Total reflection x ray fluorescence analysis and related methods

Vitha, Series Editor Total-Relection X-ray Fluorescence Analysis and Related Methods SECOND EDITION REINHOLD KLOCKENKÄMPER ALEX VON BOHLEN... Total-Reflection X-Ray Fluorescence Analysi

Analytical Chemistry and Its Applications

Mark F Vitha, Series Editor

Total-Relection X-ray Fluorescence Analysis and Related Methods

SECOND EDITION

REINHOLD KLOCKENKÄMPER

ALEX VON BOHLEN

Total-Reflection X-Ray Fluorescence Analysis and Related Methods

CHEMICAL ANALYSIS

A SERIES OF MONOGRAPHS ON ANALYTICAL CHEMISTRY

AND ITS APPLICATIONS

Total-Reflection X-Ray Fluorescence Analysis and Related Methods

Second Edition

Reinhold Klockenkämper Alex von Bohlen

Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V.

Dortmund and Berlin, Germany

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Library of Congress Cataloging-in-Publication Data:

Klockenkämper, Reinhold, 1937- author.

Total-reflection X-ray fluorescence analysis and related methods.—Second edition / Reinhold Klockenkämper, Alex von Bohlen, Leibniz-Institut für Analytische Wissenschaften-ISAS-e.V., Dortmund und Berlin, Germany.

1.2.1 Retrospect on its Development 81.2.2 Relationship of XRF and TXRF 131.3 Nature and Production of X-Rays 15

1.3.2 X-Ray Tubes as X-Ray Sources 17

1.3.2.2 The Continuous Spectrum 27

1.5 Deflection of X-Rays 531.5.1 Reflection and Refraction 531.5.2 Diffraction and Bragg’s Law 591.5.3 Total External Reflection 62

2.2.1 Standing Waves in Front of a Thick

2.4.3 A Stratified Medium of Several Layers 120

3.2 High and Low-Power X-Ray Sources 130

3.3.1 Basic Setup with Bending Magnets 1363.3.2 Undulators, Wigglers, and FELs 137

3.4 The Beam Adapting Unit 150

3.7.3 Scintillation Detectors 1823.8 Spectra Registration and Evaluation 183

3.8.2 Performance Characteristics 1853.8.2.1 Detector Efficiency 1853.8.2.2 Spectral Resolution 1883.8.2.3 Input–Output Yield 1943.8.2.4 The Escape-Peak

4.1.3.4 Microdispensing of Liquids

by Triple-Jet Technology 2204.1.3.5 Solid Matter of Different Kinds 220

4.2 Acquisition of Spectra 2224.2.1 The Setup for Excitation with X-Ray

4.2.2 Excitation by Synchrotron Radiation 2254.2.3 Recording the Spectrograms 2264.2.3.1 Energy-Dispersive Variant 2274.2.3.2 Wavelength-Dispersive Mode 227

4.3.1 Shortcomings of Spectra 2284.3.1.1 Strong Spectral Interferences 2294.3.1.2 Regard of Sum Peaks 2354.3.1.3 Dealing with Escape Peaks 2354.3.2 Unambiguous Element Detection 236

4.4 Quantitative Micro- and Trace Analyses 2384.4.1 Prerequisites for Quantification 2404.4.1.1 Determination of Net Intensities 2404.4.1.2 Determination of Relative

4.4.3.2 Residues of Microliter Droplets 2514.4.3.3 Coherence Length of Radiation 2524.5 Quantitative Surface and Thin-Layer Analyses

4.5.1 Distinguishing Between Types

4.5.1.1 Bulk-Type Impurities 2574.5.1.2 Particulate Contamination 2584.5.1.3 Thin-Layer Covering 2594.5.1.4 Mixture of Contaminations 2594.5.2 Characterization of Thin Layers by TXRF 2624.5.2.1 Multifold Repeated Chemical

4.6.1 Recording Angle-Dependent Intensity

4.6.2 Considering the Footprint Effect 2704.6.3 Regarding the Coherence Length 2724.6.4 Depth Profiling at Grazing Incidence 2744.6.5 Including the Surface Roughness 283

5.1 Environmental and Geological Applications 292

5.4 Industrial or Chemical Applications 329

5.5.3 Textile Fibers and Glass Splinters 3635.5.4 Drug Abuse and Poisoning 365

7.1.3 Capillaries and Waveguides for Beam

Photoelectron Spectrometry 486

This second edition of the first and only monograph on total reflection X-rayfluorescence (TXRF) is thoroughly revised and updated with important devel-opments of the last 15 years TXRF is a universal and economic multielementmethod suitable for extreme micro- and trace analyses Its unique and inherentfeatures are elaborated in detail in this excellent monograph TXRF represents

an individual method with its own history and special peculiarities in comparison

to other XRF techniques, and is well established within the community ofelemental spectroscopy In particular, TXRF has been realized and understood

as a complementary rather than competitive instrument within the orchestra ofultramicro and ultratrace analytical instrumentation In different round-robintests, TXRF demonstrated its performance quite well in comparison withmethods such as ET-AAS, ICP-OES, ICP-MS, RBS, and INAA

Total reflection XRF is widely used in the analysis of flat sample surfacesand near-surface layers Here, it may be applied as a nondestructive methodespecially suitable for the quality control of wafers in the semiconductorindustry It can be used for the determination of impurities at the ultratracelevel and for mapping of the element distribution on flat surfaces In addition tothe composition, the nanometer-thickness of thin layers can be determined bytilting the sample at grazing incidence Direct density measurements are aspecial and unique feature of TXRF after sputter-etching

The authors have built a successful and well established team in the field ofTXRF for about 25 years In the first edition of this book, R Klockenkämperdescribed the principles and fundamentals of TXRF, the performance ofanalyses, and its applications After his retirement, he cooperated with A.von Bohlen in order to examine the latest developments and to place TXRF in

a leading position of analytical atomic spectrometry

Several new sections of this second edition demonstrate the essential gress of TXRF The new generation of silicon drift detectors, which are cooledthermo-electrically, is highlighted About 80 synchrotron facilities around thewhole world are listed—with work places that are dedicated solely to TXRFoffering an extremely brilliant and tunable radiation The previous fields ofapplications are enumerated and diversified, contamination control of wafers isshown to be standardized, and many new fields are represented especially inthe life sciences Combinations of different methods of spectrometry, such asNEXAFS and XANES, with excitation under total reflection build a trend and

pro-xiii

have been presented as future prospects The worldwide distribution ofTXRF’s instrumentation and its different fields of applications are evaluatedstatistically.

This articulate monograph on TXRF with several color pictures providesfundamental and valuable help for present and future users in the analyticalcommunity Many disciplines, such as geo-, bio-, material-, and environmentalsciences, medicine, toxicology, forensics, and archaeometry can profit from themethod in general and from this outstanding monograph in particular

Helmholtz-Zentrum Geesthacht Institute for Coastal Research Head of the Department for Marine Bioanalytical Chemistry

The authors are grateful to all the colleagues of our TXRF community for theirlaborious and important investigations and for manifold publications that buildthe basis of this monograph Special thanks go to the attendees of the lastconference on TXRF, who took part in the survey described in Chapter 6

We also wish to thank Mrs Maria Becker for carefully adapting the firstedition in a readable word document, and for the diligent compilation of allreferences and all the data of synchrotron beamlines Furthermore, we thankour former colleague Prof Dr Joachim Buddrus for proofreading chemicalterms and formulas Scientific and technical assistance of the Leibniz-Institutfür Analytische Wissenschaften – ISAS – e.V., represented by members of theExecutive Board, Prof Dr Albert Sickmann and Jürgen Bethke, is gratefullyacknowledged ISAS in Dortmund is supported by the Bundesministerium fürBildung und Forschung (BMBF) of Germany, by the Ministerium für Innova-tion, Wissenschaft und Forschung of North Rhine-Westphalia, and by theSenatsverwaltung für Wirtschaft, Technologie und Forschung, Berlin

It is a pleasure for the authors to thank our friend Prof Dr Andreas Prangefor providing a felicitous and penetrative foreword The authors are alsoobliged to the publishers John Wiley and particularly to Bob Esposito andMichael Leventhal for their reliable assistance, and to Dr Mark Vitha for hisgreat care in editing the manuscript We also pay tribute to the printers for theexcellence of their printing, especially to our project manager, Ms ShikhaPahuja, for the diligent organization

xv

LIST OF ACRONYMS

AC Alternating current

ADC Analog-to-digital converter

AFM Atomic force microscopy

AITR Attenuated internal total reflection

ALS Amyotrophic Lateral Sclerosis

AMC Adiabatic microcalorimeter

ANNA Activity of Excellence and Networking for

Nano-and Microelectronics AnalysisAPS Advanced photon source or American Physical Society

ASTM American society for testing and materials

AXIL Analytical X-ray analysis by iterative least squares

BCR Breakpoint cluster region (protein or gene) or

British Chemical Standard - Certified reference materialBESSY Berliner Elektronen Speicherring Gesellschaft

für SynchrotronstrahlungBRM Blank reference material

CAS Chemical Abstracts Services

CCD Charge-coupled device

CHA Concentric hemispherical analyzer

CHESS Cornell high-energy synchrotron source

CMA Cylindrical mirror analyzer

CMOS Complementary metal oxides

CMOS Complementary metal oxides semiconductor

CRM Certified reference material

CVD Chemical vapor deposition

CXRO Center for X-ray Optics and Advanced Light Source

xvii

DCM Double-crystal monochromator

DESY Deutsches Elektronen Synchrotron

DIN Deutsches Institut für Normung

DMM Double multilayer monochromator

DORIS Doppel Ring Speicher

EDS Energy-dispersive spectrometry or spectrometer

EDTA Ethylene-diaminetetraceticacid

EPMA Electron probe microanalysis

ESCA Electron spectroscopy for chemical analysis

ET-AAS Electrothermal atomic absorption spectrometry

EXAFS Extended X-ray absorption fine structure

FAAS Flame atomic absorption spectrometry

FCM Four-crystal monochromator

FEL Free-electron laser

FET Field effect transistor

FPS Flat panel sensor

FT-IR Fourier transform-infra red

FWHM Full width at half maximum

GC-MS Gas chromatography-mass spectrometry

GeLi Ge(Li) detector; Germanium drifted with Lithium ionsGE-XRF Grazing exit X-ray fluorescence

GF-AAS Graphite furnace-atomic absorption spectrometry

GI-XRD Grazing incidence X-ray diffractometry

GI-XRF Grazing incidence X-ray fluorescence

GIE-XRF Grazing incidence/exit X-ray fluorescence

GLP Good laboratory practice

HASYLAB Hamburger Synchrotron Strahlungslabor

HOPG Highly ordered (oriented) pyrolytic graphite

HPGe HPGe detector; high-purity Germanium

HPLC High-performance liquid chromatography

IAEA International Atomic Energy Agency

IC Integrated circuit

ICDD International Centre for Diffraction Data

ICP Inductively coupled plasma

ICP-MS Inductively coupled plasma-mass spectrometry

ICP-OES Inductively coupled plasma-optical emission spectrometryIDMS Isotope dilution-mass spectrometry

IEEE Institute of Electrical and Electronics Engineers

IFG Institut für Geräteentwicklung

IMEC Interuniversity Microelectronics Center

INAA Instrumental neutron activation analysis

IRMM Institute of Reference Materials and Measurements

ISO International Standard Organization

ITRS International Technology Roadmap for SemiconductorsIUPAC International Union for Applied Chemistry

JCPDS Joint Committee on Powder Diffraction Standards

JFET Junction Gate FET

KFA Kernforschungsanlage

LED Light emitting diode

LINAC Linear accelerator

MBI Max-Born Institut

MCA Multichannel analyzer

MRI Magnetic resonance imaging

MRT Magnetic resonance tomography

NEXAFS Near extended X-ray absorption fine structure

NIES National Institute for Environmental Studies

NIST National Institute of Standards and Technology

NSF Nephrogenic Systemic Fibrosis

NSLS National Synchrotron Light Source

PES Photoelectron spectrometry

PGM Plane grating monochromator

PIN Positive-intrinsic-negative

PIXE Proton or particle induced X-ray emission

PMM Primary methods of measurement

PTB Physikalisch-Technische Bundesanstalt

PVD Physical vapor deposition

QXAS Quantitative X-ray analysis system

RBS Rutherford backscattering spectrometry

RMS Root mean square (of the mean squared deviations)ROI Region of interest

RSD Relative standard deviation

SAXS Small angle X-ray scattering

SD Standard deviation, absolute value

SDD Silicon drift detector

SDi Strategic Directions International

SEM Scanning electron microscopy

SGM Spherical grating monochromator

SiLi Si(Li) detector; Silicium drifted with Lithium ionsSIMS Secondary ion mass spectrometry

SOP Standard operating procedure

SPM Suspended particulate matter

SQUID Superconducting quantum interference device

SR Synchrotron radiation

SRM Standard reference material

SSD Solid-state detector

SSRL Stanford Synchrotron Radiation Laboratory

STJ Superconducting tunnel junction

STM Scanning tunneling microscope or microscopy

TDS Total dissolved solids

TES Transition edge sensor

TXRF Total reflection X-ray Fluorescence

UCS Ultra-Clean Society

ULSI Ultra-large-scale integration

UPS Ultraviolet photoelectron spectrometry

USB Universal serial bus

XANES X-ray absorption near-edge structure

XPS X-ray photoelectron spectrometry

XRD X-ray diffractometry

XRF X-Ray fluorescence

XRR X-ray reflectometry

XSW X-ray standing waves

Chemical Compounds

APDC Ammonium pyrrolidine dithiocarbamate

DNA Deoxyribonucleic acid

h-BN hexagonal form of boron-nitride

HMDTC Hexamethylene-dithiocarbamate

mQC murine Glutaminyl cyclase

MIBK Methyl isobutyl ketone

NaDBDTC Sodium dibutyldithiocarbamate

PEDOT:PSS Polyethylenedioxythiophene: Polystyrene sulfonate

PEG Polyethylene glycol

PFA Polyfluoroalkoxy (polymers)

PTFE Polytetrafluoro-ethylenes

PMMA Polymethyl methacrylate

ROS Reactive oxygen species

TEAB Triethylamine borane

TMAB Trimethylamine borane

LIST OF PHYSICAL UNITS AND SUBUNITS

% per cent (10 2)

‰ per mill (10 3)ppm parts per million (10 6)ppb parts per billion (10 9)ppt parts per trillion (10 12)

xxii

LIST OF SYMBOLS

Symbols for Physical Quantities (in general they are unambiguous; in

excep-tional cases their meaning becomes clear by their individual context; for adetailed definition and distinction they can have indices)

α Glancing angle of incident primary beam

αcrit Critical angle of total reflection

αd glancing angle determined by the detector’s field of vision

αf Sommerfeld’s fine structure constant or glancing angle determined

by the footprint

αk glancing angles of Kiessig maxima

β Imaginary component of refractive index or ratio of electron

velocity and light velocity or take-off angle of the fluorescence

θ Polar angle of an electron’s position (in plane of the orbit)

Θ Tilt angle around horizontal x-axis (corresponds to α)

λC Compton wavelength

λcut Longest wavelength of radiation refracted at a given angle

μ /ρ Total mass-absorption coefficient

ν Frequency or index

ξ Horizontal coherence length

ρ Density of an element or material

ρ m Radius of curvature of the circular electron orbit

xxiii

σ Shielding constant or roughness

σ /ρ Mass-scatter coefficient or cross-section of X-ray scattering

τdead Dead-time or shaping time

τ /ρ Photoelectric mass-absorption coefficient

υ Phase velocity or velocity of light in a medium

φ Phase difference

Φ Angle of rotation around vertical z-axis or work function of

a spectrometer

χ Tilt correction around horizontal y-axis

ψ Azimuthal angle of an electron’s position (vertical to the orbit)

b Axis or constant of Wien’s displacement law or lattice constant

B Slope of calibration straight line or absolute sensitivity or magnetic

field strength

c Concentration or molar ratio of an element in a sample or lattice

constant

cA Area related mass of an element (area density)

cv Volume concentration of an element

c0 Light velocity in vacuo

C Particular constant

Cm Material constant determining αcrit

d Thickness of a sample or a particular layer or interplanar spacing

of a Bragg crystal

D Dead-time loss or thickness of a stack of layers

e Elementary charge of a single electron or energy necessary for a

special atomic reaction

E Energy of photons or amplitude of the electric field strength or

energy of radiation

Ebinding Binding energy of an electron within an atom

Ecrit Characteristic (central) photon energy of synchrotron radiation

Ecut Cut-off energy of refraction

Eel Kinetic energy of an electron (beam energy)

Ekin Kinetic energy of a particle

Emin Minimum photon or electron energy required or critical excitation

energy

Emax Maximum photon or electron energy accepted or photon energy

for maximum brilliance

f Absorption jump factor or frequency or length of the footprint or

parameter of fading

F Fano factor or Lorentz force or formfactor (fading coherence)

g Relative emission rate

h Planck’s constant or height

h̵ Planck’s constant over 2π

L Distance of two points

m Matrix element or mass or order of Bragg’s reflection

M Matrix, two-dimensional

M molar mass of ions or atoms

n Count rate or refractive index or number density

N Number of photons or layers or oscillations or net intensity

NA Avogadro’s constant

P Level of significance or probability or electrical power

q Charge of a particle

Q Auxiliary quantity of mass absorption

r Radius or distance from the origin or absorption jump ratio

rel Classical electron radius

Ra average roughness

R

∝ Rydberg’s constant

S Relative spectral sensitivity or Poynting vector

t Time or live time or thickness of a layer or student factor

T Acquire time or transmissivity or tilt center or temperature

υ Small volume

υ/V Dilution factor

w Width or spiked volume

wbeam beam width

W Radiant energy or window distance

x Lateral movement or axis

X Addenda of trinomial expression of fluorescence intensity

y Lateral movement or axis

z Depth in a sample normal to its surface or vertical shift

zn Penetration depth of radiation in a sample normal to its surface

Z Atomic number of a chemical element

zfade damping constant of fading

FUNDAMENTALS OF X-RAY FLUORESCENCE

X-ray fluorescence (XRF) is based on the irradiation of a sample by a primaryX-ray beam The individual atoms hereby excited emit secondary X-rays thatcan be detected and recorded in a spectrum The spectral lines or peaks of such

a spectrum are similar to a bar-code and are characteristic of the individualatoms, that is, of the respective elements in the sample By reading a spectrum,the elemental composition of the sample becomes obvious

Such an XRF analysis reaches near-surface layers of only about 100 μmthickness but generally is performed without any consumption of the sample.The method is fast and can be applied universally to a great variety of samples.Solids can be analyzed directly with no or only little sample preparation Apartfrom the light elements, all elements with atomic numbers greater than 11(possibly greater than 5) can be detected The method is sensitive down to themicrogram-per-gram level, and the results are precise and also accurate ifmatrix-effects can be corrected

Total-Reflection X-ray Fluorescence Analysis and Related Methods, Second Edition.

Reinhold Klockenkämper and Alex von Bohlen.

© 2015 John Wiley & Sons, Inc Published 2015 by John Wiley & Sons, Inc.

1

For these merits, XRF has become a well-known method of spectrochemicalanalysis It plays an important role in the industrial production of materials, inprospecting mineral resources, and also in environmental monitoring Thenumber of spectrometers in use is estimated to be about 15 000 worldwide Ofthese, 80% are working in the wavelength-dispersive mode with analyzingcrystals; only 20% operate in the energy-dispersive mode, mainly with Si(Li)detectors, and recently with Si-drift detectors At present, however, energy-dispersive spectrometers are four times more frequently built than wavelength-dispersive instruments due to the advantage the former provides in fastregistration of the total spectrum.

A spectrum originally means a band of colors formed by a beam of light asseen in a rainbow The Latin word “spectrum” means “image” or “apparition.”The term was defined scientifically as a record of intensity dependent on thewavelength of any type of electromagnetic radiation The “intensity” is to beinterpreted as a number of photons with particular photon energy Today, aspectrum can also be a record of a number of ions according to their atomicmass or it can demonstrate the number of electrons in dependence of theirelectron energy The visual or photographic observation of such a spectrum is

called spectroscopy The term is deduced from the Greek verb “σκoπειν,” which

means “to observe” or “to look at.” On the other hand, “μετρω” in Greek

means “to measure” so that spectrometry is a quantitative photoelectric

examination of a spectrum

1.1 A SHORT HISTORY OF XRF

The foundations of spectrochemical analysis were laid by R.W Bunsen, achemist, and G.R Kirchhoff, a physicist In 1859, they vaporized a salt in aflame and determined some alkaline and alkaline-earth metals by means of anoptical spectroscope Today, optical atomic spectroscopy has developed avariety of new analytical techniques with high efficiency, such as atomicabsorption spectroscopy (AAS) with flames (FAAS) or electrothermal fur-naces (ET-AAS), and the inductively coupled plasma technique (ICP) com-bined with atomic emission or mass spectrometry (ICP-AES and ICP-MS).These techniques do entail some consumption of the sample, but they arehighly suitable for ultratrace analyses of solutions

Nearly 40 years after the discovery by Bunsen and Kirchhoff, in 1895,Wilhelm Conrad Röntgen (Figure 1.1) discovered a remarkable, invisible, andstill unknown radiation, which he called X-rays This name has been adopted inthe English-speaking areas; only in German-speaking parts is the radiationcalled “Röntgenstrahlen” in his honor [1] In 1901, Röntgen was awarded thefirst Nobel Prize in Physics The great potential of X-rays for diagnosticpurposes in medicine and dentistry was immediately recognized worldwide.Furthermore, different researchers clarified the fundamentals of X-ray spec-troscopy and developed the methods of XRF (X-ray fluorescence) and XRD

(X-ray diffraction) applicable to material analysis Table 1.1 enumerates known and renowned scientists Most of them came from Great Britain andGermany and almost all of them won the Nobel Prize in physics.

well-Hendrik Lorentz found the dispersion of X-rays and studied the influence ofmagnetic fields on rapidly moving charged particles by the “Lorentz force,”which 50 years later has built the basis for beamlines at synchrotron facilities.Lord Rayleigh detected the coherent scattering of X-rays, and Philipp Lenardinvestigated cathode rays while Sir J.J Thomson verified them as negativelycharged electrons Lord Ernest Rutherford created his well-known model ofatoms containing a positive nucleus and several negative electrons Max vonLaue, Friedrich, and Knipping showed the diffraction of X-rays by the lattice ofcrystalline copper sulfate [2] and hereby proved both the wave nature of X-raysand simultaneously the atomic structure of crystals

In 1913, Sir William Henry and William Lawrence Bragg—father and son—built the first X-ray spectroscope as demonstrated in Figure 1.2 [3,4] Itconsisted of a cathode-ray tube with a Mo anode, a goniometer with a revolvingrock-salt crystal in the center, and a photographic film on the inside wall of a

Figure 1.1 Wilhelm Conrad Röntgen in 1895 (reproduced with permission of the “Deutsches

Röntgenmuseum” in Lennep, Germany).

metallic cylinder The Braggs explained the diffraction of X-rays at the dimensional crystal as their reflection at parallel planes of the crystal lattice anddetermined the wavelength of the X-radiation according to the law later calledBragg’s law Furthermore, the interplanar distance of different other crystalshad been determined Then, in 1913, Moseley established the basis of X-rayfluorescence analysis by replacing the Mo anode by several other metal plates.

three-He found his well-known law [3], which relates the reciprocal wavelength 1/λ of the “characteristic” X-rays to the atomic number Z of the elements causing this

radiation Moseley probably missed a Nobel Prize because he was killed duringWorld War I at the Dardanelles near Gallipoli when he was just 28 years old(Figure 1.3b)

In 1904, Barkla had already discovered the polarization of X-rays, which is ahint to their wavelike nature [5] Ten years later, he bombarded metals with

Figure 1.2 First X-ray spectroscope used by Moseley in 1913 (a) X-ray tube with T = metal target

that can be exchanged; S = slit; W = window; goniometer with B = base for the crystal; P = graphic film (b) A metal cylinder in front of an X-ray tube The cylinder with slit and rotating crystal in its center can be evacuated Figure from Ref [3], reproduced with permission from Taylor & Francis.

electrons, which led to the emission of X-rays as “primary” radiation Barklaexcited the materials by this primary X-rays and together with Sadler he foundtheir characteristic X-rays as “secondary” radiation [6] He showed that theelemental composition of a sample could be examined by X-radiation and wasawarded the Nobel Prize in 1917.

In contrast to the wavelike nature, Max Planck recognized the corpuscularnature of X-rays appearing as photons and Albert Einstein explained thephotoelectric effect by means of such photons Niels Bohr depicted the model

of atoms consisting of a heavy nucleus with several protons and with an outershell containing the same number of electrons These electrons were assumed

to revolve around the nucleus on several distinct orbits The periodic system ofthe elements was discovered by Dimitri Mendelejew and Lothar Meyer in 1869.The naturally existing elements ordered with increasing atomic mass had got

the place numbers Z = 1 for hydrogen (the lightest element) up to Z = 92 for uranium (the heaviest element) It could be explained now that Z is not an

arbitrary number but the number of protons in the nucleus and the number ofelectrons in the outer shells of an atom And the three anomalies of potassium,nickel, and iodine could be cleared up by the different atomic mass of theirisotopes Furthermore, six new elements could be predicted and had indeedbeen discovered in the next 20 years: the rare elements technetium, hafnium,rhenium, astatine, francium, and promethium

Manne Siegbahn got the Nobel Prize for his discoveries of X-ray spectra Hedetermined the wavelength of characteristic X-rays with high accuracy by theirdiffraction at mechanically carved gratings under grazing incidence [1] ArthurHolly Compton detected the incoherent scattering of X-rays In 1923, he alsodiscovered the phenomenon of external total reflection for X-rays [7] He

Figure 1.3 (a) Arthur Holly Compton in 1927 deriving his famous formula Photo is from the

public domain,  is expired (b) Henry Moseley with an X-ray tube in 1913 Photo is from the public domain,  is expired.

found that the reflectivity of a flat target strongly increased below a criticalangle of only about 0.1° In 1927, Compton was awarded the Nobel Prize inPhysics (Figure 1.3a) Ten years later, Debye won the Prize in chemistry for hisinvestigation of X-ray powder diffractometry And finally, Kay Siegbahn, son

of Manne Siegbahn, received the Noble Prize for the discovery of X-rayphotoelectron spectroscopy in 1981

The years of fundamental discoveries were gone now and the time ofindustrial applications began Already in 1924, Siemens & Halske (Germany)had built the first commercially available X-ray spectrometer with an openX-ray tube, revolving crystal, and photographic plate Coolidge developed avacuum-sealed cathode-ray tube as shown in Figure 1.4 Samples could easily

be excited now by X-rays instead of electrons Soller built a collimatorconsisting of several parallel metal sheets just right for the collimation of abroad X-ray beam In the 1930s, Geiger and Müller developed a gas-filledphotoelectric detector, which allowed for direct pulse-counting instead of acomplicated development of the photographic plate This detector wasreplaced by a gas-filled proportional detector and by a scintillation counter

in the 1940s Simultaneously, different analyzer crystals were produced withvarious spacings and high reflectivity, for example, lithium fluoride andpentaerythritol

Figure 1.4 X-ray tube of the Coolidge type used as an X-ray photon source (a) The vacuum-sealed

glass bulb is an engineering marvel of glass blowing workshops from 1905 Photo of the authors, reproduced with permission from “Deutsches Röntgenmuseum,” Lennep, Germany (b) Sketch of today’s X-ray tubes consisting of a metal–glass cylinder C = tungsten-filament used as the cathode;

A = metal block with a slant plane used as the anode; W = thin exit window Figure from Ref [8], reproduced with permission Copyright  1996, John Wiley and Sons.

After World War II, the first complete X-ray spectrometers became ble, developed for example, by Philips, The Netherlands, by Siemens,Germany, and by ARL, Switzerland In the 1960s, the spectrometers wereequipped with hardwired controllers, servo transmitters, switching circuits, andelectronic registration [4] In the 1970s, X-ray spectrometers became computer-controlled and automated for a high throughput of samples They were used forproduction and quality control in several branches of the metallurgical indus-try Furthermore, X-ray spectrometers were applied in the exploitation ofmineral resources and also in environmental protection At this time XRF-spectrometers filled a whole lab, but in the 1980s the lateral dimensionsdecreased In the decades since, XRF has developed into a powerful method

availa-of spectrochemical analysis availa-of materials However, classical XRF is not suitablefor ultratrace analyses and it is notorious for producing matrix effects that maylead to systematic errors Extensive efforts have been made to overcome thesedrawbacks, for example by matrix separation, thin-film formation, and mathe-matical corrections Nevertheless, the new techniques of optical atomic spec-trometry have surpassed conventional XRF in many respects

From the start in 1895, X-rays were immediately applied to medical anddental diagnosis and later on for security checks at airports, for materialanalysis, ore mining, and pollution control Furthermore, X-rays in astronomyhave enlarged our view of the universe In 1932, the “German RöntgenMuseum” was founded at Röntgen’s birthplace in Lennep, 50 km awayfrom Dortmund, Germany Today it is a global center of the life, research,and impact of Wilhelm Conrad Röntgen and presents numerous valuableoriginal objects of the discovery, development, and application of X-rays [9]

Simultaneously with the invention of semiconductor devices in the “siliconvalley” after 1970, a new kind of an X-ray detector was developed It could notonly count the individual X-ray photons but could also determine their energy.Such a Si(Li) detector was called “energy-dispersive” instead of the “wave-length-dispersive” spectrometers used so far The novel detectors were smalland compact, did not need a goniometer with an analyzing crystal, and couldcollect the whole spectrum simultaneously in a very short time

1.2.1 Retrospect on its Development

Additional important progress in XRF was made 50 years after the discovery oftotal reflection of X-rays by Compton In 1971, Yoneda and Horiuchi [10]evolved an ingenious idea of using total reflection for the excitation of X-rayfluorescence They proposed the analysis of a small amount of material applied

on a flat, even, and totally reflecting support An energy-dispersive Si(Li)detector, developed shortly before, was placed directly above the support for

sample analysis First, they determined uranium in sea water, iron in blood, andrare earth elements in hot-spring water The theoretical basis and the exper-imental conditions were subsequently investigated In Vienna, Austria,Wobrauschek wrote a PhD thesis on the subject [11], and together withAiginger, they reported detection limits of nanograms [12,13] In Geesthachtnear Hamburg, Germany, Knoth and Schwenke found element traces on theppb-level [14,15].

In the decade after 1980, a great variety of applications promoted a growinginterest, and different instruments became commercially available (the “Wobi”module of the IAEA in Vienna, Austria; EXTRA II of Seifert in Ahrensburg,Germany; Model 3726 of Rigaku, Japan; TREX 600 of Technos, Japan; andTXRF 8010 of Atomika, Munich, Germany) The number of instruments in useincreased to about 200 worldwide and the new variant of XRF turned out tohave considerable advantages for spectrochemical analysis of different materi-als At a first “workshop” in Geesthacht in 1986, the participants decided to callthe new method “total reflection X-ray fluorescence analysis” and introducedthe acronym “TXRF.” A series of biannual international meetings followed.Table 1.2 lists the years, locations, and chairpersons The papers presentedwere subsequently published as proceedings in special issues of scientificjournals, mostly of Spectrochimica Acta [16–27] The next conference will

be held in 2015 as a satellite meeting of the Denver conference in Denver,Colorado

In 1983, an angular dependence of the fluorescence intensities in the rangebelow the critical angle of total reflection was first observed by Becker

et al [28] It led to the nondestructive investigation of surface contaminationand thin near-surface layers This variant was also called “grazing-incidence”XRF In 1986, the X-radiation of a synchrotron was first used for excitation by

Iida et al [29] The high intensity, linear polarization, and natural collimation of

this X-ray source were shown to be very useful and favorable in comparison toconventional X-ray sources

In 1991, Wobrauschek, Aiginger, Schwenke, and Knoth (Figure 1.5) won thedistinguished Bunsen–Kirchhoff Prize of the DASp (Deutscher Arbeitskreisfür Angewandte Spektroskopie) for the development of TXRF In the yearsafter, first reviews and book contributions were published on the subject ofTXRF (e.g [30,31]) They enclose short surveys with some 10 to 50 pages In

1997, this monograph at hand was published in a first edition, exclusivelydedicated to TXRF It was very well received on the market and within oneyear after publication, 450 copies of the book were sold Today, it is still theonly comprehensive monograph on the field of TXRF Nearly 800 copies of thefirst edition have been distributed and nearly 350 different scientific articleshave used the book as a reference, so it is the most cited item in this field ofresearch In 2002, the English edition was translated into Chinese and offered

(Figure 1.6a) and TXRF (Figure 1.6b) within the last 40 years The number ofall XRF papers started in 1970 at a level of about 100 papers per year, remainedconstant for 20 years, and exponentially increased after 1990 to a rate of 2500papers per year Between 1970 and 1985, TXRF papers appeared onlysporadically But in the years after 1986, their number grew explosivelyfrom some 3 to about 125 papers per year with large fluctuations The impact

of the special issues after every single TXRF conference can be recognized asspecial peaks, repeating every 2 years after 1989 Altogether, 1250 articles havebeen published in the field of TXRF It is interesting to mention that only eightauthors are connected with 30% of all published papers in this field

The method of TXRF has been developed significantly and has become ahigh-performance variant of classical X-ray fluorescence For a lot of elements,the detection limits are on the pg-level and even below In general, all elementsexcept for the light elements can be detected TXRF analysis can be comparedwith ET-AAS, which is the high-power specialty of FAAS, and with ICP-MS,which even tops ICP-OES TXRF ranks high among these competitive meth-ods of element spectral analysis

In the last 15 years after the first edition of this monograph, differentreview articles on TXRF have been published summarizing new develop-ments and results [32–34] Book contributions furthermore describe thesubject with different aspects, for example, wafer analysis [35–37] Specificarticles deal with further developments, such as excitation with synchrotronradiation [38,39], with standing waves by grazing incidence [40,41], withbiological applications [42], with sample preparation [43], and with portableinstruments [44] Today, TXRF is successfully applied all over the world

Figure 1.5 Four pioneers of TXRF analysis, from left to right: Peter Wobrauschek, Hannes

Aiginger, Heinrich Schwenke, and Joachim Knoth were awarded the “Bunsen–Kirchhoff Prize” in

1991 Photo by R Klockenkämper, private property.

Figure 1.6 Number of annually published papers between 1970 and 2012 presented as bar plots.

(a) For XRF in total (b) Solely for TXRF The data came from ISI Web of Knowledge, January 2012; http://thomsonreuters.com