bluuebunny/crossref_metadata_2025 huggingface dataset:
Tailoring of Carbon Nanotube Microstructure Using Poly(acrylic acid) and Poly(allylamine hydrochloride)
Authors: Liu Lei , Grunlan Jaime C.
Published: April 2011

Poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) were used to tailor the microstructure of single-walled carbon nanotubes (SWNTs) in both aqueous solutions and dry composite films. Microstructural changes were achieved as the pH of aqueous suspensions were changed, as evidenced by elevated suspension viscosity, scanning electron microscopy and electrical conductivity measurements. The ability to tailor microstructure is useful for aqueous SWNT processing and solid polymer nanocomposites.
Relatively Low Temperature Growth of Carbon Nanotubes by Thermal Chemical Vapor Deposition using Novel Catalysts
Authors: Tai Han-Chung , Lin Kao-Chao , Chuang Tsung-Ying , Chang Yao-Ren , Lai Rui-Ling , Shiu Jiun-Kai , Cheng Huang-Chung
Published: April 2011

We found out the promising catalyst materials(NiPd). The NiPd not only has the low melting point but also has the Pd enhancing the surface diffusion at low temperatures(<500'c ). With the Pd film thickness increasing, we could control the CNT density and synthesize more aligned and uniform CNTs. We also obtained the better electrical properties including lower turn-on field (3.4 V/um) and higher current density (34.3 mA/cm2) for NiPd as catalyst. For the advantages described above, we believe that the difficulty of low temperature on FED can be overcome. Further, the large area field emission display might be fabricated in the future.
Microwave Synthesis of Fe-filled Carbon Nanotubes
Authors: Kharissova Oxana Vasilievna , Ortiz Ubaldo , Hinojosa Moises
Published: April 2011

A highly efficient one-step technique was developed in order to obtain long and aligned carbon nanotubes with or without Fe filling. The aligned carbon nanotubes (CNTs) were synthesized by heating ferrocene Fe(C5H5)2 using microwave (MW) irradiation. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to study the growth process of the aligned multi-layer carbon nanotubes. It was found that CNTs have a metal particle at the tip of each tube. This carbon nanostructures promise to become important in fuel cells and in nanoscale engineering of other systems.
Electron Transport in Semiconducting Chiral Carbon Nanotubes
Authors: Kauser M. Z. , Verma A. , Ruden P. P.
Published: April 2011

We report on electron transport characteristics for semiconducting, single wall, chiral carbon nanotubes. The Boltzmann transport equation is solved indirectly by the Ensemble Monte Carlo method. The basis for the transport calculations is provided by electronic structure calculations within the framework of a simple tight binding model. Scattering mechanisms considered are due to the electron-phonon interactions involving longitudinal acoustic, longitudinal optic, and radial breathing mode phonons. Results show significantly increased Umklapp scattering processes due to the reduced Brillouin zone compared to zigzag nanotubes. This results in increased transient velocity oscillation and negative differential mobility.
A Study of the Use of Novel Self-ordering Functionalized Polymers to Control Crystal Growth
Authors: Heywood Brigid R. , Ovens Adam C. D.
Published: April 2011

In this research, the ability of a series of novel oligomeric organic species to control crystal nucleation and growth of inorganic crystals was investigated. The issues under consideration were (i) the relative balance of hydrophobicity and hydrophilicity which might be programmed into a polymer; (ii) the impact metal binding, or bridging on its activity in a crystallization reaction; (iii) the mode of self organisation. An homologous series of alkyl substituted sulphonated calixarenes were used to probe these issues.The ability of a metal cation to either bridge adjacent calix[4]arenes or to adsorb into the molecular cavity had an impact upon the interaction of these molecules with the nascent crystals; selective and specific adsorption behaviours were revealed by the expression of smooth well defined new faces in the equilibrium morphology of the crystals. When the hydrophobicity index was high (increased molecular weight of alkyl substituent) these compounds segregated at the gas/liquid interface and, as a consequence of cation-induced ordering, were able to induce the oriented nucleation of crystals. When the metal ion was preferentially adsorbed into the molecular cavity the complex induced twinning in the crystal form. These studies have revealed that, in contrast to earlier studies which argued for the only for an epitaxial relationship between the polymer and crystal, a tunable range of several chemical characteristics can be programmed into a polymeric substrates if they are to be used to control nucleation and growth.
Mechanical Behavior and Microstructure of Nanoporous Gold Films
Authors: Sun Ye Sun , Balk T. John
Published: April 2011

Nanoporous gold (NPG) thin films offer an opportunity to investigate the effects of nanoscale geometric confinement on the mechanical properties of metals. In the present study, NPG films supported by substrates were fabricated by dealloying Au-Ag films on Kapton and silicon. The microstructural evolution of NPG at various stages of dealloying was observed and analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cracking occurred at grain boundaries during dealloying and is believed to result from pre-existing tensile stress in the film. Stress evolution of NPG films on silicon substrates during dealloying was measured with the wafer curvature technique and revealed an overall shift toward compressive stress.
Insitu Observation of the Formation Dynamics of Nanohelices
Authors: Yeoh Terence , Mason Maribeth , Feinberg Zack , Leung Martin , Tasci Mehmet , Elarde Victor , Coleman James J
Published: April 2011

Strained InGaAs/GaAs bridges were released by a focused ion beam in order to observe the relaxation dynamics of the structure. Releasing the bridges resulted in the formation of chiral nanotubes with diameter of 920 nm and length 8.5 microns. The total time required for nanoscroll formation took > 20 minutes. From observing the scrolling action through time, it was found that the strain relief process differed from traditional wet etched nanoscrolls due to the simultaneous relief of strain from the released structures.
The Role of Nanoscale Confinement of Adhesion Promoting Molecules on the Adhesion and Resistance to Moisture Attack at the Polymer/Silicon Nitride Interface
Authors: Sharratt Bree M. , Dauskardt Reinhold H.
Published: April 2011

The interface between a highly-crosslinked polymer film and a thin silicon nitride layer can be regulated using adhesion promoting molecules. This work compares the effects of both indirect polymer/inorganic interface chemistry modification by blending organosilane adhesion promoting molecules into the polymer layer, and direct modification by confining the organosilane molecules to the substrate surface. Of particular interest are the effects of these modifications on the occurrence of an anomalous subcritical debonding phenomenon previously observed for the unmodified interface. While significantly different adhesion values were measured, the influence of the blended organosilanes was limited to moderating moisture diffusion through the polymer layer, which correllates with moderated near-threshold growth rates. Conversely, nanoscale confinement of the adhesion promoting molecules did not result in expected universal increases in adhesion energy but did inhibit anomalous near-threshold behavior.
Improving Biomaterials from a Cellular Point of View
Authors: Varanasi Venu Gopal , Vallortigara T. , Loomer P. M. , Saiz E. , Tomsia A. P. , Marshall S. J. , Marshall G. W.
Published: April 2011

Bioactive glasses (6P55) used for coating Ti/Ti-alloy were tested for their in vitro behavior in a comparative study with commercial Bioglass™ (45S5) and commercial Ti alloy (Ti6Al4V). In vitro testing included pH and dissolution rate determination in simulated body fluid (SBF) along with in vitro cyto compatibility testing. It was seen in this work that 6P55 and 45S5 had similar dissolution behavior, demonstrating t½ dependence and maximum pH of approximately 8.1 after 10 days of immersion. This pH was reduce by 0.2 0.4 pH units when the in vitro V:A ratio was increased from 1 to 3. The dissolution rate of these glasses approached 0 after additional immersion tests after 15 days and the pH stablilized at less than 7.5. Cell culture studies showed that both glasses behaved in similar fashion after 16 hours in culture. Both glasses had an increase in cell numbers of close to 200-250%, whereas Ti6Al4V had a less pronounced cell number increase (∼ 180%)
Open-architecture Neural Probes Reduce Cellular Encapsulation
Authors: Seymour John , Kipke Daryl
Published: April 2011

Intracortical microelectrodes currently have the greatest potential for achieving a functional neural prosthesis in patients with neurodegenerative diseases or spinal cord injury. Device efficacy is lacking in long-term performance as seen in both chronological histology and biopotential recording studies.

Some researchers have shown that small single polymer fibers (less than 7-μm diameter) do not induce an encapsulation layer in the rat subcutis so we have extended this concept to neural probe design. In this experiment we investigated the brain-tissue response of polymer probes with 4-μm feature sizes that are capable of withstanding insertion forces when penetrating the rat neocortex. This polymer probe has both a stiff penetrating shank (70-μm by 42-μm) and fine polymer structures (4-μm by 5-μm) that extend laterally from the shank. Our testing verifies that despite a flexible substrate and small dimensions, these devices are mechanically robust and practical as neural probes. We developed a microfabrication process using SU-8 and parylene to create the relatively thick probe shank and thin lateral arms.

In vivo testing was conducted on seven Sprague-Dawley rats. These parylene devices were chronically implanted in the motor cortex for 4-weeks and then imaged using fluorescence microscopy. Cellular encapsulation and neuronal loss were assessed using a Hoechst counterstain and the immunomarker NeuN (neuronal nuclei).

The tissue reactivity immediately around the fine-feature structures is greatly reduced, showing mild cell encapsulation (90±68% increase) relative to the probe shank (460±320% increase). Neuronal loss was only (21±25%) out to 25-μm relative to significant loss around the probe shank (47±19%). Additionally, laminin+, fibronectin+, and Ox42+ tissue often showed greater intensity and thickness at the shank, indicating that the dense scar formation typical of cortical implants was mitigated around the fine lateral structure.

These results suggest that using MEMS-based microfabrication to create sub-cellular structures will significantly reduce encapsulation, which should extend the longevity of neural probes. We also believe this concept could be beneficial to any implantable sensor capable of scaled geometries.
Effects Of Laser Parameters On The Mechanical Response Of Laser Irradiated Micro-Joints
Authors: Mian Ahsan , Mahmood Tonfiz , Auner Greg , Witte Reiner , Herfurth Hans , Newaz Golam
Published: April 2011

This paper is devoted to the laser irradiated joints between glass and polyimide. To facilitate bonding between them, a thin titanium film with a thickness of approximately 0.2 μm was deposited on glass wafers using the physical vapor deposition (PVD) process. Two sets of samples were fabricated where the bonds were created using diode and fiber lasers. The samples were subjected to tension using a microtester for bond strength measurements. The failure strengths of the bonds generated using fiber laser are quite consistent, while a wide variation of failure strengths are observed for the bonds generated with diode laser. Few untested samples were sectioned and the microstructures near the bond areas were studied using an optical microscope. The images revealed the presence of a sharp crack in the glass substrate near the bond generated with the diode laser. However, no such crack was observed in the samples made using fiber laser. To investigate further the reasons behind such discrepancy in bond quality, three-dimensional uncoupled finite element analysis (FEA) was conducted for both types of samples. The transient heat diffusion-based FEA model utilizes the laser power intensity distribution as a time dependent heat source to calculate the temperature distribution within the substrates as a function of time.
Solid State NMR Studies of the Aluminum Hydride Phases
Authors: Hwang Son-Jong , Bowman Robert C. , Graetz Jason , Reilly J. J.
Published: April 2011

Several solid state NMR techniques including magic-angle-spinning (MAS) and multiple-quantum (MQ) MAS experiments have been used to characterize various AlH3 samples. MAS-NMR spectra for the 1H and 27Al nuclei have been obtained on a variety of AlH3 samples that include the β- and γ- phases as well as the most stable α-phase. While the dominant components in these NMR spectra correspond to the aluminum hydride phases, other species were found that include Al metal, molecular hydrogen (H2), as well as peaks that can be assigned to Al-O species in different configurations. The occurrence and concentration of these extraneous components are dependent upon the initial AlH3 phase composition and preparation procedures. Both the β-AlH3 and γ-AlH3 phases were found to generate substantial amounts of Al metal when the materials were stored at room temperature while the α-phase materials do not exhibit these changes.
The Capacity Enhancement of Room Temperature Hydrogen Storage in HiPco SWNT by Electrochemical deposition of Palladium Nanoparticles
Authors: Lee Yong-Won , Bhowmick Ranadeep , Clemens Bruce M.
Published: April 2011

A Sieverts apparatus for small quantity samples has been implemented by employing a very small volume pressure reservoir and a sample chamber of less than 1 ml. The hydrogen storage capacity of a commercially available, HiPco (high pressure CO conversion) single-wall carbon nanotube (SWNT) was measured over a hydrogen pressure range of 0-35 Bar at room temperature. The sample contained approximately 5 wt% of residual Fe catalyst, and showed 0.17 wt% of hydrogen uptake capacity at 30 Bar of hydrogen pressure. Palladium nanoparticles were deposited on the SWNT via electrochemical method (EC) from H2PdCl4 solution. The storage capacity of the SWNT with EC-doped Pd was increased to 0.52 wt% at 30 Bar, which corresponds to the capacity enhancement by a factor between 2.8 and 3.1.
Novel Approach for Fabrication of Single-Crystalline Insulator/Si/Insulator Nanostructures
Authors: Fissel Andreas , Kuehne Dirk , Bugiel Eberhard , Osten H. Joerg
Published: April 2011

Double-barrier insulator/Si/insulator nanostructures on Si(111) were prepared using molecular beam epitaxy. Ultrathin single-crystalline Si buried in a single-crystalline insulator matrix with sharp interfaces was obtained by a novel approach based on an epitaxial encapsulated solid-phase epitaxy. As an example, we demonstrate the growth of Si buried in Gd2O3 and the incorporation of epitaxial Si islands into single-crystalline Gd2O3. The I-V characteristic of the obtained nanostructures exhibited negative differential resistance at low temperatures, however, with a strong memory effect.
Development of CMR Manganite Sensors for Energy Measurement of the Linear Coherent Light Source Free Electron Laser Xray Pulses
Authors: Yong Grace J. , Kolagani Rajeswari M. , Cox David E. , Mundle Rajeh , Davidson Anthony L. , Friedrich Stephan , Ali Zaheer A. , Drury Owen B. , Li Lisa G. , Ott Linda L. , Liang Yong
Published: April 2011

We are developing Colossal Magnetoresistive (CMR) manganite thin film bolometric sensors to be employed as total energy detectors for beam diagnostics of the Linear Coherent Light Source (LCLS) Free Electron Laser (FEL) (at the Stanford Linear Accelerator). LCLS is an ultra bright, ultra short coherent x-ray source whose peak brightness will exceed that of third generation x-ray sources by about ten orders of magnitude and average brightness by three orders of magnitudes. It is expected to produce 1012 x-rays per 200 fs pulse with a repeat frequency of 120 Hz through self-amplified stimulated emission. In characterizing the beam, it will be necessary to measure the total energy of the FEL pulse. The Advanced Detector Group at Lawrence Livermore Laboratory has developed a scheme for FEL total energy measurements based on bolometric detection and are collaborating with Towson University to implement such a detector using CMR manganite thin films. Here we discuss the basic scheme, results of simulations of the thermal response and the materials development efforts towards fabricating the thin film detectors.
Characteristics of Lateral Capacitor Based on High-K Materials
Authors: Kalkur Thottam , Azadpour Mark
Published: April 2011

In order to take advantage of continued interconnect scaling dimensions in very large scale integrated circuit technology, lateral capacitors with BST dielectric have been proposed. The lateral capacitors have been implemented by platinum/titanium metallization patterned by standard photolithographic techniques and ion-milling. The high-K dielectric BST has been deposited by spin-on MOD and radio frequency magnetron sputtering. The capacitance of lateral capacitor was found to increase with increase in thickness of BST and annealing temperature. The negative temperature dependence capacitance above room temperature shows that BST is in para-electric phase.
Ohmic Contact Behavior of Pt/Ni/Au to p-ZnO
Authors: Lee Ji-Myon , Kim Kyoung-Kook , Tampo Hitoshi , Yamada Akimasa , Niki Shigeru
Published: April 2011

The electrical properties of single Pt (30 nm) and Pt (30 nm)/Ni (30nm)/Au(50nm) multilayer contacts on moderately doped p-ZnO (Na = 5.0 × 1017 /−3) were investigated. Although linear current-voltage characteristics were observed for all samples, a sample that was annealed for 1 min at a temperature above 500 °C resulted in an ohmic contact with good characteristics. The best ohmic contact to p-type ZnO was obtained using a Pt/Ni/Au multilayer contact that was annealed at 600 °C for 1 min under a N2 ambient, showing a specific contact resistance Rc of 1.97 × 10−5 Ω cm2. The fundamental mechanisms for the lower contact resistivity of Pt/Ni/Au contacts are discussed based on glancing angle x-ray diffraction results and Auger depth profile analysis of the multilayer alloying process. Furthermore, we fabricated a ZnO p-n homojunction using Pt/Ni/Au and Ti/Au as the p-type and n-type ohmic contact metal, respectively. The threshold voltage was determined to be about 3.7 V, comparable to the bandgap energy of ZnO.
Combinatorial Study on In-Ga-Zn-O Semiconductor Films as Active-channel Layers for Thin-film Transistor
Authors: Iwasaki Tatsuya , Itagaki Naho , Den Tohru , Kumomi Hideya , Nomura Kenji , Kamiya Toshio , Hosono Hideo
Published: April 2011

The device characteristics of thin-film transistors (TFTs) having amorphous In-Ga-Zn-O channel layers with various chemical compositions were studied by using combinatorial synthesis techniques. The In-Ga-Zn-O films were prepared by a radio-frequency magnetron sputtering method at room temperature in mixed-gas atmosphere of argon and oxygen. The TFT libraries enabled us to systematically survey the device characteristics of the TFTs in a wide compositional range of channel materials. It is found that the TFT characteristics are very sensitive to the chemical composition ratio of In:Ga:Zn and depend also on the oxygen partial pressure during deposition. Some devices exhibited good performance of the field-effect mobility of ∼10 cm2V−1sec−1 and on-to-off current ratio of ∼108.
Computational Investigation Into the Adsorption of Pollutants Onto Mineral Surfaces: Arsenate and Dolomite
Authors: Austen Kat F. , Wright Kate , Slater Ben , Gale Julian D.
Published: April 2011

Computational modeling techniques have been used to investigate the interaction of arsenate with the dolomite (211) surface. The suitability of a variety of techniques has been assessed in the context of their applicability to the problem, in order to determine the least computationally expensive method of modeling the mineral-solution interface. To this end, various methods of solvating arsenate have been investigated, and a reliable solvation energy has been determined for the molecule. The adsorption geometry of the primary arsenate ion at the dolomite surface has been determined under vacuum conditions. Additionally, solvation of the dolomite surface has studied using molecular dynamics, and results show that there is some layering 2Å above the surface, and that dissociation of the water molecules occurs in this layer.
Nanochemistry: The Development and Implementation of a New Graduate Elective at the Middle Eastern Technical University in Turkey
Authors: Pitcher Michael
Published: April 2011

It seems that a day cannot pass without reading a headline in the popular press or scientific magazines extolling the potential of nanotechnology and nanoscience. The excitement is justifiable and the new generation of researchers and workers in this discipline will need a whole new range of skills and vocabulary to understand and progress this exciting field and for it to reach its full potential. In higher education and research establishments around the world most nanoscience or nanotechnology courses and textbooks, that have been developed, have been done so by engineering or physics departments and approach the subject from that perspective. The interdisciplinary nature of nanoscience, however, also includes chemists, which until recently have had to rely on these courses and books to gain an insight into this rapidly developing field. This has changed in the last year, or so, with exciting new books being published by chemists and aimed at chemistry students of all levels, In addition, chemistry departments around the world, are beginning to develop nanochemistry classes, particularly at the graduate level. Presented here is the structure and content of a new graduate elective that has been offered at the Middle Eastern Technical University (METU) in Ankara, Turkey. This course was offered for the first time in spring 2006 and is designed primarily to introduce and equip chemistry graduate students with some of the skills and tools needed to contribute to the growing nano related research interests that are burgeoning on campus, in the country and in the world. The design of the course, the textbook used, comments from the students, etc are discussed.
Approach To An Interdisciplinary Bionanotechnology Education Program: International Network Perspective
Authors: Vaseashta Ashok , Irudayaraj J. , Vaseashta S. , Stamatin I. , Erdem A.
Published: April 2011

Materials in reduced dimensions demonstrate size dependence and may exhibit properties different from the bulk. Nanomaterials are a fundamentally and entirely new class of materials with remarkable electrical, optical, and mechanical properties, thus offering unique applications. With a 9.7% increase in FY 2004-05 investments and an expected worldwide labor force shortage, education and training has become a key component of the National Nanotechnology Initiative (NNI). The slow response by the academic community to develop nanotechnology curriculum is evidenced by the small number of Universities offering fundamental undergraduate level courses in nanoscience and nanotechnology. There is a strong need to develop coercive undergraduate curriculum to equip the future engineers, scientists, and researchers charged with commercializing nanotechnology applications. We are in the process of developing and implementing some core courses and laboratory modules, which can easily adapt to either a major or minor in nanotechnology, nano-biotechnology, or nanoscience programs. The course modules are being developed by a multi-disciplinary team consisting of faculty in Physics, Agricultural and Biological Engineering, Materials Engineering, and Molecular Biology at Universities in the US, Europe, and the Consortium of South East European Network on Nanoscience and Technology (COSENT). The joint effort specifically addresses a sector of nanobiotechnology emphasizing applications in agricultural and biological systems through hands-on modules and experimental kits. Selected course and laboratory modules are being developed to be affordable, flexible, accessible, and appealing to a diverse student population from across basics sciences, life sciences, agriculture, and engineering departments. Internet ready, multimedia intensive curriculum and assessment modules will include self-directed individualized learning modules as well as team-based components capitalizing on collaborative learning to address complex problems and tasks. The capital cost and site sensitivity of much of the equipment used within nanoscience courses often limits its distribution to large research centers, despite the need for it in many disperse educational programs. The creation of this seamless integration will promote and encourage an international exchange of students and ideas within interdisciplinary research. We will present our unique approach to delivery of education and training at all levels employing converging technologies to an international audience and receive feedback to enhance the effectiveness of the program to better educate the task force of tomorrow.
An Undergraduate Nanotechnology Course for Classes of Multi-discipline students in Taiwan
Authors: Chen Chu Shiang , Lin Song Shiang
Published: April 2011

We reported on our experiences with teaching several semesters of undergraduate nanotechnology courses at both the National Tsing Hua University (NTHU) and National Dong Hwa University (NDHU) in Taiwan. Students who were enrolled in our classes at NTHU represented many different disciplines, but mainly in the physical sciences, engineering and life sciences. In contrast, students who were enrolled in our classes at NDHU dominated in the social sciences and arts. There were some interesting differences in addition to the similarities in their attitude toward the nanotechnology. Since this course is aimed at introducing the nanotechnology to students trained in different disciplines, we emphasized the fundamentals, current status, potential applications, and possible consequences of nanotechnology. This course also explored the close ties between nano-science and engineering (NS/E) and our daily life. Furthermore, this course elaborated on the interrelationships of NS/E with other subjects, particularly the biomimetics, smart systems, and biotechnology.
Training Young Minds for Nanoscience and Technology: Issues and Challenges
Authors: Chattopadhyay Kamanio
Published: April 2011

This article explores issues and challenges in the field of education in nanoscience and technology with special emphasis with respect to India, where an expanding programme of research in nano science and technology is in place. The article does not concentrate on actual curricula that are needed in nano science and technology education course. Rather it focuses on the desirability of nanoscience and technology education at different levels of education and future prospect of students venturing into this within the economic and cultural milieu of India. We argue that care is needed in developing the education programme in India. However, the risk is worth taking as the education on nanoscience and technology can bridge the man power gap not only in this area of technology but also related technologies of hardware and micro electronics for which the country is a promising destination at global level. This will also unlock the demographical advantage that India will enjoy in the next five decades.
Core-shell Ge Nanoparticles on Oxide Surfaces for Enhanced Interface Stability
Authors: Stanley Scott K. , Ekerdt John G.
Published: April 2011

Germanium nanoparticles are grown on HfO2 substrates by hot-wire chemical vapor deposition (HWCVD). The oxidation and thermal stability of these unmodified Ge nanoparticles are determined with X-ray photoelectron spectroscopy (XPS). Core-shell nanoparticles were then prepared by growing the Ge cores with HWCVD and selectively growing Si or C shell layers on the Ge cores by conventional CVD. The formation of core-shell nanoparticles was monitored with XPS and low energy ion scattering. Large differences are observed in the thermal stability and oxide formation for unmodified Ge and the different core-shell nanoparticles.
Ultrafast Photoconductivity in Organic Semiconductors
Authors: Ostroverkhova Oksana , Cooke David G. , Hegmann Frank A. , Anthony John E. , Podzorov Vitaly , Gershenson Michael E. , Jurchescu Oana D. , Palstra Thomas T.M.
Published: April 2011

We present comprehensive study of ultrafast charge carrier dynamics in a variety of organic molecular crystals. In all samples, we observed sub-picosecond charge photogeneration and band-like transport, characterized by (i) an increase in charge carrier mobility as the temperature decreases in a wide temperature range of at least 20 K – 300 K and (ii) mobility anisotropy in the a-b plane of the crystals. The temperature dependence of the decay dynamics of the transient photoconductivity reveals the presence of shallow trapping sites in herring-bone-type-structured crystals (such as pentacene (Pc), tetracene (Tc), and rubrene (Rub)), while such traps are apparently absent in “brick-wall”-type crystals (such as functionalized pentacene (FPc)). We also report on the measurements of the charge carrier mobility anisotropy in the a-b plane of two types of FPc single crystals. Anisotropies of approximately 3.5 and 11.6 were obtained in the crystals characterized by crystal structures favoring two-dimensional and one-dimensional charge transport, respectively, consistent with the degree of π-overlap along different directions in the crystals.
Time-Integrated Photoluminescence Studies of In0.3Ga0.7As/GaAs Quantum Dot Molecules
Authors: Kerr William , Stoleru Valeria Gabriela , Pancholi Anup
Published: April 2011

We investigate experimentally and theoretically optical and electronic properties of In0.3Ga0.7As/GaAs quantum dot molecules (QDMs) formed by two layers of self-assembled, vertically stacked quantum dots (QDs). Structures with In0.3Ga0.7As/GaAs QD layers separated by a thin GaAs barrier were grown by solid source molecular beam epitaxy, and were characterized by time-integrated photoluminescence (PL). For the temperature-dependent PL measurements a He-flow optical cryostat was used to control the temperature between 4 and 300 K. The experimentally observed behavior is in good agreement with that expected from our eight-band k·p calculations. Optical and electronic properties of these QDMs are further compared with those of dots grown under conditions that did not promote vertical organization.
A next generation TCO Material for display systems: Molybdenum doped Indium oxide thin films
Authors: Elangovan E. , Marques A , Martins R , Fortunato E
Published: April 2011

Thin films of indium molybdenum oxide (IMO) were rf sputtered onto glass substrates at room temperature. The films were studied as a function of sputtering power (ranging 40 – 180 W) and sputtering time (ranging 2.5 – 20 min). Thickness of the films found varied between 50 – 400 nm. The films were characterized for their structural (XRD), electrical (Hall measurements) and optical (Transmittance spectra) properties. XRD studies revealed that the films are amorphous for the sputtering power ≤ 100 W and deposition time ≤ 5 min. All the other films are polycrystalline and the strongest refection along (222) plane showing a preferential orientation. A minimum bulk resistivity of 2.65 × 10−3 Ω-cm and a maximum carrier concentration of 4.16 × 1020 cm−3 have been obtained for the films sputtered at 180 W (10 min). Whereas maximum mobility (19.5 cm2 V−1 s−1) has been obtained for the films sputtered at 80 W (10 min). A maximum visible transmittance of 90 % (500 nm) has been obtained for the films sputtered at 80 W (10 min) with a minimum of 27 % for those sputtered at 180 W. The optical band gap of the films found varying between 3.75 and 3.90 eV for various sputtering parameters.
A Study of Oxygen Reduction of Tin- or Zinc-doped Indium Oxide (ITO or IZO) Film Induced by Deposition of Silicon Nitride Film in PECVD Process
Authors: Kim Byoung-June , Choi Youn-Mo , Girotra Kunal , Yang Sung-Hoon , Kim Shi-Yul , Lim Soon-Kwon , Souk Jun-Hyung
Published: April 2011

In the thin film transistor fabrication process, tin doped indium oxide (ITO) or zinc doped indium oxide (IZO) film can be easily exposed to hydrogen-containing plasma during the deposition of silicon nitride (SiNx) film. By this exposure, ITO or IZO can be easily reduced into its corresponding metallic element such as indium, which degrades the optical transmittance and the conductivity. In this study, SiNx was deposited onto ITO or IZO film, and the oxygen reduction of ITO or IZO during PECVD SiNx deposition was analyzed to clarify this phenomenon. The oxygen reduction during PECVD SiNx deposition is mainly induced by decomposed NH3 gas. However, the progress of ITO reduction is different from that of IZO reduction, due to the different atomic composition of In2O3 in the composite and the different critical temperature of reduction initiation between indium oxide, tin oxide, and zinc oxide.
Synthesis and self-assembly of photopolymerizable quarterthiophenes
Authors: Garcia Margarita , Meijer E.W. , Schenning Albertus
Published: April 2011

A variety of α, α'-subtituted quaterthiophenes containing ester, amide and polymerizable side chains have been synthesized and fully characterized. The self-assembly properties of these oligothiophenes were studied as function of the side chain. Introduction of amide functionalities highly promotes the self-assembly via π-stacking and hydrogen bond interactions, while the lack of amides prevent aggregate formation. Initial experiments show that by introducing a sorbyl moiety as a polymerizable group it is possible to achieve covalent fixation of the oligothiophene units in the self-assembled state.
Application of Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) for Analysis of Novel Organic Semiconductor Materials
Authors: Shcherbyna Svitlana , Bohme Diethard K. , Baranov Vladimir I.
Published: April 2011

ICP-MS is a well established analytical technique in the semiconductor industry for essential trace metal characterization in chemical reagents and silicon wafers. Tetracene, Antracene, Pentacene and Rubrene are among the most interesting organic semiconductors for use in molecular electronic devises such as single-crystal Organic Field Effect Transistors (OFETs). One of the most important parameter for fabrication of single-crystal OFETs is the purity of the starting material. As the crystal growth process also results in the chemical purification of the material, several re-growth cycles may be required for improving the field-effect mobility, with the grown crystals used as the starting material for the subsequent re-growth. The number of required re-growth cycles depends strongly on the purity of starting material. We report the application of ICP-MS for impurity analysis in the organic semiconductors. The ICP plasma, where samples are atomized and ionized, generates strong ion current, which is instrumental in achieving exceptional detection limits. Some elements can be measured down to part per trillion range. This study can provide a better characterization of the trace metal impurities in starting material.
Charge Injection into Bottom-Contact Pentacene Thin-Film Transistors
Authors: Hong Yi , Yan Feng , Migliorato Piero , Han S H , Jang Jin
Published: April 2011

We investigate the contact of bottom-contact pentacene-based thin-film transistors, with Au source/drain electrode. By separating the voltage drop at the contact from the source-drain voltage, the current-voltage characteristic of the injection contact is obtained. The contact characteristics are in a good agreement with a model of carrier injection from a metal electrode into a disordered hopping system.
Polymer Gate Dielectrics for High Performance Organic Field-Effect Transistors
Authors: Yildirim Faruk Altan , Meixner Ronald , Schliewe Robert Roman , Bauhofer Wolfgang , Goebel Holger , Krautschneider Wolfgang
Published: April 2011

Solution-processed bottom-gate organic field-effect transistors (OFET) with different dielectric materials were produced and characterized. As the active semiconductor layer, regioregular poly(3-hexylthiophene) (rr-P3HT) was used. In addition to the dielectrics which have been reported in literature, various other materials with simple processing conditions were used as gate-dielectrics. Also, the dielectric properties of the polymeric layers were investigated in metal-insulator-metal capacitor structures, where the thicknesses of the films were exactly the same as they were in the OFETs. The specific volume resistivity and dielectric constant values determined were then used to explain the electrical behavior of OFETs. The devices having BCB, SU-8 and NOA74 as the dielectric layers exhibited the desired transistor characteristics, whereas the transistors with Avatrel dielectric did not, due to higher gate-leakages. As a result, SU-8 and NOA74 resins were proven to be good candidates for gate-dielectric usage in solution-processed all-polymer OFETs.
Copper Phthalocyanine Single-crystal Field-effect Transistors Stable Above 100°C
Authors: Yamada Koichi , Takeya Jun , Shigeto Kunji , Tsukagoshi Kazuhito , Aoyagi Yoshinobu , Iwasa Yoshihiro
Published: April 2011

Intrinsic charge transport of copper phthalocyanine single-crystal field-effect transistors is measured as function of temperature up to above 100°C. The conduction of the accumulated carriers shows hopping-type transport, so that the field-effect mobility increases with temperature following activation-type temperature dependence throughout the measured temperature region. Due to excellent material stability at the high temperature, the mobility values are precisely reproduced after the heat cycles.
Long n-Alkane Adlayers as Templates for Tailoring Supramolecular Self-Assemblies on Surfaces
Authors: Piot Luc , Marchenko Alexandr , Wu Jishan , Müllen Klaus , Fichou Denis
Published: April 2011

In this paper we report the heteroepitaxial growth and the structural evolution of hexakis-dodecyl-peri-hexabenzocoronene (HBC-C12) adsorbed on a template monolayer (n-C50H102). STM measurements at the liquid/solid interface made it possible to follow in real time the early stage of deposition of the HBC-C12 molecules. Additionally, molecule manipulations were realized using the tip of the STM. Our measurements give direct evidence of two successive phase transitions occurring in the upper HBC monolayer weakly bonded to the underlying template layer.
Nonvolatile Carbon Nanotube Memory Device With Molecular Charge Storage
Authors: Sorger Volker J. , Yao Zhen
Published: April 2011

Nanoscale, non-volatile, multi-bit memory devices have been fabricated consisting of carbon nanotube field-effect transistors (CNT-FETs) surrounded by redox active molecules (cobalt porphyrin). Charge was stored in the cobalt center atom of the molecule. Write and erase programming was carried out with back-gate pulses. By varying the back-gate amplitude multi-level memory operation was achieved. Programmed devices were read at zero gate voltage showing distinct logic ON and OFF states at room temperature for several hours. At low temperatures strong increase in retention time was observed and single-electron sensitivity was demonstrated. Charge stability tests show insignificant device change after 105 write and erase cycles.
A Novel Non-destructive Interfacing Technique for Molecular Scale Switching Junctions
Authors: Johns Chad , Kimukin Ibrahim , Islam M. Saif , Ohlberg Doug A. A. , Donley Carrie , Stewart Duncan R. , Wang Shih-Yuan , Williams R. Stanley
Published: April 2011

Characterization of molecular scale electronic devices generally involves deposition of a metal top electrode onto an organic film. During the evaporation process, high energetic granules of metals may lead to unwanted reactions between the organic molecules and deposited top electrodes. This can cause, as commonly reported, lasting damage which leaves most junctions either short or open. To overcome this important issue of physical damage to the molecules, we developed a novel technique of interfacing molecules by laying prefabricated metallic electrodes on top of a monolayer of molecules. For the bottom electrode a monolayer of cadmium stearate ((C17H35COO)2Cd) was deposited, using the Langmuir-Blodgett technique, onto platinum (Pt) electrodes which further rested on 200nm of oxide used for isolation. A separate set of Aluminum (Al) electrodes were fabricated on a different oxide free, highly doped substrate and was gently placed on the cadmium stearate monolayer in room ambient. Conduction to the top electrode was accomplished by probing the backside of the highly doped wafer whereas the bottom electrodes were individually addressed. Pressure was applied to ensure firm contact between the molecules and the top electrodes. Preliminary results showed an observed switching voltage of 3.5V. Most of the devices with Al as the top electrodes exhibited a gradual progression from switching on the positive side, closing, and then switching towards the negative side.
The Explanation of Interfacial Property in Liquid Lens with Multilayer System: Molecular View
Authors: Shim Jihye , Park Sung Soo , Kim Jong Yun , Jung Hayong , Bae Jae Young
Published: April 2011

In order to design liquid lens which works in a severe environment such as high temperature and high humidity, several layered liquid systems are investigated. Especially, the change of the interface between conducting and non-conducting liquid layers has been traced by using empirical molecular dynamics simulation and density-functional theory calculation. The stability of the liquid layers at high temperature was evaluated by simulation results such as the density profile of liquid components, their distribution near the interface, the interface thickness and chemical reactivity between them, which depends on the molecular species consisting of liquid and their concentrations. We found that the organic solvent including halogen atoms, alkyl halide, easily penetrates into conducting liquid layer and reacts with its substances, which is added to increase refractive index and density of non-conducting liquid. We also presented an optimized solution including the minimum organic solvent and satisfying the requisites for an optical device.
Morphology Study of a Hybrid Structure Based on Porous Silicon and Polypyrrole
Authors: Arenas Ma. Concepcion , Hu Hailin , del Río J. Antonio , Nicho M. E.
Published: April 2011

Double layer structures of porous silicon (PS) and polypyrrole (PPy) were prepared in order to study their electrical properties. PS was prepared by electrochemical etching in a HF/Ethanol solution from n-type silicon wafer and PPy by galvanstatic method in a lithium perchlorate/monomer solution. The experimental parameters for preparation of PS and PPy were varied to obtain different morphology of the PS/PPy structures. The surface topography of these structures was analyzed by Atomic Force Morphology (AFM). Tip- and agglomerate-like morphologies of PPy were obtained on PS layers with different pore diameters. The electrical and AFM characterization of PS were studied with and without PPy. Current-voltage (I-V) curves of PS/PPy structures were obtained in dark and under illumination. PS without PPy shows an exponential behavior in the current ((+)Al/n-Si/PS/Cu(-)), but it is almost linear when the PPy layer is deposited over the PS layer ((+)Al/n-Si/PS-PPy/Cu(-)). All structures present photovoltage under illumination conditions. However, this parameter is smaller in Al/n-Si/PS-PPy/Cu structure than Al/n-Si/PS/Cu. The open circuit voltage (VOC) and short circuit current density (JSC) of these structures decrease when the surface morphology of PPy is tip-like, but JSC increase when the surface morphology of PPy is agglomerate-like.
Nitride and Oxide Based Nanowires Grown by Plasma-Assisted Molecular Beam Epitaxy
Authors: Kendrick Chito E , Carder Damian , Miller Pual , Reeves Roger J. , Tilley Richard , Durbin Steven M.
Published: April 2011

The growth of nanostructured material continues to attract attention for a number of applications, including highly sensitive gas sensors (due to the increased surface area), and photonic crystals (which require arrays of nanostructures). Even though nanostructures can be formed through self-assembly, they often do not possess the high crystal quality of those grown using vapour liquid solid (VLS) techniques; also, with VLS the feature size and placement can be easily controlled. To achieve VLS growth, however, several parameters have to be considered specific to the material of interest. In this study, we examine VLS growth of both InN (infrared) and ZnO (ultraviolet) nanostructures.
Domain Structures and Current-Controlled Switching Characteristics of Micron Sized Permalloy Structures with Varying Aspect Ratio
Authors: Seah S. C. , Soh Y S , Ng V
Published: April 2011

Permalloy magnetic structures were fabricated using electron beam lithography and then deposited by evaporation followed by lift-off. The structures were studied for their magnetic domain properties with respect to their aspect ratio. Instead of conventional switching using a magnetic field, a current carrying conductor was used to switch the structures. The current value was gradually increased and magnetic force microscopy was used to study the domain changes of the remanent structures after every increment. At the same time, simulation is done using object-oriented micro-magnetic framework to compare with the experimental results.
First Principles Study of the Phase Transitions of MnAs
Authors: Rungger Ivan , Sanvito Stefano
Published: April 2011

The magnetic and structural properties of MnAs are investigated by mapping ab initio total energies onto a Heisenberg Hamiltonian. We study the dependence of the Curie temperature over the unit cell volume and an orthorhombic distortion by using the mean field approximation, and find that for orthorhombically distorted cells the Curie temperature is much smaller than for hexagonal cells. We provide an explanation for the structural changes of both the first order phase transition at 318 K and the second order phase transition at 400 K, with the cell volume driving the stability of the different structures in the paramagnetic state. The stable cell is found to be orthorhombic up to a critical lattice constant of about 3.7 Å, above which it remains hexagonal.
The Effects of Surfactants on the Morphology of Colloidal Crystals in Self-assembly
Authors: Zhou Zuocheng , Li Qin , Wang Likui , Zhao Xiusong
Published: April 2011

In this research, sodium dodecyl sulfates (SDS) and N-cetyl-n,n,n-trimethyammonium bromide (CTAB) surfactant solutions are used as solvents of polystyrene (PS) colloidal suspension during the fabrication of colloidal crystals. The effects of the surfactant on the quality and the morphology of the colloidal crystals are studied. It was found that surfactants not only change the charge of PS colloidal particles, but also significantly changed the surface tension and the 3 phase contact angle of the suspension with respect to the glass substrate, in turn they change the thickness of the formed crystal as well as the crystal structure. The derived knowledge will be potentially useful in clarifying the mechanisms involved in the formation of colloidal crystals.