Electron Mikroskop

Electron Mikroskop

Scanning Electron Microscopy (SEM)
•Apa itu SEM?
•Prinsip Kerja SEM
•Komponen utama dan fungsinya
•Electron beam - spesimen interaksi
•Inteaksi volume dan escape volume
•Perbesaran, resolusi, depth of field dan
kontras bayangan
•Energy Dispersive X-ray Spectroscopy (EDS)
•Wavelength Dispersive X-ray Spectroscopy
(WDS)
•Orientation Imaging Microscopy (OIM)
•X-ray Fluorescence (XRF)

Comparison of OM,TEM and SEM
Light source
Condenser
Specimen
Objective
Eyepiece Projector
Source of
electrons
Magnetic
lenses
Specimen
OM TEM SEM
detector
CRT
Cathode
Ray Tube
Principal features of an optical microscope, a transmission
electron microscope and a scanning electron microscope,
drawn to emphasize the similarities of overall design.

Glass Magnetic
coils
Anode
Under vacuum

PERBEDAAN MO DAN SEM
MO : resolusi/daya pisah
lebih rendah
SEM: resolusi/daya
pisah lebih tinggi
Kombinasi perbesaran dan daya pisah yang lebih besar dan kemampuan deteksi unsur pada
permukaan material SEM lebih teliti untuk riset dan industri

I. Basics of Electron Microscopy
• Electro-magnetic lenses
• Scanning Transmission EM (STEM)
– Mass determination
– Elemental mapping
• Scanning EM (SEM)
– Surface relief
• Transmission EM (TEM)
– Structures
– Imaging or Diffraction
– 0.03 Å theoretical resolution
1.0 Å practical resolution

II. Electron Source
• Tungsten filament (thermionic)
• Tungsten crystal (field emission) 100x brighter
• Electrons Accelerated to defined energy
behave as a wave.
• kV (100 – 1000 kV with 200kV-> 0.025 Å)

Electron beam Source
W or LaB6 Filament
Thermionic or Field Emission Gun

ELEKTRON YANG BERHAMBUR DAN
DITANGKAP SEM SAAT SAMPEL
DITEMBAK ELEKTRON

HAMBURAN ELEKTRON DIDETEKSI DAN
ENERGINYA DITAMPILKAN DALAM BENTUK
GAMBAR DAN GRAFIK
Tiap Jenis hamburan elektron
ditangkap detektor yang
berbeda
Tempat Sampel

TEMPAT SAMPEL DI SCANNING
ELECTRON MICROSCOPE

PENGAMATAN DENGAN SCANNING
ELECTRON MICROSCOPE
Perbesaran
OM 4x – 1000x
SEM 10x – 3000000x
Aplikasi :
•Mengamati struktur maupun
bentuk permukaan yang
berskala lebih halus
•Dilengkapi Dengan EDS
(Electron Dispersive X ray
Spectroscopy)
•Dapat mendeteksi unsur2
dalam material.
•Permukaan yang diamati
harus penghantar elektron

Keuntungan SEM terhadap OM
Perbesaran Depth of Field Resolusi
OM 4x – 1000x 15.5mm – 0.19mm ~ 0.2mm
SEM 10x – 3000000x 4mm – 0.4mm 1-10nm
SEM mempunyai depth of field yang besar, yang dapat
memfokus jumlah sampel yang lebih banyak pada satu
waktu dan menghasilkan bayangan yang baik dari
sampel tiga dimensi. SEM juga menghasilkan bayangan
dengan resolusi tinggi, yang berarti mendekati bayangan
yang dapat diuji dengan perbesaran tinggi.
Kombinasi perbesaran yang lebih tinggi, dark field,
resolusi yang lebih besar, dan komposisi serta informasi
kristallografi membuat SEM merupakan satu dari
peralatan yang paling banyak digunakan dalam
penelitian, R&D industri khususnya industri
semikonductor.

• Topography
Aplikasi Utama SEM
The surface features of an object and its texture
(hardness, reflectivity… etc.)
• Morphology
The shape and size of the particles making up the
object (strength, defects in IC and chips...etc.)
• Composition
The elements and compounds that the object is
composed of and the relative amounts of them
(melting point, reactivity, hardness...etc.)
• Crystallographic Information
How the grains are arranged in the object
(conductivity, electrical properties, strength...etc.)

Electron Gun
A More
Detaile
d Look
Inside
Source: L. Reimer,
“Scanning Electron
Microscope”, 2 nd Ed.,
Springer-Verlag, 1998, p.2
e - beam

Preparasi Sampel
• Hindari semua air, larutan atau
material-material lain yang mudah
menguap dalam vakum.
• Permukaan harus rata untuk BSE dan
OIM
• Tentukan jumlah sample.
• Samples Non-logam, seperti building
materials, insulating ceramics, harus di
caoting agar konduktivitas listriknya
baik. Logam dan samples konduktivitas
dapat diletakan langsung kedalam SEM.

Image Magnification
Example of a series of increasing magnification (spherical lead
particles imaged in SE mode)

Bagaimana Elektron Beam
dihasilkan ?
• Elektron guns digunakan untuk
menghasilkan kontrol beam yang halus
dari elektron yang kemudian difokuskan
pada permukaan spesimen.
• Eelektron guns bisa dalam bentuk
thermionik gun atau field-emission gun

Thermionic Emission Gun
• A tungsten filament
heated by DC to
approximately 2700K or
LaB 6 rod heated to around
2000K
• A vacuum of 10 -3 Pa (10 -4
Pa for LaB 6) is needed to
prevent oxidation of the
filament
• Electrons “boil off” from
the tip of the filament
• Electrons are accelerated
by an acceleration voltage
of 1-50kV

Field Emission Gun
• The tip of a tungsten needle is
made very sharp (radius < 0.1
mm)
• The electric field at the tip is
very strong (> 10 7 V/cm) due
to the sharp point effect
• Electrons are pulled out from
the tip by the strong electric
field
• Ultra-high vacuum (better than
10 -6 Pa) is needed to avoid ion
bombardment to the tip from
the residual gas.
• Electron probe diameter < 1
nm is possible

Filament
Source of Electrons
T: ~1500o Thermionic Gun
C
W and LaB 6
(5-50mm)
E: >10MV/cm
(5nm)
Cold- and thermal FEG
Electron Gun Properties
Source Brightness Stability(%) Size Energy spread Vacuum
W 3X10 5 ~1 50mm 3.0(eV) 10 -5 (t )
LaB 6 3x10 6 ~2 5mm 1.5 10 -6
C-FEG 10 9 ~5 5nm 0.3 10 -10
T-FEG 10 9

Lensa Magnetik
• Lensa Condenser – focusing
determines the beam current
which impinges on the sample.
• Lensa Objective – final probe
forming
determines the final spot size of
the electron beam, i.e., the
resolution of a SEM.

Kenapa perlu Vakum?
Bila SEM digunakan, kolum elektron-optik
dan sampel chamber harus selalu pada
kondisi vakum.
1. Bila kolum ada gas didalamnya maka elektron akan
diskaterd oleh molekul gas yang menyebabkan
intensitas dan stability beam akan berkurang
2. Molekul-molekul gas lain, yang datang dari sampel
atau dari microskop itu sendiri, dapat membentuk
persenyawaan dan kondens pada sampel. Ini akan
membuatan kontras menjadi lebih rendah dan
bayangan menjadi kabur.

Electron Detectors and Sample Stage
Objective
lens
Sample stage

Coating Techniques
Sputter coater is used to coat insulating samples
Au and Al – good for SE yield
AuPd alloy – good for high resolution
C – used if X-ray microanalysis is required
Coating should have low granularity in order not to
mask the underlying structure (

OIM-Grain Boundary Maps
Grain Boundary Map Orientation Map
A Grain boundary Map can be generated by comparing the orientation
between each pair of neighboring points in an OIM scan. A line is
drawn separating a pair of points if the difference in orientation
between the points exceeds a given tolerance angle. An Orientation
Map is generated by shading each point in the OIM scan according to
some parameter reflecting the orientation at each point. Both of these
maps are shown overlaid on the digital micrograph from the SEM.