TY  - JOUR
A1  - Zhang, X. F.
A1  - Becker, Charles R.
A1  - Zhang, H.
A1  - He, L.
A1  - Landwehr, G.
T1  - Investigation of a short period (001) HgTe-Hg\(_{0.6}\)Cd\(_{0.4}\)Te  superlattice by transmission electron microscopy
N2  - No abstract available
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-38029
ER  - 
TY  - JOUR
A1  - Wu, Y. S.
A1  - Becker, Charles R.
A1  - Waag, A.
A1  - Bicknell-Tassius, R. N.
A1  - Landwehr, G.
T1  - Removal of oxygen and reduction of carbon contamination on (100) Cd\(_{0.96}\)Zn\(_{0.04}\)Te
N2  - No abstract available
Y1  - 1993
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-38014
ER  - 
TY  - JOUR
A1  - Einfeldt, S.
A1  - Heinke, H.
A1  - Behringer, M.
A1  - Becker, Charles R.
A1  - Kurtz, E.
A1  - Hommel, D.
A1  - Landwehr, G.
T1  - The growth of HgSe by molecular beam epitaxy for ohmic contacts to p-ZnSe
N2  - The structural properties of HgSe grown by molecular beam epitaxy (MBE) are investigated for different lattice mismatches to the substrate and various growth conditions. The growth rate is shown to depend strongly on the growth temperature above lOO°C as well as on the Hg/Se flux ratio. It has been found that the crystalline perfection and the electrical properties are mainly determined by the layer thickness, especially for the growth on highly lattice mismatched substrates. Changes in the surface morphology are related to growth parameters. Differences between the electrical behavior of MBE-grown and bulk HgSe are discussed. The electrical properties of HgSe contacts on p-ZnSe are investigated as a function of different annealing procedures.
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-38001
ER  - 
TY  - JOUR
A1  - Schikora, D.
A1  - Hausleitner, H.
A1  - Einfeldt, S.
A1  - Becker, Charles R.
A1  - Widmer, T.
A1  - Giftige, C.
A1  - Lischka, K.
A1  - von Ortenburg, M.
A1  - Landwehr, G.
T1  - Epitaxial overgrowth of II-VI compounds on patterned substrates
N2  - The selected area epitaxial overgrowth of narrow gap HgTe as well as wide gap CdTe and ZnTe on CdTe/GaAs substrates, which had been structured by dry etching techniques, has been investigated. A plasma etching process using a barrel reactor with CH\(_4\)-CH\(_2\) gases has been employed to prepare stripes with a width of about 1 μm with anisotropic as well as isotropic etching profiles. It has been found, that the selected area HgTe overgrowth takes place with a high local selectivity to the low index planes of the patterned surface. In contrast, the selected area overgrowth of the wide gap CdTe and ZnTe is controlled by anisotropic growth kinetics provided that the substrate temperature is not lower than 220°C and the starting surface consists of well developed low index crystallographic planes.
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37985
ER  - 
TY  - JOUR
A1  - He, L.
A1  - Becker, Charles R.
A1  - Bicknell-Tassius, R. N.
A1  - Scholl, S.
A1  - Landwehr, G.
T1  - Molecular beam epitaxial growth and evaluation of intrinsic and extrinsically doped (100) Hg\(_{0.8}\)Cd\(_{0.2}\)Te on (100) Cd\(_{0.96}\)Zn\(_{0.04}\)Te
N2  - No abstract available.
Y1  - 1993
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37885
ER  - 
TY  - JOUR
A1  - Kraus, M. M.
A1  - Regnet, M. M.
A1  - Becker, Charles R.
A1  - Bicknell-Tassius, R. N.
A1  - Landwehr, G.
T1  - Comparison of band structure calculations and photoluminescence experiments on HgTe/CdTe superlattices grown by molecular beam epitaxy
N2  - We have grown HgTe/CdTe superlattices by molecular beam epitaxy; barrier thicknesses were in the range from 15 to 91 Å and the well thickness was maintained at a constant value of 30 Å. The infrared photoluminescence was investigated by means of Fourier transform infrared spectroscopy in the temperature range from 4.2 to 300 K. All superlattices showed pronounced photoluminescence at temperatures up to 300 K. To gain more detailed insight into the band structure of the HgTe/CdTe superlattices, band structure calculations were performed. The concept of the envelope function approximation was followed. Employing the transfer matrix method, the calculations were completed taking into account an eight band k·p model. An important parameter in these calculations is the natural valence band offset (VBO) between the well and barrier materials. As a general trend, the value for the direct gap decreases with increasing VBO. The experimentally determined energies of the band gap are in reasonable agreement with the values obtained by the theoretical calculations. A comparison between theory and experiment shows that the observed transition energies are closer to calculations employing a large offset (350 meV) as opposed to a small VBO (40 meV).
Y1  - 1992
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37878
ER  - 
TY  - JOUR
A1  - Wu, Y. S.
A1  - Becker, Charles R.
A1  - Waag, A.
A1  - Schmiedl, R.
A1  - Einfeldt, S.
A1  - Landwehr, G.
T1  - Oxygen on the (100) CdTe surface
N2  - We have investigated oxygen on CdTe substrates by means of x-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED). A Te oxide layer that was at least 15 A thick was found on the surface of as-delivered CdTe substrates that were mechanically polished. This oxide is not easily evaporated at temperatures lower than 350°C. Furthermore, heating in air, which further oxidizes the CdTe layer, should be avoided. Etching with HCI acid (15% HCl) for at least 20 s and then rinsing with de-ionized water reduces the Te oxide layer on the surface down to 4% of a monoatomic layer. However, according to XPS measurements of the 0 Is peak, 20%-30% of a monoatomic layer of oxygen remains on the surface, which can be eliminated by heating at temperatures ranging between 300 and 340 cC. The RHEED patterns for a molecular beam epitaxially (MBE)-grown CdTe film on a (lOO) CdTe substrate with approximately one monoatomic layer of oxidized Te on the surface lose the characteristics of the normal RHEED pattems for a MBE-grown CdTe film on an oxygen-free CdTe substrate.
Y1  - 1993
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37869
ER  - 
TY  - JOUR
A1  - Becker, Charles R.
A1  - He, L.
A1  - Regnet, M. M.
A1  - Kraus, M.M.
A1  - Wu, Y. S.
A1  - Landwehr, G.
A1  - Zhang, X. F.
A1  - Zhang, H.
T1  - The growth and structure of short period (001) Hg\(_{1-x}\)Cd\(_x\)Te-HgTe superlattices
N2  - Molecular beam epitaxially grown short period (001) Hg\(_{1_x}\)Cd\(_x\)Te-HgTe superlattices have been systematically investigated. Several narrow well widths were chosen, e.g., 30, 35 and 40 Å, and the barrier widths were varied between 24 and 90 Å for a particular well width. Both the well width and the total period were determined directly by means of x-ray diffraction. The well width was determined by exploiting the high reflectivity from HgTe and the low reflectivity from CdTe for the (002) Bragg reflection. Knowing the well and barrier widths we have been able to set an upper limit on the average Cd concentration of the barriers, \(\overline x_b\), by annealing several superlattices and then measuring the composition of the resulting alloy. \(\overline x_b\) was shown to decrease exponentially with decreasing barrier width. The structure of a very short period superlattice, i.e., 31.4 Å, was also investigated by transmission electron microscopy, corroborating the x-ray diffraction results.
Y1  - 1993
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37858
ER  - 
TY  - JOUR
A1  - Qiu, Yueming
A1  - He, Li
A1  - Li, Jie
A1  - Yuan, Shixin
A1  - Becker, Charles R.
A1  - Landwehr, G.
T1  - Infrared photoconductor fabricated with HgTe/CdTe superlattice grown by molecular beam epitaxy
N2  - An infrared photoconductor fabricated with a HgTe/CdTe superlattice grown on a GaAs substrate by molecular beam epitaxy is described here for the first time. The growth procedure, device fabrication, and measurement results are described. The results show that the device has relatively high uniformity and 1000 K black-body detectivity 2.4 X 10\(^9\) cm Hz\(^{1/2}\) W\(^{-1}\) . The photoconductivity decay method was used for determining carrier lifetime of the HgTe/CdTe superlattice, the measured lifetime is 12\(\mu\)s at 77 K, which is the longest lifetime ever reported for HgTe/CdTe superlattices and we believe that the increase of lifetime is mainly due to the reduction of dimensions.
Y1  - 1993
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37772
ER  - 
TY  - JOUR
A1  - Wu, Y.S.
A1  - Becker, Charles R.
A1  - Waag, A.
A1  - Kraus, M. M.
A1  - Bicknell-Tassius, R. N.
A1  - Landwehr, G.
T1  - Correlation of the Cd-to-Te ratio on CdTe surfaces with the surface structure
N2  - We report here that reconstruction on (100), (1lIlA, and (1l1lB CdTe surfaces is either C(2X2), (2X2), and (l X I) or (2X I), (l X I), and (l X I) when they are Cd or Te stabilized, respectively. There is a mixed region between Cd and Te stabilization in which the reflected high-energy electron-diffraction (RHEED) patterns contain characteristics of both Cd- and Te-stabilized surfaces. We have also found that the Cd-to-Te ratio of the x-ray photoelectron intensities of their 3d\(_{3/ 2}\) core levels is about 20% larger for a Cd-stabilized (1lIlA, (1lIlB, or (100) CdTe surface than for a Te-stabilized one. According to a simple model calculation, which was normalized by means of the photoelectron intensity ratio of a Cd-stabilized (lll)A and aTe-stabilized (1l1lB CdTe surface, the experimental data for CdTe surfaces can be explained by a linear dependence of the photoelectron-intensity ratio on the fraction of Cd in the uppermost monatomic layer. This surface composition can be correlated with the surface structure, i.e., the corresponding RHEED patterns. This correlation can in turn be employed to determine Te and Cd evaporation rates. The Te reevaporation rate is increasingly slower for the Te-stabilized (Ill) A, (l1l)B, and (100) surfaces, while the opposite is true for Cd from Cd-stabilized (Ill) A and (Ill)B surfaces. In addition, Te is much more easily evaporated from all the investigated surfaces than is Cd, if the substrate is kept at normal molecular-beam-epitaxy growth temperatures ranging from 2oo·C to 300 ·C.
KW  - Festkörperphysik
Y1  - 1991
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37789
SN  - 0163-1829
ER  - 
TY  - CHAP
A1  - Bicknell-Tassius, R. N.
A1  - Scholl, S.
A1  - Becker, Charles R.
A1  - Landwehr, G.
T1  - High magnetic field transport in II-VI heterostructures
N2  - In the present work we report the results of magneto-transport measurements on some Hg-based li-VI semiconductor epitaxiallayers grown by molecular beam epitaxy. The transport measurement were carried out at temperatures in the range 0.4 - 4.2 K in magnetic fields up to 10.0 T. Further, we point out the necessity of using multicarrier models for data interpretation and show finally some Shubnikov-de-Haas results on sampies with high mobility carners.
Y1  - 1992
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37797
ER  - 
TY  - JOUR
A1  - Geis, G.
A1  - Geick, R.
A1  - Becker, Charles R.
A1  - Wagner, V.
T1  - Antiferromagnetic resonance in CoO/NiO mixed crystals
N2  - We have studied the lowest magnetic excitation of Ni\(_{1-x}\)Co\(_x\)O mixed crystals for 0.94 \(\leq\) x \(\leq\) 1. Together with previous results for 0.02 \(\leq\) x \(\leq\) 0.07 and neutron data for x = 0.14 and x = 0.30, the results are discussed by means of a model, especially the variation of AFMR frequency and preferred spin direction with Co concentration x.
Y1  - 1977
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31239
ER  - 
TY  - JOUR
A1  - Wu, Y. S.
A1  - Becker, Charles R.
A1  - Waag, A.
A1  - Bicknell-Tassius, R. N.
A1  - Landwehr, G.
T1  - The effects of laser illumination and high energy electrons on molecular-beam epitaxial growth of CdTe
N2  - We report the results of a detailed investigation on the Te-stabilized (2 x 1) and the Cdstabilized c( 2 X 2) surfaces of ( 100) CdTe substrates. The investigation demonstrates for the first time that both laser illumination and, to a greater extent, high-energy electron irradiation increase the Te desorption and reduce the Cd desorption from ( 100) CdTe surfaces. Thus it is possible by choosing the proper growth temperature and photon or electron fluxes to change the surface reconstruction from the normally Te-stabilized to a Cd-stabilized phase.
Y1  - 1991
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30795
ER  - 
TY  - JOUR
A1  - Ritter, Cathrin
A1  - Fan, Kaiji
A1  - Paulson, Kelly G.
A1  - Nghiem, Paul
A1  - Schrama, David
A1  - Becker, Jürgen C.
T1  - Reversal of epigenetic silencing of MHC class I chain-related protein A and B improves immune recognition of Merkel cell carcinoma
JF  - Scientific Reports
N2  - Merkel cell carcinoma (MCC) is a virally associated cancer characterized by its aggressive behavior and strong immunogenicity. Both viral infection and malignant transformation induce expression of MHC class I chain-related protein (MIC) A and B, which signal stress to cells of the immune system via Natural Killer group 2D (NKG2D) resulting in elimination of target cells. However, despite transformation and the continued presence of virally-encoded proteins, MICs are only expressed in a minority of MCC tumors in situ and are completely absent on MCC cell lines in vitro. This lack of MIC expression was due to epigenetic silencing via MIC promoter hypo-acetylation; indeed, MIC expression was re-induced by pharmacological inhibition of histone deacetylases (HDACs) both in vitro and in vivo. This re-induction of MICs rendered MCC cells more sensitive to immune-mediated lysis. Thus, epigenetic silencing of MICs is an important immune escape mechanism of MCCs.
KW  - epigenetic silencing
KW  - Merkel cell carcinoma
KW  - MHC class I chain-related protein
KW  - skin cancer
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-167992
IS  - 21678
ET  - 6
ER  - 
TY  - JOUR
A1  - Reuter, Christian
A1  - Hauf, Laura
A1  - Imdahl, Fabian
A1  - Sen, Rituparno
A1  - Vafadarnejad, Ehsan
A1  - Fey, Philipp
A1  - Finger, Tamara
A1  - Jones, Nicola G.
A1  - Walles, Heike
A1  - Barquist, Lars
A1  - Saliba, Antoine-Emmanuel
A1  - Groeber-Becker, Florian
A1  - Engstler, Markus
T1  - Vector-borne Trypanosoma brucei parasites develop in artificial human skin and persist as skin tissue forms
JF  - Nature Communications
N2  - Transmission of Trypanosoma brucei by tsetse flies involves the deposition of the cell cycle-arrested metacyclic life cycle stage into mammalian skin at the site of the fly’s bite. We introduce an advanced human skin equivalent and use tsetse flies to naturally infect the skin with trypanosomes. We detail the chronological order of the parasites’ development in the skin by single-cell RNA sequencing and find a rapid activation of metacyclic trypanosomes and differentiation to proliferative parasites. Here we show that after the establishment of a proliferative population, the parasites enter a reversible quiescent state characterized by slow replication and a strongly reduced metabolism. We term these quiescent trypanosomes skin tissue forms, a parasite population that may play an important role in maintaining the infection over long time periods and in asymptomatic infected individuals.
KW  - mechanisms of disease
KW  - parasitology
KW  - transcriptomics
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-358142
VL  - 14
ER  - 
TY  - JOUR
A1  - Dindas, Julian
A1  - Scherzer, Sönke
A1  - Roelfsema, M. Rob G.
A1  - Meyer, Katharina von
A1  - Müller, Heike M.
A1  - Al-Rasheid, K. A. S.
A1  - Palme, Klaus
A1  - Dietrich, Petra
A1  - Becker, Dirk
A1  - Bennett, Malcolm J.
A1  - Hedrich, Rainer
T1  - AUX1-mediated root hair auxin influx governs SCFTIR1/AFB-type Ca2+ signaling
JF  - Nature Communications
N2  - Auxin is a key regulator of plant growth and development, but the causal relationship between hormone transport and root responses remains unresolved. Here we describe auxin uptake, together with early steps in signaling, in Arabidopsis root hairs. Using intracellular microelectrodes we show membrane depolarization, in response to IAA in a concentration- and pH-dependent manner. This depolarization is strongly impaired in aux1 mutants, indicating that AUX1 is the major transporter for auxin uptake in root hairs. Local intracellular auxin application triggers Ca2+ signals that propagate as long-distance waves between root cells and modulate their auxin responses. AUX1-mediated IAA transport, as well as IAA- triggered calcium signals, are blocked by treatment with the SCFTIR1/AFB - inhibitor auxinole. Further, they are strongly reduced in the tir1afb2afb3 and the cngc14 mutant. Our study reveals that the AUX1 transporter, the SCFTIR1/AFB receptor and the CNGC14 Ca2+ channel, mediate fast auxin signaling in roots.
KW  - auxin
KW  - permeation and transport
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-225368
VL  - 9
ER  -