bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular beam epitaxy growth of metamorphic high electron mobility transistors and metamorphic heterojunction bipolar transistors on Ge and Ge-on-insulator/Si substrates
Authors: Lubyshev D. , Fastenau J. M. , Wu Y. , Liu W. K. , Bulsara M. T. , Fitzgerald E. A. , Hoke W. E.
Published: June 2008

A direct growth approach using composite metamorphic buffers was employed for monolithic integration of InP-based high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) on Ge and Ge-on-insulator (GeOI)/Si substrates using molecular beam epitaxy. GaAs layers nucleated on these substrates and grown to a thickness of 0.5μm were optimized to minimize the nucleation and propagation of antiphase boundaries and threading dislocations, and exhibited an atomic force microscopy rms roughness of ∼9Å and x-ray full width at half maximum of ∼36arcsec. A 1.1μm thick graded InAlAs buffer was used to transition from the GaAs to InP lattice parameters. The density of threading dislocations at the upper interface of this InAlAs buffer was ∼107cm−2 based on cross-sectional transmission electron microscopy analyses. HEMT structures grown metamorphically on GeOI/Si substrates using these buffer layers demonstrated transport properties equivalent to base line structures grown on InP substrates, with room temperature mobility greater than 10000cm2∕Vs. Similarly, double heterojunction bipolar transistors (D-HBTs) grown metamorphically on GeOI/Si substrates and fabricated into large area devices exhibited dc parameters close to reference D-HBTs grown on InP substrates.
Molecular beam epitaxy grown Ga2O3(Gd2O3) high κ dielectrics for germanium passivation-x-ray photoelectron spectroscopy and electrical characteristics
Authors: Lee C. H. , Lin T. D. , Tung L. T. , Huang M. L. , Hong M. , Kwo J.
Published: June 2008

Molecular beam epitaxy deposited Ga2O3(Gd2O3) on Ge, without a commonly employed interfacial layer of GeON, has demonstrated excellent electrical properties, such as a high κ value of 14.5, a low electrical leakage current density, and well behaved C-V characteristics even being subjected to 500°C annealing in N2 ambient for 5min. In situ angle-resolved x-ray photoelectron spectroscopy (XPS) studies have revealed an abrupt Ga2O3(Gd2O3)∕Ge interface without forming any interfacial layer. Further XPS studies explained the outstanding thermodynamic stability of the Ga2O3(Gd2O3)∕Ge heterostructure.
Molecular beam epitaxial growth and characteristics of 1.52μm metamorphic InAs quantum dot lasers on GaAs
Authors: Mi Z. , Wu C. , Yang J. , Bhattacharya P.
Published: June 2008

The authors report the molecular beam epitaxial growth and characteristics of 1.5μm InAs quantum dot lasers grown on GaAs utilizing both single- and multiple-step-graded InGaAs metamorphic buffer layers. 1.45μm p-doped and tunnel injection InAs metamorphic quantum dot lasers grown on a single-step In0.15Ga0.85As buffer layer exhibit an ultralow threshold current (Jth∼63A∕cm2), large T0 (620K), large modulation frequency response (f−3dB=8GHz), near-zero α parameter, a chirp of 0.1Å, and long lifetime (∼2000h). The lasing wavelength of InAs quantum dot lasers grown on multiple-step-graded InGaAs metamorphic buffer layers has also been extended, for the first time, to 1.52μm.
Temperature dependence of photoluminescence oxygen-related deep levels in Al0.2Ga0.3In0.5P:Be grown by solid source molecular beam epitaxy
Authors: Soubervielle-Montalvo C. , Mishournyi V. , Hernández I. C. , Méndez-García V. H.
Published: June 2008

In this work, the photoluminescence (PL) properties of Be-doped Al0.2Ga0.3In0.5P layers grown on GaAs by solid source molecular beam epitaxy were studied as a function of temperature. Three samples were grown varying the P-cell cracker temperature (PCT). The Be-cell temperature was 1015°C for all samples. The 77K PL spectra from samples show three main transitions located at 2.182, 2.162, and 2.065eV, related to band-to-band emission (B,B), Be acceptor levels (A0,X) and oxygen deep levels (O,DL), respectively. The authors observed that for the sample grown at the highest PCT the (O,DL) transition dominates the whole 77K PL spectra, while for the sample grown at intermediate PCT it appears with lower intensity. This peak is not observed in the PL spectra for the layers grown at PCT equal to 800°C. The authors monitored the evolution with temperature of (O,DL) and observed that it is located from 87to135meV below the conduction band when the temperature is varied from 15to120K. After 120K, this transition disappears. The NA-ND carrier concentration measured with an ECV profiler shows a diminution of the active Be doping concentration as PCT increases as a consequence of compensation of Be dopants by donorlike O traps. This phenomena is reflected in the PL properties of the samples as a reduction of the intensity of (A0,X). Also, the 300K PL spectra for the samples shows that by increasing PCT from 800to1000°C, the PL intensity of the (B,B) transition decreased dramatically due to the introduction of oxygen-related nonradiative recombination centers.
In(Ga, Al)As quantum dot/wire growth on InP
Authors: Tzeng T. E. , Feng David J. Y. , Chen C. Y. , Lay T. S.
Published: June 2008

The authors have investigated the growth of dots/wires on InP substrates by tuning the In(Ga, Al)As compositions for dots/wires and buffer layers. Dots and wires with compositions including InAs, In0.95Al0.05As, In0.95Ga0.05As, and In0.90Ga0.10As were grown on In0.53Ga0.26Al0.21As and In0.52Al0.48As buffer layers, respectively. In(Ga)As nanostructure grown on InAlAs ternary buffer layer forms elongated dots along the [0-11] direction. On the other hand, In0.95Ga0.05As and In0.90Ga0.10As nanostructures grown on InGaAlAs buffer layer form quantum wire arrays of high uniformity. The In0.90Ga0.10As quantum wires have a photoluminescence spectrum of emission peak at λ∼1680nm and a narrow full width at half maximum of 65meV at 10K. For the growth of In0.95Al0.05As nanostructures, dot formations are observed on the InAlAs and InGaAlAs buffer layers.
Statistical representation of intrinsic electronic tunneling characteristics through alkyl self-assembled monolayers in nanowell device structures
Authors: Song Hyunwook , Lee Takhee , Choi Nak-Jin , Lee Hyoyoung
Published: June 2008

Systematic electronic transport measurements in nanometer-scale junctions containing self-assembled monolayers of alkyl molecules are reported using nanowell device structures. The comprehensive temperature-variable current-voltage characterizations and statistical analysis for the acquired transport data show that direct tunneling indeed can be assigned as the dominant charge transport mechanism of the alkyl monolayers in a voltage range ⩽±1V. The intrinsic tunneling characteristics of alkyl molecular junctions are examined by excluding other parasitic conduction mechanisms by the data analyses and statistically defining representative data. The demonstrated intrinsic tunneling characteristics are well consistent with numerous previous reports for alkyl-based monolayers. The current characteristics are temperature independent and exponentially depend on the molecular length. The tunneling decay coefficient is determined as 0.83–0.73Å−1 in the bias range from 0.1to1.0V and is independent of temperature. The statistical histogram of current densities for all direct tunneling devices exhibits log-normal distribution, which is likely due to a variation in tunneling distance.
Effect of substrate temperature on structural and electrical properties of liquid-delivery metal organic chemical vapor deposited indium oxide thin films on silicon
Authors: Venkat S. , Pammi N. , Sahu B. S. , Seong Nak-Jin , Yoon Soon-Gil
Published: June 2008

Indium oxide conducting films were deposited on p-type Si (100) substrates at various temperatures by a liquid-delivery metal organic chemical vapor deposition technique using indium (III) tris(2,2,6,6-tetramethyl-3,5-heptanedionato) (dpm)3 precursors. The structural, morphological, and chemical bonding features of these films were studied by x-ray diffraction, scanning electron microscopy, and x-ray photoelectron spectroscopy. The effect of substrate temperature on the electrical and structural properties has been investigated to obtain a high mobility and highly conducting In2O3 film. All deposited films within the temperature range of 200–400°C have a [111] preferred orientation and exhibit an increase of grain size from 21to33nm with increasing deposition temperature. In this range of deposition temperature, there is no metallic indium phase in deposited films. It was observed that the electrical properties of the films are closely related to the microstructure of the films. Hall mobility and electrical resistivity values of the films are comparable to most of the presently investigated transparent conducting oxide films.
Controllable fabrication of the micropore shape of two-dimensional photonic crystals using holographic lithography
Authors: Hsieh Mei-Li , Lan Yi-Sheng
Published: June 2008

In this study, the micropore shape of two-dimensional (2D) photonic crystal structures can be modified and controlled by the intensity ratio of the incident beams of the holographic lithography. By adjusting the intensity ratio of the incident beams, the micropore shape of 2D hexagonal photonic crystal structure could be adjusted from being circular to being elliptical. Hence, we defined and analyzed the ellipticity of the micropore shape on a 2D photonic crystal structure as a function of the intensity ratio of the incident beams. In addition, we set up an optical holographic system by using three incident beams with different intensities to demonstrate the influence of the intensity ratio of the incident beams on the micropore shape. The optical experimental results show that the ellipticity of the micropore shape decreased with increasing the intensity ratio of the incident beams, which is the same trend as with the theoretical analysis.
Growth and structural characteristics of GaN∕AlN/nanothick γ-Al2O3∕Si (111)
Authors: Lee W. C. , Lee Y. J. , Tung L. T. , Wu S. Y. , Lee C. H. , Hong M. , Ng H. M. , Kwo J. , Hsu C. H.
Published: June 2008

The authors report on the growth of GaN by nitrogen plasma-assisted molecular beam epitaxy (MBE) on a 2in. Si (111) substrates with a nanothick (∼4.8nm thick) γ-Al2O3 as a template/buffer. A thin layer of MBE-AlN ∼40nm thick was inserted prior to the growth of GaN. High-resolution transmission electron microscopy (HR-TEM) and high-resolution x-ray diffraction studies indicated that both of the nanothick γ-Al2O3 and AlN are a single crystal. Reflection high-energy electron diffraction, high-resolution x-ray scattering using synchrotron radiation, and cross-sectional HR-TEM measurements indicated an orientation relationship of GaN(0002)∥AlN(0002)∥γ-Al2O3(111)∥Si(111) and GaN[10−10]∥AlN[10−10]∥γ-Al2O3[2−1−1]∥Si[2−1−1]. A dislocation density of 5×(108–109)∕cm2 in the GaN ∼0.5μm thick was determined using cross-sectional TEM images under weak-beam dark-field conditions.
Fabrication of periodically polarity-inverted ZnO films
Authors: Minegishi T. , Ishizawa A. , Kim J. , Kim D. , Ahn S. , Park S. , Park J. , Im I. , Oh D. C. , Nakano H. , Fujii K. , Jeon H. , Yao T.
Published: June 2008

One-dimensional periodically polarity-inverted (PPI) structures of ZnO for nonlinear optical devices are fabricated on c-plane Al2O3 substrates. To do so, corrugated MgO buffer layers are fabricated by etching after patterning, which is followed by the growth of ZnO layers by plasma-assisted molecular beam epitaxy. The polarity-inverted structures are confirmed by scanning piezoresponse microscopy and atomic-force microscopy. PPI structures with submicron periodicity are fabricated to satisfy the quasiphase matching condition for second harmonic generation of light.
Ion beam machining of Si layer deposited on Zerodur® substrate
Authors: Kurashima Yuichi , Tajima Tomonori , Miyamoto Iwao , Ando Manabu , Numata Atsushi
Published: June 2008

Ion beam figuring is suitable for the final correction of the surface figure error of aspherical substrates using an extreme ultraviolet lithography tool. In ion beam figuring, however, the machined surfaces of substrates become rougher than the unprocessed surfaces. Moreover, the surface is positively charged due to the positive charges of impinging ions. In this experiment, a Si layer was deposited by ion beam sputtering on a Zerodur® substrate with a depth of ∼300nm; then, this was machined by an Ar+ ion beam with energies in the range of 3–10keV. The mid-spatial-frequency roughness of the surface machined to a depth of less than 50nm was comparable to that of an unprocessed surface. The high-spatial-frequency roughness (HSFR) of the unprocessed surface was 0.21nm rms, whereas the average HSFRs of the surface machined up to a depth of 50nm were 0.25, 0.33, 0.39, and 0.59nm root mean square at energies of 3, 5, 7, and 10keV, respectively. The HSFR of the machined surface increased with the ion beam energy.
Probe current, probe size, and the practical brightness for probe forming systems
Authors: Bronsgeest M. S. , Barth J. E. , Swanson L. W. , Kruit P.
Published: June 2008

Probe size, shape, and current are important parameters for the performance of all probe forming systems such as the scanning (transmission) electron microscope, the focused ion beam microscope, and the Gaussian electron beam lithography system. Currently, however, the relation between probe current and probe size is ill defined. The key lies in a lacking definition of “size.” This problem is solved with the introduction of the “practical brightness.” In literature, many different definitions of “brightness” can be found, but for systems in which the whole of the virtual source is imaged onto the target, it is the practical brightness of a source that determines how much current is in the probe. This means that only with the practical brightness the performance of a probe forming system can be calculated quantitatively. The beauty of the practical brightness is that this source property is unaffected by the quality of the column: without interactions between electrons in the beam, the practical brightness is conserved down to the target. This makes it the only relevant brightness for probe forming systems to be used to compare different sources. The practical brightness can be measured, but can also be calculated when the source intensity profile is known. The Gaussian source intensity profile of thermionic, Schottky, and cold field emitters yields a practical brightness of 1.44ej∕π⟨ε⟩, where j is the current density on the emitting surface and ⟨ε⟩ is the average tangential electron energy.
Electron beam induced deposition of iron nanostructures
Authors: Hochleitner G. , Wanzenboeck H. D. , Bertagnolli E.
Published: June 2008

Electron beam induced deposition is among the most prospective methods for size- and position-controllable nanofabrication of three-dimensional structures. Direct-write maskless nanostructure fabrication was performed with a scanning electron microscope. Three-dimensional iron structures were obtained by locally confined electron induced dissociation of an iron carbonyl (Fe(CO)5) precursor. Vertical nanopillars consisting of Fe with O and C contaminations were deposited. Two different growth regimes—electron induced growth and autonomous growth—were observed. The precursor pressure was shown to have a significant influence on the growth mode.
Resistivity and surface states density of n- and p-type silicon nanowires
Authors: Vaurette F. , Nys J. P. , Deresmes D. , Grandidier B. , Stiévenard D.
Published: June 2008

The resistivity and the density of surface states of semiconductor nanowires are not measurable using classic electrical measurements such as capacitance-voltage techniques, because of too low capacitance associated with a single nanowire. To overcome this problem, the authors measured the resistance of a set of n- and p-doped silicon nanowires versus their length and width. Thus, the authors deduce both the resistivity and density of surface states of the nanowires. This approach could be extended to any nanowire, once its shape is known.
Fabrication of three-dimensional nanostructures by focused ion beam milling
Authors: Tjerkstra R. W. , Segerink F. B. , Kelly J. J. , Vos W. L.
Published: June 2008

The fabrication of an extended three-dimensional nanostructure with dimensions much larger than the feature size using a focused ion beam is described. By milling two identical patterns of pores with a designed diameter of 460 nm in orthogonal directions, a photonic crystal with an inverse woodpile structure was made in a gallium phosphide single crystal. The patterns are aligned with an unprecedented accuracy of 30 nm with respect to each other. The influence of GaP redeposition on the depth, shape, and size of the pores is described. A literature study revealed that the redeposition of GaP during milling is more pronounced than that of Si found in previous studies. An explanation for this phenomenon is given.
Influence of As-stabilized surface on the formation of InAs∕GaAs quantum dots
Authors: Tseng Chi-Che , Chou Shu-Ting , Chen Yi-Hao , Chung Tung-Hsun , Lin Shih-Yen , Wu Meng-Chyi
Published: June 2008

In this article, we report the growth of InAs∕GaAs quantum dots (QDs) grown under different As4-supply procedures. The growth of the investigated samples carried out by the three procedures of As shutter always opened, As shutter initially opened, and As shutter initially closed. The samples grown by the former two approaches show a uniform QD distribution and the multiple-peak luminescence, which correspond to ground-state, first-excited-state, and second-excited-state luminescence, while that grown by the latter only shows large InAs islands. The results suggest that the As-stabilized condition at the initial stage of QD growth is very critical for the high-quality QD formation.
Growth and characterization of ZnxCd1−xSe∕Znx′Cdy′Mg1−x′−y′Se asymmetric coupled quantum well structures for quantum cascade laser applications
Authors: Charles W. O. , Shen A. , Franz K. , Gmachl C. , Zhang Q. , Gong Y. , Neumark G. F. , Tamargo Maria C.
Published: June 2008

The authors report the growth of a II-VI ZnxCd1−xSe∕Znx′Cdy′Mg1−x′−y′Se asymmetric coupled quantum well (asymmetric-CQW) structure that was used to investigate the active region of an intersubband electroluminescence structure designed for emission at λ=4.5μm. Such a structure could comprise the active region of a quantum cascade laser. The results of photoluminescence and Fourier transform infrared spectroscopy analysis show good agreement with the expected transition energies predicted by simulation results for the asymmetric-CQW structure. High resolution x-ray diffraction analysis indicates high structural quality of the sample and good control of the growth.
Molecular beam epitaxy growth of InAs and In0.8Ga0.2As channel materials on GaAs substrate for metal oxide semiconductor field effect transistor applications
Authors: Li Ning , Harmon Eric S. , Salzman David B. , Zakharov Dmitri N. , Jeon Jong-Hyeok , Stach Eric , Woodall Jerry M. , Wang X. W. , Ma T. P. , Walker Fred
Published: June 2008

InAs and high indium concentration InGaAs have very high electron mobilities and saturation velocities. Using them as the metal oxide semiconductor field effect transistor (MOSFET) channel materials is a very promising way to keep improving the integrated circuit chip performance beyond Moore’s law. One major obstacle is the growth of these high mobility channel materials on lattice-mismatched substratcs. In this work, we studied the molecular beam epitaxy growth of InAs, In0.8Al0.2As, and In0.8Ga0.2As on lattice-mismatched GaAs substrate using a thin indium-rich InAs wetting layer. Reflection high energy electron diffraction and atomic force microscopy were used to optimize the growth conditions. A surface roughness of ∼0.5nm rms was obtained for InAs layers. A new MOSFET structure with In0.8Ga0.2As channel and In0.8Al0.2As buffer layer was also demonstrated. High mobility depletion mode MOSFET characteristics were demonstrated.
Si metal-oxide-semiconductor devices with high κ HfO2 fabricated using a novel MBE template approach followed by atomic layer deposition
Authors: Pan C. H. , Kwo J. , Lee K. Y. , Lee W. C. , Chu L. K. , Huang M. L. , Lee Y. J. , Hong M.
Published: June 2008

Molecular beam epitaxy (MBE) was employed to grow nanothick high κ HfO2 films on Si (100) as templates to suppress the formation of the oxide/Si interfacial layer during the subsequent atomic layer deposited (ALD) HfO2 growth. A metal-oxide-semiconductor (MOS) diode with the ALD/MBE bilayer stack of an equivalent oxide thickness (EOT) of ∼1.1nm has demonstrated markedly low electrical leakage of 8.3×10−3A∕cm2 at Vfb−1V, a reduction by five order of magnitudes, comparing with those using SiO2 of the same EOT. The attainment of high dielectric constant and very small frequency dispersion in capacitance-voltage (C-V) curves suggests the absence of low κ capacitors in series near the oxide/Si interface. Furthermore, MOS field-effect transistors (MOSFETs) based on the ALD/MBE-HfO2 composites have been fabricated having excellent device performance, with a drain current (ID) of 240mA∕mm and transconductance (Gm) of 120mS∕mm. These are superior to those of the MOSFETs using either ALD (55mA∕mm, 60mS∕mm) or MBE (80mA∕mm, 35mS∕mm) gate dielectric.
Selective growth of CdTe on patterned CdTe∕Si(211)
Authors: Seldrum T. , Bommena R. , Samain L. , Dumont J. , Sivananthan S. , Sporken R.
Published: June 2008

The authors have studied selective growth of cadmium telluride on Si(211) by molecular beam epitaxy (MBE). Patterned substrates were produced by optical lithography of MBE-grown CdTe∕As∕Si(211). Photoemission microscopy was used as the main tool to study selective growth. This is very powerful because Si or SiO2 can be very easily distinguished from areas covered with even small amounts of CdTe due to contrast from work function differences. It was found that CdTe grows on CdTe without sticking on bare Si areas if the temperature is sufficiently high. Based on the analysis of the temperature dependence of the growth rate of CdTe, we suggest that different physisorption energies on Si and CdTe are the main cause of this selective growth.
Nitrogen and hydrogen plasma treatments of multiwalled carbon nanotubes
Authors: Jones J. G. , Waite A. R. , Muratore C. , Voevodin A. A.
Published: June 2008

This article investigates plasma treatment of vertically aligned multiwall carbon nanotube (CNT) films in different plasma environments for modification of surface chemistry and morphology. The surfaces of the CNTs were functionalized with a pulsed dc plasma treatment, where the power was directly applied to the nanotube film in low pressure argon/nitrogen and argon/hydrogen backgrounds. Optical emission spectroscopy was used to detect atomic and molecular excitations in the gas mixtures as well as in pure gases in the vicinity of the CNT films. In situ x-ray photoelectron spectroscopy was performed on the treated samples to examine CNT surface chemistry after treatment. The analysis of CNT films after nitrogen and hydrogen treatment indicated formation of both CN and CH bonds, respectively. Correlations of the plasma characteristics to the surface chemistry and morphology of the CNT surfaces are discussed.
Linewidth roughness transfer measured by critical dimension atomic force microscopy during plasma patterning of polysilicon gate transistors
Authors: Pargon E. , Martin M. , Thiault J. , Joubert O. , Foucher J. , Lill T.
Published: June 2008

With the continuous scaling down of the critical dimensions (CDs) of semiconductor devices, the linewidth roughness (LWR) becomes a non-negligible parameter that needs to be controlled within 1nm (at 3σ) for the 32nm node and beyond. In this article, the authors have used a CD-atomic force microscopy to investigate the evolution of the LWR during the subsequent lithography and plasma etching steps involved in the patterning of polysilicon transistor gates. The authors demonstrate that the LWR present on the etching mask [photoresist/bottom antireflective coating (BARC), SiO2 or amorphous carbon hard masks] right before the gate etching is transferred into the polysilicon during the HBr∕Cl2∕O2 gate etching step. Thus, the final polysilicon LWR directly is strongly dependent on the lithography and plasma etching steps preceding the gate etching step. The authors show that by applying plasma treatment to minimize the resist mask LWR prior to all the other etching steps or by optimizing the BARC opening plasma chemistry, the final polysilicon LWR can be minimized. The authors also demonstrate that the introduction of hard masks (SiO2 or amorphous carbon) helps to reduce further the final polysilicon gate LWR. Finally, the authors discuss the role of the ion bombardment in the smoothening/roughening of the pattern sidewalls during plasma processes.
Conformal metal oxide coatings on nanotubes by direct low temperature metal-organic pyrolysis in supercritical carbon dioxide
Authors: Peng Qing , Spagnola Joseph C. , Daisuke Hojo , Park Kie Jin , Parsons Gregory N.
Published: June 2008

The authors demonstrate that low temperature (<200 °C) thermal decomposition of metal-organic precursors dissolved in supercritical carbon dioxide (scCO2) is an effective method to penetrate into dense three-dimensional networks and deposit conformal metal oxide films with tunable thickness. The results specifically show that thermal decomposition of gallium acetylacetonate in scCO2, leads to conformal coatings of gallium oxide on multiwalled carbon nanotube forests with a fast deposition rate (∼3–4 nm/min), without the need for any cosolvent. Moreover, as-formed metal oxide/nanotube structures can be further conformally coated by metal atomic layer deposition to produce nanotube/oxide/metal nanocomposites.
Stable room temperature deposited amorphous InGaZnO4 thin film transistors
Authors: Lim Wantae , Kim S.-H. , Wang Yu-Lin , Lee J. W. , Norton D. P. , Pearton S. J. , Ren F. , Kravchenko I. I.
Published: June 2008

Enhancement-mode amorphous indium gallium zinc oxide (α-IGZO) channel thin film transistors (TFTs) with a 6μm gate length and a 100μm gate width were fabricated on glass substrates by rf magnetron sputtering near room temperature. The resistivities of the α-IGZO films were controlled from 10−1to103Ωcm by varying the deposition power of 75–300W. The n-type carrier concentration in the channel was 6.5×1017cm−3. The gate oxide was 90-nm-thick SiNx, deposited by plasma enhanced chemical vapor deposition at 70°C. The bottom-gate TFTs had saturation mobility of ∼17cm2V−1s−1 and the drain current on-to-off ratio of ∼>105, a subthreshold gate-voltage swing of ∼0.5Vdecade−1, and a threshold voltage of 2.1V. In the TFT with a gate length of 6μm and a gate width of 100μm, the relative change of saturation mobility and threshold voltage was less than ±1.5% after 500h aging time at room temperature. This demonstrates that α-IGZO films are promising semiconductor materials for long-term-stable transparent TFT applications.
Inhibiting spontaneous etching of nanoscale electron beam induced etching features: Solutions for nanoscale repair of extreme ultraviolet lithography masks
Authors: Lassiter Matthew G. , Liang Ted , Rack Philip D.
Published: June 2008

Electron beam induced etching (EBIE) is an important technique for repairing nanoscale defects on extreme ultraviolet (EUV) lithography masks as it provides excellent spatial resolution and etch selectivity while minimizing collateral damage to the mask. While EBIE itself is a complex process, a current problem with EBIE of the TaN EUV mask absorber layer using XeF2 is the spontaneous etching of repaired features during subsequent edits of the mask. This work explores three passivation techniques for controlling the spontaneous etching after an EBIE repair is made. An oxygen plasma was used to attempt to oxidize the TaN sidewalls, but it was not successful at stopping the spontaneous etching. An active electron beam induced passivation using water was successful at stopping the spontaneous etching. Also, simple adsorption of water molecules on the TaN sidewalls was successful at inhibiting spontaneous etching. The successful passivation strategies are affected by subsequent scanning electron beam imaging. It was determined that the electron beam activated passivation can be damaged by electron beam imaging in the presence of residual XeF2 on the surface. Also, the adsorbed water passivation strategy is susceptible to electron induced desorption of the water.
Dependence of Zn1−xMgxO:P film properties on magnesium concentration
Authors: Kim H. S. , Lugo F. , Pearton S. J. , Norton D. P. , Ren F.
Published: June 2008

The dependence of p-type conversion on Mg content in Zn1−xMgxO:P films (x=0.1,0.05) is examined. As-grown Zn0.95Mg0.05O:P films were n type but converted to p type after rapid thermal annealing. p-type Zn1−xMgxO:P films were successfully achieved without post-thermal annealing treatments for a Mg content of x=0.10. Increasing magnesium content in the ZnMgO:P solid solution generally degrades the luminescence properties, suggesting the formation of nonradiative states.
Potential of pulsed electron-beam deposition for nanomaterial fabrication: Spatial distribution of deposited materials
Authors: Steigerwald A. , Mu R.
Published: June 2008

Pulsed electron-beam deposition (PED) is a recently developed pulsed energy ablation/deposition technique with distinct advantages for its cost effectiveness, nature of the electron-material interactions, and large-scale production. By the proper control of the ablation/deposition parameters, one can produce high purity quantum dots and thin films in situ in vacuum chamber. Further, PED can also be used for unique material syntheses by introducing reactive gases in the chamber. However, little systematic work has been done to demonstrate PED’s potential applications except for few on film and nanoparticle fabrications. Particular efforts are made here to study the spatial variations of the deposited materials.
Field emission properties of individual zinc oxide nanowire field emitter
Authors: Yeong K. S. , Thong J. T. L.
Published: June 2008

The authors report the field emission (FE) properties of individual ZnO nanowire field emitters. ZnO nanowire field emitter directly grown on a Pt tip showed a much better field emission current delivery than the attached nanowire emitters due to better contact properties. The emission current and field emission microscopy pattern of the ZnO nanowire are strongly influenced by adsorbates. After thermal-field desorption of adsorbates from the emission tip, the I-V curve shows a complex behavior that is different from that of the adsorbate-covered tips or ideal FE. For completeness, the effects of O2 and H2 gas exposure, and UV illumination on the FE current are also discussed.
Effects of laterally overgrown n-GaN thickness on defect and deep level concentrations
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Markov A. V. , Yakimov E. B. , Vergeles P. S. , Lee In-Hwan , Lee Cheul Ro , Pearton S. J.
Published: June 2008

The effects of the layer thickness and of Si doping on the dislocation type and density, electron concentration, and deep trap spectra were studied for epitaxially laterally overgrown (ELOG) GaN films with the ELOG region thickness varying from 6to12μm. Electron beam induced current imaging shows that for the thickest layers, the major part of the threading dislocations are filtered out while for thinner films they bend, but do not go out of play. The concentration of residual donors and major electron traps is found to decrease with increasing the film thickness. Si doping suppresses the concentration of the main electron trap with activation energy of 0.6eV and enhances the concentration of the main hole trap at Ev+0.85eV.
Insights into the electron-field emission mechanism from nanostructured carbons: A multistep phenomenon and modeling
Authors: Gupta Sanju
Published: June 2008

This study was prompted by the open question concerning the mechanism and corresponding nonlinearity in traditional Fowler-Nordheim (FN) plots of electron-field emission from advanced nanocarbons. Experimental field emission results from nanostructured carbons, including sulfur-incorporated nanocrystalline diamond as well as carbon nanotubes, are discussed that do not provide traditional linear FN plots. To overcome this difficulty, the authors suggest a multistep phenomenological model that divides the FN plots into high and low regimes of applied macroscopic electrostatic field. The authors describe the difference of FN slopes between high and low field by using a distribution function for energy levels. The authors suggest that the field emission mechanism from nanostructured carbons consists of two successive processes: (1) tunneling of electrons through the low-energy barrier from highly doped semiconducting or metallic region into the semiconducting (metallic) region under the external macroscopic electric field; and (2) tunneling through the high (low) energy barrier from the semiconducting (metallic) region into vacuum under the Coulomb field of an additional electron appearing in the first-step process. The metallic region in step (2) is assigned to the multiwalled nanotubes, which are invariably metallic in nature in contrast to the single-walled nanotubes, which consist of an electrically heterogeneous mixture of semiconducting and metallic types with a finite band gap.
Field emission properties of ZnO nanorods coated with NiO film
Authors: Yang Ji Hoon , Lee Seung Youb , Song Woo Seok , Shin Yong Sook , Park Chong-Yun , Kim Hyun-Jin , Cho Wontae , An Ki-Seok
Published: June 2008

The field emission (FE) properties of ZnO and NiO-coated ZnO (NiO∕ZnO) nanorods are investigated under vacuum of 7×10−7Torr and oxygen rich vacuum of 1×10−5Torr. The ZnO nanorods were synthesized on a Si(100) substrate by metal-organic chemical vapor deposition, and the NiO film with the thickness of ∼15nm was coated by using atomic layer deposition. The turn-on voltages of the NiO∕ZnO nanorod and the ZnO nanorod were ∼5.2 and ∼3.0V∕μm at 1μA∕cm2, respectively. The electron FE stability of the NiO∕ZnO nanorods to the ZnO nanorod was significantly improved in oxygen rich vacuum even.
Observation and control of electrochemical etching effects in the fabrication of InAs∕AlSb∕GaSb heterostructure devices
Authors: Su Ning , Tang Yong , Zhang Ze , Kuech T. F. , Fay P.
Published: June 2008

In the fabrication of InAs∕AlSb∕GaSb heterostructure devices, the etching characteristics of Sb-bearing materials were observed to be significantly modified through electrochemically induced effects arising from the use of metal etch masks during etching in dilute ammonium hydroxide. Samples with different etch mask materials, such as SiNx, Ti, Cr, Ni, Pt, and Au, exhibited markedly different etching characteristics. In comparison to an insulating SiNx mask, etch masks with Au as the surface metal enhance the etch rate by factors of 2 and 7 in the vertical and lateral directions, respectively. The increase in etch rate depends strongly on the choice of the surface metal of the etch mask; higher etch rates were experimentally observed for surface metals with larger standard electrode potentials. The observed trends are consistent with interplay between electrochemical reaction and reaction rate kinetics in the etch solution. The electrochemical features of the etch process provide a potentially useful means for controlling the etch profile and may be useful for achieving enhanced device performance.
Role of ion damage on unintentional Ca incorporation during the plasma-assisted molecular-beam epitaxy growth of dilute nitrides using N2∕Ar source gas mixtures
Authors: Oye Michael M. , Bank Seth R. , Ptak Aaron J. , Reedy Robert C. , Goorsky Mark S. , Holmes Archie L.
Published: June 2008

Unintentional Ca incorporation caused by Ca-contaminated substrate surfaces on as-purchased GaAs wafers are known to limit the efficiency of solar cells based on dilute nitride materials. This article focuses on further understanding the conditions and mechanisms by which these Ca impurities incorporate. Plasma-assisted molecular-beam epitaxy utilizing a 1% N2 in Ar precursor gas mixture was used to grow GaAs at 400 and 580°C, and GaN0.01As0.99 at 400°C. Two plasma operating combinations of rf power and gas flow rate were used to generate different amounts and energies of both ions and other plasma species, while keeping nitrogen incorporation constant. The ions were characterized with a dual-grid, retarding-field ion energy analyzer, and the corresponding ion energy distributions are presented to correlate ions with Ca incorporation. When appropriate, dc-biased deflector plates were used to remove ions during growth. Secondary ion mass spectrometry was used to measure Ca in GaAs and GaN0.01As0.99. Ca incorporation was observed in the dilute nitride samples, but the effects of ions did not exceed other Ca incorporation mechanisms associated with defects due to both low temperature growth and nitrogen incorporation; however, different neutral active nitrogen species (atomic N and metastable N2*) may be a factor. Ca incorporation measured in GaAs grown at 400°C with a pure Ar plasma is predominantly due to defects associated with low temperature growth, as opposed to plasma damage caused by the ions. GaAs growths at 580°C without a plasma did not exhibit Ca incorporation, but growth at 580°C with ions from a pure Ar plasma caused Ca incorporation.
Fully sealed carbon nanotube flat-panel light source and its application as thin film transistor–liquid-crystal display backlight
Authors: Zhang Yu , Deng S. Z. , Xu N. S. , Chen Jun
Published: June 2008

The authors investigated a full sealed flat-panel light source, which is based on a triode structure with a metal mesh gate electrode and uses a carbon nanotube cold cathode. It has a flat surface luminance distribution with good uniformity, a stable luminance of 12000cd∕m2, and a luminous efficiency that was measured to be 14.5lm∕W. It also shows a high color rendering index of 88 and a wide optical emission spectrum. Further, its application as thin film transistor–liquid-crystal display (TFT-LCD) backlight was demonstrated and the resulted performance of the TFT-LCD display was studied and compared to the commercial TFT-LCD products, which use the cold-cathode fluorescent lamp backlight and light emitting diode backlight. It is shown that the light transmission ratio in the TFT-LCD module using our light source is ∼8%, as compared to ∼4% of the commercial products. With this and the very high luminance, our light source is very useful to the situation, in which the TFT-LCD screen is employed to work under outdoor sunshine conditions.
Performance improvement of CuOx with gradual oxygen concentration for nonvolatile memory application
Authors: Zhou P. , Lv H. B. , Yin M. , Tang L. , Song Y. L. , Tang T. A. , Lin Y. Y. , Bao A. , Wu A. , Cai S. , Wu H. , Liang C. , Chi M. H.
Published: June 2008

The authors found CuOx thin film with gradual oxygen concentration (GOC) distribution enhances resistive switching characteristics for nonvolatile memory applications. By using Al/GOC CuOx∕Cu structure, not only no forming is needed but also the endurance of switching is greatly enhanced. The device with GOC CuOx demonstrates resistance on/off ratio of greater than 100 and endurance of more than 12000cycles. The “forming-free” characteristics appear related to thinner CuO and the endurance enhancement appears related to gradual gradient of oxygen vacancies in CuOx. Thus, the thickness of CuO and distribution of oxygen (as well as vacancies) play important roles for performance improvement.
Enhancement of the Alcoholytic Activity of α-Amylase AmyA fromThermotoga maritimaMSB8 (DSM 3109) by Site-Directed Mutagenesis
Authors: Damián-Almazo Juanita Yazmin , Moreno Alina , López-Munguía Agustin , Soberón Xavier , González-Muñoz Fernando , Saab-Rincón Gloria
Published: June 2008

AmyA, an α-amylase from the hyperthermophilic bacteriumThermotoga maritima, is able to hydrolyze internal α-1,4-glycosidic bonds in various α-glucans at 85°C as the optimal temperature. Like other glycoside hydrolases, AmyA also catalyzes transglycosylation reactions, particularly when oligosaccharides are used as substrates. It was found that when methanol or butanol was used as the nucleophile instead of water, AmyA was able to catalyze alcoholysis reactions. This capability has been evaluated in the past for some α-amylases, with the finding that only the saccharifying fungal amylases fromAspergillus nigerand fromAspergillus oryzaepresent measurable alcoholysis activity (R. I. Santamaria, G. Del Rio, G. Saab, M. E. Rodriguez, X. Soberon, and A. Lopez, FEBS Lett. 452:346-350, 1999). In the present work, we found that AmyA generates larger quantities of alkyl glycosides than any amylase reported so far. In order to increase the alcoholytic activity observed in AmyA, several residues were identified and mutated based on previous analogous positions in amylases, defining the polarity and geometry of the active site. Replacement of residue His222 by glutamine generated an increase in the alkyl glucoside yield as a consequence of a higher alcoholysis/hydrolysis ratio. The same change in specificity was observed for the mutants H222E and H222D, but instability of these mutants toward alcohols decreased the yield of alkyl glucoside.
Isomaltose Production by Modification of the Fructose-Binding Site on the Basis of the Predicted Structure of Sucrose Isomerase from “
Protaminobacter rubrum
”
Authors: Lee Hyeon Cheol , Kim Jin Ha , Kim Sang Yong , Lee Jung Kul
Published: June 2008

“
Protaminobacter rubrum
” sucrose isomerase (SI) catalyzes the isomerization of sucrose to isomaltulose and trehalulose. SI catalyzes the hydrolysis of the glycosidic bond with retention of the anomeric configuration via a mechanism that involves a covalent glycosyl enzyme intermediate. It possesses a
325
RLDRD
329
motif, which is highly conserved and plays an important role in fructose binding. The predicted three-dimensional active-site structure of SI was superimposed on and compared with those of other α-glucosidases in family 13. We identified two Arg residues that may play important roles in SI-substrate binding with weak ionic strength. Mutations at Arg
325
and Arg
328
in the fructose-binding site reduced isomaltulose production and slightly increased trehalulose production. In addition, the perturbed interactions between the mutated residues and fructose at the fructose-binding site seemed to have altered the binding affinity of the site, where glucose could now bind and be utilized as a second substrate for isomaltose production. From eight mutant enzymes designed based on structural analysis, the R
325
Q mutant enzyme exhibiting high relative activity for isomaltose production was selected. We recorded 40.0% relative activity at 15% (wt/vol) additive glucose with no temperature shift; the maximum isomaltose concentration and production yield were 57.9 g liter
−1
and 0.55 g of isomaltose/g of sucrose, respectively. Furthermore, isomaltose production increased with temperature but decreased at a temperature of >35°C. Maximum isomaltose production (75.7 g liter
−1
) was recorded at 35°C, and its yield for the consumed sucrose was 0.61 g g
−1
with the addition of 15% (wt/vol) glucose. The relative activity for isomaltose production increased progressively with temperature and reached 45.9% under the same conditions.
Quantification of Target Molecules Needed To Detect Microorganisms by Fluorescence In Situ Hybridization (FISH) and Catalyzed Reporter Deposition-FISH
Authors: Hoshino Tatsuhiko , Yilmaz L. Safak , Noguera Daniel R. , Daims Holger , Wagner Michael
Published: June 2008

Fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes is a method that is widely used to detect and quantify microorganisms in environmental samples and medical specimens by fluorescence microscopy. Difficulties with FISH arise if the rRNA content of the probe target organisms is low, causing dim fluorescence signals that are not detectable against the background fluorescence. This limitation is ameliorated by technical modifications such as catalyzed reporter deposition (CARD)-FISH, but the minimal numbers of rRNA copies needed to obtain a visible signal of a microbial cell after FISH or CARD-FISH have not been determined previously. In this study, a novel competitive FISH approach was developed and used to determine, based on a thermodynamic model of probe competition, the numbers of 16S rRNA copies per cell required to detect bacteria by FISH and CARD-FISH with oligonucleotide probes in mixed pure cultures and in activated sludge. The detection limits of conventional FISH with Cy3-labeled probe EUB338-I were found to be 370 ± 45 16S rRNA molecules per cell for
Escherichia coli
hybridized on glass microscope slides and 1,400 ± 170 16S rRNA copies per
E. coli
cell in activated sludge. For CARD-FISH the values ranged from 8.9 ± 1.5 to 14 ± 2 and from 36 ± 6 to 54 ± 7 16S rRNA molecules per cell, respectively, indicating that the sensitivity of CARD-FISH was 26- to 41-fold higher than that of conventional FISH. These results suggest that optimized FISH protocols using oligonucleotide probes could be suitable for more recent applications of FISH (for example, to detect mRNA in situ in microbial cells).
Emulsifying and Metal Ion Binding Activity of a Glycoprotein Exopolymer Produced byPseudoalteromonassp. Strain TG12
Authors: Gutierrez Tony , Shimmield Tracy , Haidon Cheryl , Black Kenny , Green David H.
Published: June 2008

In this study, we describe the isolation and characterization of a new exopolymer that exhibits high emulsifying activities against a range of oil substrates and demonstrates a differential capacity to desorb various mono-, di-, and trivalent metal species from marine sediment under nonionic and seawater ionic-strength conditions. This polymer, PE12, was produced by a new isolate,Pseudoalteromonassp. strain TG12 (accession number EF685033), during growth in a modified Zobell's 2216 medium amended with 1% glucose. Chemical and chromatographic analysis showed it to be a high-molecular-mass (>2,000 kDa) glycoprotein composed of carbohydrate (32.3%) and protein (8.2%). PE12 was notable in that it contained xylose as the major sugar component at unusually high levels (27.7%) not previously reported for aPseudoalteromonasexopolymer. The polymer was shown to desorb various metal species from marine sediment—a function putatively conferred by its high content of uronic acids (28.7%). Seawater ionic strength (simulated using 0.6 M NaCl), however, caused a significant reduction in PE12's ability to desorb the sediment-adsorbed metals. These results demonstrate the importance of electrolytes, a physical parameter intrinsic of seawater, in influencing the interaction of microbial exopolymers with metal ions. In summary, PE12 may represent a new class ofPseudoalteromonasexopolymer with a potential for use in biotechnological applications as an emulsifying or metal-chelating agent. In addition to the biotechnological potential of these findings, the ecological aspects of this and related bacterial exopolymers in marine environments are also discussed.