Field-Effect Transistors Based on Single-Layer Graphene and Graphene-Derived Materials.

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 ≊4.9×10-3 A V-1, and a charge carrier mobility of ≊2.86×10-4 cm2 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.

UV-Nanoimprint and Deep Reactive Ion Etching of High Efficiency Silicon Metalenses: High Throughput at Low Cost with Excellent Resolution and Repeatability.

As metasurfaces begin to find industrial applications there is a need to develop scalable and cost-effective fabrication techniques which offer sub-100 nm resolution while providing high throughput and large area patterning. Here we demonstrate the use of UV-Nanoimprint Lithography and Deep Reactive Ion Etching (Bosch and Cryogenic) towards this goal. Robust processes are described for the fabrication of silicon rectangular pillars of high pattern fidelity. To demonstrate the quality of the structures, metasurface lenses, which demonstrate diffraction limited focusing and close to theoretical efficiency for NIR wavelengths λ ∈ (1.3 µm, 1.6 µm), are fabricated. We demonstrate a process which removes the characteristic sidewall surface roughness of the Bosch process, allowing for smooth 90-degree vertical sidewalls. We also demonstrate that the optical performance of the metasurface lenses is not affected adversely in the case of Bosch sidewall surface roughness with 45 nm indentations (or scallops). Next steps of development are defined for achieving full wafer coverage.

Ultralow voltage (1µV) electrical switching of SnS thin films driven by a vertical electric field.

In this paper, we show in a series of experiments on 10 nm thick SnS thin film-based back-gate transistors that in the absence of the gate voltage, the drain current versus drain voltage (ID-VD) dependence is characterized by a weak drain current and by an ambipolar transport mechanism. When we apply a gate voltage as low as 1µV, the current increases by several orders of magnitude and theID-VDdependence changes drastically, with the SnS behaving as ap-type semiconductor. This happens because the current flows from the source (S) to the drain (D) electrode through a discontinuous superficial region of the SnS film when no gate voltage is applied. On the contrary, when minute gate voltages are applied, the vertical electric field applied to the multilayer SnS induces a change in the flow path of the charge carriers, involving the inner and continuous SnS layer in the electrical conduction. Moreover, we show that high gate voltages can tune significantly the SnS bandgap.

Vertical Graphene-Based Biosensor for Tumor Cell Dielectric Signature Evaluation.

The selective and rapid detection of tumor cells is of critical consequence for the theragnostic field of tumorigenesis; conventional methods, such as histopathological diagnostic methods, often require a long analysis time, excessive analytical costs, complex operations, qualified personnel and deliver many false-positive results. We are considering a new approach of an electrochemical biosensor based on graphene, which is evidenced to be a revolutionary nanomaterial enabling the specific and selective capture of tumor cells. In this paper, we report a biosensor fabricated by growing vertically aligned graphene nanosheets on the conductive surface of interdigitated electrodes which is functionalized with anti-EpCAM antibodies. The dielectric signature of the three types of tumor cells is determined by correlating the values from the Nyquist and Bode diagram: charge transfer resistance, electrical double layer capacity, Debye length, characteristic relaxation times of mobile charges, diffusion/adsorption coefficients, and variation in the electrical permittivity complex and of the phase shift with frequency. These characteristics are strongly dependent on the type of membrane molecules and the electromagnetic resonance frequency. We were able to use the fabricated sensor to differentiate between three types of tumor cell lines, HT-29, SW403 and MCF-7, by dielectric signature. The proposed evaluation method showed the permittivity at 1 MHz to be 3.63 nF for SW403 cells, 4.97 nF for HT 29 cells and 6.9 nF for MCF-7 cells.

Ultrathin tin sulfide field-effect transistors with subthreshold slope below 60 mV/decade.

In this paper, we present for the first time a field-effect-transistor (FET) having a 10 nm thick tin sulfide (SnS) channel fabricated at the wafer scale with high reproducibility. SnS-based FETs are in on-state for increasing positive back-gate voltages up to 6 V, whereas the off-state is attained for negative back-gate voltages not exceeding -6 V, the on/off ratio being in the range 102-103depending on FET dimensions. The SnS FETs show a subthreshold slope (SS) below 60 mV/decade thanks to the in-plane ferroelectricity of SnS and attaining a minimum value SS = 21 mV/decade. Moreover, the low SS values can be explained by the existence of a negative value of the capacitance of the SnS thin film up to 10 GHz (for any DC bias voltage between 1 and 5 V), with the minimum value being -12.87 pF at 0.1 GHz.

Metasurface Fabrication by Cryogenic and Bosch Deep Reactive Ion Etching.

The research field of metasurfaces has attracted considerable attention in recent years due to its high potential to achieve flat, ultrathin optical devices of high performance. Metasurfaces, consisting of artificial patterns of subwavelength dimensions, often require fabrication techniques with high aspect ratios (HARs). Bosch and Cryogenic methods are the best etching candidates of industrial relevance towards the fabrication of these nanostructures. In this paper, we present the fabrication of Silicon (Si) metalenses by the UV-Nanoimprint Lithography method and cryogenic Deep Reactive Ion Etching (DRIE) process and compare the results with the same structures manufactured by Bosch DRIE both in terms of technological achievements and lens efficiencies. The Cryo- and Bosch-etched lenses attain efficiencies of around 39% at wavelength λ = 1.50 µm and λ = 1.45 µm against a theoretical level of around 61% (for Si pillars on a Si substrate), respectively, and process modifications are suggested towards raising the efficiencies further. Our results indicate that some sidewall surface roughness of the Bosch DRIE is acceptable in metalense fabrication, as even significant sidewall surface roughness in a non-optimized Bosch process yields reasonable efficiency levels.

Dataset on large area nano-crystalline graphite film (NCG) grown on SiO2 using plasma-enhanced chemical vapour deposition.

A Si wafer coated with a low temperature oxide (LTO) was used as substrate (Si/SiO2) during the deposition of a thick nano-crystalline graphite (NCG) film by means of plasma-enhanced chemical vapour deposition (PECVD) procedure. The process parameters, the atomic force (AFM) and scanning electron (SEM) micrographs, Raman spectrum and X-ray diffraction (XRD) pattern are herein illustrated. The as deposited NCG film was electrochemically pretreated (3 mA applied current, during 240 s, in 10 mM phosphate buffer saline (PBS) solution containing 0.1 M KCl, pH 7) and thereafter used as electrode for sensing the caffeic acid content in lyophilised berries and dried chokeberries in "Nano-crystalline graphite film on SiO2: Electrochemistry and electro-analytical application" [1].

Superficial and Inner Examination of a Microwave-Irradiated Dental Acrylic Resin and Its Metal-Polymer Interface.

The aim of this study is to conduct an extended surface and cross-section characterization of a denture base acrylic resin subjected to 500, 650, and 750 W microwave irradiation for 2, 3, and 5 min to assess its morphological modifications. A commercial heat-cured powder was polymerized according to the manufacturer's specifications and distributed into 20 circular samples. A stainless-steel wire was partially embedded in half of the discs, in order to investigate the metal-polymer interface. High-resolution scanning electron microscopy (SEM) imaging, white light interferometry, roughness measurements and Fourier transform infrared spectrometry were employed for morphological and structural evaluation of the irradiated polymer. Superficial adaptation was discovered after 5 min exposure at 500 W, 650 W, and 750 W, revealing significant roughness correction for 750 W. SEM characterization revealed the inner alteration of the resin for the 750 W protocol and a metal-polymer gap developed regardless of the irradiation conditions. The considerable temperature fluctuations that the samples were subject to during the experiments did not essentially change the poly(methyl-methacrylate) bond structure.

Detection of Circulating Tumor Cells Using Microfluidics.

Metastasis is the main cause of death in cancer patients worldwide. During metastasis, cancer cells detach from the primary tumor and invade distant tissue. The cells that undergo this process are called circulating tumor cells (CTCs). Studies show that the number of CTCs in the peripheral blood can predict progression-free survival and overall survival and can be informative concerning the efficacy of treatment. Research is now concentrated on developing devices that can detect CTCs in the blood of cancer patients with improved sensitivity and specificity that can lead to improved clinical evaluation. This review focuses on devices that detect and capture CTCs using different cell properties (surface markers, size, deformability, electrical properties, etc.). We also discuss the process of tumor cell dissemination, the biology of CTCs, epithelial-mesenchymal transition (EMT), and several challenges and clinical applications of CTC detection.

FTIR Spectroscopy for Carbon Family Study.

Fourier transform Infrared (FTIR) spectroscopy is a versatile technique for the characterization of materials belonging to the carbon family. Based on the interaction of the IR radiation with matter this technique may be used for the identification and characterization of chemical structures. Most important features of this method are: non-destructive, real-time measurement and relatively easy to use. Carbon basis for all living systems has found numerous industrial applications from carbon coatings (i.e. amorphous and nanocrystalline carbon films: diamond-like carbon (DLC) films) to nanostructured materials (fullerenes, nanotubes, graphene) and carbon materials at nanoscale or carbon dots (CDots). In this paper, we present the FTIR vibrational spectroscopy for the characterization of diamond, amorphous carbon, graphite, graphene, carbon nanotubes (CNTs), fullerene and carbon quantum dots (CQDs), without claiming to cover entire field.

Development of the A§E test battery for assessment of pitch perception in speech.

OBJECTIVES: The auditory speech sounds evaluation 2009 test battery for assessment of speech pitch perception is presented. It was designed to (a) assess perception of pitch in linguistic contexts without the confounds of secondary acoustic cues, (b) be usable with listeners from different language backgrounds, and (c) be suitable for use in a clinical setting. The need for this test battery arises from increased awareness of the importance of prosody in clinical practice, and the development of methods for improving pitch perception in listeners with profound hearing losses. METHODS: Identification and discrimination tasks based on linguistic contexts were developed to establish listeners' just noticeable differences (JNDs) for pitch changes. Stimuli were pseudosentences and pseudowords based on speech from a female speaker, overlain with stylized pitch contours. Target pitch excursions were varied from the 200 Hz baseline to a maximum of 349 Hz. Ninety normal-hearing listeners participated in test validation that assessed goals (a)-(c), established test-retest reliability, and gathered normative data. RESULTS: The JNDs on non-linguistic, control tasks were lower than on linguistic ones, showing that non-linguistic tasks may overestimate pitch perception in speech. Listeners from different language backgrounds scored comparably on most linguistic tasks, and test-retest differences were non-significant. Test usability as evidenced by task duration and subject experience seemed satisfactory for clinical use.