Thermal Cleaning Research Articles

Measurement of GaAs surface oxide desorption temperatures

Auger analysis of oxidized GaAs surfaces, heat treated in vacuo, has been used to establish an accurate value for the oxide desorption temperature Tox. Major differences are found in the value of Tox for the surface oxides produced by thermal and ozone oxidation: 582±1 °C and 638±1°C, respectively. These temperature differences are also confirmed by reflection high-energy electron diffraction observations of the thermal cleaning of GaAs substrates prior to epitaxial growth in a molecular beam epitaxy system. It is suggested that the measured temperatures can be used in establishing appropriate growth conditions for ‘‘indium-free’’ GaAs substrates during molecular beam epitaxial growth.

AES and PYS studies of the polar GaAs(111) as surface after thermal cleaning in ultrahigh vacuum

Auger Electron Spectroscopy (AES) and Photoemission Yield Spectroscopy (PYS) have been used in the investigations of elemental composition and electronic properties of the polar GaAs-(111) As surface after thermal cleaning by electron bombardment heating at 770 K in an ultrahigh vacuum of 10 −7 Pa. The surface concentration of As was 0.01 ML which corresponds to the (1 × 1) and weak (3 × 3) atomic structure, whereas the work function and absolute band bending were 4.05 ± 0.02 eV and −0.21 ± 0.04 eV, respectively. Moreover, two filled electronic surface state bands localized in the band gap below the Fermi level EF and in the upper part of the valence band were observed which have been described as the dangling-bond surface state and back-bond surface state bands, respectively.

Paleomagnetic study of the Late Ordovician–Early Silurian platform sequence of Anticosti Island, Quebec

Eighteen sites (152 samples, 441 specimens) from the Late Ordovician — Early Silurian sequence of Anticosti Island were studied paleomagnetically. Six sites were collected in the Vauréal Formation, seven in the Ellis Bay Formation, three in the Becscie Formation, and one each in the Gun River and Jupiter formations. The lithologies sampled consisted of limestones, sandy limestones, marls, and sandy calcareous shales drawn from a sedimentary platform sequence of predominantly inter-bedded limestones and shales. The specimens were demagnetized in alternating fields (AF) and thermally and were found to be quite stable. Two components of magnetization were isolated. The memory carrier is fine- to medium-grained magnetite; AF and thermal cleanings are about equally efficient. The average directions of residual magnetization are D = 167°, I = 37°, α95 = 18°; D = 315°, I = −24°, α95 = 17 °for components B and C, respectively. The corresponding paleopoles for the B and C components are 129°E, 19°N (dp = 12°, dm = 21°) and 341°E, 16°S (dp = 10°, dm = 18°).Component A is most probably composed of component C and the present Earth's field (PEF); it was chiefly observed in the more altered Vauréal Formation and in the altered top part of the cored samples. The most common component in the Ellis Bay, Becscie, Gun River, and Jupiter formations is component C. Component B is mainly found in the Becscie and Ellis Bay formations. Both components B and C are isolated in the 300–500 °C and 10–40 mT ranges. Component C is either older than component B or synchronous and of reverse polarity to component B. If this last alternative is correct, then the Ordovician and Silurian formations are overprinted by a pre-Kiaman magnetization. The more plausible scenario is the following: component B is secondary, of pre-Middle Carboniferous age, and overprinted on an older secondary magnetization (component C), the acquisition age of which is confined to the Silurian–Carboniferous time interval.

Analysis of Thermoluminescence Glow Curves of Mineral Sphene and Epidote for Radiation Damage Studies

Abstract Thermoluminescence (TL) properties of sphene and epidote are of interest in studies related to their radiation damage. Natural and artifically induced TL of these minerals has, therefore, been investigated. Both minerals exhibit complex glow curves with several overlapping peaks. The Tm-TSTOP thermal cleaning procedure has revealed three peaks in the ? ray induced glow curve of each mineral. That these peaks obey second order kinetics was indicated by the continuously slanting structure of the Tm-TSTOP curve. The TL parameters E and s have been calculated using (i) the initial rise method, and (ii) the glow-peak shape method. In general, the values of E calculated by the first method are found to be higher than those from the second. The TL curve-fitting method is also applied in order to calculate these parameters and to serve as a cross-check on the results.

A paleomagnetic study of Rangitoto Island, Auckland, New Zealand

Abstract A paleomagnetic study has been made of 99 specimens from 11 sites in the recent basalt lavas of Rangitoto Island. The measured natural remanent magnetisation (NRM) had a formation mean direction of 1.9°0E, –62.1°, α95 = 2.6°; thermal cleaning changed the formation mean NRM direction only slightly to 0.2°E, –61.7°, α95= 1.8°. The densities, magnetisations, and magnetic susceptibilities measured for each site are recorded. Since Konigsberger's Qn ratio is large in every case, it follows that the aeromagnetic total force anomaly is symmetrical about the geographic meridian. Paleomagnetic declinations, at each site, when compared with historically recorded declinations of the geomagnetic field, confirm the dating results previously obtained by the l4C method; that is, Rangitoto was an active volcano between A.D. 850 and A.D. 1800, with a maximum of activity between A.D. 1200 and A.D. 1500. It is inferred that near Auckland the geomagnetic field has changed direction at approximately 2.87 × 10-2 deg/y...

Interaction of monochlorinated phenols with granular activated carbon

The validity of an empirical model to estimate the adsorption affinity of a solute from its acidity constant (pKa) was confirmed through study of the adsorption of monochlorinated phenols on granular activated carbon.Neglecting possible adsorbate fragmentation, simplified desorption kinetic data were obtained for the massive thermal release of the investigated solutes. The resulting non-isothermal kinetic parameters confirm that thermal cleaning of the adsorbent surface is a phase-boundary controlled process involving the interruption of physical interactions according to the calculated “activation energy” values.

Paleomagnetism of the triassic nicola volcanics and geotectonics of the quesnellia subterrane of terrane I, British Columbia

The Triassic Nicola Volcanics are the oldest strata in the Quesnellia Subterrane of composite Terrane I which is located in the southcentral Cordillera of British Columbia. A paleomagnetic study using AF and thermal demagnetization methods of 563 speciments from 56 sites in three petrologically and tectonically distinct belts of the Nicola isolates two remanence components residing dominantly in hematite. The prefolding A component found after 560°C thermal cleaning gives a pole position of 11.3°W, 52.7°N ( δ p = 4.7°, δ m = 7.2°), and appears to be caused by alteration associated with major Early Jurassic intrusive events. The dominant postfolding B component is best defined by 565°C thermal cleaning and gives a pole of 303.0°W, 82.5°N ( δ p = 6.6°, δ m = 8.6°). It likely reflects alteration associated with Eocene volcanism. Combined with previous paleomagnetic data, these results indicate that Quesnellia was translated northward by ∼ 13° of paleoatitude along with the rest of Terrane I and rotated ∼ 45° clockwise during Late Cretaceous to Oligocene time with ∼ 7° of the translation and ∼ 15° of the rotation occurring during Eocene to Oligocene time.

Magnetostratigraphy of the Red Sandstone Creek section ‐ Vail, Colorado

Samples for paleomagnetic study were collected from the area of Red Sandstone Creek (Lat. 39.73°N, Long. 253.6) near Vail, Colorado, in hopes of locating the stratigraphic base of the Kiaman Reversed Interval to within a few meters. Previous workers had sampled the same upper Pennsylvanian and Permian Minturn and Maroon Formations in this section and had placed the base of the Kiaman at 91m to 213m above the Minturn Formation. The interval from 276m below to 420m above the Maroon/Minturn contact was sampled in the present study at one meter intervals where possible. Of the 171 samples collected, only 2 had near normal components. The 2 were not consecutive and the normal components were removed easily by thermal cleaning or were shown to be a viscous overprint of the present field. The previous workers were apparently misled by a lack of magnetic cleaning of their samples. The conclusion of this study is that the base of the Kiaman must be stratigraphically lower in this section. The pole position from the sampled section is Lat. 42.6°N, Long. 115.4°E, A95=2.75 for N=145 samples.

A study of silicon MBE on porous silicon substrates

The defect structure of Si MBE layers grown on porous silicon substrates depends critically on the technique for cleaning the substrate surface. Cross-sectional TEM studies demonstrate that a combined sputter-clean and thermal cycle markedly reduces the density of microtwins and dislocations in the epitaxial layer when compared with simple thermal cleaning. X-ray diffraction studies show the porous silicon layer to be lattice-matched to the underlying (100) bulk silicon substrate in the plane of the wafer so that misfit dislocations are not expected in the epitaxial layer. However, both the lattice parameter of the porous layer in the direction normal to the wafer and the thermal stability of the porous layer in vacuum, depend upon the resistivity of the starting wafer. The photoluminescence of a 4-μm MBE layer grown on a sputter-cleaned, high resistivity substrate is still dominated by recombination at dislocations.

Palaeomagnetic study of the Nagssugtoqidian mobile belt in Central-West Greenland

This paper reports a palaeomagnetic study of amphibolite and granulite facies basement rocks across a 60 km wide north-south traverse through the Nagssugtoqidian mobile belt in West Greenland, which incorporates the c. 2500 Ma Itivdleq shear belt, the c. 1800 Ma Ikertôq shear belt, and adjoining terrains. It also integrates the results with earlier investigations of the belt to produce a composite record of the magnetic field during uplift and cooling of the terrain through c. 600–500°C at c. 1750–1600 Ma. Progressive a.f. and thermal cleaning of samples from 81 sites identifies a range of magnetic components. Lowest blocking temperature remanences in Nagssugtoqidian (c. 1700 Ma) amphibolite facies rocks yield steep W to N positive components residing in magnetite. Granulite facies rocks formed at c. 1800 Ma generally have a dual record incorporating steep N to NW positive components unblocked by 580°C and shallow E-W directed components of dual polarity only unblocked close to the Curie point of haematite. A common feature of relict c. 2500 Ma amphibolite and granulite facies terrains is a progressive movement of sample directions back along a palaeofield migration path with treatment and is interpreted to represent the recovery of a discrete spectrum acquired during a.p.w. Areas with a distributed spectra through the critical range of blocking temperatures, altitude-controlled sections, and blocking temperature relationships all record consistent a.p.w. during the interval of uplift-related cooling. The collective data define a clockwise palaeofield migration path between D = 174, I = 32°, and D = 348, I = 66° referred to as the ‘A’ magnetisation. The equivalent palaeopoles define one limb of an a.p.w. loop conforming to other Laurentian poles assigned to the interval 1750–1650 Ma and widely represented as a post-Hudsonian overprinting or cooling remanence. Shallow E-W directions, designated ‘B’, predominate in late tectonic diorites and are therefore younger than 1700 Ma; they appear to represent a localised reheating event near the northern margin of the Ikertôq shear belt, possibly related to this magmatism, which produced the hemoilmenite phases. The equivalent palaeopoles are provisionally interpreted to represent part of the return path of the APW loop because they are coincident with other poles dated c. 1630 Ma. Collectively the palaeofield migration data from all studies define a thermal dome broadly coincident with the Ikertôq shear belt, but it is not possible to isolate the contribution of components of vertical movement along faults running through the belt to this regional effect.

New paleomagnetic data from carboniferous volcanics and red beds from central New Brunswick

It has long been argued, on the basis of paleomagnetic data derived from Devonian, Carboniferous and Permian lithological units from eastern North America that a sinistral megashear of Carboniferous age parallels and lies within the faults delimiting the Appalachian‐Caledonian chains. Recent paleomagnetic studies in the northern Appalachians have cast doubt on the models of a Carboniferous offset. The geologic evidence suggests that only a small amount of dextral (and not sinistral) strike slip has occurred on faults which are parallel with pre‐Acadian paleogeographic realms. The purpose of this paleomagnetic study is to test the validity of the proposed left‐lateral motion at one of the sites of its presumed passage in central New Brunswick. Six sites (80 oriented specimens) in Carboniferous red beds and volcanics were collected on both sides of the Fredericton Fault and other parallel faults. After AF and thermal cleaning, the mean direction of magnetization is 158° + 38°; the fold test is indecisive. The corresponding paleopole is 135°E, 21°N and the paleolatitude 20°S. The paleopole positions and paleolatitudes are not significantly different on either side of the Fredericton fault and no left‐lateral motion was detected by paleomagnetic means. As no such motion was detected in south‐central New Brunswick and Newfoundland, it is possible but unlikely that it took place in northern New Brunswick and in the western Gaspé Peninsula. This contribution is useful in discussing possible motions of Acadia.

Paleomagnetic and petrologic evidence bearing on the age and origin of uranium deposits in the Permian Cutler Formation, Lisbon Valley, Utah

An approximate age for uranium deposits in red beds of the Permian Cutler Formation, Lisbon Valley salt anticline, Utah, was obtained using paleomagnetic techniques. Progressive thermal demagnetization of samples of mineralized sandstone isolates stable magnetization components having high (≳400 °C) unblocking temperatures that define a tilt-corrected mean direction of D = 358.1°, I = 65.5°, α 95 = 3.3°. This direction is close to expected Late Cretaceous to middle Tertiary mean directions at Lisbon Valley. In contrast, thermal cleaning of samples of unmineralized sandstone isolates tilt-corrected southeasterly, shallow mean directions (D = 140.5°, I = −9.5°, α 95 = 8.6°, and D = 155.9°, I = −4.4°, α 95 = 10.9°, for two localities in the Lisbon Valley area). These results are closely similar to results from the Cutler Formation elsewhere on the Colorado Plateau and from other Lower Permian strata in North America. In unmineralized sandstone, the stable remanent magnetization is carried predominantly by martite of postdepositional or detrital origin, whereas in mineralized sandstone, the stable magnetization is carried largely by authigenic specular hematite as uranium- and vanadium-bearing clusters in interstitial areas, and it thus reflects the time of mineralization. Partial dissolution of martite grains and grain-coating ferric oxide pigment prior to formation of abundant interstitial specular hematite has minimized or eliminated the influence of late Paleozoic magnetic components in mineralized sandstone. These results, combined with information on the structural development of the Lisbon Valley area and on nearby uranium deposits in the Triassic Chinle Formation, suggest that the growth of the Lisbon Valley anticline during Late Cretaceous to early or middle Tertiary time promoted oxidative destruction of Chinle orebodies and led to a redistribution of uranium and iron from the Chinle into the Cutler. Acidic solutions generated during destruction of sulfide minerals in Chinle orebodies may account for the simultaneous transport of significant quantities of iron and uranium and for the partial dissolution of martite in the Cutler host beds. Neutralization of these solutions by reaction with host-rock constituents (especially calcite) caused precipitation of amorphous ferric oxide, which incorporated uranium by adsorption and which aged to form specular hematite.

Growth of Sr1−xBaxF2 films on InAs by molecular beam epitaxy

Heteroepitaxial films of Sr1−x BaxF2 have been deposited onto (001), (110), and (111)B oriented InAs substrates by molecular beam epitaxy. The epitaxial growth was studied by reflection high energy electron diffraction (RHEED), electron microscopy, x-ray diffraction, and secondary ion mass spectrometry (SIMS). The films grown epitaxially on the (001) and (110) substrates exhibit {111} faceting, and smooth and featureless growth occurs only on the (111)B oriented substrates. Single crystalline Sr1−x BaxF2 films lattice-matched to the InAs substrates are grown at temperatures higher than 200, 450, and 400 °C on the (001), (110), and (111)B faces, respectively. SIMS profiles indicate that the interdiffusion between epitaxial film and substrate is rather small even at a growth temperature of 520 °C. The change in RHEED patterns during the thermal cleaning of substrate surfaces is also described.

Thermal Cleaning of InSb Surfaces in an Ultrahigh Vacuum

In and Sb surfaces of (111) crystals were analyzed by Auger electron spectroscopy (AES) before, during, and after heating them in an ultrahigh vacuum system. Heating the samples to 450°C resulted in stoichiometric and oxygen‐free surfaces. Sulfur due to chemical precleaning is removed at 470°C. Further, if the initial carbon concentration is low enough (< 10% surface coverage), then it can be almost totally removed by thermal cleaning at 450°C.

Implications of a combined biostratigraphic and palaeomagnetic study of the Umbrian Maiolica Formation

The study of a 275.5 m thick section of white, pelagic limestones occupying the valley of the Fonte del Giordano river on the southern slope of Mt. Montagnola has yielded a biostratigraphically controlled clear magnetic reversal pattern after thermal cleaning. The magnetic stratigraphy of the lower 131 m of the section (Calpionellid zones) is correlatable with the M-sequence of oceanic magnetic anomalies between M-19 and M-14. The reversal stratigraphy of the upper 81.5 m of the section (Radiolaria zone) has also been tied to the oceanic polarity time scale by making linear interpolation for a missing 63 m thickness underneath it. Besides the Fonte del Giordano section two Berriasian outcrops each with a different bedding attitude were studied at Gubbio and near Cagli for tectonic tilt test giving positive results. The mean palaeomagnetic pole position for the Late Jurassic/Early Cretaceous after bedding correction is: Φ = 19.1°, Λ = 288.2°, k = 148.7, α 95 = 10.2° ( N = 3), confirming the presence of a large swing in the polar path, a common behaviour of apparent polar wandering for the peri-Adriatic region during this time.

Correlation of the fine structure of InM4.5N4.5N4.5 Auger spectrum and thermal degradation at InP surfaces

The study of differently prepared InP surfaces by Auger electron spectroscopy (AES) shows that, contrary to previous reports, this technique can distinguish metallic In from In bonded to P in InP. Chemical shifts are indeed observed in the fine structure of InM4.5N4.5N4.5 Auger transitions when InP surface decomposes, leading to the formation of In microinclusions. A chemical shift of 2.2 eV is determined between metallic In and In in InP. Therefore, it is shown that AES can be used to detect InP surface decomposition and is suitable for controlling thermal cleaning generally performed before epitaxial growth of overlayers in molecular beam epitaxy or other vacuum deposition techniques.

Magnetism of Chinese loess deposits

The age of Chinese loess deposits has long been disputed. Biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the Pleistocene and ascertained a maximum loess age of about 1.2 Myr. A new collection of nearly 500 samples from a natural outcrop and a borehole section near Lochuan (lat. 35.8°N, long. 109.2°E; Shaanxi province) has been dated by magnetic stratigraphy. Thermal cleaning of the natural remanent magnetization (NRM) removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite. The characteristic NRM component is due to haematite which is thought to be of chemical origin. Rhythmical intensity variations of NRM and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition. The palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation. The Brunhes-Matuyama boundary and the Jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level. The Olduvai subchron has been found in the borehole section which records the entire loess sequence. Most probably the formation of Chinese loess began shortly after the Matuyama-Gauss polarity transition. Therefore a late Pliocene age of about 2.4 Myr is assigned to the oldest loess sediments measured.

Electronic properties of the NiO(100) surface after thermal cleaning in ultrahigh vacuum

Photoemission yield spectroscopy (PYS) together with Auger electron spectroscopy (AES) have been used in an investigation of the electronic properties of the NiO(100) surface, thermally cleaned in ultrahigh vacuum (UHV). The work function and ionization energy were determined. The origin of the filled electronic states band localized below the Fermi level, E F, is briefly discussed.

A study of complex glow curves of Quenched NaCl:Ca crystals

AbstractGlow curves of the thermally pretreated NaCl:Ca crystals are recorded and are found to be complex in nature. The complex glow curve is analysed using thermal cleaning technique and the trap parameters are calculated by various methods. The glow peaks have been tentatively attributed to impurity and various types of colour centers.

Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince

The Wabigoon gabbro of the Archean Wabigoon greenstone belt in northwestern Ontario preserves a univectorial natural remanent magnetization (NRM) with D = 246°, I = 12° (k = 19.5, α95 = 10.5°, N = 11 sites). The precision is reduced if sample means are averaged, however (k = 9.3, α95 = 9.2°, N = 29 samples). The paleomagnetic pole falls either at 160°W, 11°S (δp = 5.3°, δm = 10.6°), corresponding to an age of ~1300 Ma on the Laurentian apparent polar wander path, or the reverse of this, 20°E, 11° N, corresponding to a late Archean age (~2800 Ma). No ~1300 Ma igneous or metamorphic event is known in the area; a major west-northwest-trending dike about 9 km south of the gabbro yields a virtual geomagnetic pole at 122°W, 45°N and seems to be of Abitibi age (~2150 Ma) rather than Mackenzie age (~1250 Ma). A few gabbro samples and some greenstones from the intrusive baked zone have hybrid remanences in which a higher blocking temperature Kenoran-age (~2600 Ma) NRM is superimposed on the gabbro characteristic NRM. However, the Kenoran component may be a younger chemical remanent magnetization (CRM) residing in hematite. The hypothesis that the gabbro characteristic remanence is itself a hybrid of Kenoran and Keweenawan (~1100 Ma) NRM's, which would explain both the high between-sample scatter and the lack of a ~1300 Ma remagnetizing event, is considered but rejected because fewer than 10% of the gabbro samples exhibit multivectorial swings during alternating field or thermal cleaning. Two geomagnetic field reversals are recorded at interior sites, but only one or none is recorded near the margin of the intrusion. The different cooling histories of margin and interior, as well as the bulk of the other evidence, favour magnetization during initial cooling in late Archean time.