bluuebunny/crossref_metadata_2025 huggingface dataset:
Low resistance, nonalloyed Ohmic contacts to InGaAs
Authors: Crook Adam M. , Lind Erik , Griffith Zach , Rodwell Mark J. W. , Zimmerman Jeremy D. , Gossard Arthur C. , Bank Seth R.
Published: November 2007

We report extremely low specific contact resistivity (ρc) nonalloyed Ohmic contacts to n-type In0.53Ga0.47As, lattice matched to InP. Contacts were formed by oxidizing the semiconductor surface through exposure to ultraviolet-generated ozone, subsequently immersing the wafer in ammonium hydroxide (NH4OH, 14.8 normality), and finally depositing either Ti∕Pd∕Au contact metal by electron-beam evaporation or TiW contact metal by vacuum sputtering. Ti∕Pd∕Au contacts exhibited ρc of (0.73±0.44)Ωμm2—i.e., (7.3±4.4)×10−9Ωcm2—while TiW contacts exhibited ρc of (0.84±0.48)Ωμm2. The TiW contacts are thermally stable, showing no observable degradation in resistivity after a 500°C annealing of 1min duration.
Generalized Einstein-Podolsky-Rosen states
Authors: Huang Siendong
Published: November 2007

Based on Bohr’s ideas two families of states ωθ and ωϕ sharing the same perfect correlation of the Einstein-Podolsky-Rosen state and maximally violating Bell’s inequalities are constructed. Unlike their finite-dimensional counterpartner, these states are not unitarily equivalent. Hence they cannot be transformed into each other by physical operations of local algebras. This is a new entanglement phenomenon emerging in infinite-dimensional systems. Due to the uncertainty principle the existence of unbounded observables depends on the states ωθ and ωϕ. Therefore the manipulation of unbounded observables in quantum information processes cannot provide information for all states. Especially, the canonical unbounded observables q̂i and p̂i, i=1,2 of individual particles do not exist in the GNS representations associated with ωθ and ωϕ, and hence properties of individual particles cannot be obtained in such states.
Glide and multiplication of basal plane dislocations during 4H-SiC homoepitaxy
Authors: Zhang X. , Skowronski M. , Liu K. X. , Stahlbush R. E. , Sumakeris J. J. , Paisley M. J. , O’Loughlin M. J.
Published: November 2007

Basal plane dislocations (BPDs) are an important category of extended defects in SiC epilayers. They act as nucleation sites for single layer Shockley-type stacking faults which account for the degradation of the bipolar devices operating under forward bias. It is well documented that most of the BPDs in the SiC epilayers propagate from the substrates. However, two characteristic types of BPDs were suggested to be due to either nucleation or multiplication during epitaxy, including interfacial dislocations and short BPD arrays connected to the epilayer surface by threading segments. Combining molten KOH etching, plan-view transmission x-ray topography, and photoluminescence mapping, both types are determined to be two parts of one defect produced by the sideway glide of a BPD under the influence of shear stress. During the glide, the down-step end of the BPD frequently produces a series of short BPD segments at the moving growth front. These BPD segments will grow into an array of dislocation half loops. At the same time, the sideway glide of the BPD in the epilayer leaves an edge-type BPD segment at the epilayer∕substrate interface, which is the interfacial dislocation. The defect morphology provides the evidence of significant level of shear stresses present in SiC homoepitaxy of typical power device structures. The magnitude of such stresses is estimated.
Intersubband relaxation dynamics in single and double quantum wells based on strained InGaAs∕AlAs∕AlAsSb
Authors: Grimm C. V.-B. , Priegnitz M. , Winnerl S. , Schneider H. , Helm M. , Biermann K. , Künzel H.
Published: November 2007

Intersubband relaxation dynamics in single and coupled double quantum well (QW) structures based on strained InGaAs∕AlAs∕AlAsSb are studied by femtosecond pump probe spectroscopy at wavelengths around 2μm. For single QWs, the transient transmission was observed to decay exponentially with a time constant of 2ps, showing that side valleys have negligible influence on the intersubband relaxation dynamics for strained InGaAs QWs. For double QWs, the pump-probe signal at the intersubband energy involving the two electronic levels located at the wider QW exhibits an induced absorption component attributed to the population of the second subband (associated with the narrow QW) by hot electrons.
Interface effects on the external quantum efficiency of organic bulk heterojunction photodetectors
Authors: Kim Y. , Ballarotto M. , Park D. , Du M. , Cao W. , Lee C. H. , Herman W. N. , Romero D. B.
Published: November 2007

We investigate the effects of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and LiF interfacial layers on the efficiency of organic bulk heterojunction photodetectors fabricated with blends of regioregular poly(3-hexylthiophene-2,5-diyl) as electron donor and {6}-1-[3-(methoxycarbonyl)propyl]-{5}-1-phenyl-[5,6]-C61 as electron acceptor. At high reverse bias voltage, we find that the efficiency of these devices is limited only by the rate of creating excitons in the organic layer. Upon correction for the optical loss at the interfacial layers, the internal quantum efficiency can approach 100% in this highly disordered network of donor-acceptor molecular heterojunctions.
Integrated waveguide-coupled terahertz microcavity resonators
Authors: George Paul A. , Manolatou Christina , Rana Farhan , Bingham Adam L. , Grischkowsky Daniel R.
Published: November 2007

We demonstrate integrated square terahertz microcavity resonators side coupled to waveguides. We present the microcavity transmission spectra for different resonator sizes and coupling strengths. The measured quality factors due to external coupling and cavity loss are found to be between 40 and 90 and between 30 and 40, respectively, for cavity resonance frequencies between 1.077 and 1.331THz.
Polarization dependence study of electroluminescence and absorption from InAs∕GaAs columnar quantum dots
Authors: Ridha Philipp , Li Lianhe , Fiore Andrea , Patriarche Gilles , Mexis Meletios , Smowton Peter M.
Published: November 2007

Semiconductor optical amplifiers based on InGaAs columnar quantum dots (CQDs) with different numbers of superlattice periods were fabricated and tested. The polarization dependence of the electroluminescence (EL) and absorption of such CQDs structures were measured. Compared to standard QDs a large improvement in the ratio of transverse-magnetic (TM) and -electric (TE) integrated EL was obtained in CQDs, depending on the number of stacked GaAs∕InAs superlattice periods, which can be attributed to the more symmetric shape of CQDs. TM and TE resolved photovoltage absorption spectroscopy confirmed this improvement. A small spectral separation between TE- and TM-EL peaks has been observed showing that heavy and light holelike states are energetically close in these QDs.
Critical condition for growth of silicon nanowires
Authors: Dhalluin Florian , Desré Pierre J. , den Hertog Martien I. , Rouvière Jean-Luc , Ferret Pierre , Gentile Pascal , Baron Thierry
Published: November 2007

The existence of a critical radius on the growth of Si nanowires by the vapor-liquid-solid mechanism is examined. By varying the experimental growth parameters, we have shown a dependence of the minimum nanowires radius with the Si reactive species partial pressure, demonstrating that the critical radius is not a limited one. A thermodynamical model giving a quantitative aspect of the dependence of a critical nanowire diameter on Si supersaturation in a Au-Si droplet is proposed. These results open up a way to grow many kinds of nanowires with nanometric diameter. The size control has important implications for electronic and optical properties of nanowires based devices.
Ultralow equivalent oxide thickness obtained for thin amorphous LaAlO3 layers grown on Si(001)
Authors: Becerra L. , Merckling C. , Baboux N. , Plossu C. , Marty O. , El-Kazzi M. , Saint-Girons G. , Vilquin B. , Hollinger G.
Published: November 2007

Electron beam evaporation in a molecular beam epitaxy reactor was used to deposit, at 400°C, amorphous LaAlO3 high-κ oxide films on p-type Si(001). X-ray photoelectron spectroscopy and transmission electron microscopy showed that the interface with Si is free of SiO2 or silicates. Electrical measurements performed on as-deposited samples reveal an equivalent oxide thickness as low as 5Å for a film having a physical thickness of 41Å, a leakage current of 5.6×10−2A∕cm2 at ∣Vg−VFB∣=1V, and no flatband voltage shift.
Optical spectroscopic study of the SiN∕HfO2 interfacial formation during rf sputtering of HfO2
Authors: Toledano-Luque M. , Lucía M. L. , del Prado A. , San Andrés E. , Mártil I. , González-Díaz G.
Published: November 2007

High-k stacks formed by chemical-vapor-deposited SiN and high-pressure sputtered HfO2 in either O2 or Ar atmosphere have been studied. The introduction of a SiN layer is proposed to prevent the uncontrollable SiO2 growth while sputtering. The formation of Si–O bonds after the sputtering of the HfO2 film in O2 atmosphere was observed by infrared spectroscopy. Optical diagnosis of the plasma demonstrated a high density of O radicals in the system when working with O2. The small radius and high reactivity of these O radicals are the source of the SiN oxidation. However, the structure of the SiN film is preserved during Ar sputtering.
Population dynamics of localized biexcitons in AlxGa1−xN ternary alloys
Authors: Yamada Yoichi , Murotani Hideaki , Taguchi Tsunemasa , Ishibashi Akihiko , Kawaguchi Yasutoshi , Yokogawa Toshiya
Published: November 2007

Dynamical behavior of localized biexcitons in Ga-rich AlxGa1−xN ternary alloys has been studied by means of time-resolved luminescence spectroscopy. The time-dependent luminescence was analyzed using rate equations which were modified by considering the localization times of both the biexcitons and single excitons individually. The localization times of both biexcitons and single excitons became longer with increasing aluminum composition. On the other hand, the formation time of biexcitons from single excitons remained nearly unchanged. This observation indicated that the formation rate of biexcitons in the ternary alloys was independent of the localization depth of single excitons.
Time-resolved thermal mirror for nanoscale surface displacement detection in low absorbing solids
Authors: Astrath N. G. C. , Malacarne L. C. , Pedreira P. R. B. , Bento A. C. , Baesso M. L. , Shen J.
Published: November 2007

A time-resolved thermal mirror method for measurements of absolute thermo-optical-mechanical properties of low absorbing solids is presented. The thermoelastic equation for the surface displacement and an analytical expression for the probe beam intensity at the detector plane were derived. Experimental proofs were performed in an optical glass and the fitted parameters are in good agreement with previous literature data for thermal, optical, and mechanical properties, suggesting that the method is a useful tool for the characterization of a wide range of transparent materials.
Microwave power generated by a spin-torque oscillator in the presence of noise
Authors: Tiberkevich Vasil , Slavin Andrei , Kim Joo-Von
Published: November 2007

An expression for the microwave power generated by a spin-torque oscillator in the presence of thermal noise is derived. This expression, when used in a subcritical (I<Ith) regime, demonstrates that generated power is determined by the noise level and provides a simple way to experimentally determine the threshold current Ith for microwave generation. The same expression gives a good quantitative description of the experimentally measured dependence of the generated power on the bias current p(I) in a moderate supercritical (Ith<I<1.5Ith) range of bias current variation.
Impact of high-pressure deuterium oxide annealing on the blocking efficiency and interface quality of metal-alumina-nitride-oxide-silicon-type flash memory devices
Authors: Chang Man , Hasan Musarrat , Jung Seungjae , Park Hokyung , Jo Minseok , Choi Hyejung , Hwang Hyunsang
Published: November 2007

We have investigated the effect of high-pressure deuterium oxide annealing (HPDOA) on metal-alumina-nitride-oxide-silicon-type flash memory device. HPDOA was performed in a high-pressure wet vapor ambient (N2:D2O=10atm:2atm) at 250°C for 5min. HPDOA devices achieved the improvements of blocking oxide quality as well as tunneling oxide/Si interface quality. The improvement of blocking oxide induced the lower charge loss through the blocking oxide, lower leakage current density, lower erase saturation level, and a larger memory window after the program/erase cycles. In addition, the presence of deuterium at the tunneling oxide/Si improved the interface quality by the formation of Si–D bonds.
Three-dimensional kinetic Monte Carlo simulation of prepatterned quantum-dot island growth
Authors: Pan E. , Sun M. , Chung P. W. , Zhu R.
Published: November 2007

A special prepatterning method is proposed for spatially ordered self-organizing quantum dots on anisotropic semiconductor substrates. Using three-dimensional kinetic Monte Carlo simulations, atoms are deposited with varying intermediate interruption times. We demonstrate the effect of interruption time and long-range anisotropic strain energy on island size uniformity and lateral alignment.
Threshold voltage stability of organic field-effect transistors for various chemical species in the insulator surface
Authors: Suemori Kouji , Uemura Sei , Yoshida Manabu , Hoshino Satoshi , Takada Noriyuki , Kodzasa Takehito , Kamata Toshihide
Published: November 2007

The relationship between the threshold voltage (Vt) stability and the chemical species of the insulator surface was investigated by using organic field-effect transistors with different types of self-assembled monolayers on a SiO2 insulator. The Vt shift induced by gate bias stressing was considerably increased by the introduction of long-chain chemical species to the SiO2 surface. In order to obtain high-performance and high-stability organic transistors, insulator surfaces with short-chain chemical species that can improve transistor performance without degrading stability are required.
Impurity effects on charge carrier transport in various mesophases of smectic liquid crystals
Authors: Ahn Hyonsoo , Ohno Akira , Hanna Jun-ichi
Published: November 2007

Owing to the narrowly distributed density of states, even small amounts of chemical impurities can cause relatively distinct midgap states and significantly reduce the charge carrier transport in liquid crystals. However, the effects of chemical impurities on charge carrier transport have not yet been explained sufficiently because the discovery of electronic conduction in liquid crystals is relatively recent. In this report, we investigate impurity effects in various mesophases of model smectic liquid crystals (2-phenylnaphthalene derivatives) doped with a terthiophene through transient photocurrent measurements. We discuss the effects of chemical impurities on the carrier mobility in various mesophases as a function of temperature and impurity concentration. This study provides guidelines for purity assessment of liquid crystals as organic semiconductors.
Scanning gate microscopy of copper phthalocyanine field effect transistors
Authors: Aoki Nobuyuki , Sudou Kouhei , Okamoto Kazuya , Bird Jonathan P. , Ochiai Yuichi
Published: November 2007

Various techniques are developed to implement ambient scanning gate microscopy (SGM) as a tool for the characterization of organic-thin-film field-effect transistors (OFETs). OFETs comprising copper phthalocyanine have been investigated by this technique and their SGM response has been observed only at the edges of the metal electrodes, thereby providing visualization of the Schottky barrier at the boundary between the organic channel and the metal electrode.
Influence of electric field on spectral positions of dislocation-related luminescence peaks in silicon: Stark effect
Authors: Mchedlidze T. , Arguirov T. , Kittler M. , Hoang T. , Holleman J. , Schmitz J.
Published: November 2007

Spectral positions of dislocation-related luminescence (DRL) peaks from dislocation loops located close to a p-n junction in silicon were shifted by carrier injection level. We suppose that the excitonic transition energies of DRL were reduced by an effective electric field at dislocation sites due to quadratic Stark effect (QSE). The field results from built-in junction field reduced by carrier injection. A constant of the shift, obtained from fitting of the data with QSE equation, was 0.0186meV∕(kV∕cm)2. The effect can explain the diversity of DRL spectra in silicon and may allow tuning and modulation of DRL for future photonic applications.
Barut-Girardello and Klauder-Perelomov coherent states for the Kravchuk functions
Authors: Chenaghlou A. , Faizy O.
Published: November 2007

The Barut-Girardello and Klauder-Perelomov coherent states for the Kravchuk functions are constructed. It is shown that the resolution of unity condition is satisfied for both of the coherent states. Also in the N+1-dimensional Hilbert space spanned by the Kravchuk eigenstates, the appropriate measure and analytic function are obtained.
Optical upconversion devices based on photosensitizer-doped organic light-emitting diodes
Authors: Lu Jiashu , Zheng Yuan , Chen Zhijian , Xiao Lixin , Gong Qihuang
Published: November 2007

The optical upconversion of infrared light to visible light has been achieved in photosensitizer-doped organic light-emitting diodes, where poly(N-vinylcarbazole) doped with infrared photosensitizer of 2,4,7-trinitro-9-fluorenylidene)malonitrile was used as hole-transporting layer, and tris(8-hydroxyquinoline) aluminum acted as both emitting and electron-transporting layers. Both electroluminescent intensity and current were enhanced under infrared illumination. The enhancement ratio was obtained as 2.45 times for electroluminescent emission and 1.45 times for current. This work brought forth a prototype design for novel flexible organic optical upconversion device used in near infrared field.
Anomalous temperature dependent elastic moduli of Ce-based bulk metallic glass at low temperatures
Authors: Yu P. , Wang R. J. , Zhao D. Q. , Bai H. Y.
Published: November 2007

We report the abnormal temperature dependent elastic moduli of Ce-based bulk metallic glass (BMG) at low temperatures. Unlike other BMGs with stiffness mode, the Ce-based metallic glass exhibits an anomalous softening longitudinal acoustic mode with the decrease of temperature. Particularly, the bulk modulus shows a continuous decrease upon cooling indicating the softening of the BMG, which is completely different from that of other metallic glasses and conventional alloys. The physical origin of this abnormal elastic behavior is attributed to the alterative valences and electronic configurations at low temperatures.
The effective use of exploration techniques for ore search
Authors: Cook D.R.
Published: November 2007

It has been said that mineral exploration is the "Triumph of Hope over Reality". I suggest that mineral explorationists can improve their confidence in discovery through a sound scientific and good business approach to exploration.
Lightning strokes and magnetic surveys
Authors: Facer R.A.
Published: November 2007

During a field magnetic survey of the Canobolas Mountains volcanic complex near Orange, Central Western New South Wales (Facer, 1968), the sites of several lightning strokes were detected. These showed up as very strong , localized anomalies , and were complemented by evidence additional to the field magnetic observations. Four examples will be commented on here, being discussed in the order in which they were "discovered". Readings were taken using a McPhar M500A fluxgate magnetometer.
Geoseis shooting in the cooper basin
Authors: Gray D.
Published: November 2007

The use of Geoflex (or Cordtex or Primacord, to use more familiar terms) is not new: however, it is a recent enough innovation to be of some interest when it is introduced into a new basin or a new set of circumstances. The case at hand represents, as far as we know, the first adaption of the technique to the desert areas of Central Australia. Again, as far as we know the nearest prevlous use was in south western Victoria , about 750 miles distant where, of course, the terrain and operating conditions varied greatly.
Possible consequences of a dwindling geomagnetic field
Authors: Crain I.K.
Published: November 2007

Recently, Facer (1971) has discussed the problem of the dwindling of the geomagnetic field, and estimated that in 810 years (AD 2781) the dipole and non-dipole fields will be roughly equal and that in 1931 years (AD 3902) the dipole field will be essentially zero. Various authors (Crain and Crain, 1970; Cox, 1968; Parker, 1969) have suggested that these conditions are highly favourable for the production of geomagnetic reversals.
A cost-probability approach to Induced Polorization in Australia
Authors: Shalley M.J.
Published: November 2007

The performance of Induced Polarization in Australia over the last decade has not fulfilled expectations. A general lack of theoretical understanding of the physical principles involved has resulted in poor assessment of the limitations of interpreted data.
Total interpretation - further comments
Authors: Facer R.A.
Published: November 2007

Basic agreement is reached with the thoughts expressed by Richards on total interpretation. In support of his discussion the importance of "geology" in exploration geophysics interpretation is emphasized. Assessment of data is often improved by total interpretation in both "pure" geophysics and mineral exploration. It is important that education in exploration geophysics interpretation is based on the concept presented by Richards.
Coupling, masking and detection for induced polarization surveys in areas where low resistivity surface layers occur
Authors: Baird J.G.
Published: November 2007

Detection of sulphide mineralization by Induced Polarization in many areas of Western Australia is restricted by thick, low resistivity, weathered zones. Signal attenuation due to electromagnetic coupling and masking requires special consideration in design of electrode configuration. Two field examples are discussed.
Research in exploration geoscience: The AMIRA model
Authors: May J.R. , Bailey J.D. , Cucuzza J.
Published: November 2007

The paper summarises the exploration related R&D that has been managed by AMIRA/APIRA and gives details of the complex, market oriented process used to develop new projects.The process is illustrated by three case studies taken from the more than 70 exploration projects completed.The Gold Deposits of North Queensland Project conducted by James Cook University studied the various styles of gold mineralization. The Rock Magnetism project undertaken at CSIRO Division of Exploration Geoscience allowed both general and specific research themes to be undertaken in parallel with confidential proprietary investigations on sponsors' drill core. The Palaeogeographic Mapping project undertaken at the BMR Division of Continental Geology provided sponsors with palaeogeographic maps including interpretation and structural information of 70 time slices.Some of the benefits of the AMIRA/APIRA approach are discussed as well as some of the difficulties which arise in ensuring companies obtain appropriate benefits from their sponsorship.
Interpretive evaluation of migrated data
Authors: Yilmaz Ö.
Published: November 2007

In practice, migration of seismic data requires decision making with regard to: (1) Different migration strategies ? 2-D/3-D, post-stack/prestack, and time/depth migrations; (2) different migration algorithms for a given strategy ? integral, finite-difference and frequency-wavenumber methods; (3) different parameters for a given algorithm ? aperture width, depth-step size, stretch factor; (4) the input data ? profile length, noise content, spatial aliasing and boundary effects; (5) and finally, migration velocities ? the weak link between the seismic method and the subsurface geology that the former tries to image.The seismic interpreter, whose main role is to infer subsurface geology from the migrated data, normally should not be burdened with the decisions concerning the above factors. Fortunately, migration results often are self-evident; a feature considered geologically implausible on a migrated section can be associated with one or more of the above factors. Based on large number of field data cases, I will discuss each of these factors and provide some generally applicable guidelines for migration that an interpreter can invoke in practice.
Generation of conductivity-depth pseudo-sections from coincident loop and in-loop TEM data
Authors: Fullagar P.K.
Published: November 2007

A computationally-efficient transformation has been developed to convert coincident loop or in-loop TEM profiles to apparent conductivity versus depth pseudo-sections. The transformation is based on the depth to the maximum physical current induced in a half-space, not on attributes of abstract current filaments. Tests on both synthetic and field data indicate that these pseudo-sections provide a useful qualitative portrayal of conductivity structure, thus facilitating first-pass interpretation of TEM in mapping applications.
Predicting the transient EM response of complex structures using the compact finite-element method
Authors: Raiche A. , Sugeng F.
Published: November 2007

The compact finite-element model (CFEM) method has been used to model the transient EM (TEM) response of an earth model consisting of a heterogeneous prism in a two-layered, conducting halfspace. The prism can be deformed to simulate any angle of dip and plunge without the effect of 'staircasing'. The present implementation of CFEM (program Samaya) allows for a horizontal-loop transmitter with arbitrarily oriented magnetic dipole receivers which may be on the surface or downhole. Samaya can be run on workstations or on augmented IBM PC-AT's (or clones).The use of Samaya should allow the TEM method to be used to solve a greater range of structural and target identification problems than is possible with existing interpretation aids. Having the ability to predict the TEM response of an expected geology means that surveys can be designed to yield optimum information. The program can also be used to validate hypothesized structural models against field data.The paper concludes with a discussion of the computed downhole TEM response of a dipping target.
Layered model inversion of central-loop EM soundings near a geological contact
Authors: Wilt M.J. , Williams J.P.
Published: November 2007

Central-loop time-domain EM is a widely used method for depth sounding due to its relative insensitivity to lateral changes in conductivity. Near a geological contact, however, this method produces distortions which are not easily distinguished from the layered-model response that is sought by inversion. In this paper we examine this problem for a simple two-dimensional model. Central-loop TDEM data were collected over a vertically dipping quarter-space model using a scale model system developed at U C Berkeley. Both vertical and horizontal magnetic field measurements were made within 250m radius loop transmitters with soundings spaced from 50 to 200m apart along a profile orthogonal to the contact. The sounding data from individual stations were then fitted to layered models using a standard least squares algorithm and the resulting layered models were plotted as a pieced-together cross-section. For the vertical field data the contact effect appears as a loss in field strength at lag times that depend on the distance from the contact and the conductivity of the quarter-space. At stations more distant from the edge the fields are reduced only at later times, whereas closer to the contact the effect shifts to earlier times and increases in magnitude. The layered model inversions seem to interpret this distortion as a fictitious resistive layer that grows more shallow and more resistive as the contact is approached. For stations within one loop radius of the contact the entire sounding is affected and the layered model inversions show little similarity to the true section. The scale model data also indicate that horizontal magnetic fields in the centre of the loop are diagnostic of the contact effect. These data may be used to determine which parts of a sounding may be confidently used for inversions. We have empirically found that for values of the TDEM tipper (Hx/Hz) greater than 0.5 the layered-models produce unreliable results.
Application of high resolution airborne geophysics to epithermal gold exploration in Northeast Queensland and Coromandel, New Zealand
Authors: Webster S.S. , Henley R.W.
Published: November 2007

High resolution airborne geophysical data over broad areas have been found to optimize exploration for epithermal gold deposits in differing geological environments.Genetic exploration models may be tested in favourable sites by the recognition of geophysical signatures. These signatures reflect structural, lithological and alteration patterns arising from controls on ore deposits and can be applied at regional or detailed scales, using the same data set.At regional scale (e.g. 1:100,000) the magnetic data reflect the regional tectonics and divide the area into domains for the application of appropriate genetic models. At prospect scale (e.g. 1:25,000) the radiometric data allow the extrapolation of poorly outcropping geology to provide a cost-effective mapping technique. The magnetic data can be used to supplement this interpretation or can be used to target deeper sources for direct investigation by drilling.
The application of ground and airborne magnetic methods to exploration and geological mapping in the Yilgarn goldfields of Western Australia
Authors: Williams P. , Stanley J.M. , Cattach M.K.
Published: November 2007

The performance of both ground level and airborne magnetometer systems have been greatly improved as a result of advances in digital electronics, accurate automatic positioning devices and the introduction of high resolution, fast sampling caesium magnetometer sensors. Multiple sensor, low heading error airborne surveys are now being performed at relatively low ground clearance levels. The development of the TM-3, automatic positioning ground magnetometer system has made it practical to adequately sample all spatial frequencies present in the ground level magnetic field thereby acquiring the full spectrum of magnetic information.Approximately a one square kilometre area near Coolgardie in WA has been chosen as a case-study area for investigating the relative effectiveness of conventional and new, ground level and airborne, magnetic surveying techniques. The site is geologically typical of the auriferous environments within the Yilgarn block.This is the first time that such a comparative study has been made using all of the most common magnetic survey sampling standards available to the exploration industry. Data collected from conventional, government sponsored regional airborne survey and ground level proton precession magnetometer surveys has been image processed using state-of-the-art techniques. Data from a high quality, low level, multiple sensor, airborne, caesium magnetometer survey and a "broad spectrum" (sampled at a density of 200,000 measurements per square km) ground level caesium survey have similarly been processed. Geological control has been obtained from an extensive drilling and costeaning program.This data set has provided a definitive comparison in cost spent, speed of survey and information obtained from each survey.
The application of the mise-a-la-masse electrical technique in Greenstone belt gold exploration
Authors: Polomé L.G.B.T.
Published: November 2007

Most of the gold deposits in the Barberton Greenstone belt of South Africa are relatively small and in structurally complex geological areas.The mise-a-la-masse electrical technique, where a current electrode is earthed in a mineralised zone, was used on one of our exploration projects consisting of a sulphides/gold-bearing carbonaceous banded iron formation within a succession of mafic, ultramafic and sedimentary rocks. The technique was successful in delineating individual mineralised units within a broad lithological sequence. During the survey, electrical potential measurements were recorded on surface, in underground drives and in twenty five boreholes. Measurements were also repeated by earthing the mineralised zone in a number of boreholes. Major discontinuities were recognised within the ore zones and used to interpret geological structures. These were then used to define specific units for ore reserve calculations and the application of selected mining techniques.
A swept-frequency borehole source for inverse VSP and cross-borehole surveying
Authors: Kennedy W. , Wiggins W. , Aronstam P. , Hardage B.A.
Published: November 2007

A swept-frequency borehole seismic source has been constructed and tested that consists of a portion of the borehole isolated from the remainder and driven to build up pressure oscillations by resonance.The length of the isolated portion is changed to vary the resonant frequency. The source radiates an approximately isotropic P-wave whose total energy is comparable in magnitude to that created by a surface vibrator truck. Strong shear waves are also generated.The source has been tested over a frequency range of 30 to 120 Hz, but the design can be operated from 15 to 500 Hz. Because the driven section of the borehole is isolated, strong tube waves are not generated. No damage to the casing-cement bond has been observed after prolonged operation of the source at a fixed depth.This source has the strength and uniform radiation pattern to suit it for both inverse VSP and cross-borehole surveying.
Geophysical and image processing methods for detection of fireholes in brown coal, Latrobe Valley
Authors: Pettifer G.R. , Djordjevic N. , Heislers D. , Schaeffer J. , Withers J.A.
Published: November 2007

Fireholes at the top of the thick Latrobe Valley brown coal seams pose a geotechnical hazard to overburden dredges and reduce coal reserves. Overburden thickness (typically 10 to 15 m) is up to 50 m in the fireholes, which are from 20 to hundreds of metres in diameter and are infilled with baked clays, soft lacustrine clays and alluvial deposits.Given the complexity of firehole geometry and overburden geology, firehole definition prior to overburden stripping, by drilling alone, is expensive and is not definitive. To improve firehole exploration, geophysical methods were tried in a test area with good borehole control (115 holes), near Morwell open cut.Grid geophysics (20m. � 20m., 2805 grid stations) using gravity, EM34 20 m loop conductivity and high resolution magnetics gave very good results. Shallow seismic reflection methods were not successful.Residual gravity defined overburden thickness variations best with gravity highs of up to 6.5 micrometres/sec2 over the fireholes. EM conductivity showed reasonable correlation with overburden thickness, with EM conductivity highs over fireholes infilled with lower resistivity lacustrine clays and silts. High resolution magnetics using a TM-3 caesium vapour magnetometer, despite high cultural interference, showed broad, low amplitude highs over fireholes where higher susceptibility baked clays are thickest. The three geophysical data sets and overburden data were gridded (5m. � 5m.) and the grids dumped to a MicroBrian image processing system. Conventional image processing analysis was carried out to compare, enhance, filter, display and classify the complementary data sets. A classification scheme for overburden type based on geophysical responses plus a routine firehole exploration methodology using residual gravity, EM, magnetics, progressive drilling data and the image processor was devised to reduce drilling costs and increase exploration confidence. The case history presents the results of the grid geophysics and image processing approach.
Seismic reflection investigations of the Hellyer orebody and Que-Hellyer volcanics, North West Tasmania
Authors: Read J.J.
Published: November 2007

Two separate seismic reflection surveys have been conducted over Aberfoyle Resources Hellyer orebody and the enclosing Cambrian Que-Hellyer volcanics. The initial survey, conducted as a test case to determine if seismic reflection techniques could detect massive sulphide orebodies at depth, successfully identified the Hellyer orebody, which was found to have a characteristic seismic expression. Identification and mapping of stratigraphic units within the Que-Hellyer volcanics was also possible due to the good geological control available.The second survey did not successfully identify the Hellyer orebody, although some information relating to the structure of the enclosing basin could be inferred from the seismic data. Due to data degradation conventional seismic interpretation techniques could not be applied to the second survey.High resolution seismic surveys can detect massive sulphide orebodies if low velocity overburden problems are eliminated and high frequency data is collected. High resolution surveys can also provide structural and stratigraphic information between widely spaced drill holes in volcanic terrains.
Coal mining applications of ground radar
Authors: Turner G. , Yelf R.J. , Hatherly P.J.
Published: November 2007

Coal due to its low conductivity and high electromagnetic contrast with surrounding rocks is an attractive medium for study by ground radar. Results of trials in Australian coal mines show that ground radar can be a useful tool for horizon control, locating old underground workings and mapping geological structure both from the surface and within mine roadways.
Thin-sheet EM modelling of the Tasman Sea
Authors: Heinson G.S. , Lilley F.E.M.
Published: November 2007

The Tasman Project of Seafloor Magnetotelluric Exploration (TPSME) took place between December 1983 and April 1984 (Filloux et al., 1985; Ferguson et al., 1985; Lilley etal., 1989). Seven magnetotelluric and two (additional) magnetometer sites spanned a range of tectonic features across the Tasman Sea. Initial analysis by Ferguson (1988) indicated large-scale three-dimensional induction effects to be present in the data. It was concluded that the most probable causes were the continental margin effect and changes in bathymetry.In the present paper, a method is presented of modelling the salt water of the Tasman Sea and adjoining oceans as a thin sheet of variable lateral conductance, which overlies a series of uniform layers representing the solid Earth. The theory and a suitable computer algorithm were developed in a group led by J. T. Weaver at the University of Victoria, B.C., Canada. Many of the features present in the TPSME data are reproduced by this method, and with a greater understanding of induction processes in the ocean which is thus obtained, it is possible to remove three-dimensional effects from observed data. The TPSME data are then solely a measure of the response of the Earth directly beneath the observing sites, and one-dimensional modelling techniques may be used to determine the conductivity structures.
Positive gravity anomaly over the Sydney basin
Authors: Qureshi I.R.
Published: November 2007

A prominent positive gravity anomaly overlies the Macdonald trough in the Sydney basin. Allowing for isostatic compensation and the effect of sedimentary rocks, the anomaly is determined to have an amplitude of 440 GU (mms-2) and a width of 60 km. The anomaly is smoothed using cubic splines, FFT and IFFT. It is interpreted by a large mafic body of density 2.9 g cm-3 underlying the basin to a depth of 13.5 km. A 12 km wide zone with a small positive density contrast underlies the body within the lower crust.The steep western boundary of the body represents a major basement fault underlying the Lapstone monocline and Kurrajong Fault System.The anomaly is a member of the Meandarra Gravity Ridge which marks a zone of crustal extension within which dominant nature of intrusion is mafic in character.
Comparison of magnetic and gravity terrain models
Authors: Williams J.P. , Grauch V.J.S.
Published: November 2007

Modelling of magnetic terrain and comparison with actual data is an efficient method for assessing large sets when residual anomalies are important. The technique of Blakely (1981) which utilises a rapidly converging series of Fast Fourier Transforms is an efficient and sufficiently accurate method for this assessment.The technique has been applied to a data set at Kilkivan, south eastern Queensland. Here the magnetic sources are near horizontal Triassic volcanic flows unconformably overlying a non- magnetic Palaeozoic basement.Geological control is good so that it is possible to model the bottom of the flow. It is postulated that the difference between the calculated and actual data represents paleochannels in the basement. Similar techniques applied to gravity data have not been as successful.
'Rig 3D' ? A revolutionary technique looking for a case history
Authors: Evans B.J.
Published: November 2007

Three dimensional (3D) marine seismic surveying is expensive and often a lengthy and technically difficult survey to perform. It is therefore only executed when an economically viable discovery is made. An alternative technique is offered which may be used when a marginally economic discovery is made. The technique is inexpensive compared to the conventional full 3D marine survey; it is cheaper than reconnaissance surveying and two boat operations, and provides a 3D migrated annular volume just over 3 kilometres in diameter for the approximate price of a single offset vertical seismic profile (VSP).The technique uses the exploration drilling rig as the energy source platform, the rig supply vessel as the receiver, and the site location system as the 3D navigation network. In using equipment conventionally mobilized with each drilling rig relocation, costs are substantially reduced and a larger portion of the 3D seismic exploration budget may be transferred to the engineering/drilling budget.Failure of the technique to be trialled is due to the conservatism found within the industry rather than technical considerations.
Stacking and velocity estimation for 3-D surveys
Authors: Kennett B.L.N. , Collins J.A. , Cao S.-H.
Published: November 2007

The standard approach to stacking and velocity estimation for 3-D seismic reflection surveys is to organise the data by CMP bins and then apply techniques originally developed for 2-D surveys. The benefit of conventional binning is primarily in the display of the 3-D data volume.Velocity estimation can be carried out directly with 3-D data provided the geometry of the survey is readily available. To minimise the effects of dip it is still desirable to restrict the location of the CMP's to lie in a restricted region without the requirement of bins of fixed size. Since the stacking velocities are azimuthally dependent, the trace gathers for velocity estimation over a narrow azimuth window should be chosen for that purpose rather than be based on stacking bins. Once the elliptic variation of stacking velocity with azimuth has been estimated, the seismic traces can be simultaneously stacked and interpolated onto a regular grid. The interpolation procedure is of most significance for short reflection times. The regular array of traces is particularly beneficial for the development of 3-D self-consistent statics procedures exploiting recent developments in large scale inverse problems.
Depth conversion using a normalized velocity ? lithology correlation
Authors: Carter M.D.
Published: November 2007

In areas where the exploration objectives require a reliable depth conversion algorithm, two methods are commonly used. In the best of the average velocity techniques, the values of average velocity are derived from the seismic velocities. For the "layer cake" method, the values of interval velocity are from either well velocity surveys, seismic times and well depths or seismic velocities. In both methods, the success of the depth conversion is dependent upon the correlation between the interval velocity and the geology of the layer.
Reconditioning marine seismic data for interactive interpretation
Authors: Carter M.D. , Kruppenbach J.A. , Mobley S.L. , Matthews R.H. , Lawrence E.
Published: November 2007

The historical interpretation approach is based upon time and amplitude. Using the modern interpretive workstation, the full range of the seismic attributes can be examined in varying color and spatial distribution. Examples of traditional seismic data displayed using conventional methods are shown before and after workstation manipulation, with striking results. The paper will also address procedures for the economical collection of additional data which will reinforce older available data, as well as planning cost effective acquisition of new data.
Porosity from seismic data, a geostatistical approach
Authors: Doyen P.M. , de Buyl M.H. , Guidish T.M.
Published: November 2007

A geostatistical modelling technique called cokriging is used to describe the lateral variations of porosity, f, in a synthetic and a real reservoir. Using this method, an error-qualified porosity model is estimated for each of the two reservoirs from sparse well porosity measurements and seismically derived velocities. The method capitalizes on the high spatial density of the seismic measurements and on their correlation with f. Compared with conventional reservoir models derived solely from sparse well control, the seismically consistent models are better spatially constrained and, hence, provide more detailed and accurate reconstructions of the porosity variations.
Multiple attenuation: some current techniques
Authors: Wardell J. , Whiting P.
Published: November 2007

Multiple attenuation techniques have to be based on some difference between the multiples and the primary reflections. The two major differences that are exploited are firstly velocity, and secondly the fact that multiples are periodic sequences of events, and hence are predictable, while the primaries are non-periodic. The widely used frequency-wavenumber (F-K) domain techniques rely on velocity difference only, but a recent variation of this method also makes use of any difference in dip between primaries and multiples to give significantly greater multiple attenuation. For short period multiples, velocity differences may be insufficient for much attenuation, and the process has to be based on the multiple's periodicity, using some type of long predictive deconvolution operator. One problem with this approach is that the multiple period varies with time, particularly at long offsets. Transforming the record to the tau-p domain removes this variation however, allowing more effective deconvolution of the multiples. Another recent approach is to model a multiples-only record by wave equation methods, and subtract it from the recorded data. At present however, this is limited to well defined multiple generators, such as the water layer. With the variety of multiple attenuation processes available today, the geophysicist needs to understand the types of multiple problem to which each is most suited, in order to select the technique most applicable to his data.