Surface characterization and SEY measurements Available XPS system

Surface characterization and SEY measurements Available: XPS system ► provides surface chemical composition in the topmost 2 nm, by measuring the energy spectrum of photoelectrons excited by X-rays (h =1. 2 or 1. 4 Ke. V) from core levels NB: XPS has lower effect of “scrubbing” than Auger e-gun (gets signal from a larger area, comparably lower current densities involved) Upgrade for SEY: ►additional UHV chamber and instrumentation (e-gun, flood-gun, picoamperemeter, UHV components) 10/05/2007 SEY, M. Taborelli, TS-MME

Methods to measure SEY Speed for single point/dose Incidence angle Other properties Constant e-gun energy and variable retarding potential A) 4 grids system and variable sample bias Fast, low dose, measure Is No - Ep-dependent size of analyzed spot - Ep min = 0 e. V - gives distribution of secondaries N(Es) Fast, low dose (Ma, Garwin, Kirby) measure Is No - Ep-dependent size of analyzed spot - Ep min = 20 -50 e. V (Hopman) B) sample bias on Auger system Variable gun energy and constant collector bias C) Collector cone at +45 V bias (CERN) Fast, low dose by pulsed beam, 2 simultaneous measurements Ic, Is no - Ep min ~ 50 e. V (10 e. V possible with sample bias) Care to avoid loss of secondaries through solid angle toward gun 10/05/2007 SEY, M. Taborelli, TS-MME

A B E const -Vret Is +HV C E var Is +45 V Ic 10/05/2007 SEY, M. Taborelli, TS-MME

Methods Speed for single point/dose Incidence angle Other properties Sample bias, variable gun energy D) Sample bias +90 V/GND and variable Egun Slow, yes 2 meas. of Is in series (NASA) -Ep min = 200 e. V (50 e. V? ) -some give very low δ, possibly due to scrubbing (dose) Normal -E min = 50 e. V, 300 e. V D) Sample bias at - Slow, meas. of Is and 23° -Negative sample bias 20 V and Ip in series deviates the beam variable Egun when changing angle (Kirby) Sample bias, variable gun energy, “collector” Slow, yes E) Cylinder 2 meas. of Is in collector at +50 V with grid ( series, pulsed beam, -50 V/+50 V), very low Farady cup curretns (Fijol) - Ep min = 20 e. V (? ) 10/05/2007 SEY, M. Taborelli, TS-MME

primary beam current D secondaries E var -20 V or GND/+90 V Is E E var Is +50 V -/+50 V backscatt. secondaries 10/05/2007 SEY, M. Taborelli, TS-MME

What is the importance of: -Incidence angle dependence -Minimum primary energy -Energy distribution Estimate of costs: e-gun Flood gun (home made) Manipulator Data acquisition UHV 100 K 45 K 12 K 15 K 30 K 10/05/2007 SEY, M. Taborelli, TS-MME