Browsing by Subject "Surface structure"
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Item Open Access Charging/discharging of Au (core)/silica (shell) nanoparticles as revealed by XPS(American Chemical Society, 2005) Tunc, I.; Demirok, U. K.; Süzer, Şefik; Correa-Duatre, M. A.; Liz-Marzan, L. M.By recording XPS spectra while applying external voltage stress to the sample rod, we can control the extent of charging developed on core-shell-type gold nanoparticles deposited on a copper substrate, in both steady-state and time-resolved fashions. The charging manifests itself as a shift in the measured binding energy of the corresponding XPS peak. Whereas the bare gold nanoparticles exhibit no measurable binding energy shift in the Au 4f peaks, both the Au 4f and the Si 2p peaks exhibit significant and highly correlated (in time and magnitude) shifts in the case of gold (core)/silica (shell) nanoparticles. Using the shift in the Au 4f peaks, the capacitance of the 15-nm gold (core)/6-nm silica (shell) nanoparticle/nanocapacitor is estimated as 60 aF. It is further estimated that, in the fully charged situation, only 1 in 1000 silicon dioxide units in the shell carries a positive charge during our XPS analysis. Our simple method of controlling the charging, by application of an external voltage stress during XPS analysis, enables us to detect, locate, and quantify the charges developed on surface structures in a completely noncontact fashion. © 2005 American Chemical Society.Item Open Access Comparison of two methods of surface profile extraction from multiple ultrasonic range measurements(Institute of Physics Publishing, 2000) Barshan, B.; Backent, D.Two novel methods for surface profile extraction based on multiple ultrasonic range measurements are described and compared. One of the methods employs morphological processing techniques, whereas the other employs a spatial voting scheme followed by simple thresholding. Morphological processing exploits neighbouring relationships between the pixels of the generated arc map. On the other hand, spatial voting relies on the number of votes accumulated in each pixel and ignores neighbouring relationships. Both approaches are extremely flexible and robust, in addition to being simple and straightforward. They can deal with arbitrary numbers and configurations of sensors as well as synthetic arrays. The methods have the intrinsic ability to suppress spurious readings, crosstalk and higher-order reflections, and process multiple reflections informatively. The performances of the two methods are compared on various examples involving both simulated and experimental data. The morphological processing method outperforms the spatial voting method in most cases with errors reduced by up to 80%. The effect of varying the measurement noise and surface roughness is also considered. Morphological processing is observed to be superior to spatial voting under these conditions as well.Item Open Access Differentiation of domains in composite surface structures by charge-contrast x-ray photoelectron spectroscopy(2007) Süzer, Şefik; Dâna, A.; Ertas, G.An external bias is applied to two samples containing composite surface structures, while recording an XPS spectrum. Altering the polarity of the bias affects the extent of differential charging in domains that are chemically or electronically different to create a charge contrast. By utilizing this charge contrast, we show that two distinct silicon nitride and silicon oxynitride domains are present in one of the composite samples. Similarly, we use this technique to show that titanium oxide and silicon oxide domains exist as separate chemical entities in another composite sample. © 2007 American Chemical Society.Item Open Access Dilbilimsel bir yaklaşım denemesi: Tekirdağ yöresinden bir ninni(Geleneksel Yayıncılık, 2010) Yavuz, Ayşe DuyguDilbilimsel kuram edebiyatta genellikle şiir incelemelerinde kullanılan bir yöntemdir. Biçimsel nitelikleri yönünden şiiri andıran ninnileri de bu kuram dâhilinde ele almak mümkündür. Bu çalışmada ninni türünün bir örneği, “yüzey yapı” özellikleri açısından, dilbilimsel kuram yardımıyla çözümlenecektir. “Yüzey yapı” incelenen metinde yer alan sözcüklerin gramer açıdan sınıflandırılması ve buna bağlı olarak niceliklerinin ortaya konulması, sözcük tekrarları, ölçü ve noktalama işaretleri gibi biçimsel özellikleri ve ninnide geçen sözcüklerin gramatikal değerleri dikkate alınarak tespit edilmektedir. “Yüzey yapı” verileri, uygulama yapılan ninninin içerik ve işlevine yönelik çıkarsamalarda bulunulabileceğini göstermesi açısından önem taşır. Ağırlıklı olarak anne ile çocuk arasındaki iletişimin yansıtıldığı ninnilerin temel işlevi çocuğun uyutulmasıdır. Dilbilimsel yaklaşım, ninnilerin temel işlevine ve bunun yanı sıra toplumsallaşma evresinde, çocuğuna rehber olan annenin veya çocuğun hayatındaki bir başka yetişkinin beklentilerini dile getirmesi gibi başka işlevlere ulaşmayı da olanaklı kılar. Sonuç olarak, ninnilerin de dilbilimsel yöntemle okunabileceği görüşü ortaya atılırken biçimden anlama ninninin içerik ve işlevine varılmaya çalışılacaktır.Item Open Access Morphological surface profile extraction with multiple range sensors(Elsevier, 2001) Barshan, B.; Başkent, D.A novel method is described for surface pro"le extraction based on morphological processing of multiple range sensor data. The approach taken is extremely #exible and robust, in addition to being simple and straightforward. It can deal with arbitrary numbers and con"gurations of sensors as well as synthetic arrays. The method has the intrinsic ability to suppress spurious readings, crosstalk, and higher-order re#ections, and process multiple re#ections informatively. The performance of the method is investigated by analyzing its dependence on surface structure and distance, sensor beamwidth, and noise on the time-of-#ight measurements. 2001 Pattern Recognition Society. Published by Elsevier Science Ltd. All rights reserved.Item Open Access Preparation, surface state and band structure studies of SrTi (1-X)Fe (x)O (3-δ) (x = 0-1) perovskite-type nano structure by X-ray and ultraviolet photoelectron spectroscopy(2012) Ghaffari, M.; Shannon, M.; Hui H.; Tan O.K.; Irannejad, A.In this report, SrTi (1 - x)Fe (x)O (3 - δ) photocatalyst powder was synthesized by a high temperature solid state reaction method. The morphology, crystalline structures of obtained samples, was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM), respectively. The electronic properties and local structure of the perovskite STF x (0 ≤ x ≤ 1) systems have been probed by extended X-ray absorption fine structure (EXAFS) spectroscopy. The effects of iron doping level x (x = 0-1) on the crystal structure and chemical state of the STF x have been investigated by X-ray photoelectron spectroscopy and the valence band edges for electronic band gaps were obtained for STF x by ultraviolet photoelectron spectroscopy (UPS). A single cubic perovskite phase of STF x oxide was successfully obtained at 1200 °C for 24 h by the solid state reaction method. The XPS results showed that the iron present in the STF x perovskite structure is composed of a mixture of Fe 3+ and Fe 4+ (SrTi (1 - x)[Fe 3+, Fe 4+] (x)O (3 - δ)). When the content x of iron doping was increased, the amount of Fe 3+ and Fe 4+ increased significantly and the oxygen lattice decreased on the surface of STF x oxide. The UPS data has confirmed that with more substitution of iron, the position of the valence band decreased. © 2011 Elsevier B.V. All rights reserved.Item Open Access Surface wave splitter based on metallic gratings with sub-wavelength aperture(Optical Society of American (OSA), 2008) Caglayan H.; Özbay, EkmelWe investigated the splitting of surface electromagnetic waves trapped at the output surface of a one-dimensional metallic grating structure. The output gratings of the structure asymmetrically such that the output surfaces at the different sides of the subwavelength aperture can support surface waves at different frequencies. The transmission amplitude as measured at the left side is 1,000 times of that at the right side at 16 GHz. At 24 GHz, the transmission measured at the right side is 20 times that of the left side of the structure. Therefore, surface waves are guided into the different sides of the aperture at different frequencies via metallic gratings. The experimental results are in agreement with the theoretical results. © 2008 Optical Society of America.Item Open Access Transient surface photovoltage in n-and p-GaN as probed by x-ray photoelectron spectroscopy(2011) Sezen, H.; Özbay, Ekmel; Aktas, O.; Süzer, ŞefikTransient surface photovoltage (SPV) of n and p-GaN was measured using x-ray photoelectron spectroscopy (XPS) with a time resolution of 0.1 s. The measured SPV transients for both n- and p-GaN are 0.1 s, and for the n-GaN they are not affected by flood-gun electrons. However, for the p-GaN, the transient character of the SPV is dramatically changed in the presence of flood-gun electrons. The combination of time-resolved XPS, flood gun, and laser illumination give us a new way to study the surface electronic structure and other surface properties of semiconducting materials in a chemically specific fashion.Item Open Access Two-dimensional x-ray photoelectron spectroscopy for composite surface analysis(2008) Süzer, Şefik; Sezen, H.; Dâna, A.We describe a method for obtaining two-dimensional X-ray photoelectron spectroscopic data derived from the frequency dependence of the XPS peaks recorded under electrical square-wave pulses, which control and affect the binding energy positions via the electrical potentials developed as a result of charging. By using cross-correlations between various peaks, our technique enables us to elucidate electrical characteristics of surface structures of composite samples and bring out various correlations between hidden/overlapping peaks. © 2008 American Chemical Society.Item Open Access XPS analysis with pulsed voltage stimuli(2006) Karabudak, E.; Demirok, U. K.; Süzer, ŞefikWe record XPS spectra while applying 0 to +10 V or 0 to -10 V square pulses to the sample rod, which normally results in twinning of all peaks at correspondingly increased (for +10 V) or decreased (for -10 V) binding energies. For poorly conducting samples, like silicon oxide layer on a silicon substrate, the twinned peaks appear at different energies due to differential charging, which also vary with respect to the frequency of the applied pulses. Moreover, the frequency dependence varies with the thickness and can be correlated with the capacitance of the oxide layer. The technique is simple and can lead to extract important information related with dielectric properties of surface structures in a totally non-contact fashion. © 2005 Elsevier B.V. All rights reserved.