ABSTRACT
Nitrogen-doped graphene quantum dots (NGQDs) have gained significant attention due to their various physical and chemical properties; however, there is a gap in the study of NGQDs' magnetic properties. This work adds to the efforts of bridging the gap by demonstrating the room temperature paramagnetism in GQDs doped with Nitrogen up to 3.26 at.%. The focus of this experimental work was to confirm the paramagnetic behavior of metal free NGQDs resulting from the pyridinic N configuration in the GQDs host. Metal-free nitrogen-doped NGQDs were synthesized using glucose and liquid ammonia as precursors by microwave-assisted synthesis. This was followed by dialysis filtration. The morphology, optical, and magnetic properties of the synthesized NGQDs were characterized carefully through atomic force microscopy (AFM), transmission electron microscopy (TEM)), UV-VIS spectroscopy, fluorescence, X-ray photon spectroscopy (XPS), and vibrating sample magnetometer (VSM). The high-resolution TEM analysis of NGQDs showed that the NGQDs have a hexagonal crystalline structure with a lattice fringe of ~0.24 nm of (1120) graphene plane. The N1s peak using XPS was assigned to pyridinic, pyrrolic, graphitic, and oxygenated NGQDs. The magnetic study showed the room-temperature paramagnetic behavior of NGQDs with pyridinic N configuration, which was found to have a magnetization of 20.8 emu/g.
ABSTRACT
Patterning semiconducting materials are important for many applications such as microelectronics, displays, and photodetectors. Lead halide perovskites are an emerging class of semiconducting materials that can be patterned via solution-based methods. Here we report an all-benchtop patterning strategy by first generating a patterned surface with contrasting wettabilities to organic solvents that have been used in the perovskite precursor solution then spin-coating the solution onto the patterned surface. The precursor solution only stays in the area with higher affinity (wettability). We applied sequential sunlight-initiated thiol-ene reactions to functionalize (and pattern) both glass and conductive fluorine-doped tin oxide (FTO) transparent glass surfaces. The functionalized surfaces were measured with the solvent contact angles of water and different organic solvents and were further characterized by XPS, selective fluorescence staining, and selective DNA adsorption. By simply spin-coating and baking the perovskite precursor solution on the patterned substrates, we obtained perovskite thin-film microarrays. The spin-coated perovskite arrays were characterized by XRD, AFM, and SEM. We concluded that patterned substrate prepared via sequential sunlight-initiated thiol-ene click reactions is suitable to fabricate perovskite arrays via the benchtop process. In addition, the same patterned substrates can be reused several times until a favorable perovskite microarray is acquired. Among a few conditions we have tested, DMSO solvent and modified FTO surfaces with alternatively carboxylic acid and alkane is the best combination to obtain high-quality perovskite microarrays. The solvent contact angle of DMSO on carboxylic acid-modified FTO surface is nearly zero and 65±3° on octadecane modified FTO surface.
ABSTRACT
We study the plasma activation systematically in an attempt to simplify and optimize the formation of hydrophilic silicon (Si) surface critical for self-assembly of nanostructures that typically uses piranha solution, a high molarity cocktail of sulfuric acid and hydrogen peroxide at elevated temperatures. In the proposed safer and simpler approach, O2 plasma is used under optimized process conditions in a capacitively coupled parallel-plate chamber to induce strong hydrophilic behavior on silicon surfaces associated with the formation of suboxide groups. Surface activation is validated and studied via contact angle measurements as well as XPS spectra and consequently optimized using a novel atomic force spectroscopy approach, which can streamline characterization. It is found that plasma power around 100 W and exposure duration of â¼65 s are the most effective parameters to enhance surface activation for the reactive ion etcher system used. Other optimum plasma process conditions for pressure and flow-rate are also reported along with temporal development of activation, which peaks within 1 h and wears off in 24 h scale in air. The applicability of the plasma approach to nanoassembly process was demonstrated using simple drop coating and spinning of polystyrene (d < 500 nm, 2.5-4.5% w/v) and inkjet printing on polydimethylsiloxane.
ABSTRACT
Binary ferromagnetic Mn(3-delta)Ga (1.2<3-delta< or =1.5) crystalline thin films have been epitaxially grown on wurtzite GaN(0001) surfaces using rf N-plasma molecular beam epitaxy. The film structure is face-centered tetragonal with CuAu type-I (L1(0)) ordering with (111) orientation. The in-plane epitaxial relationship to GaN is nearly ideal with [110](MnGa) parallel[1100](GaN) and [112](MnGa) parallel[1120](GaN). We observe magnetic anisotropy along both the in-plane and out-of-plane directions. The magnetic moments are found to depend on the Mn/(Mn+Ga) flux ratio and can be controlled by observation of the surface reconstruction during growth, which varies from 1x1 to 2x2 with increasing Mn stoichiometry.
