bluuebunny/crossref_metadata_2025 huggingface dataset:
Age Related Changes in 5‐methylcytosine Content in Human Peripheral Leukocytes and Placentas: an HPLC‐based Study
Authors: Fuke C. , Shimabukuro M. , Petronis A. , Sugimoto J. , Oda T. , Miura K. , Miyazaki T. , Ogura C. , Okazaki Y. , Jinno Y.
Published: June 2004

The goal of the present study was to investigate inter‐individual and age‐dependent variation of global DNA methylation in human tissues. In this work, we examined 5‐methyldeoxycytidine (metC) content by HPLC in human peripheral blood leukocytes obtained from 76 healthy individuals of ages varying from 4 to 94 years (yr), and 39 human placentas from various gestational stages. The HPLC analysis revealed a significant variation of metC across individuals and is consistent with the previous findings of age‐dependent decrease of global methylation levels in human tissues. The age‐dependent decrease of metC was relatively small, but statistically highly significant (p= 0.0002) in the aged group (65.9 ± 8.9 [mean age ± SD] yr; n = 22) in comparison to the young adult group (19.3 ± 1.4 yr; n = 21). Males showed a subtle but statistically significant higher mean metC content than females. In contrast to the peripheral blood samples, DNA extracted from placentas exhibited gestational stage‐dependent increase of methylation levels that appeared to inversely correlate with the expression levels of human endogenous retroviruses. These data may be helpful in further studies of DNA methylation, such as inheritance of epigenetic patterns, environment‐induced changes, and involvement of epigenetic changes in disease.
The Sib TDT Adjusted For Age Of Disease Onset
Authors: Ghosh Saurabh , Reich Theodore
Published: June 2004

Since the Sib‐TDT (Spielman & Ewens, 1998) ignores age of disease onset, there could be loss of power in detecting linkage. In this article, we propose an adjustment for age of onset using the Cox Proportional Hazard Model (Cox, 1972) with the marker allele as a covariate. The test statistic for linkage is identical to the traditional Sib‐TDT. Monte‐Carlo simulations are performed under different disease models to assess the increase in power of the age‐adjusted Sib‐TDT compared to the traditional Sib‐TDT. We extend our method to multiallelic markers. An application using data on Alzheimer's Disease is also presented.
Clinical Experience with a New Detection Algorithm for Differentiation of Supraventricular from Ventricular Tachycardia in a Dual‐Chamber Defibrillator
Authors: SINHA ANIL‐MARTIN , STELLBRINK CHRISTOPH , SCHUCHERT ANDREAS , MÖX BERNHARD , JORDAENS LUC , LAMAISON DOMINIQUE , GILL JASWINDER , KAPLAN ANDREW , MERKELY BELA ,   Phylax AV Investigator Group
Published: May 2004

Introduction: Inadequate therapy for supraventricular tachyarrhythmias (SVT) is a frequent problem of implantable cardioverter defibrillators (ICD). Dual‐chamber ICDs have been developed to improve discrimination of SVT from ventricular tachycardia (VT). We investigated the positive predictivity, sensitivity, and specificity of a new algorithm, the SMART detection™ algorithm, incorporated in the Phylax AV (Biotronik) dual‐chamber ICD.

Methods and Results: Two hundred nine patients (185 men, age 64 ± 11 years) received a Phylax AV ICD with SMART detection™ activated. In 138 of these patients, 1,245 sustained tachycardia episodes with a detailed electrogram were stored in the device during a follow‐up period of 10 ± 6 months. Episodes were correctly classified as ventricular fibrillation (VF, n = 178) in 52 patients, VT (n = 641) in 98 patients, and SVT (n = 385) in 48 patients by the algorithm. Forty‐one true SVT episodes (3.3%) were misclassified as VT: atrial fibrillation (n = 7) and flutter (n = 1), sinus tachycardia (n = 12), and other SVT (n = 21). The positive predictivity for VF/VT was 94.5% (95% CI 92.7–95.8) uncorrected and 94.5% (95% CI 92.9–95.8%) corrected with the generalized equation estimation (GEE) method. The positive predictivity for SVT was 100%. The specificity was 88.9% (95% CI 85.6–91.6%) uncorrected and 89.0% (95% CI 85.6–91.6%) corrected with the GEE method with a sensitivity of 100%.

Conclusion: The SMART detection™ algorithm was safe and reliable for the detection of all ventricular tachycardias. Although its specificity was high, it should be improved with regard to SVT to avoid inappropriate ICD therapies. (J Cardiovasc Electrophysiol, Vol. 15, pp. 1‐7, June 2004)
Successful Implantable Cardioverter Defibrillator Placement in an Ambulatory Patient Without Thoracic Venous Access
Authors: ELDADAH ZAYD A. , DONAHUE J. KEVIN
Published: May 2004

Evaluation of an individual requiring permanent cardiac pacing and implantable cardioverter defibrillator (ICD) function revealed no suitable thoracic vascular access for traditional device implantation. Because the patient refused cardiac surgery, a left femoral venous approach was used to introduce two extended‐length, active fixation leads that were positioned in the right atrium and ventricle. The leads were tunneled to the abdomen and connected to a dual‐chamber ICD. A low defibrillation threshold and robust pacing and sensing parameters were observed at implant. All of these parameters were stable at 6‐month follow‐up. In addition, no negative effects of the predominantly abdominal shock vector were observed. This case suggests that femoral ICD placement should be considered before routinely referring such patients for open chest surgery. (J Cardiovasc Electrophysiol, Vol. 15, pp. 1‐3, June 2004)
Predictors of Recurrence Following Catheter Ablation of Atrial Fibrillation Using an Irrigated‐Tip Ablation Catheter
Authors: VASAMREDDY CHANDRASEKHAR R. , LICKFETT LARS , JAYAM VINOD K. , NASIR KHURRAM , BRADLEY DAVID J. , ELDADAH ZAYD , DICKFELD TIMM , BERGER RONALD , CALKINS HUGH
Published: May 2004

Introduction: The aims of this study were to identify predictors of recurrence after catheter ablation of atrial fibrillation (AF) and to report the safety and efficacy of catheter ablation of AF using an irrigated‐tip ablation catheter.

Methods and Results: Seventy‐five consecutive patients (51 men [68%]; age 54 ± 13 years) with symptomatic drug‐refractory paroxysmal (42 patients), persistent (21 patients), or permanent (12 patients) AF underwent catheter ablation of AF using an irrigated‐tip ablation catheter and a standard ablation strategy, which involved electrical isolation of all pulmonary veins (PVs) and creation of a cavotricuspid linear lesion. At 10.5 ± 7.5 months of follow‐up following a single (n = 75) or redo ablation procedure (n = 11), 39 (52%) of the 75 patients were free of AF, 10 were improved (13%), and 26 had experienced no benefit from the ablation procedure (35%). Seventy‐six percent of patients with paroxysmal AF were free from recurrent AF. The most significant complications were two episodes of pericardial tamponade, mitral valve injury in one patient, two strokes, and complete but asymptomatic PV stenosis in one patient. Cox proportional hazards multivariate regression analysis identified the presence of persistent AF, permanent AF, and age >50 years prior to the ablation are the only independent predictors of AF recurrence after the first PV isolation procedure.

Conclusion: Catheter ablation of AF using a strategy involving isolation of all PVs and creation of a linear lesion in the cavotricuspid isthmus using cooled radiofrequency energy is associated with moderate efficacy and an important risk for complications. The best results of this procedure are achieved in the subset of patients who are younger than 50 years and have only paroxysmal AF. (J Cardiovasc Electrophysiol, Vol. 15, pp. 692‐697, June 2004)
Clinical Characteristics of Subjects with the Brugada‐Type Electrocardiogram:
Authors: MATSUO KIYOTAKA , AKAHOSHI MASAZUMI , NAKASHIMA EIJI , SETO SHINJI , YANO KATSUSUKE
Published: May 2004

Introduction: The Brugada‐type ECG, a terminal r′ wave accompanied by ST segment elevation in the right precordial leads, is not a very rare condition. Most of the cases are men in Japan and elsewhere; however, information about the clinical features of these cases is lacking. The aim of this study was to determine the clinical characteristics of subjects with the Brugada‐type ECG, specifically Japanese men.

Methods and Results: We extracted male Brugada‐type ECG cases from 3,374 men followed biennially from 1958 through 2001 in Nagasaki, Japan, and compared the clinical characteristics at diagnosis between these cases and four age‐matched male controls for each case. A total of 34 cases with the Brugada‐type ECG were observed during follow‐up. Body mass index (BMI) at diagnosis was significantly lower in Brugada‐type ECG cases than in 136 controls (20.2 ± 2.1 kg/m2 vs 21.8 ± 2.8 kg/m2, P = 0.003). The BMI trend in cases was always lower than that in controls throughout the 8‐year observation period (from 4 years before diagnosis to 4 years after diagnosis). Pulse rate at diagnosis was also somewhat lower in Brugada‐type ECG cases than in controls (68.9 ± 7.7 beats/min vs 72.7 ± 11.1 beats/min, P = 0.038). The significance disappeared after controlling for BMI (P = 0.131) or body weight (P = 0.153).

Conclusion: The cases with the Brugada‐type ECG had lower BMI than controls, leading to a clue to possible basic mechanisms of the Brugada‐type ECG with a focus on this association. (J Cardiovasc Electrophysiol, Vol. 15, pp. 1‐5, June 2004)
Ablation of Atrioventricular Nodal Reentrant Tachycardia in Tricuspid Atresia
Authors: KHAIRY PAUL , SESLAR STEPHEN P. , TRIEDMAN JOHN K. , CECCHIN FRANK
Published: May 2004

A 31‐year‐old woman with tricuspid atresia and a palliative Waterston shunt presented with intractable poorly tolerated supraventricular tachycardia. Electrophysiologic evaluation was consistent with AV nodal reentrant tachycardia. The fast pathway region was mapped electroanatomically during tachycardia and with constant rate ventricular pacing. Successful radiofrequency ablation was achieved by placement of lesions in an area adjacent and inferior to the His‐bundle electrogram on the left side of the septum. (J Cardiovasc Electrophysiol, Vol. 15, pp. 1‐4, June 2004)
Single‐Stage Adenosine Tilt Testing in Patients with Unexplained Syncope
Authors: MITTAL SUNEET , STEIN KENNETH M. , MARKOWITZ STEVEN M. , IWAI SEI , GUTTIGOLI AMIT , LERMAN BRUCE B.
Published: May 2004

Introduction: We previously have shown that a 3‐minute single‐stage adenosine tilt test has a diagnostic yield comparable to a two‐stage protocol consisting of a 30‐minute drug‐free tilt followed by a 15‐minute isoproterenol tilt. In this study, we sought to further define the clinical utility of adenosine tilt testing in patients with unexplained syncope by prospectively evaluating test specificity and determining predictors of a positive test response.

Methods and Results: The specificity of single‐stage adenosine tilt testing was determined using 30 control subjects. To determine the diagnostic yield of this protocol, adenosine tilts were performed in 129 patients with unexplained syncope. The adenosine tilt test protocol had high specificity (100%) but a low overall diagnostic yield (18%). However, the yield was affected significantly by age. In patients ≤40 years of age, the tilt test was positive in 15 (41%) of 37 patients, which was significantly greater than the yield in patients between the ages of 41 and 64 years (6/41 patients [15%], P = 0.012) and those ≥65 years of age (2/41 patients [5%], P < 0.0001).

Conclusion: These data support single‐stage adenosine tilt testing in patients ≤40 years of age because the diagnostic yield of the test is maximal in this group and the test can be completed in ≤3 minutes. Conversely, the diagnostic yield of adenosine tilt testing in patients >40 years of age is low, suggesting that the clinical utility of this protocol is limited in these patients. (J Cardiovasc Electrophysiol, Vol. 15, pp. 1‐4, June 2004)
Entrainment Mapping of Dual‐Loop Macroreentry in Common Atrial Flutter:
Authors: FUJIKI AKIRA , NISHIDA KUNIHIRO , SAKABE MASAO , SUGAO MASATAKA , TSUNEDA TAKAYUKI , MIZUMAKI KOICHI , INOUE HIROSHI
Published: May 2004

Introduction: The aim of this study was to determine using entrainment mapping whether the reentrant circuit of common type atrial flutter (AFL) is single loop or dual loop.

Methods and Results: In 12 consecutive patients with counterclockwise (CCW) AFL, entrainment mapping was performed with evaluation of atrial electrograms from the tricuspid annulus (TA) and the posterior right atrial (RA) area. We hypothesized that a dual‐loop reentry could be surmised from “paradoxical delayed capture” of the proximal part of the circuit having a longer interval from the stimulus to the captured beat compared with the distal part of the circuit. In 6 of 12 patients with CCW AFL, during entrainment from the septal side of the posterior blocking line, the interval from the stimulus to the last captured beat was longer at the RA free wall than at the isthmus position. In these six patients with paradoxical delayed capture, flutter cycle length (FCL) was 227 ± 12 ms and postpacing interval minus FCL was significantly shorter at the posterior blocking line than at the RA free wall (20 ± 11 ms vs 48 ± 33 ms, P < 0.05). In two of these patients, early breakthrough occurred at the lateral TA. A posterior block line was confirmed in all six patients in the sinus venosa area by intracardiac echocardiography.

Conclusion: Half of the patients with common type AFL had a dual‐loop macroreentrant circuit consisting of an anterior loop (circuit around the TA) and a posterior loop (circuit around the inferior vena cava and the posterior blocking line). (J Cardiovasc Electrophysiol, Vol. 15, pp. 679‐685, June 2004)
Vagal Activity Modulates Spontaneous Augmentation of ST Elevation in the Daily Life of Patients with Brugada Syndrome
Authors: MIZUMAKI KOICHI , FUJIKI AKIRA , TSUNEDA TAKAYUKI , SAKABE MASAO , NISHIDA KUNIHIRO , SUGAO MASATAKA , INOUE HIROSHI
Published: May 2004

Introduction: In Brugada syndrome, ventricular fibrillation (VF) occurs mainly during sleep, and Brugada ECG signs are intensified by parasympathomimetic drugs; therefore, vagal activity could be a precipitating factor of VF. The aim of the present study was to elucidate the relation between spontaneous augmentation of ST elevation and changes in autonomic nervous activities in the daily life of patients with Brugada syndrome.

Methods and Results: Twenty‐three consecutive patients with Brugada syndrome were studied. Group VF(+) consisted of 7 symptomatic patients and 3 asymptomatic patients with inducible VF; group VF(–) consisted of 13 asymptomatic patients without documented or inducible VF. Two‐channel unipolar lead (V1 and V2) Holter ECG was recorded. Heart rate variability was analyzed by the maximum entropy method. Spontaneous augmentation of ST elevation (≥1.5 mm/20min) occurred more frequently during 24 hours in group VF(+) than in group VF(–) (5.7 ± 2.5 times vs 2.3 ± 2.4 times, P < 0.01). ST elevation was significantly greater in group VF(+) than in group VF(–) (2.1 ± 0.2 mm vs 1.8 ± 0.2 mm, P < 0.05). Power of the high‐frequency component (HF: 0.15–0.4 Hz) and RR interval increased progressively, and the ratio of low‐frequency component (LF; 0.04– 0.15 Hz) to high‐frequency component (LF/HF) gradually decreased toward the time of maximum ST elevation. During an entire day, daytime (0–5 P.M.), and nighttime (0–5 A.M.), both HF and LF/HF were not different between groups VF(+) and VF(–).

Conclusion: In Brugada syndrome, spontaneous augmentation of ST elevation in daily life occurred along with an increase in vagal activity. ST elevation was augmented more in patients with VF than in those without VF under similar vagal tone. (J Cardiovasc Electrophysiol, Vol. 15, pp. 1‐7, June 2004)
Interband transitions in InAs quantum dots in InP studied by photoconductivity and photoluminescence techniques
Authors: Landin L. , Pettersson H. , Kleverman M. , Borgström M. , Zhang X. , Seifert W. , Samuelson L.
Published: May 2004

We report on a detailed investigation of the interband optics of self-assembled InAs dots embedded in a matrix of InP. In photoconductivity (PC) measurements, we observe optical processes related to the dots and a wetting layer, band-to-band excitation of the InP barrier, as well as to an interesting As-related impurity. In particular, the PC measurements reveal the electronic structure of the dots and strongly suggest that an Auger effect is involved in forming the PC signal. Comparing the PC and photoluminescence (PL) signals, we observe that the fundamental transition is not observed in PC, which we interpret in terms of Pauli blocking due to electrons populating the ground state of the dots. In general, it is demonstrated that the PC technique is in many respects complementary to PL and gives additional insight into the electronic structure of quantum dots.
Temperature-dependent photoluminescence of ZnO layers grown on 6H-SiC substrates
Authors: Ashrafi A. B. M. A. , Binh N. T. , Zhang B. P. , Segawa Y.
Published: May 2004

Temperature-dependent photoluminescence (PL) of ZnO layers grown on 6H-SiC substrates has been described. The PL spectra were dominated by free exciton (FX) emission throughout the whole temperature range, which reflects shallow nonradiative centers in high crystalline ZnO layers. The temperature-dependent exciton peak energy as well as intensity quenching due to overlapping of FX and D0X (donor-bound exciton) bands has been addressed with an inclusion of donor-bound exciton-like defects. The D0X linewidth of ∼8 meV exhibited the thermal activation energy of ∼16 meV, closely consistent with the exciton-defect binding energy. This particular bound-exciton peak suggests that it dissociates into a FX and a neutral-donor-bound-like defects pair complex with the increase of temperature.
Voltage generation induced by mechanical straining in magnetic shape memory materials
Authors: Suorsa I. , Tellinen J. , Ullakko K. , Pagounis E.
Published: May 2004

Magnetic shape memory (MSM) materials change their shape with the magnetic field. They can also be used in the reverse operation as sensors or voltage generators. The present paper demonstrates that large voltages are induced when the MSM material is mechanically compressed inside a MSM actuator. The experimental results reveal that voltages of close to 100 V were generated with a Ni–Mn–Ga MSM material subjected to short mechanical impulses, because of a change in its magnetization. The induced voltage depends on the geometrical and material parameters of the MSM actuator, as well as on the speed by which the MSM material changes its shape. A magnetic model for calculating the induced voltage is proposed and the measurement results from a MSM-type actuator are presented. The magnetic model demonstrates good accordance with the experimental results. The physical reason for the voltage signal is discussed and potential applications are proposed.
Dielectric response of sputtered transition metal oxides
Authors: Iosad N. N. , Ruis G. J. , Morks E. V. , Morpurgo A. F. , van der Pers N. M. , Alkemade P. F. A. , Sivel V. G. M.
Published: May 2004

We have investigated the dielectric properties of thin layers of five oxides of transition metals (Ta2O5, HfO2, ZrO2, (ZrO2)0.91(Y2O3)0.09, and Sn0.2Zr0.2Ti0.6O2) sputtered from ceramic targets at different pressures. We find that layers deposited at low pressure behave as expected from literature, whereas layers deposited at high pressure all exhibit an anomalous dielectric response similar to that reported for the so-called “colossal” dielectric constant materials. The characterization of the thickness, frequency, and temperature dependence of the capacitance, as well as the comparison of film properties before and after annealing show that the anomalous dielectric response is due to quenched-in vacancies that act as dopants and cause the insulating layers to behave as semiconductors. An increase in quenched-in vacancies concentration with sputtering pressure results in a transition from normal to anomalous dielectric response and gradual increase in layer conductivity. In contrast, the refractive index does not depend on sputtering pressure. This observation indicates the possible application of these materials as transparent coatings with a tunable electrical conductivity.
Magnetic easy-axis switching in Pt/Co/Pt sandwiches induced by nitrogen ion beam irradiation
Authors: Blon T. , Ben Assayag G. , Chassaing D. , Hrabovsky D. , Bobo J. F. , Ousset J. C. , Snoeck E.
Published: May 2004

The effect of N+ ion irradiation on the magnetic anisotropy of ultrathin Co films in the Pt/Co(1 nm)/Pt (111) system is investigated. The magneto-optical measurements indicate that the as-deposited trilayers display a perpendicular magnetic anisotropy whose properties drastically change with the fluence in the range of 1012 to 1016 ions/cm2. The coercive field progressively decreases as the fluence increases. The superconducting quantum interference device measurements evidence that, for the highest fluences, the paramagnetic limit is not reached moreover an in-plane switching of the anisotropy is observed. Simulations are performed to evaluate damage energy induced by N+ irradiation.
Contact mechanisms and design principles for alloyed ohmic contacts to n-GaN
Authors: Mohammad S. Noor
Published: May 2004

Contact mechanisms and design principles of alloyed ohmic contacts to n-GaN are investigated. For the investigation, both tunnel contacts and thermionic contacts are considered. While the tunnel contacts include the Ti/Al/Ti/Au, Ti/Al/Ni/Au, Ti/Al/Pd/Au, (Ta,Ti)/Ni/Au, Ti/Al/Mo/Au, and Ti/Au/Pd/Au contacts, the thermionic contacts include the Ni/Au contacts. The proposed design principles correctly dictate the characteristics of all these contacts. At present, tunneling is believed to be the primary mechanism for low resistivity of the tunnel contacts. The present study demonstrates that both tunneling and thermionic emission are equally important for the low resistivity of these contacts. Band-gap narrowing and/or image force lowering due to heavy doping also contribute to the resistivity reduction of these contacts. An exciting feature of the present study is the observation of a very low work function intermetallic alloy formed during annealing of an appropriate combination of large work function metals. If the annealing conditions are optimized, the contacts become very robust, thermally stable, and lowly resistive with thermionic emission as the primary mechanism for electron transport. The observation is very promising and has potential to open up avenues for different types of thermionic contacts. The fundamental physics underlying the design principles are discussed. These principles are general enough to be applicable to other III–V nitrides, at the least.
Preparation of GaN thin film and Ga2O3 nanoribbons by plasma immersion ion implantation of N into GaAs
Authors: Lo K. C. , Ho H. P. , Fu K. Y. , Chu P. K. , Li K. F. , Cheah K. W.
Published: May 2004

A method for producing gallium nitride (GaN) and gallium oxide (Ga2O3) nanoribbons by the combination of plasma immersion ion implantation of nitrogen into GaAs and rapid thermal annealing (RTA) has been investigated. Our approach uses a broad ion-impact energy distribution with variable implant doses to form a spread-out nitrogen depth profile and an amorphous surface layer. This approach circumvents the retained-dose limitation and low nitrogen content problems associated with ion beam implantation at fixed energy. Raman spectroscopy, transmission electron microscopy (TEM), x-ray diffraction and x-ray photoelectron spectroscopy were conducted on the samples. For the samples which had undergone RTA at 850 °C for 2 min, a Raman peak at 577 cm−1 associated with GaN was observed. The weak Raman intensity indicated that a small amount of GaN was present. Cross-sectional TEM imaging showed that the thickness of the region containing GaN was about 40 nm. When RTA was performed at 950 °C for 2 min, Ga2O3 nanoribbons were found on the GaAs sample surface instead. The ribbons were 0.1–2 μm in width, several tens of nanometers in thickness, and several tens of micrometers in length. Raman spectroscopy confirmed that the ribbons are single crystalline Ga2O3. In addition, the Ga2O3 ribbons were found to possess strong visible photoluminescence. The possible formation mechanism of these nanoribbons is discussed.
Storage properties of Ce3+ doped haloborate phosphors enriched with B10 isotope
Authors: Sidorenko A. V. , Bos A. J. J. , Dorenbos P. , van Eijk C. W. E. , Rodnyi P. A. , Berezovskaya I. V. , Dotsenko V. P. , Popov A. I.
Published: May 2004

In this work we investigated the suitability of newly synthesized series of haloborate phosphors with the general formula M2B5O9X:Ce3+ (M=Sr or Ca; X=Br or Cl) for thermal neutron detection and with reduced sensitivity to γ background. Storage properties such as yield of photostimulated luminescence (PSL) and thermoluminescence are reported. Based on these results the series of the haloborates with 99% enrichment of B10 was sensitized to increase neutron sensitivity. The PSL yields of enriched with B10 haloborates were compared with a common mixture of BaFBr:Eu2+ (40 wt %) and Gd2O3 (60 wt %) under γ and neutron irradiation. The PSL light yield from Ca2 10B5O9Cl:Ce,Na phosphor after neutron irradiation is 16 times less than that from BaFBr:Eu2+xGd2O3. However, the neutron to γ discrimination of Ca2 10B5O9Cl:Ce,Na (1%) is almost an order of magnitude better than that of BaFBr:Eu2+×Gd2O3. Therefore, haloborate phosphors should be more suitable when utilized in environments with a high γ background.
Strongly nonlinear electronic transport in Cr-Si composite films
Authors: Burkov A. T. , Vinzelberg H. , Schumann J. , Nakama T. , Yagasaki K.
Published: May 2004

The phase formation, the resistivity and the thermopower of amorphous Cr0.15Si0.85, and nanocrystalline CrSi2-Si thin film composites have been studied. The films were produced by a magnetron sputtering of a composite target onto unheated substrates with subsequent crystallization of the film at high temperatures. As the film composite develops under the heat treatment from the initial amorphous state into the final polycrystalline material, two percolation thresholds were found. At first, the percolating cluster of nanocrystalline CrSi2 is formed. However, this cluster is destroyed with further annealing due to crystallization and redistribution of Si. The composite films which are close to this insulating threshold reveal a strongly nonlinear conductivity. The conductivity increases with the current by two orders of magnitude.
Determination of the nature of molecular bonding in silica from time-dependent dielectric breakdown data
Authors: McPherson J. W.
Published: May 2004

An effective molecular dipole moment of 7–13 e Å is routinely observed during time-dependent dielectric breakdown testing of silica-based dielectrics. A Mie-Grüneisen analysis of the molecular bonding states indicates that the upper end of the effective dipole moment range (13 e Å) is associated with a stretched silicon-oxygen bond while the lower end (7 e Å) is consistent with a hole-captured silicon-oxygen bond.
Controlling hole-transport in aluminum tris (8-hydroxyquinoline), Alq3-based organic light emitting diodes to improve the device lifetime by an oxidized transport layer
Authors: Mathai Mathew K. , Papadimitrakopoulos Fotios , Hsieh Bing R.
Published: May 2004

A salt containing polymer, called an oxidized transport layer (OTL), was investigated for hole injection and transport into Alq3-based multilayered organic light emitting diode (OLED) devices. The OTL comprises an aryldiamine containing hole transport polymer binder with a corresponding low molecular weight radical cation salt. We demonstrate herein that the OTL behaves like a tunable resistor for holes, and its hole-transport properties can be controlled by the salt concentration and thickness of the OTL. Based on a careful analysis of the current density–voltage (J–V) device characteristics as a function of the above parameters, electron/hole currents were balanced to minimize oxidative degradation of Alq3. It was found that an OLED device (ITO/OTL/NPB/Alq3/CsF/Al) with a 5000 Å thick OTL at 5% salt concentration operated with a half-life exceeding 1000 h at a constant current of 10 mA/cm2. Similar devices with 2.5% and 10% salt doping showed an order of magnitude lower half-life attributed to unbalanced carrier concentrations. Moreover, by demonstrating that the majority of the field drops across the Alq3 layer, the doping level as opposed to OTL thickness was established as the primary contributor controlling hole transport in these OLEDs. This beneficial behavior is, however, observed only above a certain OTL thickness in the vicinity of 5000 Å.
Electronic structure and dielectric properties of dielectric gate material (ZrO2)x(SiO2)1−x
Authors: Ouyang Lizhi , Ching W. Y.
Published: May 2004

We have investigated the electronic structure and dielectric properties of (ZrO2)x(SiO2)1−x with x less than 0.5 using first-principles methods. Initial models of (ZrO2)x(SiO2)1−x were obtained by selecting random distributions of Zr and Si atoms on the cation sites of tetragonal ZrSiO4 according to x. These models were relaxed using the Vienna ab initio simulation package with high accuracy. Subsequent electronic structure and dielectric properties analysis was performed using the ab initio orthogonalized linear combination of atomic orbitals method. Our results indicate that for x less than 1/8, the SiO2 matrix is not significantly changed and that there are no signs of defect states being introduced into the band gap. Meanwhile, the optical dielectric constant was significantly increased compared to pure SiO2. For x greater than 1/8, the optical dielectric constant enters a plateau region. Our results confirm the experimental findings that low-x Zr silicate can be a viable candidate for high-k dielectric materials.
In situ measurements of thickness changes and mechanical stress upon gasochromic switching of thin MoOx films
Authors: Okumu J. , Koerfer F. , Salinga C. , Wuttig M.
Published: May 2004

Thin films of MoOx coated with platinum as a catalyst were prepared by dc magnetron sputtering from a molybdenum target in an oxygen and argon atmosphere. The films were colored and bleached by exposure to diluted hydrogen gas and air, respectively. In situ measurements of x-ray reflectance and substrate curvature were performed during switching cycles. Upon hydrogen exposure a remarkable thickness decrease of 11% and a density increase of 6.5% are observed by x-ray reflectance measurements. Corresponding changes in optical transmittance and mechanical stress up to several hundreds of MPa are also observed. These changes are not fully reversible as revealed by measurements of multiple switching cycles. Both the change of thickness and density, as well as the change of optical transmittance and mechanical stress can be explained by the existence of a mixed phase of edge and corner sharing MoO3 octahedra whereupon the first coloration the ratio between edge and corner sharing octahedra is changed.
Influence of crystal quality on the electronic properties of n-type 3C-SiC grown by low temperature low pressure chemical vapor deposition
Authors: Eickhoff M. , Möller H. , Stoemenos J. , Zappe S. , Kroetz G. , Stutzmann M.
Published: May 2004

We analyze the influence of crystal quality on the electronic properties of 3C-SiC layers deposited by low-pressure chemical vapor deposition. Single crystalline films show good electronic quality and can be efficiently doped with NH3. The transition to nanocrystalline 3C-SiC, achieved by a decrease in deposition temperature from 1200 °C to 1100 °C, results in a decrease of the carrier mobility and an increase of the residual carrier concentration in nominally undoped layers. Comparative analysis by scanning electron microscopy, transmission electron microscopy, and secondary ion mass spectroscopy reveals an enhancement of the average oxygen concentration by almost two orders of magnitude and an accumulation of oxygen at crystal defects. The density and distribution of oxygen decorated defects are shown to be responsible for the increasing density of residual carriers in polycrystalline and nanocrystalline films. In single-crystalline films, the depth distribution of such defects explains the dependence of residual carrier density and mobility on the layer thickness.
Enhanced photothermal displacement spectroscopy for thin-film characterization using a Fabry-Perot resonator
Authors: Black Eric D. , Grudinin Ivan S. , Rao Shanti R. , Libbrecht Kenneth G.
Published: May 2004

We have developed a technique for photothermal displacement spectroscopy that is potentially orders of magnitude more sensitive than conventional methods. We use a single Fabry-Perot resonator to enhance both the intensity of the pump beam and the sensitivity of the probe beam. The result is an enhancement of the response of the instrument by a factor proportional to the square of the finesse of the cavity over conventional interferometric measurements. In this paper we present a description of the technique, and we discuss how the properties of thin films can be deduced from the photothermal response. As an example of the technique, we report a measurement of the thermal properties of a multilayer dielectric mirror similar to those used in interferometric gravitational wave detectors.
Dielectric anomalies in [111] oriented 0.955Pb(Zn1/3Nb2/3)O3−0.045PbTiO3 single crystals under different electrical and thermal conditions
Authors: Shen Mingrong , Cao Wenwu
Published: May 2004

A detailed investigation has been conducted on the dielectric anomalies induced by different electrical and thermal conditions in [111] oriented 0.955Pb(Zn1/3Nb2/3)O3−0.045PbTiO3 (PZN-4.5%PT) single crystals. Application of a dc electrical field to the crystal results in field induced dielectric anomalies to occur at specific temperatures, which can be explained by the structural phase transitions from rhombohedral to orthorhombic, from orthorhombic to tetragonal, and from tetragonal to cubic phase, respectively. All transition temperatures are independent of frequency and have a threshold field that is dependent on the thermal history. The electric field–temperature diagrams based on dielectric anomalies were developed under different schemes of temperature and field variations.
Blue up-conversion emission in Yb- and Tm-codoped potassium yttrium tungstate
Authors: Kuzmin A. N. , Kachynski A. V. , Prasad P. N. , Demidovich A. A. , Batay L. E. , Bednarkiewicz A. , Strek W. , Titov A. N.
Published: May 2004

The spectroscopic characteristics of potassium yttrium tungstate crystal (KYW), codoped with ytterbium and thulium ions, have been investigated from the point of view of up-conversion blue lasing from G41 multiplet. An overall H63 multiplet splitting of ∼530 cm−1 for the trivalent thulium ion in the KYW host was obtained. A decay time of ∼112 μs for the G41→H63 blue luminescence in the material doped by 1 at. % of thulium was measured. The value of peak emission cross section for this transition is estimated to be (1.8±0.3)×10−20 cm2. Strong cross-relaxation quenching was found to be one of the main channels of nonradiative losses from the G41 and H43 multiplets. The cross-relaxation rate was significantly higher at higher concentration of thulium.
Reactive magnetron sputtering of molybdenum sulfide thin films: In situ synchrotron x-ray diffraction and transmission electron microscopy study
Authors: Weiss V. , Bohne W. , Röhrich J. , Strub E. , Bloeck U. , Sieber I. , Ellmer K. , Mientus R. , Porsch F.
Published: May 2004

The nucleation and growth of magnetron sputtered MoSx films has been investigated by in situ energy dispersive x-ray diffraction, electron microscopy, and elastic recoil detection analysis. The MoSx films (0.5⩽x⩽2) were prepared by reactive magnetron sputtering from a molybdenum target in an argon–hydrogen sulfide mixture at substrate temperatures up to 700 °C. Using time-resolved in situ x-ray diffraction it was found that the films start to grow with (001) orientation where the van der Waals planes are parallel to the substrate surface. Depending on the deposition conditions a crossover of texture to the (100) orientation occurs, which leads to very rough surfaces. This texture crossover occurs earlier at low substrate temperatures and/or high deposition rates and/or high energetic particle bombardment of the growing films. The MoSx films exhibit significant lattice strain (up to 4%) in the c direction, i.e., perpendicular to the van der Waals planes, which decreases at high substrate temperatures and/or low deposition rates. This lattice expansion is not caused by film stress. Instead, it seems to be connected with disturbed or turbostratic growth due to crystallographic defects induced by energetic bombardment of the films. Also, intercalation of hydrogen could be responsible for lattice expansion, since significant amounts of hydrogen were detected by elastic recoil detection analysis. The sulfur deficiency (up to 20%) found in films that were deposited at temperatures higher than 200 °C could have been initiated by the reducing effect of the atomic hydrogen in our Ar/H2S plasma.
An electrical characterization of a two-dimensional electron gas in GaN/AlGaN on silicon substrates
Authors: Elhamri S. , Berney R. , Mitchel W. C. , Mitchell W. D. , Roberts J. C. , Rajagopal P. , Gehrke T. , Piner E. L. , Linthicum K. J.
Published: May 2004

We present results of transport measurements performed on AlGaN/GaN heterostructures grown on silicon substrates. Variable temperature Hall effect measurements revealed that the temperature dependence of the carrier density and mobility were characteristic of a two-dimensional electron gas (2DEG). Carrier densities greater than 1×1013 cm−2 and Hall mobilities in excess of 1500 cm2/V s were measured at room temperature. Variable field Hall measurements at low temperatures, and in magnetic fields up to 6 T, indicated that conduction is dominated by a single carrier type in these samples. Shubnikov–de Haas (SdH) measurements were also performed, but no oscillations were observed in fields up to 8 T and at temperatures as low as 1.2 K. Illuminating some of the samples with a blue (λ=470 nm) light emitting diode (LED) induced a persistent increase in the carrier density. SdH measurements were repeated and again no oscillations were present following illumination. However, exposing the samples to radiation from an UV (λ=395 nm) LED induced well-defined SdH oscillations in fields as low as 4 T. The observation of SdH oscillations confirmed the presence of a 2DEG in these structures. It is hypothesized that small angle scattering suppressed the oscillations before exposure to UV light. This conclusion is supported by the observed increase in the quantum scattering time, τq, with the carrier density and the calculated quantum to transport scattering times ratio, τq/τc. For instance, in one of the samples the τq increased by 32% while the τc changed by only 3% as the carrier density increased; an indication of an increase in the screening of small angle scattering. The absence of SdH oscillations in fields up to 8 T and at temperatures as low as 1.2 K is not unique to AlGaN/GaN on silicon. This behavior was observed in AlGaN/GaN on sapphire and on silicon carbide. SdH oscillations were observed in one AlGaN/GaN on silicon carbide sample following exposure to radiation from an UV LED.
Role of thermal boundary resistance on the heat flow in carbon-nanotube composites
Authors: Shenogin Sergei , Xue Liping , Ozisik Rahmi , Keblinski Pawel , Cahill David G.
Published: May 2004

We use classical molecular dynamics simulations to study the interfacial resistance for heat flow between a carbon nanotube and octane liquid. We find a large value of the interfacial resistance associated with weak coupling between the rigid tube structure and the soft organic liquid. Our simulation demonstrates the key role played by the soft vibration modes in the mechanism of the heat flow. These results imply that the thermal conductivity of carbon-nanotube polymer composites and organic suspensions will be limited by the interface thermal resistance and are consistent with recent experiments.
Suppression of inelastic deformation of nanocoated thin film microstructures
Authors: Zhang Yanhang , Dunn Martin L. , Gall Ken , Elam Jeffrey W. , George Steven M.
Published: May 2004

We study the suppression of time-dependent inelastic deformation due to creep, stress relaxation, and microstructural evolution in multilayer thin film microstructures by the use of alumina nanocoatings realized by atomic layer deposition (ALD). Gold (0.5 μm thick)/polysilicon (1.5 or 3.5 μm thick) beam and plate microstructures were fabricated using surface micromachining. The microstructures were then coated on each side with a 40-nm-thick amorphous Al2O3 layer by ALD. The beam and plate microstructures were initially thermal cycled between room temperature and 190 °C to partially stabilize the gold microstructure. After the initial thermal cycles, the microstructures were cooled from 190 to 120 °C and held at 120 °C for about 700 h (4 weeks). We measured, using an interferometric microscope with a custom-built temperature chamber, full-field deformed shapes (and from these determined the average curvatures in the x and y directions) of the microstructures during the initial thermal cycles, during the cooling process from 190 to 120 °C, and during the isothermal hold. Measurements were made on both coated and uncoated microstructures to assess the influence of the coating. We find that while the 40-nm-thick coating has a small effect on the thermoelastic response of the microstructure, it significantly reduces the extent of inelastic deformation during the isothermal hold. We modeled the curvature evolution with time assuming the inelastic deformation mechanism can be described by power-law creep in the gold, ε̇=Aσn, and that the polysilicon and alumina deform elastically. The simple model describes the observed behavior reasonably well for the uncoated microstructures (when the power-law parameters are fit using the measured curvature), however, for the coated microstructures, the model predicts a decrease in the inelastic deformation, but nowhere near the magnitude observed. This suggests not only an alternation of the stress state in the gold film by the nanoscale coating, but also a change in the fundamental inelastic deformation mechanisms.
Yellow-green strained-InGaP quantum-well epitaxial-transparent-substrate light emitting diodes
Authors: McGill L. , Wu J. W. , Fitzgerald E. A.
Published: May 2004

We present a strained-InGaP quantum-well light emitting diode (LED) operating in the green to yellow region of the visible spectrum. The active layer consists of an undoped, compressively strained In0.32Ga0.68P or In0.37Ga0.63P quantum well deposited via metalorganic chemical vapor deposition on a transparent In0.22(Al0.2Ga0.8)0.78P/∇x[Inx(Al0.2Ga0.8)1−xP]/GaP virtual substrate. Epitaxial-transparent-substrate LEDs based on this structure emit with a primary peak at 590 nm and a secondary peak at 560 nm. The highest LED power of 0.18 μW per facet at 20 mA was observed for a quantum well composition of In0.32Ga0.68P and a threading dislocation density on the order of 7×106 cm−2. The same device structure intentionally grown with a threading dislocation density on the order of 5×107 cm−2 exhibited an identical spectral shape with a reduced power of 0.08 μW per facet at 20 mA. Based upon superspots present in transmission electron diffraction from the quantum well region, the observed spectrum is the result of emission from ordered and disordered domains in the active region. Devices with a quantum well composition of In0.37Ga0.63P and an overall threading dislocation density on the order of 5×107 cm−2 emit at a single peak wavelength of 588 nm with a power of 0.06 μW per facet at 20 mA.
Identifying Au-based Te alloys for optical data storage
Authors: Wamwangi D. , Detemple R. , Woeltgens H.-W. , Wuttig M. , Zhang X.
Published: May 2004

Au 18 Sb 23 Te 59 and Au19In26Te55 have been investigated to determine their suitability as phase change recording alloys. Recrystallization experiments identify Au18Sb23Te59 as a suitable phase change material with a recrystallization time of 110 ns and high optical contrast. Coupled to the high optical contrast is a considerable density increase of 4% upon crystallization which allows phase change recording for the Au18Sb23Te59 alloy. On the other hand no recrystallization has been observed optically for Au19In26Te55 due to its low optical contrast of less than 1%. This is related to a lower density contrast of 2%. The crystallization for the Au18Sb23Te59 and Au19In26Te55 alloys observed from temperature-dependent sheet resistance measurements have yielded transition temperatures of 113 and 175 °C, and activation barriers of 1.61±0.01 eV and 2.42±0.02 eV, respectively. We report a cubic structure (a=2.99±0.002 Å) for the Au18Sb23Te59 alloy and a chalcopyrite structure (a=6.50±0.018 Å and 12.27±0.025 Å) for the Au19In26Te55 material. These results confirm that suitable phase change alloys possess cubic structures rather than the chalcopyrite structure typical for sp3 bonded semiconductors.
Fuchs–Kliewer phonon excitations in GaNAs alloys
Authors: Veal T. D. , Mahboob I. , Piper L. F. J. , McConville C. F. , Hopkinson M.
Published: May 2004

The surface optical phonon spectra of GaNxAs1−x alloys have been measured using high-resolution electron-energy-loss spectroscopy. Multiple excitations of both GaAs-like and GaN-like Fuchs–Kliewer phonons were observed. Comparison is made with surface optical phonon spectra obtained from GaAs and GaN, semiclassical dielectric theory calculations and previous Raman scattering measurements of bulk phonon spectra of GaNxAs1−x alloys.
Bounds and estimates for power absorption in two-dimensional highly lossy configurations
Authors: Razansky D. , Soldea D. F. , Einziger P. D.
Published: May 2004

Electromagnetic power absorption in biological tissues has recently received due scientific and public attention, particularly, in the areas of cellular communication and hyperthermic treatments. While efficient numerical algorithms, such as the finite difference time domain technique and the method of moments, have been developed as to obtain accurate power distributions in complicated configurations, their physical interpretation and explicit dependence on problem’s parameters are still difficult to achieve. In attempt to gain a clear insight into the electromagnetic power absorption mechanism as well as its estimation and relation to the Specific Absorption Rate (SAR), we have recently proposed an infinite-extent current-sheet model. Herein, the model is further extended by incorporating finite-extent sources, i.e., electric and magnetic line-sources, exciting a highly lossy semi-infinite half-space. This modification results in deeper insight and understanding of the crucially important parameters, commonly involved in realistic configurations, namely, bounds and estimates on the power absorption and radiation efficiencies, local and total SAR coupling coefficients, and effective absorption dimensions.
Multistage thermoelectric microcoolers
Authors: Yang Ronggui , Chen Gang , Snyder G. Jeffrey , Fleurial Jean-Pierre
Published: May 2004

Multistage thermoelectric coolers have been used for a long time because they offer a larger temperature difference than single-stage thermoelectric coolers. Microelectromechanical systems technology leads to the possibility to fabricate multistage thermoelectric microcoolers in batches without much increase in complexity compared to single-stage cooler fabrication. In this paper, we design and analyze such multistage coolers, focusing on the optimization of the maximum temperature difference, which is of particular interest for multistage microcoolers. As an example, a two-stage thermoelectric microcooler is designed for the thermal management of a 10 mW mid-infrared laser. The heat leakage issue, the most important degradation mechanism for the performance of thermoelectric microcoolers, is discussed and possible solutions are also outlined.