bluuebunny/crossref_metadata_2025 huggingface dataset:
Intentional Harmony in the Lives of Working Parents: Program Development and Evaluation*
Authors: Wiley Angela R. , Branscomb Kathryn , Wang Yan Z.
Published: June 2007

Abstract: Family life practitioners are increasingly being called upon to help families meet work‐life challenges. This article describes the grassroots beginnings, program development, and formative evaluation findings for 1 module of a Cooperative Extension work‐life management program. Although the curriculum module is based on theory and research, it emphasizes practical strategies. A total of 101 employed parents participated. An intervention group received the curriculum and materials, whereas a comparison group did not. Pretest and posttest comparisons provide initial support for the success of the curriculum in encouraging effective work‐life management practices among employed parents. Directions for further program revision and evaluation are discussed.
The C‐terminal region of the proprotein convertase 1/3 (PC1/3) exerts a bimodal regulation of the enzyme activity in vitro
Authors: Rabah Nadia , Gauthier Dany , Dikeakos Jimmy D. , Reudelhuber Timothy L. , Lazure Claude
Published: June 2007

The proprotein convertase PC1/3 preferentially cleaves its substrates in the dense core secretory granules of endocrine and neuroendocrine cells. Similar to most proteinases synthesized first as zymogens, PC1/3 is synthesized as a larger precursor that undergoes proteolytic processing of its signal peptide and propeptide. The N‐terminally located propeptide has been shown to be essential for folding and self‐inhibition. Furthermore, PC1/3 also possesses a C‐terminal region (CT‐peptide) which, for maximal enzymatic activity, must also be cleaved. To date, its role has been documented through transfection studies in terms of sorting and targeting of PC1/3 and chimeric proteins into secretory granules. In this study, we examined the properties of a 135‐residue purified bacterially produced CT‐peptide on the in vitro enzymatic activity of PC1/3. Depending on the amount of CT‐peptide used, it is shown that the CT‐peptide increases PC1/3 activity at low concentrations (nm) and decreases it at high concentrations (µm), a feature typical of an activator. Furthermore, we show that, contrary to the propeptide, the CT‐peptide is not further cleaved by PC1/3 although it is sensitive to human furin activity. Based on these results, it is proposed that PC1/3, through its various domains, is capable of controlling its enzymatic activity in all regions of the cell that it encounters. This mode of self‐control is unique among members of all proteinases families.
CREB − a real culprit in oncogenesis
Authors: Siu Yeung‐Tung , Jin Dong‐Yan
Published: June 2007

The cAMP response element‐binding protein (CREB) is a stimulus‐induced transcription factor that responds rapidly to phosphorylation and/or coactivator activation. Regulated activation of CREB has a significant impact on cellular growth, proliferation and survival. To overturn the cellular control of these processes, tumor cells have developed various mechanisms to achieve constitutive activation of CREB, including gene amplification, chromosome translocation, interaction with viral oncoproteins, and inactivation of tumor suppressor genes. These mechanisms converge on the phosphorylation of CREB and/or the activation of transducer of regulated CREB activity (TORC) coactivators to effect uncontrolled proliferation of cells. This minireview summarizes the different lines of existing evidence that support a direct role of CREB in oncogenesis.
[Na+]i‐induced c‐Fos expression is not mediated by activation of the 5′‐promoter containing known transcriptional elements
Authors: Haloui Mounsif , Taurin Sebastien , Akimova Olga A. , Guo Deng‐Fu , Tremblay Johanne , Dulin Nickolai O. , Hamet Pavel , Orlov Sergei N.
Published: June 2007

In vascular smooth muscle cells and several other cell types, inhibition of Na+/K+‐ATPase leads to the expression of early response genes, including c‐Fos. We designed this study to examine whether or not a putative Na+i/K+i‐sensitive element is located within the c‐Fos 5′‐UTR from − 650 to + 103 containing all known response elements activated by ‘classic’ stimuli, such as growth factors and Ca2+i‐raising compounds. In HeLa cells, the highest increment of c‐Fos mRNA content was noted after 6 h of Na+/K+‐ATPase inhibition with ouabain that was abolished by actinomycin D, an inhibitor of RNA synthesis. c‐Fos protein accumulation in ouabain‐treated cells correlated with a gain of Na+i and loss of K+i. Augmented c‐Fos expression was also observed under inhibition of Na+/K+‐ATPase in K+‐free medium and in the presence of the Na+ ionophore monensin. The effect of ouabain on c‐Fos expression was sharply attenuated under dissipation of the transmembrane Na+ gradient, but was preserved in the presence of Ca2+ chelators and the extracellular regulated kinase inhibitor PD98059, thus indicating an Na+i‐mediated, Ca2+i‐ and extracellular regulated kinase‐independent mechanism of gene expression. In contrast to massive c‐Fos expression, we failed to detect any effect of ouabain on accumulation of luciferase driven by the c‐Fos 5′‐UTR. Negative results were also obtained in ouabain‐treated vascular smooth muscle cells and C11 Madin–Darby canine kidney cells possessing augmented c‐Fos expression. Our results reveal that Na+i‐induced c‐Fos expression is not mediated by the 5′‐UTR containing transcriptional elements activated by growth factors and other ‘classic stimuli’.
Analysis of dopamine transporter gene expression pattern − generation of DAT‐iCre transgenic mice
Authors: Turiault Marc , Parnaudeau Sébastien , Milet Aude , Parlato Rosanna , Rouzeau Jean‐Denis , Lazar Monique , Tronche François
Published: June 2007

The dopamine transporter is an essential component of the dopaminergic synapse. It is located in the presynaptic neurons and regulates extracellular dopamine levels. We generated a transgenic mouse line expressing the Cre recombinase under the control of the regulatory elements of the dopamine transporter gene, for investigations of gene function in dopaminergic neurons. The codon‐improved Cre recombinase (iCre) gene was inserted into the dopamine transporter gene on a bacterial artificial chromosome. The pattern of expression of the bacterial artificial chromosome–dopamine transporter–iCre transgene was similar to that of the endogenous dopamine transporter gene, as shown by immunohistochemistry. Recombinase activity was further studied in mice carrying both the bacterial artificial chromosome–dopamine transporter–iCre transgene and a construct expressing the β‐galactosidase gene after Cre‐mediated recombination. In situ studies showed that β‐galactosidase (5‐bromo‐4‐chloroindol‐3‐yl β‐d‐galactoside staining) and the dopamine transporter (immunofluorescence) had identical distributions in the ventral midbrain. We used this animal model to study the distribution of dopamine transporter gene expression in hypothalamic nuclei in detail. The expression profile of tyrosine hydroxylase (an enzyme required for dopamine synthesis) was broader than that of β‐galactosidase in A12 to A15. Thus, only a fraction of neurons synthesizing dopamine expressed the dopamine transporter gene. The bacterial artificial chromosome–dopamine transporter–iCre transgenic line is a unique tool for targeting Cre/loxP‐mediated DNA recombination to dopamine neurons for studies of gene function or for labeling living cells, following the crossing of these mice with transgenic Cre reporter lines producing fluorescent proteins.
TORC‐SIK cascade regulates CREB activity through the basic leucine zipper domain
Authors: Takemori Hiroshi , Kajimura Junko , Okamoto Mitsuhiro
Published: June 2007

The transcription factor cAMP response element‐binding protein (CREB) plays important roles in gene expression induced by cAMP signaling and is believed to be activated when its Ser133 is phosphorylated. However, the discovery of Ser133‐independent activation by the activation of transducer of regulated CREB activity coactivators (TORC) and repression by salt inducible kinase cascades suggests that Ser133‐independent regulation of CREB is also important. The activation and repression are mediated by the basic leucine zipper domain of CREB. In this review, we focus on the basic leucine zipper domain in the regulation of transcriptional activity of CREB and describe the functions of TORC and salt inducible kinase.
Transducer of regulated CREB and late phase long‐term synaptic potentiation
Authors: Wu Hao , Zhou Yang , Xiong Zhi‐Qi
Published: June 2007

In the central nervous system, long‐term adaptive responses to changes in the environment, such as the processes involved in learning and memory, require the conversion of extracellular stimuli into intracellular signals. Many of these signals involve the induction of gene expression. The late, transcription‐ and translation‐dependent phase of long‐term synaptic potentiation (L‐LTP) is an attractive cellular model for long‐lasting memory formation. The transcription factor cAMP response element‐binding protein (CREB) plays an essential role in the maintenance of L‐LTP. However, how synaptic signals propagate to the nucleus to initiate CREB‐target gene expression is unclear. Recent studies indicate that the CREB transducer of regulated CREB activity 1 coactivator undergoes neuronal activity‐dependent translocation from the cytoplasm to the nucleus, a process required for CRE‐dependent gene expression and the maintenance of L‐LTP in the hippocampus.
Childrens'and Adolescents'Use of Diaries for Sickle Cell Pain
Authors: Maikler Virginia Egbert , Broome Marion E. , Bailey Patricia , Lea Gwen
Published: June 2007

ISSUES AND PURPOSE. To evaluate the characteristics of vaso‐occlusive episodes, home management of pain and its impact on the daily activities, and a diary as a method of data collection.

DESIGN AND METHODS. Forty‐six adolescents and 75 children were asked to complete daily diaries during the intervention period of a larger study.

RESULTS. Mild pain was recorded 95% of the time; moderate pain, 3%; and severe pain, 1%. The pattern and location of pain varied greatly. Adolescents used more interventions than did children. When pain intensity was mild, 80% of the children/adolescents maintained school, social, and home activities, but decreased play/sport activities. When pain intensity was high, they decreased their participation in all activities.

PRACTICE IMPLICATIONS. Sickle cell pain episodes are unpredictable and highly variable. Diaries can enhance children's and adolescents’documentation and communication about their pain experiences.
Influence of pod maturity and level of domestication on biochemical components in wild and cultivated pigeonpea (Cajanus cajan)
Authors: Aruna R. , Rao D. Manohar , Reddy L.J. , Ramakrishnan S. Siva , Upadhyaya H.D.
Published: June 2007

Variations in the trypsin inhibitors and lectin content in the developing pods of thirty accessions of Cajanus scarabaeoides, a wild relative of pigeonpea, from wide geographical locations and six cultivated genotypes were estimated at juvenile, immature and mature stages of pod development. Genotypes differed at all three stages for these two biochemical components. Total protein and trypsin inhibitor contents were higher in the wild accessions than in the cultivated genotypes. Although lectin content in the juvenile stage of pod development in the wild accessions ICPW 138 and ICPW 98 was highest, it was absent in the mature pods in both the cultivated and the wild genotypes. Very high broad‐sense heritability estimates indicated the possibility of involvement of few genes in the inheritance of these biochemical components, which could be easily introgressed into the elite agronomic background.
Uganda's Civil War and the Politics of ICC Intervention
Authors: Branch Adam
Published: June 2007

The International Criminal Court‘s intervention into the ongoing civil war in northern Uganda evoked a chorus of confident predictions as to its capacity to bring peace and justice to the war-torn region. This optimism is unwarranted, however. The article analyzes the consequences for peace and justice of the ICC's intervention, dividing them into two categories: those resulting from the political instrumentalization of the ICC by the Ugandan government, and those resulting from the discourse and practice of the ICC as an institution of global law enforcement.

As to the first, the article argues that the Ugandan government referred the conflict to the ICC in order to obtain international support for its militarization and to entrench, not resolve, the war; the ICC, in accepting the referral and prosecuting only the Lord‘s Resistance Army, has in effect chosen to pursue a politically pragmatic case even though doing so contravenes the interests of peace, justice, and the rule of law. As to the second, the article reveals the harmful effects that ICC intervention can have on the capacity for autonomous political organization and action among civilian victims of violence, specifically how it leads to depoliticization by promoting a political dependency mediated by international law. The article draws from this analysis disturbing implications about ICC interventions generally, and concludes by asking whether ICC practice may be reformed so as to avoid these negative consequences.
The Inconveniences of Transnational Democracy
Authors: Cabrera Luis
Published: June 2007

Despite some limited moves toward openness and accountability, suprastate policy formation in such bodies as the World Trade Organization remains fundamentally exclusive of individuals within states. This article critiques the “don't kill the goose” arguments commonly offered in defense of such exclusions. It highlights similarities between those arguments and past arguments for elitist forms of democracy, where strict limitations are advocated on the participation of nonelites in the name of allowing leaders to act most effectively in the broad public interest. Advocated here is movement toward a strongly empowered WTO parliamentary body that would be guided in practice by a principle of democratic symmetry, attempting to match input to the increasing impacts of WTO governance. A parliament with codecision powers broadly similar to those of the European Parliament is offered as a long-term institutional ideal.
Acute resistance exercise increases skeletal muscle angiogenic growth factor expression
Authors: Gavin T. P. , Drew J. L. , Kubik C. J. , Pofahl W. E. , Hickner R. C.
Published: June 2007

Aims:  Both aerobic and resistance exercise training promote skeletal muscle angiogenesis. Acute aerobic exercise increases several pro‐angiogenic pathways, the best characterized being increases in vascular endothelial growth factor (VEGF). We hypothesized that acute resistance exercise also increases skeletal muscle angiogenic growth factor [VEGF and angiopoietin (Ang)] expression.

Methods:  Seven young, sedentary individuals had vastus lateralis muscle biopsies and blood drawn prior to and at 0, 2 and 4 h post‐resistance exercise for the measurement of VEGF; VEGF receptor [KDR, Flt‐1 and neuropilin 1 (Nrp1)]; Ang1 and Ang2; and the angiopoietin receptor – Tie2 expression. Resistance exercise consisted of progressive knee extensor (KE) exercise to determine one repetition maximum (1‐RM) followed by three sets of 10 repetitions (3 × 10) of KE exercise at 60–80% of 1‐RM.

Results:  Resistance exercise significantly increased skeletal muscle VEGF mRNA and protein and plasma VEGF protein at 2 and 4 h. Resistance exercise increased KDR mRNA and Tie2 mRNA at 4 h and Nrp1 mRNA at 2 and 4 h. Skeletal muscle Flt‐1, Ang1, Ang2 and Ang2/Ang1 ratio mRNA were not altered by resistance exercise.

Conclusions:  These findings suggest that acute resistance exercise increases skeletal muscle VEGF, VEGF receptor and angiopoietin receptor expression. The increases in muscle angiogenic growth factor expression in response to acute resistance exercise are similar in timing and magnitude with responses to acute aerobic exercise and are consistent with resistance exercise promoting muscle angiogenesis.
Intracellular signalling pathways in the vasoconstrictor response of mouse afferent arterioles to adenosine
Authors: Hansen P. B. , Friis U. G. , Uhrenholt T. R. , Briggs J. , Schnermann J.
Published: June 2007

Aims:  Adenosine causes vasoconstriction of afferent arterioles of the mouse kidney through activation of adenosine A1 receptors and Gi‐mediated stimulation of phospholipase C. In the present study, we further explored the signalling pathways by which adenosine causes arteriolar vasoconstriction.

Methods and results:  Adenosine (10−7 m) significantly increased the intracellular calcium concentration in mouse isolated afferent arterioles measured by fura‐2 fluorescence. Pre‐treatment with thapsigargin (2 μm) blocked the vasoconstrictor action of adenosine (10−7 m) indicating that release of calcium from the sarcoplasmic reticulum (SR), stimulated presumably by IP3, is involved in the adenosine contraction mechanism of the afferent arteriole. In agreement with this notion is the observation that 2 aminoethoxydiphenyl borate (100 μm) blocked the adenosine‐induced constriction whereas the protein kinase C inhibitor calphostin C had no effect. The calcium‐activated chloride channel inhibitor IAA‐94 (30 μm) inhibited the adenosine‐mediated constriction. Patch clamp experiments showed that adenosine treatment induced a depolarizing current in preglomerular smooth muscle cells which was abolished by IAA‐94. Furthermore, the vasoconstriction caused by adenosine was significantly inhibited by 5 μm nifedipine (control 8.3 ± 0.2 μm, ado 3.6 ± 0.6 μm, ado + nifedipine 6.8 ± 0.2 μm) suggesting involvement of voltage‐dependent calcium channels.

Conclusion:  We conclude that adenosine mediates vasoconstriction of afferent arterioles through an increase in intracellular calcium concentration resulting from release of calcium from the SR followed by activation of Ca2+‐activated chloride channels leading to depolarization and influx of calcium through voltage‐dependent calcium channels.
Molecular beam epitaxy growth of antimonide type-II “W” high-power interband cascade lasers and long-wavelength infrared photodiodes
Authors: Kim C. S. , Canedy C. L. , Aifer E. H. , Kim M. , Bewley W. W. , Tischler J. G. , Larrabee D. C. , Nolde J. A. , Warner J. H. , Vurgaftman I. , Jackson E. M. , Meyer J. R.
Published: June 2007

Interband cascade lasers with ten active stages were grown by molecular beam epitaxy (MBE). Devices emitting near 3.6μm at room temperature operated in pulsed mode to a temperature of 330K. The threshold current densities were the lowest to date for NRL growths, ranging from 9A∕cm2 at 78Kto1.7kA∕cm2 at 300K. The voltage efficiency was ≈94% at 140K, and the pulsed slope efficiency was 121mW∕A at 300K. Antimonide photodetectors with a cutoff wavelength of 12μm were also grown in the same machine by MBE. The absorbing layer consisted of an InAs∕GaInSb type-II superlattice, and the depletion region comprised a four-layer “W” structure with a graded energy gap in order to minimize the tunneling and generation currents. Quantum efficiencies of 30%–40% were achieved in the 8–10μm band.
Epitaxial growth and strain relaxation of BaTiO3 thin films on SrTiO3 buffered (001) Si by molecular beam epitaxy
Authors: Niu F. , Wessels B. W.
Published: June 2007

Epitaxial BaTiO3 (BTO) thin films were deposited by molecular beam epitaxy on (001) silicon using an approximately 5 ML thick SrTiO3 (STO) as an intermediate buffer layer. In situ reflection high-energy electron diffraction (RHEED) was employed to quantitatively determine strain relaxation from the change in the in-plane lattice spacing. The crystalline quality, composition, and surface morphology of the BTO thin films were characterized by a combination of x-ray diffraction (XRD), atomic force microscopy, and x-ray photoelectron spectroscopy. RHEED analysis indicates that the initial growth of BTO was pseudomorphic. Strain relaxation occurred when the thickness reached a critical value of 10 MLs or 4nm. The lattice spacing approached the bulk BTO value for films with 30nm thickness. The BTO layer grows via a two dimensional growth mode. XRD measurement indicates a rocking curving width of the BTO (002) peak on Si as low as 0.9° has been achieved. Strain relaxation of the BTO films grown on different substrates including MgO, MgO/STO buffered Si, and STO buffered Si are compared.
Molecular-beam epitaxy growth of device-compatible GaAs on silicon substrates with thin (∼80nm) Si1−xGex step-graded buffer layers for high-κ III-V metal-oxide-semiconductor field effect transistor applications
Authors: Oye Michael M. , Shahrjerdi Davood , Ok Injo , Hurst Jeffrey B. , Lewis Shannon D. , Dey Sagnik , Kelly David Q. , Joshi Sachin , Mattord Terry J. , Yu Xiaojun , Wistey Mark A. , Harris James S. , Holmes Archie L. , Lee Jack C. , Banerjee Sanjay K.
Published: June 2007

The authors report the fabrication of TaN–HfO2–GaAs metal-oxide-semiconductor capacitors on silicon substrates. GaAs was grown by migration-enhanced epitaxy (MEE) on Si substrates using an ∼80-nm-thick Si1−xGex step-graded buffer layer, which was grown by ultrahigh vacuum chemical vapor deposition. The MEE growth temperatures for GaAs were 375 and 400°C, with GaAs layer thicknesses of 15 and 30nm. We observed an optimal MEE growth condition at 400°C using a 30nm GaAs layer. Growth temperatures in excess of 400°C resulted in semiconductor surfaces rougher than 1nm rms, which were unsuitable for the subsequent deposition of a 6.5-nm-thick HfO2 gate dielectric. A minimum GaAs thickness of 30nm was necessary to obtain reasonable capacitance-voltage (C-V) characteristics from the GaAs layers grown on Si substrates. To improve the interface properties between HfO2 and GaAs, a thin 1.5nm Ge interfacial layer was grown by molecular-beam epitaxy in situ after the GaAs growth. The Ge-passivated GaAs samples were then transferred in air for the subsequent ex situ HfO2 formation. This Ge interfacial layer in between HfO2 and GaAs was necessary to avoid relatively flat C-V characteristics that are symptomatic of high interface state densities.
Magnetoresistance of fully epitaxial MnAs∕GaAs lateral spin valves
Authors: Holub M. , Saha D. , Bhattacharya P.
Published: June 2007

The authors report the growth, fabrication, and characterization of lateral MnAs∕GaAs spin valves where Schottky tunnel barriers enable all-electrical spin injection and detection. Through a difference in geometric aspect ratio for the MnAs contacts, parallel and antiparallel alignment between the contact magnetization is obtained by varying the external magnetic field. Temperature-dependent conductivity measurements indicate that tunneling is the dominant transport mechanism for the MnAs∕GaAs Schottky diode polarizer and analyzer contacts. Peak magnetoresistances of 3.6% at 10K and 1.1% at 125K are observed for a 0.5μm channel length spin valve.
Effects of temperature, nitrogen ions, and antimony on wide depletion width GaInNAs
Authors: Ptak A. J. , Friedman D. J. , Kurtz Sarah
Published: June 2007

GaInNAs is a promising candidate material to increase the conversion efficiency of triple junction solar cells, but the dilute nitrides suffer from low-to-nonexistent minority-carrier diffusion lengths. The use of molecular beam epitaxy grown p-i-n structures with wide depletion widths can achieve high photocurrents in dilute nitrides, but this requires background doping below 2×1014cm−3 in the i layer. Here, the authors report on a number of factors that increase the net background acceptor concentration, hindering the effects to realize wide depletion widths, including high substrate temperatures, ions from the rf plasma source used to provide active nitrogen, and the addition of Sb. In addition, low substrate temperatures lead to an increase in n-type conductivity. Solar cell results that show the deleterious effects of Sb on GaInNAs devices are presented, including decreased open-circuit voltage and fill factor.
Epitaxial overgrowth of GaN nanocolumns
Authors: Averett K. L. , Van Nostrand J. E. , Albrecht J. D. , Chen Y. S. , Yang C. C.
Published: June 2007

GaN nanocolumns of exceptional crystalline quality have been grown by molecular beam epitaxy on both silicon (111) and sapphire (0001) substrates. Reflection high energy electron diffraction produces a unique diffraction pattern for in situ verification of columnar growth. Subsequent molecular beam epitaxial overgrowth of the nanocolumns has been used to improve the quality of thin film GaN layers when compared to GaN films grown directly on sapphire substrates. Transmission electron microscopy was used to confirm the absence of threading dislocations in the selected columns. Scanning electron microscopy of overgrown material demonstrated surface morphology similar to thin films grown in the intermediate (Ga-rich) growth regime, or a pattern of densely packed hexagonal structures, depending on growth conditions. Low temperature photoluminescence (PL) spectra demonstrated a greater than two orders of magnitude improvement in PL intensity of overgrown film versus direct film growth.
Intermediate-layer lithography method for producing metal micropatterns
Authors: Liu Xinchuan , Luo Cheng
Published: June 2007

Motivated by a macrocutting process often used in manufacturing industry to pattern sheet metals, an innovative intermediate-layer lithography (ILL) approach is developed in this work to generate micropatterns in a thin metal film. In the ILL method, an intermediate layer of polymethyl methacrylate PMMA is introduced between a silicon substrate and a thin metal film. Subsequently, the metal is printed through the insertion of a silicon mold using a hot-embossing technique. Al films of thickness ranging from 100to500nm have been patterned by silicon molds of depths of 10–100μm. Various Al patterns of lateral dimensions ranging from 10to300μm have been produced, including channels, lines, square dots, square holes, and truss structures. The effects of printing temperatures, thicknesses of Al films, and geometries of silicon mold structures on the patterning results were experimentally investigated, followed by numerical exploration. As a new patterning method, the ILL approach has advantages of simplicity and massive production and is free of aggressive chemistry.
Kinetics of gallium adlayer adsorption/desorption on polar and nonpolar GaN surfaces
Authors: Choi Soojeong , Kim Tong-Ho , Everitt Henry O. , Brown April , Losurdo Maria , Bruno Giovanni , Moto Akihiro
Published: June 2007

Spectroscopic ellipsometry installed on a GEN-II plasma assisted molecular beam epitaxy machine has been shown to be an effective in situ real time tool for monitoring the kinetics of gallium adlayer adsorption/desorption on the GaN surface. In this work, the authors present data on the study of Ga adsorption/desorption on polar c-plane GaN (0001) and nonpolar m-plane GaN (1−100) surfaces for Ga beam equivalent pressures in the range of 8.96×10−8–1.86×10−7Torr, Ga pulses in the range of 5–360s, and for substrate temperatures between 650 and 750°C.
Intersubband transitions in molecular-beam-epitaxy-grown wide band gap II-VI semiconductors
Authors: Shen A. , Lu H. , Tamargo M. C. , Charles W. , Yokomizo I. , Song C. Y. , Liu H. C. , Zhang S. K. , Zhou X. , Alfano R. R. , Franz K. J. , Gmachl C.
Published: June 2007

The authors report the study of intersubband transitions in ZnCdMgSe-based wide band gap II-VI semiconductors. The samples were prepared by molecular beam epitaxy on InP substrates. Both ZnCdSe∕ZnCdMgSe multiple quantum wells and CdSe∕ZnCdMgSe quantum dot multilayer stacks were grown. Strong intersubband absorption was observed in the samples. The results show that these materials are very promising for fabricating intersubband devices in the mid- and near-infrared spectral ranges.
Excitation dependent photoluminescence measurements of the nonradiative lifetime and quantum efficiency in GaAs
Authors: Johnson S. R. , Ding D. , Wang J.-B. , Yu S.-Q. , Zhang Y.-H.
Published: June 2007

The nonradiative lifetime and spontaneous emission quantum efficiency in molecular-beam epitaxy grown bulk GaAs is determined using injection level dependent photoluminescence (PL) measurements. These measurements were performed at temperatures of 300, 230, 100, and 50K using a HeNe pump laser with powers ranging from 0.3to40mW. The quantum efficiency and lifetime is inferred from the power law relation linking pump power and integrated PL signal that is predicted by the rate equations. The nonradiative lifetime for bulk GaAs is determined to be 0.3μs, with an additional temperature dependent component attributed to the AlGaAs barriers that rapidly reduces the nonradiative lifetime at temperatures above 230K. The peak quantum efficiency is >0.96 at 300K and >0.99 at temperatures below 230K.
Comprehensive investigation on emitter ledge length of InGaP∕GaAs heterojunction bipolar transistors
Authors: Fu Ssu-I , Liu Rong-Chau , Cheng Shiou-Ying , Lai Po-Hsien , Tsai Yan-Ying , Hung Ching-Wen , Chen Tzu-Pin , Liu Wen-Chau
Published: June 2007

The influence of emitter ledge length on the performance of InGaP∕GaAs heterojunction bipolar transistors is comprehensively investigated. Due to the band-bending effect at the intersection of the emitter ledge edge with the exposed base surface, an undesired potential saddle point is formed. Moreover, emitter ledge passivations that are longer or shorter than an optimal length result in the deterioration of device performance. Based on the theoretical analysis and experimental results, the surface recombination effect of the device with an emitter ledge length of 0.8μm is negligible compared with the unpassivated device. Also, the device with the emitter ledge length of 0.8μm shows nearly the best dc characteristics and acceptable rf performance. Therefore, the optimum emitter ledge length in this study is near 0.8μm.
Sn quantum dots embedded in SiO2 formed by low energy ion implantation
Authors: Zhao J. P. , Meng Y. , Huang D. X. , Chu W. K. , Rabalais J. W.
Published: June 2007

Extremely small Sn nanodots embedded in the subsurface of SiO2, i.e., Sn–SiO2 quantum dot composites, have been formed by ion implantation of the Sn+120 isotope into (0001) Z-cut quartz at a low kinetic energy of 9keV at room temperature. Transmission electron microscopy images show that the Sn nanodots have an average size of about 3nm, and both single-crystal and amorphous nanodots have been observed at room temperature. The nanodots are randomly distributed in the lateral direction but confined in a narrow layer in the depth direction. The bimodal size distribution that is often observed in high energy implantation was not observed in the present study. The spatial morphology and crystallinity of the Sn nanodots can be modified by thermal annealing, and the extent of the modification is dependent on the annealing temperature. The distribution and crystallinity of the Sn nanodots in single-crystal bulk SiO2 are different from those of Sn nanocrystals in thin SiO2 films on silicon substrates. The mechanisms that could account for these phenomena are discussed.
Experimental investigation of micro-mesoscale Knudsen compressor performance at low pressures
Authors: Han Y.-L. , Muntz E. P.
Published: June 2007

The Knudsen compressor, based on the temperature gradient driven rarefield flow phenomenon of thermal creep, is a solid-state, micro-mesoscale gas pump or compressor with no moving parts. Experimental studies have shown that micro-mesoscale Knudsen compressors can be operated efficiently by either resistive or radiant heating techniques, from inlet pressure up to about 10atm down to 3×104Pa. A study of the fundamental limitations encountered in reducing a micro-mesoscale Knudsen compressor’s operating inlet pressures to as low as 0.1Pa is the primary focus of the present work. At low pressures, several issues that affect the efficient operation of micro-mesoscale Knudsen compressors have been identified. These include the large membrane channel sizes that are required because of relatively large molecular mean free paths, “reverse” thermal creep flows in the connector sections due to finite connector channel to membrane channel size ratios, and membrane channel exit vortices introduced by high conductance membrane channels. Mechanically machined aerogel membranes, with either capillaries or rectangular channels, have been investigated and demonstrated as attractive membrane candidates for the operation of low-pressure Knudsen compressors. Flow coefficients calculated from the linearized Boltzmann equation for long straight channels were adapted to estimate a Knudsen compressor’s performance. The Knudsen compressor pressure ratios observed in the experiments were lower than those estimated using the flow coefficients. Complex internal flow circulations, induced by a synergistic combination of membrane channel exit vortices and reverse thermal creep flows, are proposed as the cause of the lower pressure ratios. Such flow phenomena cannot be estimated by flow coefficients alone. Rigorous and computationally intensive simulation studies will be necessary to predict accurately the effects of these internal flow circulations.
Nanoscale resist morphologies of dense gratings using electron-beam lithography
Authors: Mohammad M. A. , Dew S. K. , Westra K. , Li P. , Aktary M. , Lauw Y. , Kovalenko A. , Stepanova M.
Published: June 2007

The authors report a systematic investigation, both by experiment and by numerical modeling, of resolution limits for dense nanoscale gratings fabricated in polymethylmethacrylate through low-energy electron-beam lithography (EBL) using 10keV electrons. In particular, they have studied the resist morphologies that develop in various exposure regimes for gratings with periods from 20to100nm and categorized the potential sources of resist damage in such gratings. Through comparison of their experimental and numerical results, they have elucidated the major mechanisms that limit the EBL process resolution at the stages of exposure and resist development. The authors have also suggested semiempirical criteria to predict the risk of resist damage when fabricating dense nanostructures.
Improved performance of a dual-passivated heterojunction bipolar transistor
Authors: Cheng Shiou-Ying , Fu Ssu-I , Liu Wen-Chau
Published: June 2007

Dual passivation (with ledge structure and sulfur treatment) on base surface is employed to improve device performance of an InGaP∕GaAs heterojunction bipolar transistor (HBT). By using this dual-passivation technique, good transistor characteristics such as dc current gain βF, offset voltage ΔVCE, specific contact resistance ρC, and sheet resistance Rsh are obtained. In addition, the InGaP∕GaAs HBT with dual passivation exhibits improved thermal stability and microwave characteristics. Our experimental results suggest that the dual-passivated device can be used for high-temperature and/or low-power electronics applications.
Epitaxial growth of Sc2O3 films on GaN (0001) by pulsed laser deposition
Authors: Liu Chang , Chor Eng Fong , Tan Leng Seow , Du Anyan
Published: June 2007

The authors have demonstrated the epitaxial growth of Sc2O3 films on GaN (0001) using pulsed laser deposition (PLD) (with KrF excimer laser). The characteristics of these Sc2O3 films were found to be highly dependent on the substrate temperature (Ts) and the oxygen partial pressure (P) during the PLD process. Under optimized deposition conditions (Ts of 700°C and Po of 10mTorr), highly c-axis oriented Sc2O3 films have been epitaxially grown on GaN (0001) template with fine film crystallinity, smooth surface morphology, good film stoichiometry, and a refractive index close to that of the bulk material. Cross-sectional transmission electron microscopy measurements confirmed the heteroepitaxial nature of the Sc2O3 films on the GaN template and revealed an epitaxial relationship of [112]Sc2O3‖[213¯0]GaN and (222)Sc2O3‖(0002)GaN.
Profile control of novel non-Si gates using BCl3∕N2 plasma
Authors: Shamiryan Denis , Paraschiv Vasile , Eslava-Fernandez Salvador , Demand Marc , Baklanov Mikhail , Beckx Stephan , Boullart Werner
Published: June 2007

The authors found that a BCl3∕N2 plasma is very suitable for metal gate patterning and profile control as it produces a passivating film during the etching. On blanket wafers, a boron-nitride-like film is deposited from a boron trichloride/nitride plasma mixture in a standard etch chamber at temperatures as low as 60°C. Deposition rate can be varied from 10 to more than 100nm∕min depending on the plasma conditions and BCl3∕N2 ratio. The film contains hexagonal boron nitride but is very unlikely to be a stoichiometric BN. It decomposes at elevated temperatures and is water soluble. The latter property makes the postetch clean relatively straightforward. This film can be used for sidewall passivation during the patterning of advanced non-Si gates, e.g., metal gates. They are presenting the use of BCl3∕N2 plasma for patterning of Ge and TaN gates as examples. The Ge gate profile is damaged by a pure BCl3 plasma during high-k dielectric (HfO2) etching after the gate patterning. Addition of 10% N2 to the BCl3 plasma preserves the gate profile while removing the high k. In the other example, a TaN gate is etched isotopically by pure BCl3 plasma. Addition of 5% N2 prevents the lateral attack providing straight TaN profile.
Study of photoresist etching and roughness formation in electron-beam generated plasmas
Authors: Orf Bryan J. , Walton Scott G. , Leonhardt Darrin , Oehrlein Gottlieb S.
Published: June 2007

A modulated, electron-beam generated plasma processing system was used to study plasma-polymer interactions for 193 and 248nm photoresists (PRs) that differed significantly in polymer structure. Because of the low plasma potential of the electron-beam generated plasma, the authors were able to study plasma etching and surface roughening of the photoresists at very low ion energies (<5eV) without sacrificing high ion flux (>1014cm−2). Typical conditions in the experiments were 2kV∕4ms electron-beam pulses with a 20ms period. The effects of ion bombardment energy, chemically assisted etching using fluorine, and the presence of a thin fluorocarbon overlayer on surface roughness formation during PR etching were examined. Gas mixtures containing SF6 resulted in much higher etch rates and an increased surface roughness relative to values measured in pure Ar plasmas. However, the rms roughness per nanometer of photoresist removed was greater for pure Ar plasmas. Overall the 248nm PR showed less surface roughness than 193nm PR after identical treatments, which was explained by a higher etching rate of the 193nm photoresist material. Finally, it was found in a pure argon plasma that the thickness of a fluorocarbon overlayer determined the roughness of the underlying photoresist; specifically, thicker layers resulted in smoother PR surfaces after plasma exposure.
Analysis of the driving characteristic of carbon nanotube triode with high frequency
Authors: Chai Weiqiang , Lou Chaogang , Wang Qilong , Lei Wei , Zhang Xiaobing
Published: June 2007

A circuit model is proposed to analyze the driving characteristics of the carbon nanotube field emission triode. In the model, the current gain magnitude, the cutoff frequency, and the transition frequency can be calculated, and the result is confirmed by PSPICE simulation. In addition, the parameters that affect the cutoff frequency and the transition frequency are discussed, which include capacities, inductances, and transconductance. The influence of the traverse time of electrons on the triode’s frequency performance will play an important role in the range of very high frequency.
Real time optical monitoring of molecular beam epitaxy of InN on SiC substrates
Authors: Losurdo Maria , Kim Tong-Ho , Choi Soojeong , Wu Pae , Giangregorio Maria M. , Bruno Giovanni , Brown April
Published: June 2007

Spectroscopic ellipsometry has been used to monitor in real time and in situ the molecular beam epitaxial growth of InN on SiC substrates. A three-step growth process consisting of (i) low-temperature (200°C) nitridation of the SiC surface, (ii) low-temperature (350°C) nucleation of a thin InN buffer layer, and (iii) growth of the InN epitaxial layer at 450°C has been applied. The impact of the In flux on the growth kinetics, morphology, and structural and optical properties of InN has been investigated. It is found that independent of the In flux the low-temperature buffer shows In surface accumulation. This In surface accumulation increases during InN growth under In-rich conditions and is depleted during growth under intermediate and N-rich conditions. Better structural, morphological, and optical properties are obtained when the films are grown under In-rich conditions.
Position measurement method for alignment in UV imprint using a high index mold and “electronic” moiré technique
Authors: Suehira Nobuhito , Terasaki Atsunori , Okushima Shingo , Seki Junichi , Ono Haruhito , Ina Hideki
Published: June 2007

In UV imprint, positioning errors can occur between a mold and a wafer due to pressure when there is a contact with the UV resin. The moiré technique, which is produced by superimposition of two gratings, is a well-known and simple method for high-resolution position measurement. However, the authors believe that a direct observation of two separate gratings is more appropriate for higher positioning accuracy. Here they propose a new method for the position measurement, which obtains “electronic” moiré fringes by combining the images of two separate gratings from different areas of the mold and the wafer. The fundamental detection error was σ=0.15nm. The repeatabilities of the total system was σ=0.68nm in air and σ=0.73nm in resin. The linearity of the measurement value to control signal was R2=0.97.
Nanopattern transfer to SiO2 by ion track lithography and highly selective HF vapor etching
Authors: Skupiński M. , Jensen J. , Johansson A. , Possnert G. , Boman M. , Hjort K. , Razpet A.
Published: June 2007

The authors present a method for high aspect ratio nanopatterning of high density (1010pores∕cm2) self-assembled porous alumina membrane pattern into thermally grown SiO2 on silicon. The pattern transfer is accomplished by irradiating through 2μm thick porous alumina membrane with swift heavy ions (4MeV Cl2+). Ions passing through the nanopores in the mask at a fairly high fluence (typically 1014ions∕cm2) are impinging on the substrate and creating a continuous volume of overlapping ion tracks of damage. The damage is sufficient to be selectively etched by HF vapor from an aqueous HF solution. From an alumina mask with pores of 70nm diameter, a pattern of pores of 77nm in diameter and the same distance of 100nm between the centers of the pores was transferred. The deepest observed etched pores were 355nm, giving an aspect ratio of 5, which is up to 40 times larger compare to earlier work where HF wet etching was used. This ion track lithography technique shows a potential to produce nanostructures with even higher aspect ratios.
Fabrication of nanostructures using a C-methylcalix[4]resorcinarene dielectric spacer
Authors: Fleischer M. , Panteleit F. , Wharam D. A.
Published: June 2007

Since the first low-temperature transport measurements on nanostructures, various techniques have been applied to fabricate devices of reduced dimensionality from GaAs∕AlGaAs heterostructures. Here a method is presented using a lithographically patterned dielectric resist spacer to locally screen the underlying two-dimensional electron gas, which requires fewer gates than the conventional split-gate approach. Various calixarene and resorcinarene derivatives are characterized and compared as potential high-resolution spacer materials. Typical nanostructures defined with the novel resist, C-methylcalix[4]resorcinarene, as well as a capacitance model for the effectiveness of the screening are presented.
Nanosized tungsten carbide for NOx reduction
Authors: Rumaiz A. K. , Lin H. Y. , Baldytchev I. , Shah S. Ismat
Published: June 2007

WC nanoparticles were synthesized using a variation of pulsed laser deposition (PLD) process. In this modified PLD the ablated plume is carried away by a circulating carrier gas from the evaporation region. It is then allowed to condense heterogeneously and the condensed particles are collected on a filter. Using this technique we synthesized two different types of particles, as-prepared WC and pure W nanoparticles. Pure W nanoparticles were subsequently carburized to form WC. These nanoparticles were used to study the feasibility for the use in NOx reduction. The structural and chemical properties of these samples were analyzed using x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Catalytic activity was measured using a tube reactor. A combination of 1% NO and 99% He gas was used. Both the pure WC and carburized WC samples were found to be catalytically active with an activation temperature of about 400°C. The stability of the catalysts was studied by performing de-NOx experiments for an extended period of time. Both XRD and XPS analyses of the samples after de-NOx confirm the formation of oxide. CO addition helped to reduce the extent of oxide formation.
Effect of surface pretreatment and substrate orientation on the characteristics of InAs quantum dots on Si and SiO2 substrates
Authors: Yoon I. , Yi C. , Kim T. , Brown A. S. , Seabaugh A.
Published: June 2007

The surface morphology of InAs quantum dots (QDs) on undoped Si (100) shows a strong dependency on surface pretreatments, with as much as 30% difference in island density with different size distributions. Lowering the V∕III fluxes ratio (58:1 to 10:1) effectively suppresses the average height (47%) and increases density (75%) of QDs. While changing the growth temperature (220–300°C) increased the average height by 62% on chemically etched Si surfaces, nucleation on the SiO2 surface was less sensitive to surface preparation. The authors also observe that the specific substrate orientation and annealing at 500°C do not significantly impact the morphology of QDs.
High gain AlGaAs∕GaAs heterojunction bipolar transistor fabricated on SiGe∕Si substrate
Authors: Lew K. L. , Yoon S. F. , Loke W. K. , Tanoto H. , Dohrman C. L. , Isaacson D. M. , Fitzgerald E. A.
Published: June 2007

High gain AlGaAs∕GaAs heterojunction bipolar transistors grown on SiGe∕Si substrate have been fabricated. Measured peak dc current gain of ∼100 is obtained for a device with emitter area of ∼1.6×103μm2, with base concentration of 1×1019cm−3. The dominant base current component is discussed and determined. The breakdown characteristic is studied and compared with that of the device grown on GaAs substrate. Our experimental results demonstrate that SiGe∕Si substrate could provide a robust method for monolithic integration of high speed GaAs-based electronic devices with silicon-based circuitry.
Focused ion beam tomography of a microelectronic device with sub-2-nm resolution
Authors: Yeoh T. S. , Ives N. A. , Presser N. , Stupian G. W. , Leung M. S. , McCollum J. L. , Hawley F. W.
Published: June 2007

A method for implementing focused ion beam tomography with two dimensional images separated by less than 2nm per slice has been developed. The calculated resolution of the voxel dataset is estimated to be less than 1×1×2nm3 ∼2nm3. A programed antifuse structure in a field programable gate array antifuse structure was analyzed using this method of imaging, showing the individual nanoscale components of the antifuse structure and the fusing region.
A simple derivation of the Lorentz transformation and of the accompanying velocity and acceleration changes
Authors: Lévy J.-M.
Published: June 2007

The Lorentz transformation is derived from a simple thought experiment by using a vector formula from elementary geometry. The result is used to obtain general velocity and acceleration transformation equations.