Composition Analysis Flashcards
What is sputter yield
Number of atoms removed per incident ion
Sputter yields of different elements are different leading to surface enrichment - requiring correction
How to avoid surface enricment
At a steady state, surface concentration must be constant so sputtering rate must be proportional to bulk concentration?
When is a steady state reached
Initially surface will enrich in the element with the lowest yield
Eventually steady state reached when R1 (prop) C1b
R2 (prop) C2b
R being rate of sputtering
Cb being concentration of bulk which is concentration before sputtering
What is atomic force microscopy
Small tip at the end of a cantilever is attracted or repulsed from the surface
Laser shone on the cantilever which reflects onto a photodiode (4 quadrant)
Photodiode tracks changes in the reflected beam
AFM maintain constant force / distance via a feedback loop in contact mode
Piezoacutators for scanning the surface
Name AFM techniques
- Contact mode where tip always in contact with surface to map topography
- non-contact (tapping) mode where tip is mechanically vibrating at a resonance above surface. Monitoring change in frequency whilst scanning
What modifications can be made with AFM to map different things
Conductive tip for mapping conductivity
Electrostatic or magnetic interaction with magnetic tips
Additional electric potential for electrostatic or piezoforce microscopy
What ways are film resistance measured
van der Pauw - measured at four corners Rs = piR/ln2
R = V4,3/I1,2
In-line four probes
Benefit of using 4 point probes?
Avoids voltage drop due to contact resistance
Propertied of x-ray diffraction
XRD provides lattice parameters and crystal (grain) orientation
Scherrer Equation = size of crystallite
Epitaxy and strain engineering
Only if mismatch is <3%
do question
Properties of x-ray reflectivity
Optical interference of x-rays in a thin film
Surface specific
Same geometry as in XRD 2theta < 5 degrees
Reflectivity decays as roughness increases
How do you analyse surface thickness?
XRR, RHEED oscillations, Van der Pauw - sheet sensitivity
How to determine surface composition?
Auger electron spectroscopy or X-ray photoelectron spectroscopy
How to determine a surfaces structure?
X-ray diffraction
How to determine a surfaces roughness?
Scanning tunnelling microscopy
Atomic force microscopy
X-ray reflectivity
