The unique planar structures and high surface area of graphene oxide (GO) and reduced graphene oxide (rGO) has induced great interest as drug delivery platforms. Silver and platinum nanoparticles are used in medicine, biotechnology and cosmetics and have electrocatalytic properties. However, GO has been found to be toxic to a variety of cells; pure graphene is insoluble; and nanoparticles aggregate, diminishing their activity. This research functionalized GO and rGO with silver or platinum nanoparticles (Ag/PtNPs) and experimental solutions were then tested on bacteria, dermal fibroblasts (DFBC’s), and cancerous (SCC13’s) and non-cancerous (DO33’s) epidermal cells to determine toxicity and/or cell viability.

GO was functionalized with Ag or Pt salts, forming metalized-GO; then reduced with NaBH4. Ag-rGO, depending on nanoparticle size, killed either S. Aureus or K. Pneumoniae, while Pt-rGO and rGO had no effect. 1mM Ag-prGO concentrations diluted 1:100 with DMEM was toxic to SCC13 cancerous keratinocytes but showed reduced toxicity to DO33 non-cancerous keratinocytes; whereas Pt-rGO and rGO exerted little effect on SCC13’s and DO33’s at all concentrations. All test solutions adhered to DFBC’s and influenced the orientation of their growth, suggesting potential use in wound dressings to aid healing.

Germanene, the 2D graphene-like Ge nanosheet, has been recently the subject of many theoretical studies and experimental attempts to synthesize it on Ag(111), Au(111) and Pt(111) surfaces. The experimental and theoretical evidences of germanene show a 2D continuous honeycomb layer with a buckled conformation. Density functional theory (DFT) calculations have predicted a larger buckling for germanene than silicene whose origin is also associated with a pseudo Jahn–Teller (PJT) effect. In this work we show that despite the fact that both, silicene and germanene possess a buckled conformation with a PJT origin, their vibronic coupling have different origins. The analysis is based on the PJT puckering instability of the hexagermabenzene molecule, the single hexagonal unit of germanene. This is done through the linear vibronic coupling model between the ground and the lowest excited states, which leads to a puckering distortion of the more symmetric cluster. We study both, the multilevel superposition vibronic model and possible mixing of excited states of different irreducible representations, which have been used to show the origin of similar structural transitions in hexagonal silicon and gold ring systems respectively. We show that contrary to other cases with one six-member rings, for the hexagermabenzene molecule a mixture of both the multilevel PJT and a ground state coupling with two quasi-degenerate excited states is necessary for a satisfactory explanation of puckering. Our model allows a determination of the coupling constants and predicts simultaneously the Adiabatic Potential Energy Surface (APES) behavior for the ground and excited states around the maximum symmetry point. The analysis is based on a scalar relativistic DFT and time-dependent DFT (TD-DFT) calculations in the Zero Order Regular Approximation (ZORA) using the B3LYP hybrid functional.

Graphene-based field effect transistors (GFETs) were assessed when interfaced with well separated and precisely placed core/shell CdSe/ZnS semiconductor quantum dot (QD) arrays. The QDs were imbedded in a hexagonal hole-array, which was formed in a layer of anodized aluminum oxide on Si/SiO2 substrates. Graphene (single, or two layers), grown by chemical vapor deposition (CVD) on Cu foils, was transferred and placed on top of the QDs imbedded films and served as the transistor channel. Electrical characteristics under white-light illumination at various biasing conditions revealed that the photo current was decreasing upon increasing biasing. The device's photoluminescence (PL) as a function of both the drain-source and gate-source potentials also reduced as a function of the potential biases. We observed two maxima in the PL data while tilting the sample with respect to the incident laser beam. We attributed it to the optimal coupling between the incident and the emission wavelengths to resonating surface modes.

Novel 2D materials with interesting properties have been synthetized and characterized recently. In particular, unlike graphene, silicene or germanene, phosphorene has attracted a lot of attention because of its intrinsic band gap. This property allows for a wide range of applications where semiconductor thin films are traditionally used (e.g. electronics, optoelectronics, thermoelectrics). For each application, the device efficiency depends on how well an electrical current is extracted from the active materials, and depends on a variety of electron scattering processes. Some of these scattering processes can considerably improve or degrade device efficiencies. In this contribution we focus on non-radiative electron-hole pair generation and recombination processes, i.e. impact ionization (charge carrier multiplication) and Auger processes (charge carrier recombination). The rate of these processes is calculated from first principles and their effects on device operation are estimated.

In this study, density functional theory (DFT) is employed to investigate the electronic properties of armchair silicene nanoribbons perforated with periodic nanoholes (ASiNRPNHs). The dangling bonds of armchair silicene nanoribbons (ASiNR) are passivated by mono- (:H) or di-hydrogen (:2H) atoms. Our results show that the ASiNRs can be categorized into three groups based on their width: W = 3P − 1, 3P, and 3P + 1, P is an integer. The band gap value order changes from “EG (3P − 1) < EG (3P) < EG (3P + 1)” to “EG (3P + 1) < EG (3P − 1) < EG (3P)” when edge hydrogenation varies from mono- to di-hydrogenated. The energy band gap values for ASiNRPNHs depend on the nanoribbons width and the repeat periodicity of the nanoholes. The band gap value of ASiNRPNHs is larger than that of pristine ASiNRs when repeat periodicity is even, while it is smaller than that of pristine ASiNRs when repeat periodicity is odd. In general, the value of energy band gap for ASiNRPNHs:2H is larger than that of ASiNRPNHs:H. So a band gap as large as 0.92 eV is achievable with ASiNRPNHs of width 12 and repeat periodicity of 2. Furthermore, creating periodic nanoholes near the edge of the nanoribbons cause a larger band gap due to a strong quantum confinement effect.

A method for synthesizing and structuring 2D-MoS2/rGO (molybdenum disulfide/reduced graphene oxide) nanocomposite-based electric double layer capacitor (EDLC) that has a slower discharge rate and higher energy density than rGO-based EDLC (RG-EDLC) is reported. The rGO electrode and the nanocomposite were characterized using powder XRD and SEM for their physical and structural properties. Cyclic voltammetry (CV) was used to analyze the electrochemical behavior of the EDLCs. A maximum current density at which the MoS2/rGO nanocomposite-based EDLC (MRG-EDLC) can charge and discharge was 2.5 A/g, while it was 1A/g for the RG-EDLC. The specific capacitance of the MRG-EDLC was 14.52 F/g at 0.5 A/g with an energy density of 8.06 Wh/kg.

The room temperature electronic characteristics of resonant tunneling diodes (RTDs) containing AlAs/InGaAs quantum wells are studied. Differences in the peak current and voltages, associated with device-to-device variations in the structure and width of the quantum well are analyzed. A method to use these differences between devices is introduced and shown to uniquely identify each of the individual devices under test. This investigation shows that quantum confinement in RTDs allows them to operate as physical unclonable functions.

The cross-plane thermal conductivities of InGaZnO (IGZO) thin films in different morphologies were measured on three occasions within 19 months, using the 3ω method at room temperature 300 K. Amorphous (a-), semi-crystalline (semi-c-) and crystalline (c-) IGZO films were grown by pulsed laser deposition (PLD), followed by X-ray diffraction (XRD) for evaluation of film quality and crystallinity. Semi-c-IGZO shows the highest thermal conductivity, even higher than the most ordered crystal-like phase. After being stored in dry low-oxygen environment for months, a drastic decrease of semi-c-IGZO thermal conductivity was observed, while the thermal conductivity slightly reduced in c-IGZO and remained unchanged in a-IGZO. This change in thermal conductivity with storage time can be attributed to film structural relaxation and vacancy diffusion to grain boundaries.

The thermal and electrical properties of organic semiconductor are playing critical roles in the device applications especially on the devices with large area. Although the effect may be minor in a single device like field effect transistors, the unwanted waste heat would cause much more severe problems in large-scale devices as the power density will go up significantly. The waste heat would lead to performance degradation or even failure of the devices, and thus a more detailed study on the thermal conductivity and carrier mobility of the organic thin film would be beneficial to predict the limits of the device or design a thermally stable device. Here we explore the thermal annealing effect on the thermal and electrical properties of the small molecule organic semiconductor, dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene (DNTT). After the post deposition thermal annealing, the grain size of the film increases and in-plane crystallinity improves while cross-plane crystallinity keeps relatively constant. We demonstrated the cross-plane thermal conductivity is independent of the thermal annealing temperature and high annealing temperature will reduce the space-charge-limited current (SCLC) mobility. When the annealing temperature increase from 24 °C to 140 °C, the field effect mobility shows a gradual increase while the threshold voltage shifts from positive to negative. The different dependence of the SCLC mobility and field effect mobility on the annealing temperature suggest the improvement of the film crystallinity after thermal annealing is not the only dominating effect. Our investigation provides the constructive information to tune the thermal and electrical properties of organic semiconductors.

Using scanning tunneling microscopy (STM) we observed atomic scale interference patterns on quasi-freestanding WSe2 islands grown on top of graphene. The bias-independent double atomic size periodicity of these patterns and the sharp Brillouin zone edge revealed by 2D STM Fourier analysis indicate formation of optical phonon standing waves due to scattering on intercalating defects supporting these islands. Standing wave patterns of both synchronized and non-synchronized optical phonons, corresponding to resonant and non-resonant phonon scattering regimes, were experimentally observed. We also found the symmetry breaking effect for individual phonon wave packets, one of the unique features distinguishing phonon standing waves. We show that vibrational and electronic anharmonicities are responsible for STM detection of these patterns. A significant contribution to the interference contrast arises from quantum zero-point oscillations.

We demonstrate a compact tunable photonic modulator driven by surface acoustic waves (SAWs) in the low GHz frequency range. The device follows a well-known Mach-Zehnder interferometer (MZI) structure with three output channels, built upon multi-mode interference (MMI) couplers. The light continuously switches paths between the central and the side channels, avoiding losses and granting a 180◦-dephasing synchronization between them. The modulator was monolithically fabricated on (Al,Ga)As, and can be used as a building block for more complex photonic functionalities. It can also be implemented in other material platforms such as Silicon or (In,Ga)P. Light modulated at multiples of the fundamental acoustic frequency can be accomplished by adjusting the applied acoustic power. An excellent agreement between theory and experiment is achieved.