Search Results - (Author, Cooperation:C. C. Williams)

2014-11-08

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

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Medicine

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Animals ; Endoplasmic Reticulum/metabolism ; Mitochondria/*metabolism ; Mitochondrial Proteins/biosynthesis/chemistry/*metabolism ; *Peptide Chain Initiation, Translational ; Protein Folding ; Ribosomes/*metabolism ; Saccharomyces cerevisiae/genetics/*metabolism ; Saccharomyces cerevisiae Proteins/metabolism ; Succinate Dehydrogenase/metabolism

2014-11-08

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Biotinylation ; Carbon-Nitrogen Ligases/genetics/metabolism ; Cells/*metabolism ; Endoplasmic Reticulum/*metabolism ; Escherichia coli Proteins/genetics/metabolism ; HEK293 Cells ; High-Throughput Nucleotide Sequencing/methods ; Humans ; Membrane Glycoproteins/genetics/metabolism ; Mitochondria/*metabolism ; Phosphoprotein Phosphatases/genetics/metabolism ; *Protein Biosynthesis ; Protein Sorting Signals ; Protein Transport ; Recombinant Fusion Proteins/genetics/metabolism ; Repressor Proteins/genetics/metabolism ; Ribosomes/genetics/*metabolism ; Saccharomyces cerevisiae/genetics/metabolism ; Saccharomyces cerevisiae Proteins/genetics/metabolism

2015-06-13

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Cells/*metabolism ; Endoplasmic Reticulum/*metabolism ; Humans ; Mitochondria/*metabolism ; *Protein Biosynthesis ; Ribosomes/*metabolism

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Several advances have been made toward the achievement of quantitative two-dimensional dopant and carrier profiling. To improve the dielectric and charge properties of the oxide–silicon interface, a method of low temperature heat treatment has been developed which produces an insulating layer with consistent quality and reproducibility. After a standard polishing procedure is applied to cross-sectional samples, the samples are heated to 300 °C for 30 min under ultraviolet illumination. This additional surface treatment dramatically improves dielectric layer uniformity, scanning capacitance microscopy (SCM) signal to noise ratio, and C–V curve flat band offset. Examples of the improvement in the surface quality and comparisons of converted SCM data with secondary ion mass spectrometry (SIMS) data are shown. A SCM tip study has also been performed that indicates significant tip depletion problems can occur. It is shown that doped silicon tips are often depleted by the applied SCM bias voltage causing errors in the SCM measured profile. Worn metal coated and silicided silicon tips also can cause similar problems. When these effects are tested for and eliminated, excellent agreement can be achieved between quantitative SCM profiles and SIMS data over a five-decade range of dopant density using a proper physical model. The impact of the tip size and shape on SCM spatial accuracy is simulated. A flat tip model gives a good agreement with experimental data. It is found that the dc offset used to compensate the C–V curve flat band shift has a consistently opposite sign on p- and n-type substrates. This corresponds to a positive surface on p-type silicon and to a negative surface on n-type silicon. Rectification of the large capacitance probing voltage is considered as a mechanism responsible for the apparent flat band shift of (0.4–1) V measured on the samples after heating under UV irradiation. To explain the larger flat band shift of (1–5) V, tip induced charging of water-related traps is proposed and discussed. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Single and two variant ordered GaInP samples are studied in cross section with the scanning capacitance microscope. Our study shows significant differences in the electronic properties of single and two variant GaInP. In unintentionally doped, ordered two variant samples, both n and p-type like domains are observed with the scanning capacitance microscope. In contrast, a spatially uniform capacitance signal is observed in unintentionally doped single variant ordered GaInP. These microscopic capacitance observations can be qualitatively explained by bend bending or internal electric fields. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Measurement of dopant density in silicon with lateral resolution on the 200 nm scale has been demonstrated with a near-field capacitance technique. The technique is based upon the measurement of local capacitance between a 100 nm tip and a semiconducting surface. Lateral dopant imaging is achieved by the measurement of the voltage-dependent capacitance between tip and sample due to the depletion of carriers in the semiconductor, as the tip is scanned laterally over the surface. Measurements of dopant density have been demonstrated over a dopant range of 1015–1020 cm−3. Capacitance-voltage measurements have been made on a submicrometer scale.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We report the results of a two-step two-dimensional (2D) diffusion study by scanning capacitance microscopy (SCM) and 2D SUPREM IV process simulation. A quantitative 2D dopant profile of a gate-like structure is measured with the SCM on a cross-sectioned polished silicon wafer. The gate-like structures consist of heavily implanted n+ regions separated by a lighter doped n-type region underneath 0.56 μm gates. The SCM is operated in the constant-change-in-capacitance mode. The 2D SCM data are converted to dopant density through a physical model of the SCM/silicon interaction. This profile has been directly compared with 2D SUPREM IV process simulation and used to calibrate the simulation parameters. The sample is then further subjected to an additional diffusion in a furnace for 80 min at 1000 °C. The SCM measurement is repeated on the diffused sample. This final 2D dopant profile is compared with a SUPREM IV process simulation tuned to fit the earlier profile with no change in the parameters except the temperature and time for the additional diffusion. Our results indicate that there is still a significant disagreement between the two profiles in the lateral direction. SUPREM IV simulation considerably underestimates the diffusion under the gate region. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We present data which show that the magnetic force microscope is capable of detecting the component of the magnetic field parallel to the surface of a sample under study. Images of bits in a Co-alloy thin-film disk and of laser-written bits in a TbFe film were taken with a magnetized tip tilted at 45° with respect to the surface normal. In both cases the asymmetric part of the image of a domain is interpreted in terms of gradients in the in-plane component of the magnetic field. The bits written in the Co-alloy disk were decorated with small magnetized particles, allowing identification of the domain boundaries and the asymmetric component of the force microscope image due to in-plane magnetization.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A near-field capacitance microscope has been demonstrated on a 25 nm scale. A resonant circuit provides the means for sensing the capacitance variations between a sub-100-nm tip and surface with a sensitivity of 1×10−19 F in a 1 kHz bandwidth. Feedback control is used to scan the tip at constant gap across a sample, providing a means of noncontact surface profiling. Images of conducting and nonconducting structures are presented.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Noise stemming from mechanical vibration, electronic noise, or low frequency (1/f power spectrum) inherent in the tunneling process, often limits the resolution, speed, or range of application of scanning tunneling microscopy (STM). We demonstrate a technique for minimizing the effect of these noise sources on the STM image. In our method, the tunneling tip is vibrated parallel to the sample surface at a frequency f0, above that of the feedback response frequency. Two signals are obtained simultaneously: the conventional topography, and a differential image corresponding to the amplitude of current modulation at f0. The resultant ac signal can be simply related to the normal STM topographic image, with significant improvement in the signal-to-noise ratio.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A modified version of the atomic force microscope is introduced that enables a precise measurement of the force between a tip and a sample over a tip-sample distance range of 30–150 A(ring). As an application, the force signal is used to maintain the tip-sample spacing constant, so that profiling can be achieved with a spatial resolution of 50 A(ring). A second scheme allows the simultaneous measurement of force and surface profile; this scheme has been used to obtain material-dependent information from surfaces of electronic materials.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A new optical technique is described for measurement of absolute distance. The approach is based upon a wavelength multiplexed heterodyne interferometer with FM demodulation. By temporally multiplexing discrete wavelengths in a heterodyne interferometer, a complete elimination of interferometric range ambiguity can be achieved while maintaining the high range sensitivity and resolution of interferometry. The basic theory is presented and an algorithm is described for measurement of range over meter distances with submicrometer resolution. The experimental implementation of the wavelength multiplexed interferometer is described and ranging results with 2 μm resolution from 20 cm are presented. A scanned three-dimensional map of a surface contour with 3-mm topography is also presented.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Migration of surface ions in lateral fields on insulator surfaces may modify the electrical characteristics of underlying semiconductor structures causing device instabilities. A high sensitivity electrostatic force microscope is used to image the movement and spatial distribution of surface ions on Si3N4. Mobile surface ions are distributed by the fringing fields of a p-n junction and an open-gate field-effect transistor. The surface charge distribution and topography are imaged simultaneously on a micrometer scale.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Shear force microscopy is very useful for distance regulation in near-field scanning optical microscopy (NSOM). However, the optical method used to detect the shear force can cause problems when imaging photosensitive materials, i.e., the shear force detection beam can optically pump the sample. We present here a new approach to shear force detection based upon capacitance sensing. The design, operation, and performance of the capacitance detection are presented. Shear force topographic images of hard and soft surfaces are shown using tungsten and NSOM fiber tips. The closed loop vertical sensitivity achieved is 0.01 nm/(square root of)Hz. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A submicrometer photodiode probe with a sub-50 nanometer tip radius has been developed for optical surface characterization on a nanometer scale. The nanoprobe is built to detect subwavelength optical intensity variations in the near field of an illuminated surface. The probe consists of an Al–Si Schottky diode constructed near the end of a micromachined pyramidal silicon tip. The process for batch fabrication of the nanoprobes is described. Electrical and optical characterization measurements of the nanoprobe are presented. The diode has a submicrometer optically sensitive area with a 150 fW sensitivity. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The atomic ordering of GaInP has been established and studied by a variety of methods, including transmission electron microscopy, cathodoluminescence, and photoluminescence. In this work, a Kelvin probe force microscope (KPFM) has been employed to image several GaInP samples previously characterized by these established techniques. The results of our study clearly show that the KPFM is capable of distinguishing between ordered and disordered regions in GaInP, and that the KPFM contrast strongly depends on the amplitude of the applied ac bias voltage of the KPFM. The measurements indicate that ordering in GaInP modifies the density and/or lifetime of the surface states. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Quantitative dopant profile measurements are performed on a nanometer scale by scanning capacitance microscopy (SCM). An atomic force microscope is used to position a nanometer scale tip at a semiconductor surface, and local capacitance change is measured as a function of sample bias. A new feedback method has been demonstrated in which the magnitude of the ac bias voltage applied to the sample is adjusted to maintain a constant capacitance change as the tip is scanned across the sample surface. A quasi-1D model is used to extract dopant density profiles from the SCM measurements. The inverted SCM dopant profiles are compared with profiles obtained by process simulation and secondary ion mass spectroscopy measurement. Good agreement was found between the SCM measured profile and the lateral profile predicted by SUPREM 4 over the concentration range from 1017 to 1020 cm−3. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Near-field photodetection optical microscopy (NPOM) is a fundamentally new approach to near-field optical microscopy. This scanning probe technique uses a nanometer-scale photodiode detector which absorbs optical power directly as it is scanned in the near field of an illuminated sample surface. We have applied NPOM to measure the visible absorption spectrum of dye molecules embedded in a single 300 nm polystyrene sphere. The near-field absorption spectrum is obtained by measuring the NPOM probe photocurrent while the wavelength of the illumination pump beam is scanned from 450 to 800 nm. Peaks are identified at 567, 608, and 657 nm in the near-field spectrum of the single-dyed polystyrene sphere. These peak positions are in good agreement with far-field absorption measurements performed on many dyed polystyrene spheres. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A method is introduced for measuring the tunneling of electrons between a specially fabricated scanning probe microscope tip and a surface. The technique is based upon electrostatic force detection of charge as it is transferred to and from a small (10−17 F) electrically isolated metallic dot on the scanning probe tip. The methods for dot fabrication, charging, and discharging are described and electron tunneling to a sample surface is demonstrated. © 2000 American Institute of Physics.

Electronic Resource

1750-3841

Blackwell Publishing Journal Backfiles 1879-2005

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Electronic Resource