bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Mechanical and Tribological Behavior, and Surface Characteristics of CMP Pads
Authors: Sikder A. K. , Irfan I. M. , Kumar Ashok , Belyaev A. , Ostapenko S. , Calves M. , Harmon J. P. , Anthony J. M.
Published: April 2011

Chemical Mechanical Planarization (CMP) occurs at an atomic level at the slurry/wafer interface and hence slurries and polishing pads play a critical role in the successful implementation of this process. Surface roughness, visco-elastic properties, thickness and pore size also play an important role in this process. Unfortunately the mechanical properties of polyurethane polishing pads used in CMP are poorly understood. Here we have studied the mechanical and visco-elastic properties and surface morphology of CMP pads using nano-indentation and dynamic mechanical analysis along with high resolution scanning electron microscopy. A state-of-the-art Universal Micro-Tribometer was used to measure the pad deformation behavior under load. A novel non-destructive scanning ultrasonic transmission technique was also used to characterize inhomogeneity of the visco-elastic properties of full-size CMP pads. Results obtained by different techniques were analyzed to demonstrate methods for quick and reliable evaluation of pad quality for current CMP technology.
Interplay Between Copper Electroplating and Chemical Mechanical Planarization
Authors: Watts David K. , Chikamori Yusuke , Kohama Tatsuya , Kimura Norio , Mishima Koji , Hongo Akihisa
Published: April 2011

The introduction of Chemical Mechanical Polishing (CMP) into semiconductor device processing brought a significant need for wet chemistry research and development in this industry. With the transition from aluminum to copper for advanced interconnect metallization came a tremendous amount of electrochemical research and process development towards a production worthy copper CMP process capable of meeting the stringent specifications of dual damascene integration.In addition, the dual damascene integration scheme introduced copper deposition challenges that brought significant activity in developing another wet chemistry process, electroplating. These two sequential, chemical processes have been shown to have significant interaction that has created significant challenges in process integration.
Analysis of Copper to Tantalum Transition in Copper Cmp
Authors: Kang J.M. , Wu S. , Selvaraj T. , Foo P.D.
Published: April 2011

The evolution from Cu to Ta surface during Cu CMP has been investigated. As a first step of Cu CMP, removing excess Cu on field area to Ta often gives rise to topography issues such as dishing or erosion. The exposure of Ta is detected by in-situ reflectance measurement, where the downward slope-start signifies the beginning of Ta exposure. For blanket wafers, the maximum remaining Cu thickness at slope-start increases with initial Cu thickness. Applying lower polishing pressure and table speed, so-called soft landing, near the Cu-Ta transition stage results in thicker remaining Cu. In patterned wafers, Ta exposure starts near high pattern density areas such as wide lines, and contrary to blanket wafers, remaining Cu thickness at slope-start cannot be correlated simply with initial Cu thickness. In this experiment, with increasing initial Cu thickness, remaining Cu thickness at slope-start decreased. The amount of dishing is largely proportional to the initial Cu thickness.
Direct Measurement of Planarization Length for Copper Chemical Mechanical Planarization Polishing (CMP) Processes Using a Large Pattern Test Mask
Authors: Lefevre Paul , Gonzales Albert , Brown Tom , Martin Gerald , Tugbawa Tamba , Park Tae , Boning Duane , Gostein Michael , Nguyen John
Published: April 2011

Wehaveusedalargepatterntestmaskandaspecificarrangementofstructuresonawaferfor direct measurement of an average planarization length for copper chemical mechanical polishing (CMP)processes.Weproposenewminimum,maximum,andaverageplanarizationlengthdefini-tions, based on up and down area measurements as a function of trench width. The average pla-narizationlengthisusefulforqualitativelycomparingtheplanarizationcapabilityofcopperCMP processes. We have also performed several experiments that show how the average planarization length depends on polish process settings such as down force and relative speed, as well as on consumables such as pad and slurry.
Wafer Nanotopography Effects on CMP: Experimental Validation of Modeling Methods
Authors: Lee Brian , Boning Duane S. , Baylies Winthrop , Poduje Noel , Hester Pat , Xia Yong , Valley John , Koliopoulus Chris , Hetherington Dale , Sun HongJiang , Lacy Michael
Published: April 2011

Nanotopography refers to 10-100 nm surface height variations that exist on a lateral millimeter length scale on unpatterned silicon wafers. Chemical mechanical polishing (CMP) of deposited or grown films (e.g., oxide or nitride) on such wafers can generate undesirable film thinning which can be of substantial concern in shallow trench isolation (STI) manufacturability. Proper simulation of the effect of nanotopography on post-CMP film thickness is needed to help in the measurement, analysis, diagnosis, and correction of potential problems.

Our previous work has focused on modeling approaches that seek to capture the thinning and post-CMP film thickness variation that results from nanotopography, using different modeling approaches. The importance of relative length scale of the CMP process used (planarization length) to the length scale of the nanotopography on the wafer (nanotopography length) has been suggested.

In this work, we report on extensive experiments using sets of 200 mm epi wafers with a variety of nanotopography signatures (i.e., different nanotopography lengths), and CMP processes of various planarization lengths. Experimental results indicate a clear relationship between the relative scales of planarization length and nanotopography length: when the planarization length is less than the nanotopography length, little thinning occurs; when the CMP process has a larger planarization length, surface height variations are transferred into thin film thickness variations. In addition to presenting these experimental results, modeling of the nanotopography effect on dielectric CMP processes is reviewed, and measurement data from the experiments are compared to model predictions. Results show a good correlation between the model prediction and the experimental data.
A Planarization Model in Chemical Mechanical Polishing of Silicon Oxide using High Selective CeO2 Slurry
Authors: Lee Jong Won , Yoon Bo Un , Hah Sangrok , Moon Joo Tae
Published: April 2011

This paper attempts to establish planarization model in chemical mechanical polishing of silicon oxide using high selective ceria slurry. Though removal rate of the high area is increased due to a high pressure focused on the area with abrasive and pad, the removal rate of the same area is not increased but decreased even in the very beginning of polishing with ceria slurry. It also observed that only the elevated area is polished and dishing is not occurred during the polishing in high selective ceria CMP. In this work, it is proposed that ceria abrasives are filled in the low trench area and then support the pad as well as high area during the CMP, which results in planarization without dishing.
A Characterization of New Cleaning Method Using Electrolytic Ionized Water for Poly Si Cmp Process
Authors: Miyashita N. , Uekusa Shin-ichiro , Seta S. , Nishioka T.
Published: April 2011

A Trench isolation technology has been developed and applied to high-speed bipolar LSI production. In general, the wafer surface after a conventional ploy-Si Chemical-Mechanical-Polishing (CMP) is contaminated with silica particles and chemical impurities. These contaminations produce some unexpected patterns and crystal defects in the wafer surface layer after oxidation. It is difficult to remove them by the conventional cleaning techniques. Therefore, we have established the new post CMP cleaning method, using the electrolytic ionized water containing chemical additive of a small quantity. The anode water has the cleaning effect for the metallic and organic contaminations, and the cathode water has the removing effect for the particles and the etching effect for the poly-Si surface. For this new cleaning process, it is important to avoid the chemical mechanical damages on the surface and to control the surface roughness. Our experimental work has been focused on the large numbers of the remaining particle and the surface roughness using a particle counter and an atomic force microscopy (AFM). We herein report the properties of the electrolytic ionized water and the examined results of poly-Si surface after CMP process. It was found that the electrolytic ionized water is effective for surface control, and the new cleaning process is useful for CMP process.
MOCVD ZnS:Mn Films: Grain Size Distribution and Crystal Structure as a Function of the Growth Parameters
Authors: Dunn Kathleen A. , Dovidenko Katharine , Topol Anna W. , Oktyabrsky Serge R. , Kaloyeros Alain E.
Published: April 2011

Zinc sulfide doped with manganese is extensively used for thin film electroluminescent device applications. In order to assess the key material and process challenges, ZnS:Mn layers were fabricated by metalorganic chemical vapor deposition in the 250°-500°C range on an AlTiO/InSnO/glass stack. The microstructure of the ZnS:Mn films was examined by Transmission Electron Microscopy (TEM) as part of a larger study which fully characterizes these films by a variety of structural and chemical characterization techniques, including Rutherford Backscattering, Secondary Ion Mass Spectroscopy, Atomic Force Microscopy, Scanning Electron Microscopy and X-ray Diffraction. For all the growth conditions, the films were found to be polycrystalline having predominantly 2H hexagonal ZnS structure. The ZnS grains are found to grow columnar as the film thickness increases, also widening in the direction parallel to the substrate surface and reaching the 100 - 200 nm average lateral size at the 650 nm film thickness. The presence of the 8H ZnS polytype was detected in the low-temperature ZnS:Mn films by TEM selected area electron diffraction and confirmed by X-ray diffraction analysis. Dark field TEM imaging correlated this 8H ring with very small (∼2.5 nm) grains present throughout the low temperature film with a slightly higher density at the film/substrate interface. The 700°C post-deposition annealing was found to initiate a solid state transformation to the cubic (3C) ZnS crystal structure, and resulted in an average grain size of ∼250 nm at the surface of the annealed film.
Electrode Characteristics of Sputtered Lithium Manganese Oxide Films with Diamond-Like-Carbon Top Layer
Authors: Moon Hee-Soo , Ji Kwang-Sun , Cho Won-Il , Yun Young-Soo , Park Jong-Wan
Published: April 2011

There have been increasing interests in lithium rechargeable batteries, especially microbatteries, with rapid development of portable electronic equipments and MEMS(Micro electromechanical systems) technology. In this work, lithium manganese oxide, as a strong candidate for the battery materials, which is more abundant, stable in ambient state and less toxic than the other oxides such as lithium nickel oxides and lithium cobalt oxides, was deposited by rf magnetron sputter. The effect of thermal treatment on the microstructure and electrode characteristics of lithium manganese oxide cathode was investigated. In electrochemical experiment using liquid electrolyte, half-cell failure would be caused by manganese dissolution, degradation of electrolyte materials during charging/discharging process and so on. In this research we focus on interface reaction problem that would affect the cyclability and lifetime of microbattery. In order to reduce the interface reaction during operation, we introduce DLC(Diamond-like-Carbon) film that has high electrical resistivity, mechanical hardness and chemical stability. DLC film was deposited on sputtered lithium manganese oxide electrode by ECRCVD(Electron Cyclotron Resonance Chemical Vapor Deposition). DLC-top-layer LiMn2O4 film was more stable during charging/discharging reaction and higher discharge capacity in wide voltage windows than LiMn2O4 film.
Have We Found The Final Explanation For The Onset Of Rapid Interlayer Mass Transport?
Authors: Giesen M. , Ibach H.
Published: April 2011

In recent STM experiments on multilayer island decay on Cu(111) in UHV a novel rapid interlayer mass transport was observed. This new transport mechanism may accelerate island stack decay by several orders of magnitude. Initial explanations for the onset of rapid decay events were based on the correlation between the occupation of surface states and the presence of a step edge barrier for adatom hopping over the island edges. We present new experimental data measured for Ag(111) which are in contradiction to the former interpretation of rapid interlayer mass transport. We show that all experimental results may be explained by considering an exchange mechanism when island edges in a stack are in close proximity.
The influence of the internal microstructure on the surface parameters of polycrystalline thin films
Authors: Eisenmenger-Sittner C. , Bergauer A.
Published: April 2011

Physical Vapor Deposition (PVD) processes commonly lead to the formation of polycrystalline thin films due to the effects of island nucleation and growth. Scanning probe Methods such as Atomic Force Microscopy (AFM) or Scanning Tunneling Microscopy (STM) are widely used for the characterization of the film surface. The topographic data obtained from these measurements can be converted to roughness values, Power Spectral Densities (PSD's) or correlation functions.

It is the objective of this paper to evaluate the possibilities to characterize the polycrystalline template which generates the film surface solely by quantities derived from topographic data. For this purpose roughness values, PSD's and correlation functions of polycrystalline Al-Films deposited on glass substrates and from simulated surfaces are compared. The main factors which influence the shape of PSD's and correlation functions are determined and possible connections between the constitution of the polycrystalline template (e. g. shape and size-distribution of the crystalline domains) and the film roughness are discussed.
Nanoindention studies of DC sputtered Cu and Cu/Cr thin films
Authors: Wei G. , Du J. , Rar A. , Barnard J. A.
Published: April 2011

The nanoindentation behavior of DC magnetron sputtered 10 nm Cu and 10 nm Cu/2 nm Cr thin films deposited on Si (100) has been studied using a Hysitron nanomechanical system. X- ray diffraction and X-ray reflectivity were used to measure the film structure and film thickness, respectively. The grain size and orientation of Cu and Cu/Cr thin films were measured by TEM. Atomic force microscopy (AFM) was used to evaluate the surface morphology and roughness. At the same load, the nanoindentaion displacement of Cu/Cr is smaller than that for Cu, i.e., the 2nm thick Cr underlayer enhances the hardness of Cu. X-ray, TEM, and AFM results show that the grain size of Cu/Cr (< 15 nm) is actually larger than Cu (∼ 3 nm) indicating that the inverse Hall-Petch relationship may be operative.
Nucleation and Growth During Tungsten Atomic Layer Deposition on Oxide Surfaces
Authors: George S. M. , Elam J.W. , Grubbs R.K. , Nelson C.E.
Published: April 2011

Nucleation and growth has been studied during tungsten (W) atomic layer deposition (ALD) on oxide surfaces. Auger electron spectroscopy (AES) was utilized to examine the deposition of W during the sequential (A) WF6 and (B) Si2H6 reaction cycles that define W ALD. The AES results displayed an initial nucleation period of ∼10 AB cycles to deposit one tungsten monolayer on SiO2. Subsequently, the W and Si AES signals grew and oscillated dramatically versus WF6 and Si2H6 exposures. The increase in the W AES signal in the growth region was consistent with a W ALD growth rate of 3.5 Å per AB cycle. An examination of the oxygen and tungsten AES signals versus AB cycles indicated that W ALD displayed nearly ideal “layer-by-layer”, Frank- van der Merwe growth after the nucleation period. On Al2O3, the AES results displayed a much shorter nucleation period for W ALD. Only 3 AB cycles were required to deposit one tungsten monolayer. Subsequently, the tungsten film grew at a rate of 3.6 Å per AB cycle. The initial nucleation period and growth mechanism during ALD are important because they will affect the roughness of the resulting ALD film.
Apparatusdevelopment For Diamond Synthesis From Acetone Vapor with Low Energy Consumpution
Authors: Onishi Fumitomo , Hayashi Rie , Takagi Yoshiki
Published: April 2011

We synthesized diamond via gaseous phase of vaporized acetone. Molecular acetone decomposes to two methyl radicals with thermal activation. We propose here a new method for diamond synthesis with these methyl radicals from molecular acetone. With this method, we successfully synthesized diamond particles with shorter experimental time than conventional method. With liquid carbon source, such as acetone, impurity elements will be easily substituted in synthesized diamond thin, film which has wide applications for the future electronic devices.
Reduction of Defect Density in Structures With InAs-GaAs Quantum Dots Grown at Low Temperature for 1.55 [.proportional]m Range.
Authors: Zakharov N.D. , Werner P. , Gösele U. , Ledentsov N.N. , Bimberg D. , Cherkashin N.A. , Bert N.A. , Volovik B.V. , Ustinov V.M. , Maleev N.A. , Zhukov A.E. , Tsatsul'nikov A.F.
Published: April 2011

Transmission electron microscopy (TEM), and photoluminescence (PL) have been used to evaluate defects and the efficiency of defect-reduction techniques in structures with InAs quantum dots (QDs) for the 1.55 µm range grown at low substrate temperature (LT) using molecular beam epitaxy (MBE). We show that capping of the QDs with thin GaAs layer accompanied by growth interruption at 600oC (flash) allows to eliminate large islands, containing dislocations, while the smaller islands containing local defects (e.g. dislocation dipoles) still remain. If the flash procedure is accompanied with further depositing of thin AlAs cap layer, and followed by high temperature (~700oC) annealing (HTA), an almost complete elimination of defects is observed. The structures emit in the range of 1.55 µm due to lateral agglomerates of LTQDs. Simultaneously bright luminescence due to isolated QDs and GaAs matrix are detected at high excitation densities.
Dielectric and Ferroelectric studies of Pb0.85La0.15TiO3Thin Films on solution derived RuO2Bottom Electrodes
Authors: Bhaskar S. , Majumder S. B. , Dobal P. S. , Krupanidhi S. B. , Katiyar R. S.
Published: April 2011

Sol-Gel derived Pb0.85La0.15TiO3PLT15) thin films were deposited on solution derived RuO2/Si, RuO2/Pt/Si and Pt bottom electrodes. Dielectric, tangent loss, hysteresis, J-E, measurements were also carried out on these films. X-ray results established the single phase perovskite formation with no secondary phases of PLT15 thin film on these electrodes. PLT15 thin films on RuO2bottom electrode showed relatively inferior ferroelectric and dielectric behavior as compared to Pt electrode. Low leakage currents (10-8A/cm2at 10 kV/cm) and the observed J-E characteristics have been attributed to poor film-electrode interface. Observed electrical and dielectric properties have been correlated with the film-electrode interface. The interface characteristics were further augmented by depth profile analysis using Auger Electron Spectroscopy.
Magnetism of Cobalt Base Artificial Lattice Films
Authors: Masuda Masataka , Matsumoto Shun , Taka Kunihiko , Yoshitake Naoki , Hayashi Yasunori
Published: April 2011

The Co/Pd and Co/Pd artificial lattice films have attracted much interest by their special magnetization properties. We discussed the effect of the Pt, Pd layer thickness on the magnetic anisotropy, and we showed the effect of the hydrogen ion implantation on the magnetic properties of multi-layered films. The Co/Pt and Co/Pd multi-layered films were formed on Si(111) substrates with molecular beam epitaxy. We did structure analysis, magnetic domain analysis and magnetic properties evaluation with XRD, MFM and VSM, respectively. Among the series of films of 0.4nm Co layer, XRD showed that the film of 1.0nm Pt layer had a highest periodicity and that they had (111) plane orientation completely. The magnetic domain size reduced with the increase of the thickness of Pt layer. We found out that the coercivity decreased linearly as a function of the length of magnetic domain wall in the unit area. The result of VSM showed that the multi-layered films of Pt thickness of less than 2.8nm had perpendicular magnetic anisotropy. The perpendicular anisotropy energy changed by the nonmagnetic layer thickness and had a maximum value for 0.4nm Co 0.4nm/ nonmagnetic metal 1.0nm multi-layered film. After hydrogen implantation into the films, XRD showed that the lattice spacing was swelled with hydrogen dose. Also, MFM observed that the magnetic domain size reduced with the increase of the hydrogen dose. The easy axis of magnetization changed from perpendicular to parallel in the plane with the increase of the hydrogen dose. After evacuation of hydrogen at 473K, perpendicular anisotropy was partially recovered. This phenomenon suggested that the origin of magnetic anisotropy was mainly the lattice mismatch and distortion in the layer interface. But Co/Pd film was not recovered by this thermal treatment. This means that Pd made stable hydride and did not evacuate hydrogen at this temperature.
Temperature Dependence of the Magnetoresistance of Co/Re Superlattices
Authors: Charlton Timothy , Lederman David , Felcher Gian P.
Published: April 2011

Hcp (10.0) Co/Re superlattices were grown by dc magnetron sputtering on sapphire (11.0) substrates with the [00.1] direction of the superlattice in the film plane. The temperature-dependent magnetoresistance (MR) was measured on samples patterned by photolithography from 10 K to 300 K in a 5.5 T superconducting magnet. The pattern allows the measurement of the MR with the current (I) and the magnetic field (H) parallel or perpendicular to the magnetic easy axis (c, the [00.1] direction). Measurements at 5 K on an antiferromagnetically-coupled sample shows dips in the MR near H = 0 when H ∕∕ c and H ⊥ I, dips below the saturation value at H ∼ 2.5 kOe for H ∕∕ c and H ∕∕ I configuration due to the competition between the anisotropic magnetoresistance (AMR) and the giant magnetoresistance (GMR). Since the AMR is dependent on the transport within the ferromagnetic layers, the temperature dependence yields information about the relative magnitudes of interface vs. bulk spin-dependent scattering. Our analysis shows that the GMR is anisotropic and that the spin-dependent scattering occurs predominantly at the interfaces only for certain configurations.
Magnetostriction and Microstructure of As-Deposited and Annealed Co Thin Films
Authors: Brückner Winfried , Hecker Michael , Thomas Jürgen , Tietjen Detlev , Schneider Claus M.
Published: April 2011

The magnetostriction of as-sputtered and annealed 400 nm thick Co films has been studied in longitudinal and transverse magnetic fields. The appreciable change of the magnetostriction behavior after annealing above 250 °C is correlated to grain growth and to the related change of the texture (from nearly randomly distributed hcp-Co crystallites to a c-axes texture perpendicular to the film plane). The magnetostriction behavior in the annealed samples cannot be explained by a domain magnetization within the film plane. It is assumed that a rotation of the spontaneous magnetization out of the film plane occurs due to the development of a perpendicular magnetic anisotropy.
Co/Pd Multilayer Based Recording Layers For Perpendicular Media
Authors: Litvinov Dmitri , Roscamp Thomas A. , Klemmer Timothy , Wu Mei-Ling , Howard J. Kent , Khizroev Sakhrat
Published: April 2011

The results of the experimental study of CoX/Pd multilayer based recording layers for perpendicular recording media are presented. The perpendicular magnetic recording media with multilayer recording layers and high moment soft underlayers were deposited by magnetron sputtering. It is shown how a favorable microstructure of the multilayer films can be achieved by the use of the appropriate buffer layers. The effects of boron addition to the cobalt layer in a multilayer recording layer is described. The feasibility of the aging process that leads to the reduced exchange coupling in the multilayer recording layer, is demonstrated. It is shown that boron addition to the cobalt layer accelerates the aging process.
Ferromagnetic and Structural Properties of Mn-Implanted p-GaN
Authors: Theodoropoulou N. , Hebard A.F. , Overberg M.E. , Abernathy C.R. , Pearton S.J. , Chu S.N.G. , Wilson R.G.
Published: April 2011

High doses (1015 – 5×x1016 cm−2) of Mn+ ions were implanted into p-GaN at ∼350oC and annealed at 700-1000°C. At the high end of this dose range, platelet structures of GaxMn1−xN were formed. The presence of these regions correlated with ferromagnetic behavior in the samples up to ∼250K. At low doses, the implantation led to a buried band of defects at the end of the ion range.
Electrochemical Deposition of FeCo Alloys and FeCo/TiO2 Nanocomposites
Authors: Shao I. , Vereecken P. M. , Cammarata R. C. , Searson P. C. , Chien C. L.
Published: April 2011

Electrochemical deposition of FeCo alloys with 1:1 atomic ratio has proved difficult due to cracking from high stress. By using a sulfamate electrolyte and optimizing other deposition parameters, we successfully electrodeposited high quality FeCo films of 20-25 mm in thickness and 7 mm in diameter. Using a suspension of hard oxide nanoparticles (25 nm TiO2) in the electrolyte, we produced oxide-dispersion-strengthened FeCo/TiO2 nanocomposite films with large grains. Enhanced strength was observed from these nanocomposites relative to pure FeCo alloys as determined from Knoop hardness measurements. In order to further improve the ductility of the alloys, vanadium has been codeposited with FeCo. Some preliminary results of FeCoV alloy deposition are reported.
High Strength Soft Magnetic Composites
Authors: Yu Ronghai , Corte-Real Michelle M. , Gorea Adrian , Ren Libo , Parvizi-Majidi Azar , Xiao John Q.
Published: April 2011

There has been an increasing demand for high temperature soft magnetic materials with mechanical properties better than those of existing commercial materials such as FeCo alloys. We have designed new magnetic composites by reinforcing FeCo alloys with high strength tungsten fibers. The composite materials were fabricated by electrodeposition. In general, the as-deposited composites have a relatively high coercivity Hc and low magnetic permeability μ, because of induced strain during fabrication. After appropriate thermal annealing, the composites have good soft magnetic properties, comparable to commercial bulk alloys. However, the saturation induction is reduced due to the non-magnetic inclusions. The composites also show significant enhancements in yield strength and tensile strength that increases linearly with fiber volume fraction as seen in other common composite materials. In addition, near zero creep is observed at 600 °C under a stress of 600 Mpa. The mechanical properties can be further improved by co-depositing soft magnetic material and Al2O3 onto the fibers. An approximately linear relationship was observed between the coercivity and volume fraction of Al2O3 particles. The square-root relationship was observed between the hardness and the Al2O3 concentration.
Magnetic Properties of Transition Metal-Dendrimer Nanocomposites
Authors: Fry Richard A. , Shull Robert D. , Uppuluri Srinivas , Balogh Lajos
Published: April 2011

Magnetic nanocomposites have been successfully prepared by encapsulating nanosized entities of iron, cobalt, and nickel compounds in poly(amido-amine) (PAMAM) dendrimer hosts. Problems related to the instability of the magnetic structures under the influence of an external electromagnetic field have been overcome by using a solid polystyrene matrix to embed the dendrimer hosts containing the magnetic guests. SQUID magnetometry measurements on these nanocomposites showed that after subtraction of the diamagnetic polymer background, at 300 K all samples exhibited paramagnetic behavior, with susceptibilities of 1.14, 1.68, and 0.70 × 10−6 m3/kg for Fe-, Co-, and Ni-containing samples respectively. The temperature dependence for T<300 K showed typical paramagnetic behavior, with the susceptibility increasing for decreasing temperatures. Curie-Weiss (1/M vs. T) graphs displayed a linear behavior at high temperatures, with temperature axis intercepts (θ) occurring at –139 K (Fe), –16 K (Co), and 0 K (Ni). Negative deviations from Curie-Weiss behavior occurred at T<175 K for the Fe and T<25 K for the Co samples. Magnetic moments calculated from the high temperature Curie constant indicated that Fe, Co, and Ni possessed effective moments of 3.5, 4.4, and 2.8μB. The negative intercepts and the fact that these moments are larger than those expected for metallic transition metals are indicative that these species are probably present in an oxidized form. The low-temperature behavior indicates either superparamagnetic or soft ferromagnetic behavior.
Hybrid High-Temperature Nanostructured Magnets
Authors: Sellmyer David J. , Zhou J. , Tang H. , Skomski R.
Published: April 2011

The hysteretic behavior of two-phase permanent magnets for high-temperature applications is examined. A variety of systems have been synthesized and investigated, including Sm-Co-Cu-Ti bulk magnets, SmCo5:Cu-Ti thin-film materials, and mechanically milled Sm-CoZr magnets. The hybrid character of the material leads to very high room-temperature coercivities, between 30.2 and 43.6 kOe, and to the survival of a comparatively large part of the coercivity at high temperatures (12.3 kOe at 500 °C for SmCo 6.5Cu0.8Ti0.3). The coercivity reflects the structure and chemical composition of the material. When ferromagnetic grains are separated by a ferromagnetic boundary phase, the boundary phase acts as a pinning center, but when the grain-boundary phase has a comparatively low Curie temperature, the high-temperature magnetism of the system is that of a weakly interacting ensemble of magnetic particles. In spite of some residual paramagnetic exchange coupling, which is discussed in this work, this mechanism enhances the coercivity.
In Search of the Molecular Triplet of C60 using Low Temperature Raman Spectroscopy.
Authors: Chambers G. , Dalton A.B. , Byrne H.J.
Published: April 2011

The excited state properties of C60 thin films have been probed in the temperature range 77–273K using Raman spectroscopy. The change in the Raman, 2Ag mode of C60 (whose position is largely independent of temperature) was monitored as a function of the excitation intensity at 514.5nm. This mode normally positioned at 1469cm-1, was seen to shift reversibly to a lower Raman frequency with increasing laser intensity. Two excited state species have been identified. The first, at 1466cm-1 has been associated with the molecular triplet of C60. The second species at 1463cm-1, has been speculated to be an excited state co-operative involving two or more excited states in the solid and is seen to be intrinsic to solid state C60 below the phase transition.
Density Functional Based Tight Binding Study of C2 and CN Deposition On (100) Diamond Surface
Authors: Sternberg Michael , Zapol Peter , Frauenheim Thomas , Carlisle John , Gruen Dieter M. , Curtiss Larry A.
Published: April 2011

A density-functional based tight binding method was used to study elementary steps in the growth of ultrananocrystalline (UNCD) diamond. It was shown previously that C2 dimers are the dominant growth species in hydrogen-poor argon plasmas. Recent experimental evidence shows that nitrogen addition to the plasma profoundly changes the morphology of the UNCD film. CN species are believed to play a major role. Reactions of C2 and CN molecules with reconstructed diamond (100) surfaces were studied. A single CN prefers an end-on attachment to a surface atom on the unhydrided (100) surface with its C end down. It is shown how further C2 addition to the surface leads to CN-mediated diamond growth and how the CN species remain on top of the growing diamond layer.
Spontaneous Formation and Stability of GaP Cage Structures: A Theoretical Prediction of a New Fullerene
Authors: Buda Francesco , Tozzini Valentina , Fasolino Annalisa
Published: April 2011

We report the spontaneous formation of a GaP fullerene cage in ab-initio Molecular Dynamics simulations starting from a bulk fragment. A systematic study of the geometric and electronic properties of neutral and ionized III-V (GaP, GaAs, AlAs, AIP) clusters suggests the stability of hetero-fullerenes formed by compounds with zincblend bulk structure. Our prediction is supported by several indicators: these clusters show closed electronic shells and relatively large energy gaps; the ratio between the cohesive energy per atom in the cluster and in the bulk is very close to the value found for carbon fullerenes of the same size; the clusters are thermally stable up to a temperature range of 1500–2000 K and they do not dissociate when ionized.
SWNT nucleation: Energetics of zipping—edge mechanism
Authors: Rotkin Slava V.
Published: April 2011

A novel mechanism of SWNT nucleation is considered in oppose to an existing model. The latter model based on the formation of a hemispherical carbon bowl nucleus has no correct description within the thermodynamics and kinetics of the nucleation process. The new mechanism can explain the prevalent formation of [10,10] armchair nanotube on the base of the continuum graphene energetics.
Preparation of Carbon Nanotubes by Using Mesoporous Silica
Authors: Kawasaki Shinji , Komiyama Shingo , Ohmori Shigekazu , Yao Akifumi , Okino Fujio , Touhara Hidekazu
Published: April 2011

Carbon nanotubes were synthesized using several mesoporous silica templates with different pore sizes in order to investigate the possibility of controlling the diameter of carbon nanotubes by changing the pore size of the mesoporous silica. TEM observation confirmed that carbon nanotubes with uniform diameter can be obtained by the present method. However, it was found that it is difficult to prepare carbon nanotubes having diameter smaller than ∼20 nm by the present method even if the template with small pore size is used.
Mechanics of multi walled Carbon nanotubes probed by AFM
Authors: Decossas S. , Patrone L. , Comin F. , Chevrier J.
Published: April 2011

Using the AFM tip, nanotubes are caught on a raw sample then deposited on a clean surface with an absolute precision better than 500nm. A nanostructured surface made of smooth Germanium dots on flat silicon was used as deposition sample. Nanotube mechanics is probed by AFM tip induced displacement. Nanotubes are shown to be blocked by Ge dots: it is impossible to induce a controlled displacement of the nanotube over a Ge dot when it is pushed against the dot. Elastic energy due to the bending of the nanotube is at the root of that behavior.
Transformation of Active Carbon to Onion-like Fullerenes Under Electron Beam Irradiation
Authors: Xu Bingshe , Jia Husheng , Zhou Hefeng , Ichinose Hideki , Iwamoto Chihiro
Published: April 2011

The transformation of an active carbon film with Pt nanoparticles to onion-like fullerenes has been in-situ investigated by a high-resolution transmission electron microscope. It was found that the onion-like fullerenes/metals polycrystalline film was formed under electron irradiation. The formation process was consisted of three steps: first, the flakes of onion-like fullerenes were induced by Pt nanoparticles; second, the flakes grew into a few ellipsoidal graphite shell; and third, a gradual reorganization of the formation of quasi-spheroid graphite shells and the bond of Pt particles was took place. It was a composite film of onion-like fullerenes and metal particles. It is suggested that the transformation mechanism involves an irradiation of electron and a catalytic effect of Pt nanoparticles, while any temperature rise due to electron irradiation seems to be negligibly small.
Structural Characterization of GaN Nanowires Fabricated via Direct Reaction of Ga Vapor and Ammonia
Authors: Jacobs R.N. , Salamanca-Riba L. , He M. , Harris G.L. , Zhou P. , Mohammad S. N. , Halpern J.B.
Published: April 2011

We report structural studies of large-scale wurtzite GaN nanowires fabricated by direct reaction of Ga vapor and NH3. This recently reported growth technique [1] demonstrates processing of GaN one-dimensional structures as thin as 26 nm and up to 500 μm in length. This method is both interesting and attractive in that fabrication is carried out without the assistance of template materials as required by other methods. In this study, transmission electron microscopy (TEM) is used to characterize the nanowires, while x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS) data provide supporting structural/compositional analysis. Our structural investigation reveals the presence of thin hexagonal platelets, which we believe play a critical role in the nucleation, growth, and orientation of the wires. In particular, our findings indicate that most of the wires grow along the [2110] direction, normal to the platelet edges.
Electrochemistry in Nanostructered Inorganic Molecular Materials
Authors: Williams Mary Elizabeth , Hupp Joseph T.
Published: April 2011

We have previously described the synthesis of a family of molecular ‘squares’ based on octahedral Re(I) coordination of difunctional bridging ligands. The size and chemical composition of the square cavity is highly tunable, and the inorganic cyclophanes are being actively studied in catalytic, separations, and sensing applications. Electrochemical techniques have been primary methods for characterization of the transport properties of thin films of the nanostructured materials. For example, cyclic voltammetry and rotating disk electrode voltammetry experiments have revealed size-selective permeation by redox probes, where the size cutoff is determined by the internal square dimensions. We have more recently begun to employ scanning electrochemical microscopy to spatially image micropatterned electrodes containing these thin film materials, simultaneously allowing us to obtain permeability data and topographical information. This paper describes data obtained by employing porphyrin-based molecular squares that feature chemically tailored cavities.
Nanocomposites by Covalent Bonding between Inorganic Nanoparticles and Polymers
Authors: Blum Yigal D. , Kambe Nobuyuki , Brent MacQueen D. , Kumar Sujeet , Chiruvolu Shiv , Chaloner-Gill Benjamin
Published: April 2011

A generic approach to chemically facilitate the interactions of nanoparticles with conventional polymers is developed to address the design and processing capability of inorganic-organic nanocomposites. This approach introduces homogeneity to the composite and can be used as a tailoring tool for microstructure architecture.

Nanoparticles produced by NanoGram's technology are excellent for such nanocomposites. Their spherical shape and narrow size distribution assist in the processing of homogeneous blends. High loads of particles within a polymeric matrix can be achieved without losing homogeneity. Alternatively, the particles can be selectively attracted into desired domains.
The Facile Synthesis of Nanocrystalline Semiconductor Quantum Dots
Authors: Wong Michael S. , Stucky Galen D.
Published: April 2011

Current synthetic techniques to high-quality quantum dots (“QD's”) involve organometallic precursors that are hazardous and expensive and require they be rapidly injected into an extremely hot solvent to form the QD's. A new method for synthesizing high-quality CdSe QD's while circumventing these problems has been developed. Different cadmium salts were studied as Cd precursors alternative to dimethylcadmium. High-quality CdSe QD's were found possible with cadmium acetate as the Cd precursor. Changes in solvent temperature and reaction time had a systematic effect on QD particle sizes and the accompanying optical properties. These preliminary results point to a general method for producing high-quality QD's that is safer and much more versatile.
Structural, Optical and Chemical Properties of Zns and Cds Nanoparticles Obtained by an Improved Colloidal Chemistry Synthetic Route.
Authors: Lucia Curri M. , Agostiano Angela , Monica Mario Della , Leo Gabriella , Lomascolo Mauro , Alvisi Marco , Vasanelli Lorenzo
Published: April 2011

In this work an improved synthetic route that exploits a quaternary water-in-oil microemulsion has been used to obtain nanocrystals of ZnS, CdS and their mixed compounds, - CdxZn1-xS - differing by their size and composition and having high crystalline quality, small dimensions and a quite good size distribution. The opportunity offered by the use of water-in-oil microemulsion to immobilize the nanocrystals onto solid substrate by self-assembling to obtain stable adherent layers has also been exploited.

The physical and chemical properties of obtained nanocrystals and layers have been investigated by UV-vis spectroscopy, X-Ray Diffraction X-ray Photoelectron Spectroscopy and Scanning Tunneling Microscopy. The role played by the co-surfactant (pentanol) in controlling nanocrystal size and stability has been discussed.
Chemical Processing of Nanostructured Materials
Authors: Das R. N.
Published: April 2011

Nanocrystalline ( particle diameter less than 50 nm) ceramic powders have been prepared by the rapid evaporation of precursor solutions containing the respective metal nitrates/ hydroxides, triethanolamine (TEA) and sucrose in stoichiometric amounts. Complete evaporation of the solutions yields a fluffy dried precursor mass. Heat-treatment of the precursor mass at low external temperatures (450-700 °C) resulted in the desired nanocrystalline oxides. The oxide system studied are: barium titanate (BaTiO3), lanthanum modified lead zirconate-titanate (PLZT), Nickel ferrite (NiFe2O4) and Calcium Tungstate (CaWO4).
Synthesis, Characterization and Catalytic Activity of Nanometric Complexes
Authors: Mody Kripa , Trivedi Bhavna , Pratap Arun
Published: April 2011

The preparation and characterization of nanostructured materials and catalysts is the focus of intense study in recent years. The micro emulsion technique is one of the chemical methods known for isolation of nano-sized materials and some simple compounds such as AgCl and LiF have been prepared using this technique. However, very few attempts have been made to isolate nano-sized coordination compounds, which are known to be good catalysts.

In the present paper, nano-sized complexes of Cu(II) and Ni(II) with Leucine were prepared by the reaction of metal chloride and the ligand solution in water in oil micro-emulsion medium. N-Heptane was used as oil and sodium salt of dioctyl sulfo succinate (AOT) was used as surfactant to stabilize the emulsion. The complexes were characterized by elemental analysis and spectral studies. The crystallite sizes were determined by XRD studies using single line approximation through Scherrer equation. The X- ray diffraction studies revealed that the crystallite size of the complexes prepared by micro-emulsion technique was smaller than that of the material prepared by conventional method. The difference in particle size was also observed in differential scanning calorimetric (DSC) studies, where in, the reaction peaks were observed at lower temperatures for the complexes prepared by the micro-emulsion technique. The increased surface to volume ratio is expected to give better catalytic behavior.
A ‘Building Block’ Approach To Mixed-Colloid Systems Through Electrostatic Self-Organization
Authors: Galow Trent H. , Boal Andrew K. , Rotello Vincent M.
Published: April 2011

We have developed a highly modular electrostatically-mediated approach to colloid-colloid and polymer-colloid networks using ‘building block’ and ‘bricks and mortar’ self-assembly methodologies, respectively. The former approach involved functionalization of one type of nanoparticle building block with a primary amine and a counterpart building block with a carboxylic acid derivative. After combining these two systems, acid-base chemistry followed by immediate charge-pairing resulted in the spontaneous formation of electrostatically-bound mixed-nanoparticle constructs. The shape and size of these ensembles were controlled via variation of particle size and stoichiometries. In the ‘bricks and mortar’ approach, a functionalized polymer is combined with complementary nanoparticles to provide mixed polymer-nanoparticle networked structures. A notable feature is the inherent porosity resulting from the electrostatic assembly. The shape and size of these ensembles were controlled via variation of particle size, stoichiometries and the order in which they were added.
Bifunctional Electrocatalytic Films with Gold Nanoparticles and Metalloporphyrin: Preparation and Characterization
Authors: Yang Wenjun , Li Xiaoyuan , Yu Nai-Teng
Published: April 2011

Bifunctional electrocatalytic films were prepared employing a layer-by-layer assembly approach. The cation, metalloporphyrin (MP), and the anion, potassium tetrachloroaurate (KAuCl4) were alternatively assembled on glass or indium-doped tin oxide (ITO) supports. The assembled AuCl4- ions were then converted to gold nanoparticles (Aun) under the exposure to ultraviolet light. Film growth at each adsorption step was monitored by UV-Vis absorption spectroscopy and cyclic voltammetry (CV). The formation of gold nanoparticles was characterized by UV-Vis absorption spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Bifunctional electrocatalytic activity of the film was demonstrated in the oxidative detection of nitric oxide (NO) over Aun and the reductive detection of oxygen (O2) over Co(II)P in the same CV scan.
Glass to Icosahedral Phase Transformation in Zr-based Glassy Metals
Authors: Haruyama Osami , Miyazawa Tomoaki , Saida Junji , Inoue Akihisa
Published: April 2011

Electrical properties of icosahedral phases (I-phase) that precipitated in Zr65Al7.5Cu7.5Ni10M10 (M=Ag, Pd), Zr65Al7.5Cu1.25Ni10M5 (M=Ag, Pd), Zr65Pd25Ni10 and Zr70Pd20Ni10 metallic glasses have been investigated. In-situ resistivity change with increasing temperature was measured at a heating rate of 0.67 K/s from room temperature. I-phase transformation was occurred in the supercooled liquid phase for Zr-Al-Cu-Ni-M glasses, followed by the crystallization to stable Zr2Ni- and Zr2Cu-type crystals. Ternary glasses exhibited the I-phase crystallization from the glass solid phase and subsequently the transformation of I-phase to crystal phases like Zr2Ni and Zr2Pd. The resistivity of I-phase decreased together with advancing I-phase precipitation, about 2 % compared to the resistivity of the supercooled liquid phase, for typical Zr65Al7.5Cu7.5Ni10Ag10 glass. On the other hand, Zr70Pd20Ni10 glass showed the resistivity increment of about 5 % just after completing I-phase crystallization. Low temperature conductivity of Zr65Al7.5Cu7.5Ni10Ag10 and Zr70Pd20Ni10 glasses and I-phases may be explained by the weak localization model of conduction electron in the range from about 20 K to room temperature.