Research activity

Analytical applications

Development of instruments and methods

Contact: Imre Uzonyi, uzonyi (at) atomki.hu

In the 15-year-old history of the Debrecen scanning nuclear microprobe facility significant developments were achieved in the field of analytical methods and data acquisition and data evaluation systems.

Application and development of the PIXE technique [17] belong to the main activities of the IBA group. The first significant achievement in this field was the elaboration of a fundamental parameter method and a spectrum evaluation software (PIXEKLM program package [18]) for standard-less (macro)PIXE analysis.

After the installation of the microprobe a special micro-PIXE set-up was mounted, which consists of a super ultra thin windowed (SUTW) and a Be windowed Si(Li) X-ray detector for the simultaneous detection of low energy X-rays from elements down to boron and high energy X-rays of the heavy elements [19]. For the first time, quantitative PIXE analysis became available for the light elements down to B [20]. Analytical applications motivated the further developments of the micro-PIXE technique towards the direction of true elemental mapping. The newly developed PIXEKLMTPI program [5] allows:

  • quantification of elements from B to U by K, L, and M lines;
  • production of conventional intensity, concentration and STIM maps;
  • simultaneous evaluation of major, minor and trace elements.

In deuteron induced gamma ray spectrometry, quantification is usually performed with standards or can be approximately achieved by tabulated absolute thick target yields with 15 and 25% accuracy. In order to increase analytical performance, we developed a new DIGE method which is based on the application of fundamental physical parameters such as cross-sections data for deuteron induced gamma ray emission, as well as on some standard reference materials. When this work was started, cross-sections data were not available in the literature. Therefore, we started a systematic investigation and determined them experimentally from thin target gamma ray yields for Li, Be, B, O and F in the 0.6-2 MeV energy range based on the 6Li(d,pγ)7Li, 9Be(d,nγ)10B, 11B(d,pγ)12B, 16O(d,pγ)17O and 19F(d,pγ)20F nuclear reactions. Our results are published in NIM [21] as well as in the IAEA database.

An analytical technique with a special experimental setup was developed for the analysis of boron using the 11B(p,α)8Be nuclear reaction with a proton bombardment of 675 keV [22]. The achievable limit of detection is unsurpassed (5 µg/g). This technique is particularly useful in geological/geochemical studies.

Micro-RBS and micro-ERDA analysis can be performed simultaneously with micro-PIXE measurements on the nuclear microprobe. Three ORTEC-type surface barrier silicon detectors (50 mm2 sensitive area and 18 keV system energy resolution) are used for micro-ERDA and micro-RBS experiments simultaneously. The ERDA detector is placed at a recoil angle of 30° (IBM geometry) mounted with a 6 µm Mylar absorber and 1.1 mm wide vertical aperture. Two detectors collect the backscattered particles. One of them is placed at a scattering angle of 165° at Cornell geometry while the other one is set to 135° at IBM geometry. Data are usually collected in list-mode. Spectra are evaluated with the RBX [23] or WINDF [24] computer codes.

Characteristics of the technique:

  • Quantitative for absolute areal density, stoichiometry
  • Thin film thickness measurement without standards
  • Provides multi-element depth concentration profiles
  • Non-destructive analysis
  • Matrix independent (unaffected by chemical bonding states)
  • Wide range of element coverage: from B to U
  • High precision (typically ±3%) and high sensitivity
  • Depth range is from 10 nm to a few microns from the surface with a depth resolution of about 20-200 Å

A new application area of the Laboratory of Ion Beam Applications is micromachining. Proton Beam Micromachining, also known as P-beam Writing (PBW) [25], is a new direct-writing process that uses a focused beam of MeV protons to pattern various resist materials at micro and nanodimensions. (In our laboratory the micron scale is available, but there are a few state-of-the-art laboratories offering nanobeams.) The process, although similar in many ways to direct writing using electrons, offers some interesting and unique advantages. Protons, being more massive, have deeper penetration in materials while maintaining a straight path, enabling p-beam writing to fabricate three-dimensional, high aspect ratio structures with vertical, smooth sidewalls and low line-edge roughness. Calculations have also indicated that p-beam writing exhibits minimal proximity effects, since the secondary electrons induced in proton/electron collisions have low energy. A further advantage stems from the ability of protons to displace atoms while traversing material, thereby increasing localized damage especially at the end of range. P-beam writing produces resistive patterns at depth in Si, allowing patterning of selective regions with different optical properties as well as the removal of undamaged regions via electrochemical etching. In our laboratory, we have been doing micromachining since 2002.

An X-ray Fluorescence measuring system based on a medium power (Rh anode, 60 kV; 1 mA) X-ray tube is assembled. This is a quick and low-cost method for the preliminary and bulk investigation of materials.

References:

[5] I. Uzonyi and Gy. Szabó: PIXEKLM-TPI - a software package for quantitative elemental imaging with nuclear microprobe, Nucl. Instr. and Meth. B 231 (2005) 156

[18] Gy. Szabó and I. Borbély-Kiss: PIXYKLM computer package for PIXE analyses, Nucl. Instr. and Meth. B 75 (1993) 123

[19] I. Uzonyi, I. Rajta, L. Bartha, Á.Z. Kiss, A. Nagy: Realization of the simultaneous micro-PIXE analysis of heavy and light elements at a nuclear microprobe, Nucl. Instr. and Meth. B 181 (2001) 193

[20] I. Uzonyi, Gy. Szabó, I. Borbély-Kiss, Á.Z. Kiss: Calibration of an UTW Si(Li) detector in the 0.28-22.1 keV energy range at a nuclear microprobe, Nucl. Instr. and Meth. B 210 (2003) 147

[21] G.Á. Sziki, A. Simon, Z. Szikszai, Zs. Kertész, E. Dobos: Gamma ray production cross-sections of deuteron induced nuclear reactions for light element analysis, Nucl. Instr. and Meth. B 251 (2006) 343

[22] G.Á. Szíki, E. Dobos, Zs. Kertész, Z. Szikszai, I. Uzonyi, Á.Z. Kiss: A PIN detector array for the determination of boron using nuclear reaction analysis at a nuclear microprobe, Nucl. Instr. and Meth. B 219 (2004) 420

[23] E. Kótai: Computer Methods for Analysis and Simulation of RBS and ERDA spectra, Nucl. Instr. and Meth. B 85 (1994) 588

[24] N.P. Barradas, P.K. Marriott, C. Jeynes, R.P. Webb: The RBS DataFurnace: Simulated annealing, Nucl. Instr. and Meth. B 136 (1998) 1157

[25] F. Watt, M.B.H. Breese, A.A. Bettiol, J.A. van Kan: Proton Beam Writing, Materials Today 30 (2007) 20