Výzkum

Ion beam analytical methods is a cluster of analytical techniques that use an ion beam for study of structures and composition of samples. The beam of the accelerated ions is applied for the surface modification of solids and for the analysis of their composition and structure. Ion beams are produced by a particle accelerator. The individual IBA techniques are distinguishable by the different types of interaction of ion beam and solid target. These methods have several unique characteristics which couldn't be substituted for other alternative approaches.

In department we use 3 MV electrostatic accelerator Tandetron 4130 MC on these purposes. In the last 10 years several equipments for analytical methods were assembled, such as: PIXE, RBS, ERDA, PIGE, NRM. Group of Nuclear Analytic Methods systematically partake in the study of synthesizing, structure and properties of advanced materials for microelectronic, optic, optoelectronic, cryogenic and materials with exclusive properties (micro-hardness, chemical resistance, bio-compatibility, etc.). Surface structures and systems prepared in cooperation with Czech and foreign institutes by different methods (epitaxial grow, Czochralsky's method, ion implantation, deposition of plasma polymer, CVD, PCVD, magnetron sputtering, etc.) are analyzed in our laboratory with different analytical methods. Group of Nuclear Analytic Methods systematically partake in the study of synthesizing, structure and properties of advanced materials for microelectronic, optic, optoelectronic, cryogenic and materials with exclusive properties (microhardness, chemical resistance, biocompatibility, etc.).

Nuclear analytic methods have been developed and extensively used in the NPI since the early 60s of the last century. In particular, neutron activating analysis and prompt methods of analysis with charged particles beam and beam of neutrons was handled. During the past period several analytical methods were innovated, practical experience of their application was obtained in collaboration with many Czech and foreign scientific enterprises and organizations.

Research topics

The main field is the application of nuclear physics and physics of ionizing radiation in the field of synthesis, modification and analysis of progressive materials. Scientific activities include the application of energetic ion beams for surface and volume modifications of materials by ion implantation and irradiation, ion lithography with focused beams, single ion irradiation for the creation of micro and nanostructures with specific functional properties and applications in electronics, optoelectronics , waveguide optics, flexible microelectronics, sensors and bionics, for specific applications in microfluidic, biologically and optically active microstructures and others.

We are preparing new materials, structures, composite layers, nano and microstructured materials based on semiconductor crystals, glasses, polymers, polymer composites with nanoparticles and 2D materials in cooperation with a number of Czech (MFF UK, ICT Prague, Masaryk University, Institute of Plasma Physics ASCR, UJEP etc.) and foreign (BAM Berlin, Germany, HZDR Dresden-Rossendorf, Germany, University of Messina, Italy, IFIN HH, Bucharest, Romania, University of Oslo, Norway and others) workplaces.

Part of the scientific work is the preparation of new materials, followed by their characterization by ion beam analytical methods, which provide non-destructive depth element mapping, qualitative and quantitative analysis with high sensitivity and in some cases isotopically specific quantitative analysis of materials. Part of the scientific content is also the study of solids degradation due to radiation damage, analysis and simulation of emerging radiation defects, as well as the study of energy losses of energetic ions in various types of materials.

Structures and systems prepared in cooperation with our and foreign workplaces are studied using high-energy ion beams by standard methods RBS (Rutherford Backscattering Spectrometry), ERDA (Elastic Recoil Detection Analysis), PIXE (Particle Induced X-ray Emission spectroscopy) etc. on the accelerator Tandetron in NPI. We also focus on the development of innovative ionic analytical methods in our lab - RBS-channeling, PIXE-channeling - applicable for the study of crystalline materials, for structural studies, positioning of dopants in crystals, etc. RBS-channeling and ERDA-TOF methods are unique in the Czech Republic. The Time of Flight (TOF) charged particle spectrometer, design and commissioning was completed in 2007. The RBS channeling instrument was built and commissioned in 2010. For the last 5 years, our team and also focused on strengthening the theoretical basis for our experiments. We perform simulations of ion channeling phenomena, ion transmission and backscattered particle 2D map simulations in different crystallographic orientations of crystals of different type and quality, simulation of dopant positions in crystalline materials depending on experimental data using FLUX program, etc.

Ion Implantation / Irradiation:

Parameter	Description
Ion species	selected ions (typically H, He, Li, O, C, Si, Cu, F, Ag, Au, W and upon the request except noble gasses, lathanides, radioisotopes
Ion energy	600 keV - 30 MeV depending on ion species
Depth range	100 nm - several µm depends on ion energy
Fluence	10⁷ - 10¹⁶ cm^-2
Incidence angle	Standard 0°, 7°; others on request
Beam current	nA - µA
Sample size	Small pieces (cm²) Ø 80 mm
Temperature	Liquid nitrogen - 1100°C, RT, heating stage up to 600°C
Special features	quandrupole mass spectrometry; external beam irradiation of biological samples, volatile samples etc.

Ion Beam Analysis:

Method	Elements	Detection limit [at%]	Resolution depth	Resolution lateral
RBS	O - U	1	10 nm	0.5 mm
RBS and PIXE- Channelling	crystalline structure study and dopant positioning	1	10 nm	0.5 mm
ERD with He	H, D, T	0.1	30 nm	1.5 mm
ERDA TOF	H-S	0.1	15 nm	1.5 mm
PIXE	Al-U	ppm	not applicable	1 mm
µ-Probe with RBS, PIXE, PIGE				1 µm
PIGE	B, Li, Na, F, P, Al, …	1-1000 ppm	not applicable	mm
STIM	internal structure in thin samples	not applicable	not applicable	0.3 µm
PESA	H in thin samples	0.1	not applicable	1 µm

Rutherford Backscattering Spectrometry

Rutherford Backscattering spectrometry (RBS) is most commonly used non-destructive nuclear analytical methods. RBS is widely used for study of thin layers and for study of multilayer systems with thickness from nm to µm. RBS is very suitable for elemental depth analysis. From such measurement it is possible to determine, with some limitations, both the atomic mass and concentration of elemental target constituents as a function of depth below the surface.

Measurement with this method may be performed on amorphous as well as crystalline materials. It involves measurement of the numbers and energy distribution of energetic ions (usually MeV light ions such He⁺) backscattered from atoms within the near-surface region of solid targets. Ions for RBS are usually light ions (H⁺, He⁺) with energy units MeV.

Energy of backscattered ions, which we detect, is connected with energy loss in scattering on the elements nucleus and with the energy loss of ions between passing through the sample. The RBS detection limit is between 10¹¹ – 10¹⁵ at.cm^-2. RBS depth resolution is an average of 5 nm.

Features of RBS:

high sensitivity for heavy elements on a light substrates
good detection sensitivity for light elements in a heavy matrix only in special cases
good depth resolution (average 5 nm)

Parameters of RBS:

ions: H⁺, He⁺
energy of ions: order of MeV
detection limit: up to 1mg/g
depth range: about micrometer

Theory of RBS

Sample is irradiated with light ions (usually 2-3 MeV (H⁺or He⁺)) and the elastically backscattered projectiles at large angles are detected. The mass of the target atoms could be identified from the energy of the backscattered projectile. The backscattered particles are detected by the semiconductor detectors Si(Au), the accessible depth 2-10 mm. The heavy element detection limit in the light matrix is up to 1mg/g. The lower mass causes higher transferred energy. The mass resolution is given by detector energy resolution, the energy and projectile mass. The ussage of heavier ions enables us to reach the mass resolution DM<2.

Elastic Recoil Detection Analysis and Time of Flight ERDA

Elastic Recoil Detection Analysis (ERDA) is a non-destructive nuclear analytical method. ERDA is a technique for depth profiling of light elements in thin layers and in multilayer systems. Measurement with this method may be performed on amorphous as well as crystalline materials. ERDA uses high energy (~1MeV/amu) heavy-ion beams to kinematically recoil and depth profile low atomic number target atoms. The heavy ion projectile only needs to have a greater mass than the target atom. Alpha particles are commonly used to obtain recoil spectrum for hydrogen and its isotopes.

Features of ERDA:

good sensitivity for light elements
wors mass resolution
good depth resolution (average 10 nm)

Parameters of RBS:

ions: He⁺ and heavy ions
energy of ions: order of MeV for He⁺ and order of 10 MeV for heavy ions
detection limit: 1mg/g
depth range: order 100 nm

Time of flight ERDA

The mass-depth ambiguity can complicate the interpretation of ERDA spectra. This ambiguity results because the energy of the recoiled ions depends on the mass and depth of the target atom in the sample. Here is a benefit of Time of flight - ERDA (TOF-ERDA), the recoil ion energy and mass we can measured independently. TOF-ERDA measured simultaneous the velocity and energy of the recoiled atoms from the target. The velocity of recoil atoms is determined by measuring the time required to pass between two thin foils at TOF1 ad TOF2 with a corresponding TOF distance. As the atoms passes through the foil, secondary electrons are ejected and accelerated into detector to mark a timing event.

Ions for TOF-ERDA ranging from O to Au at tens of MeV.

RBS channeling

RBS-channeling spectrometry - enables us to investigate crystalline materials. RBS channeling is based on channeling of charged particles in single crystalline structure and back-scattered ion yields in the spectra when the beam is parallel to crystallographic orientation axis can give us information about the damage and disorder depth profiles, dopant positioning and damage depth accumulation. For RBS channeling are typically used ion beams of 1-2 MeV He⁺ ions.

Simultaneous acquisition of back-scattered ions and induced X-ray emitted via RBS and PIXE detectors depending on impinging ion beam angle can give us comprehensive information about even lighter dopant positions in heavy element matrix.

PIXE, PIGE and PESA

Particle Induced X-Ray Spectroscopy (PIXE) is a very sensible non-destructive ion beam analytical method for elemental composition study. PIXE is very suitable for a study of area and bulk concentration of elements not for depth analysis. Basees for this method is that the high energetic proton beam excites, due to inner-shell ionization, the emission of characteristic X-rays from the sample atoms. Particle Induced Gamma-ray Spectroscopy (PIGE) is a versatile technique, which complements other ion beam techniques (especially PIXE) for sample analysis. It is the most common application of nuclear analysis. The PIGE method is mostly based on nuclear reactions (p, g), (p,p´g), (p, a g) induced by MeV protons, where prompt nuclear gamma-rays are produced. PIGE is very suitable for light elements analysis.

In the true sense, PIXE is not a nuclear technique, since the ionisation of the atoms by the ion beam and the subsequent emission of characteristic X-rays are purely atomic electromagnetic processes. Great benefit of PIXE is possibility of measurement at atmospheric pressure.

Features of PIXE and PIGE:

high sensitivity
measurement at atmospheric pressure

Parameters:

ions: H⁺
energy of ions: order of MeV
detection limit: up to 100 ppm (PIXE), 1000 ppm (PIGE)
depth range: order of ten micrometer

Ion Micro-beam

Basic idea of this method is focusing of a ion beam on the smallest dimension and scanning on the sample. Ion beam analytical methods are the same as with normal dimensions – classical ion beam methods (RBS, PIXE, PIGE). Ion micro-beam is versatile equipment that allows study of structures with resolution of microns. Compared to electron micro-beam have better detection limits and may study the trace quantity. Moreover one can use micro-beam for other application like proton writing.

Beam characteristic

Objects slits to sample	5m
Objects slits to collimator	4m
	Typical current
Objects slits (openning alternativelly)	20x80 µm²	40-50 pA
	30x120 µm²	70-100 pA
	40x160 µm²	100-200 pA
with sputter source	60x240 µm²	50-100 pA
Collimator slits	800x800 µm²
Energy (standard)	2 MeV
Other tested	from 0.8 MeV to 2.6 MeV (11.5 MeV for C⁴⁺)
Ions (tested)	H⁺, He⁺,C⁴⁺
Typical brightness (2 MeV protons)
Duoplasmatron	0.4 pA/µm² mr² MeV
Cs sputter source	0.1 pA/µm² mr² MeV

ion_microbeam

Ion beam implantation

Ion beam implantation is a process when accelerated ions are shooting into the solid. This methods is optimal for change of physical, chemical, electric or optic properties of the solid. Ion beam implantation is capable of preparation of layers with high density and good defined depth profile and for change of crystalline structure of substrate.

Application of ion beam implantation:

doping of semiconductors
doping of insulators with metal ions
creation of nanoparticles
change of electric and optic properties of solid

implant_chamber2

The typically produced ion beams available at Tandetron facility are provided in the table with the appropriate ion beam currents. The additionally requested ions for your experiments must be consulted with the instrument responsible and tested before the experiment will be proposed at Tandetron in the frame of CANAM.

Ing. Jiří Novotný, RNDr. Vladimír Havránek, CSc.

Annotation:

This is software dedicated for an automatic ion implantation of set of samples as an extension for an implantation chamber commercially manufactured by High Voltage Ltd. In the chamber, there is a manually rotated carousel for 12 samples and four Faraday cups are used for ion current measurements. Automatic sample implantation is realized using a stepping motor connected to the chamber; to indicate the sample in the implant position micro switches are used. The programme (written in LabView, Austin, USA) needs input data: the terminal voltage of the accelerator, ion charge and the required fluence ions/cm², which is entered into a table for each sample. The programme calculates the implantation parameters for set input data and evaluates its viability as a electrostatic steering of ion beam in X and Y, the number of pulses of the integrator. Further, the program operates the Faraday Cup located in the beamline for the beginning and the end of the implantation. During implantation, the following values are displayed: ion energy, the estimated time of implantation, current (nA/cm²), real counts, implanted fluence (ions/cm²), the time until the end of implantation, the current position of the carousel and the LED display of the sample position. For the event of a shutdown status of the implantation is every minute written into a file. At the end of the implantation is the implantation protocol written into the same file.

For the positioning of the beam over the sample, the programme graphically shows the calculated location of four Faraday cups and determines the geometric centre, to which the sample for the implantation is placed.

This software improves significantly the implantation procedure; saving the processing time of the accelerator during the implantation. It does not require the presence of the operator, thus lowering the costs of the sample implantation.

LabView program for Profile Beam Monitor

Authors:

Ing. Jiří Novotný, RNDr. Vladimír Havránek, CSc.

Annotation:

The functional sample program is expanding the commercial Beam Profile Monitor from NEC Ltd. Originally, the monitor had to be connected to an oscilloscope and it was quite complicated to measure the ion beam profile. The program (written in Labview, Austin, USA) replaced the oscilloscope and the measurement became simpler and clearer. The programme displays peaks in planes X and Y, color-coded quantity of cutting axes X and Y, and the integral spectrum in X and Y.

Since it is not necessary to connect to the oscilloscope, the information about the shape and location of the ion beam is quickly graphically indicated, saving the operator time and the machine time of the accelerators.

Software for the positioning during the irradiation on the external beam

Authors:

Ing. Jan Vitner, M. Davidkova

Annotation:

SW is used for precise positioning of samples exposed to the ion beam radiation in the ambient atmpsphere. There is a positioning device driven by two electromotors, which are controlled by the developed SW. SW allows us to control the positioning device in precision about 0,001 mm in two axis, thus the areal scanning is available. Thus we are able to irradiate the samples, which can not be placed in vacuum conditions (e.g. living cells), with the defined mathematical procedure to cover the requested irradiation area homogeneously by ion beam with maximum beam spot 1 mm² . We can choose the size of the area exposed to the radiation, to choose the quantity of the radiation (ion fluence) and to achieve uniform radiation of the sample with very low fluencies 10⁴ iontů/cm^-2.

The gate of the ion beam

Authors:

Václav Kučírek, Vladimír Havránek RNDr., CSc., Vladimír Semián, Pavel Plocek

Annotation:

It is a source of pulses plus and minus one hundred volts with a very short rising and falling edge (less than 0.2 microseconds). Normally, the output is exactly at zero. Pulses can be of any length. The pulses are fed to the deflection plates. During the deflection the beam does not pass through the ion line but ends on the screens. Actuating: TTL signal.

Indicator of neutron flux

Authors:

Václav Kučírek, Jiří Vacík Ing., CSc.

Annotation:

It is uni-module unit NIM comprising eight highly stable sources of spectrometric pulses with independently adjustable polarity and independently adjustable amplitude from zero to five volts. The device further includes a spectrometric amplifier and the related upper discriminator. From the output of the discriminator the output pulses are synchronized. To synchronize the output pulses is also possible to use external pulses or internal generator.

Internal television system

Authors:

J. Kučírek, J. Novotný, V. Semián

Annotation:

It is a closed television system for distributing signals from many cameras to two output channels, and also on several monitors. The system can be independently controlled from multiple locations including several lines RS232.

Beam Current Measuring System of the Shadowing Shields

Authors:

Ing. Jan Vitner, Václav Kučírek, Ing. Martin Švider, Pavel Plocek, Vladimír Semián

Annotation:

The system is used for the measuring of an accelerator beam of particles. There are four movable shields placed across the beam line in two rectangle axes in all directions. The beam can be falling to each of them by its small part. Each shield can evoke a current flowing between the shield and the developed measuring device. The device is able to measure the current flowing from each of those shields and the device is able to screen measured data by itself or the data could be send to an computer to be screened by a special program, which is an component of the whole developed system. Thanks to this system, we are able to center the beam. The output information is the value of the current flowing from each shield, which represents the value of the charge fallen to the current shield.