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Integration of two-dimensional (2D) layered materials like graphene with conventional semiconductors is of great interest to develop high performance optoelectronics and other electronic devices. Gallium nitride (GaN) with a direct bandgap (~3.4 eV) has been widely explored for optoelectronic and power device applications. Recently, freestanding GaN has been grown by liquid phase epitaxy. GaN device properties can be significantly changed depending on the nitrogen (N) and gallium (Ga) polar surface. In the present work, we have explored the Schottky junction properties of graphene with N and Ga polar freestanding GaN. Interestingly, Ga-polar graphene/GaN heterostructure showed higher photoresponsivity than the N-polar graphene/GaN heterostructure.

Pd is a unique substrate to explore graphene growth. Pd is a well-known “carbon sponge” which have potential to grow graphene with semiconducting properties in nature. Here, we reveal a solid phase reaction process to achieve Pd assisted graphene growth in nanoscale by in-situ transmission electron microscope (TEM). Significant structural transformation of amorphous carbon nanofiber (CNF) incorporated with Pd is observed with an applied potential in a two probe system. The Pd particle recrystallize and agglomerate starting from the middle part of CNF toward the end part of CNF with applied potential due to joule heating and large thermal gradient. Consequently, the amorphous carbon start crystallizing and forming sp2 hybridized carbon to form graphene sheet from the tip of Pd surface. The observed graphene formation in nanoscale by the in-situ TEM process can be significant to understand carbon atoms and Pd interaction.

In situ transmission electron microscopy (TEM) observation of the graphene synthesis by solid phase reaction is dealt with. For this purpose, metal-included and pristine (metal free) amorphous carbon nanofibers (CNFs) were fabricated on an edge of a graphite foil by Ar ion irradiation (Ar ion irradiation method) with and without a supply of metals at room temperature, respectively. In Ar ion irradiation method, any kinds of metals could be included in CNFs. Cu-coated pristine CNFs were also prepared. The graphite foils thus prepared were cut into small pieces to be mounted directly on a TEM sample holder equipped with a piezo-controlled nanoprobe to, measure their current-voltage characteristics in direct current (DC) and field emission (FE) modes. Depending on the included metal element in the CNFs, different types of nanocarbons, such as graphene, ring-shaped graphene, and carbon nanotubes (CNTs), were formed from amorphous CNF during the electron current flow by solid phase reaction. Here, dependence of included metal on the nanocarbon formation is reviewed, together with the visualization of graphene sheet formation in nanoscale during the electron current flow for the Cu-coated pristine CNFs. It is believed that the graphene formation by solid phase reaction is essential also for the growth area (position) control of graphene nano-ribbon.

Scanning probe techniques such as atomic force microscopy (AFM) or scanning probe lithography are powerful methods for the investigation and modification of surfaces at the nanometer scale. In these techniques, the tip curvature radius and aspect ratio of the probe play a crucial role. Here, we employ carbon nanofiber (CNF) as the tip apex of AFM probes. We show that CNF-AFM probes provide good performance in terms of both resolution and reliability when operating the AFM in dynamic mode. In addition, the CNF apex is responsible for an enhancement of the field-induced chemical reaction in a specific form of scanning probe lithography, local anodic oxidation (LAO), which allows the fabrication of silicon oxide (SiOx) patterns with sub-10 nm resolution. Keywords—carbon nanofiber; atomic force microscope

We demonstrate synthesis of large area graphene on a metal (Ni and Cu) foil by the thermal chemical vapor deposition (CVD) process using the solid camphor (C10H16O) as a carbon source. The graphene growth process on a polycrystalline metal foil significantly influence by the gas composition and quantity of solid precursor. Synthesis of high quality continuous graphene film is achieved in the developed technique. Fully flexible transparent conductor is fabricated by transferring the graphene film on a plastic substrate.

Indium tin oxide (ITO) and related oxide based materials have been widely used as transparent electrode in optoelectronic devices and organic solar cells. Here, we demonstrate application of chemical vapor deposited (CVD) graphene films as transparent electrode for organic solar cells. Large area graphene films are deposited by control pyrolysis of botanical derivative camphor (C 10 H 16 O) and transparent electrode were fabricated by direct synthesis or transfer process. Raman spectroscopy and transmission electron microcopy studies are used to characterize the synthesized graphene based materials. Direct synthesized and transferred graphene films on glass or plastic substrates show very good optical transparency, electrical conductivity and mechanical stability. P3HT:PCBM bulk heterojunction solar cells are fabricated successfully on graphene based transparent electrode and compared with ITO based device. The dark light characteristic shows very good rectification with minimum leakage current. Under illumination of light the device shows very good open circuit voltage, short circuit current density and conversion efficiency.

A vacuum-ultraviolet (VUV) light emitting device was demonstrated by employing KMgF 3 thin film as phosphor and carbon nanofibers (CNFs) field electron emitter. KMgF 3 thin film was grown on MgF 2 crystal substrate by pulse laser deposition (PLD) method. The heating-free device was realized by utilizing carbon nanofibers (CNFs) field electron emitter, which was grown by sputtering grassy carbon surface at room temperature. The device shows the spectra from 140 to 200 nm in wavelength and have two peaks at 150 and 175 nm and also an output power of 2 μW was demonstrated.

The Zn nanowires covered with ZnO were grown by oxygen plasma-assisted molecular beam irradiation method and characterized, was reported. To grow these nanowires, oxygen plasma was irradiated to Zn thin film evaporated on Si(100) substrate. Scanning electron microscopy and transmission electron microscopy observation results of nanowires revealed that the nanowire has diameter of 80 nm, and nanowires was constructed with crystalline ZnO. Moreover NWs surface was covered by crystalline ZnO. Further Zn and ZnO orientation was coincident and resulted the ZnO appeared by oxidation of Zn nanowires.

Morphology control of rapid grown vertically aligned carbon nanotube forest for fiber spinning is reported. Thermal chemical vapor deposition (CVD) system at around 700°C was used with a catalyst of iron catalyst films deposited on thin alumina supporting layers. Acetylene gas diluted with hydrogen and nitrogen was used as a carbon source. The morphology of carbon nanotube was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Graphite surfaces were irradiated by Ar+ ions at 1 keV with a simultaneous Co supply at room temperature. Various kinds of carbon nanocomposites, such as nanocones with and without nanofibers (NFs) on top, nanorods and bean-like nanoprotrusions, formed depending on Co supply rates. The NFs, ∼1.5 µm in average length, grew on the top of the nanocones at Co supply rate of 1.0 nm/min, and with increasing the Co supply rate the formation of nanoprotrusions without NFs became prominent. As confirmed by energy-dispersive X-ray analysis, NFs and nanoprotrusions were surely composed of C and Co.

Carbon doped ZnO (ZnO∶C) nanoneedles exhibiting Curie temperature above room temperature were fabricated using ion beam technique. The structural and magnetic properties of the ZnO∶C nanoneedles were studied. The magnetic moment of the ZnO∶C nanoneedles was found to be around 0.7 µ B per carbon atom. The ZnO∶C nanoneedles could be a promising intrinsic diluted magnetic semiconductor.

Ge surfaces were irradiated by Ar+ ions at 600 eV with and without a simultaneous supply of Ge, Au or Al at room temperature. The surfaces ion-irradiated without any simultaneous metal supply were characterized by densely distributed conical protrusions. By contrast, various kinds of nanostructures were formed on the Ge surfaces ion-irradiated with a simultaneous metal supply. They featured cones and nanobelts with a flattened top for Ge supply cases, whereas they were characterized by nanorods for Au supply cases and by nanorods, nanobelts and nanowalls for Al supply cases. Very interestingly, the nanorods formed with Au or Al supply possessed a bottleneck structure. Thus, the ion-induced Ge nanostructures were controllable in morphology by species and amount of simultaneously supplied metals.

One-dimensional (1D) carbon nanomaterials, such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are considered to be one of the best field emitters in the near future by virtue of their high aspect ratio, chemical inertness and extraordinary mechanical and electrical properties. A lot of research demonstrated the potential of carbon nanomaterials as the electron emission scources such as flexible field emission display[1], imaging electron microscope[2], microwave amplifier[3] and x-ray tubes for medical imaging[4] In this regard many attempt has been made to grow carbon nanomaterials on various substrates using various techniques. For their growth, however, growth temperatures higher than 500°C are usually required. Recently, an “ion-irradiation method” was proposed to fabricate CNFs on carbon and carbon pre-coated substrates without any catalyst even at room temperature[5]. In this study, we challenged the direct growth of CNFs on metal mesh substrates Copper (Cu) and Molybdenum (Mo), without carbon precoating using ion irradiation method.

Graphite plates were Ar+ ion-sputtered with a simultaneous Fe supply at room temperature. The sputtered surfaces were characterized by various kinds of carbon compostites, such as conical protrusions with and without single carbon nanocomposite fibers (CNCFs) on the top, depending on the Fe supply rates. The CNCFs thus grown were confirmed to be amorphous-like fibers without a hollow structure and possess no distinct boundary between the cone and the CNCF by transmission electron microscope. As revealed by their compositional analysis, CNCFs surely composed of carbon and iron. Since the various kind of metals can be doped into the room-temperature grown carbon nanofibers, this ion-irradiation method is believed to be promising as a new approach to synthesize one-dimensional nanomaterials at low temperatures.

This review article summarizes briefly some important achievements of our recent research on the synthesis, optical properties and novel applications of nano-structured ZnO such as nanorods and honeycomb shaped 3-D (dimension) nano random-walls. A chemical reaction/vapor transportation deposition technique was employed to fabricate those structures on ZnO/SiO2/Si substrate without any catalyst and additive in a simple tube furnace to aim the low-cost and high qualified samples. Random laser action with strong coherent feedback at the wavelength between 375 nm-395 nm has been firstly observed under 355 nm optical excitation with threshold pumping intensity 0.38 MW/cm2 in ZnO 3-D random-wall nanostructure.

We synthesize Co nanorod filled inside multi-walled CNTs (MWCNTs) by microwave plasma enhanced chemical vapor deposition (MPECVD) and utilize off-axis electron holography to observe the remanent states of the filled metal nanorod inside MWCNTs at room. The MWCNTs grew up to 100 - 110 nm in diameter and 1.5 - 1.7 mum in length. The typical bright-field transmission electron microscope (TEM) images revealed both Co/Pd multisegment nanorod and Co nanorod filled inside MWCNTs on the same substrate. We have also performed energy-dispersive X-ray spectrometer (EDS) measurements to characterize the composition of metal filled inside MWCNTs. Based on high-resolution TEM measurements, we observed the face-centered-cubic (fcc) Co filled inside MWCNT. The component of magnetic induction was then measured to be 1.2plusmn0.1 T, which is lower than the expected saturation magnetization of fcc Co of 1.7 T. The partial oxidation of the ferromagnetic metal during the process and the magnetization direction may play an important role in the determination of the quality of the remanent states.

High aspect ratio titanate nanotubes with large surface area and good uniformity were produced by alkaline hydrothermal treatment of grounded TiO2 aerogels and further by applied freeze-drying. Not only the crystal phase and diameter but also morphology of the starting materials impact on the aspect ratio and transformation efficiency of obtained nanotubes. Other parameters, such as the pH value during neutralization process and drying method for the final products, are important on control over the length and dispersion of the tubes. The high quality nanotubes with good crystallinity and uniform dispersion became a good supporter for Ag nanoparticles to exhibit multicolor photochromism behavior, which has great potential application on electronic device.

The influence of different forms of electron energy dispersion relations on the field emission properties of carbon nanotubes is investigated.