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  • 11
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    Online Resource
    Effect of impurities on the Raman spectra of spray-coated β-Ga2O3 thin films
    American Vacuum Society ; 2022
    In:  Journal of Vacuum Science & Technology A Vol. 40, No. 4 ( 2022-07-01)
    Details
    In: Journal of Vacuum Science & Technology A, American Vacuum Society, Vol. 40, No. 4 ( 2022-07-01)
    Abstract: Here, the incorporation of impurities into doped thin β-Ga2O3 films was studied by Raman spectroscopy, and a simple spring model was employed to estimate the impurity concentration from the impurity-modified frequencies of first-order phonon modes. β-Ga2O3 thin film samples were prepared using the spray-coating technique. As impurities, we used rare earth atoms (Er, Sm, and Gd) as well as Mg, Al, and Zn, with the nominal impurity concentrations varying from 0.5% up to 5.0%. As the impurities are expected to predominantly occupy Ga sites in the β-Ga2O3 lattice, heavier and lighter atoms than Ga should have a pronounced influence on Ga-related lattice vibrations. Therefore, in the Raman spectra of the thin films measured using 325-nm excitation, the impurity-induced shifts of the frequencies of vibrations involving Ga and O atoms were employed to estimate the impurity concentration. In addition, a high-impurity concentration can cause the formation of impurity-related oxides, as it is clearly visible for Zn. Besides, the Raman spectra with Mg as the impurity show that Mg most probably occupies interstitial rather than substitutional sites as the Raman modes do not shift with respect to the impurity concentration.
    Type of Medium: Online Resource
    ISSN: 0734-2101 , 1520-8559
    URL: Article
    DOI: 10.1116/6.0001822
    RVK:
    UA 4921
    Language: English
    Publisher: American Vacuum Society
    Publication Date: 2022
    detail.hit.zdb_id: 1475424-1
    detail.hit.zdb_id: 797704-9
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  • 12
    Online Resource
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    Giant polarization in organic heterostructures
    American Vacuum Society ; 2002
    In:  Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films Vol. 20, No. 5 ( 2002-09-01), p. 1597-1602
    Details
    In: Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, American Vacuum Society, Vol. 20, No. 5 ( 2002-09-01), p. 1597-1602
    Abstract: Deep levels or polarization effects can influence the charge transport through organic layers. Both effects can be identified by charge deep-level transient spectroscopy (Q-DLTS). Here, deep levels or polarization effects cause the charge transient signal Q(t) to be dependent or independent on the bias voltage, respectively. Q-DLTS, accompanied by feedback charge capacitance (FCM) measurements, has been used in the present work to investigate an organic heterostructure grown on an inorganic semiconductor. GaAs(100) substrates (n=0.34×1018 cm−3) were sulfur passivated by wet chemical etching and additional annealing under ultrahigh vacuum (UHV) conditions. Organic molecular beam deposition was used for the growth of 20 nm of 3,4,9,10-perylenetetracarboxilic dianhydride (PTCDA, Lancaster) and 27 nm of tris-(8-hydroxyquinoline) aluminum (Alq3, Syntec). Silver was evaporated on the Alq3 film through a shadow mask resulting in an array of circular contacts with an area of A=2.1×10−7 m2. The back contact to the GaAs(100) was achieved by an In–Ga alloy resulting in a series resistance of 20 Ω. The electrical characterizations were done at room temperature and in situ in the UHV system. The Q-DLTS measurements show a well resolved maximum in Q(t). The amplitude remains almost constant as a function of the bias voltage, which is a clear indication of a polarization in the organic heterostructure. From the experimental results the permittivity dispersion is determined to 2.37. The permittivity dispersion is independently obtained from FCM measurements. With the experimentally determined excess capacitance ΔC of 90 pF and the thickness of the organic heterostructure the permittivity dispersion is determined to 2.42. The FCM scans show no hysteresis due to the absence of deep levels. The ΔC/C=1 presented here clearly indicates the presence of a giant polarization.
    Type of Medium: Online Resource
    ISSN: 0734-2101 , 1520-8559
    URL: Article
    DOI: 10.1116/1.1495508
    RVK:
    UA 4921
    Language: English
    Publisher: American Vacuum Society
    Publication Date: 2002
    detail.hit.zdb_id: 1475424-1
    detail.hit.zdb_id: 797704-9
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  • 13
    Online Resource
    Online Resource
    Probing Magnetic Ordering in Air Stable Iron‐Rich Van der Waals Minerals
    Wiley ; 2023
    In:  Advanced Physics Research
    Details
    In: Advanced Physics Research, Wiley
    Abstract: Magnetic monolayers show great promise for future applications in nanoelectronics, data storage, and sensing. The research in magnetic two‐dimensional (2D) materials focuses on synthetic iodides and tellurides, which suffer from a lack of ambient stability. So far, naturally occurring layered magnetic materials have been overlooked. These minerals offer a unique opportunity to explore complex air‐stable layered systems with high concentration of magnetic ions. Magnetic ordering in iron‐rich phyllosilicates is demonstrated, focusing on minnesotaite, annite, and biotite. These naturally occurring layered materials integrate local moment baring ions of iron via magnesium/aluminum substitution in their octahedral sites. Self‐inherent capping by silicate/aluminate tetrahedral groups enables air stability of ultra‐thin layers. Their structure and iron oxidation states are determined via Raman and X‐ray spectroscopies. Superconducting quantum interference device magnetometry measurements are performed to examine the magnetic ordering. Paramagnetic or superparamagnetic characteristics at room temperature are observed. Below 40 K ferrimagnetic or antiferromagnetic ordering occurs. In‐field magnetic force microscopy on exfoliated flakes confirms that the paramagnetic response at room temperature persists down to monolayers. Further, a correlation between the mixture of the oxidation states of iron and the critical ordering temperature is established, indicating a path to design materials with higher critical temperatures via oxidation state engineering.
    Type of Medium: Online Resource
    ISSN: 2751-1200 , 2751-1200
    URL: Article
    DOI: 10.1002/apxr.202300070
    Language: English
    Publisher: Wiley
    Publication Date: 2023
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  • 14
    Online Resource
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    Flexible plasmonic graphene oxide/heterostructures for dual-channel detection
    Royal Society of Chemistry (RSC) ; 2019
    In:  The Analyst Vol. 144, No. 10 ( 2019), p. 3297-3306
    Details
    In: The Analyst, Royal Society of Chemistry (RSC), Vol. 144, No. 10 ( 2019), p. 3297-3306
    Type of Medium: Online Resource
    ISSN: 0003-2654 , 1364-5528
    URL: Article
    DOI: 10.1039/C8AN02495B
    Language: English
    Publisher: Royal Society of Chemistry (RSC)
    Publication Date: 2019
    detail.hit.zdb_id: 1472713-4
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  • 15
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    Nanoscale n++-p junction formation in GeOI probed by tip-enhanced Raman spectroscopy and conductive atomic force microscopy
    AIP Publishing ; 2019
    In:  Journal of Applied Physics Vol. 125, No. 24 ( 2019-06-28)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 125, No. 24 ( 2019-06-28)
    Abstract: Ge-on-Si and Ge-on-insulator (GeOI) are the most promising materials for the next-generation nanoelectronics that can be fully integrated with silicon technology. To this day, the fabrication of Ge-based transistors with a n-type channel doping above 5 × 1019 cm−3 remains challenging. Here, we report on n-type doping of Ge beyond the equilibrium solubility limit (ne ≈ 6 × 1020 cm−3) together with a nanoscale technique to inspect the dopant distribution in n++-p junctions in GeOI. The n++ layer in Ge is realized by P+ ion implantation followed by millisecond-flashlamp annealing. The electron concentration is found to be three times higher than the equilibrium solid solubility limit of P in Ge determined at 800 °C. The millisecond-flashlamp annealing process is used for the electrical activation of the implanted P dopant and to fully suppress its diffusion. The study of the P activation and distribution in implanted GeOI relies on the combination of Raman spectroscopy, conductive atomic force microscopy, and secondary ion mass spectrometry. The linear dependence between the Fano asymmetry parameter q and the active carrier concentration makes Raman spectroscopy a powerful tool to study the electrical properties of semiconductors. We also demonstrate the high electrical activation efficiency together with the formation of ohmic contacts through Ni germanidation via a single-step flashlamp annealing process.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.5080289
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2019
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 16
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    Raman- and Infrared-Active Phonons in Nonlinear Semiconductor AgGaGeS4
    MDPI AG ; 2023
    In:  Crystals Vol. 13, No. 1 ( 2023-01-14), p. 148-
    Details
    In: Crystals, MDPI AG, Vol. 13, No. 1 ( 2023-01-14), p. 148-
    Abstract: AgGaGeS4 is an emerging material with promising nonlinear properties in the near- and mid-infrared spectral ranges. Here, the experimental phonon spectra of AgGaGeS4 single crystals synthesized by a modified Bridgman method are presented. The infrared absorption spectra are reported. They are obtained from the fitting of reflectivity to a model dielectric function comprising a series of harmonic phonon oscillators. In the Raman spectra, several modes are registered, which were not detected in previous works. The analysis of the experimental vibrational bands is performed on the basis of a comparison with reported data on structurally related binary, ternary, and quaternary metal chalcogenides. The temperature dependence of the Raman spectra between room temperature and 15 K is also investigated.
    Type of Medium: Online Resource
    ISSN: 2073-4352
    URL: Article
    DOI: 10.3390/cryst13010148
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2661516-2
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  • 17
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    Online Resource
    Deposition of Nanosized Amino Acid Functionalized Bismuth Oxido Clusters on Gold Surfaces
    MDPI AG ; 2022
    In:  Nanomaterials Vol. 12, No. 11 ( 2022-05-26), p. 1815-
    Details
    In: Nanomaterials, MDPI AG, Vol. 12, No. 11 ( 2022-05-26), p. 1815-
    Abstract: Bismuth compounds are of growing interest with regard to potential applications in catalysis, medicine, and electronics, for which their environmentally benign nature is one of the key factors. One thing that currently hampers the further development of bismuth oxido-based materials, however, is the often low solubility of the precursors, which makes targeted immobilisation on substrates challenging. We present an approach towards the solubilisation of bismuth oxido clusters by introducing an amino carboxylate as a functional group. For this purpose, the bismuth oxido cluster [Bi38O45(NO3)20(dmso)28](NO3)4·4dmso (dmso = dimethyl sulfoxide) was reacted with the sodium salt of tert-butyloxycabonyl (Boc)-protected phenylalanine (L-Phe) to obtain the soluble and chiral nanocluster [Bi38O45(Boc–Phe–O)24(dmso)9] . The exchange of the nitrates by the amino carboxylates was proven by nuclear magnetic resonance, Fourier-transform infrared spectroscopy, as well as elemental analysis and X-ray photoemission spectroscopy. The solubility of the bismuth oxido cluster in a protic as well as an aprotic polar organic solvent and the growth mode of the clusters upon spin, dip, and drop coating on gold surfaces were studied by a variety of microscopy, as well as spectroscopic techniques. In all cases, the bismuth oxido clusters form crystalline agglomerations with size, height, and distribution on the substrate that can be controlled by the choice of the solvent and of the deposition method.
    Type of Medium: Online Resource
    ISSN: 2079-4991
    URL: Article
    DOI: 10.3390/nano12111815
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2662255-5
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  • 18
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    Influence of Thermal and Flash-Lamp Annealing on the Thermoelectrical Properties of Cu2ZnSnS4 Nanocrystals Obtained by “Green” Colloidal Synthesis
    MDPI AG ; 2023
    In:  Nanomaterials Vol. 13, No. 11 ( 2023-05-31), p. 1775-
    Details
    In: Nanomaterials, MDPI AG, Vol. 13, No. 11 ( 2023-05-31), p. 1775-
    Abstract: The problem with waste heat in solar panels has stimulated research on materials suitable for hybrid solar cells, which combine photovoltaic and thermoelectric properties. One such potential material is Cu2ZnSnS4 (CZTS). Here, we investigated thin films formed from CZTS nanocrystals obtained by “green” colloidal synthesis. The films were subjected to thermal annealing at temperatures up to 350 °C or flash-lamp annealing (FLA) at light-pulse power densities up to 12 J/cm2. The range of 250–300 °C was found to be optimal for obtaining conductive nanocrystalline films, for which the thermoelectric parameters could also be determined reliably. From phonon Raman spectra, we conclude that in this temperature range, a structural transition occurs in CZTS, accompanied by the formation of the minor CuxS phase. The latter is assumed to be a determinant for both the electrical and thermoelectrical properties of CZTS films obtained in this way. For the FLA-treated samples, the film conductivity achieved was too low to measure the thermoelectric parameters reliably, although the partial improvement of the CZTS crystallinity is observed in the Raman spectra. However, the absence of the CuxS phase supports the assumption of its importance with respect to the thermoelectric properties of such CZTS thin films.
    Type of Medium: Online Resource
    ISSN: 2079-4991
    URL: Article
    DOI: 10.3390/nano13111775
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2662255-5
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  • 19
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    Core and Shell Contributions to the Phonon Spectra of CdTe/CdS Quantum Dots
    MDPI AG ; 2023
    In:  Nanomaterials Vol. 13, No. 5 ( 2023-03-01), p. 921-
    Details
    In: Nanomaterials, MDPI AG, Vol. 13, No. 5 ( 2023-03-01), p. 921-
    Abstract: The parameters of the shell and interface in semiconductor core/shell nanocrystals (NCs) are determinant for their optical properties and charge transfer but are challenging to be studied. Raman spectroscopy was shown earlier to be a suitable informative probe of the core/shell structure. Here, we report the results of a spectroscopic study of CdTe NCs synthesized by a facile route in water, using thioglycolic acid (TGA) as a stabilizer. Both core-level X-ray photoelectron (XPS) and vibrational (Raman and infrared) spectra show that using thiol during the synthesis results in the formation of a CdS shell around the CdTe core NCs. Even though the spectral positions of the optical absorption and photoluminescence bands of such NCs are determined by the CdTe core, the far-infrared absorption and resonant Raman scattering spectra are dominated by the vibrations related with the shell. The physical mechanism of the observed effect is discussed and opposed to the results reported before for thiol-free CdTe Ns as well as CdSe/CdS and CdSe/ZnS core/shell NC systems, where the core phonons were clearly detected under similar experimental conditions.
    Type of Medium: Online Resource
    ISSN: 2079-4991
    URL: Article
    DOI: 10.3390/nano13050921
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2662255-5
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  • 20
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    Synthesis, optical properties, and photochemical activity of zinc-indium-sulfide nanoplates
    Royal Society of Chemistry (RSC) ; 2015
    In:  RSC Advances Vol. 5, No. 109 ( 2015), p. 89577-89585
    Details
    In: RSC Advances, Royal Society of Chemistry (RSC), Vol. 5, No. 109 ( 2015), p. 89577-89585
    Type of Medium: Online Resource
    ISSN: 2046-2069
    URL: Article
    DOI: 10.1039/C5RA20570K
    Language: English
    Publisher: Royal Society of Chemistry (RSC)
    Publication Date: 2015
    detail.hit.zdb_id: 2623224-8
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