Search Results - (Author, Cooperation:S. J. Pennycook)

2015-04-18

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2014-11-28

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Computer Systems ; Microscopy/economics/*standards/trends ; Microscopy, Electron/standards ; Nanotechnology/*instrumentation/trends ; Optics and Photonics ; Physics/instrumentation/trends

1089-7550

AIP Digital Archive

Physics

Single-crystal Cu has been ion implanted with C to fluences of 1×1018/cm2 followed by laser annealing with nanosecond pulses from an excimer laser and subsequently etched in dilute nitric acid. Raman spectroscopy, Rutherford backscattering, and electron microscopy have been used to identify the distribution and morphology of the carbon at different stages of sample processing. Polycrystalline graphite and amorphous carbon films are typically produced over a wide range of processing conditions; well-ordered graphite can be formed as well. Small Cu crystallites are seen in areas where the etch lifted the C films off the substrate. However, extensive analysis by Raman spectroscopy and electron microscopy provides no evidence for the formation of the diamond phase of carbon.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

In this work the buildup of damage due to deuterium implantation in highly-oriented pyrolytic graphite (HOPG) is investigated. HOPG was implanted with 10–30 keV D3+ at different target temperatures between room temperature and 773 K with fluences from 1014 to 1018 D/cm2. Subsequently, the damage due to the implantation and the retained deuterium were measured by Rutherford backscattering (RBS) in a channeling direction (RBSc) and by the D(3He, p)α nuclear reaction analysis (NRA), respectively. The damage of selected samples was additionally observed with transmission electron microscopy (TEM). The initial trapping efficiency is unity in the whole temperature and energy range. The maximum retention of the deuterium, however, depends on the temperature and implantation energy. The damage in HOPG measured with RBSc starts to saturate at 5×1015 D/cm2 (295 K) and 1.3×1017 D/cm2 (773 K). Both fluences are well below the fluence at which amorphization is observed in TEM.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

High doses (7×1016–1.3×1017/cm2) of 170-keV Er+ ions were implanted into single-crystal Si at an implantation temperature of Ti=520 °C. During Er implantation ErSi2 crystallizes as coherent precipitates within a crystalline Si matrix. During the subsequent annealing at 800 °C a discontinuous buried layer of the single crystalline ErSi2 is formed. Implanted and annealed samples were subsequently reimplanted with 170-keV Er+ ions at 250〈Ti〈520 °C. The second implantation results in a mesotaxial growth of the previously formed buried single-crystal ErSi2 layer for implantation temperatures Ti(approximately-greater-than)300 °C where ion beam induced, defect mediated diffusion of Er atoms in the Si matrix occurs during the implantation process.

Electronic Resource

1551-2916

Blackwell Publishing Journal Backfiles 1879-2005

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

An understanding of the atomic structure at internal interfaces is of crucial importance for the electronic and structural properties of most advanced materials. Here, we present a detailed study of the atomic structure at a [001] tilt grain boundary of σ5(210) in Tio2 (rutile). Z-contrast imaging is used to obtain a 2-D atomic map of the cation positions at the interface. Details of the charge state of cations and atomic structure around anion sites are then provided using electron energy loss spectroscopy. In particular, the spectroscopic data for oxygen is interpreted using multiple scattering theory to give 3-D structural information. These combined techniques allow a unique grain boundary structure to be defined.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Residual compressive stress due to plume-induced energetic particle bombardment in CeO2 films deposited by pulsed-laser deposition is reported. For laser ablation film growth in low pressures, stresses as high as 2 GPa were observed as determined by substrate curvature and four-circle x-ray diffraction. The amount of stress in the films could be manipulated by controlling the kinetic energies of the ablated species in the plume through gas-phase collisions with an inert background gas. The film stress decreased to near zero for argon background pressures greater than 50 mTorr. At these higher background pressures, the formation of nanoparticles in the deposited film was observed. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Pyrolysis of high-purity digermane (Ge2 H6 ) has been used to grow epitaxial Ge films of high crystalline quality on (100) GaAs substrates in a low-pressure environment. X-ray double-crystal diffractometry shows that fully commensurate, coherently strained epitaxial Ge films can be grown on (100) GaAs at digermane partial pressures of 0.05–40 mTorr for substrate temperatures of 380–600 °C. Amorphous films also were deposited. Information about the crystalline films surface morphology, growth mode, and microstructure was obtained from scanning electron microscopy, cross-section transmission electron microscopy, and in situ reflectivity measurements. The amorphous-to-crystalline transition temperature and the morphology of the crystalline films were both found to depend on deposition conditions (primarily the incidence rate of Ge-bearing species and the substrate temperature). Epitaxial growth rates using digermane were found to be about two orders of magnitude higher than rates using germane (GeH4 ) under similar experimental conditions.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

High quality silicon-on-insulator structures have been formed with dislocation densities in the top silicon layer below 104 cm−2 by oxygen implantation and one-step annealing at 1300 °C for 6 h. Careful control of the implantation conditions is required in order to produce a high density of cavities in the top silicon layer. These cavities provide a stress-free sink for silicon and oxygen interstitials, reducing the point-defect supersaturations and, therefore, the nucleation and growth of oxide precipitates and dislocation loops. They also provide an internal surface which blocks free propagation of dislocation loops to the surface avoiding the formation of threading dislocations. With continued annealing, both the cavities and the oxide precipitates eventually dissolve, leaving a high quality silicon surface layer with a very low dislocation density.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have investigated laser-induced oxidation of ion-implanted Si using a repetitively pulsed ArF laser, working at low-energy density (100–500 mJ/cm2). Oxidation is observed at energy densities between the melt threshold and that required for epitaxial recrystallization of the amorphous layer. At these energy densities, oxidation is not observed on virgin silicon. The factors that influence the oxidation process are discussed.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The dependence of the damage produced by self-ion implantation in Si on dose is determined and is shown to exhibit two distinct behaviors: an initial sublinear increase of damage with dose, followed by a period of greatly accelerated growth. Ion backscattering analysis using both single- and double-alignment channeling measurements is used to determine the distribution of damage in the samples. The nature of the damage is determined from its thermal annealing behavior and differences in the spectra recorded in the two channeling configurations. Damage is found to consist predominantly of two components: simple defects, such as divacancies, and regions of amorphous Si. The behavior of these components is shown to be divergent at the fluence which separates the two different growth regimes. A model is proposed which considers the amorphization process in Si as a critical-point phenomenon, one in which the onset of amorphization leads to a cooperative behavior among the various types of damage resulting in a greatly accelerated transition.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Crystalline GaAs films have been grown epitaxially on silicon and germanium substrates at 400 °C by direct deposition of alternating 69Ga and 75As layers from electromagnetically switched low-energy ion beams. Positive gallium and arsenic ions were extracted simultaneously from a single ion source and mass analyzed prior to deceleration to a controlled deposition energy of 30 or 40 eV. Atomic layers of gallium and arsenic were deposited alternately by switching the analyzing magnetic field repeatedly to select either the 69Ga+ or 75As+ species. The structure and composition of the resulting layers have been characterized by cross-section transmission electron microscopy and ion channeling/backscattering spectrometry. The best crystal quality was obtained for a GaAs layer deposited on Ge using a 30 eV beam. This layer gave an ion channeling minimum yield of ≈6%. These results demonstrate the feasibility of growing isotopically pure, single-crystal compound semiconductor layers at relatively low temperatures by deposition from alternating, fully ionized, low-energy beams.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Pulsed ArF (193 nm) excimer laser photolysis of disilane, germane, and disilane-ammonia mixtures has been used to deposit amorphous superlattices containing silicon, germanium, and silicon nitride layers. Transmission electron microscope cross-section views demonstrate that structures having thin (5–25 nm) layers and sharp interlayer boundaries can be deposited at substrate temperatures below the pyrolytic threshold, entirely under laser photolytic control.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have investigated the microstructure and properties of YBa2Cu3O9−δ that contain resistive transitions at 90 and near 290 K using high-resolution and analytical transmission electron microscopy and Raman scattering techniques. The specimens contain normal orthorhombic (Pmmm space group) phase associated with Tc=90 K, and another phase which we tentatively assign it to be associated with the resistive transitions near 290 K. The new phase has a c axis larger by about 16% and it grows epitaxially on the {100} planes of the orthorhombic (tripled perovskite unit cell) phase having Tc=90 K.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We have investigated the formation of titanium silicide by rapid thermal annealing in nitrogen and argon ambients over polycrystalline silicon. A sheet resistance of about 3 Ω per square for a 300-A(ring) Ti layer was achieved after 900 °C/10-s annealing treatment, which decreased to about 2 Ω per square after 1100 °C/10-s treatment. The silicides were found to be stable during rapid thermal annealing up to 1100 °C/10 s with no or negligible migration of titanium along the grain boundaries in polycrystalline silicon. An external layer (titanium rich, mixture of titanium oxide and nitride) was observed to form during rapid thermal annealing treatment in the nitrogen ambient, but the surface remained clean in the argon ambient.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A new model of a CoSi2/Si(111) interface structure has been generated using images produced by Z-contrast scanning transmission electron microscopy. The images indicate that the top and bottom interfaces between the type-A buried CoSi2 layer and Si(111) both have eightfold coordinated Co atoms. This is accomplished by converting the one interface structure from sevenfold to eightfold coordination by locating a twinned layer of Si at the interface. The preference for this interface over the sevenfold type-A structure is in agreement with theoretical predictions.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Ultrathin YBa2Cu3O 7−x films grown on (001) MgO substrates by pulsed-laser ablation exhibit a transition from terraced-island growth to spiral growth at ∼4–5 unit cell thickness in films grown at 720 °C. The transition appears at greater thickness in films grown at higher growth temperatures. Observations of the morphology of ultrathin films indicate that the film–substrate interfacial interaction plays an important role when films are only several unit-cells thick. Plastic deformation and oxygen disorder both may affect the epitaxial quality and superconducting properties. However, superconducting properties can be improved by achieving a relatively strain-free state. Our observations of the growth transition and resistivity measurements show that this state occurs in the thicker grains of nominally 3.5 nm films grown at 800 °C and in nominally 7 nm films grown at both 720 and 800 °C. These results also imply that a strain-relieving buffer layer will improve the superconductive properties of ultrathin YBa2Cu3O7−x films grown on misfit substrates.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The atomic structure of mesotaxial CoSi2/Si(001) interfaces has been investigated by Z-contrast scanning transmission electron microscopy. The directly interpretable images reveal a 2×1 ordered structure at the interface, which is clearly seen to involve a doubling of the periodicity of the interfacial Co atoms. From these high-resolution images, we deduce a new structure model for the CoSi2/Si(001) interface.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have studied the formation of cuspidal pits during the growth of strained SixGe1−x alloy layers at relatively high supersaturations. The pit formation is directly linked to strain in the alloy layer, and we propose a heterogeneous formation mechanism in which the pits develop from stress-driven surface diffusion associated with a localized initial perturbation of the buffer layer surface. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We demonstrate by ab initio calculations that segregation of As in a dislocation core in Si occurs in the form of an ordered chain of As atoms running along the dislocation pipe. All As atoms in the chain achieve threefold coordination and the segregation energy is close to 1 eV per As atom. © 1997 American Institute of Physics.

Electronic Resource