Browsing by Subject "Silicon compounds"

Now showing 1 - 18 of 18

Open Access
Analysis of Fe nanoparticles using XPS measurements under d.c. or pulsed-voltage bias
(2010) Süzer, Şefik; Baer, D. R.; Engelhard, M. H.
The impact of solution exposure on the charging properties of oxide coatings on Fe metal-core oxide-shell nanoparticles has been examined by sample biasing during XPS measurements. The Fe nanoparticles were suspended in relatively unreactive acetone and analyzed after particles containing solutions were deposited on SiO2/Si or Au substrates. The particle and substrate combinations were subjected to ±10V d.c. or ±5V a.c., biasing in the form of square wave (SQW) pulses. The samples experienced variable degrees of charging for which low-energy electrons at ∼1eV, 20 μA and low-energy Ar+ ions were used to minimize it. Application of d.c. bias and/or SQW pulses significantly influences the extent of charging, which is utilized to gather additional analytical information about the sample under investigation. This approach allows separation of otherwise overlapping peaks. Accordingly, the O1s peaks of the silicon oxide substrate, the iron oxide nanoparticles, and that of the casting solvent can be separated from each other. Similarly, the C1s peak belonging to the solvent can be separated from that of the adventitious carbon. The charging shifts of the iron nanoparticles are strongly influenced by the solvent to which the particles were exposed. Hence, acetone exhibited the largest shift, water the smallest, and methanol in between. Dynamical measurements performed by application of the voltage stress in the form of SQW pulses provides information about the time constants of the processes involved, which leads us to postulate that these charging properties we probe in these systems stem mainly from ionic movement(s).
Open Access
Area-selective atomic layer deposition using an inductively coupled plasma polymerized fluorocarbon layer: A case study for metal oxides
(American Chemical Society, 2016) Haider, A.; Deminskyi, P.; Khan, T. M.; Eren, H.; Bıyıklı, Necmi
Area-selective atomic layer deposition (AS-ALD) has attracted immense attention in recent years for self-aligned accurate pattern placement with subnanometer thickness control. Here, we demonstrate a methodology to achieve AS-ALD by using inductively couple plasma (ICP) grown fluorocarbon polymer film as hydrophobic blocking layer for selective deposition. Our approach has been tested for metal-oxide materials including ZnO, Al2O3, and HfO2. Contact angle, X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometer, and scanning electron microscopy (SEM) measurements were performed to investigate the blocking ability of plasma polymerized fluorocarbon layers against ALD-grown metal-oxide films. A considerable growth inhibition for ZnO has been observed on fluorocarbon coated Si(100) surfaces, while the same polymerized surface caused a relatively slow nucleation for HfO2 films. No growth selectivity was obtained for Al2O3 films, displaying almost the same nucleation behavior on Si and fluorocarbon surfaces. Thin film patterning has been demonstrated using this strategy by growing ZnO on lithographically patterned fluorocarbon/Si samples. High resolution SEM images and XPS line scan confirmed the successful patterning of ZnO up to a film thickness of ∼15 nm. © 2016 American Chemical Society.
Open Access
Charging/discharging dynamics of CdS and CdSe films under photoillumination using dynamic x-ray photoelectron spectroscopy
(A I P Publishing LLC, 2010) Sezen, H.; Süzer, Şefik
Thin films of CdS and CdSe are deposited on HF-cleaned Si O2 /Si substrates containing ∼5 nm thermally grown silicon oxide. x-ray photoelectron spectroscopy (XPS) data of these films are collected in a dynamic mode, which is based on recording the spectrum under modulation with an electrical signal in the form of ±10 V square-wave pulses. Accordingly, all peaks are twined and shifted with respect to the grounded spectrum. The binding energy difference between the twinned peaks of a dielectric system has a strong dependence on the frequency of the electrical stimuli. Therefore, dynamic XPS provides a means to extract additional properties of dielectric materials, such as effective resistance and capacitance. In this work, the authors report a new advancement to the previous method, where they now probe a photodynamic process. For this reason, photoillumination is introduced as an additional form of stimulus and used to investigate the combined optical and electrical response of the photoconductive thin films of CdS and CdSe using dynamic XPS.
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.
Open Access
Enhancement of optical switching parameter and third-order optical nonlinearities in embedded Si nanocrystals: A theoretical assessment
(Elsevier, 2008) Yildirim, H.; Bulutay, C.
Third-order bound-charge electronic nonlinearities of Si nanocrystals (NCs) embedded in a wide band-gap matrix representing silica are theoretically studied using an atomistic pseudopotential approach. Nonlinear refractive index, two-photon absorption and optical switching parameter are examined from small clusters to NCs up to a size of 3 nm. Compared to bulk values, Si NCs show higher third-order optical nonlinearities and much wider two-photon absorption-free energy gap which gives rise to enhancement in the optical switching parameter.
Open Access
Generation of new frequencies in toroid microcavities
(IEEE, 2008) Akbulut, Duygu; Tülek, Abdullah; Bayındır, Mehmet
Microtoroid cavities with ultra high Q-factor have been fabricated using a combined process of photolithography and reflow technique for observing non-linear effects such as generation of new frequency components. For this purpose SiO2 material was used to form the toroidal cavity shape, and chalcogenide material of As2S3 maintaining very high nonlinear refractive index was thermally evaporated on top with varying thicknesses. Simulation results of the fabricated structure have exhibited new frequency components around the excitation window of 1520 nm produced by non-linear interactions.
Open Access
High-efficiency and low-loss gallium nitride dielectric metasurfaces for nanophotonics at visible wavelengths
(American Institute of Physics Inc., 2017) Emani, N. K.; Khaidarov, E.; Paniagua-Domínguez, R.; Fu, Y. H.; Valuckas, V.; Lu S.; Zhang X.; Tan S.T.; Demir, Hilmi Volkan; Kuznetsov, A. I.
The dielectric nanophotonics research community is currently exploring transparent material platforms (e.g., TiO2, Si3N4, and GaP) to realize compact high efficiency optical devices at visible wavelengths. Efficient visible-light operation is key to integrating atomic quantum systems for future quantum computing. Gallium nitride (GaN), a III-V semiconductor which is highly transparent at visible wavelengths, is a promising material choice for active, nonlinear, and quantum nanophotonic applications. Here, we present the design and experimental realization of high efficiency beam deflecting and polarization beam splitting metasurfaces consisting of GaN nanostructures etched on the GaN epitaxial substrate itself. We demonstrate a polarization insensitive beam deflecting metasurface with 64% and 90% absolute and relative efficiencies. Further, a polarization beam splitter with an extinction ratio of 8.6/1 (6.2/1) and a transmission of 73% (67%) for p-polarization (s-polarization) is implemented to demonstrate the broad functionality that can be realized on this platform. The metasurfaces in our work exhibit a broadband response in the blue wavelength range of 430-470 nm. This nanophotonic platform of GaN shows the way to off- and on-chip nonlinear and quantum photonic devices working efficiently at blue emission wavelengths common to many atomic quantum emitters such as Ca+ and Sr+ ions.
Open Access
High-speed transparent indium-tin-oxide based resonant cavity Schottky photodiode with Si/sub 3/N/sub 4//SiO/sub 2/ top Bragg mirror
(IEEE, Piscataway, NJ, United States, 2000) Bıyıklı, Necmi; Kimukin, I.; Aytur, O.; Özbay, Ekmel; Gokkavas, M.; Unlu, S.
Photodetectors demonstrating high bandwidth-efficiency (BWE) products are required for high-performance optical communication and measurement systems. For conventional photodiodes the BWE product is limited due to the bandwidth-efficiency trade-off. A resonant cavity enhanced (RCE) photodetection scheme offers the possibility to overcome this limitation. Very high BWE products are achieved using Schottky and p-i-n type RCE photodiodes, which could not be reached with conventional detector structures. Even better performances should be possible for RCE Schottky photodiodes if one can get rid of the optical losses and scattering caused by the Schottky metal, Au, which also serves as the top mirror of the resonant cavity. The transparent, low resistivity material indium-tin-oxide (ITO) is a potential alternative to thin semi-transparent Au as a Schottky-barrier contact material. We report our work on high-performance ITO-based RCE Schottky photodiodes.
Open Access
Organization of bridging organics in periodic mesoporous organosilicas (PMOs)-polarization micro-raman spectroscopy
(Wiley, 2001) Dag, Ö.; Ozin, G. A.
The organization of bridging organics in oriented periodic mesoporous organosilica film (OPMOF) was demonstrated using the polarization micro-Raman spectroscopy (PMRS) in conjunction with powder x-ray diffraction (PXRD) and polarization optical microscopy (POM). The synthesis and the structural characterization of hexagonal symmetry OPMOF containing bridge-bonded ethane, ethene inside the silica channel walls were described. The mesoscale channels were found to run parallel to the surface of the underlying glass substrates as demonstrated by the PXRD measurements. A hexagonal array of channels with glassy silica organosilica walls was the best description of the structure shown by the PMRS measurements of OPMOF.
Open Access
Raman and TEM studies of Ge nanocrystal formation in SiOx: Ge/SiOx multilayers
(Wiley, 2007) Dana, Aykutlu; Aǧan, S.; Tokay, S.; Aydınlı, Atilla; Finstad, T. G.
Alternating germanosilicate-siliconoxide layers of 10-30 nm thickness were grown on Si substrates by plasma enhanced chemically vapor deposition (PECVD). The compositions of the grown films were determined by X-ray photoelectron spectroscopy measurements. The films were annealed at temperatures varying from 670 to 1000°C for 5 to 45 minutes under nitrogen atmosphere. High resolution cross section TEM images, electron diffraction and electron energy-loss spectroscopy as well as energy-dispersive X-ray analysis (EDAX) data confirm presence of Ge nanocrystals in each layer. The effect of annealing on the Ge nanocrystal formation in multilayers was investigated by Raman spectroscopy and Transmission Electron Microscopy (TEM). As the annealing temperature is raised to 850°C, single layer of Ge nanocrystals observed at lower annealing temperatures is transformed into a double layer with the smaller sized nanocrystals closer to the substrate SiO2 interface.
Open Access
Response of polyelectrolyte layers to the SiO2 substrate charging as probed by XPS
(2009) Conger, C. P.; Süzer, Şefik
A single layer of the Cationic polyelectrolyte poly(allyamine) hydrochloride (PAH) deposited, using the layer-by-layer technique, on a silicon substrate containing 5 nm oxide layer is investigated by XPS while applying an external potential bias to the sample to control and manipulate the charge built-up on the oxide layer. Under application of a -10 V bias, the oxide layer is positively charged due to Photoemission process, evidenced by the measured Si2p binding energy of 104.4 eV. Application of a +10 V bias attracts the low energy neutralizing electrons, stemming from a hot filament, and leads to a negatively charged oxide layer, also evidenced by the measured Si2p binding energy of 102.9 eV. The single polyelectrolyte overlayer also responds to this polarity change of the oxide layer underneath by displaying a somewhat larger shifts both in the C1s and Nls peaks. In addition to the shifts in the positions, the N1s peaks undergo a significant intensity depletion, mostly on the positively charged -N+ component. We interpret this intensity depletion to be the result of reorientation of some of the dangling positively charged groups by moving toward the negatively charged oxide underlayer. To our knowledge this is the first time that a chemically specific response to an electrical stimuli is reported using XPS. A bilayer LbL film consisting of PAH and PSS, exhibits even a larger charging shift, but this time no intensity alteration is observed, most probably due to locking of the -N+ groups by the -SO3 + counterions of the second layer. © 2009 American Chemical Society.
Open Access
Selective-area high-quality germanium growth for monolithic integrated optoelectronics
(Institute of Electrical and Electronics Engineers, 2012-03-02) Yu, H. Y.; Park, J. H.; Okyay, Ali Kemal; Saraswat, K. C.
Selective-area germanium (Ge) layer on silicon (Si) is desired to realize the advanced Ge devices integrated with Si very-large-scale-integration (VLSI) components. We demonstrate the area-dependent high-quality Ge growth on Si substrate through SiO 2 windows. The combination of area-dependent growth and multistep deposition/hydrogen annealing cycles has effectively reduced the surface roughness and the threading dislocation density. Low root-mean-square surface roughness of 0.6 nm is confirmed by atomic-force-microscope analysis. Low defect density in the area-dependent grown Ge layer is measured to be as low as 1 × 10 7cm -2 by plan-view transmission-electron-miscroscope analysis. In addition, the excellent metal-semiconductor-metal photodiode characteristics are shown on the grown Ge layer to open up a possibility to merge Ge optoelectronics with Si VLSI.
Open Access
Soft x-ray photoemission studies of the HfO2/SiO2/Si system
(American Institute of Physics, 2002) Sayan, S.; Garfunkel, E.; Süzer, Şefik
Soft x-ray photoelectron spectroscopy with synchrotron radiation was employed to study the valence-band offsets for the HfO2/SiO 2/Si and HfO2/SiOxNy/Si systems. We obtained a valence-band offset difference of -1.05±0.1eV between HfO 2 (in HfO2/15ÅSiO2/Si) and SiO 2 (in 15 Å SiO2/Si). There is no measurable difference between the HfO2 valence-band maximum positions of the HfO2/10ÅSiOxNy/Si and HfO 2/15ÅSiO2/Si systems. © 2002 American Institute of Physics.
Open Access
Spectroscopic ellipsometric study of Ge nanocrystals embedded in SiO 2 using parametric models
(Wiley, 2008-05) Basa, P.; Petrik, P.; Fried, M.; Dâna, Aykutlu; Aydınlı, Atilla; Foss, S.; Finstad, T. G.
Ge-rich SiO2 layers on top of Si substrates were deposited using plasma enhanced chemical vapour deposition. Ge nanocrystals embedded in the SiO2 layers were formed by high temperature annealing. The samples were measured and evaluated by spectroscopic ellipsometry. Effective medium theory (EMT) and parametric semiconductor models have been used to model the dielectric function of the layers. Systematic dependences of the layer thickness and the oscillator parameters have been found on the annealing temperature (nanocrystal size).
Open Access
Structural and loss characterization of SiON layers for optical waveguide applications
(IEEE, 2000) Ay, Feridun; Aydınlı, Atilla; Roeloffzen, C.; Driessen, A.
Silicon oxynitride films for optical waveguide applications were grown at 350°C in a PECVD reactor. ATR-FTIR spectroscopy was used to identify the bond structure and absorption characteristics in the mid-infrared region. Annealing of the films was performed together with close monitoring of the N-H bond at 3400 cm-1 and correlated with optical loss measurements. The possibility of a new method for the reduction of the N-H bonds without annealing is discussed.
Open Access
Superhydrophobic, hybrid, electrospun cellulose acetate nanofibrous mats for oil/water separation by tailored surface modification
(American Chemical Society, 2016) Arslan, O.; Aytac Z.; Uyar, Tamer
Electrospun cellulose acetate nanofibers (CA-NF) have been modified with perfluoro alkoxysilanes (FS/CA-NF) for tailoring their chemical and physical features aiming oil-water separation purposes. Strikingly, hybrid FS/CA-NF showed that perfluoro groups are rigidly positioned on the outer surface of the nanofibers providing superhydrophobic characteristic with a water contact angle of ∼155°. Detailed analysis showed that hydrolysis/condensation reactions led to the modification of the acetylated β(1 → 4) linked d-glucose chains of CA transforming it into a superhydrophobic nanofibrous mat. Analytical data have revealed that CA-NF surfaces can be selectively controlled for fabricating the durable, robust and water resistant hybrid electrospun nanofibrous mat. The -OH groups available on the CA structure allowed the basic sol-gel reactions started by the reactive FS hybrid precursor system which can be monitored by spectroscopic analysis. Since alkoxysilane groups on the perfluoro silane compound are capable of reacting for condensation together with the CA, superhydrophobic nanofibrous mat is obtained via electrospinning. This structural modification led to the facile fabrication of the novel oil/water nanofibrous separator which functions effectively demonstrated by hexane/oil and water separation experiments. Perfluoro groups consequently modified the hydrophilic CA nanofibers into superhydrophobic character and therefore FS/CA-NF could be quite practical for future applications like water/oil separators, as well as self-cleaning or water resistant nanofibrous structures.
Open Access
TEM studies of Ge nanocrystal formation in PECVD grown SiO 2: Ge / SiO2 multilayers
(Institute of Physics, 2006) Aǧan, S.; Dana, A.; Aydınlı, Atilla
We investigate the effect of annealing on the Ge nanocrystal formation in multilayered germanosilicate-oxide films grown on Si substrates by plasma enhanced chemical vapour deposition (PECVD). The multilayered samples were annealed at temperatures ranging from 750 to 900 °C for 5 min under nitrogen atmosphere. The onset of formation of Ge nanocrystals, at 750 °C, can be observed via high resolution TEM micrographs. The diameters of Ge nanocrystals were observed to be between 5 and 14 nm. As the annealing temperature is raised to 850 °C, a second layer of Ge nanocrystals forms next to the original precipitation band, positioning itself closer to the substrate SiO2 interface. High resolution cross section TEM images, electron diffraction and electron energy-loss spectroscopy as well as energy-dispersive x-ray analysis (EDAX) data all indicate that Ge nanocrystals are present in each layer. © 2006 IOP Publishing Ltd.
Open Access
X-ray photoemission for probing charging/discharging dynamics
(American Chemical Society, 2006) Süzer, Şefik; Dâna, A.
A novel technique is introduced for probing charging/discharging dynamics of dielectric materials in which X-ray photoemission data is recorded while the sample rod is subjected to ± 10.0 V square-wave pulses with varying frequencies in the range of 10-3 to 103 Hz. For a clean silicon sample, the Si2p(Si0) peak appears at correspondingly -10.0 eV and +10.0 eV binding energy positions (20.0 eV difference) with no frequency dependence. However, the corresponding peak of the oxide (Si4+) appears with less than 20.0 eV difference and exhibits a strong frequency dependence due to charging of the oxide layer, which is faithfully reproduced by a theoretical model. In the simplest application of this technique, we show that the two O1s components can be assigned to SiOx and TiO y moeties by correlating their dynamical shifts to those of the Si2p and Ti2p peaks in a composite sample. Our pulsing technique turns the powerful X-ray photoemission into an even more powerful impedance spectrometer with an added advantage of chemical resolution and specificity. © 2006 American Chemical Society.