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Applied Surface Science (v.254, #3)

A high-throughput search for direct methanol fuel cell anode electrocatalysts of type Pt_xBi_yPb_z by Jing Jin; Mark Prochaska; Dominic Rochefort; David K. Kim; Lin Zhuang; Francis J. DiSalvo; R.B. van Dover; Héctor D. Abruña (pp. 653-661).

We used a high-throughput method to screen for direct methanol fuel cell anode electrocatalysts in the Pt–Bi–Pb system. Previous studies showed that PtBi and PtPb (both NiAs structure type) were active electrocatalysts for the oxidation of formic acid, but only PtPb was active in oxidizing methanol. We synthesized thin films with continuous composition spreads of the three elements by magnetron sputtering at deposition temperatures from ambient to 510°C. A fluorescence method was then used to identify compositions that were active toward methanol oxidation. Only films deposited between temperatures of 160 and 400°C showed electrocatalytic activity. The areas that were active for methanol oxidation showed predominantly the NiAs structure type according to XRD, with optimal activity for compositions near PtBi_0.01Pb_0.53.

Keywords: PACS; 81.05.Zx; 82.47.−a; 82.47.GhCombinatorial chemistry; Fuel cell anode catalysts

Combinatorial screening of fuel cell cathode catalyst compositions by James S. Cooper; Paul J. McGinn (pp. 662-668).

An improved fuel cell cathode catalyst composition was pursued by fabricating and screening thin film combinatorial libraries. Results from the Pt–Ru, Pt–Co–Ti, Pt–Co–Cu and Pt–Co–Cr systems are reported. The discrete composition combinatorial libraries were fabricated by plasma sputtering through shadow masks. Each combinatorial library was tested by cyclic voltammetry in a multichannel electrochemical cell. Compositions were ranked based on the onset potential of the oxygen reduction reaction. Several compositions exhibited better onset potentials than pure Pt. The optimum composition from the Pt–Co–Ti system was Pt₄₄Ti₁₂Co₄₄ but showed signs of corrosion after prolonged testing. A wide range of Pt–Co–Cu compositions also outperformed Pt initially, but ultimately failed due to poor corrosion resistance. Among all of the compositions that were screened, the best performance was demonstrated by Pt₂₈Co₃₆Cr₃₆, with an onset potential 107mV higher than pure Pt and no sign of corrosion.

Keywords: PACS; 68.55.−a; 81.15.Cd; 82.47.Gh; 82.45.Bb; 82.45.Jn; 82.45.Rr; 82.65.+r; 82.80.Fk; 87.64.BxOxygen reduction; Fuel cell cathode; Platinum, ruthenium, cobalt, titanium, copper and chromium; Combinatorial library

Advances in high throughput screening of gas sensing materials by Maike Siemons; Tobias J. Koplin; Ulrich Simon (pp. 669-676).

The workflow of a high throughput screening setup for the rapid identification of new and improved gas sensor materials is presented. The polyol method was applied to prepare nanoparticulate metal oxides as base materials. These materials have been modified by surface and volume doping. Using multielectrode substrates and high throughput impedance spectroscopy (HT-IS) a wide range of materials could be screened on a short time scale. Selected examples reflect the state of the art for applying HT-IS in search of new selective gas sensing materials.

Keywords: High throughput experimentation; Gas sensor; Metal oxide; Doping; Impedance spectroscopy

Validation of the catalytic properties of Cu-Os/13X using single fixed bed reactor in selective catalytic reduction of NO by Kwang Seok Oh; Seong Ihl Woo (pp. 677-681).

Catalytic decomposition of NO over Cu-Os/13X has been carried out in a tubular fixed bed reactor at atmospheric pressure and the results were compared with literature data performed by high-throughput screening (HTS). The activity and durability of Cu-Os/13X prepared by conventional ion-exchange method have been investigated in the presence of H₂O and SO₂. It was found that Cu-Os/13X prepared by ion-exchange shows a high activity in a wide temperature range in selective catalytic reduction (SCR) of NO with C₃H₆ compared to Cu/13X, proving the existence of more NO adsorption site on Cu-Os/13X. However, Cu-Os/13X exhibited low activity in the presence of water, and was quite different from the result reported in literature. SO₂ resistance is also low and does not recover its original activity when the SO₂ was blocked in the feed gas stream. This result suggested that catalytic activity between combinatorial screening and conventional testing should be compared to confirm the validity of high-throughput screening.

Keywords: PACS; 82.65.−sDeNO; x; Cu-Os/13X; Ion-exchange method; Validity of high-throughput screening

Opto-mechanical characterization of hydrogen storage properties of Mg–Ni thin film composition spreads by A. Ludwig; J. Cao; B. Dam; R. Gremaud (pp. 682-686).

Thin film composition spreads of Mg–Ni were deposited by co-sputtering on micromachined Si-cantilevers. The investigated compositions range from about Mg₆₀Ni₄₀ to about Mg₈₀Ni₂₀. Structural properties as well as mechanical stress before and after hydrogenation were measured with X-ray diffraction (XRD) and laser profilometry, respectively. The composition spreads were hydrogenated in a special pressure vessel, which allows measuring optically the hydrogen-induced deflection (stress-change) of 16 cantilevers as a function of hydrogen pressure and/or temperature. It was found that the hydrogen-induced stress is correlated with the composition and microstructure of the films. Highest hydrogen-induced stress changes were found for compositions close to the crystalline Mg₂Ni phase.

Keywords: PACS; 68.60.Bs; 81.05.Bx; 81.15.Cd; 81.70.FyMg–Ni; Thin films; Hydrogen storage; High-throughput characterization

In situ etch rate measurements of thin film combinatorial libraries by J.D. Perkins; M.F.A.M. van Hest; C.W. Teplin; M.S. Dabney; D.S. Ginley (pp. 687-691).

We demonstrate the use of optical reflection mapping as an in situ characterization tool to evaluate the corrosion rate of compositionally graded thin film combinatorial libraries coated with a commercial glass etching paste. A multi-channel fiber-optically coupled CCD-array-based spectrometer was used to collect a series of reflectance maps from 300 to 1000nm versus time. The thin film interference oscillations in the measured reflection spectra have been fitted to determine the film thickness as a function of time and thereby the etch rate. Application of this technique to an In–Mo–O composition spread library is presented as an example.

Keywords: PACS; 78.20.CiCombinatorial material science; Thin film; Sputtering; In situ measurements

Combinatorial materials research applied to the development of new surface coatings by Bret J. Chisholm; Shane J. Stafslien; David A. Christianson; Christy Gallagher-Lein; Justin W. Daniels; Crystal Rafferty; Lyndsi Vander Wal; Dean C. Webster (pp. 692-698).

A combinatorial workflow has been produced for the development of novel, environmental-friendly marine coatings. A particularly challenging aspect of the workflow development was the selection and development of high-throughput screening methods that allow for some degree of prediction of coating performance in the aquatic environment of interest. The high-throughput screening methods currently in place include measurements of surface energy, viscoelastic properties, pseudobarnacle adhesion, and a suite of biological assays based on various marine organisms. An experiment involving a series of fouling-release coatings was used to correlate high-throughput screening data to data obtained from ocean site immersion testing. The results of the experiment showed that both bacterial biofilm surface coverage and storage modulus at 30°C showed a good correlation with barnacle adhesion strength and a fair correlation with fouling rating, but surface energy and pseudobarnacle adhesion did not correlate with the results from ocean site testing.

Keywords: Combinatorial; Marine coatings; Fouling-release; Antifouling; High-throughput screening; Surface coatings

High-throughput preparation and testing of ion-exchanged zeolites by K.P.F. Janssen; J.S. Paul; B.F. Sels; P.A. Jacobs (pp. 699-703).

A high-throughput research platform was developed for the preparation and subsequent catalytic liquid-phase screening of ion-exchanged zeolites, for instance with regard to their use as heterogeneous catalysts. In this system aqueous solutions and other liquid as well as solid reagents are employed as starting materials and 24 samples are prepared on a library plate with a 4×6 layout. Volumetric dispensing of metal precursor solutions, weighing of zeolite and subsequent mixing/washing cycles of the starting materials and distributing reaction mixtures to the library plate are automatically performed by liquid and solid handlers controlled by a single common and easy-to-use programming software interface. The thus prepared materials are automatically contacted with reagent solutions, heated, stirred and sampled continuously using a modified liquid handling. The high-throughput platform is highly promising in enhancing synthesis of catalysts and their screening. In this paper the preparation of lanthanum-exchanged NaY zeolites (LaNaY) on the platform is reported, along with their use as catalyst for the conversion of renewables.

Keywords: PACS; 82.65.−s (catalysis, heterogeneous); 82.75.Qt (zeolites, catalysis in)High-throughput; Zeolite Y; Ion exchange; Catalysis; Renewables

Exploration of layered-type pseudo four-component Li–Ni–Co–Ti oxides by Kenjiro Fujimoto; Kazuhiro Onoda; Shigeru Ito (pp. 704-708).

A series of layered-type pseudo four-component Li–Ni–Co–Ti oxides were prepared to explore optimal cathode materials for a lithium-ion secondary battery. The new layered-type compounds were prepared using a combinatorial material-preparation system based on electrostatic spray deposition (the “M-ist Combi” system), and combinatorial powder X-ray diffraction. The composition region of the new compounds (Li_α(Ni_xCo_yTi_z)O₂ (α∼1, 0≤ x≤1, 0≤ y≤1, z∼0.2, x+ y+ z=1.0)) was found to be wider than the composition region previously reported (LiNi0.8−_yCo_0.2Ti_yO₂ (0≤ y≤0.1)).

Keywords: PACS; 81.20.Ev; 81.30.Dz; 82.47.AaCombinatorial chemistry; Powder preparation; Layered-type structure; Electrode materials

Combinatorial synthesis and characterization of a ternary epitaxial film of Co and Mn doped Ge (001) by F. Tsui; B.A. Collins; L. He; A. Mellnik; Y. Zhong; S. Vogt; Y.S. Chu (pp. 709-713).

We report combinatorial molecular beam epitaxy synthesis and properties of a ternary epitaxial film of Co and Mn co-doped Ge grown on Ge (001) substrate. Structural effects were examined in situ by reflection high-energy electron diffraction and ex situ by microbeam X-ray diffraction techniques, and magnetic properties were probed by using magnetooptic Kerr effect. Ternary epitaxial phase diagrams have been studied for total doping concentrations up to 30at.%, where regions of coherent epitaxy and rough disordered growth and those of near room temperature ferromagnetic ordering have been identified.

Keywords: Epitaxial film; Magnetic semiconductor; Group IV semiconductor; Transition metal doping; Combinatorial thin film

High-resolution X-ray diffraction studies of combinatorial epitaxial Ge (001) thin-films on Ge (001) substrates by Yuncheng Zhong; Yong S. Chu; Brian A. Collins; Frank Tsui (pp. 714-719).

We report high-resolution X-ray diffraction studies of combinatorial epitaxial Ge (001) thin-films with varying doping concentrations of Co and Mn grown on Ge (001) substrates. The crystalline structure of the epitaxial thin-film has been determined using crystal-truncation rod (CTR) measurements and fitting analysis. By analyzing the fine interference fringes in the CTR intensity profile, strain sensitivity of ∼0.003% has been achieved. Using this method, the evolution of interfacial structures has been quantified as a function of doping concentration.

Keywords: PACS; 61.10.Nz; 68.55.−a; 61.80.−xX-ray diffraction; Crystal-truncation rods; Combinatorial thin-film; Strain

Combinatorial arc plasma deposition search for Ru-based thin film metallic glass by Junpei Sakurai; Seiichi Hata; Ryusuke Yamauchi; Akira Shimokohbe (pp. 720-724).

We have discovered a novel Ru-based thin film metallic glass (TFMG) using combinatorial arc plasma deposition (CAPD). To search for Ru-based TFMG, alloy systems of Ru–Zr–Al, Ru–Zr–Fe and Ru–Zr–Mo were investigated by making libraries. Each library consisted of 1089 CAPD samples deposited on a substrate by CAPD. Composition of each sample is different with each other.The composition and phases of the CAPD samples were measured by energy dispersive X-ray fluorescence spectrometry and X-ray diffractometry, respectively. Results showed the amorphous regions depended on the additive elements Al, Fe or Mo. Compared with the addition of Al, the addition of Fe or Mo exhibited high amorphous forming ability.To evaluate the mechanical properties, the glass transition temperature T_g and the crystallization temperature T_x of the amorphous samples in each Ru–Zr–X alloy, larger samples having the same compositions as the typical amorphous CAPD samples were reproduced by sputtering because the CAPD samples were too small to measure the mechanical properties, T_g and T_x.Ru₆₅Zr₃₀Al₅ and Ru₆₇Zr₂₅Al₈ samples were found to exhibit the better fracture stress and elastic limit than conventional TFMGs, while Ru–Zr–Fe and Ru–Zr–Mo samples were found to be brittle. DSC revealed that the Ru₆₅Zr₃₀Al₅ sample was a TFMG, with a T_g of 902K and T_x of 973K.

Keywords: PACS; 61.43.DqAmorphous; Metallic glass; Combinatorial arc plasma deposition; Amorphous forming ability; Glass transition temperature; Crystallization temperature

High-throughput screening of ferroelectric materials for non-volatile random access memory using multilayer perceptrons by Sookil Kang; Sohee Park; Ki Woong Kim; Seong Ihl Woo; Sunwon Park (pp. 725-733).

During the last several years, the development of combinatorial technology has enabled synthesis of a huge amount of chemical compounds in a short time. The large number of variables makes the direct human interpretation of data derived from combinatorial experimentation for high-throughput screening (HTS) very difficult. Artificial neural networks using multilayer perceptrons (MLP) have been successfully applied to the regression problems with various material data. In this work, MLP model was applied to HTS of ferroelectric materials including Bi4−_xLa_xTi₃O₁₂ (BLT) and Bi4−_xCe_xTi₃O₁₂ (BCT). The model using MLP was made to predict the ferroelectric properties of whole feasible experimental conditions. Once a neural network model with high accuracy and good generalization performance was established, we could predict the expected optimal reaction conditions with the best characteristics. The highest gradient value obtained using MLP model is higher than the maximum value found from experiments, thereby accelerating the discovery of the optimal compositions and post-annealing time of BCT and BLT.

Keywords: PACS; 07.05.Mh; 77.84.−sArtificial neural networks; Ferroelectric materials; High-throughput screening; Multilayer perceptrons; Combinatorial chemistry

High-throughput screening of magnetic properties of quenched metallic-alloy thin-film composition spreads by Jason R. Hattrick-Simpers; Cui Jun; Makoto Murakami; Antonio Orozco; Lee Knauss; Robert J. Booth; Edward W. Greve; Samuel E. Lofland; Manfred Wuttig; Ichiro Takeuchi (pp. 734-737).

A novel method for capturing and characterizing high-temperature phases of metallic-alloys in thin-film composition spreads has been developed. A high-vacuum (10⁻⁸Torr) high-temperature annealing and quenching furnace system has been developed that allows formation of high-temperature phases in thin-film composition-spread samples deposited on 3in. silicon wafers. Scanning SQUID microscopy and magneto-optical Kerr effect measurements were used to map the remnant magnetization and the hysteresis loops of the spreads of magnetic materials quenched at high temperatures. The combination of these techniques can be used to obtain comprehensive information on the magnetic properties of various metallic-alloy systems.

Keywords: PACS; 75.20.EnFerromagnetic shape memory alloys; Fe–Pd thin-films; High-throughput processing

Search for novel amorphous alloys with high crystallization temperature by combinatorial arc plasma deposition by Seiichi Hata; Junpei Sakurai; Ryusuke Yamauchi; Akira Shimokohbe (pp. 738-742).

This paper describes a combinatorial search for novel amorphous alloys with high crystallization temperatures ( T_x) using combinatorial arc plasma deposition (CAPD). The CAPD technique can deposit 1089 (33×33) thin film samples with different compositions on a substrate at one time. These 1089 samples on the substrate are individually referred to as CAPD samples and collectively referred to as a thin film library. Thin film libraries of Ir–Zr–Fe, Ir–Zr–Al, Mo–Zr–Al, Mo–Zr–Si, Ru–Zr–Fe and Ru–Zr–Si were deposited by CAPD. The compositions and phases of the CAPD samples were measured by energy dispersive X-ray fluorescence spectrometry and X-ray diffractometry, respectively. The results revealed that each library included amorphous CAPD samples. Since it is impossible to measure the T_x, fracture strength, fracture strain and Young's modulus of the CAPD samples by conventional measurement methods, larger samples having the same compositions as the amorphous CAPD samples were fabricated by a sputtering system. Since all CAPD samples of Ir–Zr–Fe and Ir–Zr–Al were too brittle, their corresponding sputter-deposited samples were not prepared. Sputter-deposited Mo–Zr–Al, Mo–Zr–Si, Ru–Zr–Fe and Ru–Zr–Si samples with ∼50at.% Mo- or Ru-content were fabricated, and T_x and mechanical properties of these sputter-deposited samples were evaluated. All the sputter-deposited samples of Mo–Zr–Al and Mo–Zr–Si showed high T_x exceeding 973K and as well as brittle characteristics. Ru₅₀Zr₃₅Fe₁₀ samples showed high T_x exceeding 1273K and a low fracture strength of 0.26GPa. Samples of Ru₅₁Zr₅Si₄₄ showed a high T_x of 923K and a high fracture strength of 1.25GPa.

Keywords: PACS; 61.43.Dq (amorphous semiconductors, metals, and alloys)Amorphous alloy; Crystallization temperature; Combinatorial search; Combinatorial arc plasma deposition

Combinatorial study of phase transformation characteristics of a Ti–Ni–Pd shape memory thin film composition spread in view of microactuator applications by R. Zarnetta; A. Savan; S. Thienhaus; A. Ludwig (pp. 743-748).

Phase transformation characteristics of a Ti–Ni–Pd shape memory thin film composition spread have been investigated. The thin film composition spread was fabricated from elemental targets using an ultra-high vacuum combinatorial magnetron sputter-deposition system and subsequent annealing at 500°C for 1h in situ. Automated temperature-dependent resistance measurements ( R( T)), energy dispersive X-ray analysis (EDX) and X-ray diffraction measurements (XRD) have been applied for the high-throughput characterization of the composition spread. Reversible phase transformations within the measurement range of −40 to 250°C within the Ti–Ni–Pd system were observed for compositions with Ti content between 50 and ∼59at.%. For Ti-richer films, Ti₂Ni and Ti₂Pd precipitates are inhibiting reversible phase transformations. The transformation temperatures and the thermal hysteresis were determined from R( T) measurements. Rising transformation temperatures with increasing Pd content and significantly lower thermal hysteresis for the B2–B19, compared to the B2–R–B19′ transformations were found in good agreement with published data. For low Pd contents (<7–12at.%, depending on the Ti content) two-stage B2–R–B19′ transformations were observed. Compositions with higher Pd contents showed a single-stage B2–B19 transformation. Increasing Ti content within the B2–B19 transformation region results in a linear increase of the thermal hysteresis and decreasing transformation temperatures.

Keywords: PACS; 62.20.Fe; 64.70.Kb; 81.30.Kf (shape memory effects)Ti–Ni–Pd; Thin films; Shape memory alloys; Combinatorial materials synthesis; High-throughput characterization

Combinatorial fabrication and screening of organic light-emitting device arrays by Joseph Shinar; Ruth Shinar; Zhaoqun Zhou (pp. 749-756).

The combinatorial fabrication and screening of 2-dimensional (2-d) small molecular UV-violet organic light-emitting device (OLED) arrays, 1-d blue-to-red arrays, 1-d intense white OLED libraries, 1-d arrays to study Förster energy transfer in guest–host OLEDs, and 2-d arrays to study exciplex emission from OLEDs is described. The results demonstrate the power of combinatorial approaches for screening OLED materials and configurations, and for studying their basic properties.

Keywords: PACS; 78.60.Fi; 81.05.Hd; 85.60.JbCombinatorial fabrication; Organic light emitting devices; OLEDs

Quantitative analysis of thin-film conductivity by scanning microwave microscope by Sohei Okazaki; Noriaki Okazaki; Yasushi Hirose; Yutaka Furubayashi; Taro Hitosugi; Toshihiro Shimada; Tetsuya Hasegawa (pp. 757-759).

We propose a novel method for high-throughput quantitative analysis of thin-film conductivity σ by using a scanning microwave microscope (SμM). We demonstrated that composition spread thin films of Ti1–_xNb_xO₂ can be utilized as a standard reference in a wide σ range. The shift in Q-value measured by SμM along the composition-spread axis showed a single peak, which moved to the lower x side with film thickness. This behavior was confirmed by electrical field simulation using the finite element method.

Keywords: PACS; 02.60.−x; 07.79.−v; 71.30.+h; 84.40.−xCombinatorial materials science; Scanning microwave microscope; Quantitative analysis; Thin-film; Conductivity; Finite element method

Magnetron sputter deposition of a 48-member cuprate superconductor library: Bi₂Sr₂Y_xCa1−_xCu₂O8+_δ (0.5≤x≤1) linearly varying in steps ofΔx=0.01 by R.J. Sanderson; K.C. Hewitt / (pp. 760-764).

Using magnetron sputtering, a spatial composition spread approach was applied successfully to obtain 48-member libraries of the Bi₂Sr₂Y_xCa1−_xCu₂O8+_δ (0.5≤x≤1) cuprate superconducting system. The libraries of each system were deposited onto (100) single crystal MgO, mounted on a water cooled rotating table, using two targets: the antiferromagnetic insulator Bi₂Sr₂YCu₂O8+_δ (P=98 W rf) and the hole doped superconductor Bi₂Sr₂CaCu₂O8+_δ (P=44 W dc). A low chamber pressure of 0.81mTorr argon was used to reduce scattering by the process gas. To minimize oxygen resputtering a substrate bias of−20V was used, as well as a process gas free of oxygen. A rapid thermal processor was used to post-anneal the amorphous deposited films. A step annealing regime was used, with a ramp rate of 5°C/s for heating and cooling, with a first plateau at 780°C held for 200s, and a second at 875°C held for 480s. X-ray diffraction reveals that the films develop crystalline order with the c-axis lattice parameter contracting linearly from 30.55Å (x=0.5) to 30.24Å (x=1.0) with increasing Y-content, consistent with bulk values. The crystallized films are polycrystalline, developing preferred orientation ( c-axis parallel to the substrate) for thinner members of the library. There is a change of 0.01 in doping per library member which will enable further studies to densely map phase space.

Keywords: PACS; 81.15.; −; z; 81.15.Cd; 74.78.; −; w; 74.78Bz; 74.72Hs; 68.55NqSpatial composition spread; Combinatorial materials science; Cuprate superconductor; X-ray diffraction; Energy dispersive spectroscopy; Magnetron sputtering; Thin films; Bi-based cuprates; Phase composition

Development of a high-throughput thermoelectric screening tool for combinatorial thin film libraries by M. Otani; K. Itaka; W. Wong-Ng; P.K. Schenck; H. Koinuma (pp. 765-767).

We have developed a high-throughput thermoelectric screening tool for the study of combinatorial thin films. This tool consists of a probe to measure resistance and Seebeck coefficient on an automated translation stage. A thin film library of the (Ca1− x−_ySr_xLa_y)₃Co₄O₉ ternary system has been fabricated on a Si (100) substrate, using combinatorial pulsed laser deposition by the natural-composition-spread method. We have demonstrated successful mapping of the resistance and Seebeck coefficient of this film library. The mapping indicates that the substitution of La for Ca results in an increase of both resistance and Seebeck coefficient, and that of Sr results in a decrease of resistance. The screening tool allows us to measure 1080 data points in 6h.

Keywords: PACS; 72.15.Jf; 81.15.−zThermoelectric measurement; Combinatorial method; High-throughput screening tool; Seebeck coefficient

Parallel syntheses and thermoelectric properties of Ce-doped SrTiO₃ thin films by Y.F. Yamada; A. Ohtomo; M. Kawasaki (pp. 768-771).

Thermoelectric properties of single crystalline Ce_xSr1−_xTiO₃ films (0≤ x≤0.5) have been studied by using combinatorial pulsed-laser deposition. Temperature gradient method was used for identifying an optimum growth temperature for SrTiO₃ homoepitaxial growth, at which both oxygen stoichiometry and persisting layer-by-layer growth mode could be accomplished. Electrical conductivity ( σ) and Seebeck coefficient ( S) were measured at room temperature for the composition-spread films grown at the optimized temperature and found to be considerably higher than those reported for bulk poly-crystalline compounds. Hall measurement revealed that carrier density linearly increased with increasing x, suggesting that a trivalent Ce ions substituted divalent Sr ions to supply electrons. A maximum power factor ( S² σ) was obtained for the x=0.2 film, being 7 and 14μW/K²cm at 300 and 900K, respectively.

Keywords: PACS; 73.50.Lw; 73.61.Le; 81.15.FgSrTiO; ₃; Thermoelectric; Combinatorial chemistry; Conductivity; Seebeck effect; Thin films; Pulsed-laser deposition

Diversity management for efficient combinatorial optimization of materials by David Farrusseng; Frédéric Clerc (pp. 772-776).

We describe the issues of evolutionary library design in the frame of Material and Catalyst discovery. Concepts of diversity management on material library to enhance the efficiency of the optimization are proposed. The diversity monitoring is implemented by two different approaches. The first deals with a dynamic monitoring of mutation and crossover rates whereas the second involves a selection step based on sample “distance”. Simulations of optimization are performed on a surface response which is designed to mimic realistic data. Algorithm performances are compared in terms of both efficiency and reliability.

Keywords: Combinatorial chemistry; High throughput screening; Material library design; Virtual screening; Catalysis; Chemoinformatic; In-silico screening; Kinetic modeling

Combinatorial synthesis and high throughput evaluation of thermoelectric power factor in Mg–Si–Ge ternary compounds by M. Watanabe; T. Kita; T. Fukumura; A. Ohtomo; K. Ueno; M. Kawasaki (pp. 777-780).

Discrete phase libraries of thermoelectric compounds, Mg_xSi_yGe1−_y, were fabricated by a combinatorial pulsed laser deposition followed by annealing as a thin film form on an integrated ceramic substrate. In the substrate are embedded four probe electrical contacts to each sample, lead wires and pads to be accessed by needle probes. Resistivity and Seebeck coefficient were evaluated electrically, while temperature difference was locally given to each sample by a local heater also embedded in the substrate. The sample temperature (300–673K) was controlled by a heating stage and temperature difference at the two contact points for each sample was evaluated by an infrared camera. The dependences of polarity and absolute values of Seebeck coefficient on the composition agree well with the data in literature.

Keywords: PACS; 72.15.Jf; 73.43.Fj; 73.50.Lw; 87.63.HgCombinatorial technology; Thermoelectric; Silicides; PLD

Design and spectroscopic reflectometry characterization of pulsed laser deposition combinatorial libraries by Peter K. Schenck; Nabil D. Bassim; Makoto Otani; Hiroyuki Oguchi; Martin L. Green (pp. 781-784).

The goal of the design of pulsed laser deposition (PLD) combinatorial library films is to optimize the compositional coverage of the films while maintaining a uniform thickness. The deposition pattern of excimer laser PLD films can be modeled with a bimodal cosⁿ distribution. Deposited films were characterized using a spectroscopic reflectometer (250–1000nm) to map the thickness of both single composition calibration films and combinatorial library films. These distribution functions were used to simulate the composition and thickness of multiple target combinatorial library films. The simulations were correlated with electron-probe microanalysis wavelength-dispersive spectroscopy (EPMA-WDS) composition maps. The composition and thickness of the library films can be fine-tuned by adjusting the laser spot size, fluence, background gas pressure, target geometry and other processing parameters which affect the deposition pattern. Results from compositionally graded combinatorial library films of the ternary system Al₂O₃–HfO₂–Y₂O₃ are discussed.

Keywords: PACS; 81.15FgCombinatorial; Thin films; Reflectometry

Effects of temperature and oxygen pressure on binary oxide growth using aperture-controlled combinatorial pulsed-laser deposition by Nabil D. Bassim; Peter K. Schenck; Eugene U. Donev; Edwin J. Heilweil; Eric Cockayne; Martin L. Green; Leonard C. Feldman (pp. 785-788).

In pulsed-laser deposition (PLD), there are many processing parameters that influence film properties such as substrate–target distance, background reactive gas pressure, laser energy, substrate temperature and composition in multi-component systems. By introducing a 12.7-mm diameter circular aperture in front of a 76.2-mm silicon wafer and rotating the substrate while changing conditions during the PLD process, these parameters may be studied in a combinatorial fashion, discretely as a function of processing conditions. We demonstrate the use of the aperture technique to systematically study the effects of oxygen partial pressure on the film stoichiometry and growth rate of VO_x, using Rutherford backscattering spectrometry (RBS). In another example, we discuss the effect of growth temperature on TiO₂ films characterized by X-ray diffraction and Fourier transform far-infrared (Terahertz) absorption spectroscopy. We demonstrate that we have considerable combinatorial control of other processing variables besides composition in our combi-PLD system. These may be used to systematically study film growth and properties.

Keywords: PACS; 81.15FgCombinatorial; Thin films

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Applied Surface Science (v.254, #3)

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Applied Surface Science (v.254, #3)