SPECIAL TOPICS IN ION BEAM ANALYSIS PART 2 SINGLE ION TECHNIQUES: - PowerPoint PPT Presentation

SPECIAL TOPICS IN ION BEAM ANALYSIS – PART 2 SINGLE ION TECHNIQUES: STIM & IBIC Milko Jakšić Laboratory for Ion Beam Interactions, Experimental physics division Ruđer Bošković Institute Zagreb, Croatia

Ion Beam Analysis & NUCLEAR MICROPROBE Nuclear reaction Charge pulse products   rays Recoil nuclei Ion beam Transmitted particles X-rays Forward scattered particles Backscattered particles TARGET Secondary electrons Light ANALYSIS (elements, isotopes) CHARACTERISATION (density, charge with MeV ION BEAMS - (nA, pA) transport, crystal structure, morphology,…) with MeV SINGLE IONS - (fA) - elements - x-rays ( PIXE ) - backscattering ( RBS ) - density - transmitted ions ( STIM ) - recoil ( ERDA ) - charge transport - charge pulse (IBIC ) - isotopes - nuclear reactions - crystal structure - channelling  - rays ( PIGE ) - morphology - secondary electrons ( SEI ) particles ( NRA )

Single ion implantation Why single ions? • Implantation of one particular atom at exactly known position in exactly known time seems to be extremely attractive! • And it is easy (to perform experimentaly) !

Single ion implantation Why single ions? • Implantation of one particular atom at exactly known position in exactly known time seems to be extremely attractive! • And it is easy (to perform experimentaly) !

Single ions – ionisation & defects Every ion: - Implants itself into the substrate - Ionises many atoms on its way - creates large number of charge pairs Heavy ions: - Create many vacancies - Some secondary electrons - Some desorbed molecules

Accelerator & nuclear microprobe Ideal radiation source  ION POSITION quadrupole doublet proton focusing lens - focusing and scanning beam object slits sample IBIC Y X signal 16 O 12 C 7 Li scan alphas generator  ION RATE - currents 0 - 10 6 p/s Y X  IONS - p,  , Li, C, O,.. IBIC - charge collection efficiency  RANGE protons - 2 to 200  m images

Accelerator & nuclear microprobe Available ion beams AT RBI ‐ terminal voltages – 0.1 to 6 MV Ion sources – sputtering, RF alphatross, duoplasmatron Good selection of ion ranges / dE/dx !! Silicon I 127‐ Si 28 C 12 He 4 H 1 Range(µm) 0.37 1.13 1.6 3.5 16.3 E=1 MeV Range (µm) 3.7 4.8 9.5 69.7 709 E=10 MeV

Single ion characterisation: STIM – Scanning Transmission Ion Microscopy: imaging of areal densities (dE/dx)

STIM – Scanning ion transmission microscopy

STIM – Scanning ion transmission microscopy

STIM – Scanning ion transmission microscopy STIM image of copper grid using 8 MeV O 3+ ions 10 µm

STIM – Scanning ion transmission microscopy Track shape characterisation Density map for flies wing: 6 MeV O ions (left) and 2 MeV protons (right)

STIM – Scanning ion transmission microscopy z Combination of STIM with 3D analysis Bi 2 Sr 2 CaCu 2 O 8+  whiskers using C ion induced coincidence y spectroscopy O distribution and concentration in z 17.7  m x direction ‐ small sample dimensions 11 MeV 12 C 3+ ions ~ 15 mm low energy loss on axis STIM high energy loss d ~ 1.45  m 28×28  m 2 d ~ 1.68  m

Channeling STIM STIM (transmission) channeling • currents ≈ 1 fA  radiation damage can be neglected • but, only transmission samples  nonchanneled ions E 0  channeled ions

Ion beam induced charge - IBIC electrons a) Ions lose their energy dE/dx b) Creation of charge pairs e/h - + + - - + + - ions + - - + 800 + + - - 700 Energy loss (keV/  m) 2 MeV  -particles 600 500 400 300 2 MeV protons 200 100 0 0 5 10 15 20 25 Depth (  m) Bethe formula:       2 4 2 2 2 4 2 dE e z m v v v       ln 0 ln 1   NZ   2 2 2   dx m v  I c c  0

Ion beam induced charge - IBIC 1. for E  0 charge drift a) Ions lose their energy dE/dx                 b) Creation of charge pairs e/h x x x x     Q Q d d d d e e h h             1 1 1 1 d d d d     e e h h e e e e         e e h h c) Charge transport:             Q Q L L L L 0 0 1. Drift - in electric field - Charge carriers produced along 2. Diffusion - + + the ion path drift in electric field + - d) Induced charge - + - Charge pulse height depends + - - on the local value of electric field, + e) IBIC signal - + mobility and lifetime of charge carriers. + + - - - Collection length ‐ d i = (  ) i E d i = (  ) i E - for constant E, 2. for E = 0 charge diffuse Induced charge signal corresponds to the value of  drift region       x x x x     dE dE dE dE x x r r       d d     diffusion region     Y Y dx dx e e dx dx d d i i ( ( ) ) L L x x     0 0 dx dx x dx x dx d d

Ion beam induced charge - IBIC v   I ( t ) q a) Ions lose their energy dE/dx d Induced current b) Creation of charge pairs e/h T   Q ( t ) I ( t ) dt Induced charge c) Charge transport: 0 1. Drift - in electric field V out 2. Diffusion T= 0 1.0 Q d) Induced charge 0.8 0.6 e) IBIC signal Q 0.4 0.2 0.0 d V V 0.075 0.050 v I 0.025 0.000 -2 0 2 4 6 8 10 12 14 Time

Ion beam induced charge - IBIC v   I ( t ) q a) Ions lose their energy dE/dx d Induced current b) Creation of charge pairs e/h T   Q ( t ) I ( t ) dt Induced charge c) Charge transport: 0 1. Drift - in electric field V out 2. Diffusion T=10 1.0 Q d) Induced charge v 0.8 0.6 e) IBIC signal Q 0.4 0.2 0.0 d V V 0.075 0.050 I 0.025 0.000 -2 0 2 4 6 8 10 12 14 Time

Ion beam induced charge - IBIC Velocity; v  d  T R Mobility;  d 2 /(T R *V Bias ) 1.0 1.0    T 0.8 0.8   Q ( t ) I ( t ) dt 0.6 0.6 Q Q 0.4 0.4 0 0.2 0.2 0.0 0.0 0.075 0.075   v t    ( ) exp 0.050 0.050 I t q   I  I   0.025 0.025 d 0.000 0.000 -2 0 2 4 6 8 10 12 14 -2 0 2 4 6 8 10 12 14 16 Time Time In reality  (charge carrier lifetime) can be short due to defects !

Ion Beam Induced Charge Pulse processing (visit ORTEC tutorial) Charge sensitive preamplification ‐ For high resolution PHA (pulse height analysis) ‐ Due to integration, time structure of the signal is forgotten ‐ Shaping time constant Current preamplifier ‐ For studying of pulse time structure – TRIBIC)

Ion Beam Induced Charge Pulse processing (time resolved IBIC) Output from the charge CdZnTe senistive preamlifier at digital osciloscope 20 18 16 2 d 14   t V 12 r VO(mV) 10 Electron mobility: 8  e = 781 cm 2 /Vs 6 -100 V -200 V 4 -40 V 2 ions -80 V -1000 V 0 - -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 + t(  s)

Ion beam induced charge - IBIC Frontal IBIC on polyCVD diamond IBIC spatial resolution  down to 0.25 μm 250 nm

Ion beam induced charge Frontal IBIC EFG silicon Schotky diode Frontal IBIC images can identify distribution of electrically active defects !

Ion beam induced charge Frontal IBIC 4.5 MeV Li range 6μm By proper selection of ion type and energy, CCE (charge collection efficiency) at different sample depths can be surface imaged. 3 MeV protons range 90 μm Si Schotky diode bulk

Ion beam induced charge - IBIC Lateral IBIC on Si power diode ion beam contact and/or heavily doped pn junction region E < 0 E = 0 z z d 0 1 0,8 0,6 28 V Collection efficiency  (z<z d ) = 1 60.4 V 0,4  (z>z d ) = exp(‐(z‐z d )/L p,n ) 90.6 V L p = ( 27.3 ± 0.8 )  m  = (0.57 ± 0.03)  s 0,2 117.5 V hole or electron diffusion length 0,1 0,1 0,08 50 100 150 200 250 Depth (  m)

Ion beam induced charge - IBIC ion beam In-Au ST=8  s 1,0 +50V fully depleted device 0,9 +100V +150V (ideal case) 0,8 +200V 0,7 CCE 100% +250V efficiency (%) 0,6 CdZnTe 0,5 electrons holes electrons 0,4 0,3 0,2 holes 0,1 0,0 0 250 500 750 1000 1250 1500 1750 2000 depth (  m) U=+50V ST=2.0  s U=+100V ST=2.0  s U=+150V ST=2.0  s U=+250V ST=2.0  s U=+50V ST=8.0  s U=+100V ST=8.0  s U=+150V ST=8.0  s U=+250V ST=8.0  s

Ion beam induced damage dE/dx – nuclear stopping dE/dx of Xe ions in silicon

Ion microprobe irradiation & IBIC probing • For 100% ion impact detection efficiency, IBIC can be used to monitor irradiation fluence • Irradiation of arbitrary shapes • On‐line monitoring of CCE degradation 6 Li 7  m ‐2 = 6 10 8 cm ‐2 (4 events per pixel) 50 Li 7  m ‐2 = 5 10 9 cm ‐2