From Microsystems to the Nanoworld - uni-freiburg.de · Svetlana Santer Freiburger Materialforschungszentrum Institut für Mikrosystemtechnik From Microsystems to the Nanoworld Svetlana

Svetlana SanterFreiburger Freiburger

MaterialforschungszentrumMaterialforschungszentrum

Institut für Institut für

MikrosystemtechnikMikrosystemtechnik

From Microsystems to From Microsystems to

the the NanoworldNanoworldSvetlana Santer

Svetlana Santer

Two commonly used techniques for Two commonly used techniques for high high resoluiotn surface investigationsresoluiotn surface investigations

��AtomicAtomic Force Force MicroscopyMicroscopy (AFM)(AFM) ��Scanning Electron Microscopy Scanning Electron Microscopy (SEM) (SEM)

50 nm

Piezo

Sample

Cantilever

Tip

PSDLaser

��Resolution down to Resolution down to the nanometer scalethe nanometer scale

��Different Different types types of of information about the surface structureinformation about the surface structure

Svetlana Santer

Electrons are generated andfocused onto a sample and imaging is performed by viewing the backscattered electrons.

The "Virtual Source" at the top represents the electron gun,producing a stream ofmonochromatic electrons.

A set of coils then "scan" or"sweep„ the beam in a grid fashion (like a television),dwelling on points for a period of time determined by the scan speed (usually in the microsecond range)

SEMSEM

Svetlana Santer

When the electron beam hits the sample, the interaction of the beam electrons from the filament and the sample atoms generates avariety of signals.

•secondary electrons (produced by interactionof primary e with the loosely held outerelectrons of the sample),

•backscattered electrons (beam electrons from the filament that bounce off nuclei of atomsin the sample(elastic-interaction of theprimary electrons with the nucleus of theatom),

•X-rays, light, heat,

•transmitted electrons (beam electrons thatpass through the sample).

Principles Principles of SEM of SEM ImagingImaging

�Secondary electrons: high spatial resolution, good topographic sensitivity

�Backscattered electorns: they have more energy and can escape from greater depths, carry some informartion of sample composition

Svetlana Santer

SampleSample--electron interactionselectron interactions

Svetlana Santer


Backscattered Electrons:

Formation: Caused by an incident electron colliding with an atom inthe specimen which is nearly normal to the incident's path. The incident electron is then scattered"backward" 180 degrees.

Utilization

The production of backscattered electrons varies directly with the specimen's atomic number. This differing production rate causes higher atomic number elements toappear brighter than lower atomic number elements. This interaction is utilized todifferentiate parts of the specimen that have different average atomic number.

Svetlana Santer


Secondary Electrons:

Source: Caused by an incident electron passing "near" an atom inthe specimen, near enough to impart some of its energy to a lower energy electron (usually in the K-shell). This causes a slight energy loss and path change in the incident electron andthe ionization of the electron in the specimen atom. This ionized electron then leaves the atom with a very small kinetic energy (5eV) and is then termed a "secondary electron." Each incident electron can produce several secondary electrons.

Utilization: Production of secondary electrons is very topography related. Due totheir low energy, 5eV, only secondaries that are very near the surface (<10nm) can exit the sample and be examined. Any changes in topography in the sample that are larger than this sampling depth will change the yield of secondaries due to collection efficiencies. Collection of these electrons is aided by using a "collector" inconjunction with the secondary electron detector. The collector is a grid or mesh with a +100V potential applied to it which is placed in front of the detector, attracting the negatively charged secondary electrons to it which then pass through the grid-holes and into the detector to be counted.

Svetlana Santer


Auger Electrons

Source: Caused by the de-energization of the specimen atom after a secondary electron is produced. Since a lower (usually K-shell) electron was emitted from the atom during the secondary electron process an inner (lower energy) shell now has avacancy. A higher energy electron from the same atom can "fall" to a lower energy,filling the vacancy. This creates an energy surplus inthe atom which can be corrected by emitting an outer (lower energy) electron; an Auger Electron.

Utilization: Auger Electrons have a characteristic energy, unique toeach element from which it was emitted from. These electrons are collected and sorted accordingto energy to give compositional information about the specimen. Since Auger Electrons have relatively low energy they are only emitted from the bulk specimen from a depth of <3 nm.

Svetlana Santer


X-rays

Source: Caused by the de-energization of the specimen atom after a secondary electron is produced. Since a lower (usually K-shell) electron was emitted from the atom during the secondary electron process an inner (lower energy) shell now has avacancy. A higher energy electron can "fall" into the lower energy shell, filling the vacancy. As the electron "falls" it emits energy, usually X-rays to balance the totalenergy of the atom.

Utilization: X-rays or Light emitted from the atom will have a characteristic energy which is unique to the element from which it originated. These signals are collected and sorted according to energy to yield micrometer diameter) of bulk specimens limiting the point-to-point comparisons available.

Svetlana Santer

Scanning Electron MicroscopyScanning Electron Microscopy (SEM)(SEM)

The SEM uses a beam of electrons to scan the surface of asample to build a three-dimensional image of the specimen.

Major Components of the Scanning Electron Microscope

All scanning electron microscopes consist of:

1. A column which generates a beam ofelectrons.

2. A specimen chamberwhere the electron beam interacts with the sample.

3. Detectorsto monitor the different signals that result from the electron beam/sample interaction.

4. A viewing systemthat builds an imagefrom the detector signal.

Svetlana Santer

Elektronenstrahlerzeugung

Elektronen werden entweder thermisch durch Aufheizen einer Kathode (Wolframhaarnadel) auf ca. 2.500 - 2.700 °C, oder durch Feldemission aus einer feinen Spitze erzeugt.

Elektronen werden emittiert, und bilden - durch die negative Vorspannung des Wehneltzylindersgegenüber der Kathode - eine Raumladungszone.

Durch Anlegen einer Hochspannung (z.B. 100kVolt) werden die Elektronen aus der Raumladungszone zur Anode beschleunigt.

SEMSEM

Svetlana Santer

Generating the beam Generating the beam of of electronselectrons

As the filament gets used, it becomes brittle and coated. If the filament is overheated or too old, it will break.

Svetlana Santer

Generating the beam Generating the beam of of electronselectrons

Electrons are very small and easily deflected by gas molecules in the air.Therefore, to allow the electrons to reach the sample,the column is under avacuum. The vacuum is maintained by two vacuum pumps: a rotary pump and anoil diffusion pump which is housed inside the SEM and is water cooled. Thus, theSEM needs a water cooling line which filters the water before it cools the oil diffusion pump.

Vacuum: 10-4-10-10 Torr

Svetlana Santer

Detectors Detectors of of the the SEMSEM

The SEM has several detectors to view the electron signals from the sample.

(1) secondary electron detectorlooks like a Faraday cage, and detects secondary electrons.

(2) backscattered electron detector (solid state detector) is located above the sample, consists of a diode with a thin gold conductor across the front surface. Backscattered electrons have sufficient energy to pass through the front surface and produce electron hole pairs which produce a curreent in the diode

Svetlana Santer

Can we see electrons directly by eyeCan we see electrons directly by eye??

The SEM scans its electron beam line by line over the sample.

It's much like using a flashlight in a dark room to scan the room from side to side.

Gradually the image is built on a TV monitor (cathode ray tube or CRT for short). The SEM has buttonson the keyboard that control the scan speed. A fast scan which takes a couple of seconds to generate an image can be very grainy - like you're looking at an object in a snow storm. A slow scan is very clear andsharp - but takes a minute or two to get a picture.

Svetlana Santer

The magnification is changed simply by altering the size of the raster on the specimen. The magnification is merely the ratio of the viewing screen’s linear size to the linear raster size.

MagnificationThe image is therefore an array of pixels, with each pixel defined byx and y spatial coordinates and a gray value proportional to the signal intensity. Magnification of the image is defined as the length of the scanline on the monitor or recording device divided by the length of the scan line on the specimen.Magnification is therefore independent of the lenses.Magnification is adjusted by changing the size of the area scanned on the specimen while the monitor or filmsize is held constant. Thus a smaller area scannedon the sample will produce a higher magnification. This is a major strength of SEM imaging, and with optimized beam conditions and focus, the image magnification can be changed through its entire range without loss of image quality. A typical magnification range for the SEM is 10´ to 100,000´

Svetlana Santer

Sample Sample preparationpreparation

Samples have to be prepared carefully to withstand the vacuum inside the microscope. Biological specimens are dried in a special way that prevents them from shriveling. Because the SEM illuminates them with electrons, they also have to be made to conduct electricity.

Sputter coater

Svetlana Santer

HistoryHistoryMax Knoll and Ernst Max Knoll and Ernst RuskaRuska --19311931

electron microscopyelectron microscopy

Svetlana Santer

HistoryHistory

••1938 1938 –– first first SEM SEM by by von Ardennevon Ardenne

••1942 1942 –– first first SEM SEM for bulk samples for bulk samples

by Zworkinby Zworkin

••1965 1965 –– first commercila instrument first commercila instrument

(Cambridge)(Cambridge)

Resolution:Resolution:

��50 nm in 194250 nm in 1942

��0.7 nm 0.7 nm todaytoday

Svetlana Santer

Comparison Comparison of of TechniquesTechniques: AFM : AFM vs vs SEMSEM

�� Surface structureSurface structure::

••atomically smooth surfacesatomically smooth surfaces

TM-AFM image of 0.14 nm monoatomic steps on epitaxial silicon deposited on (100) Si. 1 µm scan, RMS=0.07 nm

On a On a sample this smoothsample this smooth, , the the

SEM has SEM has difficulty resolving difficulty resolving

these features due these features due to to the the

subtle variations subtle variations in in heightheight

Svetlana Santer



••Thin filmsThin films

Polysilicon thin film at approximately the same lateral magnification. But they differ in the other types of information

�AFM provides with roughness and height

�SEM provides a large area view

On On most thin filmsmost thin films, , the the SEM SEM

and AFM and AFM produce produce a a similar similar

representation representation of of the sample the sample

surfacesurface

SEMSEM

AFMAFM

Svetlana Santer



••Thin filmsThin films: : interpretation interpretation of of heightheight

GaP on Si during chemical beam epitaxy deposition

In In the the SEM image, SEM image, it can be it can be

sometimes be difficult sometimes be difficult to to

determine whether the feature determine whether the feature

is sloping is sloping up up or or downdown

Svetlana Santer



••High High Aspect Aspect Ration Ration StructuresStructures

With With AFM AFM one can measure the one can measure the

structure nondestructivelystructure nondestructively, , but but

without details without details on on the sidesthe sides

SEM SEM provides measuring the provides measuring the

undercuts undercuts of of these linesthese lines

Svetlana Santer



••Rough surfacesRough surfaces

SEM has a SEM has a large depth large depth of of fieldfield::

Ability to image Ability to image very rough very rough

surfacessurfaces

Svetlana Santer


��EnvironmentEnvironment::

Liquid cell AFM

SEM SEM is conducted is conducted in a in a vacuum vacuum

environmentenvironment

AFM AFM is conducted is conducted in in vacuumvacuum, ,

gas, liquid, gas, liquid, vapourvapour, and in an , and in an

ambient ambient environmentenvironment

Svetlana Santer

ComparisonComparison ofof TechniquesTechniques: AFM: AFM vsvs SEMSEM

Although Although SEM and AFM SEM and AFM appear very appear very different , different , they they

share share a a number number of of similaritiessimilarities

��Both techniques raster Both techniques raster a probe a probe across the surfaceacross the surface

��Similar Similar lateral lateral resolutionresolution

��Both techniques can produce artifactsBoth techniques can produce artifacts

��AFM AFM can provide measurements can provide measurements in all in all three three

dimensionsdimensions, , with with a a vertical resolution vertical resolution of <0.05 nmof <0.05 nm

��SEM has SEM has the ability the ability to image to image very rough surfacesvery rough surfaces

SEM and AFM SEM and AFM are complementary techniques that are complementary techniques that

provide provide a a more complete representation more complete representation of a of a surface surface

when used together than if each were the only when used together than if each were the only

technique availabletechnique available

Svetlana Santer

Transmissionselektronenmikroskopie(TEM)(TEM)

Das Prinzip eines TEMs ist völlig analog dem eines optischen Mikroskops. Ein kollimierterElektronenstrahl wird von einem heissen Draht emittiert und auf ~120 keV beschleunigt. Nachdem er einenKondensor passiert, trifft erauf die Probe. Der Durchmesser des Strahl kannvariiert werden, beträgt typischerweise aber ~ 1 Mikrometer. Somit können kleine, ausgewählteFlächen betrachtet werden. Der Strahl passiert dann die Probe, die bei Elektronen dieser Energie bis auf ~ 200 Å ausgedünnt werden muss. Das Objektiv, das direkt unter der Probe sitzt, erzeugtdann von ihr ein vergrößertes Bild. Dies wirddann auf einem fluoreszierenden Schirm am Boden des TEM-Zylinders sichtbar gemacht.

Svetlana Santer

TEMTEM

Die dunklen Stellen auf dem Lumineszenzbild repräsentieren die Stellen auf der Probe, die wenig Elektronen durchlassen (sei es wegen der Dichte oder der Elektronestruktur). Umgekehrt verhält es sich mit den hellen Stellen des Fluoreszenzbildes.

Svetlana Santer

SEM TEM

Wechselwirkung zwischenWechselwirkung zwischen Atom und Atom und ElektronElektron

Svetlana Santer

• Elektronen werden gestreut, wenn sie dünne Stellen der Probe durchdringen

• Das Bild wird aus den transmittierten Elektronen (die nichtgestreuten) generiert.

• Dichtere Regionen in der Probe streuen mehr Elektronen und erscheinen somit dunkler.

• Auflösung des TEM : bis zu 0.2 nm (1Nanometer = 10-9 m), dies ist 1000x mehr als bei einem Lichtmikroskop

• Für TEM müssen die Proben prinzipiell sehr dünn sein

• Die Proben müssen meist chemisch modifiziert werden, um beispielsweise den Kontrast zu steigern

TEMTEM

Svetlana Santer

D = 0.61 x λλλλNA D =~ 0.5 x λ

Das Auflösungsvermögen steigt mit kleiner werdender Wellenlänge

ResolutionResolution

Wellenlänge des Elektronenstrahls= 0.005 nm(10,000 mal kleiner als bei Licht)

Theoretische Auflösungsgrenze= 0.0025 nm

Technisch bedingte Auflösungsgrenze= 0.1-0.2 nm. Gründe:

Beugung und InterferenzChromatische AberrationSphärische AberrationAstigmatismus

Svetlana Santer

Die Wellenlänge sinkt mit steigender Elektronengeschwindigkeit und damit mit größer werdender Beschleunigungsspannung

Svetlana Santer

Einer der nützlichen Eigenschaften der Elektronenmikroskopie, insbesondere der TEM, ist die Möglichkeit zur Kristallstrukturanalyse. Hier wird die Wellennatur der Elektronen ausgenutzt; bei ausreichend kleiner Wellenlänge wird der eintreffende Strahl von der atomaren Struktur gebeugt. Das resultierende Beugungsmuster ist besonders aussagekräftig, wenn die atomare Anordnung im hohen Maße regulär ist, mit wenigen Fehlstellen. Es ist leicht, vom realen Bild zum Beugungsmuster zu wechseln: im Beugungsmodus wird der Strom in der Objektivlinse abgeschaltet. Das Bild wird auf unendlich fokussiert, und auf den nahen Schirm gelangt nur das Beugungsmuster des Kristalls.

HRTEMHRTEM

Svetlana Santer

� Quantenpunkte (Quantum Dots, QD) auch „Quantenboxen“, „künstliche Atome“ genannt, sind meist Nanokristallite(Halbleiterkristalle in Molekülgröße).

� Größe: ~2-10 nm (+3%)

� Struktur: kristallin

Svetlana Santer

Svetlana Santer

SEM TEM

Svetlana Santer

SEM TEM

ProbenvorbereitungProbenvorbereitung

1. Fixieren der Probe auf den Halter.

2. Trocknung.

3. Sputtern mit Gold oder Platin.

1. Präparieren mit Kontrastmittel, z.B. OsO4 oder RuO4.

2. Einbringen in Monomerlösung

3. Polymerisierung

4. Schneiden in 10-50 nm Stücke.

5. Aufbringen auf ein Gitter.

Svetlana Santer

••AFM and SEM AFM and SEM provide provide high high resolution imagesresolution images, , but only for but only for

surface characterisation surface characterisation

••For For investigations investigations in in materials science that are conducted materials science that are conducted

in in bulkbulk, , some some of of the many variants the many variants of of thethe opticaloptical LSCM LSCM

techniques may be usedtechniques may be used

••LSCM LSCM provides lower resolutionprovides lower resolution, , but is more but is more flexible, flexible, as as

will will be demonstrated be demonstrated in in the followingthe following

Svetlana Santer

Laser Laser Scanning Confocal MicroscopeScanning Confocal Microscope

Marvin Minsky, 1953Marvin Minsky, 1953

How does it workHow does it work, , what resolution can be achievedwhat resolution can be achieved??

Svetlana Santer

The LSM 510 META Laser Scanning Microscope is one of the July 2002 winnersof the renowned R&D 100 Awards granted every year by the R&D Magazine.

LSM 510 META, ZeissLSM 510 META, Zeiss

The centerpiece of the system is a multichannel detector which not only records brightness distributions in the examined specimen, but also the spectral composition of fluorescence light in each of the scanned object spots. This technique now permits the simultaneous localization of considerably more fluorescence dyes than before. Dye combinations not usable inthe past can now be used for specimen marking. In particular,the LSM 510 META allows strongly overlapping fluorescence emission spectra, such as those of the fluorescent proteins CFP, GFP and YFP, to be precisely and efficiently sorted into separate image channels by means of digital deconvolution algorithms.The system permits single cell and tissue components to be spatially localized with high precision and followed in their natural surrounding.

Svetlana Santer

Widefield Microscope vs Confocal MicroscopeWidefield Microscope vs Confocal Microscope

•Confocal lateral resolution is related to the lateral resolutionof the objective lens, which is afunction of a NA, the confocal pinhole size and the wavelength of the projected light: theoretical resolution isλ/2 (difraction limited)

•Restricted to mainly dielectric materials

Svetlana Santer

LSCM LSCM special featurespecial feature: high : high resolution optical sections resolution optical sections in zin z--directiondirection

��Vertical resolution is Vertical resolution is of of the same the same order of order of λλλλλλλλ

Svetlana Santer

Operation Operation Modes Modes of LSCMof LSCM

��Fluorescence Fluorescence LSCMLSCM

��ReflectionReflection LSCM (LSCM (using using

unlabelled specimens as unlabelled specimens as well)well)

��Interference Interference LSCM (also on LSCM (also on

opacue materialsopacue materials))

small organisms. living cells, proteins,

Labelled organic materials, quantum dots

��Raman Confocal MicroscopeRaman Confocal Microscope

Svetlana Santer

LSCM in Material ScienceLSCM in Material Science

Bicontinuous PB/DPB polymer blend(PB fluorescence-labeled, region of interest). 3D shadow projection.C-Apochromat 40x/1.2 W; 187.5 µm x 187.5 µm x 49.5 µm,300 x 300 pixels x 99 sections.Sample and measurement: Prof. Jinnai,Kyoto Institute of Technology, Kyoto, Japan

Microfiber fabric. 3D shadow projection.Epiplan-Neofluar 20x/0.5; 651.5 µm x 651.5 µm x 304.7 µm,512 x 512 pixels x 110 sections.

LSC 5 PASCAL, ZeissLSC 5 PASCAL, Zeiss

Svetlana Santer


Svetlana Santer


Investigation of morphology and interface in polymer composites thin filmsPopielarz, R et al 2001 Mat Res Soc Symp Proc Vol 665

The filler particles and their distribution in BaTiO3-polymer composite films

Svetlana Santer


Use of LSCM for quantitative characterization of physical changes of polymer coatings after UV exposure Martin, J.W. et al 2003, Proceedings of the 81th

annual meeting technical program of the FSCT

Svetlana Santer


Surface profilometry

Zhizhan Xu 2000 Meas Sci Technol

Svetlana Santer

Raman Confocal MicroscopeRaman Confocal Microscope

A confocal Raman microscope consists of a dual-output-port spectrometer integrated with a confocal microscope. A singlemode optical fiber provides poin-source illumination and the core diameter of a multimode fiber provides the confocal pinhole in the focal plane.

WitecWitec, Ulm, Ulm

The CRM 200 offers the unique ability to acquire chemical information in a non-destructive way with a resolution down to the optical diffraction limit (down to 200 nm).This allows the user to observe and analyse the distribution of different phases within asample in ambient conditions without sophisticated sample preparation. Because of the confocal setup it is not only possible to collect information from the sample surface butalso to look deep inside transparent samples and even obtain 3D information.

Svetlana Santer

Confocal Depth Profiling Confocal Depth Profiling on a Metal on a Metal Wire Coated with Three Wire Coated with Three Different PolymersDifferent Polymers

With confocal Raman microscopy the optical characteristics of structures can be matched to chemical properties. The confocal principle even allows a „look“ deep inside non-opaque samples to determine what materials are involved

A metal wire coated with three different polymers

Scan range 100µm per 45µm. Integrated time 200ms/spectrum, 18.000 spectra. Laser power 10mW, λ=532nm

The total thickness as observed in the image is approximately 40.6 mm. The outer layers have a thickness of a bout 12.8 mm and 13.3 mm respectively, while the inner layer is about 14.5 mm thick. Some uncertainly comes from the fact that boundery between the layer does not appear to be very well defined. It is also apparent that the outer layers seem to have a „skin“ with a thickness of about 0.5 mm.

WitecWitec, Ulm, Ulm

Svetlana Santer

Characterization Characterization of of the the Polymer Blend PMMAPolymer Blend PMMA--SBRSBR

Svetlana Santer

CharacterizationCharacterization ofof thethe Polymer Blend PMMAPolymer Blend PMMA--SBRSBR

Ute Schmidt,Ute Schmidt, WitecWitec, Ulm, Ulm

Svetlana Santer

CharacterizationCharacterization ofof thethe Polymer Blend PSPolymer Blend PS--PEPPEP--PMMAPMMA

Svetlana Santer

atomic resolutionatomic resolutionhigh high field depthfield depthhigh high resolution resolution zz--directiondirection

SpecialSpecialfeaturesfeatures

ambient/ambient/liquidsliquids/vapors/vaporsvacuumvacuumambient/ambient/liquidsliquids/vapors/vaporsEnviromentEnviroment

surfacesurfacesurfacesurface// bulkbulkbulkbulkPerformancePerformance

subsub--nanometer resolutionnanometer resolutiondiffraction limiteddiffraction limited, >200nm, >200nmResolutionResolution

$100k$100k$250k$250k$30k$30k-- $200k$200k$10k$10kInstrument Instrument priceprice

70%70%10%10%30%30%10%10%Growth rateGrowth rate

$100 M$100 M$400 M$400 M$80 M$80 M$800 M$800 MMarket 1993Market 1993

20 20 yrsyrs40 40 yrsyrs20 20 yrsyrs200 200 yrsyrsTechnology ageTechnology age

AFMAFMSEM/TEMSEM/TEMconfocalconfocalopticaloptical

Comparison Comparison of different of different types types of of microscopesmicroscopes

Documents

From Microsystems to the Nanoworld - uni-freiburg.de · Svetlana Santer Freiburger Materialforschungszentrum Institut für Mikrosystemtechnik From Microsystems to the Nanoworld Svetlana