Increment In Band Gap Research Articles

Bandgap Alteration of Transparent Zinc Oxide Thin Film with Mg Dopant

We have successfully demonstrated a bandgap alteration of transparent zinc oxide (ZnO) thin film with Mg dopant by using sol-gel spin coating technique. By increasing the dopant from 0 to 30 atomic percent (at.%), a decrement value in the cutoff is observed, where the absorption edge shifts continuously to the shorter wavelength side, towards 300 nm. This resulted in a significant bandgap increment from 3.28 to 3.57 eV. However, the transmittance of the thin film at 350-800 nm gradually downgraded, from 93 to 80 % which is most probably due to the grain size that becomes bigger, and it also affected the electrical properties. The decrement from 45 to 0.05 mA at +10 V was observed in the I-V characteristics, concluding the significant relationship; where higher optical bandgap materials will exhibit lower conductivity. These findings may be useful in optoelectronics devices.

Tuning Electrical Conductance of Serpentine Single‐Walled Carbon Nanotubes

AbstractChanges in resistivity of serpentine single‐walled carbon nanotubes are presented as a function of bending radius, rb, in the range of 100–2000 nm. Resistivity (ρ) is observed to increase with curvature (1/rb), which is consistent with theoretical speculation on strain‐induced bandgap increment. Furthermore, a sharp bend (rb < 50nm) in the nanotubes results in a drastic change in the field‐effect behavior, i.e., from ambipolar to p type across the bend. Local Raman spectra show that the G‐band Raman frequencies shift along the curvature, which may be attributed to local deformation and broken cylindrical symmetry in the nanotubes. The results suggest the possibility to tune the electrical properties by bending nanotubes and to build an all‐nanotube device by modulating the structure of the same tube.

Temperature dependent optical constants of amorphous Ge 2Sb 2Te 5 thin films

This study focuses on the temperature dependent optical band gap changes in the amorphous Ge 2Sb 2Te 5 (GST) films. The behavior of the amorphous GST thin films at low temperatures has been studied. The band gap increment of around 0.2 eV is observed at low temperature (4.2 K) compared to room temperature (300 K). The band gap changes associated with the temperature are completely reversible. The other optical parameters like Urbach energy and Tauc parameter (B 1/2) are studied for different temperatures and discussed. The observed changes in optical band gap (E g) are fitting to Fan's one phonon approximation. Phonon energy (ћω) corresponding to a frequency of 3.59 THz is derived from Fan's approximation, which is close to the reported value of 3.66 THz.

Structural, optical, and electronic properties of room temperature ferromagnetic GaCuN film grown by hybrid physical-chemical vapor deposition

Ferromagnetic Cu-doped GaN film was grown on a GaN-buffered sapphire (0001) substrate by a hybrid physical-chemical-vapor-deposition method (HPCVD). The GaCuN film (Cu: 3.6 at.%) has a highly c-axis-oriented hexagonal wurtzite crystal structure, which is similar to GaN buffer but without any secondary phases such as metallic Cu, CuxNy, and CuxGay compounds. Two weak near-band edge (NBE) emissions at 3.38 eV and donor-acceptor-pair (DAP) transition at 3.2 eV with a typical strong broad yellow emission were observed in photoluminescence spectra for GaN buffer. In contrast, the yellow emission was completely quenched in GaCuN film because Ga vacancies causing the observed yellow emission in undoped GaN were substituted by Cu atoms. In addition, GaCuN film exhibits a blue shift of NBE emission, which could be explained with the +2 oxidation state of Cu ions, replacing +3 Ga ions resulting in band gap increment. The valance sate of Cu in GaCuN film was also confirmed by x-ray photoelectron spectroscopy (XPS) analysis. The GaCuN film shows ferromagnetic ordering and possesses a residual magnetization of 0.12 emu/cm3 and a coercive field of 264 Oe at room temperature. The unpaired spins in Cu2+ ions (d9) are most likely to be responsible for the observed ferromagnetism in GaCuN.

Synthesis and optical characterization of polymer-capped nanocrystalline ZnS thin films by chemical process

ZnS nanocrystals have been grown into the nanopores of polyvinyl pyrrolidone (PVP) matrix on glass and Si substrates by a simple wet-chemical route. X-ray diffraction (XRD) study confirmed the formation of cubic phase of ZnS nanocrystals into the polymer matrix. The particle size variation was achieved by varying the polymer mole fraction in the starting solution. Transmission electron microscopic image as well as XRD studies confirmed the nanometer size particles formation within the polymer matrix. The average particle size was found to lie in the range of 4–7 nm. UV–Vis–NIR optical spectra showed the 90–95% transmittance in the visible and also in the near infrared region. The direct optical bandgap of the polymer-capped nano-ZnS film was lying in the range 3.87–3.98 eV for different PVP fractions in the film. The direct band gap values are higher than the bulk value (3.6 eV) and the increment of bandgap also supports the nanometer size ZnS particle formation within the polymer matrix. The high-frequency dielectric constant ( ε) of the PVP–ZnS nanocomposite has been measured and the values lies in the range 50–90 which is much higher than that of only PVP having a dielectric constant ∼28. The dielectric constant decreases as the dispersibility increases.

Bandgap Modulation of TiO2 and its Effect on the Activity in Photocatalytic Oxidation of 2-isopropyl-6-methyl-4-pyrimidinol

Nano-size TiO2 particles were obtained using various mesoporous materials and the particle sizes were determined by the pore sizes of mesoporous materials. The bandgap increments due to quantum size effect were observed in both anatase TiO2 and rutile TiO2. The bandgap increment in anatase TiO2 did not affect the efficiency of photocatalytic oxidation of 2-isopropyl-6-methyl-4-pyrimidinol. However, the bandgap increment in rutile TiO2 enhanced the photocatalytic activity by virtue of the increase in redox potential of TiO2.