bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection and characterization of silicon nanocrystals embedded in thin oxide layers
Authors: Perego M. , Ferrari S. , Fanciulli M. , Ben Assayag G. , Bonafos C. , Carrada M. , Claverie A.
Published: December 2003

Silicon nanocrystals embedded in a thin oxide layer can be used as charge storage elements in nonvolatile memory devices. The structural characteristics of the nanocrystals and their position in the oxide determine the electrical properties of the devices. In this work, silicon nanocrystals have been formed by ultralow-energy implantation (0.65–2.0 keV) of silicon in a 10 nm thin thermally grown SiO2 film on Si (100) followed by a thermal treatment. A time of flight secondary ion mass spectrometry (TOF-SIMS) methodology has been developed to detect the presence of silicon nanocrystals and to characterize them. The methodology allows one to obtain relevant information, such as the bandwidth and tunneling distance of Si nanocrystals. Chemical information about the presence of impurities introduced into the SiO2 layer during implantation and annealing have also been obtained. The advantages and disadvantages of this technique, based on TOF-SIMS in comparison with transmission electron microscopy, are discussed as well.
Mechanics of wafer bonding: Effect of clamping
Authors: Turner K. T. , Thouless M. D. , Spearing S. M.
Published: December 2003

A mechanics-based model is developed to examine the effects of clamping during wafer bonding processes. The model provides closed-form expressions that relate the initial geometry and elastic properties of the wafers to the final shape of the bonded pair and the strain energy release rate at the interface for two different clamping configurations. The results demonstrate that the curvature of bonded pairs may be controlled through the use of specific clamping arrangements during the bonding process. Furthermore, it is demonstrated that the strain energy release rate depends on the clamping configuration and that using applied loads usually leads to an undesirable increase in the strain energy release rate. The results are discussed in detail and implications for process development and bonding tool design are highlighted.
Scaling properties of a low-actuation pressure microfluidic valve
Authors: Studer Vincent , Hang Giao , Pandolfi Anna , Ortiz Michael , French Anderson W. , Quake Stephen R.
Published: December 2003

Using basic physical arguments, we present a design and method for the fabrication of microfluidic valves using multilayer soft lithography. These on-off valves have extremely low actuation pressures and can be used to fabricate active functions, such as pumps and mixers in integrated microfluidic chips. We characterized the performance of the valves by measuring both the actuation pressure and flow resistance over a wide range of design parameters, and compared them to both finite element simulations and alternative valve geometries.
Interaction of pulsed metal vapor plasma with insulator wall
Authors: Rahmani Bouabdallah , Yasouka Kouiti , Ishii Shozo
Published: December 2003

An experimental method is proposed to investigate the radiation emitted from the boundary layer, which is formed near the insulator wall. This experimental method consists of a fast-pulsed exploding aluminum wire set initially on the low-density polyethylene (LDPE) flat wall. Various phases of brightness and darkness between the narrow bright aluminum vapor plasma and the surface of the LDPE have been observed. It was observed that a formed dark layer moves away from the LDPE surface according to the released input energy. The shape of the formed layer was affected by both the interaction with the insulator wall and the electrodes. The radial reflected visible light by the insulator wall consists of two different expansion velocities showing a cooling of the vapor plasma source and an enhancement in the radiation emitted from the formed layer. Two phases have been observed in the temporal behavior of the intensity of the aluminum and the carbon atoms lines showing an enhancement during the collisionless interaction regime. The photoablation process of the LDPE wall occurred during the plateau observed in the intensity shape of the carbon atom line which match with both the observed peak value in the emitted UV radiation and the framing picture taken at 200 ns.
Kinetics of interfacial reaction in Cu–Mg alloy films on SiO2
Authors: Frederick M. J. , Ramanath G.
Published: December 2003

We report the kinetics of Mg reduction of SiO2 at the Cu–Mg/SiO2 interface during vacuum annealing. Annealing supersaturated Cu–Mg films to T>∼400 °C results in the interfacial segregation of Mg and the formation of cubic MgO on the silica side of the interface. At ∼475 °C, the film sheet resistance (RS) increases a factor of 3 concurrent with Mg interfacial segregation, MgO formation, and Si release into the Cu film. Analysis of RS–T signatures obtained at different annealing rates reveals that the Mg reduction of SiO2 is the rate-limiting step, with an activation energy Ea=2.7±0.1 eV. The Si released from SiO2 diffuses into the top Cu layer with Ea=2.2±0.1 eV, consistent with the lattice diffusion of Si in Cu. These activation energy values would be important for designing and evaluating annealing treatments to controllably form interfacial isolation layers from Cu–Mg alloy films for device metallization structures.
Observation of magnetic structures in Fe granular films by differential phase contrast scanning transmission electron microscopy
Authors: Sannomiya Takumi , Haga Yumiko , Nakamura Yoshio , Nittono Osamu , Takahashi Yoshio
Published: December 2003

Differential phase contrast (DPC) scanning transmission electron microscopy was applied to investigate the magnetic structures of Fe granular films. The DPC images showed a cluster-like contrast of 200 nm in the lateral size, which could not be observed by Lorentz transmission electron microscopy in the Fresnel mode. The magnetization vector map reproduced from the DPC images indicated that a magnetization loop generally intersects several isolated particles of 20–40 nm in diameter. The films composed of densely dispersed magnetic particles showed larger magnetization loops, while more separately dispersed films tended to have smaller loops, or magnetization closures in one particle. The loop size is associated with the strength of magnetic interaction between magnetic particles.
Optically pumped laser characteristics of blue Znx′Cdy′Mg1−x′−y′Se/ZnxCdyMg1−x−ySe single quantum well lasers grown on InP
Authors: Zhou Xuecong , Muñoz Martin , Tamargo Maria C. , Chen Y. C.
Published: December 2003

We report the operation of a photopumped blue Znx′Cdy′Mg1−x′−y′Se/ZnxCdyMg1−x−ySe separate confinement heterostructure single quantum well laser grown lattice matched to InP with a relatively thick quaternary quantum well (∼50 Å). Laser emission at 492 nm in the blue was observed. The lasing linewidth is about 5 nm. Based on the temperature dependency of the threshold pumping intensity, the characteristic temperature (T0) was determined. We also studied a photopumped laser with a similar structure, where the only difference was the quaternary ZnxCdyMg1−x−ySe quantum well composition, having laser emission in the green. Comparison of the threshold pumping intensity and T0 for the blue and green lasers shows a lower threshold pumping intensity and higher T0 for the green laser. We explain these results on the basis of the difference in carrier confinement between these two structures. An Arrhenius treatment of the temperature dependency of the blue laser threshold pumping intensity gives an activation energy Ea very close to the band gap energy difference between the cladding layer and the quantum well in the conduction band. This points to a carrier loss process through thermalization into the cladding layer.
Electronic structure of piezoelectric double-barrier InAs/InP/InAs/InP/InAs (111) nanowires
Authors: Zervos Matthew , Feiner Lou-Fé
Published: December 2003

We present a theoretical study of an n-type InAs nanowire with built-in InAs/InP heterojunctions in the effective-mass approximation via self-consistent Poisson–Schrödinger calculations in cylindrical coordinates. Rapid convergence and efficiency are achieved by (i) a suitable transformation of the radial part of the Hamiltonian matrix thereby maintaining symmetry (ii) using quantum mechanical perturbation theory to derive an expression for the change in electron density with electrostatic potential. We calculate the energy levels in a 150 Å long InAs quantum dot surrounded by 50 Å long InP barriers within an InAs quantum wire of radius 200 Å, having a doping level of 3×1016 cm−3 and conduction-band discontinuities of ΔECB=0.6 eV. In equilibrium, the lowest quantum dot state is at 15 meV above the Fermi level and we find that upon variation of the applied collector–emitter voltage VCE, resonance occurs at VCE=88 mV. This is in good agreement with an experimental study of resonant tunneling in a nominally undoped InAs/InP nanowire of similar dimensions grown in the [111] direction, where resonance was detected at VCE=80 mV, and a small shift (<5 mV) in its position occurred upon inverting the voltage polarity. We rule out barrier asymmetry, bandbending due to impurities or defects, and contact effects as being the origin of the resonant-voltage shift, and attribute it to the strain-induced charges at the InP/InAs interfaces. Both InAs and InP segments are shown to be under in-plane compression giving a piezoelectric field of 0.155 meV/Å in the InAs quantum dot while resonant tunneling, as calculated, occurs at 84 mV for VCE<0 and at 87 mV for VCE>0. This is in contrast to two-dimensional pseudomorphic heteroepitaxy, where the InP is under in-plane tensile strain yielding a very strong resonance-voltage shift (≫5 mV). The small magnitude of the measured shift indicates that in nanowires any strain at the heterointerfaces relaxes within a few atomic layers.
Vacancy-related defect distributions in 11B-, 14N-, and 27Al-implanted 4H–SiC: Role of channeling
Authors: Janson M. S. , Slotte J. , Kuznetsov A. Yu. , Saarinen K. , Hallén A.
Published: December 2003

The defect distributions in 11B-, 14N-, and 27Al-implanted epitaxial 4H–SiC are studied using monoenergetic positron beams. At least three types of defects are needed to account for the Doppler broadening annihilation spectra and two of the defects are tentatively identified as VSi, and VSiVC. By comparing the defect profiles extracted from the annihilation spectra to the chemical profiles determined by secondary ion mass spectrometry, and to the primary defect profiles obtained from binary collision approximation simulations, it is concluded that the defects found at depths considerably deeper than the projected range of the implanted ions mainly originate from deeply channeled ions.
Effective conductivity of partially sintered solids
Authors: Dryden J. R. , Zok F. W.
Published: December 2003

An analytical model to predict the effective conductivity of a partially sintered solid is presented. It is based on an analysis of heat flow through a spherical particle embedded in a self-consistent matrix. Determination of the effective conductivity reduces to solving an integral equation, and a numerical solution of this equation is presented. In the limiting cases wherein the contact size is either small or comparable to the particle size, approximate analytical results are obtained which agree very well with the numerical solution. Furthermore, when pieced together, the two solutions are found to describe the effective conductivity over the entire range of contact sizes.
Effect of metal electrode on Seebeck coefficient of p- and n-type Si thermoelectrics
Authors: Yamashita Osamu
Published: December 2003

The measurements of thermoelectric powers and current–voltage characteristics were made on the p- and n-type Si specimens which were doped with 0.1 at. % of Al and P, respectively. The apparent Seebeck coefficients Sa of these specimens were measured using various kinds of metal electrodes at cold end and the brass at hot end. The Sa was plotted as a function of work function of metal electrodes at cold end. The Sa changes significantly with the kind of metal electrodes and has a maximum at a work function of 4.65 eV of Cu for the p-type specimen and 4.33 eV of Zn for the n-type one. These maximum Sa agreed quantitatively well with the Seebeck coefficients S measured by the conventional technique using two alumel–chromel thermocouples as an electrode. There was a negative correlation between Sa and R where the electrical resistance R is the sum of the contact resistance and the resistance of the specimen itself, so that an increase in the Sa leads directly to an enhancement in the thermoelectric power factor Sa2/R. When the p- and n-type thermoelectric materials are connected as a metal–semiconductor junction, it was thus found that it is necessary to select the metal electrode fitted to the thermoelectric material, to make the thermoelectric conversion efficiency as high as possible.
Analysis of a nonorthogonal pattern of misfit dislocation arrays in SiGe epitaxy on high-index Si substrates
Authors: Ware Morgan E. , Nemanich Robert J. , Gray Jennifer L. , Hull Robert
Published: December 2003

We have investigated the formation of misfit dislocations resulting from the growth of partially strained Si0.7Ge0.3 epitaxial films on Si substrates with surface normals rotated off of the [001] axis toward [110] by 0°, 13°, and 25°. Transmission electron microscopy has shown that the dislocations form in a modified cross-hatch pattern for samples grown on the off-axis substrates. This modified cross hatch consists of three arrays along which the dislocations align. This is in contrast to the two orthogonal arrays found on the on-axis (001) substrates. These dislocations correspond well with the intersection of the (111) slip planes with the respective surfaces. We present a simple analysis of the amount of relaxation due to probable Burger’s vectors for these dislocations, which reveals the most likely directions for these vectors and shows that the density of dislocations only accounts for a fraction of the total film relaxation as measured by Raman peak shifts. These studies form the basis for the use of high index surfaces as components in modern devices, and provide pathways to possible templates for use in the growth of nanostructures.
Effect of annealing on thermoelectric properties of bismuth telluride compounds doped with various additives
Authors: Yamashita Osamu , Tomiyoshi Shoichi
Published: December 2003

The p-type (Bi0.25Sb0.75)2Te3 doped with 8 wt % excess Te and 0.3 wt % Se and the n-type Bi2(Te0.94Se0.06)3 doped with 0.08 wt % SbI3, 0.02 wt % Te, and 0.01 wt % CuBr were grown by the Bridgman method at a rate of 6 cm/h. The thermoelectric properties of these specimens were measured before and after annealing, where annealing was done in the temperature range from 473 up to 673 K for 2-5 h in a vacuum and a hydrogen stream. When the p- and n-type specimens were annealed at 673 K for 2 h in a hydrogen stream and a vacuum, respectively, the thermoelectric figures of merit ZT at 298 K for the p- and n-type specimens reached the greatest values of 0.97 and 1.00, respectively. The rate of enhancement in the ZT due to the annealing, however, was only about 3% for both specimens, which is about a tenth of those of our previous specimens doped with different types of dopants. Combining with our previous results of bismuth telluride compounds, it was found that there is a strong correlation between the rate of enhancement in the ZT due to the annealing and the electrical resistivity ρ of the as-grown specimen, and that the rate of enhancement reaches a maximum when the as-grown bismuth telluride ingots have a ρ value of about 12 μΩ m, at least in the present fabrication method.
Coherent growth and mechanical properties of AlN/VN multilayers
Authors: Li Geyang , Lao Jijun , Tian Jiawan , Han Zenghu , Gu Mingyuan
Published: December 2003

The growth condition of metastable cubic AlN (c-AlN) in AlN/VN multilayers and the effect of c-AlN on the mechanical properties of multilayers were investigated. A series of AlN/VN multilayers with different modulation periods were prepared by reactive magnetron sputtering. The microstructure and mechanical properties of multilayers were characterized with low-angle x-ray diffraction, high-resolution transmission electron microscopy, and nanoindentation. The results show that AlN exists as a metastable cubic phase in multilayers at small modulation periods due to the “template effect” and forms a superlattice with VN through coherent epitaxial growth. Correspondingly, multilayers show the superhardness effect with the enhancement of hardness and elastic modulus. With the increase of modulation periods, c-AlN transforms to the stable hexagonal structure (h-AlN) and multilayers demonstrate a “brick-wall” structure with nanometer grains. The hardness and elastic modulus of multilayers with large modulation periods are close to the value calculated from the rule of mixtures. The discussion indicates that the prerequisite for the formation of c-AlN is the low coherent interface energy. It is the difference of volume energy between c-AlN and h-AlN that primarily determines the critical thickness of c-AlN. The change of properties with the formation of c-AlN and the alternative strain field resulted from coherent growth of c-AlN and VN are likely reasons for the superhardness effect of AlN/VN multilayers.
Blue electroluminescence from multilayered BaS:Eu/Al2S3 thin films
Authors: Smet P. F. , Poelman D. , Van Meirhaeghe R. L.
Published: December 2003

Electroluminescent (EL) BaAl2S4:Eu devices were prepared with a multilayered phosphor, composed of 10–20 alternating BaS:Eu and Al2S3 thin films and a total phosphor thickness of 300 nm. Depending on evaporation and annealing conditions, pure blue EL was obtained (CIE 1931 color coordinates x=0.120, y=0.098). The use of this multilayered BaS:Eu/Al2S3 structure gave access to additional information on the atomic composition and luminescent properties of europium-doped barium thioaluminates. The composition of the phosphor layer (diffusion properties, oxygen impurities) was characterized using x-ray photoelectron spectroscopy as a function of substrate temperature and annealing parameters. Optical and morphological properties of BaS(:Eu) and Al2S3 thin films are discussed as well.
Surface roughness and interfacial slip boundary condition for quartz crystal microbalances
Authors: McHale G. , Newton M. I.
Published: December 2003

The response of a quartz crystal microbalance (QCM) is considered using a wave equation for the substrate and the Navier-Stokes equations for a finite liquid layer under a slip boundary condition. It is shown that when the slip length to shear wave penetration depth is small, the first-order effect of slip is only present in the frequency response. Importantly, in this approximation the frequency response satisfies an additivity relation with a net response equal to a Kanazawa liquid term plus an additional Sauerbrey “rigid” liquid mass. For the slip length to result in an enhanced frequency decrease compared to a no-slip boundary condition, it is shown that the slip length must be negative so that the slip plane is located on the liquid side of the interface. It is argued that the physical application of such a negative slip length could be to the liquid phase response of a QCM with a completely wetted rough surface. Effectively, the model recovers the starting assumption of additivity used in the trapped mass model for the liquid phase response of a QCM having a rough surface. When applying the slip boundary condition to the rough surface problem, slip is not at a molecular level, but is a formal hydrodynamic boundary condition which relates the response of the QCM to that expected from a QCM with a smooth surface. Finally, possible interpretations of the results in terms of acoustic reflectivity are developed and the potential limitations of the additivity result should vapor trapping occur are discussed.
Two H1-nuclear magnetic resonance methods to measure internal porosity of bone trabeculae: By solid–liquid signal separation and by longitudinal relaxation
Authors: Fantazzini Paola , Bortolotti Villiam , Brown Robert J. S. , Camaiti Mara , Garavaglia Carla , Viola Rossella , Giavaresi Gianluca
Published: December 2003

Parameters related to pore-space structure of the trabeculae in cancellous bone are difficult to determine quantitatively, but they can be important to characterize changes induced in bone by diseases such as osteoporosis. We present two nuclear magnetic resonance (NMR) methods to measure the internal porosity φtrab of the trabeculae, based on two different measurements of the fraction of intratrabecular and intertrabecular pore-space in animal femur samples. These procedures have been developed within the more general framework of the NMR studies for fluids in porous media. In the first method we use the ratio between the amount of collagen (solid-like) H1 and that of the fluids in the samples. In the second, which can be applied only on defatted and water saturated samples, we use the distributions of longitudinal relaxation times. The φtrab values obtained are constant for porosity φ of the samples over the range 40%–70%, with each method giving φtrab=(29±4)%, which is consistent with the only data available, the porosity of related cortical bone. The traditional parameter bone volume fraction is simply given by (1−φ)/(1−φtrab).
Design of atomic step networks on Si(111) through strain distribution control
Authors: Omi Hiroo , Homma Yoshikazu , Ogino Toshio , Stoyanov Stoyan , Tonchev Vesselin
Published: December 2003

We propose an alternative method to control atomic step networks on silicon for future wafer-scale integration of self-assembling nanostructures. The method is the strain-distribution-control method that we have recently proposed in [H. Omi, D. J. Bottomley, and T. Ogino, Appl. Phys. Lett. 80, 1073 (2002)], which we apply here to design atomic step networks on vicinal Si(111) wafer. Si(111) with its strain patterned by buried silicon oxide inclusions was annealed at 1230 °C in ultrahigh vacuum and observed by in situ secondary electron microscopy and ex situ atomic force microscopy. The images show that the method enables us to create the desired arrays of atomic step networks on an arbitrary area of planar silicon wafer. The arrays remain stable during the 1230 °C annealing.
Poly(3-hexylthiophene) field-effect transistors with high dielectric constant gate insulator
Authors: Wang Guangming , Moses Daniel , Heeger Alan J. , Zhang Hong-Mei , Narasimhan Mux , Demaray R. E.
Published: December 2003

High dielectric constant (k=41) titanium oxide (TiO2) was used as the gate insulator in field-effect transistors (FETs) with regioregular poly(3-hexylthiophene) (RR-P3HT) as the electronically active semiconductor. Good FET characteristics were obtained with saturation at low drive voltages (≈−2 V) and with carrier mobilities of 1.3×10−2 cm2/V s. Deposition of a thin layer of SiO2 (thicknesses of 3 and 17 nm) on top of the TiO2 (97 nm) gate insulator resulted in a reduced effective dielectric constant (keff=31 for 3 nm of SiO2 and keff=19 for 17 nm SiO2), but with significant improvement in the FET characteristics; the field-effect mobility increased to 5.4×10−2 cm2/V s, the on/off ratio increased from 102 to 6×104, and the leakage current decreased by a factor of approximately 102. The importance of the thin SiO2 layer was confirmed using aluminum oxide (Al2O3) (k=8.4) as the gate insulator in RR-P3HT FETs.
Effect of barrier rib height variation on the luminous characteristics of ac plasma display panel
Authors: Bae Hyun Sook , Chung Woo Joon , Whang Ki-Woong
Published: December 2003

We studied the mechanism of high luminous efficiency discharge with high Xe partial pressure in ac plasma display panel using three-dimensional numerical simulation. Because the electron heating efficiency improves more than the excitation efficiency by electrons under high Xe partial pressure gas condition, it is possible to achieve high efficiency discharge with the increase in the sustain voltage. We studied the effect of barrier rib height variation using ray-optics code in conjunction with the three-dimensional plasma simulation to analyze the effects of cell geometry for varying pressure conditions. The optimal barrier rib height decreased as the Xe partial pressure increased which resulted due to the formation of local, strong sheath under high Xe partial pressure condition.
Thickness dependence of ac losses in circular disks of YBa2Cu3O7 films in perpendicular magnetic fields
Authors: Suenaga M. , Li Q. , Ye Z. , Iwakuma M. , Toyota K. , Funaki F. , Foltyn S. R. , Wang H. , Clem John R.
Published: December 2003

The ac losses in three disk-shaped YBa2Cu3O7 (YBCO) films, which were deposited on SrTiO3 by the pulsed-laser-deposition technique and had thicknesses, d, of 0.2, 1.0, and 3.0 μm, were measured in perpendicular applied ac magnetic fields to ∼0.14 T at 10 Hz in liquid nitrogen. The losses at low fields were found to be a strong function of the film thickness. The measured losses were compared with the theoretically calculated losses. The ac losses calculated using a field-independent critical-current density, the Bean model [J. R. Clem and A. Sanchez, Phys. Rev. B 50, 9355 (1994)], agreed very well with the 0.2-μm-thick film, while the calculated losses agreed well with the measured ones when a field-dependent critical-current density, the Kim model [D. V. Shantsev, Y. M. Galperin, and T. H. Johansen, Phys. Rev. B 61, 9699 (2000)], was used for the films of thickness 1.0 and 3.0 μm. However, a surprising discrepancy was found in the values of Bc and B0 for thinner YBCO films depending on whether they were determined by ac or dc measurements. Bc is defined as Bc=μ0Jc(0)d/2, B0 is the characteristic field in the Kim-model critical-current density JcK(Ba)=Jc(0)/(1+Ba/B0), and Jc(0) is the critical-current density at applied magnetic field Ba=0.
Structural and dielectric properties of thin ZrO2 films on silicon grown by atomic layer deposition from cyclopentadienyl precursor
Authors: Niinistö J. , Putkonen M. , Niinistö L. , Kukli K. , Ritala M. , Leskelä M.
Published: December 2003

ZrO 2 thin films with thicknesses below 20 nm were deposited by the atomic layer deposition process on Si(100) substrates at 350 °C. An organometallic precursor, Cp2Zr(CH3)2 (Cp=cyclopentadienyl, C5H5) was used as the zirconium source and water or ozone as oxygen source. The influence of oxygen source and substrate pretreatment on the dielectric properties of ZrO2 films was investigated. Structural characterization with high-resolution transmission electron microscopy was performed to films grown onto HF-etched or native oxide covered silicon. Strong inhibition of ZrO2 film growth was observed with the water process on HF-etched Si. Ozone process on HF-etched Si resulted in interfacial SiO2 formation between the dense and uniform film and the substrate while water process produced interfacial layer with intermixing of SiO2 and ZrO2. The effective permittivity of ZrO2 in Al/ZrO2/Si/Al capacitor structures was dependent on the ZrO2 layer thickness and oxygen source used. The interfacial layer formation increased the capacitance equivalent oxide thickness (CET). CET of 2.0 nm was achieved with 5.9 nm ZrO2 film deposited with the H2O process on HF-stripped Si. The ozone-processed films showed good dielectric properties such as low hysteresis and nearly ideal flatband voltage. The leakage current density was lower and breakdown field higher for the ozone-processed ZrO2 films.
Magnetic anisotropy and stress-impedance effect in Joule heated Fe73.5Cu1Nb3Si13.5B9 ribbons
Authors: Li D. R. , Lu Z. C. , Zhou S. X.
Published: December 2003

The stress-impedance (SI) profiles were measured in Fe73.5Cu1Nb3Si13.5B9 ribbons annealed by Joule heating in the presence of longitudinal applied tensile stress of 100 MPa and the maximum SI ratio of 350% is observed. It was found that the large SI effect is the result of induced transverse magnetic anisotropy. We present a model that explains the variations of transverse magnetic anisotropy on SI effect. The model is based on the skin effect and on the magnetization rotation due to the applied tensile stress and the ac driving current.
Perturbation analysis and memory in ferroelectric materials
Authors: Bandyopadhyay A. K. , Ray P. C.
Published: December 2003

Many ferroelectric materials like LiTaO3 and LiNbO3 exhibit peculiar behavior in terms of showing a large discrepancy between experimental and theoretical values of coercive field by the use of Landau–Ginzburg model. If a perturbation is given at zero field, then there is also perturbation or fluctuation in polarization with respect to the nondimensional value of domain-wall width. An eigenvalue problem is deduced through a linear Jacobian transformation to show that there is a finite value of “memory,” when the perturbation in the electric field is lifted. The eigenvalue gives a characteristic value of polarization, which also gives rise to a zone of stability for polarization. This perturbation formalism also allows the calculation of the limits of the coercive field and, subsequently, the values of the domain-wall width can also be estimated, which show both the lower and upper limits of theoretical values for both the above ferroelectric materials, deduced as the theoretical limits of the coercive fields. The theoretical framework is developed in this article.
Mechanical characteristics of nanoscale springs
Authors: Zhang Guigen , Zhao Yiping
Published: December 2003

In this study, we used the method of finite element analysis to investigate the mechanical stiffness of single nanoscale helical springs with two different configurations—square and round—in order to answer two questions. (1) Is the classic macroscopic-based theoretical prediction still valid to nanoscale springs? (2) What is the effect of boundary conditions on the spring stiffness? Our results indicated that the classic prediction is valid and applicable to predicting the relationship between the spring stiffness and the spring section diameter and coil width in nanoscale springs, and that boundary conditions applied to the nanosprings will significantly affect the deformation of the springs and their stiffness values. The strict boundary condition of radial symmetry used in the classic development is responsible for producing high stiffness values. When used as a stand-alone mechanical component, a nanospring will be 2–3 times stiffer than that used as part of a film structure. With equivalent dimensions, a square helical spring will be stiffer than its round counterpart. In a square configuration, the spring stiffness can be maximized at a rising angle of 30°.
Metallic precipitate contribution to carrier generation in metal–oxide–semiconductor capacitors due to the Schottky effect
Authors: Negoita M. D. , Tan T. Y.
Published: December 2003

The contribution of metallic precipitates to carrier generation has been modeled for metal–oxide–semiconductor (MOS) capacitor devices fabricated using Si, with the precipitate located in the depletion region of the device. The physical mechanism responsible for the electrical activity of the metallic precipitate is attributed to the Schottky junction property between the precipitate and the Si matrix materials. The precipitate serves as a highly effective carrier generation center when the capacitor is switched from the accumulation mode to the deep depletion mode. As a practical case, the electrical activity of the Cu3Si precipitate is investigated and the impact of the precipitate located at different positions within the depleted region of the MOS capacitor on the device performance degradation is analyzed.
Imaging material components of an integrated circuit interconnect
Authors: Levine Zachary H. , Grantham Steven , Paterson David J. , McNulty Ian , Noyan I. C. , Levin T. M.
Published: December 2003

Two regions of interest on a copper/tungsten integrated circuit interconnect were imaged using two techniques: (a) the absorption spectrum was measured at 15 x-ray energies between 1687 and 1897 eV, and (b) the x-ray fluorescence spectrum was recorded with incident photon energies of 1822, 1797, and 1722 eV. The energies were chosen to optionally excite tungsten and tantalum above their M5 edges yet stay below the silicon K edge. Four materials in the circuits, tantalum, tungsten, silica, and copper were mapped using both techniques. The two sets of images agree in their main features, but differ for finer features.
Reoxidation of silicon nitride studied using x-ray photoelectron spectroscopy and transmission electron microscopy
Authors: Gilmore Damien , Cai Will Z. , Iyer Dorai , Burgin Rebecca , Averett Guy , Kamekona Keith , Shastri Sudhama , Schoonover Brian
Published: December 2003

The chemical composition of oxynitride films obtained by furnace oxidation of silicon nitride (Si3N4) in a dry or wet oxygen ambient at a substrate temperature of 900–1000 °C is characterized using x-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy. The dependence of the oxidation kinetics on the initial nitride thickness dnit is also investigated in the range of 18–500 Å. In the case of dnit=500 Å, only the surface of the nitride is oxidized after a 13 min 900 °C oxidation in a wet ambient. In contrast, for dnit=18 and 40 Å, under the same conditions condition, the underlying Si substrate is oxidized in addition to Si3N4. Furthermore, it is found that the oxidation rate of 500 Å Si3N4 increases by approximately 14%–21% when 2% hydrogen chloride (HCl) is added to the oxidizing ambient. Increases in HCl content beyond 2% do not result in any further enhancement of the oxidation of the nitride film.
Direct imaging of self-organized anisotropic strain engineering for improved one-dimensional ordering of (In,Ga)As quantum dot arrays
Authors: Mano T. , Nötzel R. , Hamhuis G. J. , Eijkemans T. J. , Wolter J. H.
Published: December 2003

Single (In,Ga)As quantum dot (QD) arrays are formed on GaAs (100) substrates by self-organized anisotropic strain engineering of an (In,Ga)As/GaAs quantum wire (QWR) superlattice (SL) template in molecular beam epitaxy. The crucial steps in QWR template evolution, i.e., elongated QD formation at elevated temperature, thin GaAs capping, annealing, and stacking, are directly imaged by atomic force microscopy (AFM). AFM reveals a very smooth connection of the QDs into QWRs upon annealing. In addition, AFM shows the presence of height and width fluctuations of the QWRs with a significant number of bends and branches. These are attributed to excess strain accumulation during formation of the QWR template. By reducing the amount of (In,Ga)As and increasing the GaAs separation layer thickness in each SL period, a dramatic improvement of the uniformity of the QWR template is achieved. On the improved QWR template, well-defined one-dimensional single (In,Ga)As QD arrays are formed which are straight over more than 1 μm and extended to over 10 μm length with a small number of branches. After capping, the QD arrays exhibit clear photoluminescence emission up to room temperature without increase of the peak width.
Growth and characterization of atomic layer deposited WC0.7N0.3 on polymer films
Authors: Hoyas A. Martin , Schuhmacher J. , Shamiryan D. , Waeterloos J. , Besling W. , Celis J. P. , Maex K.
Published: December 2003

Atomic layer deposition (ALD) of tungsten carbide nitride (WC0.7N0.3) on a low-k (dielectric constant) dielectric aromatic polymer material is investigated. It is feasible to deposit thin WC0.7N0.3 films on polymers, but applying a nitrogen–oxygen (N2–O2) based plasma to the surface prior to ALD can significantly enhance the growth. The creation of polar surface groups by the plasma treatment is derived from the water contact angle and from O 1s to C 1s peak ratio extracted from x-ray photoelectron spectroscopy. Rutherford backscattering spectra and contact angle measurements revealed a typical ALD growth with at least two successive regimes. The first is controlled by the substrate surface, while during the last a constant amount of ALD material is added with each cycle. The plasma treatments create adsorption sites on the surface and therefore effectively enhance the growth and shorten the duration of the first regime. This observation is attributed to an improved initial ALD precursor adsorption. However, ALD island formation on the treated polymer is not merely a function of the number of available adsorption sites but depends also on the structure and composition of the substrate surface. The minimum thickness of a continuous ALD film is ∼10 nm on untreated polymer while on top of a N2 rich reactive ion etch plasma-treated polymer the WC0.7N0.3 film becomes continuous between 1.4 and 2.3 nm.
In situ size-control of CdZnSe nano-islands using shadow masks
Authors: Schallenberg T. , Borzenko T. , Schmidt G. , Molenkamp L. W. , Rodt S. , Heitz R. , Bimberg D. , Karczewski G.
Published: December 2003

We present a method which increases the versatility of molecular beam epitaxy through multiple application of a stationary shadow mask. The method is based on selected area growth in the overlap of the incidence regions of two molecular beams impinging through different apertures of the mask. The width of the overlap depends on the incidence angles of the beams which can be adjusted in situ. Size-control of CdZnSe quantum-well (QW) islands with a precision of 20 nm by varying the distance between the apertures can be obtained. Without Se beam, a minor quantity of Cd is incorporated in the matrix modulating the band-gap energy by just 5 meV. Cathodoluminescence (CL) of nanoscale QW islands shows dot-like behavior, i.e., sharp emission lines that are attributed to different excited states and a blueshift of the CL on reducing the island dimensions.
Coexistence of two different energy transfer processes in SiO2 films containing Si nanocrystals and Er
Authors: Fujii Minoru , Imakita Kenji , Watanabe Kei , Hayashi Shinji
Published: December 2003

The mechanism of energy transfer from silicon nanocrystals (nc-Si) to erbium ions (Er3+) in SiO2 films containing nc-Si and Er was studied by analyzing delayed infrared luminescence from Er3+. It was found that, to theoretically reproduce the rising part of the time-dependent luminescence intensity, two different energy transfer processes, i.e., fast and slow processes, should be considered. From the fitting of the delayed luminescence to a model, the ratio of the two energy transfer processes and the energy transfer rate of the slow process were estimated. The ratio exhibited a clear dependence on the luminescence peak energy of Si nanocrystals, which act as photosensitizers for Er3+, indicating that the ratio depends on the size of nc-Si. The ratio of slow to fast processes increased with the decrease in size; this observation is a strong indication that the fast process is the direct inheritance of the process in bulk Si:Er systems, and the slow process is a characteristic process occurring only in nc-Si:Er systems. The energy transfer rate of the slow process was found to depend on the recombination rate of excitons in nc-Si.
Diagnosis and location of pinhole defects in tunnel junctions using only electrical measurements
Authors: Zhang Zhongsheng , Rabson David A.
Published: December 2003

In the development of the first generation of sensors and memory chips based on spin-dependent tunneling through a thin trilayer, it has become clear that pinhole defects can have a deleterious effect on magnetoresistance. However, current diagnostic protocols based on Andreev reflection and the temperature dependence of junction resistance may not be suitable for production quality control. We show that the current density in a tunnel junction in the cross-strip geometry becomes very inhomogeneous in the presence of a single pinhole, yielding a four-terminal resistance that depends on the location of the pinhole in the junction. Taking advantage of this position dependence, we propose a simple protocol of four four-terminal measurements. Solving an inverse problem, we can diagnose the presence of a pinhole and estimate its position and resistance.
Minority carrier transport properties of GaInNAs heterojunction bipolar transistors with 2% nitrogen
Authors: Welty Rebecca J. , Xin Huoping , Tu Charles W. , Asbeck Peter M.
Published: December 2003

GaAs-based heterojunction bipolar transistors (HBTs) have a relatively large turn-on voltage of approximately 1.4 V that can only be decreased by reducing the band-gap energy of the base material. For a variety of applications, particularly operation with low power supply voltage and reduced power dissipation, it would be desirable to have a smaller value of turn-on voltage. We report the performance of NpN double heterojunction bipolar transistors fabricated on a GaAs substrate with a Ga0.89In0.11N0.02As0.98 base that has a band-gap energy (Eg) of 0.98 eV; this is achieved with a nitrogen composition of 2%. These devices have a turn-on voltage VBE that is 0.4 V lower than that of their GaAs-base counterparts. The peak incremental current gain HFE is 8. The current gain of nitrogen containing HBTs is degraded due to the complex change in transport properties of carriers through the GaInNAs base region. In this article, the transport properties of GaInNAs-base HBTs are investigated by temperature-dependent dc current–voltage characteristics, optical and high frequency small-signal electrical measurements. The characterization of these devices is important to understand the effect of nitrogen on the device performance.
Structural characterization and modeling of damage accumulation in In implanted Si
Authors: Lulli G. , Bianconi M. , Parisini A. , Napolitani E.
Published: December 2003

Lattice disorder and dopant distribution in silicon implanted at room temperature with In ions have been characterized by cross-sectional transmission electron microscopy (XTEM), Rutherford backscattering channeling, and secondary ion mass spectroscopy techniques. It is shown that full recoil Monte Carlo calculation in the binary collision approximation, including an empirical damage efficiency parameter varying with ion dose, can reasonably reproduce the disorder distributions extracted from ion-channeling spectra, under the assumption of defects as atoms randomly placed in a rigid lattice. The main features of the observed trend, such as, for instance, the threshold for amorphization and the width of the amorphized layer, are in good agreement with XTEM observations. Furthermore, the good agreement between calculated and experimental as-implanted In distributions shows that the dynamic evolution of dopant profiles is consistent with the simulated damage growth. The distributions of displaced atoms extracted from ion channeling spectra and the depth profiles of measured contrast on XTEM images show different trends as a function of ion dose, which are attributed to the different sensitivity of the two techniques to the structural properties of ion damage and to the evolution of defects with increasing dose. The approximations used for the damage model employed for the simulation of ion channeling measurements are strictly related to the interpretation of disorder. Such relationships are pointed out and discussed on the basis of some discrepancies observed in the fitting of backscattering spectra.
Low temperature heat capacity and magnetic susceptibility of Ti3SiC2
Authors: Drulis Monika K. , Czopnik A. , Drulis H. , Barsoum M. W.
Published: December 2003

In this paper, we report on the heat capacity and magnetic susceptibilities of bulk Ti3SiC2 samples in the 3–250-K temperature range. At 13.6 K, a nonmagnetic sharp anomaly of unknown origin, which disappeared when the sample was heated and quenched in water from 1400 °C, is observed. Curve fitting the cp data up to 100 K clearly shows that only four atoms—most likely one Si and three Ti atoms—of the six in a formula unit contribute to cp at the lowest temperatures. This reduces the Debye temperature θD calculated from over 700 K to ≈575 K. To obtain good agreement between experimental and calculated cp values in the 14<T<130 K temperature range, a θD of 552 K and an optical mode with an Einstein temperature θE of 219 K, which coincided with a soft shear mode observed in Raman spectroscopy, are assumed. At T>130 K, two other optical modes—the average of two other Raman modes observed at higher wave numbers—are required to enhance the fits to the experimental results. In the absence of the anomaly, θD rises from 575 to 593 K, whereas θE decreases slightly to 211 K. The density of states at the Fermi level [≈5 (eV unit cell)−1] is comparable to previous reports. The magnetic susceptibility is small and independent of magnetic field and temperature.
Domain structure of epitaxial PbTiO3 thin films on Pt(001)/MgO(001) substrates
Authors: Kim Y. K. , Lee K. , Baik S.
Published: December 2003

Epitaxial PbTiO3 films of various thickness were prepared on a Pt(001) bottom electrode layer, which was also grown epitaxially on MgO(001) single crystal substrates. Their ferroelectric domain structures were investigated extensively by two-dimensional reciprocal space mapping using synchrotron x-ray. In contrast to the PbTiO3 films grown directly on the MgO(001) substrate, the epitaxial films grown on Pt(001)/MgO(001) experienced compressive misfit strain at the growth temperature. At the Curie temperature (TC), the PbTiO3 films transformed to almost a fully c-axis oriented structure due to the large compressive strain. As the temperature decreased further below TC, some of the c domains turned into a domains in order to relax the tensile stress developed due to the increased tetragonality of the film. As the film thickness increased, relaxation of the initial compressive misfit stress was enhanced, reducing the initial c-domain abundance. Magnitudes of the residual misfit stresses were estimated as a function of film thickness by a finite element analysis.
Bragg diffraction of guided optical waves by magnetostatic backward volume waves in a double-layered magnetic film structure
Authors: Zhang Wen-Kang , Liu Gong-Qiang
Published: December 2003

The noncollinear interactions between the guided optical wave (GOW) and magnetostatic backward volume wave (MSBVW) in a double-layered magnetic film structure are investigated theoretically. The explicit expressions for the rf magnetization of the MSBVW and the mode conversion efficiency (MCE) of GOW were presented in terms of various geometrical parameters and the rf input power in the case that the insertion loss of the MSBVW is taken into consideration. The effects of the thicknesses of two magnetic layers and a separation layer on the MCE of GOW and magneto-optic (MO) coupling bandwidth are calculated in detail. The MCE of the GOW and the MO bandwidth can be increased significantly in a double-layered magnetic film structure by properly choosing the thicknesses of two magnetic layers and a separation layer.
Quantum mechanical analysis of channel access geometry and series resistance in nanoscale transistors
Authors: Venugopal R. , Goasguen S. , Datta S. , Lundstrom M. S.
Published: December 2003

We apply a two-dimensional quantum mechanical simulation scheme to study the effect of channel access geometries on device performance. This simulation scheme solves the nonequilibrium Green’s function equations self-consistently with Poisson’s equation and treats the effect of scattering using a simple approximation inspired by Büttiker. It is based on an expansion of the device Hamiltonian in coupled mode space. Simulation results are used to highlight quantum effects and discuss the importance of scattering when examining the transport properties of nanoscale transistors with differing channel access geometries. Additionally, an efficient domain decomposition scheme for evaluating the performance of nanoscale transistors is also presented. This article highlights the importance of scattering in understanding the performance of transistors with different channel access geometries.