%0 Journal Article %1 Campbell1985 %A Campbell, J. H. %A Bretz, Michael %D 1985 %I American Physical Society %J Phys. Rev. B %K graphite, helium, microcalorimetry, ordering, science, sensor; surface %N 5 %P 2861--2869 %R 10.1103/PhysRevB.32.2861 %T He4 ordering transition on single-leaf pyrolytic graphite: A microcalorimetry study %U http://link.aps.org/doi/10.1103/PhysRevB.32.2861 %V 32 %X We have developed an ac microcalorimeter for the thermodynamic study of adsorbed gases on a single cleaved leaf of pyrolytic graphite. Our sensitivity of about 0.1 nJ/deg was sufficient to probe details of the 4He ordering transition. After in situ baking of the sample we found heat-capacity peaks comparable to those measured on the best exfoliated graphite substrates. The phase diagram near ordering is narrower than previously measured and a critical analysis yields asymmetric peaks: The low-T side diverges logarithmically for the six coverages analyzed between 0.0633/ \AA 2 and 0.0649/ \AA 2 while the high-T side of the peak displays a power-law divergence. The critical-heat-capacity exponent in this coverage range drops from 0.48 (stronger than that in the three-state Potts model) to -0.07 (slightly cusped). We interpret the narrow ordered-phase region as reflecting our excellent film geometry and the unexpected nonuniversality as caused by residual impurity, rather than size-limiting effects. Additional ac calorimetry studies should complement adsorbed-film single-crystal diffraction research.

@article{Campbell1985, abstract = {We have developed an ac microcalorimeter for the thermodynamic study of adsorbed gases on a single cleaved leaf of pyrolytic graphite. Our sensitivity of about 0.1 nJ/deg was sufficient to probe details of the 4He ordering transition. After in situ baking of the sample we found heat-capacity peaks comparable to those measured on the best exfoliated graphite substrates. The phase diagram near ordering is narrower than previously measured and a critical analysis yields asymmetric peaks: The low-T side diverges logarithmically for the six coverages analyzed between 0.0633/ \AA 2 and 0.0649/ \AA 2 while the high-T side of the peak displays a power-law divergence. The critical-heat-capacity exponent \alpha in this coverage range drops from 0.48 (stronger than that in the three-state Potts model) to -0.07 (slightly cusped). We interpret the narrow ordered-phase region as reflecting our excellent film geometry and the unexpected nonuniversality as caused by residual impurity, rather than size-limiting effects. Additional ac calorimetry studies should complement adsorbed-film single-crystal diffraction research.}, added-at = {2009-10-30T10:04:05.000+0100}, author = {Campbell, J. H. and Bretz, Michael}, biburl = {https://www.bibsonomy.org/bibtex/254300cc2158c3f5345b2f860db9f215d/jfischer}, doi = {10.1103/PhysRevB.32.2861}, interhash = {56c831fd611d2b0dc85c46d3a7767c31}, intrahash = {54300cc2158c3f5345b2f860db9f215d}, journal = {Phys. Rev. B}, keywords = {graphite, helium, microcalorimetry, ordering, science, sensor; surface}, month = Sep, number = 5, numpages = {8}, pages = {2861--2869}, publisher = {American Physical Society}, timestamp = {2009-10-30T10:04:10.000+0100}, title = {He4 ordering transition on single-leaf pyrolytic graphite: A microcalorimetry study}, url = {http://link.aps.org/doi/10.1103/PhysRevB.32.2861}, volume = 32, year = 1985 }