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 Source of electrons
Light source Condenser
Magnetic lenses
Specimen Objective Projector Eyepiece
Specimen
CRT
Cathode Ray Tube
detector OM
TEM
SEM
Principal features of an optical microscope, a transmission electron microscope and a scanning electron microscope, drawn to emphasize the similarities of overall design.
Anode
Glass Magnetic coils
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 OM SEM
Perbesaran 4x – 1000x 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
OM 4x – 1000x SEM 10x – 3000000x
Resolusi
15.5mm – 0.19mm
~ 0.2mm
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.
Aplikasi Utama SEM • Topography 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”, 2nd 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 LaB6 rod heated to around 2000K • A vacuum of 10-3 Pa (10-4 Pa for LaB6) 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 (> 107 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
Source of Electrons Thermionic Gun T: ~1500oC
Filament
E: >10MV/cm
W
(5-50mm)
(5nm)
W and LaB6
Cold- and thermal FEG
Electron Gun Properties
Source Brightness Stability(%) Size Energy spread W 3X105 ~1 50mm 3.0(eV) LaB6 3x106 ~2 5mm 1.5 C-FEG 109 ~5 5nm 0.3 T-FEG 109 <1 20nm 0.7
Vacuum 10-5 (t ) 10-6 10-10 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 (<20nm thick).
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.
