Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 13 de 13
Filtrar
Más filtros










Base de datos
Intervalo de año de publicación
1.
Sci Rep ; 11(1): 17037, 2021 Aug 23.
Artículo en Inglés | MEDLINE | ID: mdl-34426607

RESUMEN

Two-dimensional layered materials offer the possibility to create artificial vertically stacked structures possessing an additional degree of freedom-the interlayer twist. We present a comprehensive optical study of artificially stacked bilayers (BLs) MoS[Formula: see text] encapsulated in hexagonal BN with interlayer twist angle ranging from 0[Formula: see text] to 60[Formula: see text] using Raman scattering and photoluminescence spectroscopies. It is found that the strength of the interlayer coupling in the studied BLs can be estimated using the energy dependence of indirect emission versus the A[Formula: see text]-E[Formula: see text] energy separation. Due to the hybridization of electronic states in the valence band, the emission line related to the interlayer exciton is apparent in both the natural (2H) and artificial (62[Formula: see text]) MoS[Formula: see text] BLs, while it is absent in the structures with other twist angles. The interlayer coupling energy is estimated to be of about 50 meV. The effect of temperature on energies and intensities of the direct and indirect emission lines in MoS[Formula: see text] BLs is also quantified.

2.
Sci Rep ; 11(1): 924, 2021 Jan 13.
Artículo en Inglés | MEDLINE | ID: mdl-33441595

RESUMEN

The temperature effect on the Raman scattering efficiency is investigated in [Formula: see text]-GaSe and [Formula: see text]-InSe crystals. We found that varying the temperature over a broad range from 5 to 350 K permits to achieve both the resonant conditions and the antiresonance behaviour in Raman scattering of the studied materials. The resonant conditions of Raman scattering are observed at about 270 K under the 1.96 eV excitation for GaSe due to the energy proximity of the optical band gap. In the case of InSe, the resonant Raman spectra are apparent at about 50 and 270 K under correspondingly the 2.41 eV and 2.54 eV excitations as a result of the energy proximity of the so-called B transition. Interestingly, the observed resonances for both materials are followed by an antiresonance behaviour noticeable at higher temperatures than the detected resonances. The significant variations of phonon-modes intensities can be explained in terms of electron-phonon coupling and quantum interference of contributions from different points of the Brillouin zone.

3.
Nanoscale ; 12(35): 18153-18159, 2020 Sep 17.
Artículo en Inglés | MEDLINE | ID: mdl-32853305

RESUMEN

Low temperature and polarization resolved magneto-photoluminescence experiments are used to investigate the properties of dark excitons and dark trions in a monolayer of WS2 encapsulated in hexagonal BN (hBN). We find that this system is an n-type doped semiconductor and that dark trions dominate the emission spectrum. In line with previous studies on WSe2, we identify the Coulomb exchange interaction coupled neutral dark and grey excitons through their polarization properties, while an analogous effect is not observed for dark trions. Applying the magnetic field in both perpendicular and parallel configurations with respect to the monolayer plane, we determine the g-factor of dark trions to be g ∼ -8.6. Their decay rate is close to 0.5 ns, more than 2 orders of magnitude longer than that of bright excitons.

4.
Sci Rep ; 10(1): 4981, 2020 Mar 18.
Artículo en Inglés | MEDLINE | ID: mdl-32188877

RESUMEN

Atomically thin materials, like semiconducting transition metal dichalcogenides (S-TMDs), are highly sensitive to the environment. This opens up an opportunity to externally control their properties by changing their surroundings. Photoluminescence and reflectance contrast techniques are employed to investigate the effect of metallic substrates on optical properties of MoSe2 monolayer (ML). The optical spectra of MoSe2 MLs deposited on Pt, Au, Mo and Zr have distinctive metal-related lineshapes. In particular, a substantial variation in the intensity ratio and the energy separation between a negative trion and a neutral exciton is observed. It is shown that using metals as substrates affects the doping of S-TMD MLs. The explanation of the effect involves the Schottky barrier formation at the interface between the MoSe2 ML and the metallic substrates. The alignment of energy levels at the metal/semiconductor junction allows for the transfer of charge carriers between them. We argue that a proper selection of metallic substrates can be a way to inject appropriate types of carriers into the respective bands of S-TMDs.

5.
Phys Rev Lett ; 123(13): 136801, 2019 Sep 27.
Artículo en Inglés | MEDLINE | ID: mdl-31697524

RESUMEN

We demonstrate that, in monolayers (MLs) of semiconducting transition metal dichalcogenides, the s-type Rydberg series of excitonic states follows a simple energy ladder: ε_{n}=-Ry^{*}/(n+δ)^{2}, n=1,2,…, in which Ry^{*} is very close to the Rydberg energy scaled by the dielectric constant of the medium surrounding the ML and by the reduced effective electron-hole mass, whereas the ML polarizability is accounted for only by δ. This is justified by the analysis of experimental data on excitonic resonances, as extracted from magneto-optical measurements of a high-quality WSe_{2} ML encapsulated in hexagonal boron nitride (hBN), and well reproduced with an analytically solvable Schrödinger equation when approximating the electron-hole potential in the form of a modified Kratzer potential. Applying our convention to other MoSe_{2}, WS_{2}, MoS_{2} MLs encapsulated in hBN, we estimate an apparent magnitude of δ for each of the studied structures. Intriguingly, δ is found to be close to zero for WSe_{2} as well as for MoS_{2} monolayers, what implies that the energy ladder of excitonic states in these two-dimensional structures resembles that of Rydberg states of a three-dimensional hydrogen atom.

6.
Sci Rep ; 8(1): 17745, 2018 Dec 10.
Artículo en Inglés | MEDLINE | ID: mdl-30531971

RESUMEN

We report a study of Raman scattering in few-layer MoTe2 focused on high-frequency out-of-plane vibrational modes near 291 cm-1 which are associated with the bulk-inactive [Formula: see text] mode. Our temperature-dependent measurements reveal a double peak structure of the feature related to these modes in the Raman scattering spectra of 4- and 5-layer MoTe2. In accordance with literature data, the doublet's lower- and higher-energy components are ascribed to the Raman-active A1g/[Formula: see text] vibrations involving, respectively, only the inner and surface layers. We demonstrate a strong enhancement of the inner mode's intensity at low temperature for 1.91 eV and 1.96 eV laser light excitation which suggests a resonant character of the Raman scattering processes probed under such conditions. A resonance of the laser light with a singularity of the electronic density of states at the M point of the MoTe2 Brillouin zone is proposed to be responsible for the observed effects.

7.
J Phys Condens Matter ; 28(36): 365301, 2016 09 14.
Artículo en Inglés | MEDLINE | ID: mdl-27391126

RESUMEN

We report on spectroscopic studies of resonances related to ladder of states of a charged exciton in single GaAlAs/AlAs quantum dot structures. Polarization-resolved photoluminescence, photoluminescence excitation and photon-correlation measurements were performed at low (T = 4.2 K) temperature also in magnetic field applied in Faraday configuration. The investigated resonances are assigned to three different configurations of a positively charged exciton. Together with a singlet ground state and a conventional triplet state (involving an electron from the ground state electronic s-shell), an excited triplet state, which involved an electron from the excited electronic p-shell was identified in single dots. The appearance of an emission line related to the latter complex is due to a partially suppressed electron relaxation in the investigated dots. An analysis of this emission line allows us to scrupulously determine properties of the excited triplet state and compare them with those of the conventional triplet state. Both triplets exhibit similar patterns of anisotropic fine structure and Zeeman splitting, however their amplitudes significantly differ for those two states. Presented results emphasize the role of the symmetry of the electronic state on the properties of the triplet states of two holes + electron excitonic complex.

8.
Anticancer Res ; 30(5): 1869-74, 2010 May.
Artículo en Inglés | MEDLINE | ID: mdl-20592394

RESUMEN

In order to investigate the use of CA19-9 serum concentration kinetics during first-line chemotherapy of pancreatic cancer as a potential predictive prognostic factor for overall survival, we retrospectively analysed the data of 47 patients suffering from proven exocrine pancreatic cancer. The patients were treated following our concept of efficacy-orientated sequential palliative chemotherapy (EOSPC), on the basis of a short-term follow-up including CA19-9 determinations at least monthly and imaging methods CT and/or MR every 2 months. The results are in agreement with our previous reports suggesting an increase of survival of pancreatic cancer patients in relation to the number of effective treatment regimens applied. However, apart from a weak correlation between the lowest CA19-9 levels induced by the first-line therapy (as a % of the initial pretherapeutical CA19-9 levels) and progression-free survival there was no correlation between the various parameters of serum kinetics of CA19-9 in the course of the first-line therapy and overall survival of the patients. A potential correlation as reported by others seems to be confirmed in our patient group by the potential antitumoral and life-prolonging effects of the second- and third-line therapies.


Asunto(s)
Biomarcadores de Tumor/sangre , Antígeno CA-19-9/sangre , Neoplasias Pancreáticas/sangre , Neoplasias Pancreáticas/diagnóstico , Adulto , Anciano , Anciano de 80 o más Años , Antineoplásicos/uso terapéutico , Supervivencia sin Enfermedad , Humanos , Cinética , Persona de Mediana Edad , Cuidados Paliativos , Neoplasias Pancreáticas/tratamiento farmacológico , Neoplasias Pancreáticas/mortalidad , Pronóstico , Estudios Retrospectivos , Resultado del Tratamiento
9.
Phys Rev Lett ; 92(18): 187402, 2004 May 07.
Artículo en Inglés | MEDLINE | ID: mdl-15169530

RESUMEN

Performing optical spectroscopy of highly homogeneous quantum dot arrays in ultrahigh magnetic fields, an unprecedently well resolved Fock-Darwin spectrum is observed. The existence of up to four degenerate electronic shells is demonstrated where the magnetic field lifts the initial degeneracies, which reappear when levels with different angular momenta come into resonance. The resulting level shifting and crossing pattern also show evidence of many-body effects such as the mixing of configurations and exciton condensation at the resonances.

10.
Anticancer Res ; 23(2A): 841-4, 2003.
Artículo en Inglés | MEDLINE | ID: mdl-12820310

RESUMEN

The results of palliative chemotherapy in 162 patients suffering from exocrine pancreatic cancer are presented. They are mainly discussed with respect to the possibility of improving survival of exocrine pancreatic cancer patients by an efficacy-orientated sequential polychemotherapy (EOSP). In about 40% of the patients treated between 1998 and 2001, sequential chemotherapy induced more than one effective treatment in the case that SD after a progressive prephase as well as MR, PR and CR are considered as antitumoral efficacy. Sequential polychemotherapy seems to be able to prolong the survival of these patients. The whole group of patients showed a 1-year survival of 56% and a 2-year survival of 16%. Especially in the case of metastasized tumor disease (M1), sequential polychemotherapy seems to be able to prolong survival: 45% of the metastasized tumor patients survived more than 1 year, 12% more than 2 years. The median survival for the whole group of locally advanced tumors was 15 months and the median survival for the whole group of metastasized tumors was 8 months. The results should stimulate clinicians to try palliative chemotherapy for pancreatic cancer more actively than before and to rediscuss the actual concepts of prospective therapeutical trials mainly based on analysing the effects of single agents or drug combinations on survival.


Asunto(s)
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Neoplasias Pancreáticas/tratamiento farmacológico , Adulto , Anciano , Anciano de 80 o más Años , Protocolos de Quimioterapia Combinada Antineoplásica/administración & dosificación , Biomarcadores de Tumor/análisis , Esquema de Medicación , Estudios de Seguimiento , Humanos , Persona de Mediana Edad , Estadificación de Neoplasias , Cuidados Paliativos , Neoplasias Pancreáticas/mortalidad , Neoplasias Pancreáticas/patología , Estudios Retrospectivos , Análisis de Supervivencia , Factores de Tiempo
11.
Anticancer Res ; 23(2A): 845-50, 2003.
Artículo en Inglés | MEDLINE | ID: mdl-12820311

RESUMEN

We report on 4 cancer patients with transient unspecific elevations of the serum tumor markers CA 19-9, CEA, CA 125 and CA 72-4, respectively. In one patient cholangitis due to biliary obstruction induced a significant transient increase of CA 19-9, in another patient HUS, probably as a severe complication after Mitomycin-C + Gemcitabine therapy resulted in a significant increase of serum CA 125. One patient demonstrated an extensively elevated and inexplicable serum CA 19-9 concentration (9450 u/ml) during a period of abdominal pain with continuous decrease and finally normalization within the following 5 years. Also inexplicable is an unexpected remittent increase of serum CA 72-4 in the course of chemotherapy after gastrectomy for gastric carcinoma. The presented data underline the necessity of interpreting serum courses of tumor markers only in the light of all available clinical data, imaging data and other laboratory tests in order to avoid misinterpretations.


Asunto(s)
Biomarcadores de Tumor/sangre , Neoplasias de la Vesícula Biliar/sangre , Neoplasias Pancreáticas/sangre , Neoplasias Gástricas/sangre , Adulto , Anciano , Antígenos de Carbohidratos Asociados a Tumores/sangre , Antígeno Ca-125/sangre , Antígeno CA-19-9/sangre , Antígeno Carcinoembrionario/sangre , Femenino , Neoplasias de la Vesícula Biliar/cirugía , Humanos , Masculino , Persona de Mediana Edad , Pronóstico , Sensibilidad y Especificidad , Neoplasias Gástricas/cirugía
12.
Phys Rev B Condens Matter ; 50(15): 10656-10660, 1994 Oct 15.
Artículo en Inglés | MEDLINE | ID: mdl-9975163
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA
...