Alloying of high purity copper surfaces with cathodic arc aluminum plasma

Al-Cu sistemi uzunca bir süredir bilimsel ve teknolojik alanda ilgi odağı olmuştur. Özellikle bakırca zengin aluminyum alaşımları yüksek elektrik ve termal iletkenlikleri ve kolay şekil verilebilir olmalarından dolayı yaygın bir şekilde mühendislik malzemesi olarak kullanılmaktadırlar. Buna ek olarak, Al-Cu faz diagramının bakırca zengin kısmında yer alan aluminyum bronzları mekanik ve fiziksel özelliklerinden dolayı ilgi çekicidirler. Kompozisyonları ağırlıkça %5-%11 arasında aluminyum içeren aluminyum bronzları yüksek mukavemet, sertlik, aşınma dayanımı ve korozyon direncine sahip olmalarından dolayı endüstride yaygın olarak kullanılmaktadırlar. Çeşitli taban malzemelerin yüzeylerinde aluminyum bronz tabakası oluşturmak amacıyla bir takım fiziksel buhar biriktirme teknikleri kullanılmıştır. Bu tekniklerin hemen hemen tamamında, kaplama işleminden sonra, istenilen yapının elde edilmesi için değişik sıcaklık ve sürelerde ısıl işlemlerin yapılması gerekmektedir. Bu çalışmada, katodik ark fiziksel buhar biriktirme (KA-FBB) yöntemi ile yüksek saflıktaki bakır taban malzemesinin yüzeyinin herhangi bir ısıl işleme gerek duyulmadan alaşımlandırılması hedeflenmiştir. KA-FBB deneyleri sırasında aluminyum katod kullanılmış ve taban malzemeye sırasıyla -150 V (kaplama) ve -1000 V (yayındırma) bias voltajı uygulanmıştır. KA-FBB işlemi sırasında uygulanan kaplama ve yayındırma basamaklarının yüzey mikroyapısı üzerindeki etkileri, x ışınları kırınım (XRD) ve taramalı elektron mikroskobu (SEM) çalışmaları ile incelenmiştir. Yapılan deneyler sonucunda yüksek saflıktaki bakır taban malzemenin yüzeyinde ağırlıklı olarak martensitik yapıda β1-AlCu3 yapısı ve (Cu) katı çözeltisi oluşmuştur. Bu fazlara ek olarak, modifiye edilmiş yüzeyde az miktarda γ1-Al4Cu9 intermetalik yapısının da varlığı tespit edilmiştir. Anahtar Kelimeler: Katodik ark fiziksel buhar biriktirme, yüzey modifikasyonu, Al-Cu sistemi, aluminyum bronzları, intermetalik.The Al-Cu system has been a focus of scientific and technological interest over decades. The system is theoretically interesting because of its unresolved phases (Dong et al., 2000; Gulay and Harbrecht, 2004; Liu et al., 1998; Hannech et al., 2003) microstructural characteristics depending on cooling rates (Eskin et al., 2005) and applied magnetic and electrical fields during solidification (Liu et al., 2004; Li et al., 2006), martensitic and massive transformations (Murray, 1985) and metastable Guinier Preston zones (Lochte et al., 1980; Lokker et al., 2001). Al-Cu alloys are used as interconnects in integrated circuits because of their high conductivity and their acceptable processing properties (Lokker et al., 2001) and they could be employed in semi-conductor devices (Ene et al., 2007). Cu-based aluminum alloys are used as engineering materials because of their high electrical and thermal conductivity and easy formability. Considering the copper rich side of Al-Cu phase diagram, aluminum bronze and γ1-Al4Cu9 structures are interesting due to their mechanical and physical properties. A variety of aluminium bronzes of differing compositions ranging from 5% to 11% aluminium by weight have been used in industry for their high strength, high hardness, wear resistance, corrosion resistance and biostatic effects (Alam et al., 2001). The intermetallic compound γ1-Al4Cu9  is reported as one of the hardest and strongest intermetallic compounds in Al-Cu binary system (Rabkin et al., 1970). In addition, low electrical resistivity of γ1-Al4Cu9 intermetallic phase could make them suitable for metallization material application for large scale integration (LSI) technology (Atsushi and Sasaki, 1991). Al-Cu is a complex system which contains many phases and invariant transformations, most of which exists in the Cu-rich side of the binary phase diagram (Murray, 1985). The phase relations of the system are not yet completely clarified and the structures of some high temperature phases are still unresolved (Hannech et al., 2003; Gulay and Harbrecht, 2004). Cu-rich side of the Al-Cu phase diagram involves a eutectoid reaction through which β-AlCu3 phase transforms into α-Cu solid solution and γ-Al4Cu9 at ~567°C. β-AlCu3 phase can also be retained metastably due to the sluggishness of the eutectoid reaction and several metastable reactions such as β→ β1+(Cu) are also present in that region of the phase diagram (Murray, 1985). Aluminum bronze structures have been obtained on the surfaces of various substrates by PVD (Liang et al., 2000) arc spraying (Zhang et al., 2006), thermal spraying (Barik et al., 2005), low pressure plasma spraying (Alam et al., 2001) and laser surface alloying (Tang et al., 2006). In addition, numerous studies about PVD processes that used layered growth and annealing for alloying of the surfaces, have been published (Kanjilal et al., 2002; Cekada et al., 2004). Recently, a cathodic arc physical vapour deposition (CAPVD) technique has been introduced, based on sequential deposition (at low bias voltages) and bombardment (at high bias voltages) of the selected target material on the surface of the substrate (Şireli, 2005; Çorlu and Ürgen, 2009). It was proposed that, surface heating and momentum transfer effects created during energetic metal ion bombardment and the defective structure of the deposits resulted in alloying of the surfaces and formation of intermetallics at the surface. In this study, we aimed to modify the surfaces of copper substrates in order to obtain aluminum bronze (>70 at.% Cu) structures at the surfaces of the substrates by using the CAPVD technique. Surface alloying and intermetallic formation was realized by sequential deposition and bombardment of aluminum on surfaces of copper substrates. The effects of the duration of the deposition- bombardment stages of the process on the structure and chemistry of the treated surfaces were investigated with XRD and SEM. XRD patterns showed that the modified zone mainly consisted of a mixture of martensitic β1-AlCu3 and (Cu) solid solution, which was accompanied by γ1-Al4Cu9 intermetallic phase. For a detailed microstructural analysis, the cross-sectional samples were etched with FeCl3 solution in order to dissolve the (Cu) phase and reveal the β-AlCu3 phase. According to SEM investigations after etching with FeCl3 solution, modified zone, with a thickness of ~15µm, consisted of three phases, which corresponded to (Cu) solid solution, β1-AlCu3 phase and γ1-Al4Cu9 intermetallic phase. Keywords: Cathodic arc physical vapor deposition, surface modification, Al-Cu binary system, aluminum bronzes, intermetallics

Performance optimization of drill bits using design of experiments

Deney tasarımı teknikleri mühendislik çalışmalarına önemli avantajlar getirmektedirler. Çalışmada bu yaklaşımın detayları, ince sert seramik kaplı (TiAlN ve TiN) matkap uçlarının performans optimizasyonu örneği ele alınarak incelenmiştir. Hedeflenen optimum noktaya ulaşabilmek için endüstriyel ortamda en önemli faktörler olan kaplama türü, kesme hızı ve ilerleme hızının etkileri Taguchi Deney Tasarımı tekniği yardımı ile incelenmiştir. Deney sonuçlarının değerlendirilmesinde varyans analizi ve sinyal/gürültü oranı kullanılmış, deneyler ise Taguchi L9 dik düzenine göre yapılarak, Tam Faktöriyel Deney Tasarımında gereken deney sayısının sadece üçte biri ile (27 yerine 9 deney) hedeflenen sonuçların elde edilmesi mümkün olmuştur.Anahtar Kelimeler: Deney tasarımı, ince sert seramik kaplamalar, Taguchi.In this paper advantages of design of experiment techniques in engineering applications were investigated by the example of the performance optimization problem of hard ceramic coatings on HSS drills. TiN and TiAlN coatings on HSS tools have shown significant improvements on tool life. To achieve the limits of the improvements, optimization of processing parameters is as important as the selection of proper coating type. Cutting speed and feeding rate have been chosen as the most important process parameter, which can be easily adjusted under industrial conditions. The work focused on the main effects of coating type, cutting speed and feeding rate on the overall performance by using design of experiment techniques. The statistical methods of signal-to-noise ratio and analysis of variance are applied for the analysis of the results and for the determination of the effects of each parameter on the drilling process. Design of the experiments is based on Taguchi L9 orthogonal array, which provides a decrease of the necessary number of experiments to 1/3 of a conventional full factorial design. As a result, the analyses show that an optimum cutting force is provided in case of TiAlN coatings, when cutting speed is 25 m/min and feeding rate is 164 mm/min. The efficiency of the optimization by Taguchi technique under industrial conditions has been proved by the decrease of the number of necessary experiments from 27 to 9.Keywords: Design of experiments, hard ceramic coatings, Taguchi

Tribological properties of MoN-Ag nanocomposite coatings

Birbirleri ile temas halinde olan yüzeylerden, mekanik etkilerle oluşan malzeme kaybı, yüzyıllardır insanoğlunun mekanik problemlerinin başında gelmiştir. Dünyadaki mekanik enerjinin yüzde otuzunun mekanik kayıplara harcandığı düşünülürse, sürtünme ve aşınmanın önemi daha da iyi anlaşılabilir. Teknolojik ilerlemelerle birlikte sürtünme ve bunun neden olduğu aşınma problemlerinin aşılması için sert yüzey kaplamaları kullanılmıştır. TiN, CrN gibi ince film kaplamalar endüstriyel uygulamalar için en yaygın olarak kullanılan kaplamalardır. Molibden esaslı nitrür kaplamalarda, sürtünme ve aşınma açısından oldukça üstün özelliklere sahiptirler. Molibden esaslı kaplamalar da düşük sürtünme katsayısı elde edilmesine rağmen temel problem, karşıt malzemede meydana gelen aşınmadır. Çok sert olan molibden kaplamlara yumuşak Ag, Cu gibi elementlerin ilavesi ile elde edilen yapılar, kuru şartlarda ticari olarak kullanılan kaplamalardan daha üstün sürtünme-aşınma özelliklerine sahiptirler. Bu çalışmada katodik ark ve manyetik alanda sıçratma sistemlerinin hibrit kullanıldığı fiziksel buhar biriktirme yöntemi ile yüksek hız takım çeliği malzemelere üzerine kaplanan farklı Ag içeriğine sahip MoN-Ag kaplamaların Al2O3 karşıt malzeme kullanılarak atmosferik koşullardaki sürtünme ve aşınma özellikleri incelenmiştir. Aşınma deneylerinde katkısız MoN kaplamaların yanı sıra düşük, orta ve yüksek (at.%1.4, %8, %24Ag) Ag içeriğine sahip kaplamalara sürtünme-aşınma deneyi yapılmıştır. MoN yapılara Ag ilavesi ile sürtünme deneyleri sonucunda yüksek Ag içeren kaplamalar dışındaki kaplamalarda önemli bir aşınma görülmemesinin yanında Ag’ün yararlı etkisi özellikle at.%8 oranında Ag içeren kaplamalarda tespit edilmiştir. Anahtar Kelimeler: Nanokompozit kaplama, Mo-N-Ag,hibrit kaplama, mikro-Raman.Nanostructured coatings have been recently of great interest because of the possibility of synthesizing unique physical and chemical properties. Different approaches exist for the production of nanostructured coatings such as superlattice coatings, nano-scale multilayer coating, super lattice coating and nanocomposite coatings. The nanocomposite type coatings have attracted the greatest interest by the researchers. Completely new properties are exhibited by nanocrystalline coatings with decreasing the grain size to about 10 nm. The mechanical properties of these materials are determined by processes in boundary regions because the number of atoms in grain is smaller than in the boundary regions. High fracture toughness can be obtained in the nanocomposite structure due to the nano size grain structure. Currently, two main practices exist for the production of nanocomposite coatings. In the first one, the nanocomposite structure is obtained by the combination of two hard and immiscible phases in one coating (e.g., ncTiN/aSi3N4; a TiSi2 nc TiSi2) while in the other practice, the mixture of one hard (MeN) and one soft (X) immiscible phase (e.g., Zr Cu N, Cr N  Cu, Ti Cu N and Mo Cu N) are used. In these coatings, one metal may be converted into nitride as a nanocrystalline phase and the other participated in the growing film without any reaction. Nanocomposite coatings based on hard/hard phases have attracted in recent years and there are now numerous studies that deal with the production, characterization, and application of these coatings. The coatings with hard-soft structure have a very promising structure with respect to tribological applications. One can easily formulate these coatings by selecting the hard and soft phase combinations for the required tribological application. Examples of such formulations have been put forward in our research group especially for coating applications suitable for systems working under boundary lubrication conditions. The main approach used in these formulations relies on functioning of the hard phase (such as MoN) as load bearing material and soft phase (copper, silver, tin, antimony etc.) or their compounds. In this study, further verification of this approach is aimed using a hard-soft nanocomposite system based on Mo-N-Ag. MoN is selected as the hard phase because of its better tribological properties compared to other hard phases. On the other hand silver is an easily shearable soft material that is mainly used in high temperature applications as solid lubricant. Silver also has a potential of forming solid lubricant compounds with the oxides of the hard phase (such as silver molybdates) and it can also react with the formulated oil ingredients and form lubricous structures. For achieving this aim, not only the effect the composition of the coating material but also the effects of different sliding velocity on the tribological behavior is investigated and the results are correlated with the character of the debris that are determined with micro-Raman spectroscopy.  Hence, this is a unique study, in which the tribological behavior of the Mo-N-Ag nanocomposite coatings is investigated in detail by taking into consideration both formulation of the coatings and the tribo -mechanical and -chemical properties of the system. Moreover, in this study a hybrid coating system based on cathodic arc and magnetron sputtering that is previously used extensively in our group for the production of other MeN-X type structures, is used for the first time for the production of MoN-Ag nanocomposite coatings. Molybdenum nitride and MoN-Ag nanocomposite coatings were deposited using cathodic arc and cathodic arc + magnetron sputtering hybrid physical vapor deposition techniques. Hardened M2 discs were used as substrates. Hardness of the coatings were measured with a dynamic ultra micro-hardness tester (Fischerscope H 100) equipped with an elongated Vickers type indenter; a total load of 20 mN was applied in 120 steps with a time interval of 0.5s at each step. The phase structure of the coatings was analyzed by a glancing angle X-ray diffractometer. EDS equipped field emission scanning electron microscope (Jeol JSM 700F) was used for investigation of coating growth and wear tracks morphology. Wear tracks and chemical composition of wear debris were examined by 3D profilometer and micro-Raman, respectively. Observations of the wear traces with the micro-Raman investigation showed that formation of lubricious oxide and silver molybdate into the wear track caused decreasing the wear and friction. Silver addition showed its beneficial effect by lowering the wear of counter face material and decreasing the coefficient of friction. Keywords: Nanocomposite coating, MoN-Ag, hibride coating, micro-Raman

TiO2 photocatalysts

Son yıllarda, titanyum dioksit (TiO2) üzerinde, fotokatalitik aktivite özelliğinden dolayı yoğun olarak çalışılmaktadır. TiO2, UV ışığı ile uyarıldığı zaman fotoaktif özellik gösteren ve organik grupları parçalayabilen yarıiletken bir malzemedir. TiO2, ışığa maruz bırakıldığında, suyun arıtılmasında, kendi kendini temizleyebilen, buğulanmayan yüzeylerin elde edilmesinde, fotokimyasal olarak kanser tedavisi uygulamalarında, havanın arındırılmasında kullanılabilir. TiO2 filmler, kimyasal buhar biriktirme, sıçratma, elektron demeti ile buharlaştırma, iyon ışını destekli biriktirme ve sol-jel gibi yöntemlerle değişik yüzeyler üzerine kaplanabilirler. TiO2, anataz, rutil ve brukit olmak üzere üç farklı kristal yapıya sahiptir. Birçok uygulamada TiO2’in anataz formu en iyi fotoaktivite özelliği göstermektedir. TiO2’in, solar spektrumun çok az bir bölümünü oluşturan UV ışığı ile aktive edilebiliyor olması bu malzemenin pratik uygulamalardaki kullanımını sınırlandırmaktadır. Bundan dolayı, pratik uygulamalar için, TiO2’in fotoaktivitesinin geliştirilmesi gerekmektedir. Fotoaktiviteyi arttırmanın bir yolu, TiO2’in geçiş metalleri veya soy metallerle katkılandırma işlemi yaparak soğurma (absorption) bandının UV bölgesinden, görünür bölgeye kaydırılmasıdır. Literatürde, titanyum oksit filmlere gümüş, tungsten ve molibden katkılandırılmasına yönelik çalışmalar yapılmış ve üç katkılandırmanın da, titanyum oksit filmlerin fonksiyonalitesine farklı mekanizmalar üzerinden ciddi katkılar yapacak nitelikte olduğu belirtilmiştir. Bu çalışmada, TiO2’in fotokatalitik aktivite mekanizması tartışılmış ve TiO2’in kullanım alanları anti-bakteriyel özelliklerine odaklanarak özetlenmiştir. Buna ek olarak, gümüş, tungsten ve molibden katkısının TiO2’in, anti-bakteriyel aktivitesine olan etkileri tartışılmıştır.  Anahtar Kelimeler: TiO2, sol-jel, anti-bakteriyel, fotokatalitik aktivite.Recently, titanium dioxide (TiO2) has been studied extensively due to its high photocatalytic activity for handling of several types of environmental problems. Major areas of activity in TiO2 photocatalysis are; water purification, photochemical cancer treatment, air purification, self-sterilizing, fog-proof and self-cleaning surfaces. Photocatalysis can be defined as ?acceleration of a photoreaction by the presence of a photocatalyst?. Photocatalytic reactions necessitate a photocatalyst that absorbs the phonons and drives the redox reactions. TiO2 is a semiconductor and it can be chemically activated by UV light. TiO2 has three different crystal structures which are anatase, brookite and rutile. TiO2 in the anatase form is the most efficient of photocatalysts for many applications. The band gap energy of anatase TiO2 is 3.2 eV and it can be only activated by UV light. Although UV light is present in the solar spectrum it is only a very limited part. For practical applications the photocatalytic activity of TiO2 needs further improvement. Doping TiO2 with transition metals or noble metals is an effective way to improve photocatalytic activity. When TiO2 is exposed to UV light, electron-hole pairs are created. The photogenerated holes in the valence band, which has strong oxidizing power, diffuse to the surface and react with adsorbed water in order to produce hydroxyl radicals (?OH). These hydroxyl radicals participate in oxidizing organic molecules. On the other hand, electrons in the conduction band react with molecular oxygen in the air to produce the superoxide radical anion (O2-?), which also participates in further oxidation processes. The photocatalytic efficiency of TiO2 strongly depends on surface area and electron-hole recombination rate. The surface area of the photocatalyst increases with a smaller particle size and the active surface sites increase. For improving photocatalytic efficiency, electron-hole recombination rate should be reduced. An effective way to seperate electron-hole pairs is to introduce foreign materials into TiO2 matrix. As mentioned above, TiO2 can be used in different application areas. One of the remarkable property of TiO2 is its self-cleaning effect. The surfaces of glasses, ceramic tiles can be contaminated by organic particles such as smoke residue, oil and dirt. TiO2 thin films can be applied to these surfaces in order to decompose those organic species. Another excellent property of TiO2 photocatalysts is their anti-bacterial effect. TiO2 can decompose bacteria and virus when it is exposed to UV light. TiO2 has advantages over conventional self-sterilizing surfaces. For instance, in the case of E.coli, TiO2 decompose both the living cells as well as the endotoxin released from these cells during their death. TiO2 photocatalysts can also be used for cancer treatment. TiO2 particles which are injected to the tumor  clearly inhibit the tumor growth. In literature, there are several studies which are related to the doping effect of silver. Studies which are performed on the effect of silver dopant are focused on the change of optical and electronical properties of TiO2. Moreover, since silver itself is known as strong anti-bacterial agent it is used as dopant for improving anti-bacterial properties of TiO2. Doping silver can give rise to the separation of electron-hole pairs and can accelerate the formations of oxidative species. In addition to this, silver can reduce particle size which is needed for increasing surface area of TiO2. In order to obtain anti-bacterial effect in the dark, energy storage photocatalyst can be produced by doping TiO2 with tungsten. TiO2-WO3 photocatalyst can be photo-charged by irradiating their surfaces with UV light. Photo-charged tungsten doped TiO2 films are able to show anti-bacterial effect when the light is turned off. Molybdenum also is an energy storage material and it can be used as an alternative to those of tungsten. In this study, the mechanism of photocatalytic activity is discussed and the application fields of TiO2 photocatalysts were summarized by focussing on the bacterial activity of TiO2. Moreover, the effect of silver, tungsten and molybdenum dopants on the bacterial activity of TiO2 were discussed.  Keywords: TiO2, sol-gel, photocatalyst, anti-bacterial, photocatalytic activity

Spinodal phases in Cr coated low carbon steel through cathodic arc PVD technique

Bu çalışmada, katodik ark fiziksel buhar biriktirme yöntemi ile krom kaplanan, krom kaplama sonrası farklı sürelerde yüksek bias voltajı etkisi ile krom iyonu bombardımanı uygulanan ve darbeli bias voltajı uygulaması ile krom kaplanan düşük karbonlu çelik malzemelerde meydana gelen spinodal fazlar karakterize edilerek, gelişimleri incelenmiştir. Elektron mikroskopisi, elementel analizler ve kesitlerden alınan derinlik profili çalışmaları ile gerek kaplama sonrası uygulanan krom bombardımanı, gerekse darbeli bias uygulamasında yüksek bias periyodlarındaki krom bombardımanının, krom kaplama ve düşük karbonlu çelik taban malzeme arasında radyasyon destekli yayınma mekanizması ile gerçekleşen bir iyon demeti karışımı prosesine neden olduğu tespit edilmiştir. Bunun sonucunda, taban malzemeden kaplama yüzeyine büyük oranda demir atomu yayınmış ve yüzeylerde çok kısa süreler içerisinde spinodal ayrışma fazları meydana gelmiştir. Bu fazların morfolojileri, literatürde demir-krom (Fe-Cr) sistemindeki spinodal ayrışma çalışmalarında elde edilen mikroyapılar ve bilgisayar simülasyonu ile oluşturulan spinodal yapılar ile oldukça büyük benzerlikler göstermiştir. Ayrıca bombardıman uygulanan örneklerde, spinodal ayrışma yapılarının bir karakteristiği olan tepe/vadi oluşumları ile fazlar arasındaki bileşimsel dalgalanmalar gibi sonuçların gözlenmesi de spinodal fazların oluşumunu doğrulamaktadır.  Elde edilen mikroyapılara bakıldığında, taneli taban malzeme üzerinde epitaksik olarak büyüyen kaplamalardaki bazı tanelerde, spinodal ayrışma fazları oluşmadığı görülmüştür. Bununla birlikte, bombardıman süresinin artması ile bu tanelerde de spinodal ayrışma yapılarına benzer oluşumlar gözlenmiştir. Anahtar Kelimeler: İyon bombardımanı, radyasyon destekli yayınma, spinodal ayrışma.In this study, spinodal decomposition phases formed in low carbon steel samples which were Cr coated, Cr coated and bombarded with Cr ions through applying high bias voltage (1 keV) and Cr coated through applying pulsed bias voltage in a cathodic arc physical vapour deposition (PVD) system were characterized and compared. 1.5 mm thick IF (interstitial free) steel sheets were used as substrate. The bombardment periods after the coating were 1 minute, 2 minutes and 3 minutes. In pulsed bias mode, bias voltage was alternately increased to 1 keV for 5 seconds (bombardment section) and decreased to 150 eV for 10 seconds (coating section) along 10 minutes. Total bombardment time was 3.3 minutes in 10 minutes of pulsed bias. In order to determine the spinodal decomposition phases, Field Emission Microscopy (FEM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectral Analysis (EDS) and Glow Discharge Optic Emission Spectroscopy (GDOES) studies were performed. Not only the bombardment applied after the coating process, but also the one applied during the high bias voltage period in the pulsed bias mode caused radiation enhanced diffusion between Cr coating and low carbon steel substrate. This was proven by EDS analysis, GDOES analysis and elemental maps taken from cross sections of the samples. Fe content of coatings increased gradually by increasing bombardment time. As a result of ion beam mixing, severe iron diffusion from the substrate to the Cr coating?s surface took place and this resulted in formation of spinodal decomposition phases in a very short time. These phases? morphologies were quite similar to microstructures obtained from spinodal decomposition studies in Fe-Cr system and computer simulated spinodal structures in literature. Besides, it was observed through the EDS analysis and FEM studies of the bombarded samples that hill/valley formations and compositional fluctuations which were the characteristics of spinodal decomposition process were also present. Hills were Cr rich and valleys were Fe rich parts of the spinodal structures. It was observed in FEM micrographs that hills and valleys were getting wider with increasing bombardment period and it was another characteristic of spinodal decomposition structures. When the average cohesive energy of the Fe-Cr system (4.19 eV)  and the relationship between the cohesive energy and the critical temperature (Tc»100Ekoh)  at which radiation enhanced diffusion (RED) would be efficient were taken into consideration, ion beam mixing in our system woud take place through RED regime. Altough both metals have similar cohesive energies, dominant Fe movement to the Cr coating was observed in pulsed bias mode instead of an isotropic mixing. While Fe-Cr alloys must be heat treated for very long times (up to 500 hours) in conventional spinodal decomposition processes, it is very interesting that the spinodal decomposition phases formed in 1-3 minutes in this study. It is believed that the diffusion enhanced by the radiation effected the spinodal decomposition kinetics. As a result of thermally activated migration of  defects caused by Cr ion bombardment and short range diffusions in very hot thermal spikes formed by the collisions between bombarding ions and target atoms accelerated the diffusion processes which make the spinodal decomposition occur. In some grains of the coatings which grew on grained microstructure of the substrate material epitaxially, spinodal decomposition was not observed. These smooth grains with no hill/valley structure were supposed to be s phase which was not decomposed during the bombardment and cooling periods. The coherency strain between the grains may have displaced the spinodal line (coherent  spinodal) in some grains resulting in not occuring spinodal decomposition in chemical spinodal line. However, spinodal structures started to form in those smooth grains by increasing the bombardment time and temperature. It was observed via EDS analysis taken from the samples which were not only bombarded after coating but also coated through applying pulsed bias that Fe content increased by increasing the bombardment time. Formation of spinodal structures in smooth grains and increasing of the Fe content concurrently by increasing the bombardment time points that spinodal decomposition occurs in Fe rich part of the spinodal line in those smooth grains. As a potential development of this study, more efficient temperature control should be applied to determine chemical and coherent spinodal lines in Fe-Cr alloys produced by ion bombardment of Cr coated low carbon steels.Keywords: Ion bombardment, radiation enhanced diffusion, spinodal decomposition

Structure and photovoltaic properties of Ag/p-CuPc/a-Si/c-Si/Ag organic-inorganic hybrid heterojunction fabricated by chemical spray pyrolysis technique

This investigation refers to the fabrication of an organic-inorganic hybrid heterojunction photovoltaic device. Heterojunctions PV devices were fabricated by growing p-type organic CuPc films onto inorganic amorphous silicon substrates using chemical spray pyrolysis technique. The structural and morphological properties of the amorphous silicon thin films and CuPc thin films were investigated by XRD, RAMAN and FEG-SEM analysis. The XRD pattern indicated that the films were polycrystalline in nature of CuPc thin films that crystallized in the orthorhombic alpha-phase structure. We determined 17 Raman active peaks belong to CuPc thin films and our results are compatible with polarized Raman spectra. We have characterized the electrical and photovoltaic properties of Ag/p-CuPc/a-Si/c-Si/Ag heterojunction devices. The measured electrical parameters were used to determine the conduction mechanisms of these heterojunctions. Electrical parameters such as barrier height Phi(B), diode ideality factor eta, series resistance R-s and shunt resistance R-sh were determined from the I-V characteristic in the dark conditions for Ag/p-CuPc/a-Si/n-Si/Ag and Ag/p-CuPc/a-Si/p-Si/Ag heterojunctions were found to be 2.5-5.7, 0.95-0.99 eV, 26-28.6 k Omega, and 9.2-3.7 M Omega, respectively. The photovoltaic properties of organic-inorganic hybrid heterojunction devices were evaluated by current-voltage characteristics under illumination. The hybrid heterojunctions shows a photovoltaic behavior and the photovoltaic parameters, such as open circuit voltage and short circuit current were obtained as V-oc = 167 mV and J(sc) = 18.4 mA/m(2), respectively. The Ag/p-CuPc/a-Si/c-Si/Ag hybrid heterojunctions can be using as a heterojunction photovoltaic devices. (c) 2013 Elsevier B.V. All rights reserved.TUBITAK The Scientific and Technological Research Council of Turkey Engineering Research GroupTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112M319]This work was carried out with the support of TUBITAK The Scientific and Technological Research Council of Turkey Engineering Research Group (Project No:112M319). Author is thankful to The Scientific and Technological Research Council of Turkey

Investigation of structural and electrical properties of p-CuPc/c-Si and p-CuPc/a-Si/c-Si hybrid photodiodes prepared by CSP technique

To produce p-CuPc/c-Si and p-CuPc/a-Si/c-Si heterojunctions, at first, amorphous silicon thin film was deposited on p-Si (111) and n-Si (100) single crystalline substrates by high vacuum electron beam evaporation technique. Subsequently p-type organic semiconductor CuPc thin film was prepared on different substrates, which are Si single crystalline wafer, amorphous silicon and corning glass substrates by chemical spray pyrolysis (CSP) technique. The structural properties of CuPc thin films were investigated by XRD and Raman analysis. The CuPc thin film grown on corning glass and c-Si wafer substrate have orthorhombic alpha-phase crystalline nature and show only one characteristic peak oriented in (200) direction. The CuPc thin film grown on a-Si substrate has an amorphous structure. Surface and cross-sectional morphology of CuPc/c-Si and CuPc/a-Si/c-Si heterojunctions were investigated by FESEM images. The electrical transport and diode parameters of these organic-inorganic hybrid heterojunction have been investigated by means of dc current-voltage (I-V) measurements at room temperature in dark condition. The current-voltage characteristics of these hybrid heterojunctions demonstrated good rectifying behavior and have good photosensitivity in light conditions. The diode parameters such as barrier height Phi(B), diode ideality factor n, series resistance R-s and shunt resistance R-sh were determined from the I-V characteristic. The values of the ideality factor (n) and zero-bias barrier height (Phi(B0)) of CuPc/c-Si and CuPc/a-Si hybrid heterojunctions were found to be 9.64-8.06 and 0.93-0.89 eV respectively. It is revealed that the dominant conducting mechanism type of these organic-inorganic heterojunction diodes which have space charge limited conduction mechanism (SCLC). The values of the quantum efficiency (QE) of CuPc/c-Si and CuPc/a-Si hybrid heterojunctions were found to be 19.6-41% respectively. We have fabricated CuPc/a-Si/c-Si organic-inorganic hybrid photodiode with 41% quantum efficiency which corresponds to a responsivity of 0.21 A/W at 632.8 nm wavelength. These hybrid heterojunctions based on organic CuPc and inorganic c-Si can be used in photodiode due to photosensitivity and electrical properties. (C) 2014 Elsevier B.V. All rights reserved.TUBITAK The Scientific and Technological Research Council of Turkey Engineering Research GroupTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112M319]This work was carried out with the support of TUBITAK The Scientific and Technological Research Council of Turkey Engineering Research Group (Project No. 112M319). Author is thankful to The Scientific and Technological Research Council of Turkey

Structure and photovoltaic properties of Ag/p-CuPc/a-Si/c-Si/Ag organic-inorganic hybrid heterojunction fabricated by chemical spray pyrolysis technique

This investigation refers to the fabrication of an organic-inorganic hybrid heterojunction photovoltaic device. Heterojunctions PV devices were fabricated by growing p-type organic CuPc films onto inorganic amorphous silicon substrates using chemical spray pyrolysis technique. The structural and morphological properties of the amorphous silicon thin films and CuPc thin films were investigated by XRD, RAMAN and FEG-SEM analysis. The XRD pattern indicated that the films were polycrystalline in nature of CuPc thin films that crystallized in the orthorhombic alpha-phase structure. We determined 17 Raman active peaks belong to CuPc thin films and our results are compatible with polarized Raman spectra. We have characterized the electrical and photovoltaic properties of Ag/p-CuPc/a-Si/c-Si/Ag heterojunction devices. The measured electrical parameters were used to determine the conduction mechanisms of these heterojunctions. Electrical parameters such as barrier height Phi(B), diode ideality factor eta, series resistance R-s and shunt resistance R-sh were determined from the I-V characteristic in the dark conditions for Ag/p-CuPc/a-Si/n-Si/Ag and Ag/p-CuPc/a-Si/p-Si/Ag heterojunctions were found to be 2.5-5.7, 0.95-0.99 eV, 26-28.6 k Omega, and 9.2-3.7 M Omega, respectively. The photovoltaic properties of organic-inorganic hybrid heterojunction devices were evaluated by current-voltage characteristics under illumination. The hybrid heterojunctions shows a photovoltaic behavior and the photovoltaic parameters, such as open circuit voltage and short circuit current were obtained as V-oc = 167 mV and J(sc) = 18.4 mA/m(2), respectively. The Ag/p-CuPc/a-Si/c-Si/Ag hybrid heterojunctions can be using as a heterojunction photovoltaic devices. (c) 2013 Elsevier B.V. All rights reserved