Measurement of the orthopositronium confinement energy in mesoporous thin films

Crivelli, P.; Gendotti, U.; Rubbia, A.; Liszkay, L.; Pérez, P.; Corbel, C.

doi:10.1103/physreva.81.052703

Cited by 94 publications

(113 citation statements)

References 63 publications

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“…Recently there has been a growing interest in using certain porous materials [25] to produce Ps in vacuum [26,27,28]. Ps may be formed from such materials quite efficiently (reported Ps fractions range from approximately 20 to 60%).…”

Section: Introductionmentioning

confidence: 99%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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Recent experiments combining lifetime and laser spectroscopy of positronium (Ps) show that these atoms are emitted from p-Si(100) at a rate that depends on the sample temperature, suggesting a thermal activation process, but with an energy that does not, precluding direct thermal activation as the emission mechanism. Moreover, the amount of Ps emitted is substantially increased if the target is irradiated with 532 nm laser light just prior to the implantation of the positrons. Our interpretation of these data was that the Ps was emitted via an exciton-like positron-electron surface state, not dissimilar to an electronic surface exciton observed on Si in two-photon photoemission measurements. The hypothesis that this state may be populated by electrons from one of the occupied electronic surface states, either thermally or by laser excitation, is consistent with our observations and suggests that one should expect a high Ps yield at room temperature from an n-doped Si(100) sample, since in this case the same surface states will already be occupied. Here we present data obtained with an n-Si(100) target that supports our model, and also reveals the unexpected result that the kinetic energy of Ps emitted from this material actually decreases when it is heated, an effect we attribute to shifts in the surface energy levels due to the presence of a high density of thermally generated electrons. We show data obtained with a Ge(100) sample that corroborate the idea that the effects we observe are related to surface electron states, and hence should occur for any indirect band gap semiconductor with dangling bond states. Our model is further confirmed by the observation that the Ps yield from p-Si depends linearly on the surface density of the implanted positrons due to the effects of electron-hole pairs created as the positrons slow down.

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Section: Introductionmentioning

confidence: 99%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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“…In order to maximize the signal-tobackground ratio, the width of the collimator slit is set to 5 mm and its center was placed at a distance of 20 mm from the target. More details concerning the experimental setup can be found in [21].…”

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confidence: 99%

“…The time Ps spends in the crystal is related to the e + implantation depth, so for e + implanted with greater energy, lower energy Ps is emitted. At room temperature, only the ground state should be populated, as in silica with 3-4 nm pores [21,27], so for sufficient e + implantation energy, one should observe Ps only with energies in the range of 200-400 meV (we use the cluster-to-cluster distance of the MOFs reported in Table I to set this lower bound).…”

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confidence: 99%

“…The H-H distance is the distance from the closest H atoms on opposite sides of the framework having subtracted the van der Waals radii (2 × 1.2Å). For this study we used the ETHZ slow e + beam [20,21]. The slow positrons from the beam are accelerated to 1-20 keV towards the MOF target.…”

mentioning

confidence: 99%

“…To determine the emission energy of Ps into vacuum we fit the measured TOF distributions with a sum of spectra simulated with Geant4 code [21,32]. We use monoenergetic distributions emitted isotropically with their fractions as the free parameters.…”

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confidence: 99%

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Positronium emission spectra from self-assembled metal-organic frameworks

et al. 2014

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Recently, evidence for positronium (Ps) in a Bloch state in self-assembled metal-organic frameworks (MOFs) has been reported [Dutta et al., Phys. Rev. Lett. 110, 197403 (2013)]. In this paper, we study Ps emission into vacuum from four different MOF crystals: MOF-5, IRMOF-8, ZnO4(FMA)3 and IRMOF-20. Our measurements of Ps yield and emission energy into vacuum provide definitive evidence of Ps delocalization. We determine with a different technique Ps diffusion lengths in agreement with the recently published results. Furthermore, we measure that a fraction of the Ps is emitted into vacuum with a distinctly smaller energy than what one would expect for Ps localized in the MOFs' cells. We show that a calculation assuming Ps delocalized in a Kronig-Penney potential reproduces the measured Ps emission energy.

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Quantifying the Complex Pore Architecture of Hierarchical Faujasite Zeolites and the Impact on Diffusion

Kenvin

Mitchell

Sterling

et al. 2016

Adv Funct Materials

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An exact knowledge of the architecture of complex pore networks and the impact on transport processes is critical to understand and optimize their integration in many functional solids. Here, a robust and versatile approach is demonstrated to quantitatively map pore constrictions within hierarchical faujasite-type (Y and USY) zeolites, the most widely applied zeolitic materials in industry. Differential hysteresis scanning measurements by high-resolution argon sorption coupled with an advanced modeling framework enable the derivation of the amount and size of pyramidal, constricted, and occluded mesopores. This yields unprecedented insight into the impact of widely practiced demetallation treatments on the porosity evolution and clearly highlights the interplay between the geometry of mesopores developed by a given treatment and those introduced by previously applied postsynthetic modifications. Based on the findings, the dynamic assessment by positron annihilation spectroscopy confirms the effectiveness of each mesopore type at enhancing the diffusion of ortho-positronium within the crystal. The quantitative descriptors attained by these complementary techniques can revolutionize the design of porous materials for a wide range of applications.

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Measurement of the orthopositronium confinement energy in mesoporous thin films

Cited by 94 publications

References 63 publications

Positronium formation via excitonlike states on Si and Ge surfaces

Positronium formation via excitonlike states on Si and Ge surfaces

Positronium emission spectra from self-assembled metal-organic frameworks

Quantifying the Complex Pore Architecture of Hierarchical Faujasite Zeolites and the Impact on Diffusion

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