L. Borucki

Hydrogen depth profiling using18O ions

Nuclear resonant reaction analysis techniques for hydrogen depth profiling in solid materials typically have used15N ion beams at 6.40 MeV and19F ion beams at 6.42 MeV, which require a tandem accelerator. We report a new technique using an18O ion beam at a resonance energy of 2.70 MeV, which requires only a single stage accelerator. Improved values of the nuclear parameters for the 2.70 MeV (18O) and 6.40 MeV (15N) resonances are reported. The beam energy spread was investigated for different ions and ion charge states and found to scale with the charge state. Data obtained using atomic and molecular gas targets reveal the research potential of Doppler spectroscopy. Examples of hydrogen depth profiling in solid materials using15N and18O ion beams are presented.

Gamma-ray detection with a 4π NaI spectrometer for material analysis

Abstract A γ-ray detection system with nearly 4π geometry for applications in materials science is described. The energy resolution of the NaI(Tl)-bore hole detector was found to be about 2% for 10 MeV γ-rays. The total detection efficiency has been determined to be above 80% for γ-energies between 0.5 and 20 MeV. A precision of the efficiency calibration of about 2% has been obtained for a wide range of γ-energies. The experimental results were found to be in excellent agreement with computer simulations using the GEANT computer code. The high efficiency of the system combined with its relatively high energy resolution opened a wide range of applications. Examples are the simultaneous detection of light isotopes in thin films by (d,pγ) nuclear reactions, high depth resolution profiling of isotopes by narrow, low-energy resonances in (p,γ) reactions, and hydrogen profiling using the 6.4 MeV resonance in the 1H(15N,αγ)12C reaction.

Isotopic tracing of Si during thermal growth of Si3N4 ultrathin films

Abstract We investigated the mobility of Si atoms during the thermal growth of silicon nitride films in ammonia using Si isotopic labeling, together with nuclear resonant reaction analysis for depth profiling. A thin 29Si-enriched layer of silicon with nominal thickness of 1.4 nm was deposited on a Si(001) wafer with natural isotopic composition (92.2% 28Si, 4.7% 29Si). After epitaxial recrystallisation of the enriched layer, a Si3N4 film with nominal thickness of 2.86 nm was thermally grown in ammonia atmosphere. Excitation curves of the narrow resonance in the 29Si(p,γ)30P nuclear reaction at ER = 324 keV were measured using a high efficiency γ-ray detection system (solid angle around 4π). The very close similarity between the excitation curves obtained for two pieces of the same sample, one without and one with thermal nitridation led us to conclude that the Si atoms are not mobile during thermal growth.

Total cross section of the 14N(d,pγ)15N nuclear reaction for analytical applications

Abstract In order to supply long-needed basic data for nitrogen determination in thin films by the deuteron induced gamma-ray emission method (DIGE, or d-PIGE), gamma yields of the reaction 14 N(d,pγ) 15 N were measured by bombarding thin Si 3 N 4 films on silicon substrates. The γ-rays were detected by a high efficiency detection system (solid angle around 4π, photo-peak-efficiency 47% for 8 MeV γ-rays) including a 12 in. × 12 in. NaI(Tl) bore hole detector. Total cross section curves for the γ-rays of 7.3 and 8.3 MeV are presented in the deuteron energy range of 500–1500 keV. An example of its use in determining nitrogen content of an ultra-thin silicon oxynitride films is given.

Efficient γ-ray detection in ion beam analysis☆

Abstract A γ-ray detection system of nearly 100% efficiency is described allowing analytical techniques such as nuclear reaction analysis (NRA), nuclear resonance reaction analysis (NRRA) and deuteron induced γ-ray emission (DIGME) to be performed with a minimum of beam induced sample damage. Using this system together with ion beams of low energy spread and narrow resonances at sub-Coulomb energies, NRRA can be performed with a depth resolution of about 1 nm in the surface region of a sample. The energy scanning of the accelerator and the data acquisition are performed by a computer controlled system.

Concept and status of the new sample preparation and analyzing facility at Bochum

Abstract The technical conditions of the activities at the Dynamitron Tandem Accelerator Laboratory at Bochum in the field of ion beam modification and analysis of thin films will be improved. A new 500 kV accelerator with high energy resolution of the ion beams as well as a UHV system consisting of several chambers are presently being built up. The beam lines of the new accelerator and of the 4 MV Tandem are interconnected, providing a wide range of ion species and energies at the target sites. The UHV system not only allows the use of ion beam techniques but also provides standard electron spectroscopic techniques for surface analyses. For sample preparation techniques such as standard furnace evaporation, electron gun evaporation and rapid thermal processing are available.

Interconnected UHV facilities for materials preparation and analysis

Abstract A UHV system for in-situ preparation and analysis of ultra thin films has been built. The system includes a rapid thermal processing furnace which allows production of samples over a wide range of temperatures and pressures using isotopically enriched gases. XPS, AES, and LEED analyses provide information on the surface structure and composition. With a transportable UHV chamber, the samples can be transferred to a 4π γ-ray spectrometer facility (in UHV), where analytical ion beam methods can be used to determine isotopic depth profiles and total amounts of isotopes in the films. Furthermore, an ion beam deposition facility (in UHV) can produce isotopically enriched silicon films on Si substrates for in situ isotopic tracing.

VIBRATIONS OF SURFACE ATOMS STUDIED BY NRRA

The motion of the target nuclei in the surface of a solid affects the shape of yield curves of narrow nuclear resonances. We measured yield curves for the 272 keV resonance in 21Ne(p,γ)22Na with frozen neon. The in-situ preparation of the targets and the measurements were carried out under UHV conditions. The targets were cooled by a He evaporation cryostat to temperatures below 10 K. This temperature could be maintained even with beam currents of about 1 μA. The measurements were carried out with the 400 kV high energy resolution accelerator at the University of Munster. The measured yield curves showed a huge Lewis peak with a peak-to-plateau ratio of 2.5. The influence of atomic motion on the width of the Lewis peak was calculated with two different theoretical models. The calculated values are in good agreement with the experimental width.