Multi-Technique Approach for Work Function Exploration of Sc2O3 Thin Films

Thin films based on scandium oxide (Sc₂O₃) were deposited on silicon substrates to investigate the thickness effect on the reduction of work function. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), energy dispersive X-ray reflectivity (EDXR), atomic force microscopy (AFM), and ultraviolet photoelectron spectroscopy (UPS) measurements were performed on the films deposited by electron-beam evaporation with different nominal thicknesses (in the range of 2-50 nm) and in multi-layered mixed structures with barium fluoride (BaF₂) films. The obtained results indicate that non-continuous films are required to minimize the work function (down to 2.7 eV at room temperature), thanks to the formation of surface dipole effects between crystalline islands and substrates, even if the stoichiometry is far from the ideal one (Sc/O = 0.38). Finally, the presence of BaF₂ in multi-layered films is not beneficial for a further reduction in the work function.

Control of Ni/β-Ga(2)O(3) Vertical Schottky Diode Output Parameters at Forward Bias by Insertion of a Graphene Layer

Controlling the Schottky barrier height (ϕB) and other parameters of Schottky barrier diodes (SBD) is critical for many applications. In this work, the effect of inserting a graphene interfacial monolayer between a Ni Schottky metal and a β-Ga2O3 semiconductor was investigated using numerical simulation. We confirmed that the simulation-based on Ni workfunction, interfacial trap concentration, and surface electron affinity was well-matched with the actual device characterization. Insertion of the graphene layer achieved a remarkable decrease in the barrier height (ϕB), from 1.32 to 0.43 eV, and in the series resistance (RS), from 60.3 to 2.90 mΩ.cm2. However, the saturation current (JS) increased from 1.26×10−11 to 8.3×10−7(A/cm2). The effects of a graphene bandgap and workfunction were studied. With an increase in the graphene workfunction and bandgap, the Schottky barrier height and series resistance increased and the saturation current decreased. This behavior was related to the tunneling rate variations in the graphene layer. Therefore, control of Schottky barrier diode output parameters was achieved by monitoring the tunneling rate in the graphene layer (through the control of the bandgap) and by controlling the Schottky barrier height according to the Schottky−Mott role (through the control of the workfunction). Furthermore, a zero-bandgap and low-workfunction graphene layer behaves as an ohmic contact, which is in agreement with published results.

Tunable Optical Properties of Amorphous-Like Ga2O3 Thin Films Deposited by Electron-Beam Evaporation with Varying Oxygen Partial Pressures

Ga₂O₃ thin films were fabricated by the electron-beam evaporation technique at a varying oxygen partial pressure from 0 to 2.0 × 10⁻² Pa. The effect of oxygen partial pressure on the crystalline structure and optical properties of the Ga₂O₃ films was analyzed using sophisticated techniques including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, spectroscopic ellipsometry, ultraviolet-visible spectroscopy and a laser-induced damage test system. The correlation between the oxygen partial pressure and the film’s properties in optics and materials were investigated. XRD and Raman revealed that all films were amorphous in spite of applying a varying oxygen partial pressure. With the change of oxygen partial pressure, XPS data indicated that the content of oxygen in the Ga₂O₃ films could be broadly modulable. As a result, a changeable refractive index of the Ga₂O₃ film is realizable and a variable blue-shift of absorption edges in transmittance spectra of the films is achievable. Moreover, the damage threshold value varied from 0.41 to 7.51 J/cm² according to the rise of oxygen partial pressure. These results demonstrated that the optical properties of Ga₂O₃ film can be broadly tunable by controlling the oxygen content in the film.

Laser Treatment of Nanoparticulated Metal Thin Films for Ceramic Tile Decoration

This paper presents a new method for the fabrication of metal-like decorative layers on glazed ceramic tiles. It consists of the laser treatment of Cu thin films prepared by electron-beam evaporation at glancing angles. A thin film of discontinuous Cu nanoparticles was electron-beam-evaporated in an oblique angle configuration onto ceramic tiles and an ample palette of colors obtained by laser treatment both in air and in vacuum. Scanning electron microscopy along with UV-vis-near-IR spectroscopy and time-of-flight secondary ion mass spectrometry analysis were used to characterize the differently colored layers. On the basis of these analyses, color development has been accounted for by a simple model considering surface melting phenomena and different microstructural and chemical transformations of the outmost surface layers of the samples.

Continuous-Gradient Plasmonic Nanostructures Fabricated by Evaporation on a Partially Exposed Rotating Substrate

A continuous-gradient approach of material evaporation is employed to fabricate nanostructures with varying geometric parameters, such as thickness, lateral positioning, and orientation on a single substrate. The method developed for mask lithography allows continuous tuning of the physical properties of a sample. The technique is highly valuable in simplifying the overall optimization process for constructing metasurfaces.

Metasurfaces: Continuous-Gradient Plasmonic Nanostructures Fabricated by Evaporation on a Partially Exposed Rotating Substrate (Adv. Mater. 23/2016)

A continuous-gradient approach of material evaporation is employed by L. Shao, M. Käll, and co-workers to fabricate nanostructures with varying geometric parameters such as thickness, lateral positioning, and orientation on a single substrate. This method for mask lithography, described on page 4658, allows continuous tuning of the physical properties of a sample. The technique is highly valuable in simplifying the overall optimization process for constructing metasurfaces.