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The continuously expanding portfolio of 2D materials represents a precious set of building blocks for engineering next generation electronic and optical devices. A recent addition to this family is represented by silicene, the 2D allotrope of silicon. This material is characterised by a structure similar to the one of graphene, showing a hexagonal arrangement of Si atoms, albeit slightly buckled out of plane. This new, synthetic material combines an ultrahigh carrier mobility with the unique opportunity to tune its band gap by applying an external electric field. For these reasons it could be exploited to realise field effect transistors with a two-dimensional channel. Silicene still remains a vastly unexplored material: to fully unleash its potential, it is crucial to acquire additional knowledge regarding its chemical and physical properties as well as optimised growth processes and substrates. Furthermore, it is of pivotal importance to develop and investigate processes that allow to integrate this 2D material in functional devices. In this thesis, the well-known growth of silicene on Ag(111) is firstly replicated. The grown layer is thoroughly analysed by means of low energy electron diffraction, X-ray photoemission spectroscopy, angle resolved UV photoemission spectroscopy and low energy electron microscopy. Additionally, a novel method for encapsulating silicene and protecting it from oxidation is developed: the 2D layer is capped, directly in-UHV, by exfoliated few-layer graphene or hBN flakes, enabling the utilisation of ex situ analysis tools, such as Raman spectroscopy and spectroscopic ellipsometry. The vibrational properties of silicene are studied, with particular focus on the polarisability properties, which strictly reflect the two-dimensional nature of the grown layers. In the second part, the growth of silicene on Au(111) is explored. By using a combination of LEED, LEEM, ARUPS and Raman analysis, as well as first principle calculations, the grown layer is fully characterised, showing that it comprises a highly biaxially strained silicene phase. This offers a powerful new platform for future investigations of the effects of strain in 2D silicon-based materials. In the final part of the thesis, CaF2 is epitaxially grown on silicene/Ag(111), to study the possibility of engineering a gate insulation layer to efficiently control the flow of carriers through the two-dimensional material. The presented data show that CaF2 grows well on silicene, forming an ordered structure and maintaining its insulating properties. At the same time, silicon atoms in the silicene layer do not change their chemical state due to the presence of CaF2. Raman spectroscopy data reveal that the buried silicene layer undergoes a structural modification, due to the presence of the insulating layer, nevertheless maintaining a 2D configuration. It is shown that the modified silicene layer possesses an enhanced optical absorption in the visible range, if compared to crystalline-diamond or amorphous silicon thin layers. The results pave the way for combining CaF2 and silicene in next-generation electronic devices.

Die Ramanspektroskopie (RS) ist eine analytische Technik, die in Folge einer optischen Anregung eines Stoffes materialspezifische Informationen über dessen molekulare Schwingungen und Kristallstruktur liefert. Da sowohl Minerale als auch biologische Materialien untersucht werden können, ist die RS in der Weltraumforschung von besonderem Interesse. So werden im Jahr 2020 gleich zwei Marsrover (ExoMars und Mars 2020) Ramanspektrometer mitführen, deren Aufgabe unter anderem die Detektion von Spuren von vergangenem oder gegenwärtigem extraterrestrischen Leben sein wird. Die Charakterisierung von stark lumineszierenden biologischen Proben und Mineralen stellt eine der größten Herausforderungen in der konventionellen RS dar. Daher beschäftigt sich diese Dissertation mit dem Problem der Lumineszenz in der RS. Dazu wird das Potenzial von fünf verschiedenen ramanspektroskopischen Techniken zur Handhabung der Lumineszenz evaluiert. Diese Techniken beinhalten (i) die Auswahl von verschiedenen Anregungswellenlängen (325 nm, 532 nm, 785 nm, 1064 nm), welche auf dem Konzept der spektralen Trennung des Lumineszenz- und Ramansignals basiert. (ii) Eine Alternative ist das Photobleichen, wobei die Lumineszenz durch eine lange Belichtungszeit unterdrückt wird. (iii) Eine weitere Methode für die spektrale Separation von Raman- und Lumineszenzphotonen ist die anti-Stokes RS. (iv) Bei der SERDS Technik werden zwei leicht verschobene Anregungswellenlängen verwendet. (v) Abschließend erfolgt die Untersuchung der Streu- und Emissionsstrahlung in der Zeitdomäne. Die Ergebnisse dieser Arbeit zeigen, dass es keine universelle Lösung gibt um das Problem der Lumineszenz in der RS zu überwinden. Allerdings weist die Verwendung unterschiedlicher Laserwellenlängen großes Potenzial für die erfolgreiche Handhabung der Lumineszenz in der RS auf. In Kombination mit SERDS und/oder Photobleichen steigt die Wahrscheinlichkeit verwertbare Spektren für die Probencharakterisierung zu erhalten., Raman spectroscopy (RS) is an analytical technique conveying material-specific information about a material’s molecular vibrations and crystal structure in succession of an optical excitation of the material. Due to the fact that mineralogical as well as biological material can be examined, RS is of special interest for space research. For instance, two Mars rovers (ExoMars and Mars 2020) will each carry along a Raman spectrometer in the year 2020, with the aim of detecting inter alia traces of extant or extinct extraterrestrial life. One of the biggest challenges in conventional RS is the characterization of strongly luminescent biological or mineralogical material; therefore, the dissertation at hand deals with the problem of luminescence in RS. For this purpose, the potential of five different Raman spectroscopic techniques for the handling of luminescence will be evaluated. These techniques include (i) the selection of different excitation wavelengths (325 nm, 532 nm, 785 nm and 1064 nm), which is based on the concept of the spectral separation of the luminescence signals as well as Raman signals. (ii) Photobleaching provides an alternative whereby the luminescence is suppressed by long exposure. (iii) A further method for the spectral separation of Raman photons as well as luminescence photons is provided by the anti-Stokes RS. (iv) The SERDS technique uses two slightly shifted excitation wavelengths. (v) Finally the examination of inelastic scattering and emission takes place in the time domain. The results of this dissertation show that there is no universal solution to overcome the problem of luminescence in RS. However, the usage of different excitation wavelengths offers great potential for handling luminescence in RS successfully. In combination with SERDS and/or photobleaching the probability to obtain exploitable spectra for sample characterization increases

Celitement is a new type of cement that is based on hydraulic calcium-hydrosilicate (hCHS) that possesses a potential for minimizing the ratio C/S from above 3 in OPC down to 1, which significantly reduces the amount of CO$_2$ released during processing. The reaction kinetics of hCHS differs from that of classical clinker phases due to the presence of highly reactive silicate species, which involve silanol groups instead of pure calcium silicates and aluminates and aluminoferrites. In contrast to Portland cement, no calcium hydroxide is formed during hydration, which otherwise regulates the Ca concentration. Without the buffering role of Ca(OH)$_2$ the concentration of the dissolved species c(Ca$^{2+}$) and c(SiO$_4^{4-}$) and the corresponding pH must be controlled to ensure a reproducible reaction. Pure hCHS reacts isochemically with water, resulting in a C-S-H phase with the same chemical composition as a single hydration product, with a homogeneous distribution of the main elements Ca and Si throughout the sample. Here we study via nanoindentation the mechanical properties of two different types of hardened pastes made out of Celitement (C/S=1.28), with varying amounts of hCHS and variable water to cement ratio. We couple nanoindentation grids with Raman mappings to link the nanoscale mechanical properties to individual microstructural components, yielding in-depth insight into the mechanics of the mineralogical phases constituting the hardened cement paste. We show that we can identify in hardened Celitement paste both fresh C-S-H with varying density, and C-S-H from the raw material using their specific Raman spectra, while simultaneously measuring their mechanical properties. Albeit not suitable for phase identification, EDX measurements provide valuable information about the distribution of alkalis, thus further helping to understand the reaction pattern of hCHS., Comment: 32 pages, 8 figures

Laser haben durch die Fortschritte in der Herstellung, Qualität und breiten Anwendbarkeit erfolgreich Einzug die optische Online- und Inline-Prozessanalysentechnik gehalten. Es wird gezeigt, welche Möglichkeiten sich durch den Einsatz von laserbasierten Methoden für die Gasanalytik ergeben. Dies wird anhand von Beispielen aus der Infrarotspektroskopie und Raman-Spektroskopie demonstriert. Mit der Raman-Spektroskopie in hohlen photonischen Kristallfasern lassen sich geringe Gaskonzentrationen mit Messzeiten im Sekundenbereich detektieren. Mit Quantenkaskadenlasern können Methanemissionen im Spurenbereich aus der Ferne nachgewiesen werden und mithilfe von Lasern und nichtlinear-optischen Komponenten lassen sich hochempfindliche ungekühlte Infrarotdetektoren für die Gasanalyse realisieren.

As non-toxic and sustainable materials the system of binary oxide semiconductors Cu2O, Cu4O3, and CuO is in the focus of current research, e.g., for solar-cell applications. The objective of this work is to analyse the vibrational and Raman spectroscopic properties of these binary semiconductors using ab initio methods (density functional theory).The phonon dispersions of polar semiconductors display a splitting in frequency of the longitudinal optical (LO) and transversal optical (TO) infrared active modes (LO-TO splitting) in the limit of vanishing phonon wave vector. This traces back to long-ranged dipole-dipole interactions present in these crystals. The theoretical treatment of these interactions requires the usage of certain correction schemes for the dynamical matrices. Two methods implementing these corrections [Phys. Rev. B 55, 10355 (1997) (Gonze s method); J. Phys.: Condens. Matter 22, 202201 (2010) (Wang s method)] are employed. Gonze s method, which is traditionally in the framework of density function perturbation theory, is shown to be applicable together with the real space method. Both correction schemes are compared using the insulator CaF2 as test system. The evolution of the phonon frequencies of the modes showing LO-TO splitting close to the Brillouin zone centre in many cases is better described by Gonze s method. Wang s method, on the contrary, can introduce artificial features in the phonon dispersion.The phonon dispersion and derived quantities of all three copper oxide phases are calculated and compared to experiment. It becomes particularly clear that the corrections following Gonze s method are necessary to obtain agreement with experimentally determined phonon dispersions. Good agreement with experiment is obtained for the vibrational contributions to the specific heat and the entropy. Based on Gonze s method the velocities of sound are calculated along several directions also yielding good accordance with experiment.The focus of the Raman spectroscopy investigations is on Cu4O3 and CuO. Cu4O3 is not too extensively studied theoretically as well as experimentally, and for CuO different crystal structures must be considered for room temperature (RT) and low temperatures (LT) (below 213 K). While group theory predicts three Raman active modes for CuO at RT additional modes appear in the experimental LT Raman spectrum [Phys. Rev. B 52, R13130 (1995)]. The appearance of the extra Raman active modes can be explained by a local symmetry lowering of the atomic positions compared to the RT structure owing to a change in the antiferromagnetic ordering. Additional measured Raman active modes can be identified in the calculations; more extra modes are calculated than measured, while each of those not visible in experiment shows a small intensity in the calculated Raman spectrum. Additionally, a rather different behaviour of the Raman intensities of the modes common to both the RT and the LT structures as a function of the laser energy is found. For Cu4O3 the dependence of the Raman intensities on the crystal orientation and the chosen polarisations are investigated in detail. Particularly, the totally symmetric A1g mode has noteworthy angular intensity dependence since it depends on the relative phase of the complex-valued Raman tensor elements. The effect of hydrostatic pressure is also studied showing that the frequencies of the Raman active modes are very sensitive to the exerted pressure.

In this work the development and investigation of two different concepts of miniaturized electrostatic propulsion methods are discussed. In order to fulfill the propulsion-related challenges emerging with a growing number of nano- and microsatellites and high-precision research missions, propulsion systems have to be miniaturized to enable lower system masses, thrust and impulse-bit ranges. Common thruster types with respect to miniaturization prospects and propellant-massefficiency were evaluated and state-of-the-art miniaturized propulsion systems (including propellant and thruster mass, packaging and power processing costs) were reviewed to study their working range in terms of satellite mass. As common propulsion systems cannot be down-scaled forever, modern techniques and novel scalable concepts going beyond established schemes have to be employed. The first part of this work treats the development and design of miniaturized colloid emitters as such emitters become more efficient when miniaturized. The colloid emitters studied in this work were mainly made out of the photo resist SU-8, which is well-established in the microfabrication field as a photoresist allowing one to prepare robust microstructures with a high aspect ratio. The ionic liquid EMI-BF4 was chosen as propellant, which enables the operation of a 1colloid emitter in bipolar mode — no additional neutralizer is required. The wetting behavior of EMI-BF4 on SU-8 was investigated and varied by applying different surface treatments. Sample emitters were fabricated and extraction tests were conducted. In the second part of this work a novel electrostatic emitter concept with an alternative approach for generating charged particles is proposed and investigated—the solid-state ion-emitter (SSIE). The fabrication and investigation of thin solid-electrolyte membranes were conducted in this work. In particular, the influence of lateral membrane dimensions on the stability of such ion conductor membranes was investigated. The residual stress in YSZ thin-film membranes and the resulting strain patterns were analyzed using Raman spectroscopy.

Vibrational modes introduced by the incorporation of N into GaAs and GaInAs have been studied by Raman spectroscopy on samples grown by molecular-beam epitaxy using a rf nitrogen plasma source. When proceeding from GaAs(1-x)N(x) to Ga(1-y)In(y)As(1-x)N(x) with x

In(0.53)Ga(0.47)As/InP/In(0.53)Ga(0.47)As heterostructures with InP barrier widths between 2 and 20 nm, grown by metal-organic chemical-vapor deposition (MOCVD), were analyzed with respect to interfacial intermixing and As incorporation in the InP. Raman scattering in conjunction with spectroscopic ellipsometry revealed the formation of intermixed (InGa)(AsP) interface layers with a width of about 2 nm. A second effect to be distinguished from interfacial intermixing was detected by the same experimental techniques, namely, the incorporation of As into the InP at an almost constant concentration for InP layer thicknesses up to at least 20 nm. The cross incorporation of As into the InP was attributed to memory effects in the MOCVD growth system.

The aim of the Karlsruhe Tritium Neutrino (KATRIN) experiment is a neutrino mass measurement with a sensitivity of 0.2 eV/c2 (90% C.L.) by the investigation of tritium beta-spectrum. It requires the continuous monitoring of the isotopic composition of the tritium gas by Raman spectroscopy. The aim of this work was to design and commission the Raman system. Special emphasize was put on the metrological performance and reliable operation over the projected operating time of several years.

Im ersten Teil der Arbeit werden Graphen sowie von Monolagen von auf Nanometer großen Graphenen basierenden Hexa-peri(Dodekyl)-Hexabenzocoronen-Molekülen (HBC-C12), adsorbiert auf Graphen, mit Rastertunnelmikroskopie und –spektroskopie an der Fest-Flüssig-Grenzfläche untersucht. Nanographen-Moleküle selbstaggregieren epitaktisch zu hochgeordneten Monolagen. Die Einheitszellen der Moleküllagen auf Monolage Graphen, Bilage Graphen und auf Graphit sind ununterscheidbar. Die Strukturen der Moleküllagen auf gewellten und flachen Teilen des Graphens stimmen überein. Strom-Spannungs-Kennlinien an Nanographen auf Graphen und auf Graphit weisen auf sehr ähnliche elektronische Eigenschaften hin. Zusammengefasst sind strukturelle sowie elektronische Eigenschaften der Nanographenlage homogen, stabil und definiert. Graphen erweist sich als bestens als Substrat und gleichzeitig als Elektrode für hochgeordnete Lagen von Nanographen-Molekülen geeignet. Im zweiten Teil der Arbeit wird Graphen mit der Sonde eines Rasterkraftmikroskops im Kontaktmodus mechanisch manipuliert. Es wird gezeigt, dass Graphen in nur einem Manipulationsschritt zu Streifen und Spalt geschnitten werden kann. Dieses Verhalten wird mit einem klassischen Modell des Biegens theoretisch erklärt. Das Schnittverhalten liegt in der 2-Dimensionalität des Graphens sowie in dessen Faltbarkeit auf Grund hinreichender Elastizität begründet. Durch mechanische Manipulation mit der Sonde des Rasterkraftmikroskops im Kontaktmodus unter atmosphärischen Bedingungen wird eine Flüssigkeitsschicht zwischen Graphen und dem Siliziumdioxidsubstrat nachgewiesen, welche eine mögliche Erklärung des stark kraftabhängigen Materialkontrasts zwischen Graphen und Siliziumdioxid im Amplitudenmodulationsmodus des Rasterkraftmikroskops darstellt. Weiter wird gezeigt, dass das Falten des Graphens durch mechanische Manipulation eine geeignete Methode zur Herstellung nicht epitaktisch aufeinander gestapelter Graphene darstellt. In the first part of the thesis graphene as well as monolayers of hexa-peri(dodecyl)-hexabenzocoronene molecules (HBC-C12) based on nanometer sized graphenes adsorbed on graphene is investigated by scanning tunnelling microscopy and tunneling spectroscopy at the solid-liquid interface. The nanographene molecules self-assemble on graphene epitaxially to form highly ordered monolayers. The unit cells of the molecular layers on monolayer graphene, bilayer graphene and on graphite appear identical. The structures of the molecular layers occur equal on corrugated and on flat parts of graphene. Current-voltage-characteristics show that the electronic properties of nanographene on graphene and on graphite are very similar. Summarized, structural as well as electronic properties of the nanographene layer are homogeneous, stable and defined. Graphene proves to be excellently qualified for simultaneously being substrate as well as electrode for highly ordered layers of nanographene based molecules. In the second part of the thesis graphene is mechanically manipulated in air in contact mode of a scanning force microscope. It is shown that a single manipulation process can lead to a stripe cut out of graphene. This behaviour is theoretically explained by a classical bending model. The cutting behavior originates from the 2-dimensionality of graphene and its folding ability because of sufficient elasticity. A liquid layer between graphene and the silicon dioxide substrate is verified by mechanical manipulation in contact mode of a scanning force microscope. Hence a possible explanation could be found for the strongly force dependent material contrast between graphene and silicon dioxide in amplitude modulation mode of the scanning force microscope. Further, it is demonstrated that folding graphene by mechanical manipulation is a proper method for the production of graphene stacked on each other non-epitaxially.

Molecular hydrogen was directly observed in crystalline GaAs by Raman spectroscopy. At Tau = 77 K, GaAs samples that have been exposed to a hydrogen/deuterium plasma exhibit four vibrational lines at 2842.6, 3446.5. 3925.9, and 3934.1 cm (exp -1), respectively. With a pure hydrogen plasma only the two high frequency lines can be seen and with a pure deuterium plasma only the lowest frequency is observed. We attribute these frequencies to the rovibrational modes of isolated interstitial D2, HD, and H2 molecules, respectively.

We have studied InAs/GaSb superlattices ~SL’s ! grown with either InSb-like or GaAs-like interfaces ~IF’s ! on top of a GaSb buffer layer on ~100! GaAs substrates. The InAs layer thickness was varied from 4 to 14 monolayers ~ML! while the GaSb layer thickness was kept fixed at 10 ML. The type of IF bonds realized was verified by Raman scattering from mechanical IF modes. High-resolution x-ray diffraction using one- and two-dimensional mapping of symmetric and asymmetric reflections allowed us to determine independently the lattice parameters parallel and perpendicular to the growth direction. The GaSb buffer layer was found to be fully relaxed whereas the SL’s with InSb-like IF’s were coherently strained to the in-plane lattice parameter of the GaSb buffer for InAs layer thicknesses exceeding 6 ML. The strain distribution within the SL’s with GaAs-like IF’s was obtained from simulations of the x-ray reflection profiles. The SL’s were found to be coherently strained close to the GaSb buffer and showed increasing strain relaxation with increasing distance from the buffer layer. In addition, these simulations provide an accurate determination of the SL periods. Well-resolved Raman spectra of backfolded longitudinal acoustic ~LA! phonons were observed showing for SL’s with InSb-like IF’s folded LA phonon lines up to the seventh order. The spectrum of quasiconfined optical SL phonons was examined by Raman spectroscopy and by IR reflection. A detailed analysis of the IR reflection spectra allowed an independent determination of the individual layer widths within the SL stack, including the spatial extent of the GaAs-like IF mode. @S0163-1829~96!06820-8#

Die vorliegende Dissertation untersucht mittels inelastischer Lichtstreuung sowohl die elektronische Struktur als auch die Schwingungseigenschaften von unterschiedlichen Kohlenstoffsystemen. Der erste Teil befasst sich mit der Frage, inwieweit korrelierte Elektron-Loch Paare, sogenannte Exzitonen in ein-dimensionalen metallischen Kohlenstoffnanoröhren existieren. Für gewöhnlich wird die Entstehung von Exzitonen in metallischen drei-dimensionalen Festkörpern auf Grund der Coulomb-Abschirmung verhindert. Diese Abschirmung ist stark reduziert in niedrigeren Dimensionen. Theoretische Rechnungen sagen eine Bindungsenergievon 50-100 meV voraus, folglich werden die optischen Übergänge selbst bei Raumtemperatur durch Exzitonen bestimmt. Mittels resonanter Raman Streuung kann der optische Übergang von spezifischen Kohlenstoffnanoröhren, insbesondere auch in einem Ensemble von unterschiedlichen Chiralitäten, bestimmt und einzelne Chiralitäten können unterschieden werden. Der optische Übergang wurde als Funktion der Temperatur für metallische und halbleitende Kohlenstoffröhren gemessen. Bei einer Temperatur, die der thermischen Energie der Exzitonen entspricht, konnte bei der metallischen Kohlenstoffröhre eine plötzliche Änderung der Übergangsenergie hin zu höheren Energien gemessen werden, während die halbleitende diese Änderung nicht aufweist. Dies erklärt sich dadurch, dass die thermische Energie zur Dissoziation der Exzitonen führt und folglich die exzitonische Oszillatorstärke vom Exziton in einen quasi Band-zu-Band Übergang übergeht. Es konnte nachgewiesen werden, dass die Bindungsenergie der korrelierten Elektron-Loch Paare in der Größenordnung von 50 meV liegt. Der zweite Teil der Arbeit beschäftigt sich mit Streuprozessen auf mikroskopischer Ebene der doppel-resonanten Raman Streuung. Aufgrund der Impulserhaltung tragen üblicherweise nur Phononen am Γ Punkt zum Raman Streuprozess bei. Bei der Doppelresonanz, einem Raman Prozess zweiter Ordnung, hingegen tragen Phononen aus der ganzen Brillouin-Zone bei. Phononen, welche die Bedingung für die Doppelresonanz erfüllen, tragen hierzu verstärkt bei. Durch Variation der Anregungswellenlänge ändern sich die Bedingungen für die Doppelresonanz, weshalb andere Phononen beteiligt werden und folglich der Raman Peak seine Frequenz ändert. Somit lässt sich die Phononendispersion messen, sofern ausreichende Kenntnisse über die elektronische Struktur und die Streuprozesse auf mikroskopischer Ebene bekannt sind. Charakteristisch ist die sogenannte 2D Mode, die das Spektrum von Graphene dominiert und sich auch zur Bestimmung der Anzahl der Atomlagen nutzen lässt. Allerdings sind die relevanten Streuprozesse, die zu dieser Mode beitragen derzeit in der Diskussion. Man unterscheidet hier zwischen äußeren Prozessen, bei denen die Elektronen zwischen dem Γ Punkt und dem K Punkt, und inneren Prozessen, bei denen die Elektronen zwischen dem M Punkt und dem K Punkt angeregt werden. Zuerst werden die Beiträge der 2D Mode in freistehendem zweilagigem Graphen (sog. bilayer graphene) untersucht. Es werden die Raman Frequenzen berechnet und mit dem Experiment verglichen. Darüber hinaus werden die Raman Spektren explizit ausgerechnet. Die relative Raman Intensität der unterschiedlichen Beiträge wird in Hinblick auf Elektron-Photon und Elektron- Phonon Matrixelemente diskutiert und es wird gezeigt, dass eine Reduzierung der Streuprozesse auf eine Dimension sowohl eine sehr gute Übereinstimmung der Frequenzen bringt, als auch die relativen Intensitäten reproduzieren kann. Eine anschließende kurze Betrachtung der Streuprozesse in zwei Dimensionen befasst sich mit den Begriffen des innereren und äußereren Prozesses und inwieweit sich die Begrifflichkeiten auf zwei Dimensionen ausweiten lassen. Es kann gezeigt und argumentiert werden, dass die gängige Notation beibehalten werden kann., The present thesis studies the electronic and vibrational properties of carbon systems with inelastic light scattering. The work comprises two parts. The first part addresses the question of the existence of correlated electron-hole pairs, so-called excitons, in metallic single-walled carbon nanotubes. However, excitons are expected to be prevented in metallic systems due to Coulomb screening at the Fermi level. However, this screening is strongly suppressed in lower dimensions such as the one-dimensional carbon nanotubes and excitonic binding energies on the order of 50 - 100 meV have been predicted. Here, the excitonic binding energy of metallic single-walled carbon nanotubes is measured with temperature-dependent resonant Raman spectroscopy. By changing the temperature, variations in the optical transition energy E_ii are observed between metallic and semiconducting nanotubes. Both dependences are found to be different for semiconducting and metallic single-walled carbon nanotubes. This behavior is explained in terms of excitons dissociated into free electron-hole pairs at temperatures related to the exciton binding energy. The excitonic oscillator strength is transferred back to the band-edge and thus the optical transition is determined by a quasi band-to-band transition. The exciton binding energy was derived and found to be on the order of 50 meV for the metallic nanotube. The interpretation is further supported by the observation of a stronger temperature-induced decrease in the Raman scattering efficiency in case of the metallic nanotube compared to the semiconducting tube. The second part addresses the question of scattering paths contributing to the double-resonant process. Due to momentum conservation only Γ point phonons contribute to the Raman spectrum. Double- resonant Raman scattering provides a powerful technique for probing the phonon dispersion of graphene and related systems. The double-resonant process, however, permits that phonons from the entire Brillouin zone contribute to the Raman spectrum. Double-resonant processes that satisfy the double- resonant condition are enhanced. By tuning the excitation energy this condition alters and changes the contributing phonons and hence the Raman frequency. An understanding of the scattering paths is essential, since by Raman spectroscopy it is possible to probe both the electronic structure and phonon dispersion. However, the contributing processes are under recent discussion. The dominant Raman feature is the so-called 2D mode, which also allows the determination of the number of graphene layers. Theoretical and experimental studies of strain in graphene gave first evidences for the contribution of phonons stemming from different sides of the K point. So-called inner and outer processes were dis- tinguished. Inner processes refer to the excitation of electrons between the K and M-point, whereas outer processes refer to the electronic excitation of electrons between the Γ and K-point. First, the double-resonant process is investigated in free-standing bilayer graphene. Experimental results are combined with a one-dimensional calculation along the high-symmetry line. Different scenarios of double-resonant scattering paths are probed, and a combination of both inner and outer processes is found to reproduce the experimental data very well. The Raman spectrum for different excitation energies is calculated and it is shown that a reduction of the double-resonant process in one- dimension provides very good agreement with the experiment. The relative intensities of the 2D mode are discussed in terms of electron-phonon and optical matrix elements. A brief consideration towards a two-dimensional calculation of the scattering processes indicate that the terms of inner and outer processes is not uniquely determined but can be maintained under certain aspects. Then a double-resonant combination mode consisting of a transverse (TO) optical and a longitudinal acoustic (LA) phonon is investigated. By analyzing the dispersion, this mode is assigned to an inner process. Further, the asymmetric lineshape is found to be a direct consequence of the strong angular dependence of the LA phonon branch. It is shown that the main contribution is due to a scattering process along the high-symmetry line. The decrease in intensity towards higher frequencies is explained by the angular dependence of the optical matrix element. The one-dimensional scattering paths of the double-resonance is then applied to graphite. Here the LA phonon dispersion is monitored by an analysis of the 2D and TO + LA mode. Es wird schließlich noch eine Kombinationsmode untersucht, die sich aus einem transversal optischen (TO) und einem longitudinal akustischen (LA) Phonon zusammensetzt. Diese doppel-resonante Mode wurde in der Literatur bislang wenig untersucht. Aufgrund der Dispersion dieser Raman Mode kann sie eindeutig einem inneren Prozess zugeordnet werden, so dass hier gezeigt werden konnte, dass innere Prozesse zum Raman Spektrum beitragen. Zudem ist diese Mode die einzige im Spektrum, die eine starke Asymmetrie zu höheren Frequenzen aufweist. Die Asymmetrie lässt sich durch die Winkelabhängigkeit der LA Phononendispersion in der zweidimensionalen Brillouinzone erklären. Es konnte gezeigt werden, dass der Hauptbeitrag von inneren Prozessen aus der Hochsymmetrie-Richtung stammt.

Using Raman scattering by local vibrational modes (LVM) and collective electronic excitations we have investigated the ordered incorporation of Si dopant atoms on vicinal GaAs(001) surfaces. LVM spectra revealed for a sequence of delta-doped samples grown by molecular beam epitaxy (MBE) under specific conditions that the Si dopant atoms are predominantly incorporated on Ga-sites even at a doping concentration as high as 1.8 x 10high13 cmhigh-2. For a sample grown under conditions established by real-time high-energy electron diffraction (RHEED) to be favourable for the wire-like Si incorporation, a pronounced polarization asymmetry in the Raman scattering intensity of collective intersubband plasmon-phonon modes arising from the delta-doping layer has been found.

Kohlenstoffnanotubes sind winzige Zylinder, die man sich wie aufgerollte Graphenmonolagen vorstellen kann. Sie besitzen die gleiche sechseckige Wabenstruktur, wie sie auch in Graphit vorkommt. Unter Funktionalisierung versteht man die chemische Veränderung der Tubes, dabei werden Moleküle an die Seitenwand der Nanotubes gebunden. Man unterscheidet kovalente und nicht-kovalente Funktionalisierungen. Funktionalisierte Nanotubes sind in vielen Bereichen der Nanotechnik und der Chemie einsetzbar; die Funktionalisierung erlaubt das Anpassen der Röhren an bestimmte Umgebungen, z.B. durch Verändern ihrer Löslichkeit. Kovalente Bindungen beinflussen die atomare Sturuktur der Seitenwände, u.a. führt die Bindung lokal zu einer Entspannung des Gitters. Dieser Effekt wird in der Durchmesserabhängigkeit der Reaktivität verschiedener Tubes sichtbar, Röhren kleiner Durchmesser werden bevorzugt funktionalisiert. Durch geeignete Reaktionsbedingungen kann auch die Reaktivität halbleitender oder metallischer Nanotubes bevorzugt sein. Je nach Art der funktionellen Gruppen wird die elektronische Struktur der Nanotubes unterschiedlich stark beeinflusst. Die resonante Ramanspektroskopie erlaubt eine detaillierte Untersuchung dieser Einflüsse. Die Ver änderungen der optischen Übergänge lassen sich anhand der Resonanzprofile der sog. Atmungsmode der Tubes untersuchen. Dabei können elektronische Effekte durch Ladungstransfer von Einflüssen durch strukturelle Ver- änderungen, hervorgerufen durch die kovalenten Bindungen, unterschieden werden. Die außergewöhnlichen mechanischen Eigenschaften der Nanotubes machen diese auch interessant für Verbundmaterialien, insbesondere in Verbindungen mit Polymeren. Die elektronischen Eigenschaften der Röhren nach der Polymerisation werden untersucht. Üblicherweise werden funktionalisierte Nanotubes anhand von Ensembles untersucht. Einzelne Tubes, auf einem Gitter gewachsen, ermöglichen auch polarisationsabhängige Ramanmessugen. Darüber hinaus ergeben sich interessante experimentelle Möglichkeiten durch die Kombination von Ramanmessungen mit hochauflösender Elektronenmikroskopie., Carbon nanotubes are tiny cylinders which can be imagined as rolled up graphene monolayers. Their fundamental architecture is the honeycomb lattice with sp2-hybridized carbon as known from natural graphite. Functionalization means a chemical treatment, which adds molecules to the nanotubes by covalent or non-covalent bonding. Functionalized carbon nanotubes have many potential applications in the fields of nanoelectronics and chemistry. The functionalities allow to design tubes for special needs in specific environments and drastically increase the processability of nanotubes, e.g., by increasing the solubility in certain media. Chemical functionalization highly influences the carbon lattice. The addition leads to local strain relaxation, which is revealed in the diameter dependence of the tube reactivity. Due to the different curvature of the tubes, small diameter tubes are more affected than larger ones. Depending on the applied reaction conditions also a preferred reaction to either metallic or semiconducting tubes can be achieved. The charge transfer between the tube and the addend causes changes in the electronic structure of the tubes, depending on the moiety. This is probed via resonant Raman spectroscopy of the tubes, which reveals changes in the optical transitions. Due to their extraordinary mechanical properties, nanotubes are also desirable for composite materials, e.g., the integration into polymers. The electronic properties of such composites after polymerization are studied. It is shown that electronic effects can be separated from pure structural effects after covalent sidewall additions. The investigation of functionalized material is typically performed on nanotube ensembles, i.e., solutions or bulk material. Isolated tubes or small bundles on a grid allow polarization dependent measurements in addition to the experimental benefit to combine the spectroscopical analysis with the structural characterization by the transmission electron microscopy measurements

We report on Raman scattering by longitudinal optical (LO) phonons in GaAs/AlAs superlattices with AlAs barrier thicknesses of nominally 1, 2, and 3 monolayers (ML). A Stark ladder of two-dimensional subbands equidistant in energy was produced by applying an electric field along the growth direction of these structures. The energy difference separating these states was tuned into resonance with the LO phonon energies. Single, double, and triple resonance conditions for Raman scattering by one and two LO phonons, respectively, have thus been realized. For the 3 ML sample, the triply resonant process is observed both for the case that the second intermediate state is at ksub2 is not equal 0 in the same Stark ladder level as the third intermediate state as well as for the second intermediate state being located at ksub2 is equal to 0 in a separate Stark ladder level. The 2 ML and 1 ML samples show a drastic enhancement of the spatially indirect transitions giving rise to a variety of reso nance effects in the Raman signal. For these samples, however, triple resonance effects are difficult to observe due to the relatively weak 2 LO phonon scattering. This is probably due to lifetime broadening of the subbands giving rise to less pronounced resonant enhancement in the Raman scattering cross section.

CdSe Nanorods sind Nanopartikel, die in einerLösung synthetisiert werden. Die Nanorods können in eine epitaktische Hülle aus einem Halbleitermaterial mit einer größeren Bandlücke, ZnS, eingebettet werden. In dieser Arbeit werden der Einfluss der ZnS H\ülle auf den CdSe Kern und die Schwingungseigenschaften von CdSe Nanorods mit Ramanspektroskopie untersucht. Es wird gezeigt, dass die Frequenzen der longitudinal-optischen Phononen vom Durchmesser der Nanorods bestimmt werden. Dies liegt daran, dass die Wellenfunktion der Phononen im Nanokristall eingeschlossen ist. Die Kopplung der longitudinal-optischen Phononen an Exzitonen hängt ebenfalls vom Durchmesser ab. Eine radiale Atmungsmode in den Nanorods wird nachgewiesen. Die Frequenz dieser hängt stark vom Nanorod-Durchmesser ab, und die Messung der Frequenz erlaubt die Bestimmung des Durchmessers mittels Ramanspektroskopie. Die durch die Hülle verursachten Verpannungen werden mit ab-initio-Berechnungen untersucht. Bindungen entlang der c-Achse sind kaum verspannt, die lateralen Bindungen sind homogen verspannt. Die Größe der Verspannungen kann quantitativ mit Ramanspektroskopie bestimmt werden. Das durch die Hülle geänderte Nanorod-Umfeld führt zu einer Änderung der Exziton-Wellenfunktion und dadurch zu einer stark abnehmenden Exziton-Phonon-Kopplung., Colloidal CdSe nanorods are nanoparticles synthesized in solution. The nanorods can be epitaxially covered with a graded CdS/ZnS shell of a few monolayers in thickness. In this work Raman spectroscopy, accompanied by ab-initio calculations, is used to determine the amount of this strain, the exciton-phonon coupling strength in the nanorods and to investigate confinement effects. The longitudinal optical phonons in a nanorod are confined to the nanorod volume. The coupling strength between longitudinal optical phonons and excitons depends on the nanorod diameter. The total coupling strength is much lower than in bulk material due to a decrease of the influence of the Coulomb interaction in nanoparticles. A radial breathing mode with a diameter dependent frequency is investigated verified experimentally. In core-shell structures, the coverage of a CdSe nanorod with a ZnS shell leads to a compressive strain of the CdSe core due to the smaller lattice parameter of ZnS compared to CdSe. The amount of strain is estimated from the Raman spectra.

[no abstract]

presented by Sonja Gamsjäger Abweichender Titel laut Übersetzung der Verfasserin/des Verfassers Salzburg, Univ., Diss., 2007

The physical and thennodynamicproperties ofmagmas control the rate and style of a wide range of igneous processes. To a large extent, these properties are determined by the properties of the Silicate melt phase. Thus, Silicate melts play an essential role in the mass and heat transfer in the earth and terrestrial planets. For multi-component melts, the properties generally are not simple additive functions of the chemical composition,but strongly depend on the microscopic structure. This thesis focuses on the structureof silica glass and alkali Silicate glasses and melts. The results are then related to the bulk melt properties. The influence of the structure on the properties of alkali Silicate glasses was investigated by Si Single Quantum and Double Quantum MASNMRspectroscopy. The chemical shifts and the relative abundance of the ff species correlate with the cationic field strength (Z/r) of the network modifier. A correlation is observed between the glass transitiontemperature(Tg) and the inverse of the entropy of mixing of the differentff species, whichis explainedin the frameworkof the Adam-Gibbs relaxation theory. At high alkali content, up to 44% of the Si04 tetrahedra are part of three-membered rings. At a given alkali content, the abundance of these rings increases with increasing cation size. The abundance of three-membered rings in K-silicate melts correlates with a temperaUireand a non-linear composition dependence of the heat capacity. It is also a possible cause for the anomalous Volumetrie behaviorof potassium Silicate glasses. Because of the generally low sensitivity for 29Si NMR spectroscopy, the use of a Carr-Purcell- Meiboom-Gill (CPMG) echotrain to increase the sensitivity in glasses was investigated. The echo intensitydecay follows a stretched exponential behavior M(t) = M0 exp[-(t/t2)ß] with values for the exponent ß in the ränge of 0.41 to 0.65. The signal to noise in the spectra can be increased by a factor of up to 4 by taking the weighted sum of the spectra of the individual echoes. However, differential T2 relaxation for the different ff species is observed, with a shorter relaxation time for Q4 than Q. Thus, summing of the echoes leads to distorted spectral intensities and quantitative information can no longer be obtained from the spectra. To circumventthe problemwith differential T2 relaxation, an alternative approach is developed in which the spectral intensity for each chemical shift value is determined from the stretched exponential fit to its echo decay. With this approach,the sensitivity can be increased by a factor of up to 2.4, while quantitative informationcan still be obtained from the spectra. A 2ySi NMR spectrum with high signal to noise ratio was collected from a well characterized, isotopicallyenriched Si02 glass with a single scan after füll relaxation of the magnetization. Fromthe spectrum, the average Si-O-Si bond angle was estimated at 150° with a minimum fwhm of the bond angle distribution of 16°. The 29Si spin-lattice relaxation times were measured by Saturation recovery and differential Tl relaxation was observed for the various Si sites. In order to quantify the data from Raman spectroscopie measurements at high temperature, we developed a mathematical approach to interpret Raman spectra of binary Silicate glasses and melts withoutthe necessity of extemal calibration, e.g., from NMRspectroscopy, and without the need for any a priori assumptionsabout the linshape for the differentff species. We applied the quantification and the experimental approaches to investigate the speciation in potassium Silicate glasses. The equilibrium constant for the reaction 2Q3 = Q2 + Q4 was found to be logK3=-2.37±0.07,in excellent agreement withboth our own and previous NMRstudies. The enthalpy of formation(AH°) associated with the speciation reaction was determined to be 33.Ü7.3 kJ/mol with this approach. For the sodium Silicate system, we determined logK3 to be -1.88±0.04at room temperature, also in good agreement with NMRresults. The temperature dependence of the speciation is smaller for the sodium Silicate system than for the potassium Silicate system; AH° in sodium Silicate melts is 20.3±7.9 kJ/mol. Tn addition to the speciation, we also obtainedthe partial Raman spectra for the ff species for a ränge in temperatures for both Systems. By combining both isothennal and rate heating experiments, structural relaxation times were determined in the glass transition range with in situ, high-temperature Raman spectroscopy. The obtained relaxation times agree well with the shear relaxation times obtained from viscosity data. Thus, the timescale for viscous flow is the same as the timescale of the rearrangement of the Silicate network structure towards chemical equilibrium. This demonstrates that Si-O bond breaking is the primary control on Silicate melt viscosity.

Die Absorption sichtbaren Lichtes lässt sich in vielen Fällen qualitativ und quantitativ durch ein recht einfaches Modell beschreiben. Die inelastische Lichtstreuung führt zur Anregung von Schwingungen des Moleküls. Beide Wechselwirkungen des Lichtes werden genutzt, um die Eigenschaften von Molekülen zu untersuchen. Die erreichbare Genauigkeit der Bestimmung von Lichtmengen wird diskutiert und Kriterien für die Wahl des Detektors bestimmt. Mit dem Transientenspektrometer wird die Absorption angeregter Farbstoffmoleküle bestimmt. Diese Daten sind die Grundlage für die Experimente zur resonanten Ramanstreuung an anregten Molekülzuständen. Untersuchungen mit einem Ramanspektrometer für schwach fluoreszierende Proben geben Hinweise auf die erforderliche Messgenauigkeit. Es werden Untersuchungen über Ursprung und Größe des vorhandenen Rauschens durchgeführt. Anhand der gewonnen Daten lassen sich Strategien zur Optimierung finden. Eine Modulationstechnik zur Unterdrückung der Fluoreszenz durch 2-λ-Anregung wird vorgestellt und die Ergebnisse analysiert. Mit dem Ziel, das Signal-zu-Rausch Verhältnis zu steigern, werden die Anforderungen und Kenngrößen des Monochromators untersucht. Die notwendigen Verbesserungen werden in dem Ramanmikroskop umgesetzt. Dessen Funktion wird optimiert, bis die Messung von Ramanspektren angeregter Molekülzustände stark fluoreszierender Moleküle gelingt. Zur Interpretation der Schwingungseigenschaften von Rhodaminfarbstoffen werden Vergleiche zur Literatur und quantenmechanischen Rechnungen herangezogen. In many cases a comparatively simple model is capable to explain the absorption of visible light in a qualitative and quantitative matter. Inelastic scattering leads to a stimulation of molecular vibrations. Both interactions are used to determine important properties of molecules. The discussion of the achievable sensitivity on the quantification of the power of light leads to criteria for the choice of a detector. With the help of a transient-state spectrometer the absorption of excited states of dye molecules is measured. This data is essential for the experiments related to resonant raman scattering on transient states. Using a raman-spectrometer for weakly fluorescent probes, the necessary sensitivity is determined. Origin and magnitude of the noise level are studied carefully. The results give clues to several optimisation strategies. A modulation technique for suppression of the fluorescence by 2-λ- excitation is presented and the results are analyzed. Obligations and key parameters of the monochromator are examined with respect to the signal-to-noise ratio. The necessary improvements are accomplished in the raman microscope. Its function is optimised till the measurement of raman spectra of excited states of strongly fluorescent dyes is achieved. The properties of the vibrational spectra of rhodamine dyes are discussed with respect to literature data and quantum-mechanical calculations.

We have studied the effects of growth temperature and subsequent thermal annealing on nitrogen incorporation into lattice-matched dilute Ga(0.942)In(0.058)NAs-on-GaAs epilayers, which were grown by the molecular-beam epitaxy method. The samples were studied experimentally by means of x-ray diffraction and Raman spectroscopy and theoretically by calculations within the density-functional theory. Over the entire range of growth temperatures applied (410-470 deg C), nitrogen appeared to be mainly located on substitutional sites in ""short-range-order clusters"" as N-Ga-(4) and, to a lesser extent, as N-Ga(3)In. There were also indications of the presence of nitrogen dimers NN, as suggested by Raman spectroscopy, in qualitative agreement with the calculations. An increase in growth temperature reduced the amount of substitutional nitrogen and decreased the number of N-Ga-(4) clusters relative to N-Ga(3)In. Postgrowth thermal annealing promoted the formation of In-N bonds and caused a blueshift in the optical band gap, which increased as the growth temperature was lowered.

AlAs barriers embedded in GaAs were studied by spectroscopic ellipsometry and resonant Raman scattering. Heterostructures with AlAs barrier widths ranging from 2 to 30 nm were grown by molecular-beam epitaxy at growth temperatures between 410 and 660 Degree C. For layer widths below 10 nm the E(ind 1) and E(ind 1)+ Delta(ind 1) critical point resonance in the dielectric function of the AlAs was found to broaden and to be smeared out completely for a width of 2 nm. Resonant Raman scattering by the AlAs LO phonon reveals for layer widths equal or smaller than 10 nm a considerable broadening of also the E(ind 0) interband transition in the AlAs. The magnitude of the critical point broadening and redistribution of oscillator strength, however, was found to be independent of the growth temperature and thus of the cation intermixing observed by Raman spectroscopy for growth temperatures equal or greater than 600 Degree øC. Therefore, the observed critical point broadening is not caused by th e formation of graded composition (AlGa)As barriers. Instead, the broadening of interband resonances is attributed to a spread of the carrier wave functions into the surrounding GaAs, which are not confined within the AlAs barrier for neither the E(ind 0) nor the E(ind 1) and E (ind 1) + Delta(ind 1) interband transitions.

We performed resonant Raman scattering in hexagonal GaN using discrete laser lines in the violet and UV spectral range for optical excitation. To tune the energetic position of the fundamental gap E(ind 0) of GaN relative to the exciting photon energy the sample temperature was varied between 77 and 870 K. Analyzing both Stokes and anti-Stokes Raman spectra, the resonance profiles for Fröhlich-induced one-E(ind 1)(L0) and two-E(ind 1)(L0) phonon scattering could be deduced, covering the energy range from 0.5 eV below the E(ind 0) gap up to the gap energy. The strength of deformation-potential scattering by the A(ind1)(T0) mode was used as an internal reference. For excitation slightly above the E(ind 0) gap energy E(ind 1)(L0) multiphonon scattering up to the fourth order was observed, which reflects the stronger polarity of the Ga-N bond as corn~ to conventional III-V semiconductors.

We have studied backfolded longitudinal acoustic (LA) phonons in InAs/GaSb superlattices (SLs) intentionally grown with either InSb-like or GaAs-like interfaces (IFs). Raman scattering by folded LA phonons was found to be resonantly enhanced for incident photon energies slightly below the 2.0 eV electronic SL interband transition, observed previously by spectroscopic ellipsometry and by resonant Raman scattering from longitudinal optical SL phonons. Under resonant excitation, InAs/GaSb SLs with InSb-like IFs showed scattering by folded LA phonons up to the 7th order. For SLs with GaAs-like IFs, the folded LA phonon modes occurred at systematically higher frequencies than for SLs with the same nominal period and InSb-like IFs. The difference in frequency increased with decreasing SL period.

Im Rahmen dieser Arbeit werden zwei Perylen-Derivate als Zwischenschichten in Ag/organischen Schichten/GaAs(100)-Heterostrukturen eingesetzt, um den Einfluss von unterschiedlichen chemischen Endgruppen auf die chemischen und strukturellen Eigenschaften beider Grenzflächen, sowie auf die Morphologie, Struktur und Kristallinität von organischen Schichten zu charakterisieren. Die molekularen Schichten von 3,4,9,10-Perylentetracarbonsäure Dianhydrid (PTCDA) und Dimethyl-3,4,9,10-Perylentetracarbonsäure Diimid (DiMe-PTCDI) werden durch organische Molekularstrahldeposition (OMBD) im Ultrahochvakuum auf S-passivierten GaAs(100):2x1-Substraten hergestellt. Weiterhin wird der Einfluss des Substrats untersucht, indem PTCDA-Wachstum auf H-passiviertem Si(100):1x1 durchgeführt wird. Als Hauptcharakterisierungsmethode wird die Ramanspektroskopie eingesetzt. Diese ist eine nicht-destruktive Methode, die auch in situ Untersuchungen des Wachstumsprozesses ermöglicht. Die komplementäre Infrarotspektroskopie sowie die Rasterkraftmikroskopie, Rasterelektronenmikroskopie und Röntgenbeugung (XRD) werden zur Ergänzung des Verständnisses der Heterostruktureigenschaften verwendet. Die Empfindlichkeit von Raman- und Infrarot-Spektroskopien auf die chemisch unterschiedlichen Endgruppen wird durch experimentelle Untersuchungen an PTCDA- und DiMe-PTCDI-Kristallen, beziehungsweise dicken Schichten und mit Hilfe theoretischer Berechnungen nachgewiesen. So wird zum ersten Mal eine vollständige Zuordnung der Schwingunsfrequenzen zu den internen Schwingungsmoden von DiMe-PTCDI vorgeschlagen. Im niedrigen Frequenzbereich der Ramanspektren werden die externen molekularen Schwingungsmoden, oder molekularen „Phononen“, die eine Signatur der Kristallinität darstellen, beobachtet. Die Phononen von DiMe-PTCDI werden in dieser Arbeit zum ersten Mal in einem Ramanexperiment beobachtet. Mittels resonanter Ramanspektroskopie wird die Detektion von C-H-Deformationsmoden und C-C-Streckmoden sogar im Sub-Monolagenbereich molekularer Bedeckung auf Halbleiteroberflächen möglich. Anhand dieser Ramanspektren konnte die Art der Wechselwirkung zwischen Molekülen und passivierten Oberflächen näher charakterisiert werden. Zusätzliche Information bringen die GaAs LO- und Plasmon-gekoppelten LO- Phononen, deren Intensitätsverhältnis im Ramanspektrum die Bandverbiegung im GaAs-Substrat widerspiegelt. Die Kristallinität der hergestellten organischen Schichten mit Dicken größer als 2 nm wird durch Beobachtung der molekularen „Phononen“ nachgewiesen. Als allgemeine Tendenz konnte bewiesen werden, dass mit steigender Substrattemperatur während des Wachstums größere Kristalldomänen entstehen. Weiterhin wird eine Methode vorgeschlagen, um den Anteil von zwei PTCDA- Kristallphasen mit ähnlichen Gitterparametern anhand der Raman- beziehungsweise XRD-Spektren zu bestimmen. Durch ihre sehr gute Ordnung können die DiMe-PTCDI- Schichten als Modellsystem dienen, um eine Methode zu entwickeln, die die Molekülorientierung im Bezug zum Substrat aus polarisationsabhängigen Raman- und Infrarotmessungen bestimmt. Bei der Metall-Bedampfung wird die Empfindlichkeit der Ramanstreuung an internen molekularen Schwingungsmoden von PTCDA und DiMe-PTCDI-Schichten durch oberflächenverstärkte Ramanstreuung (SERS) erhöht. Anhand der unterschiedlichen Signalverstärkungsmechanismen werden Informationen über die Ag/Molekül- Wechselwirkung und die Morphologie der Ag-Schichten abgeleitet.

To gain information on the local bonding of the nitrogen, Ga1� xInxAs1� yNy with x 6 0:12 and y 6 0:04 and AlxGa1� xAs1� yNy with x 6 0:05 and y 6 0:04 have been studied by Raman spectroscopy. When adding In to GaAsN, the nitrogen-induced vibrational mode near 470 cm � 1 observed in GaAsN was found to split into up to three components, with one of the In–N related modes at higher and the other at lower frequencies than the Ga–N mode. Upon thermal annealing, the relative mode intensities were found to change in favor of the In–N related modes, indicating a redistribution of the III–N bonds. For AlxGa1� xAs0:99N0:01, in contrast, the almost exclusive formation of complexes with Alto-N bonding was observed already for a low Al content of x ¼ 0:05, as seen from a complete switchin mode intensity from the Ga–N mode at 470 cm � 1 to a new Al–N related mode near 450 cm � 1 . This result was confirmed by a corresponding analysis of the quinary compound AlGaInAsN. 2002 Elsevier Science Ltd. All rights reserved.