Positronium Formation as a Probe of Polymer Surfaces and Thin Films

Xie, Li; Demaggio, G. B.; Frieze, W. E.; DeVries, Jeffrey M.; Gidley, D. W.; Hristov, Hristo; Yee, A. F.

doi:10.1103/physrevlett.74.4947

Cited by 149 publications

(151 citation statements)

References 24 publications

Supporting

Mentioning

136

Contrasting

Order By: Relevance

“…It is still a matter of debate whether or not the density of a polymer in an ultra-thin film is different from its density in bulk. polymer density in annealed films thicker than 10 nm is the same as in bulk [33,34], and the density at the interface with air and with a supporting substrate differs from the bulk density over distances of at most a few nanometers [35][36][37][38].…”

Section: Thickness Dependencementioning

confidence: 74%

Solvent retention in thin polymer films studied by gas chromatography

Garcia-Turiel

Jérôme

2007

Colloid Polym Sci

View full text Add to dashboard Cite

Thin polystyrene films were produced by spin coating from solutions in toluene. The amount of solvent retained in the films after drying for different times was measured using gas chromatography. Whereas for thicker films (thickness > 200 nm), the relative amount of solvent in the films is less than a few percent, the proportion of toluene increases significantly in thinner films. The thickness dependence of the mass of retained solvent shows that the solvent is mainly retained at the polymer-substrate interface. The solvent desorption rate exhibits no variation on the film thickness.

show abstract

Section: Thickness Dependencementioning

confidence: 74%

Solvent retention in thin polymer films studied by gas chromatography

Garcia-Turiel

Jérôme

2007

Colloid Polym Sci

View full text Add to dashboard Cite

show abstract

“…Although initial AFM results on polymer-air surfaces indicate rubbery properties of surface layers, 16 more recent experimental results have shown very small or negligible changes in surface polymer properties. 8,18 Experiments using near-edge X-ray absorption fine-structure (NEXAFS) on rubbed polystyrene films have shown almost no difference in the rate of relaxation between polymer chains within 1 nm of the surface and chains within 10 nm of the surface, again indicating a small influence of the surface on the system's dynamics. 18 On the other hand, Monte Carlo simulations have shown a higher mobility at polymer-air surfaces, due to a reduction in density.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Surface properties such as glass transition temperatures, liquid-crystal melting points, and surface mobility have important technological implications in the areas of adhesion, alignment of liquid crystals, and biocompatibility of polymers. A variety of experimental studies have established that surfacepolymer interactions greatly influence the glass transition temperature (T g ) of ultrathin polymer films.…”

Section: Introductionmentioning

confidence: 99%

Surface Dynamics in Rubbed Polymer Thin Films Probed with Optical Birefringence Measurements

et al. 2000

View full text Add to dashboard Cite

Measurements of the optical birefringence were used to probe the relaxation of rubbed ultrathin polystyrene (PS) films on glass substrates. It was found that the glass transition temperature, T g, of the films dropped by 15-20 K as the film thickness decreased from 10 µm to 5.8 nm. Experiments on thick films (∼10 µm) revealed that molecules closer to the polymer-air interface relax more quickly than molecules farther from the interface. These results are explained in the context of past experimental studies of thermal properties of similar ultrathin polymer films.

show abstract

“…For positronium in its ground state, the annihilation rate depends on the relative spin states of the electron and positron: if the spins are parallel (triplet states) the mean lifetime is relatively long (142 ns) whereas the antiparallel (singlet) configuration is short lived (0.125 ns). Despite its relatively short lifetime, Ps can still be used in a wide array of experiments, including precision laser spectroscopy [4], Ps ion [5] or molecule [6] formation, Psatom scattering cross section measurements [7], studies of defects [8], thin film polymers [9], surface magnetism [10], electronic densities of states [11], quantum sticking [12], and fundamental symmetry tests [13].…”

Section: Introductionmentioning

confidence: 99%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

View full text Add to dashboard Cite

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.

show abstract

Positronium Formation as a Probe of Polymer Surfaces and Thin Films

Cited by 149 publications

References 24 publications

Solvent retention in thin polymer films studied by gas chromatography

Solvent retention in thin polymer films studied by gas chromatography

Surface Dynamics in Rubbed Polymer Thin Films Probed with Optical Birefringence Measurements

Positronium formation via excitonlike states on Si and Ge surfaces

Contact Info

Product

Resources

About