Real-space observation of surface structuring induced by ultra-fast-laser illumination far below the melting threshold.

Intense short laser pulses are an intriguing tool for tailoring surface properties via ultra-fast melting of the surface layer of an irradiated target. Despite extensive studies on the interaction of femto-second laser interaction with matter, the initial steps of the morphological changes are not yet fully understood. Here, we reveal that substantial surface structure changes occur at energy densities far below the melting threshold. By using low-temperature scanning tunneling microscopy we resolve atomic-scale changes, i.e. the creation of nanosized adatom and vacancy clusters. The two cluster types have distinct non-linear fluence-dependencies. A theoretical analysis reveals their creation and motion to be non-thermal in nature. The formation of these atomistic changes, individually resolved here for the first time, recast our understanding of how surfaces respond to low-intensity ultra-short laser illumination. A visualization and control of the initial morphological changes upon laser illumination are not only of fundamental interest, but pave the way for the designing material properties through surface structuring.

Competition between Coulomb and van der Waals Interactions in Xe-Cs

Microscopic insight into interactions is a key for understanding the properties of heterogenous interfaces. We analyze local attraction in noncovalently bonded Xe-Cs^{+} aggregates and monolayers on Cu(111) as well as repulsion upon electron transfer. Using two-photon photoemission spectroscopy, scanning tunneling microscopy, and coupled cluster calculations combined with an image-charge model, we explain the intricate impact Xe has on Cs^{+}/Cu(111). We find that attraction between Cs^{+} and Xe counterbalances the screened Coulomb repulsion between Cs^{+} ions on Cu(111). Furthermore, we observe that the Cs 6s electron is repelled from Cu(111) due to xenon's electron density. Together, this yields a dual, i.e., attractive or repulsive, response of Xe depending on the positive or negative charge of the respective counterparticle, which emphasizes the importance of the Coulomb interaction in these systems.

Understanding the Enhancement of Surface Diffusivity by Dimerization.

Beyond dilute coverage, the collective diffusion of molecules might enhance material transport. We reveal an enhanced mobility of molecular dimers by separating two motions, diffusion and rotation, of CO dimers on elemental Ag(100) as well as on a dilute Cu alloy of Ag(100). From time-lapsed scanning tunneling microscopy movies recorded between 15 and 25 K, we determine the activation energy of dimer diffusion on elemental Ag(100) to be, at (40±2) meV, considerably smaller than the one for monomer diffusion, at (72±1) meV. The alloyed Cu atoms reduce the dimer mobility facilitating to determine their rotational barrier separately to be (39±3) meV. Disentangling different degrees of freedom suggests that a rotational motion is at the origin of enhanced dimer diffusivity.

How Atomic Steps Modify Diffusion and Inter-adsorbate Forces: Empirical Evidence from Hopping Dynamics in Na/Cu(115).

We followed the collective atomic-scale motion of Na atoms on a vicinal Cu(115) surface within a time scale of pico- to nanoseconds using helium spin echo spectroscopy. The well-defined stepped structure of Cu(115) allows us to study the effect that atomic steps have on the adsorption properties, the rate for motion parallel and perpendicular to the step edge, and the interaction between the Na atoms. With the support of a molecular dynamics simulation we show that the Na atoms perform strongly anisotropic 1D hopping motion parallel to the step edges. Furthermore, we observe that the spatial and temporal correlations between the Na atoms that lead to collective motion are also anisotropic, suggesting the steps efficiently screen the lateral interaction between Na atoms residing on different terraces.

A molecular switch based on the manipulation of 1,3-dichlorobenzene on Ge(001) between two adsorption sites by inelastic tunneling electrons.

Meta-dichlorobenzene is adsorbed on Ge(001) and investigated by low temperature scanning tunneling microscopy. The molecule is altered between two adsorption sites by inelastic electron tunneling manipulation. These adsorption sites differ largely in conductivity. The necessary energy for switching the molecule between the sites and its polarity dependence indicate that the manipulation is initiated by the electronic excitation of the molecule.

Differences between thermal and laser-induced diffusion.

A combination of femtosecond laser excitation with a low-temperature scanning tunneling microscope is used to study long-range interaction during diffusion of CO on Cu(111). Both thermal and laser-driven diffusion show an oscillatory energy dependence on the distance to neighboring molecules. Surprisingly, the phase is inverted; i.e., at distances at which thermal diffusion is most difficult, it is easiest for laser-driven diffusion and vice versa. We explain this unexpected behavior by a transient stabilization of the negative ion during diffusion as corroborated by ab initio calculations.

Local determination of the amount of integration of an atom into a crystal surface.

Collective vibrational modes of crystal lattices, called phonons, determine fundamental material properties, such as their thermal and electrical conductivities. Bulk phonon spectra are influenced by point defects. More recently, the importance of phonons on nanostructures has come into the focus of attention. Here we show a spatially resolved phonon spectra of point defects that reveal distinctly different signatures for a cavity alone and an impurity atom fully integrated into the surface as opposed to one placed into a cavity. The spectra are indicative for delocalized phonons and localized vibrations, respectively, as confirmed by theory.

Restructuring of cobalt nanoparticles induced by formation and diffusion of monodisperse metal-sulfur complexes.

Time-resolved scanning tunneling microscopy (STM) is used to investigate a massive sulfur-induced transformation of a homogeneous array of approximately 2 nm Co nanoparticles into a new cobalt sulfide phase. The underlying atomistic mass-transport process is revealed and, surprisingly, found to be mediated exclusively by the formation and detachment of monosized Co3S4 complexes at the perimeter of the Co nanoparticles. The process is followed by fast diffusion, agglomeration of the complexes, and subsequent crystallization into a cobalt sulfide phase.

Imaging phonon excitation with atomic resolution.

Inelastic electron tunneling spectroscopy at low temperatures was used to investigate vibrations of Au(111) and Cu(111). The low-energy peaks at 9 millielectron volts (meV) on Au(111) and 21 meV on Cu(111) are attributed to phonons at surfaces. On Au(111), the phonon energy is not influenced by the different stacking of the surface atoms, but it is considerably influenced by different atomic distances within the surface layer. The spatial variation of the phonon excitation is measured in inelastic electron tunneling maps on Au(111), which display atomic resolution. This atomic resolution is explained in terms of site-specific phonon excitation probabilities.

Impact of ice structure on ultrafast electron dynamics in D2O clusters on Cu(111).

The structure of D2O clusters on a Cu(111) surface and the femtosecond dynamics of photoexcited excess electrons are investigated by low-temperature scanning tunneling microscopy and two-photon photoemission spectroscopy. Two types of amorphous ice clusters, porous and compact, which exhibit characteristic differences in electron dynamics, are identified. By titration with Xe we show that in both structures solvated electrons preferentially bind on the cluster surface.

Contribution of the surface state to the observation of the surface Kondo resonance.

Tunneling spectra obtained on and near Co atoms adsorbed on Ag(111) show at 5 to 6 K a Kondo resonance that appears as a characteristic dip around the Fermi energy. The feature is present up to 1.5 nm around Co atoms adsorbed on terraces with the surface state onset in the occupied region of the density of states. On a narrow terrace, where the surface state onset lies in the unoccupied region of the density of states, it is only present up to 0.5 nm. This difference demonstrates directly the importance of the surface state electrons in the observation of the surface Kondo resonance.

Electron induced ortho-meta isomerization of single molecules.

A scanning tunneling microscope operating at 5 K is used to induce the isomerization of single chloronitrobenzene molecules on Cu(111) and verify the reaction. The threshold voltage of (227+/-7) mV for this reaction is explained based on electron-induced vibrational heating. We propose that the isomerization is initiated by simultaneous excitation of two vibrational molecular modes via inelastically tunneling electrons. This excitation results in a shift of the distribution probability of chlorine and hydrogen positions, which facilitates their mutual exchange.

Changes in net ecosystem productivity with forest age following clearcutting of a coastal Douglas-fir forest: testing a mathematical model with eddy covariance measurements along a forest chronosequence.

We hypothesized that changes in net ecosystem productivity (NEP) during aging of coastal Douglas-fir (Pseudotsuga menziesii Mirb. Franco) stands could be explained by (1) changing nutrient uptake caused by different time scales for decomposition of fine, non-woody and coarse woody litter left after harvesting, (2) declines in canopy water status with lengthening of the water uptake pathway during bole and branch growth, and (3) increases in the ratio of autotrophic respiration (R (a)) to gross primary productivity (GPP) with phytomass accumulation. These hypotheses were implemented and tested in the mathematical model ecosys against eddy covariance (EC) measurements of forest CO(2) and energy exchange in a post-clearcut Douglas-fir chronosequence. Hypothesis 1 explained how (a) an initial rise in GPP observed during the first 3 years after clearcutting could be caused by nutrient mineralization from rapid decomposition of fine, non-woody litter with lower C:N ratios (assart effect), (b) a slower rise in GPP during the next 20 years could be caused by immobilization during later decomposition of coarse woody litter, and (c) a rapid rise in GPP between 20 and 40 years after clearcutting could be caused by nutrient mineralization with further decomposition of coarse woody litter and of its decomposition products. During periods (a) and (b), heterotrophic respiration (R (h)) from decomposition of fine and coarse litter greatly exceeded net primary productivity (NPP = GPP - R (a)) so that Douglas-fir stands were large sources of CO(2). During period (c), NPP exceeded R (h) so that these stands became large sinks for CO(2). Hypothesis 2 explained how declines in NPP during later growth in period (c) could be caused by lower hydraulic conductances in taller trees that would force lower canopy water potentials and hence greater sensitivity of stomatal conductances and CO(2) uptake to vapor pressure deficits. Enhanced sensitivity to vapor pressure deficits was also apparent in the EC measurements over the post-clearcut chronosequence. Hypothesis 3 did not contribute to the explanation of forest age effects on NEP.

Amino-nitro-azobenzene dimers as a prototype for a molecular-level machine.

Low-temperature scanning tunnelling microscope measurements of an X-shaped dimer, consisting of two amino-nitro-azobenzene molecules, on a Au(111)-surface are presented. Electron-induced manipulation switches either the upper- or the lower-lying molecule. These reversible switching processes are based on the cis-trans isomerization of the azobenzene molecules. The switching of the upper molecule moves the lower-lying molecule in a controlled way. Thus mechanical work is performed. This proof-of-principle shows the ability of azobenzene molecules to act as a molecular-level machine.

Botulinum toxin type a for dysthyroid upper eyelid retraction.

PURPOSE: To evaluate the safety and efficacy of botulinum toxin type A for treatment of eyelid retraction resulting from thyroid eye disease (TED) during the inflammatory phase of the condition. METHODS: In this prospective, nonrandomized case series, 18 patients with inflammatory eyelid retraction caused by active TED received botulinum toxin type A injection (10, 5, or 2.5 U) for treatment of upper eyelid retraction. Botulinum toxin type A (Allergan, Irvine, CA, U.S.A.) was injected transconjunctivally just above the superior tarsal border in the elevator complex of the upper eyelid. RESULTS: Seventeen of 18 patients (94%) demonstrated a reduced marginal reflex distance (MRD1) after botulinum toxin injection. The average change in MRD1 of the treated eyelid after injection was -2.35 mm (range, 0 to -8.0 mm). Of the 27 eyelids injected, 33% had a 0- to 1-mm drop in eyelid height, 30% had a 1.5- to 2-mm decrease, 22% had a 2.5- to 3-mm decrease, and 15% had a greater than 3-mm decrease in eyelid height. None of the treated eyelids were noted to increase in height. One patient showed no alteration inafter treatment. One patient had clinically MRD1 significant ptosis and one patient reported worsening of preexisting diplopia after injection. Three patients undergoing unilateral injection had relative contralateral eyelid elevation. All untoward effects resolved spontaneously without sequelae. CONCLUSIONS: : Botulinum toxin type A may be used in the inflammatory stage of thyroid eye disease to improve upper eyelid retraction. Individual response to treatment is variable, but this modality should be considered as a temporizing measure until stability for surgery is reached.

Nasolacrimal obstruction secondary to I(131) therapy.

PURPOSE: To report the finding of nasolacrimal drainage system obstruction associated with I(131) therapy for thyroid carcinoma from an updated and expanded cohort. METHODS: Patients with a history of epithelial derived thyroid carcinoma who had tearing were offered referral for evaluation by an oculoplastic surgeon. Patients underwent nasolacrimal probing and irrigation procedures with localization of their nasolacrimal obstruction. Therapy for the site of obstruction was instituted. RESULTS: Clinically significant tearing was identified in 26 patients, all of whom had previously undergone I(131) therapy (n = 563). Nineteen patients were evaluated and confirmed to have nasolacrimal drainage system obstruction; 7 have yet to be formally evaluated. Areas of obstruction included nasolacrimal duct, common canaliculus, and, rarely, distal upper and lower canaliculi. Patients were treated with a variety of modalities including silicone intubation, balloon dacryoplasty, dacryocystorhinostomy, and conjunctival dacryocystorhinostomy. CONCLUSIONS: The use of I(131) for thyroid carcinoma is associated with a 3.4% incidence of documented nasolacrimal drainage obstruction and an overall 4.6% incidence of documented or suspected obstruction. The true incidence may be higher, since - I(131) treated individuals were neither systematically evaluated nor questioned about tearing. It has yet to be established if the obstructions result from local toxicity caused by the passive flow of radioactive iodine containing tears through these tissues or the active uptake and concentration of I(131) in lacrimal drainage system tissues through the sodium/iodide supporter.

Advances in cosmetic oculoplastic surgery.

According to the American Society for Aesthetic Plastic Surgery, in the year 2000 over 5.7 million cosmetic surgical and nonsurgical procedures were performed in the United States. This was a 25% increase above the total number performed in 1999. The most popular of these procedures was botulinum toxin injection, followed by chemical peels and microdermabrasion. As the field of plastic and reconstructive surgery changes, so does the scope of the oculoplastic surgeon. This review article summarizes those developments in aesthetic surgery that are recent additions to the practice of aesthetic oculoplastic surgery. It highlights the most recent literature discussing brow and midface lifts, skin lasers, microdermabrasion, upper and lower blepharoplasty, chemical peels, botulinum toxin, and fat sculpturing.

Atomic-scale structure of dislocations revealed by scanning tunneling microscopy and molecular dynamics.

The intersection between dislocations and a Ag(111) surface has been studied using an interplay of scanning tunneling microscopy (STM) and molecular dynamics. Whereas the STM provides atomically resolved information about the surface structure and Burgers vectors of the dislocations, the simulations can be used to determine dislocation structure and orientation in the near-surface region. In a similar way, the subsurface structure of other extended defects can be studied. The simulations show dislocations to reorient the partials in the surface region leading to an increased splitting width at the surface, in agreement with the STM observations. Implications for surface-induced cross slip are discussed.

Congenital intraocular teratoma associated with eyelid coloboma.

PURPOSE: To describe the first case of intraocular teratoma associated with eyelid coloboma and the second reported case of intraocular teratoma. DESIGN: Interventional case report. METHODS: A left intraocular tumor was surgically resected from a 2-day-old female with an associated lower eyelid coloboma. RESULTS: Pathologic evaluation revealed a completely intraocular tumor comprising derivatives of all three germ cell layers giving a diagnosis of intraocular teratoma. The eyelid coloboma was repaired, and a scleral-wrapped hydoxyapatite-integrated orbital implant was placed. CONCLUSION: To our knowledge, this is the second reported instance of teratoma originating within the globe and the only reported case of teratoma associated with eyelid coloboma. Although exceedingly rare, intraocular teratoma should be added to the differential diagnosis of congenital intraocular tumors.