Browsing by Subject "Aluminum"

Now showing 1 - 20 of 34

Open Access
All-aluminum hierarchical plasmonic surfaces in the infrared
(The Optical Society, 2016) Ayas S.; Bakan, G.; Dana, A.
All-Aluminum metal-insulator-metal resonator structures withmultiple metal-insulator stacks showing resonances in the mid-infrared(MIR) are fabricated. Ultrathin native Al2O3 is used as the insulator layersenabling simple fabrication of the resonator structures. The structures withtwo oxide layers exhibit two distinct resonances in the MIR. Simulation ofthese structures shows confinement of magnetic field to the thicker bottomoxide at the shorter wavelength resonance and to the thinner top oxide at theother resonance. Simulations of higher order hierarchical structures with 3 and 4 oxide layers show multispectral response with precise control of theoxide thicknesses. The studied structures show great potential for IRapplications that require durability and multispectral characteristics.
Open Access
Atomic layer deposited Al 2O 3 passivation of type II InAs/GaSb superlattice photodetectors
(AIP, 2012) Salihoğlu, Ömer; Muti, Abdullah; Kutluer, Kutlu; Tansel, T.; Turan, R.; Kocabaş, Coşkun; Aydınlı, Atilla
Taking advantage of the favorable Gibbs free energies, atomic layer deposited (ALD) aluminum oxide (Al 2O 3) was used as a novel approach for passivation of type II InAs/GaSb superlattice (SL) midwave infrared (MWIR) single pixel photodetectors in a self cleaning process (λ cut-off ∼ 5.1 m). Al 2O 3 passivated and unpassivated diodes were compared for their electrical and optical performances. For passivated diodes, the dark current density was improved by an order of magnitude at 77 K. The zero bias responsivity and detectivity was 1.33 A/W and 1.9 × 10 13 Jones, respectively at 4μm and 77 K. Quantum efficiency (QE) was determined as 41 for these detectors. This conformal passivation technique is promising for focal plane array (FPA) applications. © 2012 American Institute of Physics.
Open Access
Bioactive nanomaterials for neural engineering
(Springer, Cham, 2016) Sever, Melike; Uyan, İdil; Tekinay, Ayse B.; Güler, Mustafa O.; Zhang, L. G.; Kaplan, D. L.
Nervous system is a highly complex interconnected network and higher organisms including humans have limited neural regeneration capacity. Neurodegenerative diseases result in significant cognitive, sensory, or motor impairments. Following an injury in the neural network, there is a balance between promotion and inhibition of regeneration and this balance is shifted to different directions in central nervous system (CNS) and peripheral nervous system (PNS). More regeneration capacity is observed in the PNS compared to the CNS. Although, several mechanisms play roles in the inhibitory and growth-promoting natures of the CNS and PNS, extracellular matrix (ECM) elements are key players in this process. ECM is a three-dimensional environment where the cells migrate, proliferate, and differentiate (Rutka et al. 1988; Pan et al. 1997). After a comprehensive investigation of the interactions between the ECM proteins and cell receptors, the ECM environment was found to regulate significant cellular processes such as survival, proliferation, differentiation, and migration (Yurchenco and Cheng 1994; Aszodi et al. 2006). Its components have major roles not only in neurogenesis during development of the nervous system but also in normal neural functioning during adulthood (Hubert et al. 2009).
Open Access
Charge Trapping Memory with 2.85-nm Si-Nanoparticles Embedded in HfO2
(ECS, 2015-05) El-Atab, N.; Turgut, Berk Berkan; Okyay, Ali Kemal; Nayfeh, A.
In this work, the effect of embedding 2.85-nm Si-nanoparticles charge trapping layer in between double layers of high-κ Al2O3/HfO2 oxides is studied. Using high frequency (1 MHz) C-Vgate measurements, the memory showed a large memory window at low program/erase voltages due to the charging of the Si-nanoparticles. The analysis of the C-V characteristics shows that mixed charges are being stored in the Si-nanoparticles where electrons get stored during the program operation while holes dominate in the Si-nanoparticles during the erase operation. Moreover, the retention characteristic of the memory is studied by measuring the memory hysteresis in time. The obtained retention characteristic (35.5% charge loss in 10 years) is due to the large conduction and valence band offsets between the Si-nanoparticles and the Al2O3/HfO2 tunnel oxide. The results show that band engineering is essential in future low-power non-volatile memory devices. In addition, the results show that Si-nanoparticles are promising in memory applications.
Open Access
Current transport mechanisms in plasma-enhanced atomic layer deposited AlN thin films
(A I P Publishing LLC, 2015) Altuntas, H.; Ozgit Akgun, C.; Donmez, I.; Bıyıklı, Necmi
Here, we report on the current transport mechanisms in AlN thin films deposited at a low temperature (i.e., 200°C) on p-type Si substrates by plasma-enhanced atomic layer deposition. Structural characterization of the deposited AlN was carried out using grazing-incidence X-ray diffraction, revealing polycrystalline films with a wurtzite (hexagonal) structure. Al/AlN/ p-Si metal-insulator-semiconductor (MIS) capacitor structures were fabricated and investigated under negative bias by performing current-voltage measurements. As a function of the applied electric field, different types of current transport mechanisms were observed; i.e., ohmic conduction (15.2-21.5 MV/m), Schottky emission (23.6-39.5 MV/m), Frenkel-Poole emission (63.8-211.8 MV/m), trap-assisted tunneling (226-280 MV/m), and Fowler-Nordheim tunneling (290-447 MV/m). Electrical properties of the insulating AlN layer and the fabricated Al/AlN/p-Si MIS capacitor structure such as dielectric constant, flat-band voltage, effective charge density, and threshold voltage were also determined from the capacitance-voltage measurements.
Restricted
Demir atölyesinden imparatorluğa: Çuhadaroğlu Holding
(Bilkent University, 2023) Çelikkaya, İlayda Şevval; Ertunç, Münevver; Şahin, Mehmet Akif; Şimşek, Onur Umut; Yeşil, Mehmet Anıl
Ahmet Çuhadaroğlu 1954’te kurduğu demir atölyesi ile Çuhadaroğlu Holding’in temellerini atmıştır. Ardından çelik yapı üretimi, yapı kimyasalları ve alüminyum doğrama sektörlerinde yer alan Çuhadaroğlu Holding günümüzde alüminyum ekstrüzyon alanında çalışmaktadır. Ahmet Çuhadaroğlu’ndan sonra yönetim ikinci nesile, Nejat ve Murat Çuhadaroğlu’na geçti. Babalarının izinden giden yeni yöneticiler de sosyal ve kültürel alanda birçok faaliyet gerçekleştirdi. Bu makalede Ahmet Çuhadaroğlu ve Çuhadaroğlu Holding’in tarihçesi anlatıldıktan sonra holdingin Türkiye’de ve dünyadaki konumu incelenecektir. Bunun yanı sıra, Çuhadaroğlu Holding'in sosyal ve kültürel projeleri de ele alınacaktır.
Open Access
The effect of insulator layer thickness on the main electrical parameters in (Ni/Au)/AlxGa1-xN/AIN/GaN heterostructures
(Wiley, 2010) Altindal, S.; Şafak, Y.; Taşçloǧlu I.; Özbay, Ekmel
(Ni/Au)Alx Ga1-x N/AlN/GaN(x = 0.22) heterostructures with and without a passivation layer of the SiNx were fabricated in order to see the effect of the insulator layer on the main electrical parameters such as zero-bias barrier height (BH) (φBO), ideality factor (n), series resistance (Rs) of the structure, and the interface state density (Nss). Some of these parameters were determined from both I-V and admittance (C-V and G/ω-V) measurements at room temperature and at 1 MHz and were compared. The experimental results show that the value of N ss in a Schottky contact without passivation is nearly 1 order of magnitude larger than that in a Schottky contact with SiNx passivation layers. Also, the values of Rs increase with the increasing thickness of the passivation layer. In the forward bias region, the negative values of capacitance are an attractive result of this study. This negative capacitance disappears in presence of the passivation layer. Copyright © 2010 John Wiley & Sons, Ltd.
Open Access
Electrical conduction and dielectric relaxation properties of AlN thin films grown by hollow-cathode plasma-assisted atomic layer deposition
(Institute of Physics Publishing, 2016) Altuntas, H.; Bayrak, T.; Kizir, S.; Haider, A.; Bıyıklı, Necmi
In this study, aluminum nitride (AlN) thin films were deposited at 200 ï¿½C, on p-type silicon substrates utilizing a capacitively coupled hollow-cathode plasma source integrated atomic layer deposition (ALD) reactor. The structural properties of AlN were characterized by grazing incidence x-ray diffraction, by which we confirmed the hexagonal wurtzite single-phase crystalline structure. The films exhibited an optical band edge around ∼5.7 eV. The refractive index and extinction coefficient of the AlN films were measured via a spectroscopic ellipsometer. In addition, to investigate the electrical conduction mechanisms and dielectric properties, Al/AlN/p-Si metal-insulator-semiconductor capacitor structures were fabricated, and current density-voltage and frequency dependent (7 kHz-5 MHz) dielectric constant measurements (within the strong accumulation region) were performed. A peak of dielectric loss was observed at a frequency of 3 MHz and the Cole-Davidson empirical formula was used to determine the relaxation time. It was concluded that the native point defects such as nitrogen vacancies and DX centers formed with the involvement of Si atoms into the AlN layers might have influenced the electrical conduction and dielectric relaxation properties of the plasma-assisted ALD grown AlN films.
Open Access
Electronic properties of polypyrrole/polyindene composite/metal junctions
(Elsevier, 1997) Bozkurt, A.; Ercelebi, C.; Toppare, L.
Junction properties between conducting polymer composites of polypyrrole/polyindene (PPy/PIn) with different conductivities and metals like Pt, Au, Al and In have been investigated. Rectifying junctions were observed for low work function metals, In and Al; however, high work function metals, Pt and Au, were observed to form ohmic contacts to PPy/PIn composite in the sandwich geometry. The rectifying behavior of the metal/composite/Pt junctions improved when the conductivity of the composite was decreased from 1 to 0.01 S/cm. Using the ideal Schottky theory various junction parameters have been determined. All planar junctions were ohmic regardless of the conductivities of the samples.
Open Access
Enhanced non-volatile memory characteristics with quattro-layer graphene nanoplatelets vs. 2.85-nm Si nanoparticles with asymmetric Al2O3/HfO2 tunnel oxide
(Springer New York LLC, 2015) El-Atab, N.; Turgut, B. B.; Okyay, Ali Kemal; Nayfeh, M.; Nayfeh, A.
In this work, we demonstrate a non-volatile metal-oxide semiconductor (MOS) memory with Quattro-layer graphene nanoplatelets as charge storage layer with asymmetric Al2O3/HfO2 tunnel oxide and we compare it to the same memory structure with 2.85-nm Si nanoparticles charge trapping layer. The results show that graphene nanoplatelets with Al2O3/HfO2 tunnel oxide allow for larger memory windows at the same operating voltages, enhanced retention, and endurance characteristics. The measurements are further confirmed by plotting the energy band diagram of the structures, calculating the quantum tunneling probabilities, and analyzing the charge transport mechanism. Also, the required program time of the memory with ultra-thin asymmetric Al2O3/HfO2 tunnel oxide with graphene nanoplatelets storage layer is calculated under Fowler-Nordheim tunneling regime and found to be 4.1 ns making it the fastest fully programmed MOS memory due to the observed pure electrons storage in the graphene nanoplatelets. With Si nanoparticles, however, the program time is larger due to the mixed charge storage. The results confirm that band-engineering of both tunnel oxide and charge trapping layer is required to enhance the current non-volatile memory characteristics.
Open Access
Enhanced transmission of microwave radiation in one-dimensional metallic gratings with subwavelength aperture
(American Institute of Physics, 2004) Akarca-Biyikli, S. S.; Bulu, I.; Özbay, Ekmel
We report a theoretical and experimental demonstration of enhanced microwave transmission through subwavelength apertures in metallic structures with double-sided gratings. Three different types of aluminum gratings (sinusoidal, symmetric rectangular, and asymmetric rectangular shaped) are designed and analyzed. Our samples have a periodicity of 16 mm, and a slit width of 2 mm. Transmission measurements are taken in the 10–37.5 GHz frequency spectrum, which corresponds to 8–30 mm wavelength region. All three structures display significantly enhanced transmission around surface plasmon resonance frequencies. The experimental results agree well with finite-difference-time-domain based theoretical simulations. Asymmetric rectangular grating structure exhibits the best results with ,50% transmission at 20.7 mm, enhancement factor of ,25, and ±4° angular divergence.
Open Access
Fine-tuning the dispersion and the mobility of BaO domains on NO x storage materials via TiO2 anchoring sites
(American Chemical Society, 2010) Andonova, S. M.; Şentürk, G. S.; Ozensoy, E.
In an attempt to control the surface dispersion and the mobility of BaO domains on NOx storage materials, TiO2/TiOx anchoring sites were introduced on/inside the conventional γ-Al 2O3 support matrix. BaO/TiO2/Al 2O3 ternary oxide materials were synthesized via two different sol-gel preparation techniques, with varying surface compositions and morphologies. The synthesized NOx storage materials were studied via XRD, Raman spectroscopy, BET surface area analysis, TPD, XPS, SEM, EDX-mapping, and in situ FTIR spectroscopy of adsorbed NO2. NOx uptake properties of the BaO/TiO2/Al2O3 materials were found to be strongly influenced by the morphology and the surface structure of the TiO2/TiOx domains. An improved Ba surface dispersion was observed for the BaO/TiO2/Al2O3 materials synthesized via the coprecipitation of alkoxide precursors, which was found to originate mostly from the increased fraction of accessible TiO 2/TiOx sites on the surface. These TiO2/ TiOx sites function as strong anchoring sites for surface BaO domains and can be tailored to enhance surface dispersion of BaO. TPD experiments suggested the presence of at least two different types of NOx species adsorbed on the TiO2/TiOx sites, with distinctively different thermal stabilities. The relative stability of the NOx species adsorbed on the BaO/TiO2/Al2O3 system was found to increase in the following order: NO+/N2O 3 on alumina ≪ nitrates on alumina < surface nitrates on BaO < bridged/bidentate nitrates on large/isolated TiO2 clusters < bulk nitrates on BaO on alumina surface and bridged/bidentate nitrates on TiO2 crystallites homogenously distributed on the surface < bulk nitrates on the BaO sites located on the TiO2 domains. © 2010 American Chemical Society.
Open Access
Gold supported on ceria doped by Me3+ (Me = Al and Sm) for water gas shift reaction: Influence of dopant and preparation method
(2010) Andreeva, D.; Kantcheva, M.; Ivanov, I.; Ilieva, L.; Sobczak, J. W.; Lisowski, W.
Gold catalysts supported on ceria doped by Sm and Al were studied. The influence of the preparation method, as well as the nature of dopants on the structure, properties and WGS activity are investigated. The applied methods of preparation cause the modification of ceria in a different extent. In the sample prepared by co-precipitation (CP) and doped by Al, the vacancies are located within the bulk of ceria structure, whereas in the corresponding AuCeSmCP sample the vacancies are located most likely around Sm and the ceria structure seems to be better ordered than the Al doped ceria. There is no distinct correlation between the reducibility and WGS activity of the studied catalysts. The Au 4f XPS spectra of fresh samples reveal higher contribution of dispersed form of Au for Sm doped catalysts than for the corresponding Al doped samples. The Ce 3d XPS spectra disclose also a higher concentration of Ce3+ evaluated before the catalytic operation for Sm doped catalysts as compared with the Al doped fresh samples. The observations by "in situ" FT-IR spectroscopy agree well with the model of active sites and the, mechanism of the WGS reaction proposed recently by some of us. The amount of formate species observed on the AuCeSmCP is higher than that on the AuCeAlCP catalyst and parallels the catalytic activity. The higher concentration of active sites on the surface of the AuCeSmCP catalyst facilitates the dissociation of water.
Open Access
High capacity anode materials for lithium - ion batteries
(2017-01) Kudu, Ömer Ulaş
Huge energy demand in the world has caused depletion in non - renewable energy sources, and global climate change due to the consumed fuel exhausts. Renewable energy sources are eco - friendly alternatives. Electrochemical energy storage systems (EESS) are useful tools to store the energy, which is harvested from the renewable sources. Lithium - ion batteries are currently the most popular EESS owing to their several advantages over other systems. However, for their use in high energy demanding applications like electric vehicles, new electrode materials with higher capacities are required. Here, we demonstrate two anode materials with high capacities, aluminum and silicon. We address problems regarding their commercial applications and offer solutions. To improve the properties of aluminum, we fabricate aluminum - copper thin films via sputtering, then we apply age hardening to the alloy. We observe that age hardening indeed increase stability of aluminum anodes. In the second work, we synthesize silicon nanoparticles via laser ablation, whose sizes are smaller than 20 nm, and embed them into carbon nanofibers (CNFs) via electrospinning. The electrochemical battery tests are conducted with only CNFs, CNFs with commercial Si nanoparticles and CNFs with laser ablased Si nanoparticles. The cyclic stability of these composites are observed along with their rate capabilities.
Open Access
Increasing Ti-6Al-4V brazed joint strength equal to the base metal by Ti and Zr amorphous filler alloys
(2012) Ganjeh, E.; Sarkhosh H.; Bajgholi, M.E.; Khorsand H.; Ghaffari, M.
Microstructural features developed along with mechanical properties in furnace brazing of Ti-6Al-4V alloy using STEMET 1228 (Ti-26.8Zr-13Ni-13.9Cu, wt.%) and STEMET 1406 (Zr-9.7Ti-12.4Ni-11.2Cu, wt.%) amorphous filler alloys. Brazing temperatures employed were 900-950 °C for the titanium-based filler and 900-990 °C for the zirconium-based filler alloys, respectively. The brazing time durations were 600, 1200 and 1800 s. The brazed joints were evaluated by ultrasonic test, and their microstructures and phase constitutions analyzed by metallography, scanning electron microscopy and X-ray diffraction analysis. Since microstructural evolution across the furnace brazed joints primarily depends on their alloying elements such as Cu, Ni and Zr along the joint. Accordingly, existence of Zr 2Cu, Ti 2Cu and (Ti,Zr) 2Ni intermetallic compounds was identified in the brazed joints. The chemical composition of segregation region in the center of brazed joints was identical to virgin filler alloy content which greatly deteriorated the shear strength of the joints. Adequate brazing time (1800 s) and/or temperature (950 °C for Ti-based and 990 °C for Zr-based) resulted in an acicular Widmanstätten microstructure throughout the entire joint section due to eutectoid reaction. This microstructure increased the shear strength of the brazed joints up to the Ti-6Al-4V tensile strength level. Consequently, Ti-6Al-4V can be furnace brazed by Ti and Zr base foils produced excellent joint strengths. © 2012 Elsevier Inc. All rights reserved.
Open Access
LSPR enhanced MSM UV photodetectors
(IOP Publishing, 2012-10-18) Butun, S.; Cinel, N. A.; Özbay, Ekmel
We fabricated localized surface plasmon resonance enhanced UV photodetectors on MOCVD grown semi-insulating GaN. Plasmonic resonance in the UV region was attained using 36nm diameter Al nanoparticles. Extinction spectra of the nanoparticles were measured through spectral transmission measurements. A resonant extinction peak around 300nm was obtained with Al nanoparticles. These particles gave rise to enhanced absorption in GaN at 340nm. Spectral responsivity measurements revealed an enhancement factor of 1.5. These results provided experimental verification for obtaining field enhancement by using Al nanoparticles on GaN.
Open Access
Memory effect by charging of ultra‐small 2‐nm laser‐synthesized solution processable Si‐nanoparticles embedded in Si–Al2O3–SiO2 structure
(Wiley-VCH Verlag, 2015) El-Atab, N.; Rizk, A.; Tekcan, B.; Alkis, S.; Okyay, Ali Kemal; Nayfeh, A.
A memory structure containing ultra-small 2-nm laser-synthesized silicon nanoparticles is demonstrated. The Si-nanoparticles are embedded between an atomic layer deposited high-κ dielectric Al2O3 layer and a sputtered SiO2 layer. A memory effect due to charging of the Si nanoparticles is observed using high frequency C-V measurements. The shift of the threshold voltage obtained from the hysteresis measurements is around 3.3V at 10/-10V gate voltage sweeping. The analysis of the energy band diagram of the memory structure and the negative shift of the programmed C-V curve indicate that holes are tunneling from p-type Si via Fowler-Nordheim tunneling and are being trapped in the Si nanoparticles. In addition, the structures show good endurance characteristic (>105program/erase cycles) and long retention time (>10 years), which make them promising for applications in non-volatile memory devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Metal nanoring and tube formation on carbon nanotubes
(American Physical Society, 2002) Bagci, V. M. K.; Gülseren, O.; Yildirim, T.; Gedik, Z.; Ciracil, S.
The structural and electronic properties of aluminum-covered single-wall carbon nanotubes (SWNT's) are studied from first principles for a large number of coverages. Aluminum-aluminum interaction, that is stronger than aluminum-tube interaction, prevents uniform metal coverage, and hence gives rise to the clustering. However, a stable aluminum ring and aluminum nanotube with well defined patterns can also form around the semiconducting SWNT's and lead to metallization. The persistent current in the Al nanoring is discussed to show that a high magnetic field can be induced at the center of SWNT.
Open Access
MIMIM photodetectors using plasmonically enhanced MIM absorbers
(SPIE, 2017) Dereshgi, S. Abedini; Okyay, Ali Kemal
We demonstrate super absorbing metal-insulator-metal (MIM) stacks and MIMIM photosensitive devices operating at visible and near-infrared (VIS-NIR) spectrum, where absorbing (top) MIM and photocollecting (bottom) MIM can be optimized separately. We investigate different bottom metals in absorbing MIM with nanoparticles realized by dewetting of silver thin film on top. While gold and silver have conventionally been considered the most appropriate plasmonic absorbers, we demonstrate different absorbing metals like aluminum and specifically chromium, with its plasma frequency happening at 850 nm, as more efficient layers for absorption. Absorption in chromium hits 82 percent around 1000 nm. We provide convincing evidences by doing reflection experiment and computational simulations for absorbing MIM part. We also suggest for the first time investigating electric loss tangent of metal or coherently, surface plasmon quality factor of absorbing metals which are reliable tools for engineering different metal layers. They reveal that despite the fact that gold and silver are good plasmonic scatterers in VIS-NIR and reliable absorbers in VIS region, they are not proper choices as absorbers for NIR applications. Once the most optimum absorbing design is pointed out, we integrate it on top of another metal-insulator to form an MIMIM photodetector with tunneling photocurrent path. The final optimized sample consisting of silver - hafnium oxide - chromium - aluminum oxide - silver nanoparticles (from bottom to top) has a dark current of 7nA and a photoresponsivity peak of 0.962 mA/W at 1000 nm and a full width at half maximum of 300 nm, while applied bias is 50 mV and device areas are 300 μm x 600 μm. This photoresponse shows 70 times enhancement compared to former reported spin coated rare nanoparticle MIMIMs.
Open Access
Multispectral plasmonic structures using native aluminum oxide and aluminum
(OSA, 2017) Ayaş, Sencer; Bakan, Gökan; Dana, Aykutlu
We report the use of native aluminum oxide to fabricate periodic metal-insulator-metal resonators with simultaneous resonances in the visible and IR wavelengths. The cavity size is in the order of λ3/25000 in the NIR.