Handbook of Analytical Methods for Materials Part 2 ppt

AUGER ELECTRON SPECTROSCOPYDESCRIPTION OF TECHNIQUE Auger Electron Spectroscopy AES provides information about the chemical composition of the outermost material comprising a solid surfa

AUGER ELECTRON SPECTROSCOPY

DESCRIPTION OF TECHNIQUE

Auger Electron Spectroscopy (AES) provides information about the chemical composition of the

outermost material comprising a solid surface or interface The principal advantages of AES over

other surface analysis methods are excellent spatial resolution (< 1 µm), surface sensitivity (~20 Å), and detection of light elements Detection limits for most elements range from about 0.01 to 0.1 at%

AES uses a primary electron beam to excite the sample surface When an inner-shell electron is

ejected from a sample atom by the interaction with a primary electron, an electron from an outer shell fills the vacancy To compensate for the energy change from this transition, an Auger electron or an x-ray is emitted For light elements, the

prob-ability is greatest for the emission of an Auger

electron, which accounts for the light-element

sensitivity for this technique

The energy of the emitted Auger electron is

characteristic of the element from which it was

emitted Detection and energy analysis of the

emitted Auger electrons produces a spectrum

of Auger electron energy versus the relative

abundance of electrons Peaks in the

spec-trum identify the elemental composition of the

sample surface In some cases, the chemical

state of the surface atoms can also be

deter-mined from energy shifts and peak shapes

Auger electrons have relatively low kinetic

energy, which limits their escape depth Any Auger electrons emitted from an interaction below the surface will lose energy through additional scattering reactions along its path to the surface Auger electrons emitted at a depth greater than about 2 - 3 nm will not have sufficient energy to escape the surface and reach the detector Thus, the analysis volume for AES extends only to a depth of about 2

nm Analysis depth is not affected by the energy of the primary electron energy

The AES instrumentation can include a tungsten filament or field emission electron gun for the primary electron beam The instruments are equipped for secondary electron imaging (SEM) to facilitate

location of selected analysis areas, and micrographs of the sample surface can be obtained The

sample chamber is maintained at ultrahigh vacuum to minimize interception of the Auger electrons by gas molecules between the sample and the detector Some instruments include special stages for

fracturing samples to examine interfaces that have been freshly exposed within the vacuum chamber

A computer is used for acquisition, analysis, and display of the AES data

AES Spectrum for Passivated Stainless Steel

ANALYTICAL INFORMATION

Survey Scan - The position of the peaks in the AES

spectrum obtained in a survey scan identifies the

elemental composition of the uppermost 20 Å of the

analyzed surface

Multiplex Scan - A higher resolution analysis of the

Auger spectrum in the region around a characteristic

peak is used for determination of the atomic

concen-tration of the elements identified in the survey scans

and, in some cases, chemical state information

Quantitation - The AES analysis results can be

quantified without standards by using the area under the peaks in the AES spectrum and corrections based on elemental sensitivity factors

Mapping and Line Scans - These are imaging techniques that measure the lateral distribution of

elements on the surface The electron beam is scanned across the sample surface, either along a fixed line (line scan) or across a given area (mapping) while the AES signal is analyzed for specific energy channels The AES signal intensity is a function of the relative concentration of the element(s) corre-sponding to the selected energy channel(s) Spatial resolution is approximately 0.3 µm

Depth Profile - Material is removed from the surface by sputtering with an energetic ion beam concurrent

with successive AES analyses This process measures the elemental distribution as a function of depth into the sample Depth resolution of < 100 Å is possible

TYPICAL APPLICATIONS

• Microscopic particle identification

• Passive oxide film thickness

• Contamination on integrated circuits

• Quantitation of light element surface films

• Mapping spatial distribution of surface

constituents

SAMPLE REQUIREMENTS

Samples should be no larger than approximately 3/4 in by 1/2 in (18 mm by 12 mm) Height of samples should not exceed 1/2 in (12mm) Samples must be conductive or area of interest must be properly grounded Insulating samples, including thick insulating films (>300 Å), cannot be analyzed Samples must also be compatible with a high vacuum environment (<1x10-9 Torr)

A UGER E LECTRON S PECTROSCOPY

Auger maps of defect in glass coating (250x250 mm)

Composition Profile for Ni-Ti Alloy

ENERGY DISPERSIVE X-RAY SPECTROSCOPY

DESCRIPTION OF TECHNIQUE

Energy Dispersive X-Ray Spectroscopy (EDS or EDX) is a chemical microanalysis technique used in conjunction with scanning electron microscopy (SEM) (See Handbook section on SEM.)The EDS technique detects x-rays emitted from the sample during bombardment by an electron beam to

characterize the elemental composition of the analyzed volume

Features or phases as small as 1 µm or less can be analyzed

When the sample is bombarded by the SEM's electron beam,

electrons are ejected from the atoms comprising the sample's

surface The resulting electron vacancies are filled by electrons

from a higher state, and an x-ray is emitted to balance the

energy difference between the two electrons' states The x-ray

energy is characteristic of the element from which it was emitted

The EDS x-ray detector measures the relative abundance of

emitted x-rays versus their energy The detector is typically a lithium-drifted silicon, solid-state device When an incident x-ray strikes the detector, it creates a charge pulse that is proportional to the energy

of the ray The charge pulse is converted to a voltage pulse (which remains proportional to the x-ray energy) by a charge-sensitive preamplifier The signal is then sent to a multichannel analyzer where the pulses are sorted by voltage The energy, as determined from the voltage measurement, for each incident x-ray is sent to a computer for display and further data evaluation The spectrum of x-ray energy versus counts is evaluated to determine the elemental composition of the sampled volume

ANALYTICAL INFORMATION

Qualitative Analysis - The sample x-ray energy values from the EDS spectrum are compared with

known characteristic x-ray energy values to determine the presence of an element in the sample

Elements with atomic numbers ranging

from that of beryllium to uranium can be

detected The minimum detection limits

vary from approximately 0.1 to a few

atom percent, depending on the element

and the sample matrix

Quantitative Analysis - Quantitative

results can be obtained from the relative

x-ray counts at the characteristic energy

EDS Spectrum for Alloy MP35N

Elemental Map for the Microstructure of a White Iron Casting

levels for the sample constituents Semi-quantitative results are readily available without standards by using mathematical corrections based on the analysis parameters and the sample composition The accuracy of standardless analysis depends on the sample composition Greater accuracy is obtained using known standards with similar structure and composition to that of the unknown sample

Elemental Mapping - Characteristic x-ray intensity is measured relative to lateral position on the

sample Variations in x-ray intensity at any characteristic energy value indicate the relative concentra-tion for the applicable element across the surface One or more maps are recorded simultaneously using image brightness intensity as a function of the local relative concentration of the element(s) present About 1 µm lateral resolution is possible

Line Profile Analysis - The SEM electron beam is

scanned along a preselected line across the sample while

x-rays are detected for discrete positions along the line

Analysis of the x-ray energy spectrum at each position

provides plots of the relative elemental concentration for

each element versus position along the line

TYPICAL APPLICATIONS

• Foreign material analysis

• Corrosion evaluation

• Coating composition analysis

• Rapid material alloy identification

• Small component material analysis

• Phase identification and distribution

SAMPLE REQUIREMENTS

Samples up to 8 in (200 mm) in diameter can be readily analyzed in the SEM Larger samples, up to approximately 12 in (300 mm) in diameter, can be loaded with limited stage movement A maximum sample height of approximately 2 in (50 mm) can be accommodated Samples must also be compat-ible with a moderate vacuum atmosphere (pressures of 2 Torr or less)

E NERGY D ISPERSIVE X-R AY S PECTROSCOPY

EDS Linescan Across Plated PCB Layers

FOURIER TRANSFORM-INFRARED SPECTROSCOPY

DESCRIPTION OF TECHNIQUE

Fourier Transform-Infrared Spectroscopy (FTIR) is an analytical technique used to identify organic (and in some cases inorganic) materials This technique measures the absorption of infrared radiation

by the sample material versus wavelength The infrared absorption bands identify molecular compo-nents and structures

When a material is irradiated with infrared radiation, absorbed IR radiation usually excites molecules into a higher vibrational state The wavelength of light absorbed by a particular molecule is a function

of the energy difference between the at-rest and excited vibrational states The wavelengths that are absorbed by the sample are characteristic of its molecular structure

The FTIR spectrometer uses an interferometer to modulate the wavelength from a broadband infra-red source A detector measures the intensity of transmitted or reflected light as a function of its

wavelength The signal obtained from the detector is an interferogram, which must be analyzed with a computer using Fourier transforms to obtain a single-beam infrared spectrum The FTIR spectra are usually presented as plots of intensity versus wavenumber (in cm-1) Wavenumber is the reciprocal of the wavelength The intensity can be plotted as the percentage of light transmittance or absorbance at each wavenumber

ANALYTICAL INFORMATION

Qualitative Material Identification - To identify the material being analyzed, the unknown IR

absorption spectrum is compared with standard spectra in computer databases or with a spectrum obtained from a known material Spectrum matches identify the polymer or other constituent(s) in the sample Absorption bands in the range of 4000 - 1500 wavenumbers are typically due to functional groups (e.g., -OH, C=O, N-H, CH3, etc.) The

region from 1500 - 400 wavenumbers is

referred to as the fingerprint region Absorption

bands in this region are generally due to

in-tramolecular phenomena and are highly specific

to each material The specificity of these bands

allows computerized data searches within

reference libraries to identify a material

Quantitation - Quantitative concentration of a

compound can be determined from the area

under the curve in characteristic regions of the

FTIR Spectrum for Paint Analysis

F OURIER T RANSFORM -I NFRARED S PECTROSCOPY

IR spectrum Concentration calibration is obtained by establishing a standard curve from spectra for known concentrations

TYPICAL APPLICATIONS

• Identification of foreign materials

- Particulates

- Fibers

- Residues

• Identification of bulk material compounds

• Identification of constituents in multilayered materials

• Quantitation of silicone, esters, etc., as contamination on various materials

SAMPLE REQUIREMENTS

Sample requirements vary depending on the sample form and instrument Samples may be in liquid, solid or gaseous form When using a microscope attachment on the spectrometer, the analysis area can be as small as 10 µm Thin organic films on a reflective surface (e.g., gold) can be analyzed in situ using the microscope's reflectance mode The outer 1-10 µm of a material can be analyzed using attenuated total reflectance (ATR)

GAS CHROMATOGRAPHY / MASS SPECTROSCOPY

DESCRIPTION OF TECHNIQUE

Gas chromatography / mass spectrometry (GC/MS) is the marriage of two analytical methods into a versatile technique for the identification of complex volatile materials Gas chromatography (GC)

effectively separates the different constituents of the sample for subsequent analysis and identification

by mass spectrometry (MS)

The chromatographic separation relies on the interaction of the sample with a mobile phase and a

stationary phase within the GC instrument column The sample is carried through the column by the mobile phase, typically an inert gas However, the sample is slowed in its travel through the column as the sample molecules repeatedly adsorb and desorb from the stationary phase in the column The affinity of a particular molecule for the stationary phase determines the retention time of that constitu-ent in the column The molecules for each componconstitu-ent of

the sample will travel through the column at nearly the

same rate and exit (elute) from the column within a

narrow time band that is specific to that component

Thus, compounds with different retention times in the

column are physically separated for presentation to a

detector and analyzer

The typical GC capillary column consists of a

small-diameter tube with a thin film of a

high-molecular-weight polymer coated on the inside The polymer is the

stationary phase for the chromatographic process The

mobile phase can be any inert gas, but is typically

helium The instrument also includes a heated injection

port to vaporize all volatile constituents of the sample and an oven to keep the constituents in gas

form as they pass through the column

As a sample constituent elutes from the GC column, it enters the ionization chamber of the mass

spectrometer where the molecules are ionized, typically by electron impact When an electron impact with a sample molecule results in the loss of an electron from the molecule, a positive ion is formed Some of the molecular ions are further fragmented into daughter ions and neutral fragments The

positive ions are then repelled out of the ionization chamber by a small positive charge within the

chamber Negative ions are also formed by the electron impact, but are not analyzed

The positive ions are separated according to their mass by a mass analyzer The mass analyzer most commonly used in GC/MS is the quadrapole filter, in which the ions pass by four hyperbolic magnetic poles created by a radio frequency field The magnetic poles separate the ions by their mass/charge ratio, successively focusing ions with increasing mass onto a detector for counting The analyzer scans step-wise through a set range of mass values to evaluate the relative abundance of ions at each mass value The quadrapole filter can perform a complete mass scan within the duration of a single GC

elution band

Total Ion Chromatogram for Two Vegetable Oils

ANALYTICAL INFORMATION

Material Identification - The first result from the compiled data is a total-ion chromatogram (TIC),

which is a plot of the total mass eluting from the GC and detected by MS as a function of time Each peak or band in the chromatogram represents a discrete chemical compound, or a mixture of com-pounds with identical retention times The

reten-tion times in the chromatogram provide the first

indication of the sample constituents

More specific identification of the compound(s)

for each band can then be made from the mass

spectrum corresponding to the band

Com-pounds are identified from the mass spectrum by

their unique ion fragmentation patterns This

compound identification analysis is performed by

a computerized comparison of the mass spectra

for the sample with spectra library for known

compounds

Quantitation - The analysis results can be quantified using the data from the chromatogram The

area under each peak in the chromatogram is proportional to the concentration of the compounds represented by that peak The concentration for each compound in the sample is calculated from a standard curve of known concentrations established for that compound The analysis sensitivity can

be as low as a few nanograms

TYPICAL APPLICATIONS

• Identification of foreign material contamination

• Analysis of outgassing products for disk drive components

• Identification of polymer additives

• Analysis of polymer cure by-products

SAMPLE REQUIREMENTS

The samples for GC/MS can be gases, liquids, or solids However, only those constituents that are gaseous and stable at the analysis temperature can be analyzed Gases and liquids can be injected directly into the sample injector Volatile compounds from solid materials are collected using a

headspace sampler The sample from a headspace attachment can be collected and injected at one time (static headspace), or the sample can be collected and analyzed continuously over a set time period (dynamic headspace)

G AS C HROMATOGRAPHY /M ASS S PECTROSCOPY

Chromotagram for Outgassing Compounds from Two Epoxies

ION CHROMATOGRAPHY

DESCRIPTION OF TECHNIQUE

Ion chromatography (IC) is the separation and quantitative analysis of anions and cations in an ionic solution using the ion exchange method of liquid chromatography (LC) The chromatographic process separates the different ions within the sample The amount of an anion/cation is measured by the

change in conductivity as the species passes through the detector

The ions in the sample solution are carried through the system by an ionic solution, or eluent (mobile phase) The different ions in the eluent are separated in a column packed with an ion exchange resin (stationary phase) The resin has a thin surface layer of

active material with limited ion exchange sites If anions are

to be analyzed, the active sites will have a fixed positive

charge to attract the anions Resins for cation analysis will

have a negative charge Individual ions attach and detach

from the resins at a rate depending on the affinity of the

specific ion to the active sites Ions with greater affinity for

the stationary phase are retained in the column for a longer

time than those with less affinity for the stationary phase

Thus, the ions of particular chemical species in the solution

exit or elute from the column within a narrow time band

specific to that ion The detector at the end of the column

continuously measures the conductivity of the eluent to determine the quantity of the eluting ions as a function of time The data from the detector are compiled into a plot of ion abundance versus time, referred to as a chromatogram The position of a peak in the chromatogram is characteristic of a

specific ion The peak size is a function of the concentration for the ion represented by that peak

ANALYTICAL INFORMATION

Material Identification - The presence of specific anions and cations in the sample can be

determined through comparison of the sample chromatograms against results for known refer-ence materials

Quantitation - Anion and cation concentrations can be quantified by establishing a standard curve of

known concentrations for each species The peak height or the area under the peak in the chromato-gram for each anion or cation is compared to the standardization curve to determine the concentration

of the ion the sample

Sensitivity - Minimum concentration detection limits can be as low as a few parts per billion (ppb).

Ion Chromatogram

TYPICAL APPLICATIONS

• Determination of ionic species in plating baths

• Determination of acidic thermal decomposition products of polymer materials

• Determination of ionic contamination on critical components

MINIMUM DETECTION LIMITS FOR IC

SAMPLE REQUIREMENTS

Samples must be immersible in a solution that is compatible with the LC system, or the components

of interest must be extractable from the sample Components must cause a change in the conductivity

of the solution to be detected

I ON C HROMATOGRAPHY

Sulfate (SO

4