bluuebunny/crossref_metadata_2025 huggingface dataset:
The use of ion implantation and annealing for the fabrication of strained silicon on thin SiGe virtual substrates
Authors: Buca D. , Mörschbächer M.J. , Holländer B. , Luysberg M. , Loo R. , Caymax M. , Mantl S.
Published: April 2011

Strain relaxed Si1−xGex layers are attractive virtual substrates for the epitaxial growth of strained Si. Tensile strained Si has attracted a lot of attention due its superior electronic properties. In this study, the strain relaxation of pseudomorphic Si1−xGex layers grown by chemical vapor deposition (CVD) on Si(100) substrates was investigated after He+ ion implantation and thermal annealing. The implantation induced defects underneath the SiGe/Si interface promote strain relaxation during annealing via preferred nucleation of dislocation loops which form misfit dislocations at the interface to the substrate. The amount of strain relaxation as well as the final threading dislocation density depend on the implantation dose and energy. Si1−xGex layers with thicknesses between 75 and 420 nm and Ge concentrations between 19 and 29 at% were investigated. The strain relaxation strongly depends on the layer thickness. Typically the structures show ≈70 % strain relaxation and threading dislocation densities in the low 106 cm−2 range. AFM investigations proved excellent surface morphology with an rms roughness of 0.6 nm. The samples were investigated by Rutherford backscattering spectrometry, ion channeling, transmission electron microscopy and atomic force microscopy.
Effect of Carbon on Diffusion of Boron in SiGe between 940 – 1050 °C
Authors: Karunaratne Mudith S. A. , Bonar Janet M. , Zhang Jing , Willoughby Arthur F. W.
Published: April 2011

The effect of carbon on boron diffusion was studied in Si and strained SiGe. Several types B containing matrices were grown: (i) Si, (ii) Si containing 0.1% C peak, (iii) SiGe with 11% Ge and (iv) SiGe with 11% Ge and with a 0.1% C peak, using gas-source molecular beam epitaxy (MBE). The combination of Si, Si with C, SiGe and SiGe with C matrices allowed us to separate the effects of Ge and C on B diffusivity. To ensure non-injection surface conditions, low temperature silicon dioxide (LTO) and silicon nitride layers were deposited on top of samples in that order. These samples were then rapid thermal annealed (RTA) at 940, 1000 and 1050°C in an O2 ambient.

Diffusion coefficients of B in each type of matrix were extracted by computer simulation, using SIMS profiles obtained from samples before and after the RTA treatment. Diffusion coefficient is reduced by both Ge and C, the suppression by C being more profound. The results are compared to and found to be in reasonable agreement with limited data available in literature.
Optimizing SiGe HBTs technology using small-signal and high frequency noise device's modeling
Authors: Tartarin J.G , Cibiel G. , Monroy A. , Goascoz V. Le , Graffeuil J.
Published: April 2011

The rapid expansion of SiGe technologies during the last decade essentially due to civil telecommunication's applications have led Si/SiGe based heterojunction bipolar transistors (HBTs) to excellent performance levels, allowing high frequency low noise circuit designs such as linear low noise amplifiers( RF noise) or also low-phase noise oscillators (LF noise). Among these technologies, the SiGe BiCMOS one integrates digital and RF functions on the same chip. Fast improvements of the technological process have been performed thanks to large efforts allowed to characterization and modeling of the devices. We have investigated on the influence of technological parameters such as Germanium profile, doping level and thickness of the base layer (5 different wafers) on the dynamic and high frequency noise performances to converge towards the optimum technological process (now available with the BiCMOS6G processed by ST microelectronics). We made use of scattering parameters [S] measurements on the devices to extract the electrical parameters of our small signal model. The high frequency noise parameters based on the electrical model (with noise sources added to the junction, resistances) are simulated and compared with the measured noise parameters of the devices. The four noise parameters (Fmin, Rn, and complex Γopt) measurements have been performed from 1 GHz to 12 GHz, and the dynamic S parameters measurements have been realized in the 40 MHz-40 GHz range. These models have been used to enable the identification of the limiting parameters on the dynamic performances and on the high frequency noise parameters.
Evaluation of AlOx in Co/AlOx/Co spin tunneling junctions by XPS
Authors: Otaka Yuki , Kaiju Hideo , Nishiyama Mao , Sakaguchi Naoki , Shiiki Kazuo
Published: April 2011

Oxidation states of AlOx in Co/AlOx/Co spin tunneling junctions were studied using X-ray photoelectron spectroscopy. Co(10nm)/AlOx/Co(50nm) spin tunneling junctions were fabricated on glass substrates by ion-beam mask sputtering. The Al layers were deposited in various thicknesses and were oxidized in pure O2 gas for 24-48 hours at room temperature. Co/AlOx bilayers simultaneously fabricated were analyzed by XPS. The thicker the Al layer is deposited, the more the unoxidized Al remains. MR ratio of the junctions increasedas the unoxidized Al decreased, and this result is qualitatively in agreement with the LMTO calculation result. The O/Al ratio of AlOx layer is about 1.9-2.0, which means existence of the higher order oxides than Al2O3. XPS depth profiles showed that the unoxidized Al remains not only near the interface with Co but also near the surface when the deposited Al layer thickness isthick.
Characterization and Mapping of Crystal Defects in Silicon Carbide
Authors: Emorhokpor E. , Kerr T. , Zwieback I. , Elkington W. , Dudley M. , Anderson T. , Chen J.
Published: April 2011

A method is presented for detecting, counting and mapping micropipes and dislocations in n+, undoped, and semi-insulating Silicon Carbide wafers. The technique is based on etching in molten Potassium Hydroxide (KOH), and it employs image processing that automatically detects etch pits, discriminates between micropipes and dislocations, and generate micropipe and dislocation density maps. We demonstrate a novel way of detecting and mapping dislocations and micropipes in semi-insulating SiC. This is achieved by combining a properly tuned etching technique that reliably produces well defined etch pits with image processing that enables quick and accurate analysis of the etch pit contrast. We show that the results of optical evaluation are close to those obtained using the Synchrotron White Beam X-Ray Topography (SWBXT) technique.
Structural characterization of 3C-SiC films grown on Si layers wafer bonded to polycrystalline SiC substrates
Authors: Myers R.L. , Hobart K.D. , Twigg M. , Rao S. , Fatemi M. , Kub F.J. , Saddow S.E.
Published: April 2011

Single crystal 3C-SiC epitaxial layers have been grown on SOI substrates using low-pressure chemical vapour deposition (LPCVD). The SOI substrates consist of nominally 150 Å Si layers bonded to 100 mm poly 3C-SiC substrates using direct wafer bonding and SOI film transfer techniques. Miscut Si(100) films were incorporated into the wafer bonding process for the first time in an effort to further reduce anti-phase domain formation in the 3C-SiC films. The Si films were transferred from Si(100) wafers miscut 4° toward the (110) direction. For growth of 3C-SiC layers, a two-step process is needed. First the Si is carbonized using propane mixed in a hydrogen carrier gas to convert the surface to SiC at atmospheric pressure. Next SiC growth is conducted by the addition of silane into the gas mix and a reduction of the process to 150 Torr. Previous characterization of these films via SEM and XRD indicated that the films were single crystal and oriented with respect to the starting Si bonded film. In this work we present results of TEM analysis of these films which show details of the atomic structure at the 3C-SiC/poly-crystalline SiC interface where a thin (6 nm thick) amorphous region has been detected, likely due to SiO2 used to wafer bond the Si film to the poly substrate. A detailed study of this material system is presented with the aim of providing feedback for possible improvements in the 3C-SiC growth process.
Thermoplastic Deformation and Residual Stress Topography of 4H-SiC Wafers
Authors: Okojie Robert. S. , Zhang Ming
Published: April 2011

We have measured thermoplastic deformation in as-received, single-side polished, 4H-SiC wafers and also residual stresses in homoepitaxially grown epilayers on wafers by radius curvature measurements. The wafers studied had n-type resistivities of 0.010-0.011 ω-cm and p-type resistivities of 4.42, 4.72, 9.57 ω-cm. In a first thermal excursion to 900 °C in vacuum, the bow height of the bare substrates in all cases decreased with temperature. Upon cooling down, however, the bow heights remained largely unchanged from their values at 900 °C. A second cyclic excursion to 900 °C did not yield any significant change in the curvature, thus indicating that the substrates had thermoplastically deformed in the first heating cycle. Epilayers having nitrogen doping between 5 × 1017 and 2 × 1019 cm−3 grown on the n- and p-type substrates resulted in compressive stresses ranging between 190 and 400 MPa in the epilayers. Transmission electron microscopy (TEM) examination of the n-type epilayer (with doping levels of 5 × 1017 cm−3 and 5 × 1018 cm−3) on the n-type substrate, revealed bands of stacking faults (SFs) confined within the epilayers after the bicrystals were further annealed at 1150°C in nitrogen for thirty minutes. These doping levels are approximately one and two orders of magnitude below the reported threshold value of 3 × 1019 cm−3 previously suggested for the onset generation of SFs in annealed n-type 4H-SiC epilayers. The calculated residual stresses in all the epilayers were above the critical stress for the motion of dislocations above 1000 °C in 4H-SiC. Thus the SFs that form by glide of pre-existing partial dislocations may actually be stress induced and occur across a much wider range of doping levels. Therefore, it is possible that a significant mechanism for formation of the stacking faults and 3C bands observed in thermally treated 4H-SiC wafer is stress relief via the generation and motion of new and pre-existing partial dislocations on the basal planes of 4H-SiC.
Reliability of Nitrided Oxides in N- and P-type 4H-SiC MOS Structures
Authors: Krishnaswami Sumi , Das Mrinal K. , Agarwal Anant K. , Palmour John W.
Published: April 2011

TDDB measurements of NMOS capacitor fabricated with 1200°C dry oxide with 1300°C N2O anneal were performed at 175°C and 300°C under high positive bias stress. The devices are biased into strong accumulation mode such that the field in the oxide is high enough to collect breakdown data in a reasonable period of time. We observe that at 175°C, a 100-year Mean Time to Failure (MTTF) is obtained at an electric field of 3 MV/cm in the oxide. The TDDB measurement has also been performed at 300°C where lifetime has been reduced by a few orders of magnitude, but with an acceptable 100-year MTTF. Recent reliability results on similarly oxidized MOSFETs have shown failures along the same trend as the n-type capacitors, indicating that MOSFETs and MOS capacitors can have similar reliability despite inherent processing and structural differences. PMOS capacitors fabricated with the aforementioned dry + N2O process as well as capacitors fabricated using the low DIT nitridation techniques show acceptable MTTF of 100 years at the nominal operating electric field of 3 MV/cm.
Comprehensive Study of Impact Ionization Coefficients of 4H-SiC
Authors: Hatakeyama T. , Watanabe T. , Kojima K. , Sano N. , Shinohe T. , Arai K.
Published: April 2011

The electric field dependence and anisotropy of the impact ionization coefficients of 4H-SiC are investigated by means of the avalanche breakdown behavior of p+n diodes. The breakdown voltages as a function of doping density and the multiplication factors of a leakage current are obtained using p+n diode fabricated on (0001) and (1120) 4H-SiC epitaxial wafers. The obtained impact ionization coefficients show large anisotropy; the breakdown voltage of a p+n diode on (1120) wafer is 60% of that on (0001) wafer. We have shown that anisotropy of the impact ionization coefficients is attributable to the anisotropy of saturation velocity originated from the electronic structure of 4H-SiC.
Growth and Metrology of Silicon Oxides on Silicon Carbide
Authors: Hoff Andrew M.
Published: April 2011

Thermal oxidation of SiC by the afterglow method has opened new pathways of opportunity to address both thin film growth and defects that hinder electronic device development with this important semiconductor material. Oxide growth, with rates up to 700Å per hour, on SiC has been demonstrated using this technique over a temperature range from 400°C to 1100°C at 1 Torr total pressure. Electrical and physical properties of oxide films grown by conventional means or by the afterglow method were obtained with a novel, non-contact charge-voltage (Q-V) metrology approach. This instrument employs a combination of incremental contact potential difference values obtained in response to applied corona charge generated from air. The slope of the Q-V characteristic within a bias range corresponding to accumulation of the semiconductor provides an effective dielectric permittivity value for the grown film. Effective permittivity values for afterglow oxides grown on SiC approach that of SiO2 grown on silicon substrates whereas the values for oxides grown on SiC in an atmospheric steam oxidation process are always depressed relative to SiO2 on silicon, indicating that the latter process always produces low-k oxides. A mechanistic discussion regarding these observed differences between the two oxidation methods is presented along with suggestions for an integrated process and metrology approach to reduce defects in oxide films on SiC.
Effect of Hydrogen Peroxide on Oxidation of Copper in CMP Slurries Containing Glycine and Cu Sulfate
Authors: Du Tianbao , Vijayakumar Arun , Desai Vimal
Published: April 2011

This study compares the oxidative dissolution, passivation, and polishing behavior of copper chemical mechanical polishing in the presence of hydrogen peroxide, glycine and copper sulfate. High purity discs were used to study the dissolution and oxidation kinetics under static and dynamic conditions at pH 4 with varying H2O2 concentrations. Changes in surface chemistry of the statically etched copper-disc were investigated using X-ray photoelectron spectroscopy (XPS). With the addition of glycine and copper sulfate to the slurry, the copper removal rates increased significantly and the maximum removal rate shifted to a H2O2 concentration of 3%. Electrochemical investigation indicates an enhanced dissolution of copper, which might be due to the strong catalytic activity of Cu(II)-glycine complexes in decomposing H2O2 to yield hydroxyl radicals. XPS results suggest that the passivation at higher H2O2 concentrations in the presence of glycine and copper sulfate is provided by the OH radicals adsorbed on Cu surface.
Interaction between abrasive particles and film surfaces in low down force Cu CMP
Authors: Wang Yuchun , Zomora Isaac , Hawkins Joe , Zhou Renjie , Sun Fred , Martinez Roy , Zhang Jian , Lu Bin , Wang Shumin
Published: April 2011

A robust copper slurry should have high removal rate, efficient planarization, optimal over polishing window and fast clearing without corrosion. These requirements were addressed in the choice of abrasive particles, film formation for copper passivation, selectivity of copper to barrier, and interactions between particles and film surfaces. The performance results of low dishing erosion and surface finish are discussed with the proposed mechanism.
In-Situ Friction and Pad Topography Measurements During CMP
Authors: Gray Caprice , Apone Daniel , Barns Chris , Monsour Moinpour , +Anjur' Sriram , Manno Vincent , Rogers Chris
Published: April 2011

Duel Emission Laser Induced Fluorescence (DELIF) and friction measurements are taken in-situ during CMP to observe slurry flow beneath a model of an integrated circuit (IC) wafer. Friction measurements average around 7.5 lb and multiple frequencies are observed. Slurry film thicknesses on the order of a 10±3μm were observed during CMP of a flat wafer. The film thickness seems uncorrelated to friction measurements except when the pad and wafer rotation speeds are significantly slowed. DELIF has also accurately measured a 9μm etched step, with noise in the image equal to ±3 μm.
Influence of Electrochemical Plating Process Parameters on Corrosion of Cu Damascene Interconnects
Authors: Ernur D. , Wu W. , Brongersma S. H. , Terzieva V. , Maex K.
Published: April 2011

We present the influence of the electrochemical plating recipe and the bath chemistry on Cu grain size evolution and its link to corrosion of Cu interconnects. Our results demonstrate the fact that Cu corrosion depends on the combination of (i) solution type and (ii) Cu quality. The latter is influenced by geometrical factors such as line width and pattern density as well as the electroplating parameters such as plating recipe and bath chemistry. Organic and inorganic acid based model-CMP solutions are used to make a comparison in terms of the interactions with the Cu surface. It is shown that an organic acid based solution etches Cu independent of the Cu quality. However, etching by an inorganic acid based solution reveals line width (0.2 μm <w<1.0 μm) and pattern density dependence (16%< pd< 72 %) with the narrow lines being etched more rapidly both for isolated and semi-dense structures. This kind of geometry dependent etch behavior by the inorganic acid based solution is also shown to be a function of the electroplating process parameters in contrast to an organic acid based one.
Analysis of Nanotopography in Silicon Generated by the Polishing Process
Authors: Isogai Hiromichi , Kojima Katsuyoshi
Published: April 2011

This paper describes a new model, which analyzes the effects of the polishing conditions on nanotopography after polishing silicon (Si) substrates. The thickness uniformity of dielectric oxide-films after Chemical Mechanical Polishing (CMP) is affected by nanotopography of the Si substrate. Therefore, reducing nanotopography in Si substrates is essential in order to obtain highly uniform dielectric film thickness after CMP. We have developed a model based on Preston's equation for estimating the change in nanotopography of Si substrates due to polishing. In this model, various conditions relating to the structure of the polishing apparatus, the polishing pad material and the motion of the substrate can be taken into consideration. To investigate the influence of the polishing conditions on nanotopography, we compared experimental polishing results with calculations using this model. Thus, it was clarified that the generation of nanotopography in the polishing process that determines the final shape of the substrate, depends on the history of the pressure and contact distance produced during the process.
Investigation and Control of Chemical and Surface Chemical Effects During Dielectric CMP
Authors: Abiade J. T. , Choi W. , Khosla V. , Singh R. K.
Published: April 2011

Due to the ever-increasing popularity of STI in microelectronic device fabrication, designer slurries must be tailored to meet increasingly stringent planarity requirements. Although dielectric polishing is primarily mechanical in nature, the chemical and surface chemical effects can be tailored to enhance selectivity and planarity. Examples of chemical and surface chemical effects in dielectric CMP include; control of slurry pH, use of reactive particles such as cerium dioxide, and addition of surfactants to modulate the particle-substrate interactions. Cerium dioxide particles are utilized due to an increase in substrate dissolution through particle-substrate bonding, which accelerates the material removal of the dielectric surface. The increased efficiency of reactive particles is largely dependent on the area of contact between particle and substrate during polishing. The chemical nature of the interaction between the particles and silica substrates has been investigated using polishing experiments, AFM, and an in-situ friction force apparatus. Both the pH and cerium dioxide particles have been found to significantly affect the near surface region of the oxide film.
Hydrothermal Synthesis of Ce3+ and Tb3+ co-doped Ca3Al2(OH)12 Luminescent Material
Authors: Wen Fushan , Chen Jiesheng , Kim Jin Hyeok , Kim Taeun , Li Wenlian
Published: April 2011

Ce3+ and Tb3+co-doped calcium aluminates luminescent material (Ca3Al2(OH)12: Ce3+, Tb3+) was synthesized at 453 K in hydrothermal system without any protective atmospheres. All the reactants used in the system were simple inorganic salts. The crystallinity and luminescent property of as-synthesized compound were investigated using X-ray diffraction and luminescence spectrometer. The compound formula was confirmed to be Ca3Al2(OH)12. The emission spectrum showed that only typical Tb3+ emission was observed and the emission from Ce3+ was almost not observed, which should be attributed to the energy transfer from Ce3+ to Tb3+ in the compound. The emission peaks at about 486 nm, 498 nm, 540 nm, 549 nm, 582 nm, 595 nm and 623 nm should be assigned to 5D4-7F6, 5D4-7F5, 5D4-7F4, and 5D4-7F3 transitions of Tb3+ ions. The weak emission peak at about 380 nm should be assigned to the emission of Ce3+ ions in the compound.
Fabrication of Photonic Crystals in Microchannels
Authors: Kuo Chun-Wen , Hsieh Hui-Mei , Ting Jung-Chuan , Cho Yi-Hong , Wei Kung Hwa , Chen Peilin
Published: April 2011

We have developed a fabrication procedure for growing photonic crystals in the lithographic defined microchannels, which enables easy integration with other planar optical components. This technique is based on the directed evaporation induced self-assembly of nanoparticles in the microchannels. Substrates with pre-patterned microchannels (30-100 μm wide) were dipped into solution of nanoparticles for several days. By controlling the evaporation rate, the meniscus contacting the microchannels will undergo evaporation-induced self-assembly. The capillary forces cause nanospheres to crystallize within the microchannels forming colloidal photonic crystals in the microchannels. Two types of colloidal particles, polystyrene and silica, have been employed to fabricate colloidal photonic crystals in the microchannels. Both types of colloidal particles were found to form large-area well-ordered colloidal single crystals in the microchannels. The optical reflection spectra from the (111) surfaces of the colloidal crystals formed by various sizes of nanoparticles have been measured. And the measured reflection peaks agree with the photonic bandgap calculated by the plane wave expansion method.
Template-Assisted Growth of Nanowires Using Novel Nanoporous Films Fabricated by Inorganic Nano Phase Separation
Authors: Fukutani Kazuhiko , Motoi Taiko , Den Tohru
Published: April 2011

Ultrahigh pore density nanoporous films with a pore diameter of less than 10nm and a pore density exceeding 1016 pores/m2 were developed. Nano phase separation of a eutectic Al-Si system was used for the fabrication of these nanoporous films. Co-sputtered AlSi films form Al nano-cylinders, perpendicular to the substrate and parallel to each other, embedded in an amorphous Si matrix during film growth due to phase separation. Removal of the Al nano-cylinders from the co-sputtered AlSi films by chemical etching gives us ultrahigh pore density nanoporous films. The nanoporous films consist of mainly oxidized silicon. Depending on the film compositions and the film preparation conditions, such as RF power and the deposition temperature, the average pore diameter can be varied systematically from less than 5nm to 13nm with the pore density from 1015 to exceeding 1016 pores/m2. Furthermore we have demonstrated a template-assisted growth of ultrahigh-density Ni nanowire arrays with an aspect ratio of ∼100 in the nanoporous films by electrodeposition. The fabrication method for nanowire arrays using the nanoporous films is quite simple and promising for the fabrication of nanostructured devices.
Simple Fabrication of High Density Quantum Dot Arrays Using Anodic Aluminum Oxide Mask
Authors: Sung Joon-Ho , Moon Heesung , Bahng Jae Ho , Koo Ja-Yong , Kim Bongsoo
Published: April 2011

We fabricated quantum dot arrays using anodic alumina mask. We grew an alumina template on Si wafers by two-step anodization. The porous alumina template thus grown is used as a mask for metal deposition. After thermal evaporation and removal of the mask, we fabricated the quantum dot arrarys on a Si substrate. Using this template-assisted method we obtained a high density array of quantum dots in a large scale. These quantum dots have a narrow size distribution which can be easily controlled by a pore widening of templates from 20 to 60 nm.
Surface Oriented Self-Assembly of Carbon Nanotubes
Authors: Sivakumar Kousik , Panchapakesan Balaji
Published: April 2011

In this paper, we demonstrate the self assembled growth of nanotubes along the surface of (100), (110) and (111) silicon wafers using thermal CVD. Iron nanoparticles, 10 nm in diameter, were used as the catalyst. Carbon nanotubes were grown in a methane atmosphere at 1000°C. SEM and AFM characterization revealed single wall carbon nanotubes, about 10 nm in diameter and up to 10 νm in length, growing along the <111> direction of the silicon wafer. The mechanism of growth of nanotubes is similar to that of molecular epitaxy which occurs due to the lattice matching of the silicon and iron crystal lattices forming self aligned silicides at high temperature which help orient the nanotubes. This process may enable the integration of nanotubes with CMOS processing technology.
Analysis of the Three-Dimensional Nanoscale Relationship of Ge Quantum Dots in a Si Matrix Using Focused Ion Beam Tomography.
Authors: Kubis Alan J. , Vandervelde Thomas E. , Bean John C. , Dunn Derren N. , Hull Robert
Published: April 2011

It is well documented that buried layers in quantum dot (QD) superlattices influence the position of quantum dots in the subsequently grown layers through strain field interactions (e.g.1,2, 3,4). Using the Focused Ion Beam (FIB) tomographic technique we have reconstructed the 3D relationship of successive layers of coherent Ge QDs separated by epitaxial Si capping layers - a “QD superlattice”.

Techniques such as Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) can only look at a single surface layer of QDs or, in the case of Transmission Electron Microscopy (TEM), look at a two-dimensional projection of a three-dimensional volume so that 3D relationships need to be inferred. Since the strain interactions are complex, an enhanced fundamental understanding of these self-organization mechanisms can more directly be obtained from full 3D reconstructions of these structures.

By capping with Si at 300°C we were able to grow QD superlattices with QDs tens of nanometers in height. This places them within the resolution of the FIB tomographic technique to reconstruct. Using the FIB we performed in-situ serial sectioning of the QD superlattice and then reconstructed the QD superlattice. The reconstruction was then analyzed to investigate the ordering of the QDs.

Results from a reconstruction of a superlattice matrix will be presented with analysis of the self-ordering of the QDs. Observations of a novel self-limiting (in height) morphology, the quantum mesa, associated with the capping technique used will also be discussed.
Templated Formation of Ordered Metallic Nano-Particle Arrays
Authors: Giermann Amanda L. , Thompson Carl V. , Smith Henry I.
Published: April 2011

We have used interference lithography to create surfaces with di-periodic topography with periods less than 400 nm and formed gold particle arrays on these substrates through the dewetting of thin solid films. Under appropriate conditions, we have found that dewetting of gold films on di-periodic arrays of {111} bound pits in silicon leads to periodic square arrays of particles with very narrow size distributions. In addition, we find that topography can significantly reduce the diameter of particles formed by the dewetting process. We present a mechanism for this self-organization process based on modulation of the local curvature of a conformal film on topography.
Biotemplate Synthesis of Ag Nanoparticles and Nanowires
Authors: Behrens S. , Unger E. , Wu J. , Habicht W. , Dinjus E.
Published: April 2011

We address the template-directed deposition of metals on microtubule supports for generating metal nanostructures with different morphologies. Microtubules are highly ordered protein assemblies of tubular structure with a high aspect ratio. In this approach, the biostructure serves as a functionalised scaffold where the metal is generated in situ and shaped into a nanostructure with its morphology complementary to that of the biotemplate. When the biotemplate is coupled to an appropriate chemical reaction, different Ag / protein structures are produced, ranging from microtubules densely covered by small Ag nanoparticles to continuous Ag nanowires.
Preparation and Characterization of Tin Oxide Nanowires for Gas Sensing
Authors: Zhang Daihua , Liu Zuqin , Li Chao , Zhou Chongwu
Published: April 2011

Efficient and reliable laser-ablation approaches for large-scale synthesis of SnO2 nanowires are reported. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) were used to confirm the crystal structure of the nanowires. The results show that these nanowires had uniform diameters around 20 nm and lengths in the order of 10 νm. In addition, field effect transistors have been constructed based on individual SnO2 nanowires. Excellent n-type transistor characteristics have been observed for SnO2 nanowire transistors. Detailed analysis revealed threshold voltages ∼ -50V with on/off ratios as high as 103 at room temperature. These nanowire transistors were further demonstrated to work as sensitive UV detectors and gas sensors.
The Strain-Assisted Nucleation and Growth Behavior of Co Islands: An Indirect Study of Nanopatterning Using the Remanent Magnetization Measurement (Δm)
Authors: Lee Yong-Won , Clemens Bruce M.
Published: April 2011

Nanopatterning through strain-assisted nucleation of metal adatom islands is experimentally studied using a magnetic remanence or Δm measurement. The strain field is generated by a square array of interfacial misfit dislocations with a spacing of 4.1 nm due to the lattice mismatch of the epitaxial Pt(002) film on MgO(002) substrates. The intensity of strain is controlled by changing the thickness of the Pt underlayer ranging from 2.0 to 10.0 nm. The amount of exchange coupling among the Co grains grown on Pt template is measured using the μm technique as an indirect indicator of magnetic grain distribution. From the measured μm values, the morphology of adatom islands is indirectly deduced. The Co islands on a 5.0 nm thick Pt underlayer show the overall negative behavior of Δm curve, i.e., the strongest nanopatterning effect. Strain driven nucleation is found to be achievable through a narrow selection of experimental growth conditions.
Covalent immobilization of DNA and hybridization on microchips by microsecond electric field pulses
Authors: Fixe F. , Branz H.M. , Prazeres D.M.F. , Chu V. , Conde J.P.
Published: April 2011

Single square voltage pulses were used to enhance by 7 and 9 orders of magnitude the rate of covalent immobilization and hybridization, respectively, of single stranded DNA probes on a chemically functionalized thin film surface (silicon dioxide) using 2 mm size electrodes. These electrodes were scaled down to 20 μm. Photolithography was used to define the electrode voltage line, ground line, and functionalized thin-film area on a plastic substrate (polyimide). At all electrode dimensions, electric field-assisted DNA immobilization and hybridization can be achieved in the microsecond time scale, far faster than the 2 hr or 16 hr needed for immobilization and hybridization, respectively, without the electric field. Pulse conditions optimized with the large-size electrodes (2 mm) were used in the microelectrodes.
Characterization of Alumina and Silica Sol-Gel Encapsulated Fe/Co/Ru Nanocatalysts in Microchannel Reactors for F-T Synthesis of Higher Alkanes
Authors: Kuila D. , Nagineni V.S. , Zhao S. , Indukuri H. , Liang Y. , Potluri A. , Siriwardane U. , Seetala N. , Fang J.
Published: April 2011

We have been investigating conversion of syngas (CO: H2) to higher alkanes [Fischer-Tropsch (F-T) Process] in 5 μm and 25 μm channel microreactors coated with sol-gel encapsulated Fe/Co-nanocatalysts. These nano-metal-catalysts were incorporated into the sol-gel matrix by two methods: 1) metal nitrate solutions; 2) metal oxide nanoparticles. Characterization of these catalysts containing Co and Fe in alumina and silica sol-gel has been carried out by several techniques. The surface area measurements by BET method show an average specific surface area of 285 m2/g for alumina and 300 m2/g for silica sol-gel encapsulated catalysts. In order to optimize the sol-gel preparation and deposition in the microchannels, the elemental composition of sol-gel encapsulated catalyst was examined by EDX. The SEM and AFM images of the reactors before and after deposition of the catalysts have also been studied. Hydrogenation-reduction efficiency of the activated Fe-Co catalysts and the level of poisoning after the reaction were estimated using a vibrating sample magnetometer (VSM). The result suggests more efficient reduction in the case of the nano-particle metal oxides compared to that derived from metal nitrate solutions. In overall, 85% of the catalyst is poisoned after 25 hrs of catalytic reaction. The surface area and the syngas conversion results indicate that silica sol-gel matrix may be a better catalyst support. For alumina sol-gel support, higher conversion of syn-gas is observed with 25 μm microreactor channels. For silica sol-gel, syngas conversion as high as 73% has been achieved by adding Ru as a promoter to the Fe/Co catalyst mixture.
Photophysical Properties of CdS Nanoparticles in Thin Films for Opto-Chemical Sensing
Authors: Guliants Elena A. , Haruff Barbara A. , Gord James R. , Bunker Christopher E.
Published: April 2011

In recent years, II-VI compound semiconductor nanoparticles synthesized in a liquid solution have been shown to possess unique optoelectronic properties which are highly attractive for the fabrication of various sensors based on the optical signal readout scheme. The challenge has been to immobilize these nanoparticles into films on solid surfaces, i.e. on a chip, so that they do not suffer any property deterioration as a sensing medium. In the presented work, synthesis of CdS nanoparticles in reverse micelle solution using AOT surfactant as a stabilizer has led to particles with relatively bright photoemission identified as originating from both shallow and deep traps inside the bandgap. Moreover, slightly altering the preparation procedure has produced samples with two distinctive crystal structures. Both types of CdS nanoparticles suspended in commonly utilized solvents such as chloroform and hexane were subject to chemical quenching when various organic compounds were introduced into the solution, demonstrating the sensitivity of trap states to their chemical environment. However, the two structures have shown very different optical properties. While post-synthesis treatment had no effect on one type of particle, the other type was able to undergo a photochemical reaction via prolonged UV irradiation, which resulted in an increased luminescence quantum yield ÖL from 2% to 14%. The same particle type was also responsive to thermal treatment, showing even higher values of ÖL (∼40%). The CdS/AOT particles have been cast into thin films by spin-coating on a Si wafer. Coating parameters have been investigated in order to achieve optimal control over the film thickness, uniformity, overall film durability, etc. These nanostructured films capped with various porous polymeric and sol-gel protective coatings were exposed to a series of organic compounds. Photoluminescence data collected for these samples served for identification of the compounds and their concentrations. This paper offers the discussion of photophysical response in CdS nanoparticle-based thin films with respect to development of novel nanostructured opto-chemical sensors.
NanoLiterBioReactor: Monitoring of Long-Term Mammalian Cell Physiology at Nanofabricated Scale
Authors: Prokop Ales , Prokop Zdenka , Schaffer David , Kozlov Eugene , Wikswo John , Cliffel David , Baudenbacher Franz
Published: April 2011

There is a need for microminiaturized cell-culture environments, i.e., NanoLiter BioReactors (NBRs), for growing and maintaining populations of up to several hundred cultured mammalian cells in volumes three orders of magnitude smaller than those contained in standard multi-well screening plates. Reduced NBR volumes would not only shorten the time required for diffusive mixing, for achieving thermal equilibrium, and for cells to grow to confluence, but also simplify accurate cell counting, minimize required volumes of expensive analytical pharmaceuticals or toxins, and allow for thousands of culture chambers on a single instrumented chip. These devices would enable the development of a new class of miniature, automated cell-based bioanalysis arrays for monitoring the immediate environment of multiple cell lines and assessing the effects of drug or toxin exposure. The challenge, beyond that of optimizing the NBR physically, is to detect cellular response, provide appropriate control signals, and, eventually, facilitate closed-loop adjustments of the environment--e.g., to control temperature, pH, ionic concentration, etc., to maintain homeostasis, or to apply drugs or toxins followed by the adaptive administration of a selective toxin antidote. To characterize in a nonspecific manner the metabolic activity of cells, the biosensor elements of the NBR might include planar pH, dissolved oxygen, and redox potential sensors, or even an isothermal picocalorimeter (pC) to monitor thermodynamic response. Equipped with such sensors, the NBR could be used to perform short- and long-term cultivation of several mammalian cell lines in a perfused system, and to monitor their response to analytes in a massively parallel format. This approach will enable automated, parallel, and multiphasic monitoring of multiple cell lines for drug and toxicology screening. An added bonus is the possibility of studying cell populations with low cell counts whose constituents are completely detached from typical tissue environment, or populations in controlled physical and chemical gradients.
Implanted 3D Micro/Nano-Structure Fabrication: New Processing Techniques for the Creation of Nanoscale Opto-Mechanical Machines in Silicon Dioxide on a Silicon wafer
Authors: Abraham Meg
Published: April 2011

A novel method of making nanoscale devices in silicon dioxide on a silicon wafer has been developed in our laboratory. The method is both inexpensive and can be fully integrated with existing VLSI type electronic processing technology. The devices are defined using conventional micronscale photolithography and then reduced in scale during the processing sequence to form nanoscale structures. Further, since the structures are defined using lithography, they can be made to span the range of scales from macro to nano in one processing step. Finally, we have found that by using laser assisted chemical etches, we can “release” these very fine structures without the damage associated with wet processes such as stiction.
Fabrication of 2-D and 3-D Photonic Bandgap Structures Using Laser-assisted Imprinting of Self-assembled Particles
Authors: Lu Y.F. , Li L.P. , Mendu K.K. , Shi J. , Doerr D.W. , Alexander D.R.
Published: April 2011

Fabrication of 2-D and 3-D photonic bandgap (PBG) structures on silicon substrates using laser-assisted nanoimprinting of silica particles has been investigated. Monolayers of silica particles, with different diameters ranging from 160 nm to 5 νm, were deposited on silicon substrates by self-assembly. A quartz plate, which is transparent to the laser wavelength of 248 nm, was tightly placed on the substrate surface. A KrF excimer laser beam with the wavelength of 248 nm was vertically irradiated on the quartz/nanoparticle/silicon structure. The silica particles were imprinted into silicon substrates by the quartz to form a 2-D PBG structure due to the transient Si surface melting during the laser pulse. 3-D PBG structures can be fabricated by directly imprinting multilayer self-assembled silica particles into Si substrates. They can also be fabricated by repeating a process cycle of silica nanoparticles self-assembly, amorphous Si layer deposition, and simultaneous laser melting, imprinting and recrystallization.
Synthesis and Self-Assembly of Metal-Coated Nanoparticles
Authors: Park W. , Borsa T.
Published: April 2011

We report theoretical and experimental studies on the metal-dielectric photonic crystal structure, which is constructed by the self-assembly of metal-coated nanoparticles. The finite- difference time-domain (FDTD) simulations were carried out to predict the width and position of the 3D photonic bandgap. For fabrication, we first prepared gold-embedded silica nanoparticles containing extremely small gold nanoparticles. The core particles are then immersed in a gold- containing solution in which the gold shells were formed by subsequent reduction. Formation of continuous shells was confirmed by scanning electron microscope (SEM) and the optical response due to the surface plasmons. We also performed self-assembly of both the gold- embedded core particles and metal-coated particles. SEM micrographs showed the formation highly ordered structures. The optical reflectance spectra exhibited shifts of the Bragg reflection peak due to the change in refractive index produced by gold nanoparticles.
Anatase Inverse Opal: Preparation and Electrochemical Properties
Authors: Zukalova Marketa , Kalbac Martin , Kavan Ladislav , Heyrovsky J.
Published: April 2011

Anatase inverse opal was synthesized both in the powder form and in the thin layer by means of templating with latex spheres. The voids between close-packed latex particles were filled via deposition from the titanium (IV) isopropoxide solution, electrochemical deposition from the solution of TiCl3, and liquid phase deposition from the (NH4)2TiF6 solution. The resulting material exhibited a regular fcc ordering of macropores surrounded with the framework consisting of the anatase nanocrystallites of 20 nm in size. Electrochemical performance for lithium insertion of anatase inverse opal was sluggish compared to that of non-templated anatase with more dense packing of nanocrystals.
Investigation of the Layer-by-Layer Assembly of Colloid Crystals on a Templated Substrate
Authors: Grego Sonia , Jarvis Thomas , Stoner Brian , Lewis Jay
Published: April 2011

We investigated the fabrication of a 3D colloid crystal assembled in a layer-by-layer fashion on a template substrate. This method of assembling an ordered structure offers flexibility in the choice of crystal orientation, because of the template, and the capability to insert a “defect” layer to introduce defect modes in the stop bands of the crystal. The assembly of layers of 4.4 νm polystyrene microspheres on the patterned (100) substrates was studied using a combination of evaporation and chemical binding. It was observed that the ordering process depends on the physical parameters of the template such as well size and depth. A good adhesion of the beads to the template required chemical functionalization of the substrate.
Constrained Grain Boundary Diffusion In Thin Copper Films
Authors: Buehler Markus J. , Hartmaier Alexander , Gao Huajian
Published: April 2011

In a recent study of diffusional creep in polycrystalline thin films deposited on substrates, we have discovered a new class of defects called the grain boundary diffusion wedges (Gao et al., Acta Mat. 47, pp. 2865-2878, 1999). These diffusion wedges are formed by stress driven mass transport between the free surface of the film and the grain boundaries during the process of substrate-constrained grain boundary diffusion. The mathematical modeling involves solution of integro-differential equations representing a strong coupling between elasticity and diffusion. The solution can be decomposed into diffusional eigenmodes reminiscent of crack-like opening displacement along the grain boundary which leads to a singular stress field at the root of the grain boundary. We find that the theoretical analysis successfully explains the difference between the mechanical behaviors of passivated and unpassivated copper films during thermal cycling on a silicon substrate. An important implication of our theoretical analysis is that dislocations with Burgers vector parallel to the interface can be nucleated at the root of the grain boundary. This is a new dislocation mechanism in thin films which contrasts to the well known Mathews-Freund-Nix mechanism of threading dislocation propagation. Recent TEM experiments at the Max Planck Institute for Metals Research have shown that, while threading dislocations dominate in passivated metal films, parallel glide dislocations begin to dominate in unpassivated copper films with thickness below 400 nm. This is consistent with our theoretical predictions. We have developed large scale molecular dynamics simulations of grain boundary diffusion wedges to clarify the nucleation mechanisms of parallel glide in thin films. Such atomic scale simulations of thin film diffusion not only show results which are consistent with both continuum theoretical and experimental studies, but also revealed the atomic processes of dislocation nucleation, climb, glide and storage in grain boundaries. The study should have far reaching implications for modeling deformation and diffusion in micro- and nanostructured materials.
Modeling the Elastic Fields in Epitaxially Grown Multilayers
Authors: Vanamu Ganesh , Khraishi Tariq A. , Datye Abhaya K. , Zaidi Saleem H.
Published: April 2011

A model was developed to calculate the elastic fields, including strain energy density, in multilayers grown epitaxially on a planar substrate. This model works well for compliant and non-compliant substrates. In particular we illustrate the model for four layer heterostructure and apply it for graded Ge (SixGe1−x) grown on a planar silicon substrate. Using the equations for static equilibrium and Hooke's law for isotropic materials under a plane stress condition, the elastic fields associated with each layer were calculated. The strain partitioning in this model reduces to the limiting case of a two- layer structure available in the literature. As it turns out here, strain partitioning is a function of the bulk unstrained lattice parameters, elastic constants and thicknesses of the layers. The model was qualitatively verified by comparing the strain energy density with the dislocation density away from a relatively thick substrate. This model helps shed some light on the factors important in achieving defect free multilayers for optoelectronic devices.