Maria M. Giangregorio

Dielectric function of nanocrystalline silicon with few nanometers (<3 nm) grain size

The dielectric function of nanocrystalline silicon (nc-Si) with crystallite size in the range of 1 to 3 nm has been determined by spectroscopic ellipsometry in the range of 1.5 to 5.5 eV. A Tauc–Lorentz parameterization is used to model the nc-Si optical properties. The nc-Si dielectric function can be used to analyze nondestructively nc-Si thin films where nanocrystallites cannot be detected by x-ray diffraction and Raman spectroscopy.

Er2O3 as a high-K dielectric candidate

Erbium oxide (Er2O3) films have been deposited by metal organic chemical vapor deposition on Si(001) using tris(isopropylcyclopentadienyl)erbium. The impact of Si surface passivation by the metal organic prior growth initiation was investigated. The correlation between the Er2O3 films structure, the optical response, the static dielectric constant (K), and density of interface traps is discussed. An Er-silicate interfacial layer with a thickness of 1.5nm, a static dielectric constant of 10–12.4, and a density of interface traps of 4.2×1010cm2eV−1 measured for a film with a physical thickness of 8.2nm (with an equivalent oxide thickness of 2.7nm) render Er2O3 an interesting candidate as a high-K dielectric.

Structural and optical investigation of plasma deposited silicon carbon alloys: Insights on Si-C bond configuration using spectroscopic ellipsometry

Amorphous (a–Si1−xCx:H) and microcrystalline (μc–Si1−xCx:H) thin films have been deposited by plasma-enhanced chemical-vapor deposition using SiF4–CH4−H2 rf plasmas. Gas flow rates have been varied to deposit films with different carbon content and microstructure. The microstructure and optical properties have been investigated by IR/Raman spectroscopy and by spectroscopic ellipsometry in the energy range of 1.5–5.0 eV. Ellipsometric spectra have been analyzed in terms of the tetrahedron model combined with the Bruggeman effective-medium approximation to determine the film microstructure and silicon–carbon-bond configurations. Correlation between Si–C bond configurations and optical properties of films has been studied as a function of carbon content and microstructure. It is found that the optical properties and the band gap value depend not only on the carbon content, but also on the Si–C bond configuration and microcrystallinity. The films consist of Si-centered Si–Si4−vCv(v=0–3) Si-centered tetrahedra...

Interaction of atomic hydrogen with Zn-polar and O-polar ZnO surfaces

The interaction of Zn-polar and O-polar ZnO surfaces with atomic hydrogen produced by a remote rf plasma source is investigated in situ and in real time using spectroscopic ellipsometry. It is found that the reactivity of ZnO with atomic hydrogen depends on polarity. The interaction of O-polar surfaces with atomic hydrogen at 100 °C is suitable for producing clean surfaces, while Zn-polar surfaces strongly react with atomic hydrogen resulting in a disruption of the ZnO lattice with formation of Zn surface clusters.

A two-step plasma processing for gold nanoparticles supported on silicon near-infrared plasmonics

A two-step sputtering methodology for fabricating gold nanoparticles supported on silicon with tuneable surface plasmon resonance down to the near-infrared spectral range has been developed. This methodology uses modification of the wettability of Si surfaces by an intermediate O2 plasma treatment to decouple diameter and height of nanoparticles as tuneable parameters to tailor the plasmon resonance.

Spectroscopic ellipsometry for characterization of organic semiconductor polymeric thin films

Abstract The correlation between the optical properties and microstructural parameters of organic semiconductor polymeric thin films is investigated by spectroscopic ellipsometry. Different poly(arylenephenylene)-based films have been deposited by spincoating. The effect of deposition conditions on the microstructure and, hence, optical constants of the polymeric thin films and the dependence of the optical properties and π–π ∗ transition on the structure of the chain backbone are studied.

Demonstrating the capability of the high-performance plasmonic gallium-graphene couple

Metal nanoparticle (NP)-graphene multifunctional platforms are of great interest for exploring strong light-graphene interactions enhanced by plasmons and for improving performance of numerous applications, such as sensing and catalysis. These platforms can also be used to carry out fundamental studies on charge transfer, and the findings can lead to new strategies for doping graphene. There have been a large number of studies on noble metal Au-graphene and Ag-graphene platforms that have shown their potential for a number of applications. These studies have also highlighted some drawbacks that must be overcome to realize high performance. Here we demonstrate the promise of plasmonic gallium (Ga) nanoparticle (NP)-graphene hybrids as a means of modulating the graphene Fermi level, creating tunable localized surface plasmon resonances and, consequently, creating high-performance surface-enhanced Raman scattering (SERS) platforms. Four prominent peculiarities of Ga, differentiating it from the commonly used noble (gold and silver) metals are (1) the ability to create tunable (from the UV to the visible) plasmonic platforms, (2) its chemical stability leading to long-lifetime plasmonic platforms, (3) its ability to n-type dope graphene, and (4) its weak chemical interaction with graphene, which preserves the integrity of the graphene lattice. As a result of these factors, a Ga NP-enhanced graphene Raman intensity effect has been observed. To further elucidate the roles of the electromagnetic enhancement (or plasmonic) mechanism in relation to electron transfer, we compare graphene-on-Ga NP and Ga NP-on-graphene SERS platforms using the cationic dye rhodamine B, a drug model biomolecule, as the analyte.

Interplay between GaN polarity and surface reactivity towards atomic hydrogen

GaN epitaxial layers have been grown by molecular beam epitaxy (MBE). Low (200 °C) and high (700 °C) temperature nitrided sapphire substrates, and GaN and AlN buffer layers have been used as the platforms for investigating polarity selection processes of GaN grown by RF-MBE, aimed at presenting a comprehensive understanding of the issues of GaN polarity and growth conditions. The results show that Ga-polar GaN results from the use of AlN buffer layers, and when the substrate/bulk interface has a Ga- or Al-rich interface. In contrast, a large density of N-polar domains is found when GaN epitaxial films are grown on GaN buffer layers on sapphire when nitrided at 200 °C. The impact of the polarity of GaN on the interaction of GaN surfaces with atomic hydrogen is also studied. A different reaction rate and reaction extent is found for N- and Ga-polar GaN with atomic hydrogen, with N-polar GaN exhibiting greater reactivity. It is also demonstrated that the reactivity of GaN with atomic hydrogen coupled with su...

GaMg alloy nanoparticles for broadly tunable plasmonics.

Manipulating the properties of well understood materials systems for novel technological applications can be achieved by creating nanoscale structures and mixed compounds. The design of novel nanomaterials that underpin plasmonic applications drives the rapid progress in advancing plasmonic materials over the last few years. [ 1 , 2 ] Control of metal nanoparticle shape, [ 3 , 4 ] density, and spacing [ 5 ] is continually improving with novel synthetic techniques. Nevertheless, to continue advancing plasmonics, new metallic nanostructure systems must be developed that offer unique properties and are superior to Ag, [ 6 ] Au, [ 3 , 7 ] and mixtures thereof—the most widely exploited metals [ 8–10 ] and bimetallic systems. [ 11 ]

Characteristics of InN grown on SiC under the in-rich regime by molecular beam heteroepitaxy

InN epitaxial films were grown by N2 plasma-assisted molecular beam epitaxy on 4H- and 6H-SiC substrates using low-temperature InN nucleation layers. InN films grown at various In fluxes under the In-rich regime show improved crystal quality, surface morphology, and optical properties, without sizable metallic In incorporation. Photoluminescence measurements show emission up to room temperature, band gap values as low as 0.64eV at T=10K, and carrier concentrations of the order of 8×1017cm−3.