PacSurf2014 Session TF-WeP: Thin Films Poster Session

The etch characteristics of Pd for the fabrication of blue laser and light emitting diodes were investigated by using inductively coupled Ar–based plasma for low damage in underlayer.Up to date, the etch characteristics of Pd was not fully understood, because the suitable gas to form a volatile etch-product was not known due to the chemical inertness of Pd. Furthermore, the control of gas mixture for the low damage in underlying GaN semiconductor is more preferable in order to fabricate high quality optical devices. Therfore, it is important to selection of gas mixture in plasma. Furthermore, it was found that the photoresist was eroded when the ICP souurce power was increased above 100 W, when the Ar plasma were used as active etchant.

Strontium titanate(SrTiO₃, STO) has been attracting a great deal of attention as the capacitor dielectric material for DRAM with design rule < 20 nm due to its much higher dielectric constant (k > 100) compared with those of presently adopted dielectrics based on ZrO₂ (k ~30 – 40). Because of the severe three-dimensional geometry of DRAM capacitors, atomic layer deposition (ALD), which provides the ultimate step coverage, is indispensable. The conformality of film is generally induced by self-limited growth mechanism of the ALD. However, in previous studies, non-ideal excess growth was observed during the early stage of STO deposition on Ru electrode, the most promising electrode material. The excessive growth was more dominant for the incorporation of Sr into the film compared with Ti. This was mainly attributed to the reduction of in-situ oxidized Ru substrate during the O₃ pulses in the previous ALD steps.^{[1, 2]} Such adverse effect was further aggravated by the high growth temperature (370 ^oC), which was adopted for the in-situ crystallization of the STO film. Also, the weak chemical bonding between the cyclopentadienyl(Cp)-based ligands and Sr ions in the conventional Cp-based Sr-precursor induced such problem.

In this study, therefore, [Sr(demamp)(tmhd)]₂, developed by Korea Research Institute of Chemical Technology,^[3] which is supposed to have a chemical properties in medium of the Cp-based Sr-precursor and tmhd-based homoleptic Sr-precursor, was adopted as the new Sr-precursor and attempted ALD process of STO film. A high density (250 g/m³) O₃ was employed as the oxygen source for SrO deposition and sputtered Ru was used as the substrate with its temperature of 370 ^oC. Ti(Me₅Cp)(O Me)₃ was employed as the Ti-precursor which is also reacted with O­₃. With this novel heteroleptic Sr-precursor, good ALD-specific saturation growth behaviors were observed with respect to the precursor injection, Ar purge, O₃ injection, and Ar purge step times. Most importantly, the unwanted overgrowth of Sr element in initial stage of film growth decreased substantially, and the linear growth behavior of both Sr and Ti were achieved. Meanwhile, the growth rate was decreased to 0.50 Å /cycle, which was lower than the previous case with Cp-based Sr-precursor (1.23 Å /cycle) but assisted to have a denser as-deposited film. With more ideal-like ALD process, the deposited film showed excellent film properties including high purity, high crystallinity, high electrical properties, and excellent step coverage.

[1] S. W. Lee, et al., Chem. Mater. 23, 2227, 2011.

[2] W. Lee, et al., Chem. Mater. 25, 953, 2013.

[3] S. M. George, et al., Eur. J. Inorg. Chem. 2014, 2002, 2014.

Research on topological wrinkle structures at the nano- or micrometer scale is continuously growing because of the development of robust techniques for controlled patterning of polymer and the emergence of novel applications that benefit from the wrinkle structures. The wrinkle structures can be applied to various systems such as stretchable electronics, microlens arrays, microelectromechanical devices, tunable surface adhesion, friction and robotics. To produce a wrinkle structure on this scale, photolithographic, printing, embossing or writing techniques have traditionally been used. However, these methods have relatively high costs and limited throughput when producing customized features. Therefore, alternative spontaneous wrinkle structure fabrication methods have attracted considerable attention in recent decates. These methods, including plasma activation, UV/ozone treatment, laser excitation, and ion-beam (IB) treatment, use surface reformation on the polymer layer, which minimizes the combination of the bending energy of the outer layer and the stretching energy of the inner layer. Among the various alternative methods, IB bombardment has excellent penetrability with high-energy Ar⁺ ions, which leads to stable and reliable wrinkle structure fabrication. Recently, we have shown that irradiation of Ar⁺ ions on the surface of a polydimethylsiloxane (PDMS) substrate results in the formation of a stiff skin on the substrate, which has a chemical composition resembling amorphous silica. Since the stiff skin deformation is constrained by the PDMS substrate, the skin experiences in-plane compressive strain upon ion beam irradiation and buckles to accommodate the induced mismatch strain between the skin and the polymeric substrate.

In this paper, we demonstrate that K-doped coronene and picene monolayers form well-defined structures and they are model systems suitable to clarify the mechanism of electronic and structural modifications of aromatic hydrocarbon crystals due to alkali doping. It can be a basis to control the electronic properties of organic materials by foreign metal-doping.

Modification of the electronic properties of organic materials by doping with foreign metals is one of the key technologies used in next-generation organic electronics. In general, microscopic structural information is essential for understanding the underlying mechanisms. However quite few number of investigations have addressed the microscopic structural features with respect to doping, mainly due to difficulties in the measurement of inhomogeneous samples. Therefore, basic investigation into the microscopic structural nature of metal-doped organic systems utilizing well-defined models is necessary.

In the present study, we have investigated molecular-scale structure and electronic state of K-doped coronene and picene monolayer. For the substrate, we employ inert surfaces, such as Au(111) and highly oriented pyrolytic graphite (HOPG), to minimize the effect of the substrate on the reaction between K and molecules.

After the coronene and picene monolayers were prepared on Au(111) or HOPG using vacuum deposition, K was deposited on the monolayer from alkali dispensers.

The structures were observed by means of scanning tunneling microscope (STM). STM images show significant structural changes of coronene and picene monolayers upon K deposition. Both the K-doped monolayers exhibit well-defined herringbone-like molecular arrangement. In this phase, while the surface reconstruction of Au(111) is still visible, individual K atoms are not observed. We speculate that K atoms intercalate between molecular planes and directly interact with the molecules.

The electronic states were investigated by means of photoemission spectroscopy on a HOPG substrate. In both the monolayers, with increasing doping, a new state appears more clearly just below the Fermi level. The formation of this state is very sensitive to the molecular arrangement [1].

Moreover, it should be noted that a very similar photoemission spectrum has been reported in K-doped thick picene film on HOPG [1]. This similarity ensures the perspective that the well-defined K-doped monolayer can be a model for the doped aromatic hydrocarbons crystals.

[1] H. Okazaki et al., Phys. Rev. B 88, 245414 (2013).

Oxide thin-film transistors (TFTs) have been actively studied to this day and suggest the promising technique with carbon nanotube, nanowire, nanoparticle, or small molecules. Oxide TFTs are made of metals that have sufficiently large ns orbitals to overlap with each other. Thus, they can transport charge carriers without being sensitive to the crystalline structure. An advantage of these devices is that they can be conductive even when the material is in an amorphous phase. With this technique, solution processing is a useful method for generating amorphous oxide TFTs. In addition to its low manufacturing cost, easy deposition, and simple procedure, this method is important because of its outstanding synthesis capacity. With this method, each material can be simply mixed, and uniform films can be formed to achieve multi-component systems. Thus, this property is essential for making oxide films that consist of more than two materials.

Among a variety of solution-processed oxide TFTs, InGaZnO TFTs are the most widely used materials. In InGaZnO TFTs, Ga suppresses carriers and suppression of carriers is achieved by increasing the number of oxygen vacancies. Oxidization of the material is highly related to an electronegativity and a lower electronegativity increases the tendency to be oxidized. In this study, we chose yttrium because the electronegativity of Y is 1.2 which is much lower than that for Ga. Therefore, more oxidization occurs in the channel lattice, which leads to additional suppressing oxygen vacancies.

Azobenzene is a small organic molecule that has been frequently used for organic TFTs. Furthermore, the photo-induced isomerization of azobenzene is an interesting property. In each phase, which is trans- or cis-phase, the molecular structure is different. Normally, the molecule remains in the trans-phase because of higher stability. When exposed to an appropriate light source, azobenzene changes into the cis-phase.

Herein, we investigated solution-processed amorphous InYZnO with azobenzene channel TFTs. The effects on the electrical and structural characteristics of TFT channels due to the photo-induced isomerization of azobenzene were analyzed using a field effect-scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), and electric characteristic analysis.

Liquid crystal displays (LCD) are useful and important device because it is closely related in our daily life, such as mobile display, portable devices, TV and so on. The uniform LC orientation on the alignment film is very important to obtain high quality display. The conventional method, rubbing on the polyimide layer, has some drawback such as generation of debris and accumulation of electrostatic charge. To resolve the shortcomings of LC alignment, alternatives have been investigated for a long time but it is difficult to apply to a commercial purpose. We investigate the solution process using tin-oxide as an alignment layer. In this process we can obtain alignment layer of self-alignment properties. LC molecules are well aligned in higher annealing temperature process along to the filling direction. Because fully oxidized films keep strong van der Waals force between LC molecules and solution-based oxide films. At higher annealing temperature, a tin oxide alignment layer has uniform and increasing nano-crystalline. The average transmittance of oxide alignment layer at higher annealing temperature has 81.21%. This transparency is similar to those of conventional LC alignment materials. The electro-optical properties of solution-based oxide films can be obtained by electrically controlled birefringence (ECB). At higher annealing temperature, the threshold voltage is 1.408V and this result is better performance to conventional method and material. Because process of solution-based oxide films allows for uniform alignment as well as high performance property, it is very simple and useful method.

Silicon carbide thin films were deposited on Si(100) substrates by metal-organic chemical vapor deposition(MOCVD) in high vacuum condition at 2.0 × 10^-7 Torr using 1,3-disilabutane as a single source precursor which contains silicon and carbide in 1:1 ratio at various temperature in the range of 700 ~ 1000 ^oC. The XPS result shows that the SiC thin film grown at 950 ^oC which have carbon rich for silicon and carbon at 1:1.2 ratio. XRD result shows that the SiC thin film grown at 900 ^oC which appeared at 2 = 41.6^o for SiC (200) reflection at a large intensity and a single shape diffraction peck. SEM images result show that the SiC thin film grown at 900 ^oC which has influence on the small grain size and single crystallinity. AFM images result show that the SiC thin film has smooth surface at RMS = 20nm. In this paper, we fabricated the small aperture for the better performance such as less noise, higher resonant frequencies and fast imaging. We will apply that silicon carbide thin film has smooth surface on NSOM application.

We demonstrate OLED device on ITO/Ag NW/ITO thin film on PES substrate and investigate degradation of life time. Transparent conducting layers are fabricated in three type of ITO, ITO/Ag thin film (TF)/ITO, and ITO/Ag nano wire (NW)/ITO. The total thickness of TCO layers is set to be 150 nm. Single ITO thin film shows the highest transparency of 97%, ITO/Ag NW/ITO 90%, and ITO/Ag TF/ITO is the lowest of 81%. Sheet resistance of ITO/Ag NW/ITO is reduced to be 12.74 Ω/□ compared to single ITO TF of 32.42 Ω/□. Figure of merit of Ag nano wire inserted TCO shows the best value. According to bending test, Single ITO thin film layer shows abrupt failure on just one time bending, resistance of ITO/Ag TF/ITO increases 130% at 60 times bending, but ITO/Ag NW/ITO shows only 26% increase. Double layered simple OLED device of NPB and Alq₃ is fabricated and resultant device properties will be discussed.

In this work, the adhesion properties sputtered molybdenum (Mo) thin films as a copper (Cu) diffusion barrier layer on polymer substrates were examined using micro-scratch tests. We fabricated trench type copper interconnect rather than typical metal inlaying type.

There was made a comparison of the mechanical properties between a new trench copper layer and a traditional metal inlay type copper interconnect by means of photolithography technique followed by wet patterning. The metal / polymer interface were examined by using the auger electron spectroscopy. Cu/Mo trench typed films have 50% higher values of adhesion forces than that of Cu/Mo inlay type. A physical modeling is proposed, on average volume stress analysis to explain an improvement in the mechanical stability of the buried Cu interconnects in the flexible substrate.

A new class of catalytically active materials based on mesostructured multimetallic thin films with adjustable structure and composition will be presented. These thin films have been tailored to mimic unique properties of bulk single crystalline metal and metal oxide alloys ^[1], and hence, superior catalytic behavior defines them as a novel class of catalytically active materials.

Thin film based materials are obtained by magnetron sputtering simultaneous deposition from several targets on the amorphous substrates. Our findings demonstrate feasibility of controlling surface ordering of extended thin films deposited over a non-crystalline substrates, i.e., without use of templates or single crystals that would induce epitaxial growth. Instead of building the crystal lattice from a seed or underlying crystalline substrate, individual randomly oriented nanoscale grains coalesce due to applied thermal treatment and form large well-ordered (111) facets.

In-situ high resolution- SEM and TEM are simultaneously employed during annealing in controlled atmosphere. This allows us to visualize real-time structural changes at atomic level and to follow rearrangements of the surface and sub-surface morphology of thin films. In-situ results obtained during thermal annealing of a single PtNi-thin film will be presented in details. The thin film based materials are mounted onto the HRTEM heating stage and introduced to a reductive atmosphere of argon and hydrogen gasses. Specifically, randomly oriented nanoscale grains coalesce and give rise to a mesostructured thin film with unique physicochemical properties, for that reason, the materials after this treatment is referred to as mesostructured thin films. Close inspection of HRTEM micrographs, CRD and electrochemical characterization after applied thermal treatment confirms that emerged facets with (111) structure prevail on the surface while undercoordinated sites are diminished, which also has important implications towards improved electrochemical stability^[2,3] .

Considering that deveopment of the thin film mesoscale materials chemistry is still in its infancy, it is expected that this approach will open novel pathways in the design of materials that is based on the rational control of physicochemical properties and unique functionality of mesostructured systems. Based on this approach an ultra-high-vacuum system is designed for the synthesis of thin-film materials for electrochemical energy storage applications.

[1] Stamenkovic et al. Science 315 (2007) 493.

[2] van der Vliet et al. Nature Mat. 11 (2012) 1051.

Diamond-like carbon (DLC) consisting of sp² carbon (Csp²) and sp³ carbon (Csp³) has low friction property. Therefore, DLC is used as solid lubricant in the sliding parts of machinery to decrease energy loss by friction. It was suggested that the low friction property of DLC is caused by formation of a graphene layer on the surface [1]. Moreover, Si-doped DLC (Si-DLC) films show excellent tribological property because of formation of Csp² on the surface [2]. Therefore, transformation from Csp³ to Csp² on the DLC surface is important for the low friction. For further decrease in the friction of the DLC films, we need to clarify the mechanism of the transformation from Csp³ to Csp² at atomic scale. In this study, to elucidate the transition mechanism from Csp³ to Csp² on the DLC films by Si-doping, we develop our tight-binding quantum molecular dynamics simulator [3].

First, to reproduce van der Waals interaction and transformation for Csp² and Csp³, we add Lennard-Jones and trigonometric functional potential to our simulator. Next, to confirm the accuracy of our developed simulator, we perform compression simulation of a-graphite layers under a pressure. Here, the bottom layer is fixed and load pressure is applied to the top layer. From 1 to 15 GPa, the structure change is not observed for 50 ps. At a pressure of 16 GPa, Csp³-Csp³ bonds continuously increase when graphite layers become close. Then, the six-membered rings of diamond structure are generated from graphite layers. This indicates the transformation from Csp² to Csp³. In the experiment, the structure change from graphene to diamond takes place at 17 GPa [4]. Thus, the simulation result is in good agreement with the experimental result. Thus, our developed program succeeds to reveal the transformation from Csp³ to Csp².

Next, to investigate how Si-doping influences on the surface structure of the DLC films, we perform relaxation calculation for Si-doped diamond(111) surface with 3.225 % Si content. At 48.9 ps, the chemical bond between the C atom bound with the doped Si atom and C atom of the lower layer is dissociated. Furthermore, we observe generation of the Csp² atoms after the dissociation. This indicates that the Si-doping induces the transformation from Csp³ to Csp² and generation of graphene-like structure on the surface. Thus, we propose that Si-DLC films show low friction because Si-doping generates Csp² on the surface of the DLC films.

[1] Y. Liu, et al., Surf. Coat. Technol, 82, 48 (1996).

[2] A. Varma, et al., Surface, Engineering, 15, 301 (1999).

[3] K. Hayashi, M. Kubo et al., J. Phys. Chem. C, 115, 22981 (2011).

In recent years, diamond-like carbon (DLC) is expected as a solid lubricant material for engines because of its excellent friction properties such as low friction and high wear resistance. DLC films are lubricated with oil in the engine. Furthermore, molybdenum dithiocarbamate (MoDTC) is used as friction modifier in oil. DLC coating with oil and MoDTC solution showed a low friction coefficient [1]. Moreover, the low friction of the DLC films with MoDTC was enhanced by a chemical reaction during friction, since the friction coefficient gradually decreased with increasing friction time. Understanding of the low friction mechanism of DLC with MoDTC is strongly required to decrease in the friction of the DLC films. Then, our purpose is to reveal the chemical reactions between the MoDTC and DLC films by our tight-binding quantum chemical molecular dynamics code [2].

To investigate chemical reaction between MoDTC and DLC film during friction, we perform the friction simulation of MoDTC sandwiched by the DLC surfaces. At first, we compress linkage isomer of MoDTC (LI-MoTC) by the DLC surfaces. Here, we use LI-MoDTC because it is isomerized in oil phase [3]. We apply a pressure of 1 GPa to the upper DLC film. After the compression, the C atom of the DLC surface binds with the S atom of LI-MoDTC and the C-S bond is generated between the DLC surface and LI-MoDTC. Next, to perform the friction simulation of DLC films with LI-MoDTC, we apply a pressure of 1 GPa to the DLC film and forcibly slide it with 100 m/s. The S-Mo bond in the adsorbed LI-MoDTC is elongated from 2.52 Å to 3.76 Å and the S-Mo bond is dissociated during the sliding. To reveal chemical reaction during the S-Mo bond dissociation in detail, we investigate electron transfer between LI-MoDTC and the DLC surface during the compression. The charge of S atom of LI-MoDTC changes from +0.45 to +0.82 before and after the generation of C-S bond. This indicates that electrons transfer from the sulfur atom of LI-MoDTC to the DLC films. We think that S-Mo bond is weakened due to the electron transfer between LI-MoDTC and DLC film. Thus, we suggest that the electron transfer from LI-MoDTC to DLC films during the LI-MoDTC adsorption on the DLC surface weakens the S-Mo bond and the mechanical force dissociates the weakened S-Mo bond during the friction.

[1] B. Vengudusamy et al., Tribology Intern., 54, 68-76 (2012).

[2] K. Hayashi, M. Kubo et al., J. Phys. Chem. C, 115, 22981-22986 (2011).

Last years zinc oxide (ZnO) research has been renewed for its application in optoelectronic devices and nanotechnology due to its excellent electric conductivity and optical transmittance, whereby it has been suggested as ITO substitute. Generally Al and N are used in order to get p and n type dopping respectively, in this way micro-Raman spectroscopy is a very important tool to assess these dopants. In this work we present the Raman study of ZnO, AZO and AZO:N grown by sputter deposition. ZnO Raman spectrums show vibration modes E₂ (low), E₂ (high) and E₁ at 99 cm^-1, 437 cm^-1 and 583 cm^-1, respectively, related to wurzite structure Zn-O bonds [1]. In AZO films grown over corning glass we can see broadened E₂ (low), besides a shift appears towards 443 cm^-1 suggested for E₂ (high) which is presumed caused by aluminum incorporation, 573 cm^-1 peak appears which is related to A₁ (LO) ZnO mode. In AZO films grown over silicon substrate, we found a 73 cm^-1 mode that decrease its intensity when Al is increased, at 583 cm^-1 E₁ (LO) ZnO is observed. For AZO:N grown over corning glass are shown two vibration modes at 275 cm^-1 and 518 cm^-1 related to bonds Zn_i-N_O [2] whose intensity decreases when N increases. Moreover 464 and 578 cm^-1 peaks are observed which could be related to E₂ (high) and A₁ (LO) ZnO frequencies. On the other hand 639 cm^-1 band can be attributed to N-Al bond [3]. Finally in AZO:N samples deposited on silicon a couple of phonon vibration modes are shown at 275 and 580 cm^-1 related to N incorporation.

Key words

ZnO, AZO, AZO:N, Raman spectroscopy

References

[1] Ramon Cuscó, Esther Alarcón-Lladó, Jordi Ibáñez, Luis Artús, Juan Jiménez, Buguo Wang, and Michael J. Callahan, Phys. Rev. B 75 (2007) pp.165202.

[2] Keyue Wu, Quingqing Fang, M. Allan Thomas, and Jingbiao Cui, J. Appl. Phys. 111 (2002) pp. 063530.

[3] M. Kuball, Surf. Interface Anal. 31 (2001) pp. 987-999.

*Thanks to CONACYT and SENER for financial support with project number 151076.

In this work CdS thin films were successfully grown on glass substrates at room temperature using a direct, fast, simple, quick and inexpensive photochemical via through UV radiation. In the present research thin films were deposited from ammonia-free process in order to reduce the amount of toxic chemical waste, using sodium citrate instead of ammonia as the complexing agent of cadmium ions in the reaction solution; for the synthesis of the films aqueous solution of cadmium chloride, sodium citrate, potassium hydroxide and thiourea were used, thin films were synthesized at different deposition times from 10 minutes to 120 minutes every ten minutes, to obtain growth rates and layer structural properties. The structural nature of CdS thin films were characterized using XRD, preliminary results demonstrated polycrystalline and highly oriented films starting from 50 minutes of deposition, having an hexagonal phase with a preferred orientation at plane (0 0 2). Optical properties showed high quality and good absorption in the visible region. The energy band gap value was found around 2.35 eV in agreement with the reported value for hexagonal phase at room temperature (2.5 eV). The thickness was controlled by deposition time and it grows up to 35-50 nm. The surface morphology of deposited films has been studied using scanning electron microscope; homogeneous smooth films were observed, having a uniform size and shape of CdS grains very well adhered to the substrate surface. Due to the simplicity and the very economical experimental setup, the photochemical deposition process proposed has optimal features for photovoltaic device applications. Besides being an easier method compared with chemical bath deposition (CBD), this method has a great potential to be implemented in low-cost and environmental friendly approach.

The effects of the power sputtering target on GaAs and InGaAS layers prepared by magnetron sputtering on glass and Si (100) is presented. The morphology of GaAs and InGaAs layers were analyzed by means of atomic force microscopy (AFM) and scanning electron microscopy (FE-SEM), in order to determine the topography and growth mode. The compositional analysis was performed by means of energy dispersive X-ray spectroscopy (EDS), and SIMS. The results of depth profiling secondary ion mass spectroscopy (SIMS), show that Ga, In and As are uniformly distributed along of thickness. Using x-ray photoelectron spectroscopy (XPS) chemical composition variations on surface of the layers was evidenced. The optical properties of the layers deposited on glass substrate were discussed from UV-Vis absorption measurements. The optical emission is associated to the inter-band electronic transition between the valence band and the conduction band by extrapolating the curve (ανh)² vs νh when (ανh) 2→0. Direct band gaps of 1.44, 1.19 and 1.00 eV for GaAs and InGaAs, respectively were obtained. Finally, the Raman shift of the GaAs and InAs phonon modes are studied as function of the penetration depth of laser wavelength used to excite the sample on Raman microscopy. The shift observed in the Raman frequencies on InGaAs alloy is due to a combined result of the Indium content and stress development during growth. We conclude that R.F magnetron sputtering technique is a good method for preparing GaAs and InGaAs layers, and their physical properties depend on growth conditions.

ZnO films doped with CdS nanoparticles were deposited by the sol- gel method. The synthesis was carried out by the incorporation of CdS nanoparticles prepared by ball milling on the growing solution to grow the ZnO films, in this way the nanoparticles remained suspended in the sol-gel solution. Samples with different thickness have been obtained by changing the number of immersions into the solution, thus we determine the optimum thickness for a more efficient photocatalytic activity. Different characterizations were carried out: in X- ray diffraction patterns was observed that ZnO grows in the hexagonal wurtzite crystalline structure. Raman spectroscopy confirms the hexagonal carácter of ZnO. Photocatalytic activity was measured by mean of the degradation of methylene blue solution. Photoluminescence tests were made to check the different defect levels in the forbidden band gap which can affect the photocatalityc reactivity.

One of primary technical obstacles toward commercialization in organic device is the achievement of reliable long lifetimes. The low work function materials and transparent conductive oxides used to form electrical contacts to the active layers are generally reactive and susceptible to water vapor and oxygen. Thus, developing thin-film encapsulation technologies protecting organic electronic devices from water vapor and oxygen is critical. In addition, variable environment of photovoltaic modules makes it difficult in predicting lifetime of them.

In this study, the lifetime of encapsulated organic device under specific weather condition was predicted based on total amount of permeated water permeated through barrier layers. Previous study presented the relation between the overall barrier performance and the shelf lifetime of encapsulated organic solar cells experimentally. Based on previous study, the total permeated water vapor through identical barrier layer under continuously varying environment can be calculated and compared to experimental data. For analytical calculation, diffusion and solubility coefficients were experimentally determined using quartz crystal microbalance as well as water vapor permeation instrument.

Since the discovery of GMR and TMR effects, spin-dependent carrier transport has received attention from physical and engineering viewpoints. Whereas GMR and TMR films generally employ nonmagnetic metal and insulator spacers, respectively, we have studied Fe₃Si/FeSi₂ artificial lattices, in which FeSi₂ is semiconducting and its employment as spacers is specific to our research. The combination of Fe₃Si and FeSi₂ has the following merits: (i) a magnetoresistance effect in the CPP structures is easily detectable since the electrical conductivity of FeSi₂ spacer layers is distinctively larger than that of Fe₃Si layers; (ii) a spin injection efficiency might be higher than that in TMR films; (iii) the epitaxial growth of Fe₃Si layers on Si(111) substrates is successively kept up to the top Fe₃Si layer across FeSi₂ spacer layers, which is beneficial to the coherent transportation of spin-polarized electrons; (iv) Fe₃Si is feasible for a practical use since it has a high Curie temperature of 840 K and a large saturation magnetization, which is half of that of Fe.

A spin valve is one of the most important principle for spin-dependent carrier transport, and the formation of parallel or antiparallel alignments of ferromagnetic layer magnetizations should be realized and controlled in devices with spin valves. Previously, we have prepared Fe₃Si/FeSi₂ artificial films, wherein interlayer coupling was induced between Fe₃Si layers across FeSi₂ spacers and the formation of parallel and antiparallel alignments of ferromagnetic layer magnetizations was induced owing to the interlayer coupling [1,2]. The parallel or antiparallel alignments of layer magnetizations can be realized in multilayered films comprising ferromagnetic layers with different coercive forces, and it needs not the precise control of the spacer thickness. In this work, Fe₃Si/FeSi₂/Fe₃Si trilayered films were prepared and the magnetic properties as spin valves were investigated.

An Fe₃Si(7000 Å)/FeSi₂(7.5 Å)/Fe₃Si(1000 Å) artificial film was fabricated by facing-targets direct current sputtering with using a mask method. The magnetization curve was measured using a VSM. The shape of the magnetization curve clearly exhibited the formation of parallel and antiparallel alignments with the magnetic field. This should originate from a difference in the coercive force between the top and bottom FeSi₂ layers. The electrical properties accompanied by the change in the magnetization alignment will be presented at the conference.

[1] Ken-ichiro Sakai et al., Jpn. J. Appl. Phys. 51, 028004 (2012).

[2] Ken-ichiro Sakai et al., Jpn. J. Appl. Phys. 53, 02BC15 (2014).

There are several line-shapes widely employed in XPS spectra analysis, such as Gaussian, Lorentzian, Voigt, Doniach-Sunjic, among others. In the case of transition metals, the high asymmetry present in the main core levels peaks might lead to misinterpretation as considering artificial peaks during fitting. Some of this problems could be avoided by employing the double-Lorentzian line-shape. In this study, analysis of XPS spectra of Zn and ZnO films (including the early oxidation stages at room temperature) were performed using double-Lorentzian line-shape. The chemical composition of ZnO samples were calculated and different peaks for the metallic Zn 2p, Zn 3p, Zn 3s and Zn 3d core levels were identified.

Atomic layer deposition (ALD) is a modified chemical vapor (CVD) deposition tool, which is suitable for depositing high quality thin films or locally modifying the surface properties. Due to its advantages such as conformality, low pin-hole density, and the easiness of composition/doping control, ALD can used for engineering wide variety of thin film devices.

Crystallizing and densifying thin films to increase their relative permittivities are critical issues in fabricating high information density dynamic random access memory (DRAM) capacitors. The high process temperature (> 600 ° C) is usually necessary for thin film crystallization and densification, which could be detrimental to other components of DRAM. In this manuscript, we report a simple and novel method to simultaneously increase the dielectric constant and decrease the leakage current density of atomic layer deposited BaTiO₃ thin films using post-deposition remote oxygen plasma treatment while keeping the process temperature low (250 °C). The dielectric constant increases from 53 (as-deposited) to 122 (plasma-treated) and the leakage current density decreases by one order of magnitude. The dielectric constant of the plasma-treated BaTiO₃ film is one of the highest values ever reported for ultra-thin (5 nm thick) films. We ascribe such improvements to the crystallization and densification of the film induced by high-energy ion bombardments on the film surface during the plasma treatment. We think that plasma-induced crystallization presented in this work may have an immediate impact on fabricating and manufacturing DRAM capacitors due to its simplicity and compatibility with industrial standard thin film processes.

The current methods for quantitative analysis of X-ray photoelectron spectroscopy (XPS) data are clearly insufficient for closely reproducing the high asymmetry and strong background signal of the core level peaks of transition metals and their oxides. Using the double-Lorentzian asymmetric line-shape [1] and the active background approach [2], it is possible to obtain close fits to these core levels. The samples were prepared by metal sublimation on Si (100) wafers. The asymmetry factor found from the analysis was 1.83 for Ni 2p, 2.84 for Cr 2p and 2.9 for Co 2p. Previously unreported shake-up satellites were identified at 0.45, 1.1 and 1.9 eV away from the main peak in the metallic films of the Cr 2p, Co 2p and Ni 2p core levels, respectively. The evolution of the oxidation of metals was also studied by exposing metallic films to UHP oxygen in a range from 4 L to 400 GL. Further oxidation was obtained using a tubular oven with UHP oxygen with positive pressure. The final thickness of oxide films ranged from 2 to 3 nm. The composition was calculated employing the MultiLayer Model. The close agreement with the expected values (1:1 for nickel oxide, NiO; 2:3 for chromium oxide, Cr₂O₃; and 1:1 for cobalt oxide, CoO) validates the peak areas obtained with the double-Lorentzian line-shape.

Acknowledgements: This work was supported in part by CONACyT Projects INFR-2011-01 #163219 and CB-2012-01 #179304. The authors would like to acknowledge Alfredo Muñoz for his technical support.

References

[1] A. Herrera-Gomez. A double Lorentzian shape for asymmetric photoelectron peaks. Internal Report. Cinvestav-Querétaro (2011). http://www.qro.cinvestav.mx/~aherrera/reportesInternos/doubleLorentzian.pdf

[2] A. Herrera-Gomez, M. Bravo-Sanchez, O. Ceballos-Sanchez, and M.O. Vazquez-Lepe. Practical methods for background subtraction in photoemission spectra. Journal of Electron Spectroscopy and Related Phenomena (in press) DOI/ 10.1002/sia.5453.

Diamond like carbon (DLC) film has been widely used because of its good properties such as good biocompatibility, anti-corrosion, high hardness, and high wear resistance. Therefore, DLC film has been applied to practical uses in medical and industrial fields. However, lack of film adhesion onto metallic materials has limited DLC coating applications. In order to improve adhesion strength of DLC film onto a substrate, intermediate layer such as Si layer has been introduced between the DLC layer and the substrate.

In this study, DLC films were deposited on stainless steel substrate by using r.f. plasma chemical vapor deposition (r.f. plasma CVD) without intermediate layer. To improve adhesion of DLC film onto metallic materials, the cylindrical electrode around a sample was installed on the cathode side electrode (Fig. 1, 2). Cylindrical electrode was selected for the height of 5, 10, and 20 mm, respectively. DLC film was deposited under the following condition ( CH₄ gas pressure: 10 Pa, r.f. electrical power: 200 W, film thickness: 200 nm).

The adhesion of the DLC films was measured by using a scratch test. The characteristics of the DLC films were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS).

In the scratch test, the critical load of the film with 10mm-cylinder height showed 8.5 N, as compared with the film without the cylinder (4.6 N) (Fig. 3). Additionally, the Raman spectrum of the film on the stainless steel substrate showed peaks at approximately 1550 cm^-1 and 1350 cm^-1, referred to the G-band and D-band, respectively.

These results showed that the films were a typical DLC film and the DLC film was completely deposited with strong adhesion between the films and substrates by using only r.f. plasma CVD technique. This technique affects to DLC film adhesion property onto metallic materials under r.f. plasma CVD process.

The thermoelectric devices base their operation on the Seebeck effect. Metal oxides are attractive for high-temperature applications as they are potentially stable. In particular different phases of cobalt oxide (CoO₂, Co₂O₃ and Co₃O₄) in compounds with different elements such as sodium and calcium have become important, due to their outstanding values of Seebeck coefficient S. Some works show that lithium cobalt oxide exhibits high values of S for temperatures around 300 K.

In this work shown thin films containing lithium cobalt oxide obtained by spray pyrolysis, and characterized by using XPS, Raman, FTIR. Also, the Seebeck coefficient was measured above room temperature up to 423 K. At temperatures near 300 K, S is about -100 mV/K and decreases to values -390μV/K when the temperature of measurement is T > 350 K.

According to Raman and FTIR measurements, the thin films correspond to amorphous alloys of LixCo_3-xO₄ structure. Co 2p, Co 3d, and O 1s core levels were identified by XPS. The effect of adding lithium induces changes in the intensity of shake-up satellite O 1s characteristic of Co₃O₄. However, this change may be associated to the presence of unpaired electrons or multiplet splitting. The correlation values of S and relative intensities of the shake-up satellite is evidence of one change of the chemical state of the element or available electron in valence levels.

Magnetic random access memory (MRAM) holds the promise of replacing traditional memory devices such as DRAM, SRAM and flash memory. The MRAM device compared to its counterparts (DRAM, SRAM, flash memory, etc.), offers higher density, faster access time, unlimited read/write endurance and non-volatility. MRAM devices are mainly composed of a magnetic tunnel junction (MTJ) stack and CMOS.

In order to achieve high storage densities in MRAM devices, the pattern transfer in magnetic layers that comprise the MTJ stacks is a critical step. In the early stage of research, a wide range of etching gases such as HBr, Cl₂ etc has been employed for the ICPRIE of CoFeB thin films. In general, when using halogen gases, the etch rates are extremely high; but the sidewall redeposition and corrosion problems are common. Recently, an effort to improve the etching characteristics of magnetic layers, while at the same time reducing post-etching treatment, non- corrosive etching gases such as CO/NH₃, CH₃OH, CH₄ have been researched. The use of this etching gases mixed with Ar gas had to prove to yield a redeposition-free anisotropic etch profile despite the low etch rates compared to halogen gas mixtures.

In this paper the inductively coupled plasma etching characteristics of TiN hard masked CoFeB thin films was studied by using a CH3COOH/Ar gas mixture. A CH₃COOH solution was introduced into the chamber using a specially designed feeding system. The etch rates were obtained using a surface profilometer (Tencor P-1) and etch profiles were observed by using a field emission scanning electron microscopy (FESEM-HITACHI 4300SE). The surface chemistry and etch mechanism were analyzed by using optical emission spectroscopy (OES-Ocean Optics Maya 2000 Pro) and X-ray photoelectron spectroscopy (XPS).

In 1904, J.A. Fleming patented the first thermionic diode. Then in 1947, J. Barden, W. H. Brattain, and W. B. Shockley invented the bipolar transistor. Later in 1958, J. S. Kilby and R. Noyce developed the first integrated circuit. Since then it has researched, developed and implemented analog electronics. Both the diode and bipolar transistor structures have pn and pnp or npn respectively. However, there is another device having a pnpn structure, known as the thyristor. This device has different applications, but its main function is to control high power systems. This paper presents a study on the transport properties of Dirac electrons through a structure of two, three and four magneto-electrostatic barriers on a sheet of graphene, an approach to the structures of a diode, transistor and thyristor is presented. The calculation of pn, pnp, and pnpn structures was conducted using the transfer matrix method and the formalism of linear Landauer-Büttiker scheme. The results show that at normal incidence, with increasing two, three and four barriers increases the number of oscillations in the transmission bands. Furthermore, increasing the value of the thickness ratio of the barrier / well width, the transmission bands are shifted toward the blue and decrease transmission windows. Increasing the electrostatic potential decreases the size of the transmission bands. The effect of the magnetic field causes the transmission spectra increase the width of the central maximum band, and reduces the width of the bands of transmission side. Also, the increase of the magnetic field produces peaks in the transmission bands that arise in this type of structure, number of peaks in the transmission bands, corresponding to the number of wells in the structure. The conductance shows oscillations, which has an explanation by the bound states. Exists interest from the authors continue to explore further the benefits presented graphene in the development of new devices.

In this presentation the experimental data such as the cross-sectional SEM images, voltage pulse shapes, pulse target power densities for directional sputtering of Ta and Cu in different sizes and aspect ratios trenches and vias will be presented. The experiments were performed with Zpulser CypriumTM pulse plasma generator that can generate oscillatory voltage pulse shapes (oscillations frequency is about 20-60 kHz) and deliver up to 2-3 MW during the oscillation. It was found that substrate ion current is a function of voltage oscillations frequency in the pulse. The substrates during all these experiments either had floating potential or were connected to the substrate bias power supply. DC power supply or RF power supply were used as a bias power supply. The RF bias is an important feature for the directional sputtering process for nonconductive substrates. The DC bias and RF voltage as a function of RF power at different level of peak power will be presented, as well as the experimental data about field, side and bottom coverage for the trenches and vias.

References:

1. Abrahams E. et. al., Phys. Rev. Lett. 42, 673 (1979)

2. Pollak M. and Knotek M., J. Non-crystalline Solids 32, 141 (1979)

3. Fleishman L. and Anderson P.W., Phys. Rev. B 21, 2366 (1980)

4. Shepelyanki D.I., Phys. Rev. Lett. 73, 2607 (1994)

5. Eperlein F,, Schreiber M. and Vojta T., Phys. Rev. B 56, 5890 (1997)

6. Kravchenko S.V. and Sarachik M.P., Reports on Progress in Physics 67, 1 (2004)

7. Basco D.L. et. Al., Annals of Physics 321, 1126 (2006)

8. Anderson P.W., Phys. Rev. 109, 1492 (1958) 9. Mott, N.F., e.g. Advances in Physics 16, 49 (1967)