bluuebunny/crossref_metadata_2025 huggingface dataset:
A 0–30 keV low-energy focused ion beam system
Authors: Kasahara H. , Sawaragi H. , Aihara R. , Gamo K. , Namba S. , Hassel Shearer M.
Published: July 2002

Low-energy focused ion beam (FIB) is a useful tool for shallow doping, gas-assisted etching, and other uses to minimize substrate damage in semiconductor device fabrication. The possibility to form a finely FIB of low energy under 1 keV was suggested in the investigations on the retarding mode in electron optical systems. The abilities of the simplest type of retarding mode FIB column are examined here. The optical properties are calculated for the corresponding model and some images are observed with Ga+ ion beams <0.3 μm in diameter for beam energies, 10, 5, and 1 keV, using a retarding mode one-lens FIB system. 1-keV and 100-eV Ga+ FIB was implanted to Ga/As substrate, and the defects are analyzed by deep-level transient spectroscopy. The defect concentration for 100 eV was < (1)/(5) that for 1000 keV.
Adsorption of NO on diamond C(111)-(2×1) by band-gap excitation
Authors: Hamza A. V. , Kubiak G. D.
Published: July 2002

Band-gap excitation promoted the adsorption of nitric oxide on diamond C(111)-(2×1). In the absence of laser excitation the sticking probability for NO was ∼10−8. Laser excitation of the surface at 226 nm, with a duty cycle of 10−7, significantly enhanced the adsorption of NO. The time-averaged reactive sticking probability for the laser-irradiated surface increased by more than a factor of 100. However, the reaction saturated at ∼1.2% of a monolayer oxygen adatom coverage, indicative of adsorption mediated by defect sites. Similar behavior was observed on the diamond C(100)-(1×1) surface. Translational activation of the adsorption of NO was also observed. The adsorption probability for NO accelerated to ∼280 meV by supersonic molecular-beam techniques was ∼6×10−4 for the diamond C(111)-(2×1) surface, but again chemisorption saturated at ∼1.6% of a monolayer O adatom coverage.
Ultraviolet laser excited adsorbate–surface interactions: NH3, C2H4, and CH2I2 on Al and oxidized Al surfaces
Authors: Chuang T. J. , Domen K.
Published: July 2002

The chemical interactions and the 308-nm laser radiation effects on NH3, C2H4, and CH2I2 adsorbed on Al and oxidized Al surfaces have been studied by x-ray photoemission, thermal desorption, and time-of-flight mass spectrometry. The mass and the translational energy distributions are determined as a function of surface coverage and laser fluence. For NH3 and C2H4, the major radiation effect appears to be laser-induced thermal desorption. For CH2I2 on Al, the adsorbate electronic excitation effect is evident at both submonolayer and multilayer coverages. At a submonolayer coverage, CH2 radicals and C2H4 molecules are produced and can be desorbed by laser pulses. Part of the products may be trapped on the surface. At a multilayer coverage on Al and any coverage on the oxidized Al, photodissociation leads to CH2I and I formation. At very high coverages, adsorbate-mediated ‘‘explosive’’ desorption can take place on any substrate. The results yield the characteristic electronic, thermal, and explosive desorption patterns depending on the gaseous exposure, the substrate, and the laser irradiation conditions.
Focused ion beam secondary ion mass spectrometry: Ion images and end-point detection
Authors: Harriott L. R. , Vasile M. J.
Published: July 2002

A secondary ion mass spectrometer (SIMS) has been added to a liquid metal source instrument which was designed as a micromachining apparatus. The SIMS performance rivals any reports to date on similar devices, even though no compromises were made with the primary function of the apparatus. End-point detection for ion milling allows depth control within a few hundred angstroms, on micron sized raster fields. A sensitivity of 4×10 5 cps/nA is routinely measured on 52Cr+ signals; similar count rates are also obtained from Al. Ion images on Cr or Al with sub-micron resolution with a 25-μm field are obtained in as little as 10 s collection time. Features as small as 0.3 μm can be defined by the secondary ion imaging, with the removal of only a few monolayers of material.
Schottky barrier heights and interface chemistry in Ag, In, and Al overlayers on GaP(110)
Authors: Alonso M. , Cimino R. , Maierhofer Ch. , Chassé Th. , Braun W. , Horn K.
Published: July 2002

We have carried out a study of the chemical reaction of silver, indium, and aluminium layers with cleaved GaP(110) surfaces using photoemission with synchrotron radiation. Core level photoelectron spectra show that silver and indium overlayers do not cause an interface reaction with GaP(110). The deposition of Al, on the other hand, leads to an extensive exchange reaction which also proceeds at low temperature, although influenced by changes in overlayer growth morphology. Surface band bending induced by the metallic overlayers was investigated as a function of deposition for n- and p-type material. In contrast to earlier findings, almost identical Schottky barrier heights for In and Ag deposition are obtained, despite the large difference in work function between these two metals. Results for Al also suggest that a small range of pinning positions is responsible for the Schottky barrier heights for junctions of these metals with GaP(110). We find that large peak shifts due to a surface photovoltage induced by the photoemission light source affect the determination of the Schottky barrier heights. This and other possible reasons for the discrepancy with earlier work are discussed.
Scattering from ionized dopants in Schottky barriers
Authors: van Schilfgaarde Mark
Published: July 2002

We calculate the true electrostatic potential that forms a Schottky barrier, arising from a random distribution of dopants in the depletion region. It is customary to model the electrostatic potential in a Schottky barrier by a one-dimensional quadratic potential, as would obtain from a jellium of charge in the depletion region. The difference between the true potential and the ‘‘ideal’’ one acts as a perturbation to electrons traversing the depletion region. This perturbation is found to be small, and effectively one dimensional. Its effect on the transmission probability of an electron tunneling through the depletion region is shown to be negligible. It is shown, however, that because of the large quantum dipoles near the metal–semiconductor interface, the image-force lowering correction does not in general vary as N1/4d, as is widely thought, at least for heavily doped materials. Local-density calculations of the Schottky barrier height were made for several metal/GaAs interfaces, to obtain the magnitude and range of the interfacial dipoles. They are found to be large and persist sufficiently far from the interface that they dominate the slowly varying potential from the ionized dopants. Thus, the interplay between the image-force potential and the interfacial dipoles determines the maximum in Schottky barrier height; moreover the quantum dipoles add an additional correction of the same magnitude as the image-force correction in the heavily doped case.
A double crystal x-ray diffraction characterization of AlxGa1−xAs grown on an offcut GaAs(100) substrate
Authors: Leiberich A. , Levkoff J.
Published: July 2002

Important corrections are required for x-ray diffraction characterization of epitaxial AlxGa1−xAs grown on offcut GaAs substrates. These corrections can have technological impacts for thin film fabrication where precise and reproducible process control is required. Double crystal x-ray diffraction measurements of AlxGa1−xAs grown on an offcut GaAs(100) substrate are interpreted in terms of a three step distortion of the film unit cell producing ‘‘defect free’’ heteroepitaxy: the film unit cell is first tetragonally, then triclinicly distorted, and finally tilted with respect to the substrate unit cell. The results indicate that the unit cell distortion and tilt angles oppose each other, forming a crystal geometry where the vector normals of the film and substrate (100) planes are approximately coplanar with the vector normal of the substrate’s surface. The film unit cell is triclinicly distorted in a way such that the film 〈100〉 axis remains approximately parallel to the substrate 〈100〉 axis. Application of conventional x-ray diffraction formalism based on a tetragonal distortion of the film unit cell to this more complicated unit cell geometry, can result in significant errors. Double crystal x-ray diffraction formalism is presented which accounts for a triclinic distortion and external tilt of the AlxGa1−xAs unit cell, leading to correct measurement of the film concentration and film/substrate crystal geometry.
I
n s
i
t
u patterning of GaAs by focused ion beam
Authors: Kosugi T. , Yamashiro T. , Aihara R. , Gamo K. , Namba S.
Published: July 2002

We have investigated the characteristics of ion beam induced spontaneous etching (IBISE) of GaAs by 15 keV Ga focused ion beam (FIB) irradiation and Cl2 gas. The area irradiated by the FIB showed high spontaneous etch rate to the exposure to Cl2 ambient. It was observed that the spontaneous etching depends on the residual H2O partial pressure. At H2O partial pressure less than 6×10−7 Torr, the threshold dose to observe IBISE was about 1015 ions/cm2 at a substrate temperature of 100 °C. However, at H2O partial pressure of 3×10−6 Torr, the threshold dose decreased below 1014 ions/cm2 at a substrate temperature of 90 °C. The small amount of H2O in Cl2 gas effectively decreases the threshold dose resulting in a reduction of radiation damage of the substrate and increasing the processing rate.
Scanning tunneling microscopy of laser-activated carbon electrodes used in studies of electrochemical charge-transfer reactions
Authors: Robinson R. S. , Sternitzke Kent , McCreery Richard L.
Published: July 2002

Carbon electrodes form the basis of a variety of electroanalytical sensors, in part due to their low cost, wide potential range, and suitability for modification. A major research effort is underway in many laboratories to understand better the properties of carbon electrodes regarding electrocatalytic activity and other factors such as background current and electron transfer activity. One method of improving the performance of these electrode materials involves the application of pulses from a Nd:YAG or N2 laser, either during or prior to electrochemical use. Both electrochemical and spectroscopic probes indicate dramatic changes to the surface of the electrodes after the pulses. Raman spectroscopy of the electrode surface indicates damage to the carbon lattice, with an increase in intensity of the Raman band at 1360 cm−1. This band is active in crystallites of finite size, and indicates increased exposure of graphitic edge plane. Also, there is a dramatic increase (≥106×) in heterogeneous charge-transfer rates measured with redox benchmark probes [Fe(CN)6−3/−4, dopamine]. Mechanisms of electrode activation by the laser pulses can involve roughening of the electrode surface, or ablation or cleaning of the electrode. Scanning tunneling microscope (STM) images of graphite and glassy carbon surfaces before and after delivery of laser pulses of various energies show a roughening of the surface from the laser treatment, with the appearance of new features of submicron size. The graphite electrodes show a highly disrupted surface, with jagged features and high roughness factors, determined from the STM images. None of the types of features observed in the laser-activated regions of graphite electrodes have been previously observed in our laboratory, in the course of dozens of experiments involving the imaging of different samples and grades of fresh or mechanically damaged graphite electrodes.
Scanning tunneling microscope as a probe for local conductivity
Authors: García Cantú Rigoberto , Huerta Garnica Miguel A.
Published: July 2002

A new technique useful to detect local changes on surface conductivity while tunneling is described. It is possible to obtain scanning tunneling microscopy topographic images simultaneously with well defined patterns of conductivity variations, working at air pressure, from a cooper sample. We also show results obtained from austenitic steel samples.
I
n s
i
t
u electrochemical scanning tunneling microscopy of single-crystal surfaces of Pt(111), Rh(111), and Pd(111) in aqueous sulfuric acid solution
Authors: Sashikata Kenji , Furuya Nagakazu , Itaya Kingo
Published: July 2002

I n situ electrochemical scanning tunneling microscopy (STM) was applied to single-crystal platinum(111), rhodium(111), and palladium(111) surfaces in an aqueous sulfuric acid solution. Atomically flat surfaces of Pt(111) are roughened in solutions by the electrochemical oxidation–reduction cycle. It is shown that a single potential cycle causes the formation of many adatoms and very small clusters on the Pt(111) terrace. A steady-state surface structure can be clearly observed after applying a few potential cycles. The STM image is composed of regularly arrayed islands whose diameter and height are in the ranges of 2–3 and 0.5–0.75 nm, respectively. Atomically flat terrace-step structures can be also observed on Rh(111) and Pd(111) surfaces. The effect of oxidation–reduction cycle on these surfaces is also discussed.
Internal structure and two-dimensional order of monolayer C60 molecules on gold substrate
Authors: Chen T. , Howells S. , Gallagher M. , Yi L. , Sarid D. , Lichtenberger D. L. , Nebesny K. W. , Ray C. D.
Published: July 2002

Monolayer coverages of C60 on a gold substrate have been studied using scanning tunneling microscopy. The images reveal various packing arrangements and reproducible intramolecular contrasts of the C60 molecules. We find that approximately every other carbon atom is highlighted on the π-electron surface of the molecule as a result of a preferential electron transfer from the gold substrate, in agreement with a theoretical analysis of the high-lying π-electron density of a C60 molecule adsorbed on metallic surfaces.
Substrate temperature dependence of arsenic precipitate formation in AlGaAs and GaAs
Authors: Mahalingam K. , Otsuka N. , Melloch M. R. , Woodall J. M. , Warren A. C.
Published: July 2002

GaAs epilayers which are grown by molecular-beam epitaxy under ‘‘normal’’ group III–V fluxes but at very low substrate temperatures contain as much as 1% excess arsenic. Upon annealing these epilayers at a temperature of 600 °C, the excess arsenic forms precipitates. We have undertaken a systematic study of the substrate growth temperature dependence of this incorporation of excess arsenic in both GaAs and Al0.3Ga0.7As epilayers. The substrate growth temperature was varied in increments of 25 °C from 225 to 375 °C after every 0.25 μm of film growth for a GaAs and an Al0.3Ga0.7As epilayer. Both epilayers were grown using a dimer arsenic source and a group V to total group III beam equivalent pressure ∼20. After growth the films were annealed for 1 h in the As2 flux at a temperature of 600 °C. Cross-sectional samples were than prepared by the ion thinning technique and examined by transmission electron microscopy (TEM). Both epilayers contained arsenic precipitates; this is the first observation of arsenic precipitates in an Al0.3Ga0.7As epilayer. The density of the arsenic precipitates in the two epilayers had a strong dependence on substrate growth temperature. Details of the film growth and of the TEM observations are reported.
Etching of polysilicon in a high-density electron cyclotron resonance plasma with collimated magnetic field
Authors: Dane D. , Gadgil P. , Mantei T. D. , Carlson M. A. , Weber M. E.
Published: July 2002

Polysilicon etch rates and polysilicon-silicon dioxide selectivities have been measured in a collimated electron cyclotron resonance (ECR) chlorine discharge as a function of microwave power, pressure, gas flow rate, O2 addition, and substrate position. High chlorine flow rates, moderate input microwave power, and reduced wafer separation from the ECR plane were found to provide simultaneous high polysilicon etch rates and high polysilicon-oxide selectivities. The addition of a small amount of oxygen to the chlorine plasma establishes an etch-deposition competition which can increase the polysilicon-oxide etch selectivity. Polysilicon etch rates of 4000–5000 Å/min are obtained in combination with stable polysilicon-oxide etch selectivity values of 50–150 and polysilicon-resist selectivities of 13–15, using 150 sccm Cl2, 0.6% O2, 3 mTorr total pressure, and 700 W input microwave power. The etched profiles are anisotropic with residue-free surfaces.
Defect repair for soft x-ray projection lithography masks
Authors: Tennant D. M. , Fetter L. A. , Harriott L. R. , MacDowell A. A. , Mulgrew P. P. , Waskiewicz W. K. , Windt D. L. , Wood O. R.
Published: July 2002

The most promising option for masks intended for use in soft x-ray projection lithography (SXPL) at λ=13 nm is a reflective mask which uses a Mo/Si multilayer reflective coating. A variety of multilayer coated reflective mask technologies have been reported which can provide both high-resolution features and good reflectance contrast between the patterned and unpatterned regions. Repair of defects generated during patterning is a necessary feature of any practical mask technology. We have investigated the application of focused ion beam milling and deposition to programmed defects in the absorber layer of a SXPL Mo/Si multilayer reflection mask. Use of a sacrificial polymer barrier layer is described as well as milling and deposition conditions. The effect of ion implantation of the barrier layer on its removal after absorber repair is also reported. Both reflectivity measurements and resist images comparing repaired and unrepaired regions of masks are used to demonstrate the efficacy of the technique.
100 kV field emission electron optics for nanolithography
Authors: Gesley Mark
Published: July 2002

A 100 kV optics with field emission source is designed for an electron-beam nanolithography system. A new electrostatic gun lens permits high-voltage operation with low aberrations. A demagnifying double-lens column with fixed magnification and variable aperture is used. The optics are weighted towards 100 kV operation, but the beam voltage can be varied from 25 to 100 kV with resolution maintained below 20 nm. The gun uses a Zr/O/W<100≳ cathode operated near the extended-Schottky emission regime to achieve 1%/h current stability at a fixed extraction voltage. With the source emitting a 0.5 mA/sr angular intensity, 1.5 nA can be focused to 6 and 10 nm with beam voltages of 100 and 50 kV, respectively. A target current density of 2000 A/cm2 with an effective brightness of 1×108 A/cm2 sr enables 2 MHz pixel rate exposures of PMMA at 100 kV with a vector-scan deflection system.
Electrical characteristics of Ar-ion sputter induced defects in epitaxially grown n-GaAs
Authors: Auret F. D. , Goodman S. A. , Myburg G. , Meyer W. E.
Published: July 2002

Epitaxially grown n-type GaAs was sputtered by bombarding it with Ar ions at energies of between 0.5 and 5 keV at a dose of 1013 ions/cm2. The fabrication of Au Schottky barrier contacts followed directly after the sputtering. The electrical characteristics of the the sputter induced defects were studied using deep-level transient spectroscopy (DLTS). Several defects with discrete defect levels ranging from 0.05–0.70 eV below the conduction band, as well as defects with continuously distributed energies in the conduction band, were introduced during sputtering. Concentration depth profiling revealed that whereas some defects are located very close to the interface, others were detected several microns below the interface. The depth of some of these deep lying defects increased with sputter voltage. A possible explanation of the reduction in EL2 DLTS signal previously observed after sputtering is shown to be the sputter induced barrier height lowering.
Electronic and optical characterization of InGaP grown by gas-source molecular-beam epitaxy
Authors: Masselink W. Ted , Zachau Martin , Hickmott T. W. , Hendrickson Kristi
Published: July 2002

We have prepared films of InGaP on GaAs substrates using gas-source molecular-beam epitaxy. Unintentionally doped InGaP is n-type, with the net electron concentration as low as 1× 1015 cm−3 with associated 300 K mobility of 2100 cm2/V s. Photoluminescence and photoluminescence excitation spectra at 2 K of undoped InGaP films show free exciton luminescence with line widths as narrow as 8.5 meV. Such high quality InGaP layers were incorporated as the insulating layer into p−-i-p+ and n−-i-n+ GaAs–InGaP–GaAs heterojunction capacitors. Current–voltage characteristics of these structures indicate thermionic-emission barrier heights for holes of between 420 and 450 meV, indicating that the valence band discontinuity between GaAs and InGaP is very large, comprising up to 90% of the total band gap difference.
10 nm Si pillars fabricated using electron-beam lithography, reactive ion etching, and HF etching
Authors: Fischer Paul B. , Dai Kevin , Chen Erli , Chou Stephen Y.
Published: July 2002

This article reports the fabrication and preliminary photoluminescence (PL) study of free-standing Si pillars with diameters of about 10 nm and aspect ratios greater than 15. The pillars were fabricated using electron-beam lithography, chlorine based reactive ion etching (RIE), and subsequent HF wet etching. Using HF etching offers several advantages: (a) it is a relatively stress independent process and therefore preserves the original shape of the structure; (b) it is a room temperature process; (c) it has a very controllable etch rate, ∼1.9 nm/h; and (d) it can remove RIE damage and passivate the Si surface. PL with a peak at 720 nm was repeatedly observed from an array of nanoscale pillars with ∼20 nm diameters. However, the cause of such PL is still unclear.
Identification of the volatile reaction products of the Cl2+GaAs etching reaction
Authors: Su Chaochin , Hou Hui-qui , Lee Gang Ho , Dai Zi-Guo , Luo Weiang , Vernon Matthew F. , Bent Brian E.
Published: July 2002

A molecular beam of Cl2 is reactively scattered from a single crystal GaAs (100) surface. Analysis of the mass spectra and of the angular and velocity distributions for the volatile reaction products over the surface temperature range 330–950 K shows that the major volatile reaction products are AsCl3, As4, As2, GaCl3, and GaCl. To correctly identify the GaCl3 and AsCl3 reaction products by mass spectrometry, the vibrational energy dependence of the daughter ion fragmentation patterns was measured by injecting GaCl3 and AsCl3 from a heated nozzle into the mass spectrometer. To convert the ion signals from the mass spectrometer (which are proportional to product density in the ionizer region) to quantities proportional to product flux from the surface, measurements of the product angular and velocity distributions were utilized. The relative product fluxes were then determined by assuming stoichiometric etching of GaAs. The five relative sensitivity factors determined from this fit are consistent with stoichiometric etching and achieve a chlorine mass balance to within 5% over the entire temperature range studied (330–950 K). The absolute reaction probability was determined by comparing the product fluxes and the flux of unreacted Cl2, and the absolute etch rate was established by correlating the ion intensities measured for the evaporation of GaAs with the absolute evaporation rate reported in the literature. For a Cl2 flux of 1.75×1015 molecules/cm2/s and a surface temperature of 750 K, the reaction probability is 0.42±0.05 and the etch rate is ∼2 ML/s. Finally, the effect of translational energy on the absolute etch rate and relative product flux distributions was measured by changing the rare gas diluent of the adiabatic expansion. No change in the etch rate or relative product yields was observed within experimental error for a variation of 0.025–0.15 eV in the translational energy directed along the surface normal.
Combined scanning tunneling and force microscopy
Authors: Anselmetti D. , Baratoff A. , Güntherodt H.-J. , Gerber Ch. , Michel B. , Rohrer H.
Published: July 2002

A combined scanning tunneling and force microscope (STM/FM) was built which allows for the simultaneous measurement of forces and force gradients along STM constant current contours. Measuring Au(111) surfaces with this combined STM/FM, very low tip–sample interaction forces and variations of the local stiffness (force gradient) in the vicinity of single adsorbates and domain boundaries of the Au(111) (√3×23) surface reconstruction were found. On Au(111) substrates covered by a compact thin organic film the interaction force is higher, indicating repulsive contact between tip and sample. An elastic theory for the deconvolution of real topography from local electronic and sample deformation effects on STM constant current contours of soft samples was developed.
50-kV pulse generator for plasma source ion implantation*
Authors: Böhm G. , Günzel R.
Published: July 2002

The pulse generator has been especially designed by Puls-Plasmatechnik GmbH for the application of the field of plasma source ion implantation. The maximum output voltage is −50 kV. The pulse frequency can be adjusted up to 100 Hz. A brief survey is given in this article.
Scanning tunneling microscopy tip-dependent image contrast of S/Pt(111) by controlled atom transfer*
Authors: McIntyre B. J. , Sautet P. , Dunphy J. C. , Salmeron M. , Somorjai G. A.
Published: July 2002

Sudden changes in the detailed appearance and corrugation of atomic-resolution scanning tunneling microscopy (STM) images are commonly observed. In particular, these effects for the Pt(111)(√3×√3)R30°-sulfur structure have been studied. Corrugation changes have been investigated by the controlled transfer of atoms between tip and sample. Theoretical image simulations using electron scattering quantum chemical methods show that the image contrast is strongly dependent on the chemical identity of the STM tip atom. Observed changes in the sulfur images can be explained by changes from platinum-terminated to sulfur-terminated STM tips.
Scanning probe microscopy on the surface of Si(111)
Authors: Meyer E. , Howald L. , Lüthi R. , Haefke H. , Rüetschi M. , Bonner T. , Overney R. , Frommer J. , Hofer R. , Güntherodt H.-J.
Published: July 2002

An ultrahigh vacuum atomic force microscope, operated in the noncontact mode, is used to characterize n-doped Si(111) surfaces. Ionized impurities are observed with electrostatic forces, demonstrating contrast reversal by changing the polarity of the voltage between probing tip and sample. The impurities form one-dimensional domains on the silicon surface. Steps and lines, connecting kink sites, are preferentially occupied by these impurities.
Laser-frequency mixing in a scanning force microscope and its application to detect local conductivity
Authors: Völcker M. , Krieger W. , Walther H.
Published: July 2002

When two infrared laser beams are coupled into the tip of a scanning tunneling microscope, the difference frequency is generated in the tunneling junction and can be observed via an emitted wave. In order to obtain a detectable signal also in the case of a force microscope, a locally conducting area has to be opposite to the tip. This allows one to distinguish between conducting and nonconducting regions of a sample when a force microscope is used for the experiments. The difference-frequency signal is found to decrease with decreasing size of conducting islands. The detection is limited at present to islands larger than about 1 μm in diameter. A simple model for the difference-frequency generation in the tip–sample junction is presented. From this model, improvements of the method can be derived which lead to the possibility that still smaller structures can be investigated.
Nanometer-scale recording, erasing, and reproducing using scanning tunneling microscopy
Authors: Sato Akinobu , Momose Satoru , Tsukamoto Yuji
Published: July 2002

We demonstrate using a scanning tunneling microscope reproducible and reversible recording and erasing of marks about 10 nm in size. Studies on both data storage devices and nanometer fabrication using a scanning tunneling microscope have been carried out, involving a variety of techniques and materials. However, most studies neglect erasing, despite the fact that erasing is a major requisite, as well as recording and reading. Using a thin layer of a vanadate glass deposited on vanadium bronze, β-NaxV2O5, has made it possible to record, erase, and read 10 nm level marks at ambient temperature and pressure. The main mechanism for reversible recording is sodium ion migration between the vanadium bronze crystal phase and the vanadate amorphous phase along the electric field. The organic medium of a hemiquinone molecule was proposed for higher recording speed.
Surface structure of ferroelectric domains on the triglycine sulfate (010) surface
Authors: Bluhm H. , Wiesendanger R. , Meyer K.-P.
Published: July 2002

Scanning force microscopy investigations on the triglycine sulfate (010) surface were carried out employing the method of matched faces. The difference in the etch rate of surfaces of ferroelectric domains with opposite polarity as observed with optical microscopy and scanning electron microscopy could be confirmed. The shape of the etch products on domains with equal polarity on the matching surfaces was found to vary widely. The height and direction of steps at the domain boundaries were measured and discussed with respect to earlier work done by means of transmission electron microscopy. A model which explains the differences in the step heights at the domain boundaries is given under consideration of the shift in the atom positions during ferroelectric polarization reversal.
Impact of reduced resist thickness on deep ultraviolet lithography
Authors: Azuma T. , Ohiwa T. , Okumura K. , Farrell T. , Nunes R. , Dobuzinsky D. , Fichtl G. , Gutmann A.
Published: July 2002

Potential capabilities of a thinner resist process are verified from both points of view—lithography and etch processes. The experimental results for lines and spaces indicate that a larger gain in process window could absolutely go along with reduced resist thickness. It is found that the thinner resist process could successfully improve not only the optical proximity effect in lithography processes but also the microloading effect in etch processes. It is also demonstrated that an application of the thinner resist process would be useful to further extend advantages of higher numerical aperture exposure systems. The thinner resist process is found to be effective to improve the process window of contact holes. Moreover, a novel pattern transfer process could be demonstrated using the practical limit of resolution capability up to k1=0.4.
Photoluminescence blueshift induced by reactive ion etching of strained CdZnSe/ZnSe quantum well structures
Authors: Sparing L. M. , Wang P. D. , Xin S. H. , Short S. W. , Shi S. S. , Furdyna J. K. , Merz J. L. , Snider G. L.
Published: July 2002

A study of the effects of reactive ion etching (RIE) on molecular beam epitaxy-grown Zn1−xCdxSe/ZnSe strained multiple quantum well samples using low temperature photoluminescence reveals a blueshift in the characteristic peak positions of the wells when etched with CH4/H2. Based on the experimental results, we suggest that the blueshift is not a result of hydrogen incorporation, but that etch induced damage relaxes the compressive strain present in the as-grown quantum well, producing the observed blueshift. After thermal annealing the energy of the photoluminescence signal returns to its original value, suggesting a restoration of the strain by elimination of the structural damage induced by RIE. However, the original photoluminescence intensity is not recovered by annealing.
Improved cathodoluminescence properties of GaAs/Al0.3Ga0.7As tilted T-shaped quantum wires fabricated on (111)B facet by glancing-angle molecular beam epitaxy
Authors: Tomita N. , Tanaka M. , Saeki T. , Shimomura S. , Hiyamizu S. , Fujita K. , Watanabe T. , Higuchi T. , Sano N. , Adachi A.
Published: July 2002

GaAs/Al0.3Ga0.7As tilted T-shaped quantum wires (T-QWRs) were fabricated by growing Al0.3Ga0.7As/GaAs (well thickness of GaAs Lw=4.4 nm) on a (111)B facet plane that was formed when a GaAs/Al0.3Ga0.7As multi-quantum well (MQW) layer (Lw=4.5 nm) was grown on a reverse-mesa etched GaAs(100) substrate by glancing-angle molecular beam epitaxy (GA-MBE). Growth conditions of the tilted T-QWR were optimized, and full width at half-maximum (FWHM) of a cathodoluminescence (CL) peak from the tilted T-QWRs was reduced down to 19 meV at 78 K, which is about one-third of that (61 meV) of previous GaAs/Al0.3Ga0.7As tilted T-QWRs.
Critical humidity for removal of atoms from the gold surface with scanning tunneling microscopy
Authors: Lebreton C. , Wang Z. Z.
Published: July 2002

By applying voltage pulses (<3 V, 100 ms) across the tunneling gap in nitrogen gas in the presence of water or ethanol vapor, nanometer-scale holes can be produced on the Au(111) surface. It is impossible to make holes by applying negative pulses to the sample. After applying voltage pulses with the scanning tunneling microscopy, the created features are imaged by atomic force microscopy. We have measured the relationship between threshold voltage and relative humidity (Rh) and have discovered the existence of a critical humidity (Rhc) for hole formation. When above Rhc, the threshold voltage (Vt) is nearly constant and the probability of hole formation changes dramatically at Vt. Below Rhc, Vt increases rapidly with reducing Rh until it becomes higher than the threshold voltage for mound formation. Different types of tips (Pt/Ir, Au, W, Au/Pd, Ag) have been used in this study, but the relationship between Vt and Rh is basically independent of the tip material and the tip geometry. The effect of the pulse width on the hole and mound formation are also examined. We conclude from these experiments that the mechanism of this surface modification (removal of atoms from the gold surface) may be electrochemical in origin.
Low-temperature scanning tunneling microscopy on vicinal Ge(100)
Authors: Röttger B. , Bertrams Th. , Neddermeyer H.
Published: July 2002

Using variable temperature scanning tunneling microscopy vicinal surfaces of Ge(100) have been studied in a temperature range between 80 and 300 K (room temperature). Annealing the sample gives rise to a nonuniform terrace and step distribution. Terraces with dimer rows perpendicular to the step edges cover approximately 3/4 of the entire surface. At room temperature about 1/2 of the surface is covered by buckled dimers. Dimers of straight SA steps are always pinned, i.e., they appear in their buckled form. On top of terraces buckling is also found, associated either with kinks in the step edges or in the formation of a single antisite dimer. At 80 K all dimers appear asymmetric in c(2×4) or p(2×2) geometry. A transition between both structures may occur due to sample–tip interaction which indicates that the energies of both reconstructions are rather similar.
Electrical characterization of diamond and graphite coated Mo field emitters
Authors: McClure M. T. , Schlesser R. , McCarson B. L. , Sitar Z.
Published: July 2002

Current–voltage characteristics of tip-shaped molybdenum field emitters were investigated before and after coating with diamond or graphite powders. Stable emission was observed only after annealing and formation of a conductive Mo carbide layer at the metal-coating interface. Both coated emitters displayed enhanced emission and “turn-on” voltages reduced by a factor of 2 as compared to the uncoated emitters. For the graphite coated emitter, the enhancement was attributed to an increase in the field enhancement factor due to the coating morphology. Roughening of the Mo-diamond interface via carbide formation during the annealing step was presumed to have been the cause for the enhanced emission for the diamond coated emitter. The transmission probabilities for the Mo-diamond and diamond-vacuum interfaces were calculated, using the WKB method, based on an emission mechanism from the intrinsic diamond’s conduction band minimum. With a field locally enhanced to 108 V/cm, the transmission probability for the diamond-vacuum interface was 108 times larger than that of the Mo-diamond interface. This evaluation confirmed that the electron affinity of the diamond surface is not a governing factor in the emission from intrinsic diamond.
Comparison of electron affinity and Schottky barrier height of zirconium and copper–diamond interfaces
Authors: Baumann P. K. , Nemanich R. J.
Published: July 2002

In this study, the evolution from diamond surfaces to metal–diamond interfaces has been examined. The electron affinity and the Schottky barrier height of a few Å thick films of Zr and Cu deposited in ultrahigh vacuum (UHV) onto IIb substrates were correlated. Prior to metal deposition, the diamond surfaces have been cleaned by different anneals and plasma treatments in UHV, and the surfaces were characterized by Auger electron spectroscopy and atomic force microscopy. The initial surfaces were terminated with oxygen, or free of chemisorbed species. Ultraviolet photoemission spectroscopy was employed to determine whether the samples exhibited a positive electron affinity or a negative electron affinity (NEA) before and after metal deposition. For Zr, the Schottky barrier height was found to change very little with the presence or absence of chemisorbed species at the interface. A NEA was observed for Zr on diamond independent of the surface termination. However, for Cu, the surface cleaning prior to metal deposition had a more significant effect. The Schottky barrier height changed strongly depending on the chemical species at the interface. A NEA was only detected for Cu on clean diamond surfaces. The differences between Zr on the one hand and Cu on the other are correlated with differences in interface chemistry and structure.
Self-aligned silicon tips coated with diamondlike carbon
Authors: Lee Sanjo , Lee Sunnup , Lee Sungwoon , Jeon D. , Lee Kwang-Ryeol
Published: July 2002

Silicon field emitter tips are coated with diamondlike carbon (DLC) film. Argon-ion bombardment of the tips increased the aspect ratio and helped uniform DLC coating. Using DLC-coated tips, we have fabricated a self-aligned gated field emission array.
Two-dimensional imaging of charge carrier profiles using local metal–semiconductor capacitance–voltage measurement
Authors: Li Y. , Nxumalo J. N. , Thomson D. J.
Published: July 2002

We will report a variation of the scanning capacitance microscopy for two-dimensional delineation of semiconductor charge carrier profiles based on the measurement of the local Schottky contact capacitance. When a metal probe is brought into contact with a semiconductor, a space-charged depletion region and therefore a capacitor is formed at the junction. By applying a small ac voltage, the voltage derivative of the contact capacitance can be measured with a lock-in amplifier. The amplitude of the derivative signal is a function of the carrier concentration, and the sign gives the type of carrier. We have carried out the local contact capacitance–voltage measurements on standard doping concentration samples and two-dimensional (2D) carrier concentration profiling on device structures. The results demonstrate that the contact capacitance measurement is capable of quantitative 2D characterization of semiconductor devices. These preliminary results also demonstrate that this technique, when used as a method for carrier profiling, is relatively insensitive to the sample surface condition.
Field emitter array development for microwave applications. II
Authors: Spindt C. A. , Holland C. E. , Schwoebel P. R. , Brodie I.
Published: July 2002

Microfabricated field emitter arrays are being used in an ongoing DARPA/NRL program as a means for gating or prebunching electrons in a microwave amplifier tube. The goals of the program are to demonstrate 10 dB gain at 50 W and 10 GHz in a gated Klystrode amplifier tube with 50% efficiency. The proposed cathode specifications call for 160 mA peak emission and 10 GHz emission modulation from an annular emitter array having a 600 μm outer diameter and an inner diameter to be determined by transconductance and capacitance requirements. Experimental results have shown an average array capacitance of 6 nF/cm2, and that a transconductance of 1 μS/tip can be achieved at emitter–tip loadings of 10 μA/tip. Calculations based on these results show that emitter arrays having 0.4 μm diam gate apertures on 1 μm centers, a 600 μm outer diameter, and a 560 μm inner diameter should meet the tube specifications. Such arrays have been fabricated and shown to have essentially the same characteristics (Fowler/Nordheim coefficients) as the test cathodes used to develop the design parameters. These microwave cathodes have been successfully modulated at 10 GHz rates in an experimental Klystrode amplifier tube at CPI (formerly the Varian Associates Microwave Power Tube Division), and microwave output power has been achieved. Ongoing trials are showing steady progress toward the program goals.
Self-assembled Ge dots: Growth, characterization, ordering, and applications
Authors: Schittenhelm P. , Engel C. , Findeis F. , Abstreiter G. , Darhuber A. A. , Bauer G. , Kosogov A. O. , Werner P.
Published: July 2002

The Stranski–Krastanow growth mode, which leads to the self-assembled formation of dots, allows one to exceed the critical thickness without introducing dislocations. We report the coverage limits for the dislocation-free dot regime in dependence of the Ge content, and also the composition dependent thickness of the two-dimensional wetting layer. To reduce the size inhomogeneity of the self-assembled dots, we investigated ordering effects in Si/Ge-dot multilayers. The experiments do not only reveal a strong vertical ordering of the dots, but also a lateral correlation and a significantly increased size homogeneity is observed. Results on first device structures, a npn-infrared detector and a silicon based tunneling structure, both with embedded layers of self-assembled Ge dots, are presented.
Experimental and theoretical considerations on evacuation of vacuum package for field emission display
Authors: Han Jeong-In , Kwak Min-Gi , Park Yong-Kuy , Lim Sang-Cheul , Lee In-Kyu , Cho Kyong-Ik , Yoo Hyung-Joun
Published: July 2002

In order to obtain the practical vacuum data in field emission display packages which are composed of very thin gapped glass plates, the effects of heating time and temperature as well as geometrical factors such as the gap size between the glass plates, the inner diameter, and length of the evacuation tube were investigated. Even though the evacuation system is in an ultrahigh vacuum of more than 1.0×10−7 Torr, the attained vacuum level with 55 mm×55 mm×1.1 mm panel was 3.0×10−5 Torr. The attainable vacuum level for the panel was calculated by considering conductance of the evacuation system. The calculated and measured values are consistent (2.8×10−5 and 3.0×10−5 Torr). Heating glass frit sealed packages do not improve vacuum level and H, H2O, CO, and CO2 were identified as impurities remaining inside of the panels.
Dry etching of Si field emitters and high aspect ratio resonators using an inductively coupled plasma source
Authors: Rakhshandehroo M. R. , Weigold J. W. , Tian W.-C. , Pang S. W.
Published: July 2002

An inductively coupled plasma (ICP) source has been used to generate a Cl2 plasma for the etching of Si field emitters and resonators. An optimized etch condition was used to etch Si field emission devices with controllable sidewall angles as well as good uniformity for large arrays of emitters. A mask erosion technique was used to control the Si emitter profile. The sidewall angle of Si emitters increased from 55° to 75° as plasma pressure was increased from 0.1 to 5.0 mTorr. Sharp tips with good uniformity and a high packing density of 6.25×106 tips/cm2 were fabricated using 200 W ICP source power, 100 W stage power at 1 mTorr with 20 sccm of Cl2 flowing and an ICP source to sample distance of 8 cm. Released Si mechanical resonators were also fabricated with a vertical etch profile and smooth surfaces. An optimized etch condition of 250 W ICP source power and 70 W stage power at 5 mTorr with 20 sccm of Cl2 flow and an ICP source to sample distance of 6 cm provided an etch rate of 219 nm/min and a selectivity to a Ni–Ti mask of 26. Due to the high selectivity and etch rate, resonators and cantilevered beams as thick as 40 μm were fabricated giving improved device performance compared to thinner devices. Submicrometer Si resonators were also fabricated that were 3.1 μm thick with 1.7 μm wide comb drive fingers and 0.2 μm gaps between them.
What can electron paramagnetic resonance tell us about the Si/SiO2 system?
Authors: Lenahan P. M. , Conley J. F.
Published: July 2002

Electron paramagnetic resonance (EPR) measurements of Si/SiO2 systems began over 30 years ago. Most EPR studies of Si/SiO2 systems have dealt with two families of defects: Pb centers and E′ centers. Several variants from each group have been observed in a wide range of Si/SiO2 samples. Some of the most basic aspects of this extensive, body of work remain controversial. EPR is an extraordinary powerful analytical tool quite widely utilized in chemistry, biomedical research, and solid state physics. Although uniquely well suited for metal–oxide–silicon (MOS) device studies, its capabilities are not widely understood in the MOS research and development community. The impact of EPR has been limited in the MOS community by a failure of EPR spectroscopists to effectively communicate with other engineers and scientists in the MOS community. In this article we hope to, first of all, ameliorate the communications problem by providing a brief but quantitative introduction to those aspects of EPR which are most relevant to MOS systems. We review, critically, those aspects of the MOS/EPR literature which are most relevant to MOS technology and show how this information can be used to develop physically based reliability models. Finally, we briefly review EPR work dealing with impurity defects in oxide thin films.
Optical data storage in LiF using electron beam encoding
Authors: Caine E. J. , Miller S. D.
Published: July 2002

Electron beam generated color centers in LiF are presented as the basis for a new optical data storage scheme. Data are “read” with a confocal microscope. The alkali halide medium is capable of gray scale and multilevel or volumetric storage demonstrating a thermally stable coloration. This initial investigation shows that data can be resolved to less than 0.25 μ resolution with at least three orders of magnitude data scaling. An assessment is made for future work.
Using neutral atoms and standing light waves to form a calibration artifact for length metrology
Authors: Thywissen J. H. , Johnson K. S. , Dekker N. H. , Chu A. P. , Prentiss M.
Published: July 2002

Beams of neutral metastable atoms can be patterned by spatially dependent deexcitation in a standing wave of laser light. Metastable atoms which hit a substrate transfer their internal energy (10–20 eV) to the surface and activate the formation of a durable carbonaceous resist from a vapor precursor. The resist can be used as an etch mask to transfer patterns into the substrate material. In this work, we report a recent experimental demonstration of this “standing wave quenching” (SWQ) patterning technique. We also present an analysis of the accuracy to which atom lithography and SWQ can form a periodic reference array for length metrology. We find that, with some modification of the experimental setup and parameters, the absolute period across a 1 mm2 patterned area can be known to one part in 106.