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We investigate the structural, optical and electrical properties of single-layer graphene exposed to oxygen plasma treatment. We find that the pristine semimetallic behavior of graphene disappears upon plasma treatment, in favour of the opening of a bandgap and the featuring of semiconducting properties. The metal-to-semiconductor transition observed appears to be dependent on the plasma treatment time. The semiconducting behavior is also confirmed by photoluminescence measurements. The opening of a bandgap in graphene is explained in terms of graphene surface functionalization with oxygen atoms, bonded as epoxy groups. Ab initio calculations of the density of states show more details about the oxygen–graphene interaction and its effects on the graphene optoelectronic properties, predicting no states near the Fermi level at increasing epoxy group density. The structural changes are also monitored by Raman spectroscopy, showing the progressive evolution of the sp2 character of pristine graphene to sp3, due to the lattice decoration with out-of-plane epoxy groups.

The g-tensors of dangling bonds at defective Ge atoms in GeO2 are computed using density functional theory. The isotropic g-values of these defects are found to increase with the number of Ge backbonds. By comparing these calculations with the isotropic g-value of a Ge-related defect at Ge/GeO2 interfaces, recently observed by electron spin resonance and electrically detected magnetic resonance experiments, we tentatively identify this defect as a Ge2O≡Ge• center, i.e. a dangling bond on a Ge atom backbonded to two Ge atoms and one O atom, likely present near the Ge/GeO2 interface. The interaction of this defect with molecular hydrogen is investigated using first-principles molecular dynamics simulations. Our simulations predict that the Ge dangling bond can be hardly passivated by H2 molecules, in agreement with the electron spin resonance study.

We report a change in the semimetallic nature of single-layer graphene after exposure to oxygen plasma. The resulting transition from semimetallic to semiconducting behavior appears to depend on the duration of the exposure to the plasma treatment. The observation is confirmed by electrical, photoluminescence and Raman spectroscopy measurements. We explain the opening of a bandgap in graphene in terms of functionalization of its pristine lattice with oxygen atoms. Ab initio calculations show more details about the interaction between carbon and oxygen atoms and the consequences on the optoelectronic properties, that is, on the extent of the bandgap opening upon increased functionalisation density.

The use of high mobility channel materials such as Ge and III/V compounds for CMOS applications is being explored. The introduction of these new materials also opens the path towards the introduction of novel device structures which can be used to lower the supply voltage and reduce the power consumption. The results illustrate the possibilities that are created by the combination of new materials and devices to allow scaling of nanoelectronics beyond the Si roadmap.

A parameter set describing the Ge-H bonds in the framework of the many-body interatomic potential proposed by Tersoff and Murty has been derived using first-principles calculations. The potential was fitted to reproduce structural, energetic, and vibration properties of gas phase germanium hydrides and radicals. It demonstrates a good transferability for the description of hydrogen terminated germanium surfaces. The potential has been used to simulate the epitaxial growth of a Si layer on a Ge(100) surface using SiH4 precursor molecules. The obtained results faithfully reproduce the impact of chemisorbed hydrogen on the mechanism of Ge diffusion in the grown Si layer. ispartof: Physical Review B, Condensed Matter and Materials Physics vol:79 issue:16 status: published

The use of Ge and III/V materials for future CMOS applications is investigated. Good passivation of the Ge surface can be obtained by either GeO 2 or Si passivation. Short channel Ge pMOS devices with low EOT are fabricated using Si passivation at 350 and 500°C. The passivation of III/V materials is a very challenging topic. Some critical issues and passivation schemes are discussed.

Future CMOS technologies will require the use of substrate material with a very high mobility. Therefore, the combination of Ge pMOS with GaAs nMOS devices is investigated for its possible use in advanced CMOS applications. In this work, the physical, chemical and electrical properties of a-GeO2 interfacial passivation layer (IPL) for n-Ge(001) and p-GaAs(001) have been investigated, using Molecular Beam Epitaxy (MBE) technique. The efficient electrical passivation of Ge/GeO2 will be demonstrated, and in the case of GaAs, the use of a thin a-GeO2 interlayer reduces the defects at the interface.

The introduction of high mobility channel materials together with new device structures with improved subthreshold slope provides a pathway into continuing the performance scaling of CMOS technology beyond the classical Si roadmap. The combination of Ge pMOS devices with nMOS devices made on very high electron mobility III/V compounds such as InGaAs can be achieved by selective growth on a Si-wafer, The key challenge towards achieving excellent device performance is the electrical passivation of the interface between the high-x dielectric and the alternative channel materials.

Carbon nanotubes (CNTs) are a promising candidate to replace copper interconnects. An ab initio study is presented on the conductance of a closed-packed bundle of very narrow metallic (4,0) CNTs, which is vertically placed on a Cu (100) surface. The intertube interactions have no significant impact on the conductance. The conductance is highly dependent on the exact geometry of the interface, which is varying between 0.6 and 1.8 conductance quanta, while the theoretical maximum of the CNT is three conductance quanta. The wave-function interference can lead to conductance suppression when the packing is too high. Both features are explained by using an orbital picture. ispartof: Physical Review B, Condensed Matter and Materials Physics vol:77 issue:19 status: published

We derive an analytical model for the electrostatics and the drive current in a silicon nanowire operating in JFET mode. We show that there exists a range of nanowire radii and doping densities for which the nanowire JFET satisfies reasonable device characteristics. For thin nanowires we have developed a self-consistent quantum mechanical model to obtain the electronic structure.

In order to investigate the technological potential ascribed to semiconductor nanowires, it is paramount to include quantum effects into the models used to simulate carrier trans-port as well as optical and excitonic features of various nanowire layouts.

In this work, we propose a new, effective, and cost-efficient method of introducing fluorine into metal/Hf-based gate stack of planar and multi-gate devices (MuGFET), resulting in significant improvements in both NBTI and PBTI characteristics. The key advantage of this method is that it uses the SF6-based metal gate etch for F introduction, requiring no extra implantation steps. In addition to the significant BTI improvement with the novel method, we also demonstrate, for the first time, better Vth control and increased drive current on MuGFET devices.

We present ab initio density-functional and self-interaction-corrected calculations on the structure, electronic properties, $k=0$ vibrational modes, and static dielectric properties of the crystalline high-$\ensuremath{\kappa}$ distorted-perovskite oxide $\mathrm{Dy}\mathrm{Sc}{\mathrm{O}}_{3}$. We find a gap of $6.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (close to $5.7\char21{}5.9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ experimentally) and a participation of both Sc and Dy in the mixed ionic-covalent bonding to O by means of which they both contribute to realizing the orthorhombic rotationally distorted equilibrium structure. In accordance with their role in the electronic structure, both Sc and Dy share essentially the same effective charge anomaly, at variance with other perovskites where anomalous effective charges are exclusive of either cation (e.g., La in $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ and Ti in $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_{3}$). The orientationally averaged dielectric constant $\ensuremath{\kappa}\ensuremath{\simeq}21\char21{}24$ is in good agreement with experiment. The dielectric response is dominated by the vibrational ionic component, with a dominant mode featuring Sc-O units vibrating against the Dy sublattice. We provide details about the full (IR, Raman, and silent) vibrational spectrum.

We report calculations indicating that amorphous RAO$_3$ oxides, with R and A trivalent cations, have approximately the same static dielectric constant as their perovskite crystal phase. The effect is due to the disorder-activated polar response of non-polar crystal modes at low frequency, which compensates a moderate but appreciable reduction of the ionic dynamical charges. The dielectric response was studied via density-functional perturbation theory. Amorphous samples were generated by molecular dynamics melt-and-quench simulations., Comment: 5 pages, 3 figures

We show for the first time that conduction and valence band-edge effective work functions (WF) are achieved simultaneously by one single Dy2O3 capping layer on HfO2 for both nMOS and pMOS with TaCx-based metals. Low Vt's (0.23 and -0.36 V) are obtained without degrading the EOT-JG scalability and hole mobility. A model based on competing intermixes of cap/host dielectric and cap/metal is proposed to explain the positive WF shift with TaCxNy and the negative shift with TaCx as compared to the uncapped HfO2 reference. Finally, by developing a novel nitridation process to modify TaCx into TaCxNy, this work shows that single-metal-single-dielectric gate stacks are feasible, allowing cost-effective low-Vt CMOS integration.

The use of nanostructured materials can make a significant contribution to the development of solid-state batteries [1-3]. We here focus on a class of nanostructured materials called metal-organic frameworks (MOFs), which exhibits promising properties that potentially meet the requirements of a solid-state Li-ion electrolyte in terms of high ionic conductivity (> 10-4 S/cm) and low electronic leakage. MOFs are hybrid nanoporous solids that result from a reaction of organic ligands and metallic cations to create a three-dimensional controlled skeleton. Fig. 1 illustrates the crystal structure of the so called MIL-121 MOF [4]. The 1D pores of this structure by which the transport of ions is carried out have promising dimensions. Indeed, the large nano-crystalline pores of the MOFs are expected to lead to a high ionic conductivity, as the mobile ions are not sterically hindered inside the pores. The diffusion mechanism in a functionalized MOF is expected to occur in a similar way to the one of an adatom on top of a surface. A general used approach to create a Li+ ion conductive MOF focusses on the inclusion of a lithium salt in the MOF pores. Yanai et al. [5] reported that the incorporation of a complex of polyethylene glycol with LiBF4 into the nanochannels of a Zn-MOF leads to a liquid-like mobility of the Li-ions (activation energy of diffusion equals 0.18 eV). Wiers et al. demonstrates the uptake of lithium isopropoxide (LiOiPr) salt in a Mg-MOF. The salt is electrostatically bound to the open metal centers of this Mg-MOF. An ionic conductivity of 3.1x10-4 S/cm is reported. By a similar approach Ameloot et al. [6] introduced a lithium salt in a Zr-MOF. Here, the lithium salt is chemically bound to the organic ligands of the MOF. Fig. 1 shows the crystal structure of the MIL-121 which we investigated with first-principles techniques based on density functional theory (DFT). The carboxyl-groups in this structure rotate themselves such that their acidic framework protons (labeled A in Fig. 1) interact with two carboxyl-groups. Consequently, an open-pore structure is obtained. To include lithium in the pores of the MIL-121 the acidic framework protons labeled A in Fig. 1 are substituted by Li+ ions. This idea is similar to the one proposed by Himsl et al. [7]. Only here, the lithium-proton exchange reaction occurs on a carboxyl-group rather than on a hydroxyl one. The higher acidity of the carboxyl-groups with respect to the hydroxyl ones potentially results in a higher lithium concentration. Furthermore, the weak bond between the –COO- anion and the Li+ cation, and the rotational freedom of the carboxyl-group are expected to further improve the ionic conductivity. We will present the modeling methodology that enables us to simulate Li+ ion conductivity in the MOF pores, followed by a discussion on the obtained results. The results cover the evolution of the structural parameters and the electronic structure of the MIL-121 unit cell for different lithium concentrations. Furthermore, the binding energies of the different acidic framework protons A, B, and C (see Fig. 1) are compared to each other. Finally, the dynamics of the atoms in the unit cell of the MIL-121 is studied for the highest possible lithium concentration in which all acidic framework protons A are substituted by a Li+ ion. The results of this study give us atomistic insight on the behavior of the Li-ions in MOF pores. These results lead to useful suggestion to further develop MOF as solid-state Li+ ion electrolytes. [1] Liu, C., Li, F., Ma, L.-P., and Cheng, H.-M. (2010) Advanced Materials, 22, E28 – E62. [2] Patil, A., Patil, V., Shin, D. W., Choi, J.-W., Paik, D.-S., and Yoon, S.-J. (2008) Materials Research Bulletin, 43, 1913–1942. [3] Wang, Y. and Cao, G. (2008) Advanced Materials, 20, 2251–2269. [4] Volkringer, C., Loiseau, T., Guillou, N., Férey, G., Haouas, M., Taulelle, F., Elkaim, E., and Stock, N. (2010) Inorganic chemistry, 49, 9852. [5] Yanai, N., Uemura, T., Horike, S., Shimomura, S., and Kitagawa, S. (2011) Chemical Communications (Cambridge, United Kingdom), 47, 1722. [6] Ameloot, R., Aubrey, M., Wiers, B. M., Gómora-figueroa, A. P., Patel, S. N., Balsara, N. P., and Long, J. R. (2013) Chemistry - A European Journal, 19, 5533. [7] Himsl, D., Wallacher, D., and Hartmann, M. (2009) Angewandte Chemie (International ed. In English), 48, 4639 Figure 1

In this study comprehensive experimental measurements together with a physical picture demonstrate that, regardless of poly-Si doping, the defects creation in the dielectric close to the poly-Si/HfO/sub 2/ interface is responsible for the observed effective WF change. These defects are amphoteric and spatially nonuniformly distributed.

This paper presents an overview of Ni-alloy (Ni, Ni-Pt and Ni-Ta) silicide development for the 45 nm node and beyond, including applications to self-aligned silicide (SALICIDE) processes, reaction with SiGe and strained Si on SiGe, and applications to fully silicided (FUSI) gates. Key SALICIDE issues addressed include the use of spike or low temperature rapid thermal processes (RTP) to control silicidation and junction leakage on small features, factors affecting the formation of epitaxial pyramidal NiSi2 grains, and NiSi thermal stability and agglomeration kinetics. Alloying with Pt or Ta is shown to improve thermal stability of NiSi films, although with quite different behaviors. While Pt is incorporated predominantly in solution in NiSi, Ta segregates to the surface of the films. Ni-Pt alloy silicides were also found to achieve low sheet resistance on narrow gates, low contact resistivity and low junction leakage, making them attractive for CMOS applications. For the Ni/SiGe reaction, a narrower RTP process window for low sheet resistance and a lower activation energy for agglomeration were observed when compared to the Ni/Si reaction. The lower thermal stability was correlated to Ge segregation from the Ni(SiGe) films. The Ni/doped poly-Si reaction was studied for FUSI gate applications, showing a retardation of the silicidation kinetics for high B doses and a large pile- up of dopants (for As, B or P) at the NiSi/SiO2 interface due to dopant snowplow during silicidation. The work function (WF) of NiSi was observed to shift with the addition of dopants, effect attributed to modifications of the interface dipole by the pile-up of dopants. No significant degradation was observed when comparing gate oxide breakdown statistics for Ni FUSI to conventional poly-Si gates. The process window for a FUSI gate-last process (performed after S/D Ni silicidation) was evaluated showing a potential integration problem due to possible degradation of the S/D silicide during the FUSI gate reaction.

The energy-transfer processes taking place in conjugated polymers are investigated by means of ultrafast spectroscopy and correlated quantum-chemical calculations applied to polyindenofluorenes end-capped with a perylene derivative. Comparison between the time-integrated luminescence and transient absorption spectra measured in solution and in films allows disentangling of the contributions arising from intrachain and from interchain energy-migration phenomena. Intrachain processes dominate in solution where photoexcitation of the polyindenofluorene units induces a rather slow energy transfer to the perylene end moieties. In films, close contacts between chains favors interchain transport of the excited singlet species (from the conjugated bridge of one chain to the perylene unit of a neighboring one); this process is characterized by a 1-order-of-magnitude increase in transfer rate with respect to solution. This description is supported fully by the results of quantum-chemical calculations that go beyond the usual point-dipole model approximation and account for geometric relaxation phenomena in the excited state before energy migration. The calculations indicate a two-step mechanism for intrachain energy transfer with hopping along the conjugated chains as the rate-limiting step; the higher efficiency of the interchain transfer process is mainly due to larger electronic coupling matrix elements between closely lying chains.

We study the structural, mechanical and electronic properties of the twodimensional (2D) allotrope of tin: tinene/stanene using first-principles calculation within density functional theory, implemented in a set of computer codes. Continuing the trend of the group-IV 2D materials graphene, silicene and germanene; tinene is predicted to have a honeycomb lattice with lattice parameter of a0 = 4.62Å and a buckling of d0 = 0.92. The electronic dispersion shows a Dirac cone with zero gap at the Fermi energy and a Fermi velocity of ρF = 0.97 × 106 ms-1; including spin-orbit coupling yields a bandgap of 0.10 eV. The monolayer is thermally stable up to 700 K, as indicated by firstprinciples molecular dynamics, and has a phonon dispersion without imaginary frequencies. We explore applied electric field and applied strain as functionalization mechanisms. Combining these two mechanisms allows for an induced bandgap up to 0.21 eV, whilst retaining the linear dispersion, albeit with degraded electronic transport parameters

Introduction III-V fin-shaped field-effect transistors (FinFETs) are considered to be attractive candidates for high-performance n-type FETs, thanks to both the light electron effective mass and to the improved electrostatic control. III-V FinFETs integrated on a Si substrate are advantageous with respect to their cost effectiveness. Aspect Ratio Trapping (ART) is one of the possible integration roads to be followed to achieve the growth of non-silicon channels on a Si substrate by reducing the density of defects obtained in the filled trenches [1]. In the ART process, the III-V fin is grown inside trenches of SiO2by using a metal organic vapor phase epitaxy (MOVPE) process, which implies that the precursors interact not only with the semiconductors but also with the oxides. The reaction of the precursors with the oxides could lead to the formation of defects around the interface which could be responsible for the degradation of the electrical reliability of III-V FinFETs. In this study, we report the evaluation of the formation of defects due to the reactions between the precursors and the oxides using first-principles simulations. Methodology The formation enthalpies [2] of the defects are calculated using the Quantum Espresso package [3] based on density functional theory. The lower the formation enthalpy is, the more likely the reaction is to occur. We used the Perdue-Burke-Ernzerhof exchange-correlation potential [4] combined with ultrasoft pseudopotentials to compute the energetics of the reactions. The charge states of the defects are assumed to be neutral. One of the considered reactions consists into the formation of interstitial defects in SiO2 due to the diffusion of the III-V components and of the doping atoms from the precursors. The list of considered precursors and oxides are summarized in Table 1. Mg and Zn could be used as acceptor doping sources for the III-V compounds. For the SiO2, an amorphous model is used, built from classical molecular dynamics simulations with the LAMMPS package [5]. Results and Discussion Fig. 1 shows the calculated formation enthalpies. For the precursors, we also envisaged some intermediate atomic configurations that correspond to the transition products active during the MOVPE process. Our simulations show that the initial states of the precursors have high formation enthalpies, indicating that there is no driving force to promote the diffusions of the III-V elements and of the dopants into the STI. However, as the growth proceeds and that the precursors begin losing their organic ligands, the formation enthalpies are significantly reduced. Zn and Mg have the lowest formation enthalpies of all of the reactants considered, which suggests that the diffusion of doping sources into SiO2 could be favored. In order to confirm the latter for the Mg case, secondary ion mass spectrometry measurements (SIMS) were performed on a SiO2 blanket exposed to the Mg-precursors (see Fig. 2). The diffusion of Mg is clearly observed near the SiO2surface, which is consistent with the theoretical picture (Fig. 1). In order to prevent these defect-related issues, it will be important to understand a risk of formation of defects using the ab initio approaches. Acknowledgment This work has been supported by the IMEC core partners and IMEC Industrial Affiliation Programs (IIAP). References [1] C. Merckling et al., J. Appl. Phys. 115, 023710 (2014). [2] C. G. Van de Walle et al., J. Appl. Phys. 95, 3851 (2004). [3] P. Gianozzi et al., J. Phys.: Condens. Matter 21, 395502 (2009). [4] J. P. Perdew et al., Phys. Rev. Lett. 77, 3865 (1996). [5] S. Plimpton, J. Comp. Phys. 117, 1 (1995).

Silicene, the silicon counterpart of graphene, has recently attracted a lot of attention as an alternative 2D materials to graphene for nanoelectronic devices. So far, the likely existence of silicene on Ag(111) surfaces has recently been reported, by combining experimental and first-principles simulations (1,2). The growth of silicene has also been reported on other metallic substrates, like (0001) ZrB2 (3) and (111)Ir (4). However, the characterization of the electronic and electrical properties of silicene on metallic substrates is very challenging, since these properties can be largely dominated by the substrates. In addition, potential applications of silicene in nanoelectronic devices will also require its growth on non-metallic substrates. We report here on the theoretical study of the interaction of silicene and germanene (2D Ge counterpart of graphene) with non-metallic substrates, using first-principles simulations. We first studied the weak (van der Waals) interaction between silicene or germanene with metal chalcogenide substrates (5,6). The buckling of the silicene/germanene layer is found to be correlated to the in-plane lattice mismatch between the free-standing silicene or germanene layer and the metal dichalcogenide layer. Highly buckled silicene (e.g. on MoS2) is predicted to be metallic, while low buckled silicene (on e.g. GaSe) is predicted to have Dirac cones at the K-points. We next investigated the interaction between silicene or germanene with (0001) ZnS or (0001) ZnSe surfaces (7,8). In this case, part of the Si (Ge) atoms form covalent bonds with the substrate, leading to the opening of a gap in their energy band structure. Very interestingly, the value of this energy gap can be controlled by an out-of-plane electric field, leading to field-driven semiconductor to metal transitions at these interfaces – which could be very promising for the potential use of silicene and germanene in field effect transistors. Part of this work has been financially supported by the European Project “2D Nanolattices” within the Future and Emerging Technologies (FET) program of the European Commission, under FET-grant number 270749, as well as the KU Leuven Research Funds, project GOA/13/011. References 1. P. Vogt et al., Phys. Rev. Lett. 108, 155501 (2012). 2. D. Chiappe et al., Adv. Mat. 24, 5088 (2012). 3. A. Fleurence et al., Phys. Rev. Lett. 108, 245501 (2012). 4. L. Meng et al., Nano Lett. 13, 685 (2013). 5. D. Chiappe et al., Adv. Mat., in press (2014). 6. E. Scalise et al., 2D Materials, in press (2014). 7. M. Houssa et al., Phys. Chem. Chem. Phys. 15, 3702 (2013). 8. M. Houssa et al., Appl. Surf. Sci. 291, 98 (2014).

The origin of the ferroelectric polarization switching in orthorhombic HfO2 has been investigated by first principles calculations. The phenomenon can be regarded as being the coordinated displacement of four O ions in the orthorhombic unit cell, which can lead to a saturated polarization as high as 53 mu C/cm(2). We show the correlation between the computed polarization reversal barrier and the experimental coercive fields. (C) 2014 AIP Publishing LLC.

A joint experimental and theoretical approach is used to study the coordination of soft transition metal ions with 3,4-bis (alkylthio)thiophenes. The synthesis of [PdCl2{3,4-bis(3-methylbutylthio)thiophene}], [PdCl2{3,4-bis(3-methylbutylthio)thiophene}] and [PdCl2{3',4'-bis[2-(S)-methylbutylthio]2,2':5',2 " -terthiophene}] by exchange of the benzonitrile ligands in [PdCl2(PhCN)(2)] and [PtCl2(PhCN)(2)] for the thiophene derivatives with thioether side chains is described. Changes in the conformational and electronic structure of the molecules were studied by X-ray diffraction, cyclic voltammetry, and optical and NMR spectroscopy; these experimental data are interpreted with the help of quantum mechanical calculations based on density functional theory. The complexes crystallize in a mixture of diastereoisomers, these stereoisomers are in equilibrium in solution, as observed by variable-temperature NMR spectroscopy. The complexation diminishes the electron-donor ability of the sulfur to the thiophene ring, as observed from the blueshift of the absorption maximum and from the absence of an oxidation wave in the positive potential regime for monomeric 3,4-bis(alkylthio)thiophenes. In this way it is possible to tune the properties of thiophene derivatives by ion coordination

Because of its excellent properties in nanotechnology applications, atomic layer deposition of ruthenium (Ru) has been the subject of numerous experimental studies. Recently, two different Ru precursors were compared for plasma-enhanced atomic layer deposition (PEALD) of Ru, and their reactivity was found to be different. Inhibition was observed for bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)(2)), while nearly linear growth behavior was observed for (methylcyclopentadienyl-pyrrolyl)ruthenium (Ru(MeCp)Py). To understand this difference in reactivity, we investigate the adsorption of RuCp, and RuCpPy (i.e., without substituents) on a TiN surface using calculations based on periodic boundary conditions density functional theory (DFT) combined with experiments based on Rutherford backscattering spectroscopy (RBS). The calculations demonstrate that the RuCpPy precursor chemisorbs on the TiN(100) surface while the RuCp2 precursor only physisorbs. We propose a reaction mechanism for the chemisorption of RuCpPy. The area density of the calculated RuCpPy surface species is compared with the experimental values from RBS. The impact of a H-plasma is also investigated. The DFT calculations and experimental results from RBS provide insight into the adsorption processes of the RuCpPy and RuCp2 precursors on the TiN(100) surface.

The structural and electronic properties of silicene and germanene on metallic and non-metallic substrates are investigated theoretically, using first-principles simulations. We first study the interaction of silicene with Ag(111) surfaces, focusing on the (4x4) silicene/Ag structure. Due to symmetry breaking in the silicene layer (nonequivalent number of top and bottom Si atoms), silicene is predicted to be semiconducting, with a computed energy gap of about 0.3 eV. However, the charge transfer occurring at the silicene/Ag(111) interface leads to an overall metallic system. We next investigate the interaction of silicene and germanene with hexagonal non-metallic substrates, namely ZnS and ZnSe. On reconstructed (semiconducting) (0001)ZnS or ZnSe surfaces, silicene and germanene are found to be semiconducting. Remarkably, the nature (indirect or direct) and magnitude of their energy band gap can be controlled by an out-of-plane electric field.

Modeling the oxidation process of silicon nanowires through reactive force field based molecular dynamics simulations suggests that the formation of Si epoxide defects occurs both at the Si/SiOx interface and at the nanowire surface, whereas for flat surfaces, this defect is experimentally observed to occur only at the interface as a result of stress. In this paper, we argue that the increasing curvature stabilizes the defect at the nanowire surface, as suggested by our density functional theory calculations. The latter can have important consequences for the opto-electronic properties of thin silicon nanowires, since the epoxide induces an electronic state within the band gap. Removing the epoxide defect by hydrogenation is expected to be possible but becomes increasingly difficult with a reduction of the diameter of the nanowires.

Effective electron tunneling mass mtunnel is extracted from trap-assisted leakage in Sr-rich strontium titanate and rutile titanium oxide films in metal–insulator–metal (MIM) capacitors and compared with theoretical values obtained from first principles calculations of the imaginary band structure. Optimum orientations of films and stoichiometry impacting mtunnel are also discussed. Because future vertical DRAM integration schemes also stipulate maximum thickness of the MIM capacitor, mtunnel is shown to be a critical parameter influencing intrinsic leakage and potentially limiting further scaling.

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The g-tensors of dangling bonds at defective Ge atoms in GeO2 are computed using density functional theory. The isotropic g-values of these defects are found to increase with the number of Ge backbonds. By comparing these calculations with the isotropic g-value of a Ge-related defect at Ge/GeO2 interfaces, recently observed by electron spin resonance (ESR) experiments, we tentatively identify this defect as a Ge2O≡Ge• center, i.e., a dangling bond on a Ge atom backbonded to two Ge atoms and one O atom, likely present near the Ge/GeO2 interface. The interaction of this defect with molecular hydrogen is investigated using first-principles molecular dynamics simulations. Our simulations predict that the Ge dangling bond can be hardly passivated by H2 molecules, in agreement with the electron spin resonance study.

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The structural and vibrational properties of amorphous germanium oxide (a-GeO2) are investigated using first-principles calculations based on density functional theory. We first generate an a-GeO2structure by first-principles molecular dynamics and analyze its structural properties. The vibrational spectra is then calculated within a density-functional approach. Both static and dynamic properties are in good agreement with experimental data. We next generate defects in our structure (oxygen vacancies with several density and charge states) and consider the most stable atomic configurations, focusing on the vibrational features of threefold coordinated O and divalent Ge centers. © 2011 American Institute of Physics

Interface models between various group IV and III-V (100)semiconductors and their oxides are generated from first-principles molecular dynamics simulations. The tensile strain at the interface (from the semiconductor side) is estimated, by comparing bond lengths at/near the interface and in the bulk semiconductor phase. A linear relationship between the calculated interface stress and the density of interface defects observed at such interfaces is revealed. These results suggest that the interface stress due to the volume mismatch between the semiconductor and its oxide likely plays an important role in the creation of interface defects. These findings can explain recent results pertaining to the passivation of various high-mobility channels for their integration in high-performance metal-oxide-semiconductor field-effect transistors.

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The electronic properties of two-dimensional hexagonal silicon (silicene) are investigated using first-principles simulations. Though silicene is predicted to be a gapless semiconductor, due to the sp2-hybridization of its atomic orbitals, the weak overlapping between 3pz orbitals of neighbor Si atoms leads to a very reactive surface, resulting in a more energetically stable semiconducting surface upon the adsorption of foreign chemical species. It is predicted that silicene inserted into a graphitelike lattice, like ultrathin AlN stacks, preserves its sp2-hydridization, and hence its graphenelike electronic properties.

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The electronic properties of two-dimensional hexagonal germanium, so called germanene, are investigated using first-principles simulations. Consistent with previous reports, the surface is predicted to have a “poor” metallic behavior, i.e., being metallic with a low density of states at the Fermi level. It is found that biaxial compressively strained germanene is a gapless semiconductor with linear energy dispersions near the K points—like graphene. The calculated Fermi velocity of germanene is almost independent of the strain and is about 1.7×106 m/s, quite comparable to the value in graphene.

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We explain the basic operation of a nanowire pinch-off FET and graphene nanoribbon tunnelFET. For the nanowire pinch-off FET we construct an analytical model to obtain the threshold voltage as a function of radius and doping density. We use the gradual channel approximation to calculate the current-voltage characteristics of this device and we show that the nanowire pinch-off FET has a subthreshold slope of 60 mV/dec and good ION and ION/IOFF ratios. For the graphene nanoribbon tunnelFET we show that an improved analytical model yields more realistic results for the transmission probability and hence the tunneling current. The first simulation results for the graphene nanoribbon tunnelFET show promising subthreshold slopes.

Hafnium aluminates have been investigated as high-κ dielectrics for implementation in sub-45 nm nonvolatile memory technologies. The growth behavior and quality of these dielectrics strongly depend on the applied deposition technique. We examine the surface reactions that occur during the atomic layer deposition (ALD) of hafnium aluminates from HfCl 4 , Al(CH 3 ) 3 , and H 2 O. When grown in the ALD sequence (HfCl 4 /H 2 O) a [Al(CH 3 ) 3 )/H 2 O] b , HfCl 4 chemisorption is enhanced while that of Al(CH 3 ) 3 is inhibited compared to the reaction during ALD of the respective binary oxides. Density functional theory simulations suggest that this observation is related to the more efficient hydrolysis of the Al-C bond compared to Hf―Cl. However, earlier works on ALD of HfCl 4 /H 2 O suggest that the low growth per cycle of this process is not caused by a limited hydrolysis of the Hf―Cl bond but by dehydroxylation of the generated Hf-OH surface sites into less reactive Hf―O―Hf surface sites. Hence, we propose that the enhanced HfCl 4 and inhibited Al(CH 3 ) 3 chemisorption during ALD of hafnium aluminates results from a difference in dehydroxylation behavior between both binary oxides.

[Clima, S.; Pourtois, G.; Van Elshocht, S.; De Gendt, S.; Wouters, D. J.; Heyns, M.; Kittl, J. A.] IMEC VZW, B-3001 Louvain, Belgium. [Hardy, A.; Van Bael, M. K.] Hasselt Univ, Inst Mat Res, Lab Inorgan & Phys Chem, B-3590 Diepenbeek, Belgium. [Hardy, A.] XIOS Hogesch Limburg, Dept IWT, B-3590 Diepenbeek, Belgium. [Hardy, A.; Van Bael, M. K.] IMEC, Div IMOMEC, B-3590 Diepenbeek, Belgium. [De Gendt, S.] Katholieke Univ Leuven, Dept Chem, B-3001 Louvain, Belgium. [Heyns, M.] Katholieke Univ Leuven, Dept Met & Mat Engn, B-3001 Louvain, Belgium.

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Significant research efforts are devoted to the development of alternative high dielectric constant oxides (high-k) to sustain the requirements of the next generations of DRAM and FLASH memories. For the metal-insulator-metal applications, the identification of an oxide with a dielectric constant higher than 50 and a crystallization temperature lower than 650 C is a corner stone in the selection of the materials; while for non volatile memory (NVM) applications, an oxide with a dielectric constant ranging between 9 and 30, a large band gap (> 6 eV) are targeted. While significant efforts have been dedicated to the integration of possible material candidates, little is known on their intrinsic properties. Through this paper, we provide an overview of the parameters that determine the electronic and the polarizability response of tantalates, niobiates and rare-earth based scandates oxides eligible for the development of the next generation of memory based applications.

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The role of moisture (H 2 O) in atomic-layer-deposited (ALD) HfO 2 and HfSiO, dielectrics on equivalent oxide thickness (EOT) scaling is investigated in gate-first devices with physical-vapor-deposited TaN gates. By reducing the amount of H 2 O present in the gate stack, the EOT increase during high-temperature (1030°C) spike annealing is reduced from 0.5 to 0.25 nm. This was achieved by a premetallization degas at 350―550°C for 3 min. The origin of this improvement lies in the elimination of H 2 O-related reoxidation of the interfacial SiO 2 . By means of temperature-programmed desorption measurements, it is found that the majority of the H 2 O is desorbed between 200 and 600°C with activation energies between ~0.3 and ~0.5 eV. Furthermore, the H 2 O concentration is dependent on the Hf concentration and nitridation. Non-nitrided HfSiO, with [Hf] = 40% adsorbs twice as much H 2 O as HfO 2 . Correspondingly, a significantly larger EOT increase is observed for HfSiO x with [Hf] = 40% as compared to HfO 2 . In HfSiON, the desorbed H 2 0 concentration is independent of [Hf]. Finally, a strong metal dependency on the EOT regrowth is observed. With ALD TiN, the EOT increase after thermal treatment is found to be independent of the degas condition at ~0.2 nm.