Investigation of electrical properties of surface structures by X-Ray photoelectron spectroscopic technique under external voltage stimuli

Cataloged from PDF version of article.Electrical properties of surface structures are analyzed using XPS (X-Ray Photoelectron Spectroscopy) by means of external stimuli together with a novel technique allowing the user to record 200 conventional spectra in a period of one second with a time resolution of 5ms. Charging processes of surface structures such as SiO2 and C12-thiol-capped gold nanoclusters are monitored by time resolved XPS technique which gives an approximate charging constant of the system (RC), and electrical parameters like resistance and capacitance are estimated using external biasing and other relevant time resolved XPS data. Moreover, development and optimization of the technique are carried out by certain parameters and observing the changes in the time constants and binding energy shifts. It is also shown that application of positive and negative external bias can be used to identify two different forms of gold that exist together in the same sample, as nanoparticles and bulk metal, by means of stimulating the charging-induced-separation of the Au 4f peaks which would otherwise appear as overlapped photoemission signals in the grounded spectrum.Demirok, U KorcanM.S

X-ray photoelectron spectroscopy for resistance-capacitance measurements of surface structures

Cataloged from PDF version of article.In x-ray photoemission measurements, differential charging causes the measured binding energy difference between the Si 2p of the oxide and the silicon substrate to vary nonlinearly as a function of the applied external do voltage stress, which controls the low-energy electrons going into and out of the sample. This nonlinear variation is similar to the system where a gold metal strip is connected to the same voltage stress through an external 10 Mohm series resistor and determined again by x-ray photoelectron spectroscopy (XPS). We utilize this functional resemblance to determine the resistance of the 4 nm SiO2 layer on a silicon substrate as 8 Mohm. In addition, by performing time-dependent XPS measurements (achieved by pulsing the voltage stress), we determine the time constant for charging/discharging of the same system as 2.0 s. Using an equivalent circuit, consisting of a gold metal strip connected through a 10 Mohm series resistor and a 56 nF parallel capacitor, and performing time-dependent XPS measurements, we also determine the time constant as 0.50 s in agreement with the expected value (0.56 s). Using this time constant and the resistance (8.0 Mohm), we can determined the capacitance of the 4 nm SiO2 layer as 250 nF in excellent agreement with the calculated value. Hence, by application of external do and pulsed voltage stresses, an x-ray photoelectron spectrometer is turned into a tool for extracting electrical parameters of surface structures in a noncontact fashion. (c) 2005 American Institute of Physics

Evaluation of the voltage support strategies for the low voltage grid connected PV generators

Admissible range of grid voltage is one of the strictest constraints for the penetration of distributed photovoltaic (PV) generators especially connection to low voltage (LV) public networks. Voltage limits are usually fulfilled either by network reinforcements or limiting of power injections from PVs. In order to increase PV penetration level further, new voltage support control functions for individual inverters are required. This paper investigates distributed reactive power regulation and active power curtailment strategies regarding the development of PV connection capacity by evaluation of reactive power efforts and requirement of minimum active power curtailment. Furthermore, a small scale experimental setup is built to reflect real grid interaction in the laboratory by achieving critical types of grid (weak and sufficiently stiff).Peer Reviewe

Accuracy and precision of cap thickness in small incision lenticule extraction

Engin Bilge Ozgurhan,1 Alper Agca,1 Ercument Bozkurt,1 Baran Gencer,2 Ugur Celik,1 Kadir İlker Cankaya,1 Ahmet Demirok,1,3 Omer Faruk Yilmaz41Beyoglu Eye Training and Research Hospital, Istanbul, Turkey; 2Ophthalmology Department, Faculty of Medicine, Çanakkale Onsekiz Mart University, Çanakkale, Turkey; 3Department of Ophthalmology, Medeniyet University, Istanbul, Turkey; 4Private practice, Istanbul, TurkeyAims: To report and compare the cap thickness predictability of small incision lenticule extraction (SMILE) and flap thickness of femtosecond laser-assisted in situ keratomileusis (femto-LASIK).Settings and design: Beyoglu Eye Training and Research Hospital, Refractive Surgery Department, Istanbul, Turkey. Retrospective pilot study.Materials and methods: Medical records of patients who had SMILE in one eye and femto-LASIK in the other eye were reviewed. Visante corneal Optical Coherence Tomography (OCT) images at 1 week and 1 month post-surgery were analyzed. Both cap and flap thickness at the temporal edge and the nasal edge were measured and compared to each other.Statistical analyses used: PAWS Statistics 18 and unpaired student t-test were used to compare the groups.Results: The study included 66 eyes of 33 patients (24.7 ± 3.8 years, 20 females and 13 males). Mean flap thickness was 114.88 µm ± 4.96 µm, and mean cap thickness was 114.63 µm ± 5.18 µm. In group 1 (SMILE), cap thickness values were 115.84 µm ± 6.84 µm, 114.75 µm ± 7.36 µm, 113.66 µm ± 6.88 µm, and 114.27 µm ± 6.90 µm in measurement zones 1, 2, 3, and 4, respectively. In group 2 (FemtoLASIK), flap corneal thickness values were 115.96 mmHg ± 7.01 mmHg, 114.72 mmHg ± 7.17 mmHg, 113.54 mmHg ± 6.45 mmHg, and 115.30 mmHg ± 6.64 mmHg in measurement zones 1, 2, 3, and 4, respectively. In both groups, no statistically significant change within the measurement zones was observed.Conclusion: The predictability of cap thickness in SMILE surgery does not differ from the femto-LASIK flaps created using the same femtosecond laser platform.Keywords: SMILE, small incision lenticule extractio

Femtosecond lenticule extraction for correction of myopia: a 6 month follow-up study

Ahmet Demirok,1 Alper Agca,2 Engin Bilge Ozgurhan,2 Ercument Bozkurt,2 Ugur Celik,2 Ali Demircan,2 Nimet Burcu Guleryuz,2 Kadir Ilker Cankaya,2 Omer Faruk Yilmaz3 1Department of Ophthalmology, Medeniyet University, Istanbul, Turkey; 2Beyoglu Eye Training and Research Hospital, Istanbul, Turkey, 3Private Practice, Istanbul, Turkey Aims: To report our initial experience with femtosecond lenticule extraction (FLEX) compared with femtosecond laser-assisted in situ keratomileusis (LASIK). Settings and design: This was a prospective pilot study carried out at the Refractive Surgery Department of the Beyoglu Eye Training and Research Hospital, Istanbul, Turkey. Materials and methods: Surgery was performed on both eyes of 14 consecutive patients with myopia or myopic astigmatism. Patients underwent FLEX in one eye and femtosecond LASIK (FemtoLASIK) in the other eye. The primary outcome was based on uncorrected distance visual acuity, corrected distance visual acuity, and spherical equivalent of the subjective manifest refraction, at 1 week, 1 month, and 6 months postsurgery. Statistical analyses were performed using PAWS Statistics 18. Unpaired Student&rsquo;s t-test was used to compare the groups. Results: During the last follow-up visit (6 months postsurgery), the mean spherical was &minus;0.37 &plusmn; 0.60 diopters (D) (range &minus;1.00 to 0.50) (P < 0.001) and &minus;0.25 &plusmn; 0.41 D (range &minus;0.88 to 0.12 D) (P < 0.001) in the FLEX and FemtoLASIK eyes, respectively. The spherical was within &plusmn; 0.50 D of the intended correction in ten (72%) of the FLEX eyes and 12 (86%) of the FemtoLASIK eyes (P > 0.05). No complications occurred during surgery or the postoperative period. Conclusion: FLEX is a safe, effective, and predictable procedure for surgical correction of myopia. Refractive results were stabilized within the first postoperative week, and visual acuities were stabilized within the first month, comparable to FemtoLASIK. Keywords: FLEX, femtosecond laser-assisted in situ keratomileusi