M. Fanciulli

Silicene field-effect transistors operating at room temperature

Free-standing silicene, a silicon analogue of graphene, has a buckled honeycomb lattice and, because of its Dirac bandstructure combined with its sensitive surface, offers the potential for a widely tunable two-dimensional monolayer, where external fields and interface interactions can be exploited to influence fundamental properties such as bandgap and band character for future nanoelectronic devices. The quantum spin Hall effect, chiral superconductivity, giant magnetoresistance and various exotic field-dependent states have been predicted in monolayer silicene. Despite recent progress regarding the epitaxial synthesis of silicene and investigation of its electronic properties, to date there has been no report of experimental silicene devices because of its air stability issue. Here, we report a silicene field-effect transistor, corroborating theoretical expectations regarding its ambipolar Dirac charge transport, with a measured room-temperature mobility of ∼100 cm(2) V(-1) s(-1) attributed to acoustic phonon-limited transport and grain boundary scattering. These results are enabled by a growth-transfer-fabrication process that we have devised--silicene encapsulated delamination with native electrodes. This approach addresses a major challenge for material preservation of silicene during transfer and device fabrication and is applicable to other air-sensitive two-dimensional materials such as germanene and phosphorene. Silicenes allotropic affinity with bulk silicon and its low-temperature synthesis compared with graphene or alternative two-dimensional semiconductors suggest a more direct integration with ubiquitous semiconductor technology.

Epitaxial growth of zinc blende and wurtzitic gallium nitride thin films on (001) silicon

Zinc blende and wurtzitic GaN films have been epitaxially grown onto (001)Si by electron cyclotron resonance microwave plasma‐assisted molecular beam epitaxy, using a two‐step growth process. In this process a thin buffer layer is grown at relatively low temperatures followed by a higher temperature growth of the rest of the film. GaN films grown on a single crystalline GaN buffer have the zinc blende structure, while those grown on a polycrystalline or amorphous buffer have the wurtzitic structure.

Local Electronic Properties of Corrugated Silicene Phases

IO N Exploring new physical-chemical properties of atomically thin graphitic materials is retaining a booming interest and it is expected to have a tremendous impact on the development of future nanoelectronic devices. So far, the enormous consideration for graphene [ 1 , 2 ] has overshadowed other two dimensional (2D) counterparts which may overcome the intrinsic limitations of graphene as active material. Indeed, despite the recent advances either in graphene bandgap opening [ 3–5 ] or integration in ad hoc device structures, [ 6 , 7 ] the zero-gap character of free standing graphene poses a severe drawback for an electric fi eld modulation suitable to graphene based logic devices. A strong effort is currently made to provide theoretical and experimental evidence of stable graphene-like nanolattices of the other group-IV semiconductors, the so called silicene and germanene, [ 8–11 ] which might take benefi t from being naturally compatible with the Si technology and from an intrinsically higher spin orbit coupling. Unlike graphene, the spontaneous formation of silicene is not expected to be energetically favorable because the sp 3 hybridization of Si atoms is more stable than the sp 2 one. However, a graphene-like form of silicene has been theoretically predicted [ 8 , 9 , 12 ] and, in just a few years, experimental investigations have moved up this fascinating hypothesis to concrete evidence. Recent experiments [ 13 , 14 ] report on the epitaxial growth of silicene on Ag(111) substrates with a non-trivial surface arrangement and relevant electronic features such as a linear electronic dispersion at the K points and an estimated Fermi velocity v F = 1.3 × 10 6 ms − 1 . [ 13 ]

Conductive-filament switching analysis and self-accelerated thermal dissolution model for reset in NiO-based RRAM

This work presents detailed characterization and modeling of the reset operation in resistive-switching memories based on metal oxides. Our experimental results confirm previous observations that reset is controlled by Joule heating, providing an insight on the electrical and thermal parameters of the conductive filament (CF) in the low resistance state. The characterization of such parameters allows to model the CF rupture responsible for reset switching. Our model explains the switching by self-accelerated dissolution of the CF, and can quantitatively account for reset and data-retention experiments. The scaling of programming current is finally investigated by means of reduction of CF cross-section.

Two-dimensional Si nanosheets with local hexagonal structure on a MoS(2) surface.

The structural and electronic properties of a Si nanosheet (NS) grown onto a MoS2 substrate by means of molecular beam epitaxy are assessed. Epitaxially grown Si is shown to adapt to the trigonal prismatic surface lattice of MoS2 by forming two-dimensional nanodomains. The Si layer structure is distinguished from the underlying MoS2 surface structure. The local electronic properties of the Si nanosheet are dictated by the atomistic arrangement of the layer and unlike the MoS2 hosting substrate they are qualified by a gap-less density of states.

In situ chemical and structural investigations of the oxidation of Ge(001) substrates by atomic oxygen

The exposure of Ge(001) substrates to atomic oxygen was studied in situ to establish the stability of the germanium oxide. After preparing chemically clean and atomically flat Ge(001) surfaces, the Ge samples were exposed to atomic oxygen in a wide temperature range from room temperature to 400°C. The chemical composition of the so-formed oxides was studied by means of x-ray photoelectron spectroscopy, while the structure was observed by reflection high energy electron diffraction. At low substrate temperatures the atomic oxygen is efficiently chemisorbed and suboxides coexist with the dioxide, which in turn is remarkably promoted in the high temperature range.

Manipulation of two-dimensional arrays of Si nanocrystals embedded in thin SiO2 layers by low energy ion implantation

In silicon nanocrystal based metal–oxide–semiconductor memory structures, tuning of the electron tunneling distance between the Si substrate and Si nanocrystals located in the gate oxide is a crucial requirement for the pinpointing of optimal device architectures. In this work it is demonstrated that this tuning of the “injection distance” can be achieved by varying the Si+ ion energy or the oxide thickness during the fabrication of Si nanocrystals by ultralow-energy silicon implantation. Using an accurate cross-section transmission electron microscopy (XTEM) method, it is demonstrated that two-dimensional arrays of Si nanocrystals cannot be positioned closer than 5 nm to the channel by increasing the implantation energy. It is shown that injection distances down to much smaller values (2 nm) can be achieved only by decreasing the nominal thickness of the gate oxide. Depth profiles of excess silicon measured by time-of-flight secondary ion mass spectroscopy and Si nanocrystal locations determined by XTEM ...

Atomic-layer deposition of Lu2O3

Rare earth oxides could represent a valuable alternative to SiO2 in complementary metal–oxide–semiconductor devices. Lu2O3 is proposed because of its predicted thermodynamical stability on silicon and large conduction band offset. We report on the growth by atomic-layer deposition of lutetium oxide films using the dimeric {[C5H4(SiMe3)]2LuCl}2 complex, which has been synthesized for this purpose, and H2O. The films were found to be stoichiometric, with Lu2O3 composition, and amorphous. Annealing in nitrogen at 950°C leads to crystallization in the cubic bixbyite structure. The dielectric constant of the as-grown Lu2O3 layers is 12±1.

Evidence for graphite-like hexagonal AlN nanosheets epitaxially grown on single crystal Ag(111)

Ultrathin (sub-monolayer to 12 monolayers) AlN nanosheets are grown epitaxially by plasma assisted molecular beam epitaxy on Ag(111) single crystals. Electron diffraction and scanning tunneling microscopy provide evidence that AlN on Ag adopts a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN. This claim is further supported by ultraviolet photoelectron spectroscopy indicating a reduced energy bandgap as expected for hexagonal AlN.

Fabrication of GeO2 layers using a divalent Ge precursor

Good quality and perfectly stoichiometric GeO2 layers are promising interlayers to be implemented in alternative devices based on high dielectric constant oxide/Ge(100). In this work, the authors report on the growth by atomic layer deposition of GeO2 films using a divalent Ge precursor combined with O3. The films are composed of smooth and perfectly stoichiometric GeO2. The contamination level is extremely low. The deposited GeO2 films have a band gap of 5.81±0.04eV. The conduction and valence band offsets at the GeO2∕Ge heterojunction are found to be 0.6±0.1 and 4.5±0.1eV, respectively.