bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemistry of arsenic incorporation during GaAs/GaAs(100) molecular beam epitaxy probed by simultaneous laser flux monitoring and reflection high-energy electron diffraction
Authors: Ott Adina K. , Casey Sean M. , Alstrin April L. , Leone Stephen R.
Published: July 2002

Arsenic incorporation during GaAs/GaAs(100) molecular beam epitaxy is studied in situ with laser single-photon ionization time-of-flight mass spectrometry and reflection high-energy electron diffraction (RHEED). Incident and scattered fluxes of Ga and Asn species in front of the growing GaAs wafer are ionized repetitively by a pulsed laser beam of 118 nm (10.5 eV) photons. The methods to obtain and interpret time-of-flight mass spectra and the simultaneous RHEED measurements are described. The real time behaviors of incident Ga and desorbing As2 and As4, obtained without mass spectral cracking, are studied during growth of GaAs layers with As4 and when growth is arrested as a function of substrate temperature and Ga/As4 flux ratio. During growth only with As4, both As2 and As4 are desorbed or scattered in varying amounts depending on flux and substrate temperature conditions. Without an incident gallium flux, desorbing As4 decreases while desorbing As2 increases with increasing surface temperature. During gallium deposition and GaAs growth, the amounts of desorbing arsenic fluxes decrease linearly with increasing Ga/As4 flux ratio, but the arsenic incorporation rate saturates at a Ga/As4 flux ratio ≥2, i.e. (Ga/As≥1/2). The total integrated incorporation of arsenic increases linearly with increasing Ga/As4 flux ratio when the surface is allowed to recover with an incident arsenic flux after the gallium flux is terminated. In the range of substrate temperatures optimum for layer-by-layer GaAs growth with As4, As4 incorporation dominates at low temperatures, while As4 and As2 incorporations contribute equally at high temperatures. Surface reaction sequences and mechanisms of arsenic incorporation are discussed and compared with measured RHEED results and previous experimental and theoretical results.
Modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterostructures grown on GaAs substrates using step-graded InxGa1−xAs buffers
Authors: Goldman R. S. , Kavanagh K. L. , Wieder H. H. , Ehrlich S. N.
Published: July 2002

We have grown modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterostructures on GaAs substrates using compositionally step-graded InxGa1−xAs buffers. Triple-axis x-ray diffraction measurements indicate nearly complete and isotropic strain relaxation in the buffer, lattice matching of the active layers with the top of the buffer, and no significant epilayer tilt. The temperature dependence and the photoresponse of the electron mobility suggest that transport in the heterostructures is limited principally by remote ionized-impurity scattering, with mobility values comparable to those of heterostructures grown lattice-matched to InP.
Imaging and manipulation of nanometer-size liquid droplets by scanning polarization force microscopy
Authors: Hu Jun , Carpick Robert W. , Salmeron Miquel , Xiao Xu-dong
Published: July 2002

Using atomic force microscopy in noncontact mode, we have imaged nanometer-size liquid droplets of KOH water solutions on the surfaces of highly oriented pyrolitic graphite and mica. On graphite the droplets prefer to be adsorbed on atomic step edges. Droplets on the same step tend to be evenly spaced and of similar size. The droplets can be manipulated by the atomic force microscopy tip allowing the controllable formation of droplet patterns on the surface.
Scanning tunneling microscopy head having integrated capacitive sensors for calibration of scanner displacements
Authors: Picotto G. B. , Desogus S. , Lányi Š. , Nerino R. , Sosso A.
Published: July 2002

Scanning tunneling microscopy heads having some tip–displacement measurement capability are essential for quantitative and accurate measurements. A scanning tunneling microscopy head based on a bimorph parallelogram scanner with a metallized glass cube situated above the tunneling tip is described. The cube acts as a counterelectrode or as a mirror for capacitance-based and interferometric measurements of scanner displacements. The capacitive sensors are mounted on differential screws facing the cube in such a way that the lateral Abbe error in the measurement of actual tip–displacements is minimized. The sensor electronics uses a Howland-type alternating current source, and has a deviation from linearity of less than 0.15% up to 30 μm and a low frequency bandwidth of 1 kHz.
Examination of Ge/Si and GeSi/Si surface nanostructures using transmission electron microscopy and focused ion beam assisted processing
Authors: Deng C. , Sigmon T. W. , McCarthy J. M.
Published: July 2002

Transmission electron microscopy studies of localized Ge and GeSi surface nanostructures in the form of nanowires on a Si substrate were performed using a novel specimen preparation scheme assisted by a focused ion beam (FIB). The Ge nanowires/Si and GeSi nanowires/Si were fabricated in a lift-off process using e-beam lithography and a pulsed UV laser induced epitaxy process, respectively. By using a Pt/Au–Pd/C multilayer protection structure over the area of interest and a FIB marking technique, specimens of lattice imaging quality have been consistently obtained in which all features of interest were preserved. Multilayer protection structures of Pt/C and Pt/Au–Pd/spin-on-glass were also investigated. The versatile sample preparation procedure is applicable to a wide variety of surface structures other than the kind used in this work.
Optical emission spectroscopy of high density metal plasma formed during magnetron sputtering
Authors: Radzimski Z. J. , Hankins O. E. , Cuomo J. J. , Posadowski W. P. , Shingubara S.
Published: July 2002

The operation of a high power density magnetron source during sputtering of a copper target both in standard mode with argon as well as in self-sputtering mode without argon is discussed. Voltage–current characteristics of the source and light emission spectra were taken for various conditions of magnetron operation to understand the transition from standard to self-sputtering mode. A qualitative explanation of the ionization mechanism is offered based on the effect of electron temperature and density on the Maxwellian distribution of electron energy.
Precision transmission electron microscopy sample preparation using a focused ion beam by extraction method
Authors: Sheng T. T. , Goh G. P. , Tung C. H. , Wang L. F.
Published: July 2002

A new precision cross-sectional transmission electron microscopy (XTEM) sample preparation method was developed and is reported here. The major advantage of this method over a conventional sample prepared using a focused ion beam (FIB) microsection is that the sample sectioned with a FIB can be extracted directly from the matrix and transferred to a carbon supporting grid for TEM examination. With this technique, a XTEM sample can be prepared, totally eliminating the requirement for mechanical polishing. Samples can be made easily and quickly, thus enhancing both productivity and turnaround time.
Novel electron beam lithography technique for submicron T-gate fabrication
Authors: Ahmed M. M. , Ahmed H.
Published: July 2002

Submicron T gates have been fabricated using the high resolution electron beam lithography technique. The footprint of the T gate has been written in high molecular weight poly-methyl methacrylate (PMMA), whereas the top of the T gate is defined in AZ PF 514. A 400 nm thick layer of PMMA was first exposed and developed followed by the spinning of AZ PF 514. A wide line defining the top of the T gate was written in this resist which after development gave a T-shaped cross section. As both the bottom and the top of the T gate are dealt with independently, therefore, the technique provides a high degree of control and flexibility in the fabrication process. Moreover, the possibility of shorting of the top of the T gate with the Ohmic metallization is virtually impossible. Consequently, the process is a very good candidate for low-noise GaAs metal-semiconductor field-effect transistors (MESFETs) fabrication in which a narrow drain-to-source gap is required. GaAs MESFETs with T-shaped gates have been fabricated and characterized by dc measurements.
Photon tunneling microscopy of latent resist images
Authors: Liddle J. A. , Fernandez A. T. , Cirelli R. , Mkrtchyan M. M. , Novembre A. E. , Peabody M. L. , Watson G. P.
Published: July 2002

The ability to examine latent resist images can provide a means of separating out the influences of the exposure itself from the subsequent postexposure bake and from the development process in determining the form of the final developed image. We describe the technique of photon tunneling microscopy (PTM) and its application to examining latent resist features. The PTM is based upon the concept of frustrated total internal reflection, and can give information on latent images that is highly sensitive to both changes in topography as small as 1 nm and refractive index changes on the order of 10−2–10−3. Preliminary modeling shows how this technique can give quantitative information about the progress of the radiation induced chemistry in resist. Experimental data for two positive-tone, chemically amplified materials, ARCH2 and CAMP1 illustrate the potential of the technique.
Optical transitions in InGaN/AlGaN single quantum wells
Authors: Zeng K. C. , Smith M. , Lin J. Y. , Jiang H. X. , Robert J. C. , Piner E. L. , McIntosh F. G. , Bedair S. M. , Zavada J.
Published: July 2002

The optical transitions in InGaN/AlGaN single quantum wells (SQWs) grown by metal-organic chemical vapor deposition have been studied. The spectral lineshape and the recombination dynamics of the optical transitions have been systematically investigated at different conditions. It was found that the main photoluminescence (PL) emission line in these SQW was contributed predominantly by the localized exciton recombination. However, time-resolved PL results revealed the presence of a band-to-impurity transition which cannot be resolved spectroscopically from the localized exciton transition line due to the broad emission linewidth.
Wet oxidation of AlAs films under ultrahigh vacuum conditions
Authors: Mitchell W. J. , Chung C.-H. , Yi S. I. , Hu E. L. , Weinberg W. H.
Published: July 2002

The initial stages of oxidation of AlAs(001) (using D2O as the oxidant) have been investigated using Auger electron spectroscopy and temperature-programmed desorption. We have found that molecularly adsorbed water on AlAs(001) has two competing reaction pathways available: either desorption back into the gas phase, or dissociation resulting in aluminum oxide, aluminum hydroxide, and arsenic hydride. Recombination of the arsenic hydride produces arsine, which desorbs and depletes arsenic within the oxide film, a process which is shown to enhance the oxide growth. By identifying the various reaction steps that occur (with annealing) after the low-temperature adsorption of water on AlAs(001), we are able to propose a mechanism for the initial stages of wet AlAs oxidation.
Characterization of low-temperature grown AlSb and GaSb buffer layers
Authors: Eyink K. G. , Seaford M. L. , Haas T. W. , Tomich D. H. , Lampert W. V. , Walck S. D. , Solomon J. S. , Mitchel W. C. , Eastman L. F.
Published: July 2002

The InGaSb/InAs strained layer superlattice (SLS) system has been proposed theoretically to be a potentially useful long-wavelength infrared (IR) detector material by Mailhiot and Smith. These authors have suggested that GaSb substrates would be suitable for growth of these SLS. The benefit of InGaSb/InAs SLSs grown on GaSb(001) versus GaAs(001) substrates has been substantiated by a number of recent papers [J. L. Johnson, L. A. Samoska, A. C. Gossard, J. L. Merz, M. D. Jack, G. R. Chapman, B. A. Baumgratz, K. Kosai, and S. M. Johnson, J. Appl. Phys. 80, 1116 (1996); T. D. Golding, H. D. Shih, J. T. Zborowski, W. C. Fan, C. C. Horton, P. C. Chow, B. C. Covington, A. Chi, J. M. Anthony, and H. F. Schaake, J. Vac. Sci. Technol. B 10, 880 (1992)]. Unfortunately, the current quality of GaSb substrates does not even match those of InP, much less GaAs or Si. In particular, the poor quality of the GaSb substrates leads to free carriers that make the samples electrically conductive and absorb photons in the IR. Further studies of this materials system, therefore, require either improved GaSb substrates or a suitable buffer layer to electrically isolate the substrate from the SLS. In this work, we explore the use of low-temperature grown (LTG) AlSb and GaSb, with and without annealing, as an effective near lattice matched buffer layer for SLS growth GaSb and GaAs. The LTG layers were formed by solid source molecular beam epitaxy using monomeric Sb from a cracker cell. The LTG-AlSb was grown at 450–500 °C while the GaSb layers were grown at 250–350 °C. Characterization of the layers by transmission electron microscopy (TEM), high-resolution x-ray diffraction, atomic force microscopy, and Hall mobilities has been performed. These results show that LTG GaSb on GaAs substrates are highly defective and become polycrystalline after about 1500 Å of growth. TEM analysis showed the formation of precipitates in LTG AlSb films on GaSb after annealing. No Sb precipitates have been found in LTG GaSb.
Preparation and structural characterization of nanostructured CoAg granular films
Authors: Sang H. , Ni G. , Lu J. , Chen H. , Zhang J. R. , Du Y. W.
Published: July 2002

The microstructures of as-deposited and annealed CoAg granular films fabricated by ion-beam cosputtering technique were characterized using x-ray diffraction, transmission electron microscopy (TEM), and ferromagnetic resonance (FMR) methods. For the Co22Ag78 sample, the changes in size and shape of the nanoscale cobalt granules embedded in the film closely depend on the annealing temperature (TA). Real time observation in situ of TEM together with FMR spectra indicate that the size and shape of the cobalt granules evolve primarily along the film plane during the annealing process. Also, the FMR results indicate that the cobalt granules are still single domain particles embedded in the film as the sample is annealed up to 700 K.
Thermal desorption of Si clusters from Si and Si-deposited Ta surfaces
Authors: Tanaka Hideyuki , Kanayama Toshihiko
Published: July 2002

We performed quadrupole mass spectrometry (QMS) of Si clusters that thermally desorbed from various surfaces in ultrahigh vacuum. To investigate the effect of substrate on cluster formation, different kinds of substrates were prepared: Si(100) wafers, Si(111) wafers, and Si-deposited Ta polycrystalline sheets. When Si wafers were heated at 900–1300 °C, QMS spectra showed that clusters up to Si6 sublimed from the surfaces. Both of (100) and (111) had the same activation energy for desorption of the clusters. On the contrary, QMS spectra from Si-deposited Ta at 1500 °C showed monomeric Si only. These results agree with the thermodynamic consideration that the desorption rate of each cluster is determined by its formation energy. The relation of cluster formation with the surface structure is also discussed.
Low temperature deposition of SiNx:H using SiH4–N2 or SiH4–NH3 distributed electron cyclotron resonance microwave plasma
Authors: Delmotte F. , Hugon M. C. , Agius B. , Courant J. L.
Published: July 2002

Silicon nitride films were deposited at floating temperature using distributed electron cyclotron resonance plasma enhanced chemical vapor deposition (DECR-PECVD) on Si and InP substrates. The deposition parameters studied included the nature of gases (SiH4–N2 or SiH4–NH3) and the gas phase composition (SiH4/N2 or SiH4/NH3). The experimental results establish that to obtain device quality Si3N4, it is desirable to use N2 instead of NH3 and a high diluted SiH4 gas phase. These process parameters yield to a high resistivity (1016 Ω cm) and a high critical field (4.5 MV/cm). These properties confirm that the DECR technique is well suited for processing III–V compound semiconductors. NH3 does not induce such promising characteristics in terms of electrical properties but silicon nitride deposited with this gas is particularly interesting for applications where no stress is required.
Emission characterization of diamond-coated Si field emission arrays
Authors: Zhirnov V. V. , Givargizov E. I. , Kandidov A. V. , Seleznev B. V. , Alimova A. N.
Published: July 2002

Large-area arrays of Si tips (105–106 tips in an array) with diamond coating were tested in pulse and dc modes. The arrays demonstrated uniform emission, reproducible I–V plots, and low emission threshold. The maximum current achieved with diamond-coated Si arrays was 80 mA in pulse mode. Emission characteristics were found to be superior to the uncoated Si tip arrays or diamond-coated flat cathodes.
Resistless electron beam lithography process for the fabrication of sub-50 nm silicide structures
Authors: Drouin D. , Beauvais J. , Lavallée E. , Michel S. , Mouine J. , Gauvin R.
Published: July 2002

We report on a study of the fabrication of submicron silicide structures with a resistless lithography technique. Several different metals can be used as a basis for producing silicide using this method; in this work, results will be discussed for both platinum and nickel silicide. The feasibility of producing nanostructures using polycrystalline silicon as a base growth layer for metal–oxide–semiconductor, and other device applications have also been demonstrated. Threshold doses for this method for submicron lines (<50 nm) and square areas were obtained in order to establish a framework for the fabrication of more complex devices. Preliminary electrical measurements were carried out which indicate that the resistivity of the silicide is 45 μΩ cm, and that the barrier height of the silicide/(high resistivity silicon) interface is 0.56 eV.
Atomic force microscope studies of nanolithographic exposure and development of polymethylmethacrylate
Authors: Dobisz Elizabeth A. , Brandow Susan L. , Snow Eric , Bass Robert
Published: July 2002

Atomic force microscopy was employed to study e-beam exposure and pattern development of polymethylmethacrylate (PMMA) in molecular weights (MWs) of 950 and 50 K. The work focuses on the development of dense high resolution patterns. PMMA was found to have a nodular morphology with an average particle diameter of ∼53 nm. Submersion of unexposed PMMA in both water and mixtures of isopropanol (IPA) and 0–33% methylisobutylketone (MIBK) did not change the surface morphology. IPA mixtures with ⩾50% MIBK roughened the surface. Latent images of exposed resist were consistent with Monte Carlo simulations. The particle size limited the ability to resolve a 40 nm grating. A pillar type morphology was observed between the lines in the 40 nm period grating in 950 K MW PMMA developed in 25% and 50% MIBK. The particle size was not reduced in 50 K MW PMMA. In fact, the ability to define a 40 nm grating in 50 K molecular weight PMMA was worse. Patterns of large pads and 100 nm gratings did not exhibit the pillar morphology nor a difference in morphology between the two molecular weight resists.
Low weight spreading resistance profiling of ultrashallow dopant profiles
Authors: De Wolf P. , Clarysse T. , Vandervorst W. , Hellemans L.
Published: July 2002

The application of the conventional spreading resistance profiling (SRP) method on ultrashallow profiles is endangered by the phenomenon of pressure enhanced carrier spilling which results in false dopant and carrier profile differences, the need for large correction factors, and the presence of surfaces states on the bevel. Furthermore, the tedious preparation of the conventional SRP probes requires a lot of expertise. In this work, it is shown that some of these limitations can be resolved by the application of the nano-SRP technique on beveled samples. The use of a single conductive diamond-coated silicon tip mounted on an atomic force microscope (AFM) maintains the strong points of SRP while eliminating the need for probe conditioning. Contact sizes for nano-SRP are a factor of one hundred smaller than in conventional SRP. The small contact size combined with small probe movements allows for considerably larger bevel angles and provides a geometrical resolution as small as 0.5 nm. The smaller contact, i.e., 20–50 nm in diameter, reduces the SRP correction factor by a factor of 20. The much smaller pressure interaction volume reduces the pressure enhanced carrier spilling component. As a consequence, the application of the so-called zero field Poisson contact model becomes more feasible.
Self-aligned Si gate field emitter arrays using the transfer mold technique
Authors: Sakai Tadashi , Ono Tomio , Nakamoto Masayuki , Sakuma Naoshi
Published: July 2002

Transfer mold type field emitter arrays which integrate a novel self-aligned Si gate have been fabricated. Applying the self-limiting Si etching technique, a part of the Si-mold substrate was preserved for the gate structure to simplify the gate fabrication process and to improve the gate aperture shape reproducibility. The gate aperture (Dg) was precisely controlled and a minimum Dg of 0.15 μm was achieved with conventional photolithography techniques. Also, Dg could be widely varied by changing only the size of the emitter mold, and the relationship between Dg and the emission threshold gate voltage (Vth) under identical emitter tip conditions was studied.
Kinetic roughening of Si surfaces and surfactant effect in low temperature molecular beam epitaxy growth
Authors: Gallas B. , Berbezier I. , Derrien J. , Gandolfo D. , Ruiz J. , Zagrebnov V. A.
Published: July 2002

Thanks to an experimental (in situ reflection high-energy electron diffraction and ex situ high-resolution electron microscopy) and a theoretical probabilistic cellular automaton study of surface kinetic roughening in low temperature silicon molecular beam epitaxy, we achieve a clear correlation between the surface roughness and the microscopic morphology of the growing layer. A transition in the growth mechanisms between a perfect epitaxy regime and another one displaying structural defects is shown. It may explain previous unusually observed deviations of the surface roughness scaling behavior unpreviewed by current theories. The effect of gallium atoms as «surfactants» is also investigated. High-resolution electron microscopy comparison of layers grown with and without gallium shows its role in the surface morphology smoothing.
Structural properties of Ga2O3(Gd2O3)–GaAs interfaces
Authors: Hong M. , Marcus M. A. , Kwo J. , Mannaerts J. P. , Sergent A. M. , Chou L. J. , Hsieh K. C. , Cheng K. Y.
Published: July 2002

Ga 2 O 3 (Gd 2 O 3 )–GaAs heterostructures in situ fabricated using a multichamber ultrahigh vacuum (molecular beam epitaxy) system were studied by x-ray reflectivity measurement and high-resolution transmission electron microscopy. The oxide–GaAs interfaces were found to be very smooth with the roughness no more than 1 nm. Moreover, an interfacial roughness as small as one atomic layer of GaAs (0.33 nm) was observed using x-ray reflectivity.
Microroughness of polymer thin films studied by total-reflection x-ray fluorescence and atomic force microscopy
Authors: Wu W. L. , Wallace W. E.
Published: July 2002

The surface roughness of polymer thin films supported on nickel-coated silicon substrates was analyzed by angle-dependent total-reflection x-ray fluorescence (TXRF) in conjunction with atomic force microscopy (AFM). For highly rubbed polystyrene (PS) surfaces (500 cm rubbing length at a load of 2 g/cm2 over a velour cloth) displaying sharp grooves and ridges, the TXRF showed no significant change while the AFM results revealed an anisotropic 6.08 nm root-mean-square roughness with an average peak-to-peak distance of 170 nm. These results were compared to the isotropic, gradually varying sinusoidal surface roughness of phase-separated polystyrene/poly(vinyl methyl ether) blend thin films. The AFM results were very similar to the results from the rubbed PS in terms of root-mean-square roughness and average peak-to-peak distance; however, the TXRF results revealed enhanced nickel fluorescence at incident angles smaller than the polymer critical angle for reflection. This discrepancy highlights some of the qualitative differences in surface topography between rubbed and phase-separated polymer thin films, and demonstrates the utility of angle-dependent TXRF to study thin film roughness and planarity.
Atomically flat gold film surfaces deposited on Si (111) surfaces at room temperature
Authors: Okamoto H. , Nejo H.
Published: July 2002

We have observed atomically flat gold surfaces deposited on Si (111) 7×7 surfaces. These films are deposited by conventional evaporative deposition at a pressure below 2×10−6 Pa. The surface topography was taken by scanning tunneling microscopy. Atomically flat terraces as large as 100 Å separated by steps were observed. This surface should provide a good substrate for scanning tunneling microscopy studies.
Interface charge and nonradiative carrier recombination in Ga2O3–GaAs interface structures
Authors: Passlack M. , Yu Z. , Droopad R. , Bowers B. , Overgaard C. , Abrokwah J. , Kummel A. C.
Published: July 2002

We have investigated the dual role of interfacial defects in creating both nonradiative interface recombination and interface charge. Our studies are based on Ga2O3–GaAs interface structures with their unique properties such as low interface state density and radiative GaAs band-to-band recombination. The self-consistent analysis of the steady-state dependence of the spontaneous GaAs emission on excitation density provides all critical characteristics of interfacial defects simultaneously: the density of interface states, their capture cross sections, the interface recombination velocities, and the oxide charge.
Novel fabrication technique for 0.1 μm T-shaped gate with i-line negative resist and poly(methylmethacrylate)
Authors: Anda Yoshiharu , Matsuno Toshinobu , Tanabe Mitsuru , Uda Tomoya , Yanagihara Manabu , Nishii Katsunori , Inoue Kaoru , Hirose Nobumitsu , Matsui Toshiaki
Published: July 2002

We report on a novel fabrication technique for 0.1 μm T-shaped gates using electron beam and i-line lithography. This technique adopts a TLOR-N001 (i-line negative resist)/950k poly(methylmethacrylate) (PMMA) bilayer system. From Fourier-transform infrared spectrum analysis, we found a 70 nm mixed layer of PMMA and TLOR was formed at the interface of these resists which offers suitable overcut resist profile for the T-shaped gate but also enhances the resistance of the PMMA against dry etching. By utilizing this process, we obtained a 0.12 μm gate length T-shaped gate and applied it to the fabrication of an AlGaAs/InGaAs pseudomorphic high electron mobility transistor with a fT and fmax as high as 66 and 190 GHz.
Emission stability of anodized silicon field emitter arrays
Authors: Kim Hong-Ryong , Jessing J. R. , Parker D. L.
Published: July 2002

The electrical characteristics of porous silicon field emitter arrays (PSFEAs) was studied. The surface of silicon field emitters was modified by electrochemical etching with HF: ethanol solution. Porous silicon consists of a high density of submicroscopic fibrils which serve as increased emission sites per tip, hence significantly improving the emission characteristics. PSFEAs exhibited low turn-on voltage and high emission current with small current fluctuation and good reproducibility.
Study of field emission of acid treated diamond films
Authors: Yuan G. , Jin Y. , Jin C. , Han L. , Wang X. , Chen H. , Ji H. , Gu C. , Wang W. , Zhao H. , Jiang H. , Zhou T. , Tian Y.
Published: July 2002

A electron emission was obtained at as low as about 2 V/μm from acid treated diamond films. An atomic force microscopy study shows there are many protrusions on the surface of the diamond films and their number increased after acid treatment. These results are discussed.
Surface treatment of pure and alloyed aluminum using a new plasma-based ion implanter apparatus
Authors: Popovici D. , Terreault B. , Bolduc M. , Paynter R. W. , Ross G. G. , Sarkissian A. H. , Stansfield B. L.
Published: July 2002

The characterization of an upgraded and flexible plasma-based ion implanter has been initiated, in terms of dose rate, uniformity, and control of the implant profile. In this article, we report the preliminary results of a comparative study of different means of hardening aluminium and reducing its friction coefficient, with an emphasis on microcharacterization [Auger electron spectroscopy (AES) and Rutherford backscattering spectroscopy depth profiling, x-ray photoelectron spectroscopy (XPS), and scanning force microscopy (SFM)]. In particular we present an AES study of the N and O depth profiles produced in Al by our system; an XPS characterization of the stoichiometry and bond chemistry of ion nitrided Al; and a SFM study of the respective roles of roughness and atomic forces in friction on the N-implanted samples.
Focused ion-beam structuring of Si and Si/CoSi2 heterostructures using adsorbed hydrogen as a resist
Authors: Fuhrmann H. , Döbeli M. , Mühle R. , Suter M.
Published: July 2002

A focused ion-beam system was used for structuring of silicon by local desorption of hydrogen from the HF-passivated surface. The native oxide which was formed on the depassivated regions was used as an etch mask for KOH. The etch contrast for Ga and Si ions was studied as a function of ion energy and fluence. With a fluence on the order of 1013 cm2, a feature height of 15 nm was obtained. The method was applied to produce 160 nm wide CoSi2 wires on a Si/CoSi2 heterostructure.
Photoluminescence of as-grown and thermally annealed InGaAsN/GaAs quantum wells grown by molecular beam epitaxy
Authors: Yang X. , Heroux J. B. , Jurkovic M. J. , Wang W. I.
Published: July 2002

InGaAsN/GaAs quantum wells on GaAs substrates were grown by solid source molecular beam epitaxy using a N2 radio frequency plasma source. Photoluminescence (PL) reveals a redshift in the PL peak of InGaAsN/GaAs quantum well with increasing N concentration. Rapid thermal annealing (RTA) of InGaAsN/GaAs quantum wells is shown to increase N incorporation and photoluminescence efficiency. A PL peak of 1.35 μm has been obtained at room temperature from an InGaAsN/GaAs quantum well after RTA at 550 °C. Room temperature pulsed operation of InGaAsN/GaAs single quantum well laser was demonstrated.
Passivation of GaAs using gallium-gadolinium oxides
Authors: Kwo J. , Murphy D. W. , Hong M. , Mannaerts J. P. , Opila R. L. , Masaitis R. L. , Sergent A. M.
Published: July 2002

The role of Gd2O3 is investigated in our previously discovered oxide films of Ga2O3(Gd2O3) for GaAs surface passivation. Based on the systematic dependence of the dielectric properties of (Ga2O3)1−x(Gd2O3)x on the Gd (x) content, we showed that pure gallium oxide does not effectively passivate GaAs, and Gd2O3 is a necessary component to stabilize the gallium oxide in the 3+ fully oxidized state due to the electropositive nature of Gd+3. This gives rise to electrically insulting films of low leakage current and high electrical breakdown strength.
Two-dimensional dopant profiling of patterned Si wafers using phase imaging tapping mode atomic force microscopy with applied biases
Authors: Nelson M. W. , Schroeder P. G. , Schlaf R. , Parkinson B. A.
Published: July 2002

Tapping mode atomic force microscopy with applied bias was used to spatially resolve areas of different doping type on Si wafers patterned with photolithography and subsequent ion implantation. The application of a direct current bias between cantilever and sample during the measurement produces Coulomb (electrostatic) forces, whose magnitude depends on the spatial variation of the doping density. This effect was utilized to detect areas of different doping type by monitoring the phase angle between the driving frequency and the cantilever response while scanning areas of different doping density. In this article we present a series of measurements at various bias voltages demonstrating that the observed phase contrast between differently doped areas is directly connected to the bias induced surface potential (band bending) present on these areas. To investigate the contrast mechanism quantitatively, we also measured deflection (force), amplitude and phase versus distance curves for a typical cantilever with an applied bias on a gold thin film. This allowed correlation between phase contrast observed and the actual Coulomb force measured.
Behavior of a new ordered structural dopant source in InAs/(001) GaP heterostructures
Authors: Gopal V. , Chen E.-H. , Kvam E. P. , Woodall J. M.
Published: July 2002

We report the characteristics of molecular-beam epitaxy grown InAs on highly lattice mismatched (001) GaP substrates. Strain relaxation in this system occurs at low thickness by the generation of a periodic two-dimensional square grid network of 90° misfit dislocations at the heterointerface. The very high interface dislocation density (∼1013 intersections/cm2) exerts a unique influence on the electronic properties of the system. An extended defect structure at the intersection of 90° misfit dislocations is proposed to act as an ordered structural donor source. Hall effect measurements indicate that this source is fully ionized with a constant sheet carrier concentration of 1013 cm−2, irrespective of the InAs layer thickness, and exhibits no freeze out at low temperatures. We have also demonstrated that the electron mobility increases significantly with InAs layer thickness, reaching values in excess of 10 000 cm2/V s in nominally undoped layers. The high threading dislocation density (∼1010 cm−2) in the InAs epilayers does not appear to have a deleterious effect on the transport properties of majority carrier electrons.
Study of growth process of germanium nanocrystals using a grazing incidence x-ray diffraction method
Authors: Ninomiya Hideyuki , Itoh Nobuo , Rath Shyama , Nozaki Shinji , Morisaki Hiroshi
Published: July 2002

The growth process of germanium nanocrystals in a SiOx matrix was studied by an x-ray diffraction (XRD) technique using the grazing incidence of x rays. The conclusion based on the XRD analysis of the Ge-doped glass is in good agreement with that from Raman spectroscopy and x-ray photoelectron spectroscopy. There are two stages of crystallization: the first stage is nucleation of the Ge nanocrystals at 600 °C, and the second stage is growth of the nanocrystals at 800 °C. During the second stage, the decomposition of GeOx into Ge and O in the Ge-doped glass sample results in fast growth of Ge nanocrystals. This is the first report that studied the growth of Ge nanocrystals in an SiOx matrix by XRD.
Use of the Schiller decapitation process for the manufacture of high quality tungsten scanning tunneling microscopy tips
Authors: de Raad G. J. , Koenraad P. M. , Wolter J. H.
Published: July 2002

When tungsten scanning tunneling microscopy (STM) tips are sharpened by self-sputtering with Ne+ ions, the Schiller-decapitation process can occur. We show that this process is accompanied by a very specific pattern in the sputter voltage as a function of time. This makes it possible to use the decapitation process for the manufacture of high quality STM tips. Our tips routinely produce atomic resolution in the [−110] and [001] directions on the {110} surfaces of GaAs and InP. The occurrence of the decapitation process is recognized by the observed pattern in the sputter voltage alone, without the presence of a phosphor screen. Secondly, we present a model which enables us to calculate the radius of curvature of the tip apex based on Fowler–Nordheim plots. Verification with scanning electron microscopy shows that our model is correct within 5 nm. A slight deviation of the experimental data from the theory suggests that our polycrystalline tungsten wire possesses a preferential crystal orientation.
Characterization of (Ba1−x,Srx)TiO3 thin films deposited on Pt/Ti/SiO2/Si substrates with different Ti buffer layer thicknesses
Authors: Lee Jae-Chang , Yoon Soon-Gil
Published: July 2002

(Ba1−x,Srx)TiO3 (BST) films were deposited on Pt/Ti/SiO2/Si substrates with various Ti buffer layer thicknesses by metalorganic chemical vapor deposition. The deposition rate and surface morphologies of the BST films were strongly dependent on the titanium buffer layer thickness. The deposition rate of BST films linearly increases with increasing Ti thickness. Titanium diffusion through the platinum bottom electrode played an important role as a nucleation site for BST growth. The 50 nm thick BST films deposited on Pt/Ti/SiO2/Si substrates with a Ti thickness of 50 nm have a dielectric constant of 190 and a dissipation factor of 0.025 at 100 kHz. The films showed symmetrical J-V characteristics with respect to the bias polarity and leakage current density of 8.0×10−7 A/cm2 at an applied voltage of 1 V. The optimal thickness of the Ti buffer layer in Pt/Ti/SiO2/Si substrates is important to obtain good electrical properties of BST films.
Ultrathin oxide films deposited using electron cyclotron resonance sputter
Authors: Amazawa Takao , Ono Toshiro , Shimada Masaru , Matsuo Seitaro , Oikawa Hideo
Published: July 2002

Ultrathin oxide films (SiO2, Al2O3,Ta2O5) with a minimum thickness of 2 nm have been deposited at low temperature by electron cyclotron resonance (ECR) sputter utilizing a plasma source coupled with a divided microwave beam. The uniformity of the film thickness was within ±2% over a 150 mm wafer. The surface roughness measured by atomic force microscopy was only 0.48 nm for a 100-nm-thick Al2O3 film. The fixed charge density of the Al/SiO2/Si metal oxide semiconductor capacitors decreased with increasing oxygen flow rate and substrate temperature during SiO2 deposition. A very low fixed charge density of about 5×1010 cm−2 was obtained without annealing the capacitor. The resistivities of SiO2, Al2O3, and Ta2O5 films with thicknesses from 2 to 40 nm were on the order of 1015 Ω cm. Under low electric fields the leakage current was a hopping current and under high electric fields it was a Poole–Frenkel current. The typical dielectric strength was 10 MV/cm for SiO2 and Al2O3 films. A high dielectric constant of 25 was obtained for Ta2O5 films. We think the low energy (10–20 eV) ion irradiation during ECR sputter contributed to the formation of smooth, high-quality oxide films.
Lateral growth of focused ion beam deposited platinum for stencil mask repair
Authors: DeMarco Anthony J. , Melngailis John
Published: July 2002

Focused ion beams can repair conventional lithography masks through milling and deposition. Repairs to stencil masks for ion projection lithography present a greater challenge than conventional mask repair, as the standard model of ion induced deposition requires a surface for deposition to take place. In a stencil mask, a bridge must be formed across the open area, anchored to the mask on either side of a slot. Focused ion beam deposition can induce such horizontal growth of material. Ion-induced growth of platinum over slots up to 3 μm wide in a 2.75 μm silicon membrane is demonstrated for an average beam current density of 7 mA/cm2. The primary method used to accomplish this is by scanning the focused ion beam in a rectangular pattern that extends over the slot. Material is built up from the edges, and grows inwards to span the slot and form a bridge. The direction of gas flow is an important consideration. When gas flow is perpendicular to the slot, the downstream side of the bridge will grow much faster than the upstream side. Gas flow parallel to the slot results in uniform growth from both sides. Platinum deposition was not found to be gas flow limited within the deposition parameters used. The horizontal growth as a function of time was measured, and found linear. The slope of this line is the horizontal growth rate, 23±0.05 nm/s. The x intercept of this line yields the minimum time for deposition to begin, which is 5.96±0.11 s. Sample bridges were deposited, and trimmed of excess material and redeposited platinum. These are presented as examples that uniformly wide bridges may be obtained at submicron dimensions, both in simple spanning and zig-zag configurations.
Thin-film gated photocathodes for electron-beam lithography
Authors: Pei Z. , McCarthy J. , Berglund C. N. , Chang T. P. H. , Mankos M. , Lee K. Y. , Yu M. L.
Published: July 2002

Photoemission has often been proposed as a promising approach for achieving arrays of independently modulated photocathodes for electron-beam lithography applications. In most such proposals the modulation of the photocurrent is assumed to be achieved by controlling the incident light energy reaching each photocathode. For many applications, however, the optical complexity of such a scheme limits the attractiveness of the photocathode approach. In this article we propose a novel gated photocathode structure which resolves this concern. It allows stable and reproducible electrical modulation of the photocurrent from each photocathode in a thin-film array under continuous optical illumination. In addition, by using illumination of the photocathodes through a transparent substrate, the position, the size, and the shape of each photocathode can be accurately determined during fabrication rather than being determined by the size of the optical illumination spot on the photocathode material. A number of structures with different geometry have been fabricated and tested, and found to exhibit behavior consistent with theoretical expectations. It is found that even in accelerating fields as high as 105 volts per cm, photocurrent can be extinguished by applying only a few volts to the gate of such structures.
Thermostable trilayer resist for niobium lift-off
Authors: Dubos P. , Charlat P. , Crozes Th. , Paniez P. , Pannetier B.
Published: July 2002

We have developed a novel lift-off process for fabrication of high quality superconducting submicron niobium structures. The process makes use of a thermostable polymer with a high transition temperature Tg=235 °C and an excellent chemical stability. The superconducting critical temperature of 150-nm-wide niobium lines is above 7 K. An example of shadow evaporation of a Nb-Cu submicron hybrid structure is given. A potential application of this process is the fabrication of very small single electron devices using refractory metals.
Residual gas effects on the emission characteristics of silicon field emitter arrays
Authors: Gilkes M. J. , Nicolaescu D. , Wilshaw P. R.
Published: July 2002

Measurements have been performed on the degradation of emission from silicon field emitting devices in ultrahigh vacuum (UHV) and vacuums containing CO2 and CH4 with anode potentials of 0 and 2500 V. Degradation is very fast in CO2, slower in CH4, and very slow in UHV. Analysis of the data using a numerical simulation shows that, in UHV, the degradation can be explained by an increase in work function with time. For CO2 and CH4, however, it is primarily due to a blunting of the tips that is partly compensated for by a decrease in work function as emission progresses. There is some evidence for tip sputtering being important in the case of CO2 at high anode voltages.
Radio frequency plasma annealing of positive charge generated by Fowler–Nordheim electron injection in buried oxides in silicon
Authors: Nazarov A. N. , Kilchytska V. I. , Barchuk I. P. , Tkachenko A. S. , Ashok S.
Published: July 2002

The accumulation and localization of the positive charge generated during Fowler–Nordheim electron injection in the buried oxide (BOX) of silicon implanted by oxygen (SIMOX) silicon-on-insulator structures have been studied. It is determined that the generated positive charge is localized near the BOX–silicon substrate interface, independent of the injected electron source (film or substrate). The positive charge generation probability in the SIMOX BOX is found to be considerably higher than that in thermal oxide. The generated positive charge is stable at thermal anneal temperatures up to 400 °C, but we demonstrate for the first time that an rf hydrogen plasma treatment is very effective in reducing this positive charge. The mechanism of rf plasma annealing of the positive charge in the BOX layer is discussed.
Water Production of Comet C/1999 S4 (LINEAR) Observed with the SWAN Instrument
Authors: Mäkinen J. Teemu T. , Bertaux Jean-Loup , Combi Michael R. , Quémerais Eric
Published: July 2002

The SWAN (Solar Wind ANisotropies) Lyman-alpha all-sky camera on the SOHO spacecraft observed the hydrogen coma of comet C/1999 S4 (LINEAR) from the end of May through mid-August 2000. A systematic set of water-production rates was obtained for this well-documented event of complete fragmentation of a cometary nucleus. The observations indicate that the lower limit for the sunlit surface area of the nucleus was about 1 square kilometer before the fragmentation and that the amount of water released throughout the observing period was 3.3 × 10
9
kilograms. Evidence suggests that the activity of the comet was dominated by successive fragmentation. There were four major outbursts, occurring about every 16 days. The 21 July event led to the complete fragmentation and sublimation of what remained of the nucleus, producing the last 3 × 10
8
kilograms of water. A model where the fragment size distribution follows the power law
N
(
R
) ∼
R
−
2.7
, where
N
and
R
are the number and radius of fragments, reproduces the observed dissipation. This distribution possibly reflects the internal structure of the nucleus.
Melting of (Mg,Fe)
2
SiO
4
at the Core-Mantle Boundary of the Earth
Authors: Holland Kathleen G. , Ahrens Thomas J.
Published: July 2002

The lower mantle of the Earth is believed to be largely composed of (Mg,Fe)O (magnesiowüstite) and (Mg,Fe)SiO
3
(perovskite). Radiative temperatures of single-crystal olivine [(Mg
0.9
,Fe
0.1
)
2
SiO
4
] decreased abruptly from 7040 ± 315 to 4300 ± 270 kelvin upon shock compression above 80 gigapascals. The data indicate that an upper bound to the solidus of the magnesiowüstite and perovskite assemblage at 4300 ± 270 kelvin is 130 ± 3 gigapascals. These conditions correspond to those for partial melting at the base of the mantle, as has been suggested occurs within the ultralow-velocity zone beneath the central Pacific.
Three-Dimensional Simulations of Plume-Lithosphere Interaction at the Hawaiian Swell
Authors: Moore William B. , Schubert Gerald , Tackley Paul
Published: July 2002

Rapid lithospheric thinning by mantle plumes has not been achieved in numerical experiments performed to date. Efficient thinning depends on small-scale instabilities that convectively remove lithospheric material. These instabilities are favored by hotter plumes or stronger temperature dependence of viscosity, and a simple scaling independent of rheology controls their onset. This scaling allows extrapolation of the results of numerical experiments to the Earth's mantle. Mantle plumes between 100 and 150 kelvins hotter than the background mantle should exhibit small-scale convective rolls aligned with the plate motion. The unusual variation in heat flow across the Hawaiian swell may be due to such instabilities. It was found that the spreading of the plume creates a downwelling curtain of material that isolates it from the rest of the mantle for distances of at least 1000 kilometers from the plume origin. This isolation has important consequences for the geochemical heterogeneity of the lithosphere and upper mantle.
Natural and Engineered Disorders of Lymphocyte Development
Authors: Fischer Alain , Malissen Bernard
Published: July 2002

Mammals have evolved complex developmental pathways to generate a large repertoire of B and T lymphocytes capable of mounting effective immune responses. Analysis of natural and engineered immunodeficiencies constitutes a powerful approach to delineating these pathways and identifying the molecular sensors that couple the survival of developing lymphocytes to the achievement of successful gene rearrangements at the loci coding for B and T cell antigen receptors. Besides identifying cytokines, growth factors, and transcription factors involved in lymphocyte development, genetic analysis also makes it possible to organize most of these protagonists into gene networks that control critical events in the life of developing lymphocytes.