Key Features

Fe-LeeM/PeeM P90 FamilyCompaCt low energy eleCtron and photoeleCtron emission miCrosCopes

•high lateral resolution•integrated imaging energy Filter•robust sample stage with Five

Computer-Controllable axes•sample holder with integrated

sample heater•leem: Cold Field emission

source with low energy spread

Fe-LeeM/PeeM P90 Family

innovation in surFaCe speCtrosCopy and miCrosCopy systems

SPECS leads the way in state-of-the-art technology for surface spectromicroscopy.

speCs surface nano analysis gmbh

speCs headquarters, with more than 150 employees, is located in the center of germany’s capital Berlin, with subsidiaries in switzerland (speCs Zurich gmbh) and in the usa (speCs inc.). Furthermore, we have liaison offices in Franceand spain and are represented all over the globe by our sales partners.

we are a team of scientists and engineers who have been dedicating their knowledge and experience to the development, design, and production of instruments for surface science, materials research, and nanotechnology since 1983.

our key to success is know-how, experience, close contact to scientists from all over the world, customer orientation, reliable quality control, and dynamic research and development.

Packaging of a SPECS component after final testing

Final alignment of an UHV high precision sample manipulator

history

Eightyyearsago,ErnstBrüchedevelopedthefirstphotoelectron emission microscope (peem) in the aeg laboratories in Berlin. during the following decades, the technique developed into a powerful tool for surface science allowing the study of surfaces with a resolution of a few nanometers under illumination of various light sources, such as uv lamps, lasers or synchrotron radiation. in combinationwithimagingenergyfilters,laterallyresolved photoelectron spectroscopic studies become feasible allowing the study of chemical composition at surfaces with highest spatial resolution.

parallel to the improvement of electron optics, ernst Bauer developed low energy electron microscopy (leem): By equipping the instrument with an electron source and a beam splitter, it became possible to illuminate the sample with a parallel electron beam normal to the surface and guide the diffracted electrons through thesame electron optics as the incoming beam. this allowed laterally resolved leed measurements and thus high sensitivity on the crystallographic configurationandorientationofthesurface.

Just a stone’s throw from the first PEEM’s birthplace, SPECS produces the state-of-the-art instrument with highest resolution.

LeeM/PeeMhigh resolution eleCtron miCrosCopy oF solid state surFaCes.

during the late 20th century, dr. rudolf tromp at iBm research division became aware of the possibilities of leem for the in situ observation of deposition processes or phase transitions and began to build a system by himself. the precision in instrument design and high manufacturing quality allowed this instrument to obtain the highest lateral resolution at the time.

as a result, speCs surface nano analysis, situated in a historic aeg building just a few kilometers away from Brüche’s former laboratory, decided to commercialize tromp’s instrument. the continuous development in collaboration with dr. tromp at iBm, the improvement of the manufacturing processes and particularly the implementation of aberration correction has pushed the resolution limit even further to values below two nanometers. Follow us exploring the nanoworld using the speCs Fe-leem p90.

Fe-LeeM/PeeM P90 Family

Fully-operational system ready For high-resolution miCrosCopy

The instrument is designed as an all-in-one-system containing all components needed for work. All components are designed for low vibration operation and low maintenance.

Fe-LeeM P90/PeeM P90

the instrument is based on a sophisticated electron-optical design of magnetostatic lenses with a self-shielded design and equipped with a 90° magnetic deflector that serves both as abeam splitter and an imaging energy filter. Thebase system is the peem p90 (without electron source) or the Fe-leem p90 (equipped with a cold fieldemissionelectronsource)andisdeliveredasa turn-key system with a multi-chamber design, sample storage, all necessary vacuum equipment and a measurement pC. FE-LEEM P90

the system can be upgraded with an optional aberration corrector for improved transmission and resolution, additional uv sources, such as the deuterium lamp duvl 160 or the helium lamp uvs 300, for laterally resolved ups studies, a preparation chamber and an aarhus stm. these upgrades are mounted on the same system frame for fast sample exchange and low-vibration operation of the whole system. many different types of sample preparation sourcescan be mounted within the analysis chamber for live observation of surface processes.

Schematic illustration of the lens configuration of FE-LEEM P90

Sample

Contrast Aperture

Gun

Screen

Electrostatic Lens Magnetic LensAxial RayField Ray

5

Sample holder with integrated electron bombardment heater and mounted sample cap

sample handling

one of the most important properties of an electron microscope is the stability and control of the sample position. in the speCs Fe-leem p90, this is ensured by our piezo-controlled sample stage with five degrees of freedom (distancefrom objective lens, two tilt directions of sample normal relative to optical axis, two axes for lateral positioning). all motors are equipped with position encoders and are computer-controllable by either the leem software or an external control pad. the sample stage is mounted directly on the objective lens for minimum sample drift and allows precise and reproducible positioning on a nanometer length scale.

Sample stage with five computer-controlled degrees of freedom

the sample holder is designed for fast sample exchange: the sample is mounted in a small metallic sample cap which is installed on the sample holder containing electrical connectors and an electron bombardment heater for imaging at temperatures up to 1500 K. a thermocouple can be integrated into the sample holder and is measured by feedback electronics for precise temperature control during the heating process.

liquid nitrogen cooling of the sample and azimuthal sample rotation can be added as an option in order to extend the experimental capabilities of the instrument to low temperatures and a sixth degree of freedom for the sample motion. Sample caps

Fe-LeeM/PeeM P90 Family

electron source

in leem mode, the sample is illuminated by an electron beam formed by a high-brightness cold fieldemissiongun.Theenergywidthoflessthan300 meVismuchsmallerthanincorrespondinginstruments equipped with thermionic or schottky emitters. this feature together with a high transfer width leads to sharper images and leed patterns.

system Frame

For low vibration operation, all components are installed on one single stainless steel frame with high stiffness for efficient vibration-isolationfrom the environment. For high-resolution measurements, all mechanical pumps can be turnedoff.

the aberration-corrected instrument Fe-leem p90 aC additionally includes a reliable active vibration damping system. For installations in a noisy enviroment this option can also be added for the standard instruments.

electron optics

The 90° magnetic deflector serves both as abeam splitter for the incoming and outgoing electronbeamsandas an imaging energyfilterwith an energy resolution of 1.7 ev and <0.25 ev in imaging mode and spectroscopy, respectively.

all electron-optical components are machined with the highest precision and mounted on top of each other. this ensures the best possible mechanical alignment and allows for operation with a minimum number of electron optical deflection elements. The self-shielded lensdesignprovidesaneffectivescreeningofexternalstrayfields.

vacuum Chamber

the system consists of four independently pumped uhv chambers analysis, electron optics, transfer and load lock, enabling a vacuum of <2 x 10-10 mbar in the analysis chamber. the load lock/transfer chambers contain an in-vacuo storage for up to three samples.

View into analysis chamber of the objective lens

uv source

For threshold photoemission microscopy, the instrument is equipped with a mercury uv source. other light sources such as lasers, helium or deuterium uv sources or synchrotron beams can be connected to a number of ports pointing at the sample. these ports can also be used for in situ sample preparation by evaporation or ion beam sputtering.

electronics

high resolution electron microscopy demands high stability of the voltage and current supplies for the electron optics. speCs has developed a set of high-stability power supplies needed for driving the resolution to the physical limits. all currents and voltages are computer-controlled by theLEEM/PEEMsoftwarepackagepre-configuredon the measurement pC system.

7

Load lock with sample storage

FE-LEEM P90 electronics racks

Fe-LeeM/PeeM P90 Family

photons may excite photoelectrons from core levels and valence states, while electrons may result in elastically and inelastically scattered electrons. in addition, both kinds of excitation may result in auger electrons and secondary electrons. this variety of excitation processes gives access to the structural, chemical, electronic, and magnetic properties of the sample surface usingdifferentoperationmodes.

LEEM:ReflectivityContrast

Different areas on thesurface might show a difference in electronreflectivity, dependingon the surface material and structure. the reflectivity coefficientdepends on the incident

electron energy.

leem: phase Contrast

interference of electrons from alternating monolayers of the sample generates a vertical contrast, e.g. to make steps visible on the surface.

By illuminating the sample with electrons or photons of variable energy a wide array of contrast mechanisms can be exploited.

LeeM/PeeMoperation modes oF leem and peem

mirror electron microscopy (mem)

the electron energy is reduced such that the electrons return in the retarding field, beforehitting the sample surface. the contrast mechanism is based on local changes in the

retardingfieldonthesamplesurface.

leed

Thediffractionpatternisformed in the backfocal plane of the objective lens. using one lens in the projective column, it is possible to image this leed pattern on the screen.

Micro-diffraction

By restricting the electron beam to a small area down to 200 nm, it is possible to investigate leed patterns of small regions, such as single islands or terraces.

9Energy-filteredPEEM

By inserting an additional aperture into the exit plane of the deflector prismand switching back to imaging mode, only photoelectrons with a specific energy are

used for imaging. this mode allows carrying out element-specific studies by selecting electronswith certain specific spectrosopic features forimaging.

electron energy loss spectroscopy (eels)

when the sample is illuminated by the electron beam, in spectroscopic mode the energy loss spectrum of the reflected electronsafter interacting with the sample is displayed

on the screen. By studying the electron loss spectra with lateral resolution the local electronic structure of the sample can be investigated.

XmCd-peem

By illuminating the sample with circularly-polarized synchrotron radiation with variable photon energy, the magnetic domain structure can be imaged via the X-ray magnetic

circular dichroism (XmCd). the picture on the left (courtesy of F. nickel/Forschungszentrum Jülich) shows the domain pattern of a 8 µm permalloy square element.

leem: dark-Field imaging

usage of a single leed spot in the intermediate plane for imaging by introducing an aperture in thediffractionplane.all areas on the surface that contribute to the existence of this spot

appear bright in the image, all other areas appear dark.

threshold peem

electrons are excited with an uv light source. the contrast is based on local work function differences on thesample.

angle-resolved photoelectron spectroscopy (arpes)

when the sample is illuminated with higher energy uv light from a helium or deuterium uv lamp or with X-rays, a spectrum of photoelectrons with a broad energy distribution

is generated. The dispersion of the 90° deflectorprism provides the ability to obtain information about the kinetic energy of the electrons. By imaging the diffraction plane and inserting an entranceslit for the prism, angle-resolved photoemission experiments can be carried out.

Fe-LeeM/PeeM P90 Family

lateral resolution of a Fe-leem p90

the image shown on the right is taken on a clean si(100)-2x1 sample at a kinetic energy of 3.5 ev. this surface usually consists of two domains rotated by 90° with respect to each other. therefore, the leed pattern detected from this surface is a superposition of two leed patterns with one for each domain.

The image is taken in dark field imaging modewhere only electrons from one higher order leed spot are taken to create the respective real space images. hence, only the parts of the surface area, i.e. domain, contributing to this leed spot appear bright in the image.

the step edges at the domain bondaries are used to determine the lateral resolution. the line profilehasbeencreatedby integrating thedatain the direction parallel to the steps within the rectangle shown in the image.

The line profiles show, that the ultimate lateralresolution is well below 5 nm, down to 4.2 nm.

Dark field LEEM image of Si(100)

Line profile along a monolayer step of Si(100)

100 nm

11lateral resolution of the aberration Corrected Fe-leem p90 aCChromatic and spherical aberrations of the objective lens are the limiting factors for the lateral resolution of Fe-leem/peem p90. these limitations can be overcome by reflectingthe electrons emitted from a sample with a multielement electron mirror. this improves lateral resolution and transmission by a factor of 2 and 8, respectively.

measurements have been performed on thin graphene layers grown on SiC(0001). By flash-annealing the siC substrate, the graphene layers were grown in-situ within the leem analysis chamber. the image is taken from such a graphene layer. Areas with different numbersofcarbonlayersshowdifferentgraylevels.Stepcontrast is seen in areas with the same layer number. The figure to the right shows a stepprofileandtheareawhereithasbeentaken.Theprofilehasbeenaveragedoverstripsfivepixelswide, as indicated in the image by the blue boxes.

LEEM image of Graphene covered SiC(0001)

Line profile along the step of two successive Graphene layers

100 nm

Fe-LeeM/PeeM P90 Family

the spatial resolution of an electron microscope is limited by various processes: diffraction,spherical and chromatic aberrations and further higher-order aberration terms. these terms strongly depend on the acceptance angle of the microscope and the energy spread of the electron beam. For typical acceptance angles, the resolution is dominated by the lowest-order spherical and chromatic aberrations of the objective lens. these can be compensated by a multi-element electron mirror carefully machined and calibrated. By eliminating spherical and chromatic aberration, the minimum resolution is significantlyimprovedandisreachedwithhigheraperture sizes than with the non-corrected instrument. the resolution obtained is better by a factor of two and the transmission of the microscope is increased by a factor of eight.

in practice, the aberration correction is added by a second 90° beam splitter with transfer optics.

Picture of the four-element electron mirror

when passing the second beam splitter, the electronbeam isdeflectedback to theelectronmirror,thenreflectedtowardsthebeamsplitterwhere it is again deflected by 90° towards theprojector column.

For proper operation of the aberration corrector, all components are aligned as precisely as technically possible. this is achieved by high precision machining. the mirror itself consists of four electrodes machined by single point diamond turning, providing superior manufacturing quality.

Drastic improvement of transmission and resolution

Fe-LeeM P90 aCaBerration CorreCtion

Schematic illustration of the lens configuration of the aberration-corrected FE-LEEM P90 AC

stm aarhus 150 ht

with the stm aarhus 150, scientists will observe processes on surfaces at an atomic scale. the miniaturized design, with the smallest mechanical loop between tip and surface, results in an extreme stability which is unique in the field of commercially available STMs. Fast scanrates are achieved by high resonant frequencies of this scanner head design. the tip may be cleaned inside the chamber with no necessity for tip replacement as in other stms. the high temperature version of the stm aarhus 150 allows imaging of metals and semiconductors at elevated temperatures up to 1000°C by radiative heating during stm operation. For this reason, the Fe-leem p90 and the spm aarhus 150 ht perfectly complement each other with respect to an unambiguous interpretation of results. the stm can be installed in the same system as the leem allowing for fast sample transfer between stm and leem without breaking the vacuum.

uv source uvs 300

the high performance ultraviolet source uvs 300 is ideally suited for ultraviolet photoelectron spectromicroscopy with the integrated energy filter. The UVS 300 generates a high densityplasma by guiding the electrons extracted from a hotcathodefilamentalongthelinesofastronglyinhomogeneousmagneticfieldtowardsthesmalldischarge region (duo-plasmatron principle). the strong vacuum ultraviolet radiation is extracted from the cathode side a focussing metal capillary.

Differential pumping (50 l/s) between the twocapillaries enables operation at very low pressure in the analysis chamber (1x10-8 mbar or below). the uvs 300 will be mounted on a granite block for effective vibration isolation. For applicationexamples see tromp et al., J. phys.: Condens. matter 21 (2009), 314007.

Aarhus STM 150 HT

UV source UVS 300

Many different components from the SPECS portfolio can be combined with the LEEM instrument offering unique combinations of complementary techniques all provided from one manufacturer.

system Integrationintegration oF optional Components

Fe-LeeM/PeeM P90 Family

preparation sources

to our customers in research and industry we offer a wide variety of sources for deposition,excitation and charge neutralization. Compliance with industry standards, a good price-performance ratio, stability, and longevity are the guidelines for our product development. we focus on easy handling, user-friendliness, standardized software interfaces and safety.

sources like the ion source iQe 12/38 or the multi pocket electron Beam evaporator eBe-4 can be installed within the analysis chamber for in situstudiesofthinfilmdepositionprocesses.alternatively they can be installed in a separate preparation chamber mounted on the same system frame.

linear transfer system

For low-vibration operation, the leem typically is installed with all system components mounted on one rigid and vibration-isolated system frame for highest resolution. For certain applications, however, it can be desirable to combine several larger systems via one uhv linear transfer. in that case, all systems can be operated individually and samples can be transferred via the linear transfer system from one system to another. please contact your speCs representative for further information.

Complex Surface Nano Analysis System integrated with a Linear Transfer System

Multi pocket electron beam evaporator EBE-4

Ion source IQE 12/38

15technical Data

summary

Technical Data

resolution with Fe-leem p90

guaranteed: 5 nm, achieved: 4.2 nm

resolution with Fe-leem p90 aC

guaranteed: 3 nm, achieved: 1.6 nm

Field of view 800 nm – 100 µm

Magnification 400x – 50000x

energy resolution spectroscopy: < 250 mevimaging: < 1.7 ev

Kinetic energy in the microscope

typically 15 kev,scaleable down to 2 kev

Top View and Side View, Dimensions in mm

Technical Data

start energy up to 1000 ev

Base pressure Better than 2 x 10-10 mbar

leem spot size

< 40 µmdown to 200 nm with micro-diffractionaperture

energy width of illumination beam < 300 mev

reproducibility of sample position Better than 500 nm

maximum temperature for imaging 1500 K

dimensions of Fe-leem p90 aC

sPeCs surface nano analysis gmbh voltastrasse 513355Berlin / Germanywww.specs.com

t +49 30 46 78 24-0F +49 30 46 42 083e support@specs.com