Search Results - (Author, Cooperation:L. C. Feldman)

2011-10-01

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

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2012-07-07

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Biomimetic Materials ; Blood Circulation ; Drug Delivery Systems/*methods ; Fibrinolytic Agents/*administration & dosage ; Hemodynamics ; Hemorheology ; Lactic Acid ; Male ; Mesenteric Arteries ; Mesenteric Vascular Occlusion/*drug therapy ; Mice ; Mice, Inbred C57BL ; Microfluidic Analytical Techniques ; Models, Anatomic ; *Nanoparticles ; Polyglycolic Acid ; Pulmonary Embolism/*drug therapy ; Stress, Mechanical ; Thrombosis/*drug therapy/prevention & control ; Tissue Plasminogen Activator/*administration & dosage

1089-7550

AIP Digital Archive

Physics

Traditional techniques for growing Si-Ge layers have centered around low-temperature growth methods such as molecular-beam epitaxy and ultrahigh vacuum chemical vapor deposition in order to achieve strain metastability and good growth control. Recognizing that metastable films are probably undesirable in state-of-the-art devices on the basis of reliability considerations, and that in general, crystal perfection increases with increasing deposition temperatures, we have grown mechanically stable Si-Ge films (i.e., films whose composition and thickness places them on or below the Matthews–Blakeslee mechanical equilibrium curve) at 900 °C by rapid thermal chemical vapor deposition. Although this limits the thickness and the Ge composition range, such films are exactly those required for high-speed heterojunction bipolar transistors and Si/Si-Ge superlattices, for example. The 900 °C films contain three orders of magnitude less oxygen than their limited reaction processing counterparts grown at 625 °C. The films are thermally stable as well, and do not interdiffuse more than about 20 A(ring) after 950 °C for 20 min. Therefore, they can be processed with standard Si techniques. At 900 °C, the films exhibit growth rates of about 15–20 A(ring)/s. We have also demonstrated the growth of graded layers of Si-Ge, and have determined that a strain gradient exists in these layers.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Transparent, conductive indium tin oxide (ITO) films were fabricated by pulsed-laser deposition on substrates held at room temperature. We investigated the relationship between electrical/optical properties of the films and the material stoichiometry, measured by Rutherford backscattering. The lowest resistivity films (∼4×10−4 Ω cm) have excessive oxygen compared with the stoichiometric composition ITO. After annealing in argon at 400 °C for 1.5 h, the oxygen-to-(indium+tin) ratio approaches the stoichiometric composition of 1.5 and resistivities of annealed samples are ∼2.5×10−4 Ω cm. The room-temperature ITO resistivity dependence on chamber gas pressure is explained in terms of a gas-dynamic model and oxygen content of the film. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We have investigated the initial growth of silicon oxynitride films on a clean Si(100) single crystal in a N2O ambient under ultrahigh vacuum conditions using Auger electron spectroscopy and nuclear reaction analysis. Variations in the growth parameters, e.g., exposure, N2O pressure and sample temperature, have been systematically investigated. Nitrogen incorporated in the oxynitride film is distributed in a region close to the film/substrate interface and most nitrogen is incorporated within a film thickness of ∼2.5 nm. These studies find an important application to the semiconductor industry with regard to possible new high quality gate oxide materials. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A (2×1) surface reconstruction distinct from the clean Si(100)-(2×1) surface is formed by depositing boron onto silicon in ultrahigh vacuum. Overgrowth of epitaxial silicon at low temperature preserves a (2×1) superstructure of substitutional boron. Hall-effect measurements at 4.2 K show complete electrical activity for boron coverages of 1/2 monolayer, but additional boron above 1/2 monolayer is not electrically active.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A delta-function-shaped Sb doping spike in Si is prepared by deposition of Sb on Si(001) followed by low-temperature molecular beam epitaxy of Si. The depth profile of the Sb atoms is measured using high-resolution Rutherford backscattering spectroscopy, yielding a depth resolution of 0.3 nm. The observed profile shows two peaks corresponding to the δ-doped layer (of width 0.5 nm) and Sb atoms on the surface. The latter are due to surface segregation of Sb atoms during the growth of the Si cap layer. The surface segregation rate is derived from the observed results at temperatures 70–280 °C. It is larger than the value extrapolated from high-temperature ((approximately-greater-than)400 °C) data by several orders of magnitude and shows a very weak temperature dependence as compared to the high-temperature data. These features indicate a new surface segregation mechanism at low temperature. A mechanism for this anomalous segregation is discussed. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report measurements of the rate of growth of Ga and Sn clusters on clean Si surfaces. The volume rate of growth is linearly dependent on time, consistent with an Ostwald ripening mechanism for island growth. Activation energies for clustering, extracted from the temperature dependence, are shown to be sensitive to the underlying surface structure. This thermodynamical approach to the description of cluster formation is generally useful in determining the operational parameters and ultimate limits to heterostructure growth.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have demonstrated the existence of circumferential persistent currents in Ba2YCu3O7 ceramic toroids at 77 and 4.2 K and in thin films at 77 K. The field dependence of the critical current densities obtained from these persistent current measurements at 77 K is in fair agreement with that obtained from transport measurements. The persistent critical current densities for fields less than 10 G are 150 A/cm2 for the ceramic at 77 K and 105 A/cm2 for the thin film. A long term experiment showed that the resistivity is less than 3×10−18 Ω cm at 77 K.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the observation and characterization of luminescence in the wavelength range 1.1 μm〈λ〈 1.4 μm from silicon-rich silicon-germanium alloys, grown by molecular beam epitaxy, implanted with beryllium atoms. The luminescence originates with the radiative decay of an exciton bound to an isoelectronic impurity complex. The wavelength of this emission can be controlled by varying the Ge concentration.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A model for the morphology of the first layers of GaAs on Si(111) is proposed based on observations of gallium cluster formation on As-terminated Si(111). In this model Ga is mobile and tends to form clusters, but is immobilized by arriving As atoms. Substrate-temperature-dependent ion scattering and transmission electron microscopy investigations are in agreement with this model and allow the extraction of a clustering related activation energy. These results establish conditions necessary for uniform film growth of GaAs/Si at the important film/substrate interface.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have undertaken a new set of experiments to investigate the behavior of adsorbed-impurity induced reconstructions at growth interfaces. We have observed a striking difference in the stability of the B(3)1/2×(3)1/2 and Ga(3)1/2×(3)1/2 two-dimensional structures at the interface between Si(111) and a-Si, and in their segregation behavior during molecular beam epitaxy crystal growth. This leads to a new model of dopant behavior in silicon molecular beam epitaxy.

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1089-7550

AIP Digital Archive

Physics

We report on the use of Rutherford backscattering spectroscopy for thickness analysis of organic light-emitting diode structures (OLEDs) with subnanometer resolution and a spatial resolution 〈1 mm. A careful study of ion beam induced effects revealed some organic film degradation, but not so severe as to inhibit meaningful measurements. The method is independent of the substrate and is still applicable if the organic film is capped with a metal cathode. Common OLED materials have been the subject of this study: poly(2-methoxy,5-(2′-ethylhexoxy)-1,4-phenylene-vinylene (MEH-PPV), N′,N′-diphenyl-N, N′-bis(3-methylphenyl)-1,1′ biphenyl-4,4′-diamine (TPD), and tris-(8-hydroxyquinoline) aluminum (Alq3). The densities of thin films of evaporated TPD (ρ=1.22±0.05 g/cm3) and Alq3 (ρ=1.51±0.03 g/cm3) have been established. © 1998 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

We report a boron δ-doping layer in crystalline silicon with an electrically active concentration of 1×1022 cm−3 and a mobility of ∼20 cm2/V s. This structure was fabricated by low-temperature molecular-beam epitaxy with boron confined to 3 monolayers in the silicon growth direction. Complete electrical activation is observed, showing metallic conduction down to 4 K. This two-dimensional doped layer, incorporated into the crystal lattice, represents a volume concentration exceeding the solid solubility of boron in silicon by two orders of magnitude. These high-concentration structures fill an unexplored region of the mobility versus concentration curve.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The absolute nitrogen concentration in SiOxNy/Si films grown by rapid thermal oxidation in N2O has been determined by nuclear reaction analysis. Compared with conventional surface analysis methods, i.e., Auger electron spectroscopy, x-ray photoelectron spectroscopy, and secondary ion mass spectrometry, the nuclear reaction 14N(d,α)12C provides more accurate depth profiles of 14N due to the quantitative nature of the technique and its high sensitivity, ∼6.0×1013 atoms cm2. Silicon oxynitride films prepared under various conditions, specifically different growing temperatures and times, were analyzed. Nitrogen is observed to accumulate in a narrow region in the oxynitride (within (approximately-less-than)2.5 nm) close to the interface; the total amount of nitrogen increases with increasing temperature and growth time.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Depth profiles of vacancylike defects have been determined by positron annihilation spectroscopy in 200-nm-thick Si films grown by molecular beam epitaxy on Si(100) substrates at growth temperatures Tgrowth=200–560 °C. The line shape of the radiation emitted from implanted positrons annihilating in the near-surface region of a solid gives quantitative, depth-resolved information on defect concentrations in a nondestructive way. In particular, the method is sensitive to vacancylike defects in a concentration range inaccessible to electron microscopy or ion scattering, but important for electrical device characteristics. The sensitivity limit for these defects in the present experiments is estimated as 5×1015 cm−3. Films grown at Tgrowth≥475±20 °C are indistinguishable from virgin wafers. So are samples with Tgrowth=220±20 °C, subjected to a 2 min, TRTA(approximately-greater-than)500 °C rapid thermal anneal (RTA) after every ≈30 nm of Si growth. If TRTA=450±20 °C, part of the film contains a concentration of vacancylike defects on the order of 1018 cm−3. Our results indicate the importance of the growth parameters, such as temperature and substrate preparation, for the production of high quality films.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A scheme for selective electroless copper patterning of Si wafers has been developed with palladium silicide as the catalytic layer initiating copper deposition. Thermal conversion of a palladium layer to silicides on a SiO2 patterned silicon substrate, followed by an acid etching of the unreacted palladium on the SiO2 surfaces, leaves only the silicided regions at the base of the windows for electroless copper deposition. Excellent via-filling down to 0.5-μm dimensions and an aspect ratio of 6 has been demonstrated. The thin copper deposited on the Pd2Si has a resistivity of ∼2.0 μΩ cm. Contactless photocarrier decay measurements indicate virtually no degradation of Si lifetimes by these processing steps.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have compared ion channeling results with molecular dynamics simulations to investigate low-temperature molecular beam homoepitaxy on silicon. We report the temperature dependence, rate dependence, and thickness dependence of films grown on Si(111). For 350 A(ring) films, a transition to good crystalline quality is seen in ion channeling at growth temperatures of ≈400 °C; this is compared to ≈100 °C for (100) epitaxy. The evolution of surface microstructure leading to breakdown of epitaxial growth at low temperatures is discussed.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Oxynitrides can suppress the diffusion of boron from the polycrystalline silicon gate electrode to the channel region of an ultralarge scale integrated device, and are therefore important potential substrates for thin SiO2 gates. Direct oxynitridation of Si in N2O is a simple and manufacturable N incorporation scheme. We have used rapid thermal oxidation to grow O2- and N2O-oxides of technological importance (∼10 nm thick) in the temperature range 800–1200 °C. Accurate measurements of the N content of the N2O-oxides were made using nuclear reaction analysis. N content increases linearly with oxidation temperature, but is in general small. A 1000 °C N2O-oxide contains about 7×1014 N/cm2, or the equivalent of about one monolayer of N on Si (100). Nonetheless, this small amount of N can retard boron penetration through the dielectric by two orders of magnitude as compared to O2-oxides. The N is contained in a Si-O-N phase within about 1.5 nm of the Si/SiO2 interface, and can be pushed away from the interface by O2-reoxidation. We have measured Si/SiO2 interfacial roughness by x-ray reflectometry, and found that it decreases with increasing oxidation temperature for both O2- and N2O-oxides, although the N2O-oxides are smoother. The enhanced smoothness of N2O-oxides is greater the greater the N content. N2O-oxides are promising candidates for thin ultralarge scale integrated circuit gate dielectrics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report a quantitative theoretical and experimental analysis of strain relaxation in GexSi1−x/Si(110) heterostructures. It is shown that above a critical composition, the critical thickness for edge a/6〈112〉 Shockley partial dislocations is less than that for 60° a/2〈110〉 total dislocations. The net (excess) stress is greater on the edge a/6〈112〉 dislocations for epilayer thicknesses, h〈hx, but greater on the 60° a/2〈110〉 dislocations for h(approximately-greater-than)hx. The sensitive calculated dependence of hx upon the stacking fault energy per unit area γ allows an experimental determination of γ=65±10 mJ m−2 for x∼0.3 in GexSi1−x.

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