen, L.-O. Pietilä, and L. Ahjopalo, Density functional studies of conforma-tional properties of conjugated systems containing hetero-atoms, J. Mol. Struct. (Theochem) 393 (1997) 39-58
2. B. Mannfors, J.T. Koskinen and L.-O. Pietilä, Conformational study of glyoxal bis(amidinohydrazone) by ab initio methods, J. Mol. Struct. 415 (1997) 135-151
3. J.T. Koskinen, M. Koskinen, I. Mutikainen, B. Mannfors and H. Elo, Experimental and computa-tional studies on aminoguanidine free base, mono-cation and dication, Part I: The crystal and mo-lecular structure of aminoguanidine monohydro-chloride and the ab initio structure of the en-diamine tautomer of aminoguanidine free base, Z. Naturforsch. 51b (1996) 1771-1778
4. J.T. Koskinen, M. Koskinen, I. Mutikainen, P. Tilus, B. Mannfors and H. Elo, Experimental and computational studies on aminoguanidine free base, monocation and dication, Part II: Acid-base properties, gas phase protonation energies and total energies of two tautomers of the free base, Z. Naturforsch., in press
5. J.T. Koskinen, Experimental and Computational Studies on Aminoguanidine Free Base, Monoca-tion and Dication. Part III: Proton Affinities of Guanidine, Amino-guanidine and Glyoxal Bis(amidinohydrazone) Z. Naturforsch. 53b, in press
6. B. Mannfors, T. Sundius, K. Palmö, L.-O. Pietilä and S. Krimm, Molecular mechanics energy func-tions from vibrational spectroscopy and quantum chemistry, J. Mol Struct.408/409 (1997) 63-69
7. J.T. Koskinen, M. Koskinen, I. Mutikainen, B. Mannfors and H. Elo, Ethylmethylglyoxal bis(amidinohydrazone) dichloride-water (1/2), Acta Cryst. C52 (1996) 3167-3169
8. J. Blomqvist, L. Ahjopalo, B. Mannfors and L.-O. Pietilä, Ab initio, DFT and RIS Metropolis Monte Carlo studies of aliphatic polyesters I: The pcff force field as basis for RMMC studies, submitted for publication
9. J. Blomqvist, L. Ahjopalo, B. Mannfors and L.-O. Pietilä, Ab initio, DFT and RIS Metropolis Monte Carlo studies of aliphatic polyesters II: Conformational properties of polyglycolic and poly-L-lactic acids, manuscript in preparation
10. V. Korpelainen, L. Ahjopalo, B. Mannfors and L.-O. Pietilä, Ab initio, DFT and RIS Metropolis Monte Carlo studies of aliphatic polyesters III: Tartaric ester units in the chain, manuscript in preparation
THEORETICAL STUDIES OF THE POTENTIAL ENERGY SURFACES OF THE SILYLIUM CATIONS
In collaboration with Igor Ignatyev (Russian Academy of Sciences, St. Petersburg) a series of silylium cations has been theoretically investigated. A paper dealing with the isomers of SiC2H7 and their interconversion has already been published . In the present work , equilibrium geometries of the nine low-energy isomers and the transition states for their interconversion in the SiC3H9 system have been optimized at the SCF and B3LYP levels of theory.
1. I. S. Ignatyev and T. Sundius: Potential energy surface of the dimethylsilylium cation and mecha-nism of the isomer interconversion, Organometallics 15 (1996) 5674-5677
2. I. S. Ignatyev and T. Sundius: Mechanism of rearrangement and the alkene addition/elimination reactions of SiC3H9+, submitted to Organometallics
SCALED AB INITIO FORCE FIELDS AND TRANSITION MOMENT DIRECTIONS FOR PHENOL
In collaboration with Dr. Gábor Kerestury (Hungarian Academy of Sciences, Budapest) scaled force constants, based on DFT calculations on phenol and its deuterated derivatives, have been calculated. The force field was used to calculate transition moment vectors and IR intensities, which have been compared with experiment. A paper describing the results has been submitted .
1. G. Keresztury, F. Billes, M. Kubinyi and T. Sundius: A density functional, infrared linear dichroism and normal coordinates study of phenol and its deuterated derivatives: Revised interpretation of the vibrational spectra, submitted to J. Phys. Chem. A.
INVESTIGATION OF COMPLEX KINETICS USING RAMAN SPECTROSCOPY
Sisko Maria Eskola, Olli-Pekka Sievänen, Kari O. Eskola and Folke Stenman
The investigations of complexes of iodine with benzene and its derivatives have been continued with more accurate measurements in order to furnish material for developing the three-state model  of complex formation.
1. S. M. Eskola and F. Stenman: A three - state model for the kinetics of binary complex formation incorporating the transition state, manuscript in preparation
NUMERICAL METHODS FOR DATA ANALYSIS
Olli-Pekka Sievänen, Sisko Maria Eskola, Kari O. Eskola and Folke Stenman
A method for determining small spectral shifts using the shift theorem of the discrete Fourier trans-form has been finalized and published . It has been applied to the problem of resolving the iso-tope structure of the Raman spectrum of CCl4, of which extensive series of measurements of the spectrum has been performed in our laboratory .
The method developed for resolution enhancement of molecular spectra using linear prediction  has been applied further to the low-temperature Raman spectrum of powdered naphthalene [4-6].
Spectral analysis methods have been further developed and employed for analyzing and simulat-ing formation of surface structures [7-13].
1. S. M. Eskola and F.Stenman: Interpolation of spectral data using the shift theorem of the discrete Fourier transform, Applied Spectroscopy 51 (1997) 1179-1184
2. K. O. Eskola, O.-P. Sievänen, S. M. Eskola and F. Stenman: Resolving the isoptopic structure of the vibrational spectrum of CCl4 using the shift theorem of the discrete Fourier transform, manuscript in preparation
3. O.-P. Sievänen: Estimating optimum filter length in linear prediction, Applied Spectroscopy 51 (1997) 718-720
4. O.-P. Sievänen, Resolution enhancement of Raman spectra of solids using linear prediction, manuscript submitted for publication
5. O.-P. Sievänen, L. Wallenius, K.O. Eskola, P. Nevalainen, S.M. Eskola and F. Stenman, High-resolution Raman spectroscopy of solid naphthalene, Abstract 7.38, Proc. of the XXXI Annual Con-ference of the Finnish Physical Society, Report Series in Physics, HU-P-262, 1997
6. K. O. Eskola, O.- P. Sievänen, L. Wallenius, P. Nevalainen, S. M. Eskola and F. Stenman: High-resolution Raman spectroscopy of solid naph-talene, manuscript in preparation
7. I. Koponen, M. Hautala and O.-P. Sievänen, Simulations of ripple formation on ion-bombarded solid surfaces, Phys. Rev. Lett. 78 (1997) 2612-2615
8. I. Koponen, M. Hautala and O.-P. Sievänen, Simulations of amorphous carbon surfaces bombarded by low energy Ar-ions, Nucl. Instrum. and Meth. in Phys. Res. B 127/128 (1997) 230-234
9. I. Koponen, M. Hautala and O.-P. Sievänen, Simulations of self-affine roughening and ripple formation on ion bombarded amorphous carbon surfaces, Nucl. Instrum. and Meth. in Phys. Res. B 129 (1997) 349-355
10. I. Koponen, R. Lappalainen, M. Hakovirta, O.-P. Sievänen and M. Hautala, Simulations of sput-tering induced roughening of amorphous diamond films produced with mass separated kiloelectron-volt ion beams, J. Appl. Phys. 82 (1997) 488-490
11. I. Koponen, O.-P. Sievänen, M. Hautala and M. Hakovirta, Simulations of sputtering induced roughening and formation of surface topography in deposition of amorphous diamond films with mass separated kiloelectronvolt ion beams, J. Appl. Phys. 82 (1997) 6047-6055
12.I. Koponen, M. Hautala and O.-P. Sievänen, Simulations of ripple formation on ion-bombarded solid surfaces, Abstract 9.40 Proc. of the XXXI Annual Conference of the Finnish Physical Soci-ety, Report Series in Physics, HU-P-262, 1997
13. S.M. Eskola and F. Stenman, Probability-theoretic interpretation of energy reflection and transmission in stratified media, Abstract 7.37, Proc. of the XXXI Annual Conference of the Fin-nish Physical Society, Report Series in Physics, HU-P-262, 1997
RAMAN SPECTROSCOPY OF AROMATIC CRYSTALS
Olli-Pekka Sievänen, Leena Wallenius, Kari O. Eskola, Sisko Maria Eskola, Päivi Nevalainen and Folke Stenman
The experimental resolution of our Raman apparatus has been optimized so that spectra can be obtained with better than 0.4 cm1 resolution. The measurements of the Raman spectrum of powdered naphthalene have been concluded [1, 2], showing significant improvement of the exeprimental resolution over earlier investigations with grating spectrometers. The lines exhibiting complicated fine structure have been analyzed with the method developed in Ref. . The results show that an enhancement in resolution from the experimental value up to better than 0.1 cm1 is obtainable .
An extensive series of measurements of the Raman spectrum of anthracene has been initiated and, similarly to the ones on naphthalene, show significant improvement of experimental resolution.
1. O.-P. Sievänen, L. Wallenius, K.O. Eskola, P. Nevalainen, S.M. Eskola and F. Stenman, High-resolution Raman spectroscopy of solid naphthalene, Abstract 7.38, Proc. of the XXXI Annual Con-ference of the Finnish Physical Society, Report Series in Physics, HU-P-262, 1997
2. K. O. Eskola, O.- P. Sievänen, L. Wallenius, P. Nevalainen, S. M. Eskola and F. Stenman: High-resolution Raman spectroscopy of solid naphtalene, manuscript in preparation
3. O.-P. Sievänen: Estimating optimum filter length in linear prediction, Applied Spectroscopy 51 (1997) 718-720
OPTIMIZATION OF HOLOGRAPHIC DIFFRACTION GRATINGS
The project on developing optimization methods for spherical gratings has been brought to conclusion. The project is being developed towards the direction of using aspherical grating blanks.
OPTICS OF STRATIFIED MEDIA
Sisko Maria Eskola and Folke Stenman
The probability - theoretical description of transmission and reflection of an electromagnetic wave in a stratified medium has been concluded in its present form [1, 2]. The work is being extended in order to include amplitude interference terms and complex propagation constants.
1. S.M. Eskola and F. Stenman, Probability-theoretic interpretation of energy reflection and transmission in stratified media, Abstract 7.37, Proc. of the XXXI Annual Conference of the Finnish Physical Society, Report Series in Physics, HU-P-262, 1997
2. S. M. Eskola and F. Stenman, Probability-theoretic interpretation of energy reflection and transmission in stratified media, manuscipt submitted for publication
A simplified method based on first-order aberration theory for optimizing the imaging properties of lens and mirror systems has been developed and applied to the design of a.o. an intraoral video camera, a pair of ultralight binoculars and a bicycle headlamp [1, 2]. The method is based on using a commercial spreadsheet program linked to a separate ray tracing program written. Compared to ordinary high-end optimizing programs the present method demands a higher degree of user interaction, but is also very flexible.
1. F. Stenman, Optisen suunnittelun perusteet (Fundamentals of optical design), lectures notes for a course given to at Oy Talmu Ab (Hella Kg), Salo, Finland, 1997
2. F. Stenman, Education in applied and instrumental optics at the University of Helsinki, Fifth International Topical Meeting on Education and Training in Optics, August 19-21 1997, Delft, Christian H. F. Velzel, Editor, Proceedings of SPIE Vol. 3190 (1997) 254-360