Room-temperature Magnetic Ordering in Functionalized Graphene

Despite theoretical predictions, the question of room-temperature magnetic order in graphene must be conclusively resolved before graphene can fully achieve its potential as a spintronic medium. Through scanning tunneling microscopy (STM) and point I-V measurements, the current study reveals that unlike pristine samples, graphene nanostructures, when functionalized with aryl radicals, can sustain magnetic order. STM images show 1-D and 2-D periodic super-lattices originating from the functionalization of a single sub-lattice of the bipartite graphene structure. Field-dependent super-lattices in 3-nm wide “zigzag” nanoribbons indicate local moments with parallel and anti-parallel ordering along and across the edges, respectively. Anti-parallel ordering is observed in 2-D segments with sizes of over 20 nm. The field dependence of STM images and point I-V curves indicates a spin polarized local density of states (LDOS), an out-of-plane anisotropy field of less than 10 Oe, and an exchange coupling field of 100 Oe at room temperature

Enhanced photosensitivity of electro-oxidized epitaxial graphene

International audienceWe report the enhanced photosensitivity of epitaxial graphene (EG) after electrochemical oxidation in nitric acid. The onset of photoconductivity appears at a photon energy of ~1.7 eV while the responsivity reaches 2.5 A/W at a wavelength of 470 nm (blue light, energy 2.64 eV) and further increases to 200 A/W in the UV spectral range (3.5 eV, 350 nm). The observed photoresponse is attributed to the formation of deep traps at the electro-oxidized EG interface, which release charge carriers under illumination and prolong the life time of the photocarriers. Potential applications of electro-oxidized EG in ultraviolet photodetection are discusse

Spectroscopy of Covalently Functionalized Graphene

International audienceThe atomically flat surface of graphene provides an opportunity to apply carbon-carbon bond-forming chemical reactions to engineer the electronic properties of graphene circuitry. In particular, covalent functionalization of the surface or the edge of graphene ribbons provides a novel way to introduce patterning that can modulate the energy band gap, affect electron scattering, and direct current flow by producing dielectric regions in a graphene wafer. We discuss the use of Raman spectroscopy and scanning tunneling microscopy to characterize the surface functionalization periodicities and densities that have been produced by the chemical derivatization of epitaxial graphene together with the concomitant changes in the electronic and magnetic properties of the graphene surface laye

Aryl Functionalization as a Route to Band Gap Engineering in Single Layer Graphene Devices

Chemical functionalization is a promising route to band gap engineering of graphene. We chemically grafted nitrophenyl groups onto exfoliated single-layer graphene sheets in the form of substrate-supported or free-standing films. Our transport measurements demonstrate that non-suspended functionalized graphene behaves as a granular metal, with variable range hopping transport and a mobility gap ~ 0.1 eV at low temperature. For suspended graphene that allows functionalization on both surfaces, we demonstrate tuning of its electronic properties from a granular metal to a gapped semiconductor, in which charge transport occurs via thermal activation over a gap ~ 80 meV. This non-invasive and scalable functionalization technique paves the way for CMOS-compatible band gap engineering of graphene electronic devices

Passive nanotechnology based sensors for the remote detection of environmental pollutants impacting public health

Carbon nanotube sensors offer sensitivity and compactness, and provide a versatile chemical platform for ambient monitoring of environmental pollutants such as ozone, ammonia and volatile organic compounds, known to cause acute respiratory health problems (e.g., exacerbations of asthma and COPD). The advances in electronics and the feasibility to interface complex sensor materials with low-resistance metallic contacts enable novel sensor configurations, such as passive nodes scattered on ground and remotely monitored by drones or radar. Under an NIH Grant, we are developing sensor arrays to detect ambient environmental triggers of respiratory diseases in the personal microenvironment. Our approach makes use of the unique electronic properties of single-walled nanotubes (SWNTs) and the tremendous potential to modulate their sensitivity and selectivity using tailored chemical functionalization to adsorb specific molecules. In this paper, we present the first results to demonstrate the feasibility of a completely passive SWNT-based ammonia sensor remotely interrogated by an instrumented monostatic radar. It is shown that the backscattered signal produces a unique resonant response that can be used as a marker for the gas detection

Impact of 1,8-Diiodooctane (DIO) Additive on the Active Layer Properties of Cu₂ZnSnS₄ Kesterite Thin Films Prepared by Electrochemical Deposition for Photovoltaic Applications

Kesterite Cu2ZnSnS4 (CZTS) thin films using various 1,8-diiodooctane (DIO) polymer additive concentrations were fabricated by the electrochemical deposition method. The optical, electrical, morphological, and structural properties of the CZTS thin films synthesized using different concentrations of 5 mg/mL, 10 mg/mL, 15 mg/mL, and 20 mg/mL were investigated using different techniques. Cyclic voltammetry exhibited three cathodic peaks at −0.15 V, −0.54 V, and −0.73 V, corresponding to the reduction of Cu2+, Sn2+, Sn2+, and Zn2+ metal ions, respectively. The analysis of the X-ray diffraction (XRD) pattern indicated the formation of the pure kesterite crystal structure, and the Raman spectra showed pure CZTS with the A1 mode of vibration. Field emission scanning electron microscopy (FE-SEM) indicated that the films are well grown, with compact, crack-free, and uniform deposition and a grain size of approximately 4 µm. For sample DIO-20 mg/mL, the elemental composition of the CZTS thin film was modified to Cu:Zn:Sn: and S = 24.2:13.3:12.3:50.2, which indicates a zinc-rich and copper-poor composition. The X-ray photoelectron spectroscopy (XPS) results confirmed the existence of Cu, Sn, Zn, and S elements and revealed the element oxidation states. The electrochemical deposition synthesis increased the absorption of the CZTS film to more than 104 cm−1 with a band gap between 1.62 eV and 1.51 eV. Finally, the photovoltaic properties of glass/CZTS/CdS/n-ZnO/aluminum-doped zinc oxide (AZO)/Ag solar cells were investigated. The best-performing photovoltaic device, with a DIO concentration of 20 mg/mL, had a short-circuit current density of 16.44 mA/cm2, an open-circuit voltage of 0.465 V, and a fill factor of 64.3%, providing a conversion efficiency of 4.82%