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Sökning: WFRF:(Wolter JH)

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1.
  • Bobbert, PA, et al. (författare)
  • Exchange-correlation energy of a hole gas including valence band coupling
  • 1997
  • Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 56:7, s. 3664-3671
  • Tidskriftsartikel (refereegranskat)abstract
    • We have calculated an accurate exchange-correlation energy of a hole gas, including the complexities related to the valence band coupling as occurring in semiconductors like GaAs, but excluding the band warping. A parametrization for the dependence on the density and the ratio between light-and heavy-hole masses is given. We apply our results to a hole gas in an AlxGa1-xAs/GaAs/AlxGa1-xAs quantum well and calculate the two-dimensional band structure and the band-gap renormalization. The inclusion of the valence band coupling in the calculation of the exchange-correlation potentials for holes and electrons leads to a much better agreement between theoretical and experimental data than when it is omitted.
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2.
  • Croitoru, MD, et al. (författare)
  • Electroluminescence spectra of an STM-tip-induced quantum dot
  • 2003
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 68:19
  • Tidskriftsartikel (refereegranskat)abstract
    • We analyze the electroluminescence spectrum of an STM-tip-induced quantum dot in a GaAs surface layer. A flexible model has been developed that combines analytical and numerical methods and describes the key features of many-particle states in the STM-tip-induced quantum dot. The dot is characterized by its depth and lateral width, which are experimentally controlled by the bias and current. We find, in agreement with experiment, that increasing the voltage on the STM tip results in a redshift of the electroluminescence peaks, while the peak positions as a function of electron tunneling current through the STM tip reveal a blueshift.
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3.
  • Croitoru, MD, et al. (författare)
  • Electroluminescence spectra of an STM-tip-induced quantum dot
  • 2004
  • Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 21:2-4, s. 270-274
  • Tidskriftsartikel (refereegranskat)abstract
    • We analyze the electroluminescence spectrum of an STM-tip-induced quantum dot in a GaAs surface layer. A flexible model has been developed, that combines analytical and numerical methods and describes the key features of many-particle states in the STM-tip-induced quantum dot. The dot is characterized by its depth and lateral width, which are experimentally controlled by the bias and the tunneling current. We find, in agreement with experiment, that increasing voltage on the STM-tip results in a red shift of the electroluminescence peaks, while the peak positions as a function of the electron tunneling current through the STM-tip reveal a blue shift. (C) 2003 Elsevier B.V. All rights reserved.
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4.
  • Croitoru, MD, et al. (författare)
  • Influence of the characteristics of the STM-tip on the electroluminescence spectra
  • 2005
  • Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 27:1-2, s. 13-20
  • Tidskriftsartikel (refereegranskat)abstract
    • We analyze the influence of the characteristics of the STM-tip (applied voltage, tip radius) on the electroluminescence spectra from an STM-tip-induced quantum dot. We find that positions of electroluminescence peaks, attributed to the electron-hole recombination in the quantum dot, are very sensitive to the characteristics of the tip, namely increasing voltage on the STM-tip results in a red shift of the electroluminescence peaks, while the peak positions as a function of the tip radius reveal a non-monotonous behavior. (c) 2004 Elsevier B.V. All rights reserved.
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5.
  • Haverkort, JEM, et al. (författare)
  • Design of a polarization independent SOA at 1.55 mu m using composite InAsP/InGaAs quantum wells.
  • 1999
  • Ingår i: ECIO99: 9TH EUROPEAN CONFERENCE ON INTEGRATED OPTICS AND TECHNICAL EXHIBITION. - : IST INT COMUNICAZIONI. ; , s. 483-486
  • Konferensbidrag (refereegranskat)abstract
    • We aim to extend the polarization independent SOA reported by Tiemeijer(1) to 1550 nm. Conventional quantum wells (QW) do not allow TM-gain at 1550 nm without exceeding the critical layer thickness. Composite InAsP/InGaAs QWs show high TM-differential gain at 1550 nm while simultaneously providing strain compensation.
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6.
  • Haverkort, JEM, et al. (författare)
  • Design of composite InAsP/InGaAs quantum wells for a 1.55 mu m polarization independent semiconductor optical amplifier
  • 1999
  • Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 75:18, s. 2782-2784
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate a composite InAsP/InGaAs quantum well in which an 8 nm tensile strained InGaAs well is surrounded by two compressively strained InAsP layers which feature a 70:30 conduction band offset ratio. The composite quantum well is found to provide a high TM differential gain. The InAsP layers provide strain compensation while simultaneously shifting the band gap to the relevant 1.55 mu m wavelength region and increasing the electron confinement. Composite InAsP/InGaAs quantum wells are a promising candidate for realizing a polarization independent semiconductor optical amplifier at 1.55 mu m. (C) 1999 American Institute of Physics. [S0003-6951(99)01944-0].
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7.
  • Jacobs, SEJ, et al. (författare)
  • Spatially resolved scanning tunneling luminescence on self-assembled InGaAs/GaAs quantum dots
  • 2003
  • Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 83:2, s. 290-292
  • Tidskriftsartikel (refereegranskat)abstract
    • Scanning-tunneling microscope induced luminescence at low temperature has been used to study the carrier injection into single self-assembled InGaAs/GaAs quantum dots. Electrons are injected from the tip into the dots, which are located in the intrinsic region of a p-i-n junction, and contain excess holes under typical operational conditions. Only a fraction (similar to4%) of the dots is found to be optically active under local electrical excitation. Spatial dependent measurements indicate a highly nonhomogeneous electron diffusion towards the dots. By analyzing the spatial dependence of individual peaks in the measured spectra, the contributions of individual dots to the total, multidot spectrum can be disentangled. (C) 2003 American Institute of Physics.
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8.
  • Kemerink, Martijn, et al. (författare)
  • Effect of strain on a second-order van Hove singularity in AlxGa1-xAs/InyGa1-yAs quantum wells
  • 1996
  • Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 54:15, s. 10644-10651
  • Tidskriftsartikel (refereegranskat)abstract
    • We have performed low-temperature photoluminescence and photoluminescence excitation (PLE) measurements on highly degenerate p-type GaAs and InyGa1-yAs quantum wells. In the PLE spectrum of the GaAs well, evidence of a second-order van Hove singularity in the joint density of states of the ground-state light-hole and electron bands is found. This singularity results from the equality of ground-state light-hole and electron effective masses near the Gamma point, being a much more restrictive demand than the usual condition for a van Hove singularity, which requires only the equality of first derivatives of the subband dispersions. The second-order van Hove singularity gives rise to a power-law divergence at the singular point, whereas the corresponding usual van Hove singularity results in a steplike discontinuity in the joint density of states. The observed singularity could be described extremely well by a simple analytical model. The increased energy gap between light- and heavy-hole ground states in the compressively strained InyGa1-yAs well enhances the valence-band parabolicity, resulting in the disappearance of the van Hove singularity. Furthermore, it is shown that the anisotropic character of the heavy-hole ground state in GaAs is strongly suppressed in the InyGa1-yAs system. All experiments are in good agreement with our numerical modeling, based on an exact solution of the 4 x 4 Luttinger Hamiltonian.
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9.
  • Kemerink, Martijn, et al. (författare)
  • Enhancement of spin-dependent hole delocalization in degenerate asymmetric double quantum wells
  • 1996
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 53:15, s. 10000-10007
  • Tidskriftsartikel (refereegranskat)abstract
    • Exact, self-consistently calculated eigenfunctions and eigenvalues of the valence band in degenerate asymmetric double quantum wells are obtained from the full 4x4 Luttinger Hamiltonian for different hole densities. We found the solutions to be extremely sensitive to the charge density. The charge induces an extra asymmetry in the confining potential and leads to a smaller separation of the hole levels in the adjacent wells. This strongly enhances the different leakage of wave functions with opposite magnetic moment, called spin-dependent hole delocalization (SDHD). Furthermore, it is shown that the SDHD of the heavy-holt: states can be enhanced by increasing the confinement of the Light-hole states through adjustment of the height of the confining barriers. The theoretical results are shown to be in excellent agreement with transport and optical experiments, which are proven to be largely determined by space-charge effects.
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10.
  • Kemerink, Martijn, et al. (författare)
  • Exchange interaction in degenerate p-type quantum wells
  • 1998
  • Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 256, s. 503-506
  • Tidskriftsartikel (refereegranskat)abstract
    • A detailed comparison between a magneto-transport experiment on a p-type GaAs/AlGaAs quantum well and model calculations is presented. It is shown that for all magnetic fields the Shubnikov-de Haas (SdH) trace is strongly influenced by the exchange interaction, in contrast with n-type structures where this interaction is only important in high magnetic fields. As a consequence, the effective hole masses that are extracted from the temperature dependence of the SdH oscillations are not a good measure of the single-particle hole mass, and can be regarded as meaningless. (C) 1998 Elsevier Science B.V. All rights reserved.
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11.
  • Kemerink, Martijn, et al. (författare)
  • Exchange interaction in p-type GaAs/AlxGa1-xAs heterostructures studied by magnetotransport
  • 1998
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 57:11, s. 6629-6635
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-temperature magnetotransport experiments have been performed on a p-type GaAs/AlxGa1-xAs quantum well. From activation measurements on Shubnikov-de Haas conduction minima it was found that ex change interactions can be of great importance for both odd and even filling factors and strongly influence the observed periodicity. Furthermore, it was found that the temperature dependence of Shubnikov-de Haas oscillations in the low-magnetic-field regime could not be explained within a single-particle model based on a solution of the full Luttinger Hamiltonian in a magnetic field. Numerical simulations of Shubnikov-de Haas spectra, based on a model that treats hole exchange interactions in a simplified manner, show unambiguously that exchange driven enhancement of hole "spin" splittings are extremely important at magnetic fields as low as 1.5 T. Also, the inclusion of a valence-band warping in the calculations is shown to be essential. Qualitatively, most experimental observations could be described within the presented model. Our results imply that, in any hole system, the effective masses obtained from temperature-dependent SdH measurements are to be treated with extreme care as they can deviate from their single-particle value by as much as a factor of 2.
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12.
  • Kemerink, Martijn, et al. (författare)
  • Exciton bleaching in p-type single and double quantum wells: The effects of subband occupation and wave function overlap
  • 1997
  • Ingår i: Physica status solidi. A, Applied research. - : Academic Verlag GMBH. - 0031-8965 .- 1521-396X. ; 164:1, s. 73-76
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied exciton unbinding in empty and p-doped single and double quantum wells, using magneto-photoluminescence excitation measurements. The use of p-type heterostructures allows to discriminate unambiguously between exciton bleaching by Coulomb screening and by the Pauli exclusion principle. The groundstate heavy-hole exciton, which experiences both effects, is unbound at hole densities in the range (6 to 11) x 10(15) m(-2). In contrast, the groundstate light-hole and first excited heavy-hole excitons: which only experience Coulomb screening, still have a finite binding energy at these densities. We found that the excitons of excited subbands are far less efficiently screened than those of the light-hole groundstate, due to the lesser overlap of the screening groundstate heavy holes with the excited subbands than with the groundstate light holes.
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13.
  • Kemerink, Martijn, et al. (författare)
  • Imaging individual chains and aggregates on conjugated polymer films
  • 2003
  • Ingår i: ORGANIC AND POLYMERIC MATERIALS AND DEVICES. - : MATERIALS RESEARCH SOCIETY. - 1558997083 ; , s. 23-28
  • Konferensbidrag (refereegranskat)abstract
    • We demonstrate a novel method to visualize individual molecular chains in the surface layer of organic semiconducting polymer films of arbitrary thickness. The method is based on scanning force microscopy and employs a combination of a sensitive phase detection system and metal coated tips with a low (similar to1 N/m) spring constant and a relatively high Q factor (similar to200). The molecularly resolved morphology is observed in phase images that are taken simultaneously with the topography. Surprisingly, we found that, when the tip apex radius exceeds the intermolecular spacing in the surface layer, surface aggregates -when present- are visualized. In both cases, the phase contrast is shown to result from van der Waals interaction between the conjugated backbone of the polymer chains and the metallic tip, and can quantitatively be described by a simple harmonic oscillator model. We have employed this method to study the morphology of poly(p-phenylene vinylene) (PPV) derivatives with different substitutions.
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14.
  • Kemerink, Martijn, et al. (författare)
  • Low-temperature scanning-tunneling microscope for luminescence measurements in high magnetic fields
  • 2001
  • Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 72:1, s. 132-135
  • Tidskriftsartikel (refereegranskat)abstract
    • We have designed and built a low-temperature (1.3-4.2 K) scanning-tunneling microscope which is capable of collecting light that is generated in the tunneling region. Light collection is done by means of two fibers whose cleaved front is in close proximity (approximate to1 mm) to the tunneling region. The whole system can be operated in high magnetic fields (11 T) without loss of optical signal strength. As a demonstration, we measured the electroluminescence spectra of an InGaAs quantum well at various temperatures. At 4.2 K, we found an electron-to-photon conversion factor that is three orders of magnitude higher than at room temperature. (C) 2001 American Institute of Physics.
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15.
  • Kemerink, Martijn, et al. (författare)
  • Magneto-optical study on exciton screening in p-type AlxGa1-xAs/InyGa1-yAs quantum wells
  • 1997
  • Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 56:8, s. 4853-4862
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied exciton unbinding in empty and p-doped quantum wells, using magnetophotoluminescence excitation measurements. The use of p-type quantum wells allows us to discriminate unambiguously between exciton bleaching by Coulomb screening and by the Pauli exclusion principle. We found that the ground-state heavy-hole exciton, which experiences both effects, is unbound at hole densities in the range (6-9) x 10(15) m(-2). In contrast, the ground-state light-hole and first excited heavy-hole excitons, which are only screened by the Coulomb interaction, still have a finite binding energy at these densities. However, for both bands, its Value is far below what is found in an undoped well. Furthermore, we found a strong indication that, in p-doped wells, the excitons of excited subbands are less efficiently screened than those of the Light-hole ground state, due to the lesser overlap of the screening ground-state heavy holes with the excited subbands than with the ground-state light holes.
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16.
  • Kemerink, Martijn, et al. (författare)
  • Many-particle effects in Be-delta-doped GaAs/AlxGa1-xAs quantum wells
  • 1998
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 58:3, s. 1424-1435
  • Tidskriftsartikel (refereegranskat)abstract
    • We have performed photoluminescence (PL) and photoluminescence excitation measurements on two series of center-delta-doped p-type GaAs/AlxGa1-xAs quantum wells, with variable well width and doping concentration. The experimental data are compared with self-consistent field calculations. The effects of exchange and correlation were found to be extremely important and various models for the hole exchange and correlation are compared with the experimental data. It is found that the model recently proposed by Bobbert et al. [P. A. Bobbert rt al., Phys. Rev. B 56, 3664 (1997)] consistently describes our experimental observations. Furthermore, for well widths w greater than or equal to 600 Angstrom clear excitonic effects were observed, for hole densities as high as 12 X 10(12) cm(-2), which is explained in terms of small spatial overlap between the screening particles and the exciton along the growth direction. In contrast to earlier work on similar samples, we found no indication for a Fermi-edge singularity in the PL spectra of our samples. Peaked structures at the high-energy side of the PL spectra are shown to arise from bulk transitions. [S0163-1829(98)04324-0].
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17.
  • Kemerink, Martijn, et al. (författare)
  • Measuring the potential distribution inside soft organic semiconductors with a scanning-tunneling microscope
  • 2002
  • Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 1247-1250
  • Tidskriftsartikel (refereegranskat)abstract
    • For the first time, we directly measured the potential distribution inside organic semiconductors. Combined spectroscopic measurements are performed on MDMO-PPV layers on Au and Yb substrates, using a scanning-tunneling microscope. The results are analyzed with a model that treats both current injection and bulk transport in detail. It is found that tip height-bias curves, which are taken by following the height of the STM tip as a function of bias, while the STM feedback system is active, reflect the potential distribution between tip and sample electrode. (C) 2002 Elsevier Science B.V. All rights reserved.
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18.
  • Kemerink, Martijn, et al. (författare)
  • Optical detection of ballistic electrons injected by a scanning-tunneling microscope
  • 2001
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 86:11, s. 2404-2407
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate a spectroscopic technique which is based on ballistic injection of minority carriers from the lip of a scanning-tunneling microscope into a semiconductor heterostructure. Ey analyzing the resulting electroluminescence spectrum as a function of tip-sample bias, both the injection barrier height and the carrier scattering rate, in the semiconductor can be determined. This technique is complementary to ballistic electron emission spectroscopy since minority instead of majority carriers are injected, which give the opportunity to study the carrier trajectory after injection.
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19.
  • Kemerink, Martijn, et al. (författare)
  • Optical detection of ballistically injected electrons in III/V heterostructures
  • 2001
  • Ingår i: PROCEEDINGS OF THE 25TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, PTS I AND II. - : SPRINGER-VERLAG BERLIN. - 3540417788 ; , s. 819-820
  • Konferensbidrag (refereegranskat)abstract
    • We present a novel spectroscopic technique which is based on the ballistic injection of minority carriers from the tip of an STM into a semiconductor heterostructure. By analyzing the resulting electro-luminescence spectrum as a function of tip-sample bias, both the injection barrier height and the carrier relaxation rate Gamma (s) after injection can be determined. From current dependent measurements we find that carrier trapping by impurities causes a significant non-radiative recombination channel at room temperature.
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20.
  • Kemerink, Martijn, et al. (författare)
  • Optical properties of a tip-induced quantum dot
  • 2001
  • Ingår i: PROCEEDINGS OF THE 25TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, PTS I AND II. - : SPRINGER-VERLAG BERLIN. - 3540417788 ; , s. 1183-1184
  • Konferensbidrag (refereegranskat)abstract
    • We have performed optical spectroscopy measurements on an STM-tip-induced quantum dot. The dominant confinement in the (hole) quantum dot is in the direction parallel to the tip axis. Electron confinement is achieved by a sub-surface AlGaAs barrier. Current dependent measurements indicate that many-body interactions can cause spectral blue-shifts up to 75 meV.
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21.
  • Kemerink, Martijn, et al. (författare)
  • Quantitative determination of the charge density on surface steps on semiconductors by high-resolution local scanning-tunneling spectroscopy
  • 2002
  • Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 1159-1162
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel technique is developed to follow the energetic position of the conduction and valence bands with respect to the Fermi level as a function of the lateral position on semiconductor surfaces. By combining high-resolution scanning-tunneling spectroscopy measurements with model calculations it is possible to relate the apparent change in conduction and valence band position to their real counterparts. This method allows one to determine the charge on surface artifacts like steps or vacancies, For a single step on p-type GaAs we find a charge of 0.9+/-0.3q nm(-1). (C) 2002 Elsevier Science B.V. All rights reserved.
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22.
  • Kemerink, Martijn, et al. (författare)
  • Real-space measurement of the potential distribution inside organic semiconductors
  • 2002
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 88:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate that the soft nature of organic semiconductors can be exploited to directly measure the potential distribution inside such an organic layer by scanning-tunneling microscope (STM) based spectroscopy. Keeping the STM feedback system active while reducing the tip-sample bias forces the tip to penetrate the organic layer. From an analysis of the injection and bulk transport processes it follows that the tip height versus bias trace obtained in this way directly reflects the potential distribution in the organic layer.
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23.
  • Kemerink, Martijn, et al. (författare)
  • Relating substitution to single-chain conformation and aggregation in poly(p-phenylene vinylene) films
  • 2003
  • Ingår i: Nano letters (Print). - : American Chemical Society. - 1530-6984 .- 1530-6992. ; 3:9, s. 1191-1196
  • Tidskriftsartikel (refereegranskat)abstract
    • The morphology of films of PPV derivatives is studied with molecular (single chain) resolution by phase-imaging scanning force microscopy. It is found that the symmetry of substitution is directly related to surface morphology and aggregation behavior. The molecular resolution in the phase contrast is shown to result from van der Waals interaction between the conjugated backbone of the polymer chains and the metallic tip, and can quantitatively be described by a simple harmonic oscillator model.
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24.
  • Kemerink, Martijn, et al. (författare)
  • Scanning-tunneling spectroscopy on conjugated polymer flims
  • 2003
  • Ingår i: ORGANIC AND POLYMERIC MATERIALS AND DEVICES. - : MATERIALS RESEARCH SOCIETY. - 1558997083 ; , s. 49-54
  • Konferensbidrag (refereegranskat)abstract
    • Scanning-tunneling spectroscopy experiments have been performed on conjugated polymer films and have been compared to a three-dimensional numerical model for charge injection and transport. It is found that field enhancement near the tip apex leads to significant changes in the injected current, which can amount to more than an order of magnitude, and can even change the polarity of the dominant charge carrier. As a direct consequence, the single-particle band gap and band alignment of the organic material can be directly obtained from tip height-voltage (z-V) curves, provided that the tip has a sufficiently sharp apex.
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25.
  • Kemerink, Martijn, et al. (författare)
  • Scanning tunneling spectroscopy on organic semiconductors: Experiment and model
  • 2004
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 70:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Scanning-tunneling spectroscopy experiments performed on conjugated polymer films are compared with three-dimensional numerical model calculations for charge injection and transport. It is found that if a sufficiently sharp tip is used, the field enhancement near the tip apex leads to a significant increase in the injected current, which can amount to more than an order of magnitude and can even change the polarity of the predominant charge carrier. We show that when charge injection from the tip into the organic material predominates, it is possible to probe the electronic properties of the interface between the organic material and a metallic electrode directly by means of tip height versus bias voltage measurements. Thus, one can determine the alignment of the molecular orbital energy levels at the buried interface, as well as the single-particle band gap of the organic material. By comparing the single-particle energy gap and the optical absorption threshold, it is possible to obtain an estimate of the exciton binding energy. In addition, our calculations show that by using a one-dimensional model, reasonable parameters can only be extracted from z-V and I-V curves if the tip apex radius is much larger than the tip height. In all other cases, the full three-dimensional problem needs to be considered.
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26.
  • Kemerink, Martijn, et al. (författare)
  • Spectrally resolved luminescence from an InGaAs quantum well induced by an ambient scanning tunneling microscope
  • 1999
  • Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 75:23, s. 3656-3658
  • Tidskriftsartikel (refereegranskat)abstract
    • Spectrally resolved scanning tunneling microscope-induced luminescence has been obtained under ambient conditions, i.e., at room temperature, in air, by passivating the sample surface with sulfur. This passivation turned out to be essential to suppress the local anodic oxidation induced by the tunneling current. From the dependence of the luminescence signal on tunneling current and voltage, we find that the passivation solution and post-passivation annealing temperature strongly modify the surface density of states (SDOS). More specifically, we found evidence that, after annealing at 400 degrees C, no SDOS is left above the bottom of the conduction band. For annealing at 200 degrees C, the SDOS is found to be extended up to 1.0 +/- 0.2 eV above the bottom of the conduction band. In all cases, the passivated (001) surface appears to be completely pinned. (C) 1999 American Institute of Physics. [S0003-6951(99)01949-X].
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27.
  • Kemerink, Martijn, et al. (författare)
  • Spin-dependent holed delocalization enhancement by bandfilling effects in degenerate asymmetric double quantum wells
  • 1997
  • Ingår i: Superlattices and Microstructures. - : Elsevier. - 0749-6036 .- 1096-3677. ; 21:2, s. 217-222
  • Tidskriftsartikel (refereegranskat)abstract
    • We studied the wavefunctions and energy positions of the confined states in the valance band in an asymmetric double quantum well. We found these to be extremely sensitive to both the carrier density and the height of the confining barriers, which allows us to control the so-called Spin Dependent Hole Delocalization. The theoretical results are shown to be in excellent agreement with experiments. (C) 1997 Academic Press Limited
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