摘要:

A wide set of data obtained on a two-dimensional electron gas submitted to a tunable lateral modulation, induced using a split-gate technique, is presented. Owing to a unique design of the sample, it has been possible to combine in a single experimental run, far-infrared transmission measurements and electrical transport measurements in both directions parallel and perpendicular to the lateral modulation. The discussion of the results emphasizes the correspondence between various features observed in both types of measurements. Based on these features, three regimes of modulation are clearly identified, namely the weak, intermediate and strong modulation regimes. Far-infrared transmission data show that each of these regimes is characterized by plasmon modes with a distinctive behavior. These behaviors are analyzed further with the use of transport data, which allow to determine the electron concentration in the structure for every condition of gate voltage. In the weak modulation regime, a quantitative analysis shows that the collective mode energy is consistent with that of a classical 2D plasmon atq=2π/a(whereais the period of the split gate), using the average electron concentration under the gate as the relevant parameter. In the intermediate regime, the collective modes are confined plasmons. The observation of “confined Bernstein modes” indicates that the bare confinement potential is nonparabolic in this regime. In the strong modulation regime, the observation of a far-infrared resonance energy which does not depend on the modulation amplitude, while the effective 2D electron concentration (within each wire) varies with gate voltage, shows that the collective mode is a Kohn mode.

ISSN:1071-1023    

DOI:10.1116/1.590368

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We have investigated the luminescence emitted at 1.54 μm from erbium-implanted strained ultrahigh vacuum chemical vapor deposition-grown (UHVCVD-grown)Si1−xGexquantum wells. Germanium fractions of up to 13% were used, and all well widths were below the critical thickness for pseudomorphic growth. A preliminary study was carried out onSi1−xGexquantum wells implanted with amorphizing doses of silicon at 77 K in order to study the regrowth across the interfaces, and subsequent structural and optical recovery. After amorphization and regrowth by a two stage anneal process, transmission electron microscopy (TEM) clearly showed the presence of the quantum wells, with sharp contrast. X-ray diffraction (XRD) studies showed that good regrowth has been achieved, with line widths very similar to the original material. However, the photoluminescence (PL) was found to be dependent upon the duration of the first anneal. Increasing the anneal time resulted in PL spectra being dominated by broad signals between 0.9 and 0.97 eV associated with structural defects. High concentrations of erbium were incorporated into the strainedSi1−xGexquantum wells by implantation and solid phase epitaxial regrowth. TEM and XRD studies showed that the quantum wells retained their structure, with negligible segregation or diffusion of the germanium during the recrystallization. Erbium-related emission centered at 1.54 μm was observed in the implantedSi1−xGexlayers after regrowth, and generally found to be of similar intensity as that in bulk silicon implanted with more than an order of magnitude higher dose of erbium.

ISSN:1071-1023    

DOI:10.1116/1.590320

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

c-SiO2samples were implanted withAg+at an energy of 200 keV to doses in the range of2.3–9×1016 ions/cm2at room temperature. At a dose of6.7×1016 ions/cm2,the transmission electron microscopy image shows that the implanted layer consists of two major sizes of nanoclusters: the large clusters, found in the deeper layer, are about 20 nm in diameter; the smaller clusters, found near the surface, are about 5 nm in diameter. At the relatively low dose of2.3×1016 ions/cm2,there is only one optical absorption band caused by surface plasmon resonance. At a higher dose, a splitting of the absorption band and the redshift are attributed to a dipole interaction between nanoclusters for a high density of nanoclusters.

ISSN:1071-1023    

DOI:10.1116/1.590321

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Silicon nanopillars were fabricated by a novel natural lithography technique utilizing a gold colloidal particle monolayer as an etch mask. UsingSiCl4based reactive ion etching (RIE), silicon nanopillars with high density and uniformity in height and shape were obtained with 15 and 10 nm diam gold colloidal particles. The uniform pillars obtained from the 15 nm colloidal gold etch mask were subsequently sharpened to less than 5 nm diam tips by oxidation. 5 nm diam colloids were used to obtain nonuniform 5 nm diam pillars directly by RIE, but with 2 nm colloids the limit of pillar formation was reached. The pillars were also fabricated in selected areas by lithographic patterning of the substrate.

ISSN:1071-1023    

DOI:10.1116/1.590322

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

An electrostatic force microscopy (EFM) method has been used for the detection and control of the microdomain in ferroelectric single crystal [triglycine sulfate (TGS)] and thin film piezoelectric transducer (PZT). In this method, EFM is operated in adynamic contactmode that allows a simultaneous measurement of the topographic and domain contrast images. Through the analysis of the force between the tip and ferroelectric surface, the surface charge density of TGS single crystal is obtained. Polarization charge density of TGS obtained in this method is 2.7 μC/cm2at room temperature. A complex pattern was written on a PZT film by the polarization reversal. The line shape or the intensity of the reoriented domain does not show any noticeable dependence on the writing speed. The threshold bias for writing on a PZT film studied in this work was 4 V.

ISSN:1071-1023    

DOI:10.1116/1.590323

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Surface structures of Ni-deposited Si(100) have been investigated using scanning tunneling microscopy (STM). After heating at 670 °C,NiSi2islands consisting of patch features grow on the(2×n)substrate. We have proposed a new structure model forNiSi2island by taking account of the correlation of heights and lateral positions between top-layer atoms in theNiSi2and Si dimers in the substrate. In the model, the top-layer atoms, with a nearest neighbor distance of 0.38 nm, are located at bridge sites on the Ni layer ofNiSi2.Patch features consist of two equivalent anti-phase sites shifted by half the unit length of1×1along both [011] and [01̄1]directions. In addition, it is found in the empty-state STM images that the center atoms make pairs two by two.

ISSN:1071-1023    

DOI:10.1116/1.590324

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We present an experimental study of growth of silicon oxide strips drawn on hydrogenated silicon under the voltage biased tip of an atomic force microscope operating in ambient atmosphere. Oxide formation was found to occur at negative tip biases above a voltage threshold around|−2|V,corresponding to the minimum electric field required for hydrogen removal from the substrate surface. We show the influence of tip-sample distance and of the chemical composition of the atmosphere on the growth. An ozone enriched atmosphere leads to a growth kinetics enhancement.

ISSN:1071-1023    

DOI:10.1116/1.590325

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Laser micromachining with a frequency doubled Nd:YAG laser (532 nm) can replace more complex microlithographic processes for rapid turnaround in the development of prototype application-specific integrated circuits. Plasma polymerization is a rapid, dry, environmentally friendly process that yields crosslinked pinhole-free films. Plasma polymerized films of ethylene and an additional gas [PP(gas/E)] were investigated for their micromachining potential. The deposition rates, molecular structures, physical properties and optical properties of the polymers were characterized. PP(Ar/E), with relatively little oxygen and no nitrogen, with superior substrate adhesion and with no debris generated on laser micromachining was chosen as the optimal laser micromachining film. The PP(Ar/E) coefficient of optical absorption at 532 nm(α532),related to unsaturated group concentration, increased with the ratio of plasma power to ethylene mass flow rate[W/Fm(E)].α532reached an asymptote of 2.9μm−1at highW/Fm(E)and could be enhanced slightly using postpolymerization ultraviolet exposure. The optimum conditions were using Ar/E=1/1 and 75 W to produce a 0.6μmthick film for micromachining at2 J/cm2focused 0.25μmbeneath the surface. The laser pulse in a 1.2μmthick film was not fully developed at2 J/cm2and exhibited rounded corners at4 J/cm2,indicating that multiple low energy pulses would be preferable. A complicated and densely packed pattern with several different pulse sizes in which neighboring holes from pulses in close proximity do not merge was accurately reproduced in PP(Ar/E) using laser micromachining.

ISSN:1071-1023    

DOI:10.1116/1.590326

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We present an investigation to study the degradation of poly(methylmethacrylate) (PMMA) based resists during electron beam exposure and their development characteristics. After exposure to the electron beam we detect for ARP 610 resist (PMMA 74%, PMAA 26%) and for a homopolymeric PMMA resist, a similar bimodal respectively multimodal molecular weight distribution curve characterized by a shift of the maximum from105to103g/mol and an increase of low molecular weight fractions(≈103g/mol) with increasing exposure dose. The model of Greeneich can only be applied to lower deposited energy densities (ARP610<4eV/nm3,homopolymeric PMMA<8eV/nm3).The difference found between experimental data and modeling values at higher deposited energy densities for both resists, results from a formation of stable low molecular weight fractions. Comparing the measured dissolution rate with the calculated one, the determined difference proves the nonapplicability of the empirical formula for the dissolution rate given by Greeneich. The low molecular weight fractions influence the dissolution rate significantly more than given by their portion in the molecular weight distribution.

ISSN:1071-1023    

DOI:10.1116/1.590327

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

In a previous article, we reported on the possibility of predicting the development speed of a photoresist by measuring its electrical conductivity in an organic solvent [T. Takeda and M. Saka, J. Vac. Sci. Technol. B (submitted)]. The electrical conductivity of the organic solution of a photoresist base polymer at various frequencies was found to have a positive correlation with the dissolution speed of photoresist base polymers into an alkaline developer. In addition, the influence of the measurement temperature and the concentration of polymer solution on conductivity was investigated. Based on the collected data, this article derives the calibration equation, which was influenced neither by measurement temperature nor by the concentration of the solution.

ISSN:1071-1023    

DOI:10.1116/1.590328

出版商:American Vacuum Society    

年代:1998

数据来源: AIP