Christoph Janowitz

Christoph Janowitz
Humboldt-Universität zu Berlin | HU Berlin · Department of Physics

PD Dr.
https://authors.elsevier.com/c/1iA7m8MvHh3OYq

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140
Publications
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Publications

Publications (140)
Article
An Al2O3/ZnO heterojunction was grown on a Si single crystal substrate by subsequent thermal and plasma-assisted atomic layer deposition (ALD) in situ. The band offsets of the heterointerface were then studied by consecutive removal of the layers by argon sputtering, followed by in situ X-ray photoelectron spectroscopy. The valence band maximum and...
Article
Thermoelectric properties of SnSe like the maximum thermoelectric performance and the Lorenz number are obtained from density functional theory and Boltzmann transport theory. The transport properties have been engineered by assuming a rigid band shift for modeling the n- and p-type SnSe. In consistent with the experimental data close to the Fermi-...
Article
Full-text available
Indium oxide (InxOy) thin films were deposited by plasma-enhanced atomic layer deposition (PEALD) using trimethylindium and oxygen plasma in a low-temperature range of 80–200 °C. The optical properties, chemical composition, crystallographic structure, and electrical characteristics of these layers were investigated by spectroscopic ellipsometry (S...
Article
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Gallium oxide (Ga2O3) thin films were deposited by plasma-enhanced atomic layer deposition (PEALD) applying a capacitively coupled plasma source where trimethylgallium (TMGa) as the gallium precursor and oxygen (O2) plasma were used in a substrate temperature (Ts) in the range of 80–200 °C. TMGa exhibits high vapor pressure and therefore facilitate...
Article
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In situ real-time ellipsometry (irtE) with a very high time resolution of 24 ms was applied to monitor the inductively coupled plasma enhanced atomic layer deposition (ALD) process of Al2O3 thin films to precisely resolve each step of the ALD process and its complete cycle. The influence of plasma power, plasma pulse duration, and deposition temper...
Article
The electronic, phonon, and transport properties of ternary ZrSxSe2−x (x = 0, 1, and 2) have been calculated based on density functional theory (DFT), density functional perturbation theory (DFPT), and Boltzmann transport theory. Two methods for engineering of the electronic and transport properties of ternary ZrSxSe2−x (x = 0, 1, and 2) shall be t...
Article
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We experimentally investigated the electronic structure of Mo-doped BiVO 4 high-quality single-crystals with synchrotron radiation-excited angle-resolved photoelectron spectroscopy (ARPES). By photon-energy dependent ARPES, we measured the bulk-derived valence band dispersion along the direction normal to the (010) cleavage plane, while the dispers...
Chapter
This chapter reports about tin oxide (SnO2), a material which belongs to the transparent conducting oxide family and is best characterized by its high conductivity, high carrier mobility, and the ability to form p-type conductivity. We correlate these properties in terms of localized intrinsic electronic defect states which are resolved by resonant...
Article
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The electronic structure of ZnO is dominated by coexisting electron and ionic states/bonds caused by charge polarization and self-trapping phenomena of the valence charges. Their interplay manifests itself in intrinsic electronic defects which have different degree of spatial localization and electronic correlation. The relative abundance of intrin...
Article
We present an experimental and theoretical study of the electronic structure of the transparent conductive oxide semiconductor MgGa2O4. Its valence band and the core levels have been measured experimentally by angle-resolved photoemission spectroscopy and compared to theoretical ab initio density-functional calculations. The bands stem from oxygen...
Article
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In high-temperature superconductors with a layered crystal structure, the copper–oxygen planes are commonly considered to dominate the electronic properties around the Fermi energy. As a consequence, out-of-plane contributions are often neglected in the description of these materials. Here we report on a resonant photoemission study of Pb0,4Bi1,6Sr...
Article
The temperature dependence of the absorption-edge energy has been determined in mixed layered transition-metal dichalcogenides of ZrSxSe2−x, for x=0.5, 1.0, 1.5, and 2.0 in the range of 32–300 K. The single crystals of ZrSxSe2−x samples have been grown by the chemical vapor transport technique and characterized with the help of different methods. T...
Article
The electronic structure of undoped tetragonal CaxSr1−xCuO2 (x = 0, 1) has been calculated by DFT and DFT+U within the full-potential linearized augmented plane wave (FP-LAPW) method for five different exchange-correlation energy approximations and for the B3LYP hybrid functional. For calculation of DFT+U the value of 6.258 eV has been obtained for...
Article
We report on a resonant photoemission (resPES) study of PbxBi2-xSr2-yLayCan-1CunO2n+4+δ (BISCO) single crystals to unravel the resonant decay mechanisms at the Cu2p absorption edge. The resPES studies on superconducting BISCO are performed at Bessy U49/2. We investigated BISCO single crystals with different hole doping concentrations at temperature...
Article
Very high resolution angular resolved photoemission (ARPES) spectra on TiSe2 in two distinct polarization geometries (vertical and horizontal) at temperatures between 300 K and 22 K enabled the observation of details of bands near the Fermi level not reported so far. Calculations of the electronic band structure based on density functional theory (...
Article
The electronic structure of a SnO2 single crystal is determined by employing resonant photoelectron spectroscopy. We determine the core level, valence band, and X-ray absorption (XAS) data and compare these with those of amorphous SnOx thin films. We find similar properties concerning the data of the core levels, the valence band features, and the...
Article
The electronic structure of the transparent semiconductor In2O3 has been studied by angle resolved photoemission spectroscopy upon deposition of metallic indium and also tin on the surface of the semiconductor. By deposition of metallic indium on In2O3 (111) single crystals, we detected the formation of a free-electron like band of effective mass (...
Article
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The near-E F band of the in situ cleaved (111) surface of high-quality n-type In2O3 single crystals was investigated by high-resolution angle-resolved photoemission (ARPES) along the major symmetry lines of the three-dimensional Brillouin zone. Several criteria to pin down Fermi level crossings and Fermi momenta were applied. The near-E F band is o...
Article
The electronic structure of the ternary layered transition metal dichalcogenide compounds of ZrSxSe2−x, where 0 x 2, has been studied by means of high resolution angle-resolved photoemission spectroscopy (ARPES) used in conjunction with synchrotron radiation facilities. The crystals were grown by the chemical vapor transport technique using iodine...
Article
The barrier height of a metal-semiconductor contact was studied by means of angle-resolved photoemission spectroscopy, which was implemented through stepwise Ag deposition on the ultra-high vacuum cleaved (111) surface of melt-grown In2O3 single crystals. A small Schottky barrier height of 0.22 +/- 0.08 eV was determined by following the band bendi...
Article
The effects of in-plane polarization change on the determination of the hole density of weakly under-doped (Bi, Pb)-2212 single crystals has been studied by x-ray absorption spectroscopy (XAS). The XAS signal at the CuL3 edge (925–940 eV) and O K edge (525 eV to 539 eV) were recorded under continuous rotation of the CuO2 plane from 0° to 180° with...
Article
We report on spectroscopic investigations on In2O3 single crystals. We focus on the detailed analysis of the O1s resonance profile by resonant photoelectron spectroscopy. We analyze the electronic structure and assign the O2p to build the valence band and both, O2p and In5s5p states to contribute to the conduction band (CB). We determine the partia...
Article
The influence of intrinsic point defects on the electronic structure of n‐type In2O3 single crystals grown by two methods, namely chemical vapor transport and from the melt, was examined by scanning tunneling spectroscopy. This method is a very surface sensitive technique for measuring the local density of states. So far not resolved states within...
Article
Angle-resolved photoelectron spectroscopy using synchrotron radiation has been performed on 1T–ZrSxSe2−x, where x varies from 0 to 2, in order to study the influence of the spin-orbit interaction in the valence bands. The crystals were grown by chemical vapour transport technique using Iodine as transport agent. A characteristic splitting of the ch...
Article
Full-text available
The electronic properties of the lithium intercalated layered transition metal dichalcogenide semiconductors ZrSxSe2-x for x = 0-2 have been calculated by density functional theory (DFT) using the WIEN2k code. The calculations have been carried out by the PBE functional and the TB-MBJ potential as proposed by Tran and Blaha. The calculations have b...
Article
One of the most puzzling anomalies of high-TC cuprates is the strong temperature dependence of the Hall coefficient (RH) and the hole density (nH). Gor’kov and Teitel’baum (GT) proposed by using experimental data of La2−xSrxCuO4 (LSCO) a two fluid model. The number of holes per Cu atom nH, changes with temperature according to nH(T,x) = n0(x) + n1(...
Article
A new 5-m normal-incidence monochromator at the third generation synchrotron source BESSY II of the Helmholz-Zentrum Berlin (HZB) has been constructed with the emphasis on angle-resolved photoelectron spectroscopy with high-resolution and at low energy utilizing photons from 5 eV to 40 eV. Optical design and preliminary performance results of the b...
Article
The Schottky barrier height of Au deposited on (100) surfaces of n-type β-Ga2O3 single crystals was determined by current-voltage characteristics and high-resolution photoemission spectroscopy resulting in a common effective value of 1.04 ± 0.08 eV. Furthermore, the electron affinity of β-Ga2O3 and the work function of Au were determined to be 4.00...
Article
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We study the dependence of the dimensional character of the charge-density wave (CDW) in TiSe2 by a controlled variation of the number of available charge carriers in the conduction band. A change of dimensionality is realised by H2O exposure and monitored by angle-resolved photoelectron spectroscopy. The CDW spanning vector changes from 2x2x1 towa...
Article
Full-text available
The charge-density-wave phase of TiSe(2) was studied by angle-resolved photoelectron spectroscopy and resistivity measurements investigating the influence of the band gap size and of a varying population of the conduction band. A gradual suppression of the charge-density-wave-induced electronic superstructure is observed for a variation of the band...
Article
Full-text available
The electronic properties of the layered transition metal dichalcogenide ZrSxSe2−x semiconductors for x = 0 and 2 as well as for the ternary compound with x = 1 have been calculated by density functional theory for six different exchange-correlation energy approximations by the wien2k code. The results show that, among the functions we tested, a ne...
Article
Full-text available
Transparent conducting oxides (TCOs) pose a number of serious challenges. In addition to the pursuit of high-quality single crystals and thin films, their application has to be preceded by a thorough understanding of their peculiar electronic structure. It is of fundamental interest to understand why these materials, transparent up to the UV spectr...
Article
Full-text available
Ga2O3 belongs to the group of transparent conducting oxides (TCOs) with a wide band gap and electrical conductivity. It exhibits the largest band gap with Eg = 4.8 eV and thus a unique transparency from the visible into the UV region. The information on the electronic structure of β-Ga2O3 is very scarce. This is in part due to the challenging probl...
Article
To get insight into the influence of different growth conditions of 1T-TiSe2 onto its charge density wave (CDW) phase transition, we have performed angle-resolved photoelectron spectroscopy (ARPES) on TiSe2 in its CDW phase at low temperatures comparing the results with resistivity measurements. Though the local resistivity maxima become less prono...
Article
Full-text available
We report characterization results by energy dispersive x-ray analysis and AC-susceptibility for a statistically relevant number of single layer Bi-cuprate single crystals. We show that the two structurally quite different modifications of the single-layered Bi-cuprate, namely (La,Pb=0.4)-Bi2201 and La-Bi2201, exhibit anomalies in the superconducti...
Article
Full-text available
β-Ga2O3 has the widest energy gap of the transparent conducting oxides. The interest in its electronic properties has recently increased because of its applications in various optoelectronic devices, semiconductor lasers, and ultrasensitive gas detecting systems. In contrast, information on the electronic structure of β-Ga2O3 is very scarce. Here,...
Article
In the Bi cuprates, the presence of a near 1 x 5 superstructure is well known. Usually, this superstructure is suppressed by the substitution of lead but there have been reports of a phase separation in so-called alpha and beta phases. This paper shows in high detail how and why the phase separation develops and what happens to the quasi-1 x 5 supe...
Article
Full-text available
In the Bi cuprates, the presence of a near 1×5 superstructure is well known. Usually, this superstructure is suppressed by the substitution of lead but there have been reports of a phase separation in so-called α and β phases. This paper shows in high detail how and why the phase separation develops and what happens to the quasi- 1×5 superstructure...
Conference Paper
In the generic phase diagram of the hole-doped cuprates, the superconducting transition temperature (TC) versus hole-doping is typically illustrated as a flipped parabola which exhibits the maximum at around 16% of hole doping. But there is also the possibility of a generic existence of depressions within this superconducting dome: At certain hole-...
Article
Full-text available
Inhomogeneities in any form, affecting either the structural properties as superstructures or the electronic degrees of freedom as stripes, play an essential role in the unusual properties of the cuprates. Bi-cuprates, favored for photoemission studies, are unfortunately prone to structural inhomogeneity and superstructure modulations. We have ther...
Article
Single crystals of layered transition-metal dichalcogenide compounds of ZrSxSe2-x with composition 0 <= x <= 2 were grown by the chemical-vapor-transport technique and characterized with the help of different methods. Indirect gap transitions with remarkably high values of the absorption coefficient alpha (h nu) and the energy-gap values have been...
Article
Full-text available
The exact shape of the superconducting dome in the Bi-cuprates depends on the proper determination of the hole content in the CuO2 layers. Single crystals of Bi(Pb)-2201 were studied over a wide doping range from the overdoped to the heavily underdoped regime by x-ray absorption spectroscopy (XAS) in order to determine the hole content of the compo...
Article
The kink in the dispersion and the drop in the width observed by angle-resolved photoemission in the nodal direction of the Brillouin zone of Bi2-xPbxSr2CaCu2O8+delta [(Pb)Bi2212] has attracted broad interest. Surprisingly, optimally lead-doped (Pb)Bi2212 with T-C>89 K and the shadow band have not been investigated so far, although the origin of th...
Article
Full-text available
The kink in the dispersion and the drop in the width observed by angle-resolved photoemission in the nodal direction of the Brillouin zone of Bi2−xPbxSr2CaCu2O8+δ [(Pb)Bi2212] has attracted broad interest. Surprisingly, optimally lead-doped (Pb)Bi2212 with TC>89 K and the shadow band have not been investigated so far, although the origin of the kin...
Article
Electrical transport studies have been carried out on single crystals of metallic MoTe2. Temperature-dependent electrical resistivity, ρ(T)−ρ(0), was found proportional to T2 up to 50 K. The magneto-resistance measurements showed the normal characteristics of a metal, the Hall coefficient has a strong dependence on the temperature.
Article
It is well known that the (1x5) superstructure of Bi cuprate superconductors will be suppressed due to optimum doping with Pb. Nevertheless, a Fermi surface map of (Pb,La)-Bi2201 (Pb = 0.4 and La = 0.4) determined by angular resolved photoemission (ARPES) revealed additional Fermi surface features. Low energy electron diffraction and X-ray diffract...
Article
Full-text available
The momentum dependence of the split band of Bi2Sr1.6La0.4CuO6 + δ (Manzke R. et al., Phys. Rev. B, 63 (2001) R100504) is investigated by angle-resolved photoemission spectroscopy with very high resolution along the ΓM-line. The splitting is only observable in this direction and at certain experimental conditions with respect to temperature and dop...
Article
Full-text available
Bi2Sr2-xLaxCuO6+delta and Bi2-yPbySr2-xLaxCuO6+delta high- Tc superconductors in a wide doping range from overdoped to heavily underdoped were studied by x-ray absorption and photoemission spectroscopy. The hole concentration p was determined by an analysis of the Cu L3 -absorption edge. Besides the occupied density of states derived from photoemis...
Article
Full-text available
The experimental dispersion of the first removal state in the insulating Bi2Sr2Ca1− x YxCu2O8+δ regime is found to differ significantly from that of other parent materials: oxyclorides and La2CuO4. For Y contents of 0.92≥x≥0.55 due to nonstoichiometric effects in the Bi-O layers, the hole concentration in the CuO2 layers is almost constant and, on...
Article
Full-text available
Recently observed splitting in angular-resolved photoemission spectroscopy (ARPES) on Bi2Sr2-xLaxCuO6+delta high-temperature superconductor (Janowitz C. et al., Europhys. Lett., 60 (2002) 615) is interpreted within the phenomenological Luttinger-liquid framework, in which both the non-Fermi-liquid scaling exponent of the spectral function and the s...
Article
The single-layer high-T-c superconductor (BiPb)(2)Sr2-xLaxCuO6+delta represents an excellent possibility to study the almost undisturbed CuO2-plane, the substantial element of the cuprate superconductors. For this material, a new splitting of the spectral weight at E-F has been observed along the Cu-O bond (pi, 0) direction of the Brillouin zone. I...
Article
The band gaps of HfS2 (1.96 eV) and HfSe2 (1.13 eV) cover the range of ideal band gaps for photovoltaic applications which is for a single-junction cell about 1.45 eV and for a two-junction cell about 1.1 eV and 1.8 eV. Additionally, in favor of applications the transition-metal dichalcogenides have a strong tendency to grow as thin films due to th...
Article
The phase diagram of the cuprate superconductors at low doping and low temperatures in the non-superconducting state is dominated by magnetic correlations. When increasing the hole concentration in the CuO2-planes from zero an antiferromagnetic (AF) insulating phase is followed for hole concentrations greater than approximately 0.08 by the supercon...
Article
Over the last years there has been increasing evidence that the normal state of the cuprates can not be described adequately with individual quasiparticles within Fermi-liquid theory. While the low-lying excitations in the superconducting state are nevertheless possibly of quasiparticle character, this character vanishes with the loss of supercondu...
Article
Full-text available
We present a comprehensive study performed with high-resolution angle-resolved photoemission spectroscopy on triple-layered Bi2Sr2Ca2Cu3O10 + single crystals. By measurements above T C the Fermi surface topology defined by the Fermi level crossings of the CuO2-derived band was determined. A hole-like Fermi surface as for single and double-CuO2 laye...
Article
X-ray absorption spectroscopy (XAS) on the O 1s threshold was applied to Bi-based, single crystalline high temperature superconductors (HTcs), whose hole densities in the CuO2 planes were varied by different methods. XAS gives the intensity of the so-called pre-peak of the O 1s line due to the unoccupied part of the Zhang–Rice (ZR) singlet state. T...
Article
We present recent results from photon energy dependent angle resolved photoemission of the single layered Bi-based cuprate Bi2Sr2-xLaxCuO6+delta. It will be demonstrated that the variation of the photon energy has significant influence on energy distribution curves. We compare our results with measurements on Bi-2212 single crystals. (C) 2002 Elsev...
Article
We present a high-resolution study of photoemission line widths observed at Ag(110). A careful data analysis yields k-resolved hole lifetimes tau(h) of d-holes at the X-point of the bulk band structure. At the upper d-band edge we derive tau(h) greater than or equal to 22 fs, i.e. more than one order of magnitude larger than predicted for a free-el...
Article
The momentum dependence of the split band of Bi2Sr1.6La0.4CuO6+delta (Manzke R. et al., Phys. Rev. B, 63 (2001) R100504) is investigated by angle-resolved photoemission spectroscopy with very high resolution along the GM-line. The splitting is only observable in this direction and at certain experimental conditions with respect to temperature and d...
Article
Full-text available
We have measured the superconducting gap Ds in optimally doped samples of BSCCO, TBCCO, HBCCO and HSCCO by Andreev and tunnelling spectroscopy and by ARPES. We have found that the low-temperature value of the gap within experimental errors is linearly increasing with the number n of CuO2 layers in the unit cell of the investigated HTSC-families (n...
Article
A first Fermi surface map of a single-layer high-T c superconductor is presented. The experiments were carried out on optimally doped Bi2Sr2 – xLaxCuO6 + (x = 0.40) with synchrotron radiation which allow to discuss in detail the strong polarization dependence of the emissions near the Fermi edge. For the cuprates, only little is known about the imp...