Coexistence of negatively and positively buckled isomers on n+-doped Si(111) − 2 × 1.

A long-standing puzzle regarding the Si(111) − 2 × 1 surface has been solved. The surface energy gap previously determined by photoemission on heavily n-doped crystals was not compatible with a strongly bound exciton known from other considerations to exist. New low-temperature angle-resolved photoemission and scanning tunneling microscopy data, together with theory, unambiguously reveal that isomers with opposite bucklings and different energy gaps coexist on such surfaces. The subtle energetics between the isomers, dependent on doping, leads to a reconciliation of all previous results.

Unilateral visual impairment after a dental procedure: Case report.

The use of intra-oral local anaesthetics for dental procedures is a widely extended practice that may cause side effects. As such, in rare cases it may cause ocular complications such as diplopia, ptosis, blurry vision, miosis, vision loss, or amaurosis. (Most of them are transient, recovering after several hours or days). A case is presented of a 26 year-old male patient who had visual impairment in the right eye 2 days after a dental procedure was performed. Six months later he had a complete restoration of the previous visual acuity, despite the fact that he had not received any treatment. Several ways have been proposed in the literature that may explain the appearance of ocular complications following these kinds of procedures. In this case, inadvertent intravenous injection is believed to have been the cause.

Unilateral visual impairment after a dental procedure: Case report. / Disminución de la agudeza visual tras un procedimiento odontológico: A propósito de un caso.

The use of intra-oral local anaesthetics for dental procedures is a widely extended practice that may cause side effects. As such, in rare cases it may cause ocular complications such as diplopia, ptosis, blurry vision, miosis, vision loss, or amaurosis. (Most of them are transient, recovering after several hours or days). A case is presented of a 26 year-old male patient who had visual impairment in the right eye 2 days after a dental procedure was performed. Six months later he had a complete restoration of the previous visual acuity, despite the fact that he had not received any treatment. Several ways have been proposed in the literature that may explain the appearance of ocular complications following these kinds of procedures. In this case, inadvertent intravenous injection is believed to have been the cause.

[Comparative study of the effects of two anti-glaucomatous drugs on the corneal thickness in rabbits with corneal autografts]. / Estudio comparativo de los efectos de dos drogas antiglaucomatosas sobre el espesor corneal en conejos con autoinjerto de córnea.

PURPOSE: To determine the central corneal thickness after administration of the anti-glaucomatous medications latanoprost 0.005% or dorzolamide 2%, as assessed in rabbits which have had total corneal thickness autografts. METHODS: A bilateral total corneal thickness autograft was performed in ten rabbits. One rabbit was excluded from the subsequent study in which the antiglaucomatous medication was started two months post-operatively. Latanoprost 0.005% was instilled once per day into the right eye, whereas the left eyes were treated with dorzolamide 2% twice a day. The eyes were examined by biomicroscopy and ultrasound pachymetry immediately prior to commencement, and 4, 10, 17 and 27 weeks after starting the anti-glaucomatous treatment. In each instance three assessments of the central corneal thickness in each eye were made. At the end of the study, the influence of time and treatment on the corneal thickness was analyzed using a generalized linear model for repeated measurements. All penetrating keratoplasties were performed by the same surgeon (C.H.P). RESULTS: Treatment with dorzolamide resulted in corneal edema and a significant increase in central corneal thickness, whereas the treatment with latanoprost resulted in neither corneal edema nor corneal thickness changes. CONCLUSIONS: Dorzolamide, when instilled into the eyes of rabbits with corneal autografts, could have a negative effect on the graft, impairing the endothelial function through inhibition of the ionic pump. This effect could cause graft failure, which may be able to be defined with ultrasound pachimetry.

Confinement effects in π-bonded chains at group IV semiconductor (111) surfaces.

The degree of 1D character of surface chains at group IV (111)-2 × 1 reconstructed surfaces is established by surface sensitive optical spectroscopy. Optical experiments on a diamond C(111)-2 × 1 surface show that the absorption peak related to dangling-bond transitions exhibits a marked blueshift upon oxygen exposure of the clean surface. Such behaviour is analogous to that observed on a clean Si(111)-2 × 1 surface. For both surfaces the experimental finding is interpreted in terms of quantum confinement of surface electrons in quasi-one-dimensional π-bonded chains, whose length decreases with oxygen uptake. A different behaviour is observed in Ge(111)-2 × 1, where only a very slight blueshift of the surface-state optical transition is detected upon oxidation. The almost negligible blueshift in Ge(111)-2 × 1 is consistent with a significant coupling between the π-bonded chains resulting in a much less pronounced one-dimensional character of Ge(111)-2 × 1 surface electrons compared to diamond and silicon reconstructed surfaces.

Charge transfer between isomer domains on n+-doped Si(111)-2 × 1: energetic stabilization.

Domains of different surface reconstruction-negatively or positively buckled isomers-have been previously observed on highly n-doped Si(111)-2 × 1 surfaces by angle-resolved ultraviolet photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. At low temperature, separate domains of the two isomer types are apparent in the data. It was argued in the previous work that the negative isomers have a lower energy of their empty surface states than the positive isomers, providing a driving force for the formation of the negative isomers. In this work we show that the relative abundance of these two isomers shows considerable variation from sample to sample, and it is argued that the size of the isomer domains is likely to be related to this variation. A model is introduced in which the electrostatic effect of charge transfer between the domains is computed, yielding total energy differences between the two types of isomer. It is found that the transfer of electrons from domains of positive isomers to negative ones leads to an energetic stabilization of the negative isomers. The model predicts a dependence of the isomer populations on doping that is in agreement with most experimental results. Furthermore, it accounts, at least qualitatively, for the marked lineshape variation from sample to sample observed in photoemission spectra.

Growth-related properties and postgrowth phenomena in organic molecular thin films.

The problem of monitoring the structural and morphological evolutions of thin films of organic molecular materials during their growth by organic molecular beam epitaxy and in the postgrowth stage is addressed here by a combination of in situ optical reflectance anisotropy measurements, ex situ optical and morphological investigations, and theoretical simulation of the material optical response. For alpha-quaterthiophene, a representative material in the class of organic molecular semiconductors, the results show that molecules crystallize in the first stage of growth in metastable structures, even when deposition is carried out at room temperature. In the postdeposition stage, the film structure evolves within a few days to the known equilibrium structure of the low temperature polymorph. When deposition is carried out at low substrate temperatures, an evolution of the film morphology is also demonstrated.