Mohd Zamri Mohd Yusop

Highly transparent and flexible field emission devices based on single-walled carbon nanotube films

Single-walled carbon nanotubes (SWNTs) have been used successfully to fabricate highly transparent and flexible field emission displays (FEDs). Field emission measurements indicated that SWNTs films have great potential to work as building blocks for next generation transparent and flexible FEDs.

Vacuum ultraviolet field emission lamp utilizing KMgF3 thin film phosphor

We demonstrated a field emission lamp by employing a KMgF3 thin film as a solid-state vacuum ultraviolet phosphor. The output power of the lamp was 2 μW at an extraction voltage of 800 V and acceleration voltage of 1800 V, and it operated at wavelengths 140–220 nm, which is the shortest wavelength reported for solid-state phosphor lamps. The thin film was grown on MgF2 substrate by pulsed laser deposition. Its conversion efficiency was almost equivalent to a single KMgF3 crystal, and it had emission peaks of 155 and 180 nm in wavelength. These peaks are attributed to transitions from the valence anion band to the outermost core cation band and correspond well with emission peaks previously reported from the crystal. Additionally, we obtained a thermal-free and low-power consumption lamp by employing carbon nanofibres (CNFs) as a field emitter. A CNF emitter was easily grown at room temperature and can be grown on flexible materials.

Field emission characteristics of pristine and N-doped graphene measured by in-situ transmission electron microscopy

We report the field emission characteristics of a few-layer pristine and N-doped graphene by the in-situ transmission electron microscopy. The measurements were performed with a Pt-Ir nanoprobe and at a vacuum gap of 400 nm. The turn on voltage, required to draw an emission current of 1 nA from pristine and N-doped graphene, was found to be 230 and 110 V, respectively. The lower turn on voltage for the N-doped graphene can be explained from the improved electrical conductivity and up-shift of the Fermi level with nitrogen doping. Structural deformation/contraction/buckling of the N-doped graphene sheet was observed with the field emission current exceeding ∼6.9 μA, which can be attributed to the Joule heating.

Field emission from a single carbon nanofiber at sub 100nm gap

The authors report the electron field emission from a single carbon nanofiber (CNF) over a range of anode to CNF tip separations of 20–5500nm. Our results show that the field enhancement factor γ is associated with the electrode separation (S). The modified Miller equation is a reasonable empirical model to describe the behavior of γ, which varies with S over a large range of values. The γ approaches to an asymptotic value of 415 or 1 when S is very large or very small as compared to the length of the CNF, respectively. The maximum field emission current sustained by the single CNF without causing damage was estimated to be as high as 15μA.

Field emission properties of chemical vapor deposited individual graphene

Here, we report field emission (FE) properties of a chemical vapor deposited individual graphene investigated by in-situ transmission electron microscopy. Free-standing bilayer graphene is mounted on a cathode microprobe and FE processes are investigated varying the vacuum gap of cathode and anode. The threshold field for 10 nA current were found to be 515, 610, and 870 V/μm for vacuum gap of 400, 300, and 200 nm, respectively. It is observed that the structural stability of a high quality bilayer graphene is considerably stable during emission process. By contacting the nanoprobe with graphene and applying a bias voltage, structural deformation and buckling are observed with significant rise in temperature owing to Joule heating effect. The finding can be significant for practical application of graphene related materials in emitter based devices as well as understanding the contact resistance influence and heating effect.

Visualizing copper assisted graphene growth in nanoscale.

Control synthesis of high quality large-area graphene on transition metals (TMs) by chemical vapor deposition (CVD) is the most fascinating approach for practical device applications. Interaction of carbon atoms and TMs is quite critical to obtain graphene with precise layer number, crystal size and structure. Here, we reveal a solid phase reaction process to achieve Cu assisted graphene growth in nanoscale by in-situ transmission electron microscope (TEM). Significant structural transformation of amorphous carbon nanofiber (CNF) coated with Cu is observed with an applied potential in a two probe system. The coated Cu particle recrystallize and agglomerate toward the cathode 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 Cu surface. We observed structural deformation and breaking of the graphene nanoribbon with a higher applied potential, attributing to saturated current flow and induced Joule heating. The observed graphene formation in nanoscale by the in-situ TEM process can be significant to understand carbon atoms and Cu interaction.

Fabrication of nanostructured ZnO films for transparent field emission displays

A highly transparent field emitter was achieved by Ar+ ion irradiation onto highly transparent and conducting ZnO films deposited on glass substrates. The as-deposited flat ZnO films before ion irradiation, which showed 90% transmittance and 186 Ω/ sheet resistance, showed no field emission current up to 15 V µm-1. The ZnO film ion-irradiated at an ion-incidence angle of 45° showed nanocone structures about 200–400 nm in height and 6–8 µm-2 in number density. Since the nanocone size was less than the wavelength of visible light, the transmittance was maintained at 86% for the ion-irradiated ZnO film. The field emission properties of the ion-irradiated ZnO film revealed that a current density of 1 µA cm-2 was achieved at 6.2 V µm-1, and that the field enhancement factor was calculated to be 2252 from the Fowler–Nordheim plot. Thus, the nanostructured ZnO film is believed to be promising as a transparent field emitter.

Microwave plasma-induced graphene-sheet fibers from waste coffee grounds

Graphene-sheet fiber, a novel structure of graphitic carbon, grew from coffee grounds under the condition of microwave plasma irradiation. The resulting fiber consisted of only few-layer graphene without a hollow structure inside while possessing a large amount of graphene edges and high conductivity. Due to these advantages, graphene-sheet fibers may find applications in electrochemical energy conversion and storage.

Room-Temperature Fabrication of Au- and Ag-Incorporated Carbon Nanofibers by Ion Irradiation and Their Field Emission Properties

We have demonstrated the growth of Au- and Ag-incorporated carbon nanofibers (CNFs) at room temperature by Ar+ bombardment on graphite surfaces with simultaneous Au and Ag supply. The evolution of their morphology and its effects on field emission properties were investigated. The structure and density of the grown CNFs depended on the metal supply rate. The ion-irradiated surfaces with excess metal supply featured sparsely distributed conical protrusions and a wall-like structure, while the surfaces irradiated with appropriate metal supply produced densely distributed CNF-tipped cones and a needlelike structure. Compared with Ag supply, Au supply yielded fewer CNFs in terms of number density. Thus, the CNF number density was controllable by adjusting the metal supply rate and metal species. A lower threshold field and a higher emission current density were achieved in the field emission of both metal-incorporated CNFs than of pristine CNFs (without metal incorporation). Thus, it is believed that metal-incorporated CNFs are promising for practical field emission device applications.

In situ transmission electron microscopy of Ag-incorporated carbon nanofibers: The effect of Ag nanoparticle size on graphene formation

We have studied graphene formation from a single Ag-incorporated carbon nanofiber (CNF) during electron emission using in situ transmission electron microscopy. The formation of graphene from the Ag-incorporated CNF structure was observed under a high current of between 900 nA to 2.03 μA during field and thermal electron emission. Joule heating during the process generated an increased temperature, estimated at approximately 440 K to 1030 K, leading to the transformation of a significant amount of the amorphous carbon surrounding Ag particles to a graphene structure, and to the nearly simultaneous evaporation of Ag particles. This evaporation interrupted the thermal electron emission process, thus leading to a decrease of the emission current to ∼300 nA. Also, graphene stopped forming after the Ag particles had evaporated. In this paper, the effect of Ag particle size on its ability to catalyze the fabrication of high-quality graphene are discussed.