bluuebunny/crossref_metadata_2025 huggingface dataset:
Ceramic/Polymer Nanocomposite Tissue Engineering Scaffolds for More Effective Orthopedic Applications: From 2D Surfaces to Novel 3D Architectures
Authors: Liu Huinan , Webster Thomas J.
Published: April 2011

Ceramic/polymer nanocomposites simulate bone much closer in terms of its nanostructure and associated properties, thus, offering a promising opportunity for bone regeneration in a natural way. Previous studies demonstrated improved osteoblast (bone-forming cell) adhesion and long-term functions (such as alkaline phosphatase activity and calcium-containing mineral deposition) on nanometer scale surface roughness provided by well-dispersed titania nanoparticles in poly-lactide-co-glycolide (PLGA). For example, the nanocomposites with the closest surface roughness to natural bone at the nano-scale promoted the most bone cell adhesion and calcium deposition. The current studies focus on further mimicking bone by building three-dimensional structures from titania/PLGA nanocomposites using a novel aerosol based 3D printing technique (one type of rapid prototyping technique, because, similarly, natural bone assembles its three-dimensional hierarchical architecture from nanostructured building blocks). Using this technique, bone fracture data acquired by computed tomography (CT) can be transferred into CAD models and used to direct the fabrication of versatile bone substitutes. Field emission scanning electron microscopy (FESEM) was used to characterize the structure and surface features of these 3D scaffolds. The results demonstrated that 3D printed nano-scaffolds had a well-controlled, repeatable inner structure and, moreover, possessed uniformly dispersed titania nanoparticles which provided for nano-scale surface features throughout the PLGA matrix. Osteoblast adhesion tests were conducted on the 3D titania/PLGA nanocomposite scaffolds created by this technique and the results demonstrated that these 3D scaffolds further promoted osteoblast infiltration into porous structures compared to previous nanostructured surfaces. In conclusion, results of this study have evaluated a promising new orthopedic nanocomposite and a means of fabricating a hierarchical macro-structure from such nanomaterials that can mimic properties of natural bone, thus, providing a new material and approach for more effective orthopedic applications.
Study of Polymeric Microneedle Arrays for Drug Delivery
Authors: Ovsianikov Aleksandr , Doraiswamy Anand , Narayan Roger , Chichkov Boris N.
Published: April 2011

Two-photon polymerization (2PP) is a novel technology for the fabrication of complex three-dimensional (3D) microstructures. The number of applications employing this technology is rapidly increasing, and includes the fabrication of three-dimensional photonic crystals [1-4], medical devices, and scaffolds for tissue engineering [5, 6]. We have used 2PP to fabricate microneedle arrays with various geometries. These devices provide a unique approach for transdermal delivery of nucleic acid- and protein-based pharmacologic agents. Many of issues associated with conventional intravenous drug administration, including pain to the patient, trauma at the injection site, and difficulty in providing sustained release of a pharmacological agent, may be eliminated by applying the microneedles. The effect of microneedle geometry (e.g., tip sharpness and aspect ratio) on skin penetration was examined. Our results indicate that microneedles created using 2PP technique are suitable for in vivo use, and integration with next generation MEMS- and NEMS-based drug delivery devices.
Synthesis and Optical Properties of Silicon Oxide Nanowires
Authors: Gelloz Bernard , Coffinier Yannick , Salhi Billel , Koshida Nobuyoshi , Patriarche Gilles , Boukherroub Rabah
Published: April 2011

The paper reports on the synthesis and structural characterization of amorphous silicon oxide nanowires (SiONWs). The nanowires were prepared using the solid-liquid-solid (SLS) technique and display an average mean diameter in the range of 20-150 nm and 15-20 μm in length. Energy dispersive spectrometry (EDS) analysis revealed that the nanowires consist of Si and O elements in a ratio of approximately 1:2. The result was corroborated by the presence of a single peak at around 103 eV in the X-ray photoelectron (XPS) spectrum. As-prepared SiONWs display blue photoluminescence (PL) centered ∼ 400 nm. The blue luminescence is inhomogeneous with an increase in the PL peak intensity by a factor of 1.8 at certain areas of the surface. Next, we have investigated the effect of high-pressure water vapor annealing (HWA) on the PL and found that while the PL became homogeneous, a decrease of its intensity by a factor 2 was observed. The origin of the blue emission could be attributed to defect centers of oxygen deficiency in the wires.
Formation of a Thermally Stable NiSi FUSI Gate Electrode by a Novel Integration Process
Authors: Tan Shiang Yu , Chiu Hsien-Chia , Hu Chun-Yen
Published: April 2011

Nickel silicide is promising to be the choice material as contact to the source, drain, and gate for sub-65 nm and 45 nm CMOS devices. However, the thermal stability of NiSi is worse as the high resistivity phase of NiSi2 nucleates at about 750 °C and film agglomeration occurs even at a temperature as low as 600 °C. The process integration issues and formation thermally stable NiSi are needed to be understood and addressed. In order to obtain a thermally stable Ni-FUSI gate electrode, we introduced a novel integration process by using a two-step anneal process associating with properly tuned thickness of the initial Ni film and implant BF2atoms during the poly-gate formation. As results, push the transformation of NiSi2to a higher temperatures at about 900 °C. Several measurement techniques such as XRD, TEM, SEM and Resistivity are carried out to demonstrate its physical and electrical properties.
Preparation and Electrical Properties of the MWNT/Polymer Nanocomposite Fibers
Authors: Wang Guan , Tan Zhongkui , Liu Xueqing , Samuilov Vladimir , Dudley Michael
Published: April 2011

An oxidation method has been applied to functionalize multiwalled carbon nanotubes with carboxylic acid (-COOH) group. Functionalized carbon nanotubes (f-MWNT) were used for the fabrication of conducting nanocomposite fibers by electrospinning, in comparison with the composite nanofibers made of un-functionalized carbon nanotubes (u-MWNT). Our results showed that the addition of f-MWNTs into polymer solution could increase the compatibility of MWNTs with the polymer matrix, and thus result in composite nanofibers with uniform diameters. Alignment of the composite nanofibers was achieved by using a rotating drum as the collector. F-MWNTs were found to align parallel to the axis direction of the nanofibers. Temperature-dependent DC electrical properties of a single composite fiber were investigated by a two-probe method. It was shown that the conductivity of the material could be significantly improved above a percolation threshold. The conductivity could be of ten orders of magnitude higher than the pure PVAc.
Perylene Diimide as the Black-Layer Material of the OLEDs
Authors: Lee Jiun-Haw , Chuang Kai-Hsiang , Ho Yu-Hsuan , Lin Chi-Feng , Chao Chun-Chieh , Leung Man-Kit , Li Cheng-Yu , Chen Hsuen-Li
Published: April 2011

In this paper, we use a perylene diimide derivative serving as a destructive and an absorption layer of the “black cathode” of an organic light-emitting device (OLED). A thin and semitransparent metal between the electron transport layer and the perylene diimide is used for better electron injection and also serves as the destructive interference. The thickness of such layer is critical since thinner metal results in lower reflectance, but higher diving voltage due to worse electron injection. To enhance the electron injection capability, the thickness of the thin metal increases which in turns to increase the reflectance. Here, we used a double-metal configuration to decrease the reflectance and maintain the electron injection capability at the same time.
Characterization of Pyrazoline Organic Nanoparticles Encapsulated with Poly(Methyl Methacrylate-co-Ethylene Glycol Dimethacrylate) for Color Electronic Paper
Authors: Kang Hyo Sim , Oh Sun Wha , Kang Young Soo
Published: April 2011

1-Phenyl-3-naphthyl-5-((dimethylamino)phenyl)-2-pyrazoline with different diameters of 40 - 190 nm were prepared by the reprecipitation method and polymerized with poly(methyl methacrylate-co-ethylene glycol dimethacrylate) using cationic surfactants for full color electronic paper, which is expected to substitute for the future display. The electronic ink particles of pyrazoline organic nanoparticles polymerized by poly(methylmethacrylate-co-ethylene glycol dimethacrylate) were prepared and monodispersed successfully in aqueous alcohol medium. The size of mono-dispersed electronic ink particles is from 160 to 550 nm. The ink particle size was found to decrease with increasing concentration of the surfactant. The effect of surfactant was significant. The appropriate additions of surfactants result in an increase in electrophoretic mobility. The electrophoretic mobility of the resulting electronic inks was −7.5 to −3.6 × 10−5 cm2/ V·s in the presence of surfactants.
Dendritic Iridium(III)-Encapsulated Complexes for Organic Light Emitting Diodes
Authors: Son Ho-Jin , Han Won-Sik , Choi Kyu-Bum , Kim Dae-Hyun , Ko Jaejung , Noh Seung-Uk , Lee Changhee , Kang Sang Ook
Published: April 2011

The syntxhesis, photo-physics, and electroluminescence of new types of Iridium(III)-encapsulated dendrimers are described. Thus, four different iridium complexes [Ir(III)(C^N)2(LX), Blue-DCBP, Green-DCBP, Yellow-DCBP, and Red-DCBP] with ancillary ligand tethered to the CBP dendritic unit were synthesized and investigated for their photo-physical properties. A large enhancement in electroluminescence performance was observed by using these dendrimers as host/dopant hybrid materials in layered emitting diodes. In particular, host/dopant ratio can be systematically adjusted by varying dendritic generations. These results demonstrate that new Ir(III)-encapsulated dendrimers can be used as potential single-layer materials for organic light emitting diodes. Large difference in the intra-molecular charge transfer phosphorescence quantum yields and electroluminescence effiencies were observed among dendriritic generations.
Availability of Liquid Crystalline Materials for Organic Polycrystalline Semiconductor Thin Films
Authors: Iino Hiroaki , Hanna Jun-ichi
Published: April 2011

We have investigated the charge carrier transport properties of polycrystalline films fabricated with discotic and calamitic liquid crystals. The polycrystalline films of these liquid crystals exhibiting particular textures under a polarized microscope, i.e., hexagonal and co-circular patterns for discotic and calamitic liquid crystals, respectively, which indicate that the molecular alignment in the liquid crystalline phase is well preserved exhibit clear hole transport along with molecular stacks even in a 15 μm thick film, judging from transient photocurrents by time of flight method. The hole mobilities are over 0.1 cm2/Vs at room temperature. These results indicate formation of fewer grain boundaries across conduction channels. On the other hand, the carrier transport properties in the polycrystalline films of non-liquid crystalline molecules with the same molecular shape exhibit no particular patterns as described and photocurrents are annihilated in the bulk as a function of time, indicating many deep trap sites in grain boundaries. The present results indicate that the liquid crystalline molecule is a good candidate for preparing quality organic polycrystalline semiconductor thin films in opto-electronic applications.
Deep-Level Optical Spectroscopy Investigation of Trap Levels in Tris(8-Hydroxyquinoline) Aluminum
Authors: Nakano Yoshitaka , Noda Koji , Fujikawa Hisayoshi , Morikawa Takeshi , Ohwaki Takeshi
Published: April 2011

We have investigated band gap states in tris(8-hydroxyquinoline) aluminum (Alq3) with and without quinacridone (Qd) doping on fabricated indium-tin-oxide (ITO)/Alq3(:Qd)/LiF/Al devices by using a deep-level optical spectroscopy (DLOS) technique. Non-doped Alq3 sample shows a discrete trap level located at ∼1.39 eV below the lowest unoccupied molecular orbital band in addition to near-band-edge transitions at 2.2 - 3.6 eV. The pronounced 1.39 eV level is attributable to an intrinsic nature of Alq3 and can be active as an efficient generation-recombination (GR) center that may impact the photophysical properties. On the other hand, Qd-doped Alq3 sample exhibits a new deep level at ∼2.40 eV with increasing the double carrier injection rate, corresponding to the highest occupied molecular orbital band of the Qd. Simultaneously, this GR center is subject to charge up positively due to the presence of holes injected into the Qd doping level for Qd-doped Alq3.
Laser Thermoreflectance Measurement for Evaluating Heat Capacity and Interface Heat Resistance of Low-k Films
Authors: Ye Jiping , Okamura Takeo , Sato Shigeo
Published: April 2011

A novel technique that combines laser thermoreflectance measurement with the 3-omega method is proposed for evaluating the heat capacity of low-k films and the heat resistance at the interface between the low-k film and Si substrate. It was demonstrated that the heat capacity of thin films and the heat resistance at the interface can be determined by obtaining the heat effusivity of the film from laser thermoreflectance measurements, the total heat resistance obtained with the 3-omerga method, and the film density and thickness found from x-ray reflectivity measurements. The heat capacity of SiOC films was determined to be Cp(SiOC) =1.1 kJ/kgK with interface heat resistance of Rint(SiOC) = -2.37×10−8 m2k/W, while the heat capacity of Th-ox films was determined to be Cp(Th−ox) =0.61 kJ/kgK with Rint(Th−ox) = +1.74×10−8 m2k/W. A DSC heat capacity measurement confirmed the reliability of the evaluated Cp data. XRR and TEM examinations revealed that the negative interface heat resistance exhibited by the SiOC films originated from a high density layer at the interface between the film and Si substrate; and the positive interface heat resistance displayed by the Th-ox films stemmed from atomic defects at the interface between the film and Si substrate. These results confirmed that this method is a reliable and effective method for evaluating the heat capacity of low-k films and the heat resistance at the interface.
Surface Deformation of Metal Films Under Controlled Pressure for Generating Ultra-flat Metal Surfaces
Authors: Vj Logeeswaran , Chan Mei-Lin , Islam M.Saif , Horsley David A. , Wu Wei , Wang Shih Yuan , Williams R. Stanley
Published: April 2011

We present a technique to generate ultra-smooth surfaces and direct pattern imprinting on thin metal films by flattening the bumps and spikes of a freshly vacuum deposited metal film. The technique was implemented by using a small footprint mechanical imprint press that has the capability to vary the applied pressure from 100MPa to 600MPa. The mechanical press was incorporated with a tactile force sensor that enabled direct monitoring of the applied pressure. We demonstrated the feasibility of the technique on an e-beam evaporated silver (Ag) metal film with thickness ranging from 150Å (optically thin) to 1000Å (optically thick). The film was deposited on double-polished (100)-oriented silicon surface and double-polished borosilicate glass, resulting in a varying degree of film smoothness. The surface morphology of the pressed thin film was then studied using atomic force microscopy and SEM. Our demonstration with the e-beam evaporated silver thin film exhibits the potential for applications in decreasing the scattering-induced losses in optical metamaterials, plasmonic nanodevices and electrical shorts in molecular-scale electronic devices.
Chemical Routes to Ultra Thin Films for Copper Barriers and Liners
Authors: Ekerdt John , Shin Jinhong , Winkenwerder Wyatt , Kim Hyun-Woo , Thom Kelly , Hwang Gyeong S , Agapiou Kyriacos , Jones Richard A
Published: April 2011

Triruthenium dodecarbonyl and trimethylphosphine or triphenylphosphine, and cis-ruthenium(II)dihydridotetrakis-(trimethylphophine) were used in flowing hydrogen or argon at 575 K to explore the effect of changing the percentage of P on the amorphous character of the films and on the electrical properties of the films. First-principles density-functional calculations are presented that reveal the interaction of Ru with P, and that predict the amorphous structure should be most stable above 20 at.% P and 10 at.% B. The films contained a carbon impurity that depended on the delivery gas and the alkylphoshphine source; film resistivity was highly dependent on the carbon impurity level. The microstructure changed with the percentage P; amorphous films formed provided the percentage of P exceeded 15 at.%. Film resistivity was most sensitive to the carbon impurity and also changed with microstructure. A 15 nm thick, amorphous film containing ∼15 at.% P had a resistivity of 210 μohm-cm.
Phase-Change Nanowires for Non Volatile Memory
Authors: Cui Yi , Meister Stefan , Peng Hailin
Published: April 2011

We report the synthesis of GeTe, Sb2Te3 and Ge2Sb2Te5 nanowires via a gold-catalyzed vapor-liquid-solid mechanism. The nanowires are studied via electron microscopy and energy-dispersive X-ray spectrometry and are found to be single crystalline. For electrical measurements contact to individual nanowires is made via electron-beam lithography. The nanowires can be switched from their initially low resistance state to a higher resistance state by applying a 200ns voltage pulse. Switching back to the low resistance state is possible via annealing. Electric force microscopy studies show the switching takes place at the metal-nanowire contact.
Effects of Different Fluorine Dopants on the Properties of the Tin Oxide Window Layer and CdTe/CdS Solar Cell
Authors: Li Xiaonan , Bai Mailasu , Pankow Joel , Asher Sally E. , Moutinho Helio Moutinho R. , Gessert Tim
Published: April 2011

Conductive tin-oxide (SnO2) film is doped by group V or VII elements. Of all possible dopants, fluorine provides n-type SnO2 with the best electronic and optical properties. However, the commonly used fluorine dopant, bromotrifluoromethane (CBrF3), is a greenhouse gas. Thus, an alternative fluorine source is needed. In this work, we compared CIF3 as a fluorine dopant to CBrF3. With CBrF3 dopant, optimized carrier concentration and electron mobility values can reach to mid 1020 cm-3 and over 40 cm2/V-s, respectively. After carrier concentration saturates, the electronic mobility continues to improve with an increase of CBrF3 dopant concentration. As a comparison, to achieve similar carrier concentration, far less CIF3 dopant is required. However, the electron mobility is lower (<30 cm2/V-s) and does not improve with an increase of dopant concentration. The low electron mobility increases the optical absorption, especially of long wavelengthes. Considering CdTe/CdS solar cell efficiency, the device with a CIF3-doped SnO2 window layer provides the lower photocurrent.
Transparent Back Contacts in CdTe/CdS: Evaluation for Tandem Cells
Authors: Vasko Anthony , Vasko Anthony , Compaan Alvin D , Marsillac Sylvain
Published: April 2011

CdS/CdTe solar cells with 2.3 μm CdTe were prepared with four different types of p+/n+ transparent back contacts (TBCs) - ZnTe:Cu/ZnO:Al, ZnTe:N/ZnO:Al, ZnTe:Cu/ITO, and ZnTe:N/ITO. ZnTe:N/ITO was found to give the best results. This back contact was then used to make cells of lesser (1.8 μm and 0.7 μm) CdTe thickness, in those cases giving good performance up to 9.1% efficiency. Bifacial J-V was performed on all cells with the optimum ZnTe:N/ITO back contact.
Understanding Metastable Defect Creation in CIGS by Detailed Device Modeling and Measurements on Bifacial Solar Cells
Authors: Lee Jin Woo , Needleman David Berney , Shafarman William N. , Cohen J. David
Published: April 2011

We present a compensated donor-acceptor conversion model to explain the metastable light-induced changes in the performance of CIGS solar cells. In this model, compensating donors plays the role of recombination channel. Modeling using SCAPS-1D yielded reasonable fits to the I-V curves in different metastable states, matching the experimentally observed decreases in short circuit current and fill factor as well as the lack of change in open circuit voltage. Comparison of the experimental results from bifacial solar cells and SCAPS simulations strongly supports the compensated donor-acceptor conversion model both qualitatively and quantitatively.
On Industrial Production of Thin Film CdTe PV Modules
Authors: Bonnet Dieter
Published: April 2011

Due to its basic physical and chemical properties CdTe has become a favored base material for thin film solar cells using robust, high-throughput manu-facturing procedures. The technology shows significant potential for attaining cost levels of <1 $/Wp. Close-Spaced Sublimation (CSS) is the fastest and simplest deposition process for both semiconductors used, CdTe and CdS, permitting in-line production at high linear speed of about 1 m/min.. The individual manufacturing steps for integrated modules are explained in view of their incorporation in the production line. ANTEC Solar GmbH has entered production of CdTe thin film modules on a scale of 100,000 m2 per annum using CSS as the deposition procedure for the semiconductor films and high-rate in-line sputtering for transparent and opaque contacts. Standard module size is 60 × 120 cm2. The production line is operative since 2002, without major problems. This article recounts the efforts to master lab processes for application in production.
CuGaSe2-Based Solar Cells with High Open Circuit Voltage
Authors: Caballero Raquel , Siebentritt Susanne , Kaufmann Christian A. , Kelch Carola , Schweigert Daniel , Unold Thomas , Rusu Marin , Schock Hans-Werner , Lux-Steiner Martha Ch
Published: April 2011

The objective of this work is to increase the open circuit voltage of CuGaSe2(CGS)-based solar cells without decreasing their efficiency. For that, the interface between the p-type CGS absorber and the n-type CdS/ZnO window layer is compared using three different recipes for the growth of the buffer layer. Results show the importance of the adaptation of the CdS buffer layer to the CuGaSe2 absorber film. A maximum open circuit voltage of 922 mV is achieved for the devices when using 60ºC as the chemical bath temperature and a low thiourea concentration. Drive-level capacitance profiling, external quantum efficiency and temperature dependent current-voltage measurements reveal a better quality of the CdS/CuGaSe2 interface for this buffer layer deposition conditions. Factors such as the larger depletion region width and the lower doping level, reducing the tunnelling component, are pointed out as responsible of the higher Voc.
Nanoscale Forces at the Heart of Staphylococcus Infections
Authors: Yongsunthon Ruchirej , Vellano Francis Paul , Lower Brian H. , Fowler Vance G. , Alexander Emily , Lower Steven K.
Published: April 2011

Staphylococcus aureusis one of the most frequently isolated bacteria from infected medical implants.S. aureushas the capacity to adhere to the surface of an implant where it forms a biofilm. We used atomic force microscopy to probe binding forces between a fibronectin-coated tip and isolates ofS. aureus, which were obtained from either patients with infected prostheses or healthy humans. A unique force-signature was observed for binding events between the tip and the cells. There is a strong distinction (p=0.01) in the binding force-signature observed forS. aureusisolated from the infected vs. healthy populations. This observation suggests a fundamental correlation between nanometer scale binding forces and the clinical outcome of patients with implanted medical devices.
Capillary Forces Studied with Atomic Force Microscopy
Authors: Maghsoudy-Louyeh Sahar , Tittmann Bernhard R.
Published: April 2011

The deposition of films and coatings is sometimes influenced by the presence of small amounts of moisture, which can affect the nucleation and growth processes. It is important to understand the behavior of coating materials–especially in semiconductors–in terms of hydrophilicity/hydrophobicity along with adhesion forces. Our technical approach centers on the use of the atomic force microscope (AFM) which was found to be a reliable tool for studying the surface characteristics of materials. In addition to obtaining topographic information, the AFM can also probe attractive or repulsive forces between the tip and the sample surfaces. In this research, a systematic study of the influence of humidity on the adhesion forces between different AFM tips (silicon and silicon nitride) and both hydrophilic and hydrophobic materials (quartz, calcite, mica, graphite) has been conducted using atomic force microscopy. Several force-distance curves measured by the M5 AFM have been gathered at a series of different humidity levels and different locations on the samples. In this paper, measurements of the adhesion force for hydrophobic and hydrophilic materials versus humidity are presented. The results show that the adhesion force on graphite which has hydrophobic character is independent of humidity variation. Results also show that the adhesion force for fused quartz, mica, and calcite which are hydrophilic materials, change dramatically with increasing humidity due to capillary forces. This is in good agreement with theoretical calculations.
Growth and Raman Spectroscopy of Single Crystal ZnGeN2 Rods Grown from a Molten Zn/Ge Alloy
Authors: Peshek Timothy J. , Wang Shanling , Angus John C. , Kash Kathleen
Published: April 2011

We present evidence for the growth of ZnGeN2 from a molten Zn/Ge alloy via the vapor-liquid-solid mechanism. Hexagonally faceted, 3-4 microns wide by 20-40 microns long, single crystal rods of ZnGeN2 capped by a polycrystalline dome of ZnGeN2 were formed. A micro-Raman spectrum shows several individually resolved peaks and no spectral features above 825 cm−1, in contrast to a previously published spectrum for polycrystalline ZnGeN2, but in excellent agreement with recent theoretical predictions.
Obsidian Subsources Utilized at Sites in Southern Sardinia (Italy)
Authors: Tykot Robert H , Glascock Michael D. , Speakman Robert J. , Atzeni Enrico
Published: April 2011

While geochemical analysis of obsidian artifacts is now widely applied around the world, both new instrumental methods and new research questions continue to be applied in archaeology. In the Mediterranean, many analytical methods have been employed and proven successful in distinguishing all of the island sources. In this study, results are presented from the virtually non-destructive, LA-ICP-MS multi-element analysis of 95 carefully selected obsidian artifacts from four neolithic period sites in southwestern Sardinia. The patterns of exploitation of specific Monte Arci obsidian subsources revealed in this study support a down-the-line model of obsidian trade during the neolithic period, but with chronological changes that are best explained by increased socioeconomic complexity.
Anomalous Branch-structured Carbon Nanotubes on Silicon Substrates
Authors: Abdi Yaser , Mohajerzadeh Shams , Baghbani Kokab , Paydavosi Sara , Soleimani Ebrahim Asl
Published: April 2011

We have grown vertically-aligned carbon nanotubes on (100) silicon substrates by means of a plasma enhanced chemical vapor deposition method. The growth of CNTs is achieved by a mixture of hydrogen and acetylene gases in a CVD reactor and a 2-5nm thick nickel is used as the seed for the growth. Following the growth of nanotubes on the silicon substrates, they are covered by a titanium-oxide layer and then the substrate is placed back into the original chamber to expose to a hydrogen plasma. Depending on the hydrogenation step, the nickel seed layer, which is placed on the tip side of the original nanotube, is expanded. The subsequent process in the same reactor leads to the growth of carbon nanotubes in a branched manner. Scanning electron microscopy has been used to investigate the results of such tree-like nanostructures.
Resonant and Broadband Microwave Permittivity Measurements of Single-walled Carbon Nanotubes
Authors: Darne Chinmay D. , Xie Lei-Ming , Padmaraj Divya , Cherukuri Paul , Zagozdzon-Wosik Wanda , Wosik Jarek
Published: April 2011

We report on microwave measurements of complex permittivity of single-walled carbon nanotubes (SWNTs). The SWNT samples are a mixture of semiconducting and metallic nanotubes suspended using Pluronic (F108) as a stabilizing surfactant agent. Other samples that were characterized include pluronic powder and an oriented carpet of multi-walled nanotubes (MWNT). For broadband measurements, the shielded open-circuited transmission line technique was used. Single frequency (resonant) measurements for liquid-based SWNT samples were carried out by employing two different modes in specially designed microwave dielectric resonators (DR), either with a cylindrical hole in the center of a dielectric disk or with a horizontal gap (split resonator). The first resonator can operate in either TE011 or TM011 modes (3.4 GHz and 6 GHz) and was designed for liquid or powder characterization. For pluronic suspended SWNT, real (epsilon) and imaginary parts of permittivity were found at 3.4 GHz as 3.5 and 0.72, respectively.
Direct Growth of III-V Devices on Silicon
Authors: Herrick Katherine , Kazior Thomas , Liu Amy , Loubychev Dmitri I. , Fastenau Joel M. , Urteaga Miguel , Fitzgerald Eugene A. , Bulsara Mayank T. , Clark David , Brar Berinder , Ha Wonill , Bergman Joshua , Daval Nicolas , LaRoche Jeffrey
Published: April 2011

Our direct growth approach of integrating compound semiconductors (CS) and silicon CMOS is based on a unique silicon template wafer with an embedded CS template layer of Germanium (Ge). It enables selective placement of CS devices in arbitrary locations on a Silicon CMOS wafer for simple, high yield, monolithic integration and optimal circuit performance. HBTs demonstrate a peak current gain cutoff frequency ft of 170GHz at a nominal collector current density of 2mA/μm2. To the best of our knowledge this represents the first demonstration of an InP-based HBT fabricated on a silicon wafer.
Growth optimization for high quality GaN films grown by metal-organic chemical vapor deposition
Authors: Jang Jung Hun , Herrero A M , Son Seungyoung , Gila B , Abernathy C , Craciun V
Published: April 2011

GaN layers were grown on c-plane sapphire substrates by using a conventional two step growth method via metal organic chemical vapor deposition (MOCVD). The effect of different growth conditions used in the deposition of the low temperature nucleation layer and high temperature islands on the crystalline quality of the GaN layers was investigated by high resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). The polar (tilt) and azimuthal (twist) spread were estimated from the full width at half maximum (FWHM) values of the omega rocking curves (¥ø-RCs) recorded from the planes parallel and perpendicular to the sample surface. It was found from the XRD and TEM study that the edge and mixed type threading dislocations are dominant defects so that the relevant figure of merit (FOM) for the crystalline quality should be considered only by the FWHM value of ¥ø-RC of the surface perpendicular plane. The result showed that the mixed- and edge-types dislocations were strongly associated with the growth conditions used in the deposition of the nucleation layer and high temperature islands.
Power Performance of AlGaN/GaN HEMT's Grown on 6″ Si Substrates
Authors: Derluyn Joff , Das Jo , Cheng Kai , Lorenz Anne , Visalli Domenica , Degroote Stefan , Germain Marianne , Borghs Staf
Published: April 2011

AlGaN/GaN HEMT's were grown on 6″ Si <111> substrates and passivated using IMEC's in-situ SiN technique. The epitaxial growth was optimized to minimize RF losses due to the substrate-nitride interface while at the same time maintaining high buffer resistivity and low trap density.

To assess RF losses of the epitaxial layer structure, coplanar waveguides were defined on places of the wafer where the top in-situ SiN and AlGaN has been etched away. The attenuation of the RF signals on the coplanar waveguides remained below 0.3dB/mm for frequencies up to 6GHz.

The processing of HEMT's included mesa etching, the formation of TiAlMoAu ohmic contacts, 500nm long gates with source-connected field plates and an airbridge process. The gate fingers are 250µm wide, yielding a total gate periphery of 1.5mm for 6-finger devices and 5mm for the 20-finger version.

The devices' RF power performance was characterised on-wafer. To avoid damage to the RF-probes, active load-pull measurements were performed in pulsed mode with a 100µs period under 10% and 30% duty cycle respectively. As there was no difference between the performance using different duty cycles, we conclude that the channel temperature reaches steady-state in less than 10µs.

The 6-finger devices were operated in deep class AB operation mode but showed clear self-biasing effects. The bias voltage was changed from 30V to 60V in 10V increments. Under 60V bias, the devices provide an output power density of 7.9W/mm at 2GHZ with a PAE of 46% and 6.3W/mm at 4GHz with a PAE of 41%. The output power scales linearly with the bias voltage ranging from 30V to 60V, showing that there is no drain lag in the devices. We attribute this to the efficient surface passivation with the in-situ Si3N4 as well as to high crystal quality and hence the low trap density of the buffer layers. At 2GHz, the linear and saturated power gain are 22dB and 16.4dB respectively. An interesting observation is that the maximum gate current, even at power density levels of 7.9W/mm, remains below 50µA/mm which should prove beneficial for reliability.

The larger 20-finger devices of 5mm total gate periphery reach a maximum absolute output power of 20W at a bias of 40V which represents the limit of our on-wafer measurement system.

These results prove that the use of large area Si substrates is the only viable route forward for AlGaN/GaN HEMT's.
MOVPE of m-plane InGaN/GaN Buffer and LED Structures on γ-LiAlO2
Authors: Behmenburg H. , Mauder C. , Khoshroo L. Rahimzadeh , Wen T.C. , Dikme Y. , Rzheutskii M.V. , Lutsenko E.V. , Yablonskii G.P. , Chou M.M.C. , Woitok J. , Heuken M. , Kalisch H , Jansen R.H.
Published: April 2011

We report on deposition and properties of m-plane GaN/InGaN/AlInN structures on LiAlO2 substrates grown by metal organic vapor phase epitaxy (MOVPE). At first, two different buffer structures, one of them including an m-plane AlInN interlayer, were investigated concerning their suitability for the subsequent coalesced single-phase m-plane GaN growth. A series of quantum well structures with different well thickness based on one of these buffers showed absence of polarization-induced electric fields verified by room temperature photoluminescence (RT PL) measurements at different excitation intensities. Furthermore, polarization-resolved PL measurements revealed a high degree of polarization (DoP) of the emitted light with an intensity ratio of 8:1 between light polarized perpendicular and parallel to the c-axis.
AlGaN/GaN multiple quantum wells grown by using atomic layer deposition technique
Authors: Lo Ming-Hua , Li Zhen-Yu , Chen Shih-Wei , Hong Jhih-Cang , Lu Ting-Chang , Kuo Hao-Chung , Wang Shing-Chung
Published: April 2011

In this work, we report on the growth of ultraviolet (UV) AlGaN/GaN multiple quantum wells (MQWs) structure using atomic layer deposition (ALD) technique. The AlGaN/GaN MQW sample grown on the sapphire substrate consisted of three GaN QWs and four AlGaN barriers comprised AlN/GaN superlattices (SLs). The root-mean-square value of the surface morphology was only 0.35 nm observed from the atomic force microscope image and no crack was found on the surface. Both of the high resolution X-ray diffraction curves and transmission electron microscope images showed sharp interfaces between SLs layers and QWs with good periodicity. These results demonstrate that the ALD could be a very useful technique for controlling the crystalline quality and thickness of the III-nitride epilayer.
P Implantation Effect on Specific Contact Resistance in 3C-SiC Grown on Si
Authors: Bazin Anne-Elisabeth , Michaud Jean-François , Portail Marc , Chassagne Thierry , Zielinski Marcin , Lecoq Jean-Marc , Collard Emmanuel , Alquier Daniel
Published: April 2011

In this work, non-intentionally doped 3C-SiC epilayers were implanted using phosphorus at different energies and subsequently annealed at temperatures between 1100°C and 1350°C in order to form n+implanted layers. Different techniques such as Fourier Transformed InfraRed spectroscopy (FTIR) and Secondary Ion Mass Spectroscopy (SIMS) were used to characterize implanted 3C-SiC epilayers after the different annealing steps. Successively, metal layers were sputtered in order to form the contacts. The specific contact resistance (ñC) was determined by using circular Transfer Length Method (c-TLM) patterns. Specific contact resistance values were investigated as a function of doping and contact annealing conditions and compared to those obtained for highly doped 3C-SiC epilayers. As expected, ñC value is highly sensitive to post-implantation annealing and metal contact annealing. This work demonstrates that low resistance values can be achieved using phosphorus implantation and, hence, enabling device processing.
Using Thermal Oxidation and Rapid Thermal Annealing on Polycrystalline-SiGe for Ge Nanocrystals
Authors: Kao Chyuan-Haur , Lai C. S. , Tsai M. C. , Lee C. H. , Huang C. S. , Chen C. R.
Published: April 2011

In this paper, simple techniques were proposed to fabricate germanium nanocrystal capacitors by one-step thermal oxidation and/or rapid thermal annealing on polycrystalline-SiGe (poly-SiGe) deposited with a LPCVD (low pressure chemical vapor deposition) system. This thermal oxidation method can directly result in the top-control oxide layer via the oxidation of amorphous-Si film and the formation of Ge nanocrystals from the poly-SiGe film. Otherwise, the rapid thermal annealing method can be also used to form Ge nanocrystals as comparison.
Molecular Conformation-dependent Memory Effects in Non-conjugated Polymers with Pendant Carbazole Moieties
Authors: Lim Siew Lay , Ling Qidan , Teo Eric Yeow Hwee , Zhu Chun Xiang , Chan Daniel Siu Hung , Kang En Tang , Neoh Koon Gee
Published: April 2011

Single-layer devices of the structure indium-tin-oxide/polymer/aluminum were fabricated from two non-conjugated polymers with pendant carbazole groups in different spacer units. The device based on poly(2-(N-carbazolyl)ethyl methacrylate) (PMCz) exhibited non-volatile write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 106, while the device based on poly(9-(2-((4-vinylbenzyl)oxy)ethyl)-9H-carbazole) (PVBCz) exhibited volatile memory behavior with an ON/OFF current ratio of approximately 103. In the absence of a spacer unit between the pendant carbazole group and the main chain, regioregular poly(N-vinylcarbazole) (PVK) exhibited only one conductivity state (ON state). The switching and memory effects observed were attributed to conformation changes of the pendant carbazole groups.
Small Molecular Organic Nonvolatile Memory Fabricated with Ni Nanocrystals Embedded in Alq3
Authors: Oh YoungHwan , Nam WooSik , Lee GonSub , Park JeaGun , Lee YongBok
Published: April 2011

Recently, organic nonvolatile memory has attracted much interest as a candidate device for next generation nonvolatile memory because of its simple process, small device area, and high speed. To investigate electrical characteristics of small molecular organic nonvolatile memory with Ni as a middle metal layer, we developed a small molecular organic nonvolatile memory with the device structure of Aluminum tris (8-hydroxyquinolate) (Al/Alq3), Ni nanocrystals, and Alq3/Al. A high vacuum thermal deposition method was used for the device fabrication. It is critical that the fabrication process condition for Ni nanocrystals be optimized, including ∼100 Å thickness, 0.1 Å/sec-evaporation rate, and in-situ plasma oxidation for effective oxidation. The reasons we chose Ni for the middle metal layer are that Ni has a smaller grain boundary, which is beneficial for scaling down and has a larger work function (∼5.15 eV) that can make a deep quantum well in an energy band diagram, compared with that of Al. Our device showed an electrical nonvolatile memory behavior including Vth of ∼2 V, Vw (write) of ∼3.5 V, negative differential region (NDR) of 3.5∼7 V, Ve (erase) of 8 V, and symmetrical electrical behavior at reverse bias. In addition, an interesting behavior of electrical properties was that, although retention and endurance characteristics were similar to the Al device, the Ion/Ioff ratio was greater than 104 at Vr (read) of 1 V. This value of the Ni device was higher than 102 compared to that of the Al device. Also, small molecular organic nonvolatile memory with a Ni middle layer with α-NPD at same fabrication condition showed more unstable characteristics than Alq3. We can speculate that there is a relationship in fabrication condition between the middle metal material and the organic material. Finally, we conclude that our device with a Ni nanocrystals middle layer is more reliable and useful for small molecular organic nonvolatile memory.
Germanium ALD/CVD Precursors for Deposition of Ge/GeTe Films
Authors: Hunks William , Chen Philip S. , Chen Tianniu , Stender Matthias , Stauf Gregory T. , Maylott Leah , Xu Chongying , Roeder Jeffrey F.
Published: April 2011

In order to deposit conformal films in the high aspect ratio trench and via structures in future high-density phase-change memory devices, suitable ALD/CVD precursors are needed. We report on the development of novel germanium(II) metal-organic ALD/CVD precursors containing amide, cyclopentadienyl, and amidinate ligands. The physical properties, volatility, and thermal behavior of the precursors were evaluated by simultaneous thermal analysis (STA) and vapor pressure measurements. Stability studies were conducted to investigate the suitability of the precursors for use as ALD/CVD precursors for device manufacturing.
Observation of the transition from tunneling to hopping carrier transport through single oligothiophene molecules
Authors: Yamada Ryo , Kumazawa Hiroaki , Tanaka Shoji , Tada Hirokazu
Published: April 2011

Electrical conductance of single oligothiophene molecules with a length in the range from 2 to 9 nm was measured as a function of molecular length by a break junction method. The resistance of oligothiophenes increased exponentially from 5-mer to 14-mer while that of molecules longer than 17-mer showed linear dependence on their length. These results indicated that the carrier transport mechanism changed from tunneling to hopping around 14-mer of which the length is approximately 6 nm.
Low Leakage Current Patterned Polymeric Transistors with PAG Assisted Cross-linking PVP as Gate Dielectric and Passivation Layers
Authors: Liu Cheng-Chin , Chang Kuo-Jui , Yang Feng-Yu , Liao Ta-Chuan , Cheng Huang-Chung
Published: April 2011

We have successfully proposed a patterned P3HT thin-film transistor with cross-linked PVP as a passivation material which was cured at low temperature. The active P3HT layer was isolated via photolithographic technique and O2 plasma RIE etching process. In this method, the leakage current could be reduced effectively compared with that of non-patterned device. Although the mobility was degraded 40 %, but the on/off ratio was significantly improved by over three orders and also the subthreshold swing was compatible with the amorphous Si-TFTs (∼1.5 V/decade). Moreover, we also employed this low temperature curing PVP (120 0C) films as the gate dielectrics which exhibited excellent insulating property with high on/off ratio 1.58×104 and good subthreshold swing 1.66 V/decade.
In-crystal Carrier Transport in Organic Single Crystal Transistors
Authors: Takeya Jun , Yamagishi M. , Tominari Y. , Iwasaki Y. , Uno M.
Published: April 2011

We report a series of our experiments using organic single crystals to reach the maximum performance intrinsic to the materials. A consequence of the experiments is that a prescription for realizing high-mobility devices is to induce carriers in inner crystals to avoid scattering at the surfaces. Intrinsic-semiconductor character of the high-purity organic crystals favors thermal diffusion of the carriers into the crystals in the presence of weak gate-electric fields. Furthermore, it is demonstrated that the high-mobility transport of the in-crystal carriers are highlighted in double-gate single-crystal transistors with the two gate electric field balanced with each other.
Influence of Grain Interaction on the Mechanical Behavior in Shape Memory Material in Flexion Test
Authors: Cortés Jacinto , García Fernando N. , González José G. , Flores Horacio , Reyes Alberto
Published: April 2011

An experimental study of the mechanical properties of a Cu-Al-Be shape memory alloy is presented. The samples are tested in a cantilever arrangement. They consist of polycrystalline thin plates of shape memory material with a MS near 0 °C and a monocrystalline sample with MS near −90 °C. The measurements are made with strain gauges attached to the top side of the samples. In these conditions, strain Vs load curves are obtained. A polycrystalline sample is instrumented and tested and then it is cut into three samples for further testing. The results show a relationship between the transformation stress and the sample grain size which differs from the typical Hall-Petch relationship. The analysis of transformation plane stress diagrams shows the development of a stress component perpendicular to those induced by the applied load.
Synthesis and Characterization of Polyurethane Scaffolds for Biomedical Applications
Authors: Chavarría-Gaytán M.C. , Olivas-Armendáriz I. , García-Casillas P.E. , Martínez-Villafañe A. , Martínez-Pérez C. A.
Published: April 2011

Polyurethanes are interesting materials that can be used in biomedical applications for regeneration of bone tissue. In this work the synthesis and characterization of porous polyurethanes to act as scaffold is performed by a thermally induced phase separation technique. The appropriate parameters are determined in order to obtain a porous well interconnected material. Characterization by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) is made in order to determine the thermal stability of the material. Chemical characterization is made by Fourier transformed infrared spectroscopy with attenuated total reflectance (FTIR-ATR). The morphology of the material is observed by a field emission scanning electron microscope (FESEM) and the mechanical properties are measured by dynamic mechanical analysis (DMA).
Physical Modeling of Gas Jet-Liquid Free Surface in Steelmaking Processes
Authors: Solórzano-López J. , Zenit R. , González-Rivera C. , Ramírez-Argáez M. A.
Published: April 2011

Gas jets play a key role in several steelmaking processes as in the Basic Oxygen Furnace (BOF) or in the Electric Arc Furnace (EAF). They improve heat, mass and momentum transfer in the liquid bath, improve mixing of chemical species and govern the formation of foaming slag in EAF. In this work experimental measurements are performed to determine the dimensions of the cavity formed at the liquid free surface when a gas jet impinges on it as well as liquid velocity vector maps measured in the zone affected by the gas jet. Cavities are measured using a high speed camera while the vector maps are determined using a Particle Image Velocimetry (PIV) technique. Both velocities and cavities are determined as a function of the main process variables: gas flow rate, distance from the nozzle to the free surface and lance angle. Cavity dimensions (depth and diameter) are statistically treated as a function of the process variables and also as a function of the adequate dimensionless numbers that govern these phenomena. It is found that Froude number and Weber number control the depression geometry.