bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiplexed blanker array for parallel electron beam lithography
Authors: Winograd G. I. , Han L. , McCord M. A. , Pease R. F. W. , Krishnamurthi V.
Published: July 2002

Alternative electron beam technologies to conventional single beam systems have the potential to increase beam current by an order of magnitude, into the 1–10 μA range. The technique we are investigating is to insert an aperture array at an object plane in a lithography system, thus creating an array of beamlets which are imaged as a dot matrix. Each aperture is surrounded by an independently controlled electrostatic microblanker which can modulate the beamlet passing through the aperture in conjuction with a blanking aperture placed at a crossover further down the column. An existing 20 kV shaped beam column with a LaB6 source providing 5 μA of illumination current over a 150 μm×150 μm square area is used as a test stand. The column is used to test prototype microblanker chips. Power dissipation calculations show less than a 10 K temperature rise over the prototype chips. Work has begun on a second generation prototype blanker array which will overcome many of the processing difficulties encountered with the first prototype. Specifically, the new all-silicon process will allow fabrication of smaller apertures which require less demagnification and a shorter electron-optical column.
Critical dimension control at stitched subfield boundaries in a high-throughput SCALPEL® system
Authors: Stanton Stuart T. , Liddle J. Alexander , Waskiewicz Warren K. , Novembre Anthony E.
Published: July 2002

Scattering with angular limitation projection electron-beam lithography (SCALPEL®) is a stitching lithography system, using a segmented mask pattern which is assembled on the wafer by dynamic imaging. Critical objects may lie on the original pattern segment boundaries (seams), but their stitched images must adhere to conservatively interpreted +/−10% critical dimension (CD) control requirements. Stitching with butted (touching) spatial image parts requires an aggressive placement-error allocation of approximately +/−CD/20, along with allowed values for dose control, mask, resist, and process in the CD control budget. Further analysis has shown that a seam-blending scheme increases the stitching-error tolerance by as much as five times, and allows redistribution of all values in the CD error budget. The seam-blending approach provides overlapped image portions in a small area common to neighboring segments which receive complementary illumination dose portions.
Double electron layer tunneling transistors by dual-side electron beam lithography
Authors: Wendt J. R. , Simmons J. A. , Moon J. S. , Blount M. A. , Baca W. E. , Reno J. L.
Published: July 2002

We describe the first demonstration of small-area double electron layer tunneling transistors (DELTTs) fabricated by dual-side electron beam lithography. The DELTT is a planar quantum device which operates by modulating the two-dimensional (2D)-to-2D tunneling between two coupled quantum wells. The fabrication technique utilizes the epoxy-bond and stop-etch process to remove the substrate material which allows the backside gates to be placed in close proximity (less than 1 μm) to the frontside gates. The use of electron beam lithography provides precise alignment of the front and back features to each other. We have applied this technique to the fabrication of DELTTs on coupled AlGaAs/GaAs double quantum wells. Low temperature electrical characterization yields source-drain current–voltage curves that exhibit negative differential resistance with peak-to-valley ratios of up to 8:1. The height and position of the resonant peak varies strongly with gate bias, demonstrating transistor action.
25 nm pitch GaInAs/InP buried structure: Improvement by calixarene as an electron beam resist and tertiarybutylphosphine as a P source in organometallic vapor phase epitaxy regrowth
Authors: Miyamoto Y. , Kokubo A. , Hattori T. , Hongo H. , Suhara M. , Furuya K.
Published: July 2002

To achieve a fine periodic semiconductor structure by electron beam (EB) lithography, calixarene was used as an EB resist. A 25 nm pitch InP pattern was formed successfully and 40 nm pitch InP structures were achieved with good reproducibility. A shorter developing time, precise stage motion, accurate control of the widths of lines and spaces, and slight O2 ashing were important to obtain a fine InP pattern by a two-step wet chemical etching process. Furthermore, the fabricated periodic InP pattern was buried in a GaInAs structure by organometallic vapor phase epitaxy. The introduction of tertiarybutylphosphine as the phosphorus source prevented the fine structure from deforming when the temperature was raised and a 25 nm pitch periodic structure was buried successfully.
Effect of CH4 on the electron emission characteristics of active molybdenum field emitter arrays
Authors: Chalamala Babu R. , Wallace Robert M. , Gnade Bruce E.
Published: July 2002

Exposing active Spindt-type molybdenum field emission microcathode arrays to CH4 resulted in increased electron emission. Exposures of 250 and 2500 L result in electron emission enhancement of 106.2±41.0% and 200.1±20.7% and a decrease in tip work function by 10.2±5.6% and 17.6±1.7%, respectively. The measured work function changes indicate the formation of molybdenum carbides on the field emitter tips.
Imaging properties of the extreme ultraviolet mask
Authors: Bollepalli B. S. , Khan M. , Cerrina F.
Published: July 2002

The reflective mask used in extreme ultraviolet lithography is based on a multilayer stack reflector, overcoated with a suitable absorber. We show that in order to predict correctly the reflected field it is necessary to describe in detail the diffraction and multiple reflection processes that the propagating field undergoes in the multilayer stack. The finite thickness of the absorber causes the incoming field to diffract before being incident on the multilayer stack and is reflected many times in the stack before re-emerging. The fact that the effective reflecting surface of the multilayer stack is below its physical surface, adds complexity to the reflection process. An absorber line would thus appear wider and a space narrower, i.e., a diffraction bias is introduced in this process. If the incoming field is not incident normally, an asymmetry is observed in the reflected field that is angle dependent. Thus, off-axis illumination results in both an imaging bias and a feature displacement due to the image asymmetry. These effects are highly predictable and can be taken into account when writing the mask pattern.
Nanometer scattered-light alignment system using SiC x-ray masks with low optical transparency
Authors: Miyatake Tsutomu , Hirose Masaoki , Shoki Tsutomu , Ohkubo Ryo , Yamazaki Kuniaki
Published: July 2002

Previously we described a video-based scattered-light alignment (SLA) system, capable of nanometer-scale alignment accuracy. In order to meet highly accurate alignment with low optical transparency in x-ray masks, we performed the modifications of alignment marks and an optical microscope imaging system on the conventional SLA system. The advanced SLA system has achieved a high alignment accuracy of 10.2–15.7 nm (|mean|+3σ) using a silicon carbide (SiC) x-ray mask of 18% optical transparency, coated with 5 nm thick chrome (Cr) film as an etching stop, with four different processed wafers: nitride, oxide, poly-Si, and aluminum. The different SiC membranes of 2–5 μm in thickness did not have an effect on the alignment accuracy in the nitride wafer.
Properties of sputtered TaReGe used as an x-ray mask absorber material
Authors: Yoshihara Takuya , Kotsuji Setsu , Fujii Kiyoshi , Tsuboi Shinji , Suzuki Katsumi
Published: July 2002

We have investigated the characteristics of Ta-based amorphous alloy films for use in an x-ray mask absorber. The stress in the TaReGe film can be controlled by changing the concentration of Re, making it easy to obtain low-stress films through deposition with any sputtering system followed by annealing. A required mask contrast can be obtained with a TaReGe film thinner than other Ta-based alloy films because the TaReGe film has a high density and a high mass absorption coefficient. We have achieved 0±10 MPa stress control for a TaReGe film by annealing. The TaReGe films showed high durability against various strong acids and developers, and against O2 plasma. We also demonstrated the fine patterning capability (0.1μm) of a TaReGe absorber.
Characterization of pattern geometrical effect on line end shortening in x-ray lithography
Authors: Yi M. , Seo Y. , Seo E. , Yang J. , Lee K. , Choi B. K. , Kim O.
Published: July 2002

Line end shortening in x-ray proximity lithography was characterized from the viewpoint of the pattern geometry. Mask patterns from 0.1 to 0.3 μm linewidth with different pattern density were fabricated by e-beam lithography and subsequent gold electroplating. The mask patterns were printed in commonly well known chemically amplified resists using the Satellite-800 x-ray stepper developed by Sumitomo Heavy Industry with the synchrotron storage ring at the Pohang Accelerator Laboratory at Postech. A former study [J. R. Maldonado et al., J. Vac. Sci. Technol. B 13, 3094 (1995)] had shown the effect of the absorber thickness and the gap between mask and wafer on line end shortening. In this article, the effect on line end shortening of the geometry of a neighboring pattern, such as pattern shape, pattern density and position of the neighboring pattern, was considered. Several resists with different postexposure bake (PEB) temperatures and different gaps between mask and wafer were examined to characterize their effect on line end shortening. The closer neighboring pattern induced larger line end shortening and also higher PEB temperature and larger gap caused larger line end shortening. A perpendicular neighbor pattern to the test pattern induced different line end shortening than a parallel neighbor pattern. In addition, two dimensional aerial image simulations were performed and line end shortening was extracted from the calculated aerial image. Simulation results showed good agreement with the experimental results.
Nanolithography in polymethylmethacrylate: An atomic force microscope study
Authors: Dobisz Elizabeth A. , Brandow Susan L. , Bass Robert , Shirey Loretta M.
Published: July 2002

This work addresses the formation and development of very dense nanolithographic resolution patterns in polymethylmethacrylate (PMMA) of two molecular weights (MWs), 950 and 50 K. The patterns were lithographically defined by a JEOL JBX-5DII e-beam lithography system operated at 50 kV with a Gaussian probe standard deviation of 8–10 nm. The lithographic patterns consisted of pads of widths from 1 to 20 μm with a 50 nm gap of exposure in the center and single pass line gratings of periods 40, 60, 80, and 100 nm. Atomic force microscope images were acquired. Latent images of the 50 nm gap were observed over a much larger range in dose and pad size, than observed in developed samples. The morphologies of the two unpatterned resists were comparable exhibiting a granular type structure with average particle diameters of 52–53 nm and root mean square surface roughness of 0.2–0.3 nm. In developed patterns, the morphologies and resolution of the two MW resists were very different. The 950 K resist exhibited better resolution and contrast than the 50 K resist. The results are discussed in the context of the exposure and development of macromolecular resists.
Plasma immersion ion implantation for improvement of mechanical properties of AISI M2 steel
Authors: Uglov V. V. , Khodasevich V. V. , Kuleshov A. K. , Fedotova J. A. , Rusalsky D. P. , Guenzel R. , Richter E.
Published: July 2002

Plasma immersion (PI3) ion implantation of AISI M2 steel by nitrogen was carried out. The implantation voltage was 40 kV and the doses varied in the range of 2–8×1018 ions/cm2. It is established that the hardness of steel increases up to 25 GPa, the friction coefficient decreases by the factor of 2 and wear resistance is enhanced by a factor of 10 after PI3. It is explained by the formation of a highly doped face-centered-cubic γ-Fe(N,C) phase that is due to local tempering of the steel surface. The total concentration of nitrogen and carbon in this phase is about 40 at. %.
Simulation of dose uniformity for different pulse durations during inner surface plasma immersion ion implantation
Authors: Liu A. G. , Wang X. F. , Wang S. Y. , Tang B. Y. , Chu P. K. , Zeng Z. M. , Tian X. B.
Published: July 2002

Without the line-of-sight limitation, plasma immersion ion implantation (PIII) emulates conventional beam-line ion implantation in inner surface modification of industrial components. However, dose uniformity on the inner surface is critical. Inner surface PIII of a cylindrical bore is modeled using a two-dimensional fluid model. It is found that the retained dose is not uniformly distributed on the inner surface and the maximum dose is observed away from the edge. The exact location of the maximum dose, which varies with the implant pulse duration, is closer to the center when the pulse width is longer. The maximum relative difference of the retained dose along the interior also depends on the implant pulse duration. It is smaller for a longer pulse duration after a threshold value has been exceeded.
New miniaturized tunneling-based gyro for inertial measurement applications
Authors: Kubena R. L. , Vickers-Kirby D. J. , Joyce R. J. , Stratton F. P.
Published: July 2002

Microelectromechanical (MEM) technology promises to significantly reduce the size, weight, and cost of a variety of sensor systems. For vehicular, tactical, or personal inertial/GPS navigation systems, high performance MEM gyroscopes are required with 1–100°/h resolution and stability. To date, this goal has proven difficult to achieve with low cost manufacturing for many of the previous approaches using Coriolis-based devices due, in part, to the need to precisely tune the drive and sense resonant frequencies or to employ large millimeter-size structures. We have designed, fabricated, and tested a new highly miniaturized tunneling-based gyro that employs the high displacement sensitivity of quantum tunneling to obtain the desired resolution without the need for precise mechanical frequency matching. Our first tested devices with 300-μm-long cantilevers have demonstrated 27°/h/√Hz noise floors. Measurements indicate that this number can be reduced to near the thermal noise floor of 3°/h/√Hz when a closed loop servo, operating at the device’s oscillation frequency, is implemented around the sensor.
High perfection chirped grating phase masks by electron-beam definition
Authors: Rogers C. , Goodchild D. , Baulcomb R. , Butler M. , Hoyle P. , Kanellopoulos S. , Clements S. , Pugh B.
Published: July 2002

A novel electron-beam exposure strategy which has been used in the fabrication of very high quality chirped fiber gratings for use as dispersion compensators is described. A key stage of the processing is the patterning and relief etching of a quartz phase mask, which by ultraviolet exposure, is used sequentially to form long lengths of continuously chirped grating on optical fiber. The use of electron lithography has been restricted by the occurrence of stitching errors which produce prohibitively large phase errors. These tend to be even more pronounced in generating chirped gratings. For practical operation errors of only a few nanometers are probably required. The measured performance of chirped fiber gratings is presented to illustrate the degree of improvement we have achieved by use of two techniques used in the electron-beam exposure of the phase mask, i.e., compensation for residual field distortion, and the delocalization of stitch error. Long chirped gratings produced in this way on a mature e-beam system at Nortel Networks have demonstrated enhanced performance, while similar devices produced by Leica Microsystems on a state-of-the-art machine provided a significantly closer approximation to a perfectly chirped grating.
Mechanical characterization of electron-beam resist using micromachined structures
Authors: Que L. , Gianchandani Y. B. , Cerrina F.
Published: July 2002

In this effort the residual strain in exposed negative tone SAL 605 and unexposed positive tone APEX-E resists was characterized for a variety of processing conditions using surface micromachined bent-beam strain sensors fabricated with resist as the structural material. Results showed that SAL 605 is in 1035–1230 μstrain compression, whereas APEX-E is in 653–690 μstrain tension for the conditions tested. Residual stress in APEX-E was also determined by wafer curvature measurements. The ratio of the residual stress to strain at room temperature indicated that the Young’s modulus of this material is 21±5 GPa. The temperature dependence of the stress indicated that the glass transition temperature for APEX-E is 118±2 °C, and its coefficient of thermal expansion is 11.0±2.5 ppm/K.
Electron beam lithography process for T- and Γ-shaped gate fabrication using chemically amplified DUV resists and PMMA
Authors: Chen Y. , Macintyre D. , Thoms S.
Published: July 2002

A new process has been developed to fabricate T-shaped gates and Γ-shaped gates for high performance metal–semiconductor field effect transistors and high electron mobility transistors using a bilayer of Shipley UVIII DUV resist and poly(methylmethacrylate). The two resists are separated by a 20–30 nm thick layer of aluminum and after patterning by electron beam lithography a two-stage development technique is used to remove the aluminum and to produce well-defined resist profiles. The process can be used to fabricate T-shaped and Γ-shaped gates with footwidth sizes as small as 50 nm and headwidth to footwidth ratios in excess of 40:1 for T gates and 35:1 for Γ gates. The ability to fabricate gates with these dimensions arises from the fact that the UVIII resist is considerably more sensitive to electron beam exposure than PMMA. Further benefits derived from using a UVIII: PMMA bilayer are better control of footwidth dimensions and shorter electron beam patterning times compared to bilayers of PMMA with copolymers of PMMA. This article describes process optimization and the relationship between feature size and exposure dose.
Use of two beam energies in secondary ion mass spectrometry analysis of shallow implants: Resolution-matched profiling
Authors: Cooke G. A. , Ormsby T. J. , Dowsett M. G. , Parry C. , Murrell A. , Collart E. J. H.
Published: July 2002

The use of ultra-low-energy probes for the characterization of shallow implants using secondary ion mass spectrometry is now widely employed. However, as the energy is reduced, both the sputter and ion yields fall, leading to long analysis times and decreased sensitivity. This effect is most apparent when analyzing diffused low-energy implants where both dosimetry and junction depth are to be determined. To obtain accurate dosimetry of a distribution with a very narrow but high surface concentration, probes of 100–200 eV must be used (O2+ for analysis of B in Si). However, over most of the depth of the analysis, extreme depth resolution is not required. This work demonstrates the use of matching the ion energy to the task in hand, and investigates the quantification issues of changing energy within a single depth profile.
Quantitative two-dimensional profiling of 0.35 μm transistors with lightly doped drain structures
Authors: McDonald A. , Mahaffy R. , Wang X.-D. , Kuklewicz C. , Shih C. K. , Dennis M. , Tiffin D. , Kadoch D. , Duane M.
Published: July 2002

We report the first quantitative experimental two-dimensional (2D) dopant profile measurement of 0.35 μm transistors with lightly doped drain structures and its comparison with theoretical simulation. Experimentally, the 2D dopant profile is determined using dopant-selective etching followed by atomic force microscopy imaging. These results show excellent quantitative agreement with recent theoretical profile simulation for both n- and p-channel metal–oxide–semiconductor transistors.
Direct observation of oxygen-induced structural changes in stainless-steel surfaces
Authors: Cho Boklae , Chung Sukmin , Kim Kijeong , Kang Taihee , Park Chongdo , Kim Bongsoo
Published: July 2002

Oxidation of stainless was performed at 450 °C and oxygen partial pressures of 10−9–10−4 Torr. Atomic force microscopy (AFM) images and surface-sensitive photoemission spectroscopy spectra clearly show that, at 450 °C, oxygen pressures lower than the critical pressure (pc′=∼1×10−8 Torr) favor the formation of a smooth Cr2O3 oxide film whose AFM images clearly show a markedly smooth surface with no distinct grains. When oxidized at oxygen partial pressures higher than the critical pressure, the oxide film formed exhibits a rough surface with distinct grains that contain a significant amount of iron and manganese.
Effect of ambient gas in sealing process on field emission characteristics
Authors: Jung S. J. , Oh J. Y. , Woo K. J. , Kim K. S. , Moon G. J. , Kim M. S. , Lee N. Y. , Ahn S.
Published: July 2002

The effect of ambient gas in the sealing process on the field emitter array (FEA) was analyzed. The FEAs which consist of tips with 1 μm height, 1.1 μm width, and gate holes with 1 μm diameter, were fabricated and these array samples were baked in Ar, N2, and vacuum with the same temperature condition of 470 °C for 24 min. After this treatment, the measurements of the electron emission current were carried out for each sample and it was found that there was no difference between before and after baking in each sample. Also, the pieces of glass coated with Mo film of 500 Å were baked in the same condition with the arrays. Auger electron spectroscopy (AES) depth profiling and x-ray photoelectron spectroscopy analysis were performed with these samples. From AES analysis, it was found that the same depth of Mo oxide layer was formed on the surfaces of every sample.
Integration of high voltage field emission display followed by macro- and nanostructural analysis on microtip
Authors: Kim J. M. , Lee H. W. , Choi Y. S. , Lee N. S. , Jung J. E. , Kim J. W. , Choi W. B. , Park Y. J. , Choi J. H. , Jin Y. W. , Yi W. K. , Park N. S. , Park G. S. , Chee J. K.
Published: July 2002

For resolving electron beam focusing and electric field breakdown between the anode and cathode plates in a high voltage field emission display (FED), the metal mesh grids are adapted in one body with spacers. The spacer charging mechanism is modeled in the real panel domain and confirmed by experiment. We analyze the morphology and the chemical composition modifications of the microtips in the narrow vacuum gap of a 5.2 in. FED panel, and infer possible degradation mechanisms in a FED device from our experimental data. The degree of oxidation formed on the microtip surface during fabrication and device operation is studied. Gas aging method for suppressing oxidation on the microtips and stabilizing phosphor is implemented for our 5.2 in. high voltage FED.
Mechanical and structural characterization of ceramic spacers with a high aspect ratio for 5.2 in. field emission displays
Authors: Jung S. Y. , Jung J. E. , Cha S. N. , Park N. S. , Han I. T. , Lee N. S. , Kim J. M.
Published: July 2002

Ceramic spacers with a high aspect ratio (80 μm/1.1 mm) were fabricated and laid out in a high voltage 5.2 in. field emission display (FED) panel. Alumina was chosen as spacer material and sintered at 1600 °C for high mechanical strength and suitable electric resistivity. Three different types of spacers, single-trench type, double-trench type, and honey-comb types, were considered in this study. We optimized the structure and the layout of spacers in terms of stress distributions, build up profiles of glass, carrier gas flows inside a panel. Among the three different types of spacers, the double-trench structure spacer provided the most uniform gas flow and the highest mechanical strength. The optimal number of spacers with 80 μm width and 1.1 mm height was found to be 7 for an uniform stress distribution in a 5.2 in. FED panel by experiments and computer simulations.
Calculation of the field emission current density from n-SI through injection in N-doped diamond
Authors: Filip Valeriu , Nicolaescu Dan , Okuyama Fumio , Plavitu Constantin N.
Published: July 2002

A model for electron field injection from the n-silicon conduction band (CB) into the nitrogen– diamond CB is presented. The model takes into account the electric field penetration into the silicon base and the disturbance of the electron distribution therein. Allowing for a nonlinear anode voltage dependence of the field in the diamond film (and thus in vacuum too) a good fit to experimental current density–voltage (J–V) characteristics was obtained. The model can also predict the temperature dependence of the emission current in accordance with some existing experimental data.
Relationship between field emission properties and spatial distributions of emission sites: Diamond films and graphitic carbon films
Authors: Shim Jae Yeob , Chi Eung Joon , Baik Hong Koo , Song Kie Moon , Lee Se-Jong
Published: July 2002

With hot filament chemical vapor deposited samples having a diamond nature and a graphitic carbon nature, we have investigated the correlation between the field emission properties and spatial distribution of emission sites. The field emission properties are substantially improved with increasing the nondiamond carbon content. It is confirmed that emission sites are mainly observed at the edge when a small amount of nondiamond carbon is existed in diamond films while emissions occur at the center as well as the edge with increasing the nondiamond carbon content. On the other hand, the spatial distributions of emission sites for graphitic carbon films are not related to the nondiamond carbon content but to the thickness and distribution of the sheet.
Noise characteristics of emission current from conductive diamond-like carbon thin films coating on cone shaped silicon field emitters
Authors: Sawada Kazuaki , Kinoshita Haruhisa , Masuda Takeshi , Ishida Makoto
Published: July 2002

Electron emission properties and noise characteristics of emission current from the conductive diamond-like carbon (DLC) thin films, coated on cone shaped Si field emitters, were investigated. The effective work function of the emitters coated by DLC thin films was found to decrease as the conductivity of the DLC film increases. To coat the DLC film, the emission current fluctuation is decreased, but the fluctuation is not influenced by the conductivity of the DLC film. Flicker noise of the field emission current from these emitters was analyzed using fast Fourier transform. It was found that the noise power density of the DLC coated emitters is about 10 dB lower than that of Si field emitters and the flicker noise of the DLC coated field emitters is not influenced by the ambient pressure.
Electron emission from C60/C70+Pd films containing Pd nanocrystals
Authors: Czerwosz E. , Dłużewski P. , Gierałtowski W. , Sobczak J. W. , Starnawska E. , Wronka H.
Published: July 2002

C 60 /C 70 +Pd films composed of 2.5 nm sized Pd nanocrystals situated in carbonaceous matrix were grown by thermal deposition of fullerenes C60/C70 mixture (C60:C70 ratio was 8:2) and Pd organic compound (from two separated sources). The structure of films was studied by transmission electron microscopy and electron diffraction. The composition of films was studied by energy dispersive spectroscopy. Binding energy of Pd and C atoms was obtained by electron spectroscopy for chemical analysis method. The bias voltage applied along the film caused the creation of electrical conductivity paths composed of 10–20 nm sized Pd nanocrystals. The electron emission was observed for the film after the formation of the electrical conductivity path. As a result of such structural changes we observed enhanced electron emission from the film.
Field electron emission from W covered with In
Authors: Saito Yasushi , Nakane Hideaki , Adachi Hiroshi
Published: July 2002

We have investigated a liquid metal electron source that is expected to give a very bright electron beam and also to resist damage due to ion bombardment of the residual gas molecule by restoring the destruction. Although liquid metal ion sources are in use, very few experimental reports on liquid metal electron sources have been published. Here we study the fundamental characteristics of liquid metal electron sources, with emphasis on beam brightness and emission stability.
In situ etching and regrowth in III–V molecular beam epitaxy for future nanotechnology
Authors: Schuler H. , Keller M. , Lipinski M. , Eberl K. , Weis J. , Klitzing K. v.
Published: July 2002

In this article, we present a combination of molecular-beam epitaxy (MBE) growth and in situ etching which allows the growth and manipulation of single atomic layers and small sized lateral structures on a nanometer scale. A solid source III–V MBE system was extended with an in situ etching unit using AsBr3 as the etching species. AsBr3 etching of GaAs provides a crystallographic selectivity which allows to produce extremely smooth (110) facets. Here, in situ AsBr3 etching is used with prepatterned substrates providing much smoother sidewalls as compared to only reactive ion etched samples. Subsequent MBE overgrowth produces planar sidewalls and a very sharp and straight ridge on top of a mesa stripe. A slight backetching treatment on a pregrown sharp ridge provides a well-defined narrow and homogeneous plateau beyond the size limitation of standard lithography. These plateaus are used as the template for subsequent MBE growth of quantum structures. First results using this technique are demonstrated in a scanning electron microscopy study and photoluminescence measurements on InGaAs wires. Finally, we present a lithographic technique which allows micropatterning of GaAs without the use of any photoresist, different mask material, or prepatterned mesas. The native oxide surface layer is locally modified by UV light exposure and acts as a local mask in a following in situ etching procedure.
Maskless selective epitaxy of GaN by Ga low energy focused ion beam and dimethylhydrazine
Authors: Cho D. H. , Tanaka M. , Pak K.
Published: July 2002

In this study, we introduced a new growth method of gallium nitride (GaN), and demonstrated maskless selective epitaxy of cubic GaN on GaAs (100) substrates using a Ga low energy focused ion beam (Ga-LEFIB) and dimethylhydrazine (DMHy) [(CH3)2N2H2] as Ga and N sources, respectively. A Ga-LEFIB with an incident energy of 30–300 eV and DMHy were supplied simultaneously, and GaN films were grown selectively only where the focused Ga ion beam was irradiated. We have found that GaN growth was strongly dependent on growth temperature and DMHy pressure, while surface nitridation time of GaAs (100) had little effect on crystalline quality. The optimized growth conditions of GaN obtained in this experiment were ∼610 °C growth temperature with a DMHy pressure of 6.0×10−6 Torr at an ion beam incident energy of 30 eV.
High performance 1.3 μm InGaAsN:Sb/GaAs quantum well lasers grown by molecular beam epitaxy
Authors: Yang X. , Heroux J. B. , Jurkovic M. J. , Wang W. I.
Published: July 2002

1.3 μm InGaAsN:Sb/GaAs quantum well laser diodes (LDs) have been grown by solid source molecular beam epitaxy using Sb as a surfactant. A record low threshold of 1.02 kA/cm2 was achieved for broad area laser diodes under pulsed operation at room temperature. Performance of single quantum well (SQW) and multiple quantum well (MQW) InGaAsN:Sb LDs are compared. While the room temperature threshold and slope efficiency of MQW LDs remain almost the same as those of SQW LDs, the high temperature characteristics of MQW LDs are greatly improved. A record high operating temperature of 105 °C and a high characteristic temperature (T0) of 92 K below 75 °C are achieved for the InGaAsN:Sb/GaAs MQW LD.
Smoothing of textured GaAs surfaces during molecular beam epitaxy growth
Authors: Adamcyk M. , Ballestad A. , Pinnington T. , Tiedje T. , Davies M. , Feng Yan
Published: July 2002

The surface morphology of homoepitaxial GaAs layers grown by molecular beam epitaxy on random and periodically textured substrates has been measured by atomic force microscopy and elastic light scattering. The random texture was obtained by thermal evaporation of the surface oxide and the periodic texture consisted of one-dimensional grating patterns fabricated by holographic lithography. The time evolution of the surface morphology was simulated numerically with a nonlinear growth equation that includes deposition noise and anisotropy in the surface diffusion. The surface of the random substrate develops shallow mounds as the large amplitude initial texture smooths out, an effect that has previously been attributed to unstable growth.
In
0.05
Ga
0.95
As/Al
0.3
Ga
0.7
As
quantum wells grown on a (411)A-oriented In0.06Ga0.94As ternary substrate by molecular beam epitaxy
Authors: Kitano Y. , Kuriyama R. , Kitada T. , Shimomura S. , Hiyamizu S. , Nishijima Y. , Ishikawa H.
Published: July 2002

We have investigated lateral uniformity of pseudomorphic In0.05Ga0.95As/Al0.3Ga0.7As quantum wells (QWs) with well widths Lw of 2.4 and 3.6 nm grown on a (411)A InxGa1−xAs ternary substrate by molecular beam epitaxy. The lateral variation of In content (x) is from 0.054 to 0.063 over an area of 4 mm2 in this substrate. In spite of the lateral variation of x in the (411)A InGaAs substrate (x=0.054–0.063), full widths at half maximum (FWHMs) of the photoluminescence peaks (12 K) from the (411)A QWs are almost independent of the excitation position (FWHM=9.0–9.7 meV for Lw=2.4 nm and 6.9–7.3 meV for Lw=3.6 nm). Moreover they are approximately 20% smaller than those (FWHM=11.0–11.3 meV for Lw=2.4 nm and 8.6–9.0 meV for Lw=3.6 nm) of the corresponding QWs grown on a (100) In0.06Ga0.94As ternary substrate.
Intrinsic limitations on device performance and reliability from bond-constraint induced transition regions at interfaces of stacked dielectrics
Authors: Lucovsky G. , Yang H. , Niimi H. , Keister J. W. , Rowe J. E. , Thorpe M. F. , Phillips J. C.
Published: July 2002

The substitution of deposited alternative gate dielectrics for thermally grown SiO2 in aggressively scaled complementary metal–oxide–semiconductor devices requires separate and independent processing steps for (i) the oxidation of the Si substrate to form the Si-dielectric interface and (ii) the deposition of thin film dielectric. Ultrathin plasma-oxidized Si–SiO2 interface layers which contribute approximately 0.3–0.4 nm to the overall electrical oxide thickness have been integrated into devices with Si nitride, Si oxynitride, and Ta2O5 alternative dielectrics. This article proposes an analogy between (i) microscopically inhomogeneous bulk glass alloys such as GeSex with 1<x<2, and (ii) interfaces included in these composite gate dielectric-semiconductor structures including, for examples, the Si–SiO2 and internal dielectric SiO2–Si3N4 interfaces. Scaling relationships for bond defect states applied initially to microscopically inhomogeneous glasses and thin films are applied here to interfaces in stacked gate dielectrics.
Band offsets of wide-band-gap oxides and implications for future electronic devices
Authors: Robertson John
Published: July 2002

Wide-band-gap oxides such as SrTiO3 are shown to be critical tests of theories of Schottky barrier heights based on metal-induced gap states and charge neutrality levels. This theory is reviewed and used to calculate the Schottky barrier heights and band offsets for many important high dielectric constant oxides on Pt and Si. Good agreement with experiment is found for barrier heights. The band offsets for electrons on Si are found to be small for many key oxides such as SrTiO3 and Ta2O5 which limit their utility as gate oxides in future silicon field effect transistors. The calculations are extended to screen other proposed oxides such as BaZrO3. ZrO2, HfO2, La2O3, Y2O3, HfSiO4, and ZrSiO4. Predictions are also given for barrier heights of the ferroelectric oxides Pb1−xZrxTiO3 and SrBi2Ta2O9 which are used in nonvolatile memories.
Infrared optical constants of silicon dioxide thin films by measurements of R and T
Authors: Tsu David V.
Published: July 2002

Optical constants [n,k] of 30–300 nm SiO2 films, thermally grown on c-Si substrates, are obtained numerically from [R,T] data. The calculations are done at each wavelength, no a priori assumptions regarding dispersion relations are needed. The technique also provides the film thickness, whose values agree with ellipsometric measurements. The optical constants are compared to those of bulk fused silica glass (FSG) and are found to differ in subtle but important ways. The principal absorption band due to the Si–O TO stretching vibrations, and measured by the ε″ (imaginary dielectric) band, is slightly greater in magnitude and 12 cm−1 narrower for the film than for the bulk material. We interpret this to indicate a simpler strain field within the film compared to the bulk material. We find, however, that the integrated intensities are identical, indicating similar densities. We show that the shift in peak position of the absorbance band with changes in film thickness is almost entirely an optical thin film effect. The absorbance band’s character gradually changes from resembling the ε″ band for very thin samples (⩽30 nm) to resembling the corresponding [k] band for thicker samples. Although ε″ and [k] are intimately related, their positions and widths differ, thus accounting for the systematic changes in width and position of the absorbance band. Only the 30 nm sample appears to differ in any significant way from thicker samples. This difference is mainly in the low magnitude of ε″ (indicating low density for that sample). There is a modest 2 cm−1 shift in the peak position of ε″.
Interwoven Metal-Organic Framework on a Periodic Minimal Surface with Extra-Large Pores
Authors: Chen Banglin , Eddaoudi M. , Hyde S. T. , O'Keeffe M. , Yaghi O. M.
Published: July 2002

Interpenetration (catenation) has long been considered a major impediment in the achievement of stable and porous crystalline structures. A strategy for the design of highly porous and structurally stable networks makes use of metal-organic building blocks that can be assembled on a triply periodic
P
-minimal geometric surface to produce structures that are interpenetrating—more accurately considered as interwoven. We used 4,4′,4"-benzene-1,3,5-triyl-tribenzoic acid (H
3
BTB), copper(II) nitrate, and
N
,
N
′-dimethylformamide (DMF) to prepare Cu
3
(BTB)
2
(H
2
O)
3
·(DMF)
9
(H
2
O)
2
(MOF-14), whose structure reveals a pair of interwoven metal-organic frameworks that are mutually reinforced. The structure contains remarkably large pores, 16.4 angstroms in diameter, in which voluminous amounts of gases and organic solvents can be reversibly sorbed.
Taste Receptor Cells That Discriminate Between Bitter Stimuli
Authors: Caicedo Alejandro , Roper Stephen D.
Published: July 2002

Recent studies showing that single taste bud cells express multiple bitter taste receptors have reignited a long-standing controversy over whether single gustatory receptor cells respond selectively or broadly to tastants. We examined calcium responses of rat taste receptor cells in situ to a panel of bitter compounds to determine whether individual cells distinguish between bitter stimuli. Most bitter-responsive taste cells were activated by only one out of five compounds tested. In taste cells that responded to multiple stimuli, there were no significant associations between any two stimuli. Bitter sensation does not appear to occur through the activation of a homogeneous population of broadly tuned bitter-sensitive taste cells. Instead, different bitter stimuli may activate different subpopulations of bitter-sensitive taste cells.
Physical Properties Determining Self-Organization of Motors and Microtubules
Authors: Surrey Thomas , Nédélec François , Leibler Stanislas , Karsenti Eric
Published: July 2002

In eukaryotic cells, microtubules and their associated motor proteins can be organized into various large-scale patterns. Using a simplified experimental system combined with computer simulations, we examined how the concentrations and kinetic parameters of the motors contribute to their collective behavior. We observed self-organization of generic steady-state structures such as asters, vortices, and a network of interconnected poles. We identified parameter combinations that determine the generation of each of these structures. In general, this approach may become useful for correlating the morphogenetic phenomena taking place in a biological system with the biophysical characteristics of its constituents.
Approach to High-Resolution ex Situ NMR Spectroscopy
Authors: Meriles Carlos A. , Sakellariou Dimitris , Heise Henrike , Moulé Adam J. , Pines Alexander
Published: July 2002

Nuclear magnetic resonance (NMR) experiments are typically performed with samples immersed in a magnet shimmed to high homogeneity. However, there are many circumstances in which it is impractical or undesirable to insert objects or subjects into the bore of a high-field magnet. Here we present a methodology based on an adaptation of nutation echoes that provides resolved spectra in the presence of matched inhomogeneous static and radiofrequency fields, thereby opening the way to high-resolution ex situ NMR. The observation of chemical shifts is regained through the use of multiple-pulse sequences of correlated, composite
z
-rotation pulses, producing resolved NMR spectra of liquid samples.
Nanowire Nanosensors for Highly Sensitive and Selective Detection of Biological and Chemical Species
Authors: Cui Yi , Wei Qingqiao , Park Hongkun , Lieber Charles M.
Published: July 2002

Boron-doped silicon nanowires (SiNWs) were used to create highly sensitive, real-time electrically based sensors for biological and chemical species. Amine- and oxide-functionalized SiNWs exhibit pH-dependent conductance that was linear over a large dynamic range and could be understood in terms of the change in surface charge during protonation and deprotonation. Biotin-modified SiNWs were used to detect streptavidin down to at least a picomolar concentration range. In addition, antigen-functionalized SiNWs show reversible antibody binding and concentration-dependent detection in real time. Lastly, detection of the reversible binding of the metabolic indicator Ca
2+
was demonstrated. The small size and capability of these semiconductor nanowires for sensitive, label-free, real-time detection of a wide range of chemical and biological species could be exploited in array-based screening and in vivo diagnostics.
Central Role of the CNGA4 Channel Subunit in Ca
2+
-Calmodulin-Dependent Odor Adaptation
Authors: Munger Steven D. , Lane Andrew P. , Zhong Haining , Leinders-Zufall Trese , Yau King-Wai , Zufall Frank , Reed Randall R.
Published: July 2002

Heteromultimeric cyclic nucleotide–gated (CNG) channels play a central role in the transduction of odorant signals and subsequent adaptation. The contributions of individual subunits to native channel function in olfactory receptor neurons remain unclear. Here, we show that the targeted deletion of the mouse
CNGA4
gene, which encodes a modulatory CNG subunit, results in a defect in odorant-dependent adaptation. Channels in excised membrane patches from the
CNGA4
null mouse exhibited slower Ca
2+
-calmodulin-mediated channel desensitization. Thus, the CNGA4 subunit accelerates the Ca
2+
-mediated negative feedback in olfactory signaling and allows rapid adaptation in this sensory system.
Facilitation of Calmodulin-Mediated Odor Adaptation by cAMP-Gated Channel Subunits
Authors: Bradley Jonathan , Reuter Dirk , Frings Stephan
Published: July 2002

Calcium (Ca
2+
) influx through Ca
2+
-permeable ion channels plays a pivotal role in a variety of neuronal signaling processes, and negative-feedback control of this influx by Ca
2+
itself is often equally important for modulation of such signaling. Negative modulation by Ca
2+
through calmodulin (CaM) on cyclic nucleotide–gated (CNG) channels underlies the adaptation of olfactory receptor neurons to odorants. We show that this feedback requires two additional subunits of the native olfactory channel, CNGA4 and CNGB1b, even though the machinery for CaM binding and modulation is present in the principal subunit CNGA2. This provides a rationale for the presence of three distinct subunits in the native olfactory channel and underscores the subtle link between the molecular make-up of an ion channel and the physiological function it subserves.
Groundwork for a Rational Synthesis of C
60
: Cyclodehydrogenation of a C
60
H
30
Polyarene
Authors: Boorum Margaret M. , Vasil'ev Yury V. , Drewello Thomas , Scott Lawrence T.
Published: July 2002

A C
60
H
30
polycyclic aromatic hydrocarbon (PAH) that incorporates all 60 carbon atoms and 75 of the 90 carbon-carbon bonds required to form the fullerene C
60
has been synthesized in nine steps by conventional laboratory methods. Laser irradiation of this C
60
H
30
PAH at 337 nanometers induces hydrogen loss and the formation of C
60
, as detected by mass spectrometry. A specifically labeled [
13
C
3
]C
60
H
30
retains all three
13
C atoms during the cage formation process. A structurally related C
48
H
24
PAH that lacks the three peripheral benzene rings cannot be transformed into C
60
, whereas the next higher homolog, a C
80
H
40
PAH, degrades to the C
60
H
30
PAH, which then loses hydrogen to give [60]fullerene. These control experiments verify that the C
60
is formed by a molecular transformation directly from the C
60
H
30
PAH and not by fragmentation and recombination in the gas phase.
A Group-IV Ferromagnetic Semiconductor: Mn

x

Ge

1−
x
Authors: Park Y. D. , Hanbicki A. T. , Erwin S. C. , Hellberg C. S. , Sullivan J. M. , Mattson J. E. , Ambrose T. F. , Wilson A. , Spanos G. , Jonker B. T.
Published: July 2002

We report on the epitaxial growth of a group-IV ferromagnetic semiconductor, Mn

x

Ge

1−
x

, in which the Curie temperature is found to increase linearly with manganese (Mn) concentration from 25 to 116 kelvin. The
p
-type semiconducting character and hole-mediated exchange permit control of ferromagnetic order through application of a ±0.5-volt gate voltage, a value compatible with present microelectronic technology. Total-energy calculations within density-functional theory show that the magnetically ordered phase arises from a long-range ferromagnetic interaction that dominates a short-range antiferromagnetic interaction. Calculated spin interactions and percolation theory predict transition temperatures larger than measured, consistent with the observed suppression of magnetically active Mn atoms and hole concentration.
A One-Step Conversion of Benzene to Phenol with a Palladium Membrane
Authors: Niwa Shu-ichi , Eswaramoorthy Muthusamy , Nair Jalajakumari , Raj Anuj , Itoh Naotsugu , Shoji Hiroshi , Namba Takemi , Mizukami Fujio
Published: July 2002

Existing phenol production processes tend to be energy-consuming and produce unwanted by-products. We report an efficient process using a shell-and-tube reactor, in which a gaseous mixture of benzene and oxygen is fed into a porous alumina tube coated with a palladium thin layer and hydrogen is fed into the shell. Hydrogen dissociated on the palladium layer surface permeates onto the back and reacts with oxygen to give active oxygen species, which attack benzene to produce phenol. This one-step process attained phenol formation selectivities of 80 to 97% at benzene conversions of 2 to 16% below 250°C (phenol yield: 1.5 kilograms per kilogram of catalyst per hour at 150°C).