Rutile titanium oxide (TiO₂) thin films require more energy to crystallize than the anatase phase of TiO₂. It is a prime candidate for micro-optoelectronics and is usually obtained either by high substrate temperature, applying a substrate bias, pulsed gas flow to modify the pressure, or ex situ annealing. In the present work, we managed to obtain high enough energy at the substrate in order for the particles to form rutile TiO₂ at room temperature without any intentional substrate bias in a continuous gas flow. The rutile TiO₂ thin films were deposited by a reactive radiofrequency magnetron sputtering system from a titanium target, in an argon/oxygen gas mixture. Investigations regarding the film’s structure and morphology were performed by X-ray diffraction (XRD), X-ray reflectivity (XRR), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX), while the optical properties were investigated by means of ellipsometry.

The progress of advanced materials has invoked great interest in promising novel biosensing applications. Field-effect transistors (FETs) are excellent options for biosensing devices due to the variability of the utilized materials and the self-amplifying role of electrical signals. The focus on nanoelectronics and high-performance biosensors has also generated an increasing demand for easy fabrication methods, as well as for economical and revolutionary materials. One of the innovative materials used in biosensing applications is graphene, on account of its remarkable properties, such as high thermal and electrical conductivity, potent mechanical properties, and high surface area to immobilize the receptors in biosensors. Besides graphene, other competing graphene-derived materials (GDMs) have emerged in this field, with comparable properties and improved cost-efficiency and ease of fabrication. In this paper, a comparative experimental study is presented for the first time, for FETs having a channel fabricated from three different graphenic materials: single-layer graphene (SLG), graphene/graphite nanowalls (GNW), and bulk nanocrystalline graphite (bulk-NCG). The devices are investigated by scanning electron microscopy (SEM), Raman spectroscopy, and I-V measurements. An increased electrical conductance is observed for the bulk-NCG-based FET, despite its higher defect density, the channel displaying a transconductance of up to ≊$4.9\times {10}^{-3}$ A V${}^{-1}$, and a charge carrier mobility of ≊$2.86\times {10}^{-4}$ cm${}^2$ V${}^{-1}$ s${}^{-1}$, at a source-drain potential of 3 V. An improvement in sensitivity due to Au nanoparticle functionalization is also acknowledged, with an increase of the ON/OFF current ratio of over four times, from ≊$178.95$ to ≊$746.43$, for the bulk-NCG FETs.

Herein, several nitrogen-doped nano-crystalline graphite films (N-NCG) were prepared via plasma-enhanced chemical vapor deposition (PECVD); nano-crystalline graphite (NCG) was doped by adding ammonia gas during the PECVD growth. To develop electrochemical probes that can compete with glassy carbon (GC) electrodes for anthracene sensing, the N-NCG electrodes were systematically investigated using different techniques, including atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, Raman spectroscopy, cyclic voltammetry (CV), and differential pulsed voltammetry (DPV). The obtained sensors were tested against anthracene in an acetonitrile/water mixture (80/20 v/v) wherein the N-NCG 3 and N-NCG 5 electrochemical probes showed analytical features comparable with those of the GC electrode. The best competitor for GC was N-NCG 3 in terms of linear working range (2.5μM–1 mM) and sensitivity (y = 6.09 × 10⁻⁶+ 1.21 x, r²= 0.9997 and y = 1.23 × 10⁻⁵+ 0.84 x, r²= 0.9959 for GC and N-NCG 3, respectively).

Bulk nanocrystalline graphite has been investigated as a possible candidate for piezoresistive sensors. The thin films were grown using capacitively coupled plasma enhanced chemical vapor deposition and a technological workflow for the transfer of the active material onto flexible substrates was established in order to use the material as a piezoresitive element. Preliminary electrical measurements under mechanical strain were performed in order to test the piezoresistive response of the material and promising GF values of 50 − 250 at 1% strain were obtained.

In this work, we present a tunable 24-GHz antenna array based on a CMOS-compatible 110-nm-thick nanocrystalline graphite film grown by plasma enhanced chemical vapor deposition. The film has a nominal bulk conductivity exceeding 16000 S/m (hence, greater than any graphene monolayer or industrially available graphene multilayer) but still able to show an outstanding modulation of its charge carrier density in the upper microwave spectrum. The manufactured layer was used to design, simulate, fabricate, and test a 24-GHz patch antenna array, with each radiating element having overall dimensions of just λ ₀ /8×λ ₀ /7. The fabricated array exhibits a measured maximum gain of about 3 dBi around 24 GHz (unbiased state), with a half-power beam width of only 14.5° (suitable in wireless links where a high directivity is envisaged). Spanning the dc bias voltage between -25 V and 25 V at 24 GHz, the gain can be tuned continuously between -1.5 dBi and 4 dBi, whereas the resonance frequency undergoes a maximum shift of 166 MHz. This voltage-dependent tuning of the gain represents a first step in developing carbon-based applications to control amplitude and phase simultaneously and independently. These results (never reported) demonstrate the big potential of nanocrystalline graphite for high-performance microwave components that are CMOS compatible (a highly desirable characteristic for high fabrication yield and large-scale production), with unprecedented tunability for next-generation high-capacity communications.