bluuebunny/crossref_metadata_2025 huggingface dataset:
Process integration for through-silicon vias
Authors: Spiesshoefer S. , Rahman Z. , Vangara G. , Polamreddy S. , Burkett S. , Schaper L.
Published: September 2005

The formation of a through-silicon via (TSV) enables three-dimensional (3D) interconnects for chip-stacking applications that will be especially important for integrating heterogeneous devices. Many processing steps are involved with the major areas including: via formation; deposition of via insulation, barrier, and Cu seed films; Cu electroplating for via-fill; wafer thinning; and backside processing. The via diameter is 4–8μm, via depth is 15–20μm, and a 20μm pitch is used in this study. Each step will be described in the process flow with the considerations discussed for successful process integration.
Measurements and consequences of nonuniform radio frequency plasma potential due to surface asymmetry in large area radio frequency capacitive reactors
Authors: Sansonnens L. , Strahm B. , Derendinger L. , Howling A. A. , Hollenstein Ch. , Ellert Ch. , Schmitt J. P. M.
Published: September 2005

In large area reactors, a local asymmetry of the electrode area, due to lateral grounded walls, causes a perturbation in rf plasma potential, due to the redistribution of lateral rf current, which propagates along the resistive plasma between capacitive sheaths. This perturbation can be described by a telegraph equation, for which a typical damping length can be determined. In this study, the existence of this rf plasma potential perturbation is confirmed using electrostatic surface probe measurements in argon plasma. Furthermore, uniformity analysis of a-Si:H thin film deposited using silane plasma have shown that this nonuniform rf plasma potential can have a strong effect on the uniformity of plasma enhanced chemical vapor deposition processes. It is also shown that this perturbation and its effect on the deposition uniformity can be suppressed by symmetrizing the reactor walls.
Chemical mechanical planarization characteristics of WO3 thin film for gas sensing
Authors: Seo Yong-Jin , Kim Nam-Hoon , Chang Eui-Goo , Park Jinseong , Ko Pil-Ju , Lee Woo-Sun
Published: September 2005

It is important to control the microstructure and surface of films to use them in gas sensors. Chemical mechanical polishing (CMP) processing is one of the most useful methods for improving the surface roughness of films. The effects of CMP on the surface morphology of WO3 thin films prepared by the rf sputtering system were investigated in this article. The removal rate of the films increased, and the rms surface roughness decreased with the addition of an oxidizer to the tungsten slurry. Within-wafer nonuniformity was improved to below 5% when oxidizers of 5.0 and 2.5vol%, respectively, were added to the tungsten slurry. The optimized oxidizer concentration, reflected by both the rms roughness values and a hillock-free surface with the good uniformity, was 5.0vol% as shown with atomic force microscopy analysis of thin film topographies. Our CMP results will be a useful reference for advanced technology of thin films for gas sensor applications in the near future.
Dry etching of (Pb,Sr)TiO3 thin films using inductively coupled plasma
Authors: Kim Gwan-Ha , Kim Jong-Sik , Kim Kyoung-Tae , Kim Dong-Pyo , Kim Chang-Il
Published: September 2005

In this study (Pb,Sr)TiO3 (PST) thin films were etched with inductively coupled Cl2∕(Cl2+Ar) plasmas. The etch characteristics of PST thin films as a function of Cl2∕(Cl2+Ar) gas mixtures were analyzed by using a quadrupole mass spectrometer. Systematic studies were carried out as a function of the etching parameters, including the radio frequency power and the working pressure. The maximum PST film etch rate is 56.2nm∕min, because a small addition of Cl2 to the Cl2∕Ar mixture increased the chemical effect. It was proposed that sputter etching is the dominant etching mechanism while the contribution of a chemical reaction is relatively low due to low volatility of the etching products.
Vacuum microelectronic devices and vacuum requirements
Authors: Tyler Talmage , Shenderova Olga A. , McGuire Gary E.
Published: September 2005

With the emergence of microfabrication and thin film deposition techniques developed by the semiconductor industry, it became apparent that miniature vacuum microelectronic devices could be developed. Using approaches as diverse as controlled evaporation, chemical etching (both wet isotropic and anisotropic and dry plasma etching) and controlled oxidation, sharp tips were formed in both metals and semiconductor materials with a radius of less than 50 nm. When integrated with a gate electrode, field enhancement at the tip showed the promise of very high field emission electron currents, especially when arrays of more than one million tips per square centimeter could be produced. Even though currents above 1 mA have been achieved, vacuum microelectronic devices have not been adapted into widespread use. The vacuum environment of the device leads to changes in emission performance and premature failure that has limited the acceptance of the devices. Numerous approaches have been explored to improve and maintain the vacuum environment of the devices and enhance the vacuum conductance. In addition, device structures have been proposed that are less sensitive to the vacuum level and less susceptible to failure. An overview of these issues will be provided from a historical perspective.
Study of molybdenum back contact layer to achieve adherent and efficient CIGS2 absorber thin-film solar cells
Authors: Kadam Ankur A. , Dhere Neelkanth G. , Holloway Paul , Law Evan
Published: September 2005

Molybdenum is used as back contact layer in I-III-VI2 compound thin-film solar cells. Mo film was sputter deposited on 125-mm-diameter Si wafer having 100 orientation using dc magnetron sputtering. Films with similar parameters were also deposited on 2.5cm×10cm soda-lime glass for studying the adhesion to the substrate and chemical reactivity of molybdenum with H2S gas at 475°C for 20min. Mo being refractory material develops stresses. It is essential to deposit stress-free and relatively inert Mo films in order to achieve well adherent and highly efficient CuIn1−xGaxS2 absorber thin film solar cells on flexible metallic foil and glass substrates. Earlier studies have shown that films deposited at sputtering power of 300W and 0.3×10−3Torr working argon pressure develop compressive stress, while the films deposited at 200W and 5×10−3Torr pressure develop tensile stress. Four sets of experiments were carried out to achieve optimum deposition cycle to deposit stress-free Mo. In the first experiment, Mo thickness of 138nm was deposited at 300W power and 0.3×10−3Torr pressure. In the second experiment Mo thickness of 127nm was deposited at power of 200W and pressure of 5×10−3Torr. Two more experiments were carried out by using alternate layers to reduce the overall stress. In a third experiment, two high power cycles were sandwiched between three low power cycles with total film thickness of 330nm. In a fourth experiment two low power cycles were sandwiched between three high power cycles resulting in effective thickness of 315nm. This article describes the wafer bending analysis for stress measurement, x-ray diffraction for crystal quality, scanning electron microscopy for surface morphology and Auger electron spectroscopy for the extent of sulfur diffusion in Mo layer.
Investigation of process window during dry etching of ZnO thin films by CH4–H2–Ar inductively coupled plasma
Authors: Na Sun-Woong , Shin Myoung Hun , Chung Yun Mo , Han J. G. , Lee N.-E.
Published: September 2005

The etching characteristics of ZnO thin films, etched with a positive photoresist mask and a process window in inductively coupled CH4–H2–Ar plasmas were investigated by varying the various process parameters. It was found that the process window for ZnO etching is closely related to the balance between the deposition and removal processes of the a-C:H (amorphous hydrogenated carbon) layer on the ZnO surface. Under certain conditions, the etch rate selectivity of ZnO to PR is infinite, because the ZnO films continue to be etched, but a net deposition of the a-C:H polymer occurs on the top of the photoresist. The measurements of the radical species in the plasma and the surface binding states by optical emission spectroscopy (OES) and x-ray photoelectron spectroscopy (XPS), respectively, revealed that the chemical reaction of the CH radicals with the Zn atoms in ZnO and the ion-enhanced removal mechanism of the a-C:H layer play an important role in determining the ZnO etch rate, as well as the etch by-products.
Real time quantitative diagnostic technique for measuring chemical vapor deposition precursors
Authors: Yun Ju-Young , Chung Kwang-Hwa , Moon Doo-Kyung
Published: September 2005

This study proposes an accurate method of monitoring precursor consumption in chemical vapor deposition (CVD) systems. Since precursor costs are significant, finding an efficient method to monitor precursor consumption is necessary. One example is the use of noncontact and inexpensive ultrasonic sensors for determining the liquid level in a container. In this study, sensors based on ultrasonic techniques have been developed for monitoring the precursor consumption in a CVD system. Moreover, the prototype sensors developed in this study can be useful in the field of semiconductors.
Dry etching of (Ba,Sr)TiO3 thin films using an inductively coupled plasma
Authors: Kim Gwan-Ha , Kim Kyoung-Tae , Kim Chang-II
Published: September 2005

In this work, we investigated etching characteristics and mechanism of BST thin films using Cl2∕Ar,CF4∕Cl2∕Ar, and BCl3∕Cl2∕Ar gas mixtures using an inductively coupled plasma (ICP) system. A chemically assisted physical etch of BST was experimentally confirmed by ICP under various gas mixtures. The etch rate of the BST thin films had a maximum value at 20% BCl3 and 10% CF4 gas concentration, and decreased with further addition of BCl3 or CF4 gas. The maximum etch rate of the BST thin films was 57nm∕min at 30% Cl2∕(Cl2+Ar). The maximum etch rate may be explained by the simultaneously concurrence of physical sputtering and chemical reaction. The characteristics of the plasma were analyzed using an optical emission spectroscopy (OES) and a Langmuir probe.
X-ray photoemission spectroscopy and Fourier transform infrared studies of dye molecule doped conducting polymer films
Authors: Kato H. , Takemura S. , Nishikawa O. , Taniguchi M.
Published: September 2005

Conducting polymer polythiophene (PT) films incorporated with dye molecule brilliant green (BG) were prepared by electrochemical doping and diffuse injection methods. The charge transfer and interaction between the doped molecule and PT polymer chains were investigated by analyzing the core-level energies and spectral profiles of the atomic components. Vibrational states of the doped dye molecule and the polymer backbone were also investigated by Fourier transform infrared (FTIR) RAS and FTIR transmission methods in order to examine the dopant configuration into the polymer chains in the hybrid films. In the case of BG doped films, X-ray photoemission spectroscopy (XPS) core-level analysis of S2p split indicates simultaneous doping of BG cation and HSO4− in the hybrid films prepared by electrochemically reduced and dye diffuse injection methods. The synthesized film samples were categorized into two types by the difference of S2p core-level energy shift. In the cationlike doped sample, the energy shift of the lower peak of S2p suggests the charge transfer between BG molecules and polymer chains creating a n type conducting polymer state. The orientation and configuration of the dopant BG molecule is discussed by assignment of the origin of the peak at 2000cm−1 which appeared only in the FTIR transmission spectrum of the BG-doped sample not observed in the FTIR RAS spectrum. The three possible cases of the origin of the peak are presented: Benzene out-of-plane mode, -NCS, and CCN-. According to those interpretations, three possible models of the BG configuration are suggested.
Growth and characterization of nanocrystalline zirconium nitride–inconel structures
Authors: Aouadi S. M. , Maeruf T. , Sodergren M. , Mihut D. M. , Rohde S. L. , Xu J. , Mishra S. R.
Published: September 2005

This paper reports on the investigation of the physical, chemical, optical, mechanical, and tribological properties of reactively sputtered zirconium nitride–inconel composite nanocrystalline mixture films. These films were co-sputtered from a Zr and an inconel targets onto Si (111) substrates at room temperature using a fixed power to the Zr target (PZr) and a fixed flow of nitrogen and argon. Two sets of samples were produced by (1) varying the power to the inconel target (Pinc) and using a fixed bias voltage Vb and (2) by varying Vb and keeping Pinc fixed. The elemental composition was deduced from x-ray photoelectron spectroscopy, and was found to be influenced by Pinc and Vb. X-ray diffraction revealed the presence of nanocrystals of ZrN with a pattern typical of the NaCl structure. The grain size was found to decrease with the increase in “inconel” content in the film. The optical constants were measured using spectroscopic ellipsometry and were subsequently simulated using a Drude–Lorentz model. A correlation between film structure–composition and optical constants was established. The hardness and elastic modulus of each sample were measured by nanoindentation. The hardest films were produced using a Vb=−130V bias voltage and Pinc=4W. Microwear measurements were carried out using positive constant normal loads and the wear tracks were imaged and processed. The measured values for the friction coefficients, residual depth of tip indentations, wear volumes, and surface roughness were reported. The lowest recorded wear volume using a load of 4 mN was 10−3μm. Finally, the coatings were worn against ball-bearing steel using a ball-on-disk tribotester. Characterization of the wear tracks were performed by profilometry. A low wear coefficient of 1.7×10−7mm3∕s was obtained for a load of 5 N.
Adsorption and reactions of tetrabutoxysilane (TBOS) on Si(100)
Authors: Lee Nakyung , Yong Kijung , Jeong Hyun Suk , Kim Chang Min
Published: September 2005

Adsorption and reactions of tetrabutoxysilane (Si(OC4H9)4) on a Si(100) surface were investigated using temperature programmed desorption and x-ray photoelectron spectroscopy. Physisorbed tetrabutoxysilane undergoes C–O bond scission to form –O–Si(OC4H9)3 and butyl species on Si(100) at 200K. It is observed that further C–O bond scission takes place sequentially in the temperature range of 200–500K. Main desorption products are butene and hydrogen, which are desorbed at 410K and 820K, respectively. We propose that the production of butene takes place through β-hydride elimination of the butyl group on Si(100).
Oxygen ion energy distribution: Role of ionization, resonant, and nonresonant charge-exchange collisions
Authors: Babaeva N. Yu. , Lee J. K. , Shon J. W. , Hudson E. A.
Published: September 2005

Capacitively coupled rf discharge operating in oxygen/argon mixtures has been investigated using the particle-in-cell/Monte Carlo method. The roles of ionization, resonant and nonresonant charge-exchange collisions in the formation of ion energy distribution (IED) at the electrodes is investigated. By turning off/on the corresponding collisional processes, it is shown that ionization can play an essential role in formation of the IED structure. The relative contribution of ionization to IED is estimated.
Selective detection of Cr(VI) using a microcantilever electrode coated with a self-assembled monolayer
Authors: Tian F. , Boiadjiev V. I. , Pinnaduwage L. A. , Brown G. M. , Thundat T.
Published: September 2005

We have demonstrated detection of Cr(VI) ions using functionalized microcantilevers under electrochemical control. Au-coated microcantilever working electrodes are modified with self-assembled monolayers of 4-mercaptopyridine (4-mPy) in sulfuric acid solution. Differential surface stress changes at the modified microcantilever have been measured as a function of applied potential while simultaneously measuring the current-potential response by cyclic voltammetry. The selective adsorption of Cr(VI) on 4-mPy monolayer-coated microcantilever electrode is attributed to hydrogen bonding. The stressogram (first derivative of surface stress of microcantilever with respect to potential versus electrode potential) suggests that a small amount of an intermediate oxidation state of chromium is retained at the 4-mPy monolayer, and this intermediate reduction product of Cr(VI) can be reversibly oxidized on the surface. Our results demonstrate that changes of differential surface stress due to the adsorption-controlled electrochemical reaction can be observed at high sensitivity. This potential controlled microcantilever technique offers insights into the behavior of the solid-liquid interface during electrochemical reactions at modified electrodes.
Characterization of a modified Bosch-type process for silicon mold fabrication
Authors: Jo S.-B. , Lee M.-W. , Lee S.-G. , Lee E.-H. , Park S.-G. , O B.-H.
Published: September 2005

We present the results of our development of a deep silicon etching technique, the modified Bosch-type process. Its feasibility was also investigated. This modified Bosch-type process is based on the well known Bosch-type process, but our modified Bosch-type process consists of the etching/passivating time, process transition step, and ion energy control. This modified Bosch-type process has been characterized with respect to ion energy, substrate temperature, and feature size. We found that the etching and deposition characteristics of passivating film were closely related to the resulting deep silicon etch profile. Up to a 40–50 μm deep silicon structure with vertical and positively sloped profiles was realized by the modified Bosch-type process, depending on a few parameters. In this work, this modified Bosch-type process was applied to silicon mold fabrication used for a structuring microarray and optical power splitter. Replication results confirm that this process is promising for achieving high-yield, reliable microstructures on polymer films.
Electronic and optical properties of Ta1−xZrxN films: Experimental and ab initio studies
Authors: Aouadi S. M. , Bohnhoff A. , Amriou T. , Haasch R. T. , Williams M. , Hilfiker J. N.
Published: September 2005

This article reports on a systematic investigation of the electronic and optical properties of Ta1−xZrxN films fabricated using unbalanced magnetron sputtering. X-ray diffraction confirmed that the films formed a solid solution that corresponded to a rocksalt structure. Rutherford backscattering revealed the elemental composition of the films. Ultraviolet photoelectron spectroscopy was used to investigate the valence band electronic structure while vacuum ultraviolet spectroscopic ellipsometry (VUV–SE) was used to evaluate the strength and energy of their interband electronic excitations/transitions. The optical and electronic properties of these materials were simulated using density functional theory within the generalized gradient approximation. The calculated refractive indices and density of states were in good agreement with the VUV–SE data and the valence band photoelectron spectra. In addition, the computational results were instrumental in indicating the correlation between the measured optical and electronic properties to their bond strength and elemental composition.
Overview of the Spallation Neutron Source Vacuum Systems
Authors: Ladd P. , Crandall J. , Hechler M. , Henderson S. , Kersevan R. , Murdoch G. , Tang J. ,   The SNS ASD Vacuum Team
Published: September 2005

The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built in Oak Ridge, Tennessee, by the U.S. Department of Energy. The SNS will provide the most intense pulsed neutron beams in the world for scientific research and industrial development. At a total cost of $1.4 billion, construction began in 1999 and will be completed in 2006 the culmination of the collaborative efforts of six National Laboratories. An overview of the contribution of these laboratories is provided specifically addressing the design and construction of the numerous vacuum systems and their integration into an operational facility (N. Holtkamp, The SNS Linac and Storage Ring: Challenges and Progress Towards meeting them, EPAC 2002).
Improvement of nitrogen retained dose using ammonia as a precursor in nitrogen plasma immersion ion implantation of silicon
Authors: Wan G. J. , Yang P. , Fu Ricky K. Y. , Yao Zh. Q. , Huang N. , Chu Paul K.
Published: September 2005

The low nitrogen retained dose due to competition from oxygen coimplantation diminishes the efficacy of nitrogen plasma immersion ion implantation in silicon. In this work, we aim at improving the nitrogen retained dose by using ammonia as a precursor. Ammonia is introduced into the nitrogen plasma during plasma immersion ion implantation of silicon to improve the nitrogen reactivity and reduce the competition from oxygen in the residual vacuum. Our x-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy results indicate that the ammonia precursor can indeed improve the N retained dose effectively, and the hydrophilic properties of the surface change with different ammonia to nitrogen ratios.
Properties of transparent conductive In2O3:Mo thin films deposited by Channel Spark Ablation
Authors: Huang Li , Li Xi-feng , Zhang Qun , Miao Wei-na , Zhang Li , Yan Xue-jian , Zhang Zhuang-jian , Hua Zhong-yi
Published: September 2005

Molybdenum-doped indium oxide In2O3:Mo (IMO) thin films were deposited on glass substrates by a technique called channel spark ablation. The structure, surface morphology, electrical, and optical properties of these films were investigated by x-ray diffraction, atomic force microscopy (AFM), four-point probe, ultraviolet photoelectron spectroscopy (UPS), Hall analysis, and spectrophotometry. The influence of oxygen pressure on the electrical properties of IMO thin films prepared at Ts=350°C was studied, showing that increasing oxygen pressure changes the resistivity concavely and the carrier concentration convexly. The IMO films as deposited are well crystallized with a preferred orientation of (222) and the surface roughness evaluated in terms of Rrms, Ra, and Rp-v measured by AFM is 0.72, 0.44, and 15.4 nm, respectively. The lowest resistivity and corresponding carrier concentration are 4.8×10−4Ωcm and 7.1×1020cm−3. The typical work function of IMO is 4.6 eV measured by UPS. For all the samples, the average transmittance in the visible region is more than 87%.
Conductance enhancement of polymethylmethacrylate bombarded by low-energy ions
Authors: Koval Y. , Fistul M. V. , Müller P.
Published: September 2005

It has been found that films of polymethylmethacrylate (PMMA) show a substantial conductance after bombardment by Ar ions with energy of 250–1250eV. The appearance of the conductance is attributed to graphitization processes in the subsurface layer. As the energy of ions increases, the conductivity of PMMA is greatly enhanced. We have found that, at low electric fields, the conductance is provided by variable range hopping with a strong influence of Coulomb interactions. At high electric fields, the transformed PMMA reveals non-Ohmic behavior: the conductance is an exponential function of E∕T.
Threshold ionization mass spectrometry of reactive species in remote Ar∕C2H2 expanding thermal plasma
Authors: Benedikt Jan , Agarwal Sumit , Eijkman Dimitri , Vandamme Wouter , Creatore Mariadriana , van de Sanden M. C. M.
Published: September 2005

Triple stage threshold ionization mass spectrometry is successfully implemented in an Ar∕C2H2 expanding thermal plasma setup. More than 20 hydrocarbon radicals and molecules formed in the plasma, including for example the C2H, C3, C3H, and C3H2 radicals or C3H4 or C4H2 molecules, are measured and their absolute densities are determined. Thanks to a careful design, a high sensitivity of the instrument is achieved and species with densities as low as 1×1016m−3 can be detected. Issues related to the absolute density calibration procedure are considered. The proper determination of the background signal by means of a beam chopper and the influence of the chopper on the measurement are discussed and the possible composition distortion of the sampled beam due to the collisions in the sampling orifice is checked. Furthermore, reported values of electron impact ionization cross sections of hydrocarbon species are compared and, based on their similarity in the near threshold energy region, the C2H2 electron impact ionization cross section is proposed as a reasonable approximation for other hydrocarbon radicals. The results for C, CH, and C2 radicals are compared with previous cavity ringdown absorption spectroscopy measurements and a good agreement is obtained.
Thermal stability of Al- and Zr-doped HfO2 thin films grown by direct current magnetron sputtering
Authors: Hong Yeong-Eui , Kim Yong-Seok , Do Kihoon , Lee Dongwon , Ko Dae-Hong , Ku Ja-Hum , Kim Hyoungsub
Published: September 2005

Ultrathin HfO2 dielectric films doped with Al and Zr were grown on p-type Si(100) substrates by dc magnetron sputtering, and their microstructural and electrical properties were examined. Compositions and chemical states of the dielectric films were analyzed by Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy. The HfO2 films doped with Zr were crystallized even from the as-deposited state, however, the crystallization temperature of the HfO2 film doped with 16% Al2O3 was delayed up to 900 °C. As the annealing temperature increases, high-resolution transmission electron microscopy analyses of all doped HfO2 films showed an increase of the interfacial layer thickness due to the diffusion of small partial pressure of oxygen in annealing ambient. Our results also showed that the addition of Al2O3 to 14% is not useful for blocking the oxygen diffusion through the (HfO2)0.86(Al2O3)0.14 film. From the capacitance-voltage measurements, the dielectric constants of the Al- and Zr-doped HfO2 thin films were measured to be 18.7 and 7.6, respectively.
Evaluation of crystallinity and film stress in yttria-stabilized zirconia thin films
Authors: Piascik Jeffrey R. , Thompson Jeffrey Y. , Bower Christopher A. , Stoner Brian R.
Published: September 2005

Yttria (3 mol %)-stabilized zirconia (YSZ) thin films were deposited using radio frequency (rf) magnetron sputtering. The YSZ thin films were deposited over a range of temperatures (22–300 °C), pressures (5–25 mTorr), and gas compositions (Ar∕O ratio). Initial studies characterized a select set of properties in relation to deposition parameters including: refractive index, structure, and film stress. X-ray diffraction (XRD) showed that the films are comprised of mainly monoclinic and tetragonal crystal phases. The film refractive index determined by prism coupling, depends strongly on deposition conditions and ranged from 1.959 to 2.223. Wafer bow measurements indicate that the sputtered YSZ films can have initial stress ranging from 86 MPa tensile to 192 MPa compressive, depending on the deposition parameters. Exposure to ambient conditions (25  °C, 75% relative humidity) led to large increase (∼100MPa) in the compressive stress of the films. Environmental aging suggests the change in compressive stress was related to water vapor absorption. These effects were then evaluated for films formed under different deposition parameters with varying density (calculated packing density) and crystal structure (XRD).
Rate equation analysis of hydrogen uptake on Si (100) surfaces
Authors: Inanaga S. , Rahman F. , Khanom F. , Namiki A.
Published: September 2005

We have studied the uptake process of H on Si (100) surfaces by means of rate equation analysis. Flowers’ quasiequilibrium model for adsorption and desorption of H [M. C. Flowers, N. B. H. Jonathan, A. Morris, and S. Wright, Surf. Sci. 396, 227 (1998)] is extended so that in addition to the H abstraction (ABS) and β2-channel thermal desorption (TD) the proposed rate equation further includes the adsorption-induced desorption (AID) and β1-TD. The validity of the model is tested by the experiments of ABS and AID rates in the reaction system H+D∕Si (100). Consequently, we find it can well reproduce the experimental results, validating the proposed model. We find the AID rate curve as a function of surface temperature Ts exhibits a clear anti-correlation with the bulk dangling bond density versus Ts curve reported in the plasma-enhanced chemical vapor deposition (CVD) for amorphous Si films. The significance of the H chemistry in plasma-enhanced CVD is discussed.
Technical note: Monte Carlo derivation of TG‐43 dosimetric parameters for radiation therapy resources and 3M Cs‐137 sources
Authors: Pérez‐Calatayud J. , Granero D. , Ballester F. , Casal E. , Cases R. , Agramunt S.
Published: September 2005

In clinical brachytherapy dosimetry, a detailed dose rate distribution of the radioactive source in water is needed in order to plan for quality treatment. Two Cs‐137 sources are considered in this study; the Radiation Therapy Resources 67‐800 source (Radiation Therapy Resources Inc., Valencia, CA) and the 3M model 6500/6D6C source. A complete dosimetric dataset for both sources has been obtained by means of the Monte Carlo GEANT4 code. Dose rate distributions are presented in two different ways; following the TG43 formalism and in a 2D rectangular dose rate table. This 2D dose rate table is helpful for the TPS quality control and is fully consistent with the TG43 dose calculation formalism. In this work, several improvements to the previously published data for these sources have been included: the source asymmetries were taken explicitly into account in the MC calculations, TG43 data were derived directly from MC calculations, the data radial range was increased, the angular grid in the anisotropy function was increased, and TG43 data is now consistent with the along and away dose rate table as recommended by the TG43 update.
Dose reconstruction in deforming lung anatomy: Dose grid size effects and clinical implications
Authors: Rosu Mihaela , Chetty Indrin J. , Balter James M. , Kessler Marc L. , McShan Daniel L. , Ten Haken Randall K.
Published: September 2005

In this study we investigated the accumulation of dose to a deforming anatomy (such as lung) based on voxel tracking and by using time weighting factors derived from a breathing probability distribution function (p.d.f.). A mutual information registration scheme (using thin‐plate spline warping) provided a transformation that allows the tracking of points between exhale and inhale treatment planning datasets (and/or intermediate state scans). The dose distributions were computed at the same resolution on each dataset using the Dose Planning Method (DPM) Monte Carlo code. Two accumulation/interpolation approaches were assessed. The first maps exhale dose grid points onto the inhale scan, estimates the doses at the “tracked” locations by trilinear interpolation and scores the accumulated doses (via the p.d.f.) on the original exhale data set. In the second approach, the “volume” associated with each exhale dose grid point (exhale dose voxel) is first subdivided into octants, the center of each octant is mapped to locations on the inhale dose grid and doses are estimated by trilinear interpolation. The octant doses are then averaged to form the inhale voxel dose and scored at the original exhale dose grid point location. Differences between the interpolation schemes are voxel size and tissue density dependent, but in general appear primarily only in regions with steep dose gradients (e.g., penumbra). Their magnitude (small regions of few percent differences) is less than the alterations in dose due to positional and shape changes from breathing in the first place. Thus, for sufficiently small dose grid point spacing, and relative to organ motion and deformation, differences due solely to the interpolation are unlikely to result in clinically significant differences to volume‐based evaluation metrics such as mean lung dose (MLD) and tumor equivalent uniform dose (gEUD). The overall effects of deformation vary among patients. They depend on the tumor location, field size, volume expansion, tissue heterogeneity, and direction of tumor displacement with respect to the beam, and are more likely to have an impact on serial organs (such as esophagus), rather than on large parallel organs (such as lung).
Image reconstruction and image quality evaluation for a 64‐slice CT scanner with ‐flying focal spot
Authors: Flohr T. G. , Stierstorfer K. , Ulzheimer S. , Bruder H. , Primak A. N. , McCollough C. H.
Published: September 2005

We present a theoretical overview and a performance evaluation of a novel ‐sampling technique for multidetector row CT (MDCT), relying on a periodic motion of the focal spot in the longitudinal direction (‐flying focal spot) to double the number of simultaneously acquired slices. The ‐flying focal spot technique has been implemented in a recently introduced MDCT scanner. Using collimation, this scanner acquires 64 overlapping 0.6 mm slices per rotation in its spiral (helical) mode of operation, with the goal of improved longitudinal resolution and reduction of spiral artifacts. The longitudinal sampling distance at isocenter is 0.3 mm. We discuss in detail the impact of the ‐flying focal spot technique on image reconstruction. We present measurements of spiral slice sensitivity profiles (SSPs) and of longitudinal resolution, both in the isocenter and off‐center. We evaluate the pitch dependence of the image noise measured in a centered 20 cm water phantom. To investigate spiral image quality we present images of an anthropomorphic thorax phantom and patient scans. The full width at half maximum (FWHM) of the spiral SSPs shows only minor variations as a function of the pitch, measured values differ by less than 0.15 mm from the nominal values 0.6, 0.75, 1, 1.5, and 2 mm. The measured FWHM of the smallest slice ranges between 0.66 and 0.68 mm at isocenter, except for pitch 0.55 (0.72 mm). In a centered ‐resolution phantom, bar patterns up to can be visualized independent of the pitch, corresponding to 0.33 mm longitudinal resolution. 100 mm off‐center, bar patterns up to are visible, corresponding to an object size of 0.36 mm that can be resolved in the direction. Image noise for constant effective mAs is almost independent of the pitch. Measured values show a variation of less than 7% as a function of the pitch, which demonstrates correct utilization of the applied radiation dose at any pitch. The product of image noise and square root of the slice width (FWHM of the respective SSP) is the same constant for all slices except 0.6 mm. For the thinnest slice, relative image noise is increased by 17%. Spiral windmill‐type artifacts are effectively suppressed with the ‐flying focal spot technique, which has the potential to maintain a low artifact level up to pitch 1.5, in this way increasing the maximum volume coverage speed that can be clinically used.
Extension of x‐ray imaging linear systems analysis to detectors with energy discrimination capability
Authors: Marchal Julien P.
Published: September 2005

A figure of merit, the broad‐spectrum generalized detective quantum efficiency, which describes the performance of digital detectors designed for broad‐spectrum x‐ray imaging is derived from linear response theory. This measure of the imaging efficacy of an x‐ray sensor is obtained when detector contrast modulation in the domain of x‐ray energy is introduced in the Fourier‐based analysis of digital systems. A method is proposed to scale existing figures of merit according to the energy‐dependent response of the detector and the spectral shape of the x‐ray beam. The new figure of merit obtained with this method provides an extended description of system performance when comparing energy‐integrating, single‐photon counting, and future energy‐sensitive x‐ray imaging sensors. The applicability of this linear system analysis is restricted to the tasks of low‐contrast object detection in radiography. The method for scaling the figure of merit to take into consideration broad‐spectrum conditions is applied to mammography for future energy‐dependent detectors. An approximation valid in the typical mammographic x‐ray energy range is used to calculate the broad‐spectrum generalized detective quantum efficiency at zero spatial frequency, for several mammographic x‐ray spectra. X‐ray energy weighting in mammography is investigated in the context of simulated tumors and microcalcifications detection by comparing this figure of merit, calculated for different detector technologies, under ideal imaging conditions, at zero spatial frequency.
Characterization and real‐time optical measurements of the ionizing radiation dose response for a new radiochromic medium
Authors: Rink Alexandra , Vitkin I. Alex , Jaffray David A.
Published: September 2005

A new radiochromic film, GafChromic EBT, was investigated for use in a real‐time radiation dosimetry system. It was found to be approximately eight times more sensitive to ionizing radiation dose, exhibited less postexposure development and achieved stable readout faster than one of its predecessors, GafChromic MD‐55. A clear distinction in change in optical density between exposure and postexposure was observed, but the measurements obtained during exposure were not linear with time or dose. This could not be explained by a shift in wavelength of maximum change in absorbance, as it was stable at during the entire exposure range (up to ). Increasing the spectral window of interest over which calculations were performed did little to correct the nonlinearity. The radiochromic film exhibited small dose rate dependence in real‐time measurements, with an increase in standard deviation of change in optical density measurements from 0.9% to 1.8% over a sixfold variation in dose rate. Overall, GafChromic EBT has increased sensitivity and decreased postexposure darkening, and this bodes well for its potential role as a radiation dosimeter, including real‐time applications.
A new method of incorporating systematic uncertainties in intensity‐modulated radiotherapy optimization
Authors: Yang Jie , Mageras Gig S. , Spirou Spiridon V. , Jackson Andrew , Yorke Ellen , Ling C. Clifton , Chui Chen‐Shou
Published: September 2005

Uncertainties in tumor position during intensity‐modulated radiotherapy (IMRT) plan optimization are usually accounted for by adding margins to a clinical target volume (CTV), or additionally, to organs at risk (OAR). The former approach usually favors target coverage over OAR protection, whereas the latter does not account for correlation in target and OAR movement. We investigate a new approach to incorporate systematic errors in tumor and organ position. The method models a distribution of systematic errors due to setup error and organ motion with displaced replicas of volumes of interest, each representing the patient geometry for a possible systematic error, and maximizes a score function that counts the number of replicas meeting dose or biological constraints for both CTV and OAR. Dose constraints are implemented by logistic functions of Niemierko's generalized model of equivalent uniform dose (EUD). The method is applied to prostate and nasopharynx IMRT plans, in which CTV and OAR each consists of five replicas, one representing no error (the position in the planning CT) and the other four discrete systematic setup displacements in one dimension with equal probability. The resulting IMRT plans are compared with those from two other EUD‐based optimizations: a standard planning target volume (PTV) approach consisting of a single replica of each OAR in the planned position and a single PTV encompassing all CTV replicas, and a PTV‐PRV approach consisting of a single PTV and a single planning risk volume (PRV) for each OAR encompassing all replicas. When systematic error is present, multiple‐replica optimization provides better critical organ protection while maintaining similar target coverage compared with the PTV approach, and provides better CTV‐to‐OAR therapeutic ratio compared with the PTV‐PRV instances where there is substantial PTV‐PRV overlap. The method can be used for other systematic errors due to organ motion and deformation.
Digital correction of magnification in pelvic x rays for preoperative planning of hip joint replacements: Theoretical development and clinical results of a new protocol
Authors: The B. , Diercks R. L. , Stewart R. E. , van Ooijen P. M. A. , van Horn J. R.
Published: September 2005

The introduction of digital radiological facilities leads to the necessity of digital preoperative planning, which is an essential part of joint replacement surgery. To avoid errors in the preparation and execution of hip surgery, reliable correction of the magnification of the projected hip is a prerequisite. So far, no validated method exists to accomplish this. We present validated geometrical models of the x‐ray projection of spheres, relevant for the calibration procedure to correct for the radiographic magnification. With help of these models a new calibration protocol was developed. The validity and precision of this procedure was determined in clinical practice. Magnification factors could be predicted with a maximal margin of error of 1.5%. The new calibration protocol is valid and reliable. The clinical tests revealed that correction of magnification has a 95% margin of error of to . Future research might clarify if a strict calibration protocol, as presented in this study, results in more accurate preoperative planning of hip joint replacements.
Model‐based ultrasound tomography: Tissue phantom experiments
Authors: Zhao Hongzhi , Gu Xuejun , Jiang Huabei
Published: September 2005

We present a detailed experimental study to evaluate our finite element based nonlinear reconstruction algorithm for recovery of acoustic properties in heterogeneous scattering media. Using a circularly scanning ultrasound system at , tissue phantom experiments were performed to study spatial resolution and contrast issues in model‐based ultrasound tomography. Our results show that both acoustic attenuation and speed images can be quantitatively reconstructed in terms of the location, size, shape, and acoustic property value of the target when different contrast levels between the target and background were used. We also demonstrate that a high contrast target as small as in diameter can be quantitatively resolved with our acoustic speed and attenuation images.
Centerline‐based colon segmentation for CT colonography
Authors: Frimmel Hans , Näppi J. , Yoshida H.
Published: September 2005

We have developed a fully automated algorithm for colon segmentation, centerline‐based segmentation (CBS), which is faster than any of the previously presented segmentation algorithms, but also has high sensitivity as well as high specificity. The algorithm first thresholds a set of unprocessed CT slices. Outer air is removed, after which a bounding box is computed. A centerline is computed for all remaining regions in the thresholded volume, disregarding segments related to extracolonic structures. Centerline segments are connected, after which the anatomy‐based removal of segments representing extracolonic structures occurs. Segments related to the remaining centerline are locally region grown, and the colonic wall is found by dilation. Shape‐based interpolation provides an isotropic mask. For 38 CT datasets, CBS was compared with the knowledge‐guided segmentation (KGS) algorithm for sensitivity and specificity. With use of a 1.5 GHz AMD Athlon‐based PC, the average computation time for the segmentation was 14.8 s. The sensitivity was, on average, 96%, and the specificity was 99%. A total of 21% of the voxels segmented by KGS, of which 96% represented extracolonic structures and 4% represented the colon, were removed.
Evaluation of edge effect due to phase contrast imaging for mammography
Authors: Matsuo Satoru , Katafuchi Tetsuro , Tohyama Keiko , Morishita Junji , Yamada Katsuhiko , Fujita Hiroshi
Published: September 2005

It is well‐known that the edge effect produced by phase contrast imaging results in the edge enhancement of x‐ray images and thereby sharpens those images. It has recently been reported that phase contrast imaging using practical x‐ray tubes with small focal spots has improved image sharpness as observed in the phase contrast imaging with x‐ray from synchrotron radiation or micro‐focus x‐ray tubes. In this study, we conducted the phase contrast imaging of a plastic fiber and plant seeds using a customized mammography equipment with a focal spot, and the improvement of image sharpness was evaluated in terms of spatial frequency response of the images. We observed that the image contrast of the plastic fiber was increased by edge enhancement, and, as predicted elsewhere, spectral analysis revealed that as the spatial frequencies of the x‐ray images increased, so did the sharpness gained through phase contrast imaging. Thus, phase contrast imaging using a practical molybdenum anode tube with a ‐focal spot would benefit mammography, in which the morphological detectability of small species such as micro‐calcifications is of great concern. And detectability of tumor‐surrounded glandular tissues in dense breast would be also improved by the phase contrast imaging.
Circular birefringence of an atom in uniform rotation: The classical perspective
Authors: Silverman M. P.
Published: September 2005

Recent quantum analyses of the dynamics of a static field-free atom in uniform rotation have shown that the atom exhibits optical asymmetries in its interaction with left and right circularly polarized light that are strictly forbidden in an inertial reference frame. The chiral asymmetries derive from a rotationally induced splitting of inertially degenerate magnetic substates. A classical mechanical treatment of the problem given in this article shows that the same phenomena may be interpreted in terms of the differential influence of the Coriolis ‘‘pseudo’’ force on particle orbits of opposite sense. In addition to being the source of some unusual optical effects, the atom in uniform rotation is a system conceptually interesting for its inequivalent (a) kinetic and canonical dynamical variables, and (b) energy and Hamiltonian. The system is illustrative of the converse of Larmor’s theorem whereby a field-free rotating frame simulates the physics of an inertial frame with static magnetic field.
Studying chaotic systems using microcomputer simulations and Lyapunov exponents
Authors: De Souza-Machado Sergio , Rollins R. W. , Jacobs D. T. , Hartman J. L.
Published: September 2005

The study of nonlinear systems in an undergraduate setting has become important, and this article describes the use of an interactive simulation in introducing students to the new techniques used to characterize deterministic chaos. Lyapunov exponents are introduced with emphasis on their physical significance. The results of numerical experiments on the driven, damped, Duffing two-well oscillator are reported and the global behavior of the Lyapunov exponent spectra is presented. The results confirm an important sum rule satisfied by the Lyapunov exponent spectra. Interesting, structured behavior of the Lyapunov exponent spectra is observed as the Duffing oscillator system follows the period-doubling route to chaos.
Diffraction around a fine wire: How good is the single-slit approximation?
Authors: Greenler Robert G. , Hable Joel W. , Slane Patrick O.
Published: September 2005

It is commonly stated that the diameter of a cylindrical fiber can be calculated from the position of the first minimum in the diffraction pattern using the results of the single-slit diffraction theory. Calculations show that this approximation works best for the diffraction pattern of a metal wire using light polarized parallel to the axis of the wire. It will yield an error of less than 5% for wires greater than 6 μm in diameter, when the measurement is made with red light. Light polarized perpendicular to the axis gives poorer results, and the approximation is much poorer for transparent fibers.