Isotropic theoretical angular correlation of annihilation radiation spectra for positrons trapped at an Al surface?

Using a potential model for the surface of a metal and the revised Brandt-Reinheimer enhancement factor r ( n ) , we have calculated the electron wavefunction, the two-dimensional angular correlation and the lifetime of 2y annihilation from the AI( loo), A1(110), Al(111) and Cu(121) surfaces. We conclude that (i) the momenta of the electrons are filtered by the suridce potential; (ii) the momentum distribution of 2y annihilation is greatly constricted for both the parallel and perpendicular directions to the surface; (iii) it is possible to obtain simultaneously the observed isotropic angular correlation curve and the long lifetime of the positron surface state; and (iv) within a reasonable range of our model parameters, the isotropy of the angular correlation curve is rather insensitive to the parameter values. Our results are consistent with experiment.

Section: Resultsmentioning

confidence: 99%

Calculation of the angular correlation and the lifetime of positron surface states on metal surfaces

Lou¹,

Gu²,

Jia-Lin³

et al. 1989

“…The results obtained from the LDA-MDA formula (sa) with the electronic screening charge distribution A p ( r ) (appropriate for the surface problem) calculated in the way proposed by Jensen and Walker (1988) are presented in a subsequent publication (Rubaszek and Lach 1988).…”

mentioning

confidence: 99%

On surface ACAR spectra calculated within the mixed density approximation

Rubaszek

1989

Various approaches to the surface problem that enables one to calculate angular correlation of annihilation radiation (ACAR) spectra are discussed. The validity of the mixed-density approximation (MDA) in the neighborhood of metal surface is investigated. For positrons trapped at the Al surface the MDA gives results that strongly disagree with those obtained using the exact ACAR formula. A new formula for use in calculating surface ACAR spectra, allowing avoidance of this deficiency of the MDA, is proposed.

Electron-positron annihilation characteristics at a metal surface: simple metals

Rubaszek¹,

Kiejna²,

Daniuk³

1993

Self Cite

Momentum densities of annihilating elecfroc-psimn pairs. posimn lifetimes, work funcuons and binding energies as well as e l e c t r o ~s l m n enhancement factors at the surfaces of simple metals and cadmium are studied. 'Ihe effect of ekcuowposimn correlations on the surfaceitate posimn a " o n chanctellstics is set out Institute of ExperimenLll Physics, Universily of Wndaw. 50-204 Wmcfaw, PI. Maxa Boma 1 . Introduction Studies of slow positron interactions with metal surfaces (for reviews, see e.g. I11-[41) opened a new channel in investigations of the electronic structure of solids by positron annihilation. In particular, the extended well known angular correlation of annihilation radiation (ACAR) technique (for reviews, see e.g. [5,6]) has been successfully applied to probing electron and positron surface states (ss) in AI ([7-lo]), Cu [ll], Ni [9,10,12], Pb [131, Si [9,10] and graphite [14]. Slow-positron experiments have conlirmed the presence of the posiwn Ss at the clean AI [I101 surface 1151; the ss component of the measured lifetime spectrum amounts to 580 ps, i.e. about 15% more than the spin-averaged free positronium value. This result