The aim of this research is to study the work function (Фm) tuning of the HfxSiyNz metal films through the incorporation of nitrogen. The Hf and the Si targets were co-sputtered in nitrogen (N2) and argon (Ar) plasma at 12mTorr. The gas flow ratio, RN = N2/ (N2+Ar), was adjusted to vary the nitrogen concentration in HfSiN films. The work function (Фm) of HfSiN gate extracted from the capacitance-voltage (CV) and the internal photoemission (IPE) measurements was found to decrease (from ~ 4.64eV to ~ 4.42eV) for increasing gas flow ratios (from 10% to 30%). X-ray photoelectron spectroscopy (XPS) was used for material characterization. During XPS analysis, the nitrogen (N 1s) peak intensity was observed to increase with increasing gas flow ratios. The results indicate that adjusting the nitrogen concentration in HfSiN films can be used to tune the HfSiN gate work function over ~ 0.2 eV tuning window.

The aim of this research is to study the work function (Фm) tuning of the HfxSiyNz metal films through the incorporation of nitrogen. The Hf and the Si targets were co-sputtered in nitrogen (N2) and argon (Ar) plasma at 12mTorr. The gas flow ratio, RN = N2/ (N2+Ar), was adjusted to vary the nitrogen concentration in HfSiN films. The work function (Фm) of HfSiN gate extracted from the capacitance-voltage (CV) and the internal photoemission (IPE) measurements was found to decrease (from ~ 4.64eV to ~ 4.42eV) for increasing gas flow ratios (from 10% to 30%). X-ray photoelectron spectroscopy (XPS) was used for material characterization. During XPS analysis, the nitrogen (N 1s) peak intensity was observed to increase with increasing gas flow ratios. The results indicate that adjusting the nitrogen concentration in HfSiN films can be used to tune the HfSiN gate work function over ~ 0.2 eV tuning window.

The field of organic-based opto-electronic devices such as organic light- emitting diodes (OLEDs) or field-effect transistors (OFETs) has grown in interest over the past two decades. Optimizing the performance of these applications requires a better understanding of the processes taking place inside the devices and especially at their interfaces. We focused in this Ph.D. work on the electronic structure of metal/organic interfaces where the charge injection mechanism occurs. The latter process can be modulated and fine tuned by the control of the work function of the metallic electrodes. Chemisorption of self-assembled monolayers (SAMs), i.e., a two-dimensional layer of polar molecules deposited onto metal surfaces proves to be an efficient way to tune the work function of electrodes in OLED and OFET devices. However, the role played by the dipole moment of the adsorbed molecules as well as the description of the electronic effects taking place at the metal/SAM interfaces are not yet well understood. Our Ph.D. work aims at rationalizing at a theoretical level (via quantum- chemical calculations) the electronic processes occurring at metal/organic interfaces. For this goal, we focused our investigations on a well-characterized system : a methanethiolated SAM on gold-(111) surface. The adsorption energy and the influence of the anchoring site on the work function shift were evaluated beforehand in order to validate our methodology. The decomposition of the interfacial dipole moment into its interfacial and molecular components was assessed in a second stage for this system following two different procedures which differ by the treatment of the molecular backbone. The incorporation of a third component, generally not treated in an explicit way, was taken into consideration to unify the description of the interface dipole. The influence of the packing density was also described. In a next step, we have extended this study by changing the SAM chemical structure and by investigating the influence of a modification of the anchoring atom, a fluorination of the methyl group and a change in the nature of the metal surface (Ag, Cu, Pt). In order to probe the influence of intermolecular interactions, we have finally considered longer alkanethiol chains having various terminal chemical functions and analyzed the influence of the structural geometry on the change in the electrostatic potential.

Due to continued transistor scaling, work function tuning of metal gates has become important for advanced CMOS applications. Specifically, this research has been undertaken to discover the tuning of the MoxSiyNz gate work function through the incorporation of nitrogen. Metal Oxide Semiconductor (MOS) capacitors were fabricated using thermal SiO2 as gate oxide on lightly doped p-type Si wafer. A molybdenum silicide (MoSi2) target was reactively sputtered at 10mTorr in presence of N2 and Ar. The gas flow ratio, RN = N2/ (N2+Ar), was adjusted to vary the nitrogen concentration in MoSiN films. The gate work function (Фm) was extracted from capacitance-voltage (CV) measurements using the VFB-tox method. Interfacial barrier heights were measured using internal photoemission (IPE) as an independent confirmation of the MoSiN gate work function. The work function was found to decrease linearly (from ~4.7eV to ~4.4eV) for increasing gas flow ratios (from 10% to 40%). Secondary ion mass spectrometry (SIMS) depth profiles suggested that the nitrogen concentration was relatively uniform throughout the film. X-Ray Photoelectron Spectroscopy (XPS) surface analysis showed a steady increase in the total nitrogen concentration (from ~20% to 32%) in these films as gas flow ratio was increased. These data suggests that the increase in nitrogen concentration in MoSiN films corresponds directly with the lowering of MoSiN work function. These results clearly demonstrate that the work function of MoxSiyNz can be varied ~0.3 eV by adjusting the nitrogen concentration. / October 2008

Due to continued transistor scaling, work function tuning of metal gates has become important for advanced CMOS applications. Specifically, this research has been undertaken to discover the tuning of the MoxSiyNz gate work function through the incorporation of nitrogen. Metal Oxide Semiconductor (MOS) capacitors were fabricated using thermal SiO2 as gate oxide on lightly doped p-type Si wafer. A molybdenum silicide (MoSi2) target was reactively sputtered at 10mTorr in presence of N2 and Ar. The gas flow ratio, RN = N2/ (N2+Ar), was adjusted to vary the nitrogen concentration in MoSiN films. The gate work function (Фm) was extracted from capacitance-voltage (CV) measurements using the VFB-tox method. Interfacial barrier heights were measured using internal photoemission (IPE) as an independent confirmation of the MoSiN gate work function. The work function was found to decrease linearly (from ~4.7eV to ~4.4eV) for increasing gas flow ratios (from 10% to 40%). Secondary ion mass spectrometry (SIMS) depth profiles suggested that the nitrogen concentration was relatively uniform throughout the film. X-Ray Photoelectron Spectroscopy (XPS) surface analysis showed a steady increase in the total nitrogen concentration (from ~20% to 32%) in these films as gas flow ratio was increased. These data suggests that the increase in nitrogen concentration in MoSiN films corresponds directly with the lowering of MoSiN work function. These results clearly demonstrate that the work function of MoxSiyNz can be varied ~0.3 eV by adjusting the nitrogen concentration.

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Due to continued transistor scaling, work function tuning of metal gates has become important for advanced CMOS applications. Specifically, this research has been undertaken to discover the tuning of the MoxSiyNz gate work function through the incorporation of nitrogen. Metal Oxide Semiconductor (MOS) capacitors were fabricated using thermal SiO2 as gate oxide on lightly doped p-type Si wafer. A molybdenum silicide (MoSi2) target was reactively sputtered at 10mTorr in presence of N2 and Ar. The gas flow ratio, RN = N2/ (N2+Ar), was adjusted to vary the nitrogen concentration in MoSiN films. The gate work function (Фm) was extracted from capacitance-voltage (CV) measurements using the VFB-tox method. Interfacial barrier heights were measured using internal photoemission (IPE) as an independent confirmation of the MoSiN gate work function. The work function was found to decrease linearly (from ~4.7eV to ~4.4eV) for increasing gas flow ratios (from 10% to 40%). Secondary ion mass spectrometry (SIMS) depth profiles suggested that the nitrogen concentration was relatively uniform throughout the film. X-Ray Photoelectron Spectroscopy (XPS) surface analysis showed a steady increase in the total nitrogen concentration (from ~20% to 32%) in these films as gas flow ratio was increased. These data suggests that the increase in nitrogen concentration in MoSiN films corresponds directly with the lowering of MoSiN work function. These results clearly demonstrate that the work function of MoxSiyNz can be varied ~0.3 eV by adjusting the nitrogen concentration.

Thesis (Ph. D.)--Oregon Graduate Center, 1987.

As the critical dimensions of many devices, especially electronics, continue to become smaller, the ability to accurately analyze the properties at ever smaller scales becomes necessary. Optical techniques, such as confocal microscopy and various spectroscopies, have produced a wealth of information on larger length scales, above the diffraction limit. Scanning probe techniques, such as scanning tunneling microscopy and atomic force microscopy, provide information with an extremely fine resolution, often on the order of nanometers or angstroms. In this document, plasmon coupling is used to generate large signal increases, with clear future applications toward scanning probe optical spectroscopies. A variation on scanning tunneling microscopy is also used to study the surface structure of environmentally interesting nanoparticles. Traditional Raman spectroscopy is used to examine doped graphene, which is becoming a hot material for future electronic applications.

Density Functional Theory (DFT) was used to study fundamental characteristics of electrides. Electronic structure calculations were performed with the generalized gradient approximation (GGA) and GGA+U (U- “on-site" electron-electron repulsion). Fundamental properties of Y2C were investigated in the first project. The nature of strongly localized anionic electrons in Y2C was demonstrated using the distribution of charge density. Magnetic properties were analyzed with magnetization density and magnetic anisotropy energies. The magnetic anisotropy of Y2C originates from anionic electrons at interlayer spaces. The predicted work functions are in good agreement with reported experimental data. We also investigated the enhancement of magnetic properties by varying the degree of localization of anionic electrons. The exchange splitting of interstitial electrons is more prominent than that of d-orbitals of Y and exchange splitting increases with decreasing c-axis parameter. In the second study, fundamental properties of Gd2C are discussed. The GGA+U method was applied for 4f states of Gd and predicted the best U value. Our model predicted Gd2C has a layered-hexagonal structure. Local density of states (LDOS) and projected density of states (PDOS) were analyzed for understanding of anionic electrons and atoms on magnetic and electronic properties. The Curie temperatures of Gd and Gd2C were calculated and noticed that interactions in Gd2C are influential to increase the Curie temperature. The chemical formula can be written as [Gd2C]1.9.1.9e- from charge analysis. Additionally, fundamental properties of two ionized states, Q=+1 and Q=+2 were studied. Results indicate anionic electrons at interlayer spaces will initiate the ejecting of electrons. Density functional perturbation theory (DFPT) with DFT under the harmonic approximations was applied to study the structural stabilities, phase transitions and variation of thermodynamic quantities at finite temperature of two phases of Hf2S. Phonon dispersion curves without any imaginary frequencies are evidence for stability of two phases. The resulting quadratic flexural phonon branch indicates Hf2S has 2D characteristics. At T= 0 K the Helmholtz free energy of anti- NbS2 structure of Hf2S lies ≈23 kJ/f.u. below that of the higher energy phase. The critical temperature for the phase transition was estimated, and the effect of finite temperature on thermodynamics quantities were studied.