Semiconductors

Self-aligned epitaxial metal-semiconductor hybrid nanostructures for plasmonics

by Adam Urbanczyk

We demonstrate self-alignment of epitaxial Ag nanocrystals on top of low-density near-surface InAs quantum dots (QDs)... more We demonstrate self-alignment of epitaxial Ag nanocrystals on top of low-density near-surface InAs quantum dots (QDs) grown by molecular beam epitaxy. The Ag nanocrystals support a surface plasmon resonance that can be tuned to the emission wavelength of the QDs. Photoluminescence measurements of such hybrid metal-semiconductor nanostructures reveal large enhancement of the emission intensity. Our concept of epitaxial self-alignment enables the integration of plasmonic functionality with electronic and photonic semiconductor devices operating down to the single QD level.

Low-density InAs QDs with subcritical coverage obtained by conversion of In nanocrystals

by Adam Urbanczyk

We report growth of InAs/GaAs quantum dots (QDs) by molecular beam epitaxy with low density of 2 μm−2 by conversion of... more We report growth of InAs/GaAs quantum dots (QDs) by molecular beam epitaxy with low density of 2 μm−2 by conversion of In nanocrystals deposited at low temperatures. The total amount of InAs used is about one monolayer, which is less than the critical thickness for conventional Stranski–Krastanov QDs. We also demonstrate the importance of the starting surface reconstruction for obtaining uniform QDs. The QD emission wavelength is easily tunable upon post-growth annealing with no wetting layer signal visible for short anneals. Microphotoluminescence measurements reveal well separated and sharp emission lines of individual QDs.

MgyNi1-y(Hx) thin films deposited by magnetron co-sputtering

by Trygve Mongstad

Journal of Alloys and Compounds 2012
Co-authored with Chang C. You, Annett Thøgersen, Jan Petter Mæhlen, Charlotte Platzer-Björkman, Bjørn C. Hauback, Smagul Zh. Karazhanov

In this work we have synthesised thin films of MgyNi1-y(Hx) metal and metal hydride with y between 0 and 1. The films... more In this work we have synthesised thin films of MgyNi1-y(Hx) metal and metal hydride with y between 0 and 1. The films are deposited by magnetron co-sputtering of metallic targets of Mg and Ni. Metallic MgyNi1-y films were deposited with pure Ar plasma while MgyNi1-yHx hydride films were deposited reactively with 30% H2 in the Ar plasma. The depositions were done with a fixed substrate carrier, producing films with a spatial gradient in the Mg and Ni composition. The combinatorial method of co-sputtering gives an insight into the phase diagram of MgyNi1-y and MgyNi1-yHx, and allows us to investigate structural, optical and electrical properties of the resulting alloys. Our results show that reactive sputtering gives direct deposition of metal hydride films, with high purity in the case of Mg~2NiH~4. We have observed limited oxidation after several months of exposure to ambient conditions. MgyNi1-y and MgyNi1-yHx films might be applied for optical control in smart windows, optical sensors and as a semiconducting material for photovoltaic solar cells.

Politics of Global Competition in the Semiconductor Industry

by Jeffrey Hart

published in Pacific Focus, 1 (Fall 1986), 93-119.

semiconductor lasers

by farshad akhtarian

Epitaxy and chemical reactions during thin-film formation from low-energy ions: new kinetic pathways, new phases, and new properties

by Nicole Herbots

Nicole Herbots, O.C. Hellman
ARIZONA STATE UNIVERSITY, Departmentof PhysicsandAstronomy, Tempe AZ 85287
0. Vancauwenberghe* MASSACHUSETTS INSTITUTE OFTECHNOLOGY, DepartmentofMaterialsScience & Engineering,Cambridge, MA 02139

Ref: Mat. Res. Soc. Symp. Proc. Vol. 235. pp. 749-762 (1992)

ABSTRACT
Three important effects of low energy direct Ion Beam Deposition (IBD) are the athermal incorporation of... more ABSTRACT
Three important effects of low energy direct Ion Beam Deposition (IBD) are the athermal incorporation of material into a substrate, the enhancement of atomic mobility in the subsurface, and the modification of growth kinetics it creates. All lead to a significant lowering of the temperature necessary to induce epitaxial growth and chemical reactions. The fundamental understanding and new applications of low temperature kinetics induced by low energy ions in thin film growth and surface processing of semiconductors are reviewed. It is shown that the mechanism of IBD growth can be understood and computed quantitatively using a simple model including ion induced defect generation and sputtering, elastic recombination, thermal diffusion, chemical reactivity, and desorption. The energy, temperature and dose dependence of growth rate, epitaxy, and chemical reaction during IBD is found to be controlled by the net recombination rate of interstitials at the surface in the case of epitaxy and unreacted films, and by the balance between ion beam decomposition and phase formation induced by ion beam generated defects in the case of compound thin films. Recent systematic experiments on the formation of oxides and nitrides on Si, Ge/Si(100), heteroepitaxial SixGe1−x/Si(100) and GaAs(lOO) illustrate applications of this mechanism using IBD in the form of Ion Beam Nitridation (IBN), Ion Beam Oxidation (IBO) and Combined Ion and Molecular beam Deposition (CIMD). It is shown that these techniques enable (1) the formation of conventional phases in conditions never used before, (2) the control and creation of properties via new degrees of freedom such as ion energy and lowered substrate temperatures, and (3) the formation of new metastable heterostructures that cannot be grown by pure thermal means.

Kinetics of formation and properties of silicon and silicon-germanium-alloy-based insulators grown using low-energy ion beam nitridation

by Nicole Herbots

Ion beam oxidation of GaAs: The role of ion energy

by Nicole Herbots

O. Vancauwenberghe, N. Herbots. H. Manoharan,a) and M. Ahrens

Massachusetts Institute of Technology, Cambridge,
Maassachusetts 02139

J. Vac. Sci. Technot A 9 (3), May/Jun 1991, pp. 1035-1039

In this work, room temperature oxidation of GaAs was investigated using ion beam oxidation (mO). In lBO, an ion beam... more In this work, room temperature oxidation of GaAs was investigated using ion beam oxidation (mO). In lBO, an ion beam is used to introduce oxygen athermally into the substrate, in this case GaAs. GaAs bonds are broken upon collision with the ions, making gallium and arsenic atoms readily available to react with the oxygen species. Ion beam oxidation of GaAs at room temperature was studied as a function ofoxygen ion energy between 500 and is keY. The ion beam oxidized GaAs was characterized in situ by Auger electron spectroscopy (AES) and ex situ with x-ray photoelectron spectroscopy (XPS) for accurate determination of the film chemical composition. Below 1 keY, a thin oxide film is formed: it is composed of Ga20 3 and AS20 3 with almost no metallic arsenic, and presents insulating properties.
As the ion energy increases, preferential sputtering of As and decomposition of AS203 increase and prevent formation of an
insulating film. No damage was detected by Rutherford backscattering spectrometry (RES) combined with ion channeling, in the substrate subjected to IBO below 1 keV.

A New 3D Multistring Code to Identify Compound Oxide Nanophase With Ion Channeling

by Nicole Herbots

James Douglas Bradley, Nicole Herbots, Robert Culbertson, Justin Shaw and Vasu Atluri

MRS Online Proceedings Library / Volume 996

a1 james.bradley@medtronic.com, Arizona St. University, Department of Physics, PO Box 871504, Tempe, AZ, 85287-1504, United States

a2 herbots@asu.edu, Arizona St. University, Physics and Astronomy, ASU Dept. of Physics and Astronomy, Box 1530, Tempe, AZ, 85287, United States

a3 robert.culbertson@asu.edu, Arizona St. University, Department of Physics, PO Box 871504, Tempe, AZ, 85287-1504, United States

a4 justin.shaw@nist.gov, NIST Magnetics Group, Magnetics Group, 325 Broadway, Mailstop 818.03, Boulder, CO, 80305, United States

a5 vasu.atluri@asu.edu, Arizona St. University, Department of Physics, PO Box 871504, Tempe, AZ, 85287-1504, United States

A new 3DMultiString computer code of Ion Beam Analysis (IBA) using 4He++ ion channeling combined with Nuclear... more A new 3DMultiString computer code of Ion Beam Analysis (IBA) using 4He++ ion channeling combined with Nuclear Resonance Analysis (NRA) is used to analyze controlled formation of order in continuous layers of silicon dioxide nucleated on (1×1) Si(100) via the Herbots-Atluri clean (U.S. patent 6,613,677 (9/3/2003)) in air at 300 K. In our most recent work, this new 3DMultiString simulations combined with IBA leads to the identification of a new two-dimensional nanophase of tetragonally distorted β-cristobalite SiO2 (annotated b-c SiO2) with a critical thickness of 2 nm from the (1×1) Si (100)/b-c SiO2 interface to the b-c SiO2 /amorphous SiO2 interface (annotated b-c SiO2/a-SiO2). 3DMultiString simulations of IBA data taken on this new b-c SiO2/(1×1) Si(100) interphase includes channeling along the three <100>, <110>, and <111> axes of Si (100) in combination 16OO(α, α)16O 3.045 MeV NRA to measure oxygen areal densities corresponding to nm-thick films. In this way, the critical thickness of the β-c SiO2 nanophase can be established as a function of oxygen coverage. This new 3DMultiSTRING computer code is derived from the original 3DSTRING program that originated at Bell Labs, NJ.coverage.

RBS STUDY OF THE EFFECT OF ARSENIC AND PHOSPHORUS INTERFACIAL SEGREGATION UPON THE SINTERING OF CONTACTS BETWEEN IMPLANTED POLYCRYSTALLINE SILICON AND ALUMINUM -SILICON(1%)

by Nicole Herbots

Nicole HERBOTS *, Maurice LOBET and Femand Van de WIELE
Microekxtronics Lab, Uniwrsite Catholique de Lmamin, 3, place du Levant. B - 1348 Louvain -la - Neuve, Belgium
Nuclear Instruments and Methods in Physics Research B7/8 (1985) 278-286 North-Holland, Amsterdam

The sintering behavior of the interface between Al :Si(l%) alloy and polycrystalline Si (poly-Si) was studied as a... more The sintering behavior of the interface between Al :Si(l%) alloy and polycrystalline Si (poly-Si) was studied as a function of the poly-Si implantation dose by combining RBS, SEM, TEM and X-ray microanalysis. Two different N-dopants were used: arsenic and phosphorus. The dopants were implanted in the poly-Si layer and thermal annealing was used to obtain dopant segregation towards the poly-Si interfacea.
After sir&ring, two main effects were detected: (1) Al-Si eutectic phase precipitates and Si crystallites are formed at the interface. (2) The density of precipitates is a function of the implantation dose. For doses above 1 x lOI5 at./cm2. segregated arsenic and phosphorus are found to completely inhibit this precipitation process, provided that the segregation peak of the dopant profile is preserved before metallization.
Several conclusions can be drawn: for surface concentrations higher than 8~10’~ at./cm3, arsenic and phosphorus inhibit the precipitation of the Al-Si eutectic phase, and thus inhibit interactions between the films at the interface. Moreover, argon gas, usedfor sputtering deposition of aluminum, segregated at the poly-Si/Al: Si(l%) interface and may also inhibit the metal-semiconductor interdiffusion.

Stability of C49 and C54 phases of TiSi2 under ion bombardment

by Nicole Herbots

S. Motakef, J. M. E. Harper, F. M. d’Heurle, and T. A. Gallo IBM Research Division, Thomas J. Watson Research Center, P.O. Box 218, Yorktown Heights, New York 10598
N. Herbots Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
J. Appl. Phys. 70 (5), 1 September 1991, p. 2660

The transformation of C49 phaseTiSiz to the low resistivity C54 phaseis necessaryfor many microelectronic... more The transformation of C49 phaseTiSiz to the low resistivity C54 phaseis necessaryfor many microelectronic applications. Here, we report on attempts to decreasethis transformation temperature by low-energy ion bombardment at elevated temperature. Ion irradiation was performed using a broad beam Kaufman ion sourceoperatedin Nz or Ar gasbetween
0.1 and 2 keV beamenergy,with ion dosesranging from 2.0X 1016to 1.9X lo** ions/cm’, and sampletemperaturesfrom 480“C!to 735“C. For comparison,room-temperatureAr + implantation at higher energy (105-210 keV) was performed with a doseof lOI ions/cm2 with projected ranges within and beyond the TiS& layer thickness. Resistivity measurementsas a function of temperature,x-ray diffraction, and Rutherford backscattering s p e c t r o m e t r y w e r e u s e d t o d e t e r m i n e t h e c o m p o s i t i o n a n d p h a s e s .R e s u l t s s h o w t h a t l o w - energyion bombardment doesnot promote the C49-C54transformation at the temperatures studied, while ion implantation actually raisesthe temperaturefor the transformation.
In addition, bombardment of C54 TiSi, doesnot causeit to revert to the C49 phase,indicating that both phasesappearto be surprisingly stableunder ion bombardment.Simulationsof defect production using the TRIM code indicate the formation of a higher number of displaced atoms than are usually required to initiate a transformation. We conclude that the defectsintroduced into C49 TiSi, by ion bombardment at energiesup to 2 keV are either not sufficient to nucleate the C54 phaseor they are annealedout too quickly at the temperatureneededfor C54 phasegrowth.

IBMM of OH adsorbates and interphases on Si-based materials

by Nicole Herbots

N. Herbots , Qian Xing, M. Hart, J.D. Bradley, D.A. Sell, R.J. Culbertson, Barry J. Wilkens
Department of Physics, Arizona State University, Tempe, AZ 85287-1504, USA
FINAL REFERENCE:
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 272, 1 February 2012, Pages 330-333

Proceedings of the 17th International Conference on Ion Beam Modification of Materials (IBMM 2010)

Please cite this article as

N. Herbots. Q. Xing et al., IBMM of OH adsorbates and interphases on Si-based materials, Nucl. Instr. and Meth. , Vol 272, pp 330-333 (2012),
doi:10.1016/j.nimb.2011.01.094

Using ion beam modification, films composed of synthesized
‘‘interphases’’ of ordered silica on OH-passivated (1... more Using ion beam modification, films composed of synthesized
‘‘interphases’’ of ordered silica on OH-passivated (1 X 1) Si(100) underwent surface electro-chemical changes quantified by surface free energy via Sessile drop method and contact angle analysis using Young’s equation and Van Oss theory. IBMM caused the surface free energies initially ranging from 26.0 mJ/m2 to 57.3 mJ/m2 to converge to 43.1–45.4 mJ/m2 for various passivated and as-received wafer samples alike. Although TMAFM also identified topographic changes, these changes did not correlate to the change of surface free energies. Ion beam modification of the ordered silica film on Si(100) surface is analyzed using 3.045 MeV 16O(a, a)16O nuclear resonance scattering (NRS) in conjunction with channeling in (1 1 1) direction, which demonstrated the convergence of the partially ordered oxygen to amorphous at about 55 microCoulombs/mm2 He++ flux. Additionally, Si surface peak channeling in (1 0 0) and (1 1 1) directions also experienced an uptrend in areal density as incident ion flux increased, while the rotating random Si signal height remains stable, showing a disruption in the surface order during IBMM.

Atomic collisions, elastic recombination, and thermal diffusion during thin-film growth from low-energy ion beams

by Nicole Herbots

N. Herbots *, 0. Vancauwenberghe **, O.C. Hellman + and Y.C. Joo ++
Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Volumes 59-60, Part 1, 1 July 1991, Pages 326-331
doi:10.1016/0168-583X(91)95233-4 |

Low-energy (< 1 keV) ions are used in a variety of thin-film techniques. When low-energy ions are used during... more Low-energy (< 1 keV) ions are used in a variety of thin-film techniques. When low-energy ions are used during growth, the atomic mobility is athermally enhanced. This can lead to a significant lowering of the temperature necessary to induce epitaxial growth and chemical reactions. Athermal enhancement of atomic mobility in semiconductors can be described below the temperature for plastic deformation (T = 540-degrees-C in Si) by classifying the mechanisms involved into three categories according to their respective timescale: collisions, elastic recombination, and thermal diffusion. A quantitative model can then be derived to predict the conditions of temperature, dose rate, and energy to obtain thin film growth, and oxidation in techniques such as ion beam deposition (IBD), and ion beam oxidation (IBO). Using computer simulations, the dynamics of defect generation and redistribution, and the resulting thin-film growth rate can be investigated. Energies below 200 eV are found not only to minimize damage and sputtering, but also create defect distributions that favor surface recombination and hence growth. This elucidates the mechanism of thin-film formation with high atomic density, oxidation with a sharp inteface with the substrate and epitaxial growth, and experimental findings on the energy dependence of IBD and IBO.

A quantitative model of point defect diffusivity and recombination in ion beam deposition and combined ion and molecular deposition

by Nicole Herbots

O. Vancauwenberghe, N. Herbots, and O. C. Hellman MassachusettsInstituteo/Technology, 77MassachusettsAvenue. Cambridge. jWassachusetts02139
(Received 18 October 1990; accepted 12 February 1991)
J. Vac. Sci. Techno!. B 9 (4), JullAug 1991, p.2027-2033 0134-211X/911042027-07$01.00 @ 1991 American Vacuum Society 2027

We are investigating the use of low energy ions (< 1 keV) in low temperature thin film growth techniques, ion beam... more We are investigating the use of low energy ions (< 1 keV) in low temperature thin film growth techniques, ion beam deposition (IBD) and combined ion and molecular deposition (CIMD). In IBD, a thin film is directly grown from a low energy ion beam as the only source of material, while in CIMD, low temperature growth of thin films is achieved by depositing materials simultaneously from a low energy ion beam and one or several molecular beams. A simple model of the IBD process has been developed and accounts for atomic collisions and thermal diffusion during thin film growth. Computer simulation of IBD of Si on Si have been conducted as a function of ion energy to support more quantitatively this physical description of IBD. The results show that the IBD growth mechanism is mediated by the fast diffusing interstitials and establish a low energy limit to achieve epitaxial growth by IBD that depends on the point defect diffusivities. The defect generation has to be confined in the subsurface region in order to favor interstitial recombination with the surface, leading to net thin film growth, and vacancy annihilation to prevent amorphization. The effect of point defect diffusivities on the IBD growth process is also investigated. It is found that a model including fast moving interstitials can account for various experimental observations specific to IBD.

New SiGe dielectrics grown at room temperature by low‐energy ion beam oxidation and nitridation

by Nicole Herbots

Author(s): VANCAUWENBERGHE, O (VANCAUWENBERGHE, O); HELLMAN, OC (HELLMAN, OC); HERBOTS, N (HERBOTS, N); TAN, WJ (TAN, WJ)
Source: APPLIED PHYSICS LETTERS Volume: 59 Issue: 16 Pages: 2031-2033 DOI: 10.1063/1.106122 Published: OCT 14 1991

New dielectric materials based on SiGe have been formed at room temperature by direct ion beam oxidation and... more New dielectric materials based on SiGe have been formed at room temperature by direct ion beam oxidation and nitridation. Si0.8Ge0.2 layers were deposited by molecular beam epitaxy on Si(100) and then exposed to a low-energy ion beam of O-18-2+ to form oxides and N-14-2+ to form nitrides. The ion energies investigated ranged from 100 eV to 1 keV. Thin films of SiGe oxide and SiGe nitride were formed at all energies used as evidenced by in situ x-ray photoelectron spectroscopy analysis. They were found to be insulating by ex situ scanning electron microscopy observations. During the ion beam processing, the Ge content of the alloy layer decreases, due to preferential sputtering of Ge and the Ge compounds. However, as the ion energy is decreased, the concentration of Ge in the alloy remains closer to the original content. The thermal stability of these new SiGe dielectrics was also assessed up to 500-degrees-C.

Heteroepitaxial properties of SiGeC on Si (100) grown by combined ion-and molecular-beam deposition

by Nicole Herbots

Author(s): Jacobsson, H (Jacobsson, H); Xiang, J (Xiang, J); Herbots, N (Herbots, N); Whaley, S (Whaley, S); Ye, PH (Ye, PH); Hearne, S (Hearne, S)
Source: JOURNAL OF APPLIED PHYSICS Volume: 81 Issue: 7 Pages: 3081-3091 DOI: 10.1063/1.364352 Published: APR 1 1997

The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1-x-yGexCy on Si(100), has been... more The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1-x-yGexCy on Si(100), has been investigated. The epitaxial quality of Si1-x-yGexCy is found to be inferior to that of Si1-xGex with similar Si/Ge concentration ratio, grown under identical conditions, and the quality deteriorates with increasing C fraction. Also, the surface roughness, as studied by tapping mode atomic force microscopy, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank-van der Merve to Stranski-Krastanov type growth. We suggest that the very large mismatch between the average bond length in the Si1-x-yGexCy material, as determined by Vegard's law, and the equilibrium Si-C bond length, weakens the Si-C bonds and reduces the elastic range of the material, thus lowering the barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morphology, either directly by a lowered barrier for island formation or indirectly through the formation of defects. A decrease in Ge incorporation in the Si1-x-yGexCy films with increasing C incorporation suggests a repulsive Ge-C interaction. Moreover, we observe a C-rich, Ge-deficient precursor phase to SiC precipitates at a growth temperature of 560 degrees C, whereas at 450 degrees C no such phase can be observed. The temperature dependence of the precursor formation is consistent with C bulk diffusion. Infrared absorption measurements cannot be used to detect the precursor phase. Finally, the onset of epitaxial breakdown is discussed and an accurate and independent determination of the C fraction and its substitutionality is emphasized. (

Arsenic Dopant Influence upon the Sintering Behavior of the Aluminum‐Polysilicon Interface

by Nicole Herbots

REF: J. Electrochem. Soc., Volume 131, Issue 3, pp. 645-652 (1984)
(Issue Date: March 1984).

AUTHORS Nicole Herbots, Fernand Van de Wiele, and Maurice Lobet
Laboratoire de Microelectronique, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium

Robert G. Elliman
Department of Communication and Electronic Engineering, Royal Melbourne Institute of Technology, Melbourne, Australia

Interdiffusion between thin films of aluminum (Al) and polycrystalline silicon (poly-Si) has been studied with the... more Interdiffusion between thin films of aluminum (Al) and polycrystalline silicon (poly-Si) has been studied with the purposeof obtaining a stable interface upon sintering for IC metallization. The solid-phase crystal regrowth of Si due to this lowtemperature interdiffusion has also been investigated. Dopant segregation towards the interfaces and the grain boundariesof arsenic-implanted poly-Si was used successfully to control the kinetics of Al-poly-Si interactions. The correlation betweenthe arsenic depth profiles, the Si-layer microstructure, and the sintering behavior of the Al-poly-Si interface wasmeasured by RBS, (scanning) AES, SEM, TEM, and grazing incidence x-rays. Quantitative results and discussion of thediffusion mechanisms at work are presented. It is shown that the presence of an arsenic segregation peak on top of thepoly-Si layer stabilizes Al/poly-Si interface. A concentration of 1019 atom/cm3 appears to be a minimum threshold forsintering at 465°C.

1995: The stability of thiosulfate in the presence of pyrite in low-temperature aqueous solutions

by Martin Schoonen

Xu, Y., Schoonen, M.A.A., 1995. The stability of thiosulfate in the presence of pyrite in low-temperature aqueous solutions. Geochimica Cosmochimica Acta, 59(22): 4605-4622.

High Aspect Ratio Via Milling Endpoint Phenomena in Focused Ion Beam Modification of Integrated Circuits

by Ray Valery

Proceedings from 30th International Symposium for Testing and Failure Analysis, November 14 - 18 Worcester MA, USA

As integration level of semiconductor devices increases,
thickness of the internal features within... more As integration level of semiconductor devices increases,
thickness of the internal features within microelectronic
circuits reduces concurrently with the shrinkage of lateral
dimensions. Therefore precision detection of endpoint after the
milling has reached targeted conductor during the process of
circuit modification by Focused Ion Beam (FIB) system
becomes increasingly important. One method for detecting
endpoint during FIB milling is based on monitoring the yield
of secondary electrons [1, 2] generated as the ion beam strikes
the material being removed. Access vias, used in editing
circuits using FIB are scaling with circuit dimensions and as a
result the aspect ratio requirements are increasing.
While the sensitivity of the endpoint detection can be
enhanced by improved secondary electron collection [3] and
by monitoring the sample absorbed [4,5] current, a detailed
understanding of the endpoint signal distribution within a High
Aspect Ratio (HAR) via is of great interest for further
enhancement of the endpoint sensitivity.

The absolute energy positions of conduction and valence bands of selected semiconducting minerals

by Martin Schoonen

YONG XU AND MARTIN A.A. SCHOONEN American Mineralogist, Volume 85, pages 543–556, 2000

The absolute energy positions of conduction and valence band edges were compiled for about 50 each semiconducting... more The absolute energy positions of conduction and valence band edges were compiled for about 50 each semiconducting metal oxide and metal sulfide minerals. The relationships between energy levels at mineral semiconductor-electrolyte interfaces and the activities of these minerals as a cata- lyst or photocatalyst in aqueous redox reactions are reviewed. The compilation of band edge ener- gies is based on experimental flatband potential data and complementary empirical calculations from electronegativities of constituent elements. Whereas most metal oxide semiconductors have valence band edges 1 to 3 eV below the H2O oxidation potential (relative to absolute vacuum scale), energies for conduction band edges are close to, or lower than, the H2O reduction potential. These oxide minerals are strong photo-oxidation catalysts in aqueous solutions, but are limited in their reducing power. Non-transition metal sulfides generally have higher conduction and valence band edge energies than metal oxides; therefore, valence band holes in non-transition metal sulfides are less oxidizing, but conduction band electrons are exceedingly reducing. Most transition-metal sul- fides, however, are characterized by small band gaps (<1 eV) and band edges situated within or close to the H2O stability potentials. Hence, both the oxidizing power of the valence band holes and the reducing power of the conduction band electrons are lower than those of non-transition metal sulfides.