摘要:

Six different configurations for metal-oxide-semiconductor field-effect-transistor reflectance microscopy are presented, each one revealing a particular contrast of the operating structure. These different images are obtained by interchanging the modulation of gate-source and drain-source potentials, as well as by varying the probe beam intensity. Three main components were identified in the signal, their relative importance depending on the experimental configuration: the electroreflectance component, the photoinjected carrier (probe-induced) component and the bias current (Joule effect) component. The high ability of the technique to detect defects in these structures is also demonstrated. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365832

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photoablation of polyimide (Dupont Kapton™) and poly(ethylene terephthalate) (PET) (Dupont Mylar™) were studied in vacuum using 248 nm, 16 ns excimer laser pulses. A sensitive electron beam ionizer/quadrupole mass spectrometer detector was used to measure mass, translational energy, and angular distributions of the neutral photoproducts at fluences very close to the threshold (average material removal rates <100 Å/pulse). The experiments were performed by combining results from many discrete sample spots, in order to minimize the changes in yield, energy, and surface topography caused by cumulative pulsing (“radiation hardening”). For both polyimide and PET, the dominant neutral photoproducts are fragments of the monomer, although there is a weak tail of intensity extending up to and beyond 1000 amu. The mean translational energy increases with increasing mass, due to the collisional “seeded beam” effect. The mean translational energy of the majority species (i.e., those below 200 amu) is around 1.6–4.9 eV for polyimide at 30mJ/cm2, and 0.9–1.5 eV for PET at 21mJ/cm2. The translational energy distributions of the heavier species are close to Boltzmann while those of the lighter species show small but reproducible deviations from Boltzmann form. The angular distribution of the CN product from polyimide is sharply peaked about the surface normal even in this near-threshold regime. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366290

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Transmission electron microscopy and scanning electron microscopy offer evidence that the purely chemicalHF:HNO3:H2O“stain etch” used to form light-emitting porous silicon is actually composed of competing etches. A localized etch forms the porous nanostructure by propagation of a discrete reaction interface into the silicon substrate. An amorphous surface layer(SiO2)that is a significant by-product of this etch has been observed and is believed to be a primary efficiency-limiting factor in attempts to fabricate chemically etched porous silicon devices. A destructive etch competes for ions in solution and removes both the porous silicon and the amorphous layers from the surface of the specimen when it becomes dominant, eventually quenching the luminescence properties.

ISSN:0021-8979    

DOI:10.1063/1.365833

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The chemical kinetics and process–property relationships of silicon oxynitride films grown in nitrous oxide ambients were investigated. Gas phase compositions in the furnace were experimentally determined with mass spectrometry and were found to be within ±5&percent; of the ones calculated theoretically. Experimental observations in the furnace suggested that the reaction between NO and oxygen to formNO2inside the furnace was negligible. Silicon oxynitride films were grown at 950 °C and atmospheric pressure for times ranging between 30 min and 24 h. Ellipsometry was used to measure the film thickness. The observed thin-film growth was parabolic with time and appeared to saturate after about 24 h, that is, significantly slower than the oxynitride growth by rapid thermal processing. Secondary ion mass spectrometry (SIMS) used in the depth profiling of oxynitrides showed a sharp accumulation of nitrogen at the oxynitride–silicon interface. Additional experimental data suggested that nitric oxide is the species responsible for nitrogen incorporation at the interface and removal of nitrogen from the bulk film. Mass spectrometric, ellipsometric, and SIMS analyses of furnace silicon oxynitridation in nitrous oxide ambients were used for the development of a model of the process. Model predictions are in agreement with all trends of the experimental data obtained. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365835

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

1Hnuclear magnetic resonance and atomic force microscopy have been correlated in order to exploit the relation between the microscopic morphological properties and the growth dynamics of cement gels during hydration. Studies in a number of samples with different hydration kinetics show that consideration of percolation, gel surface roughness, and related scaling properties is necessary for a thorough understanding of cement hydration kinetics. It is further shown that, at late hydration times, the hydration rate is highly correlated with the cement gel surface roughness exponent &khgr;. A model based on a random walk on a three-dimensional network of rough micropores is proposed in order to explain this effect.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365836

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The performance of electron refrigeration by means of tunnel junctions between superconducting and normal-metal electrodes is studied theoretically. A suitable approximation of the basic expression for the heat current across the tunnel junctions allows the investigation of the main features of the device such as its optimal bias voltage, its maximal heat current, its optimal working point, and the maximal temperature reduction. The theoretical results are compared with those of a recent experiment. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365837

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Distortion of voltage versus flux(V–&Fgr;)relation of a dc superconducting quantum interference device (SQUID) coupled to a multiturn input coil is studied. First, resonant behavior of the coupled SQUID due to the so-called input coil resonance is clarified. It is shown that large rf noise flux is produced by the input coil resonance. This rf flux is added to the SQUID, and results in large rf voltage across the SQUID. In the case where parasitic capacitance exists between the input coil and the ground of the SQUID, this rf voltage produces the rf flux again, i.e., a feedback loop for the rf flux is formed. Taking into account this capacitive feedback, we study theV–&Fgr;relation of the coupled SQUID. Numerical simulation shows that theV–&Fgr;relation is distorted considerably by the feedback mechanism. The simulation result explains well the experimentalV–&Fgr;relation of the coupled SQUID. The combination of the input coil resonance with the capacitive feedback is the most likely mechanism for the distortedV–&Fgr;curve of the coupled SQUID. The condition for occurrence of the distortedV–&Fgr;curve due to the capacitive feedback is also obtained, and methods to prevent degradation are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365838

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The intermodulation power and quality factorQofhigh-Tcsuperconducting microstrip resonators with different shapes is calculated. Acute corners increase the losses and the intermodulation power. The influence of normal conducting regions is investigated. The case of two microstrips carrying in phase or out of phase currents is also studied. The losses and the intermodulation power are significantly reduced if the currents are in phase in the two microstrips compared to the mode with out of phase currents. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365839

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have used the advantage of the high etch selectivity between metals in a wet etching process to develop an optimized technique for engineering magnetic materials. This method is based on electron beam lithography and optimized pattern transfer by a combination of dry and wet etching. The technique has been used in fabricating mesoscopicNi80Fe20dots and wires with lateral dimensions down to 0.2 &mgr;m. We have used scanning electron microscopy to verify the lateral sizes and edge acuity of the structures. The magnetic properties were characterized using magneto-optic Kerr effect and magnetoresistance measurements. A marked increase in the coercive field and the saturation field is seen as the width of the wire is decreased. The magnetoresistance change(∂R)is found to increase significantly as the width of the wire is decreased. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365840

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Reflection anisotropy spectroscopy (RAS) and reflection high-energy electron diffraction (RHEED) were applied to study clean InP(001) surfaces prepared by molecular beam epitaxy (MBE). At phosphorus beam equivalent pressures (BEPs) between3.5×10−7and3.5×10−6mbar and substrate temperature(Ts)falling from 590 to 150 °C, (2×4), (2×1), (2×2), andc(4×4)RHEED patterns are observed. The main RAS features, observed at 1.7–1.9 and 2.6–2.9 eV are assigned to In and P dimers, respectively. The above reconstruction sequence is associated closely with transformations identified in RAS signatures that are induced by progressively increasing the P surface coverage. The RAS results also imply the existence of (2×4)&agr; and (2×4)&bgr; phases. A surface-phase diagram for MBE-grown (001) InP, in the whole range ofTsand phosphorus BEPs is proposed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365585

出版商:AIP    

年代:1997

数据来源: AIP