D. Kanjilal

White light emission from chemically synthesized ZnO–porous silicon nanocomposite

White light emission across the extended visible region of the electromagnetic spectrum from the ZnO‐porous silicon (PS) nanocomposite is reported. Nanocrystallites of ZnO were grown inside the spongy structures of PS by the chemical route of sol‐gel spin coating. The property of the material arises from versatile interactions among the host structures of PS and ZnO. The origin of the observed extended white light emission from 1.4 to 3.3eV is discussed by developing a flat band energy diagram. (Some figures in this article are in colour only in the electronic version)

Thermoluminescence and photoluminescence characteristics of nanocrystalline LiNaSO4?:?Eu phosphor

Europium doped LiNaSO4 in its nanocrystalline form has been prepared and its thermoluminescence (TL) properties are studied. The TL glow curve of the phosphor has been found to have a simple structure with a single peak at 432?K. Though the highly sensitive, commercially available TL phosphor LiF?:?Mg, Cu, P (TLD-700H) is about 1.5 times more sensitive than the nanocrystalline material, the sensitivity of the concerned nanomaterial is much higher (~10 times) than the other standard phosphor TLD-100 (LiF?:?Mg, Ti). Compared to the conventional LiNaSO4?:?Eu phosphor (prepared through a melting procedure and having particle size of 125??m), the nano-sized phosphor has a lesser TL sensitivity. However, this reduction in TL sensitivity on decreasing the particle size from micrometres to nanometres gives a better understanding of the TL phenomenon. The order of TL kinetics for the concerned nanomaterial is also found to be different from that of the conventional material. Photoluminescence studies that have been performed on these materials throw light on the reasons for such a change in the order of kinetics. Further, fading and reusability of the concerned nanomaterial has also been studied and it has been found that the phosphor is quite suitable for radiation dosimetry.

Effect of nitrogen ion implantation on the optical and structural characteristics of CR-39 polymer

The effect of nitrogen ion implantation has been examined in transparent surfaces of CR-39 polymer. Samples were implanted with 100keV N+ ions to various doses ranging from 1014to1017cm−2. The chemical and structural changes in the implanted specimens were performed using Raman spectroscopy and glancing angle x-ray diffraction. Ultraviolet-visible absorption analysis indicates a drastic decline in optical band gap from 3.50eV in virgin sample to 0.80eV at an implantation dose of 1017ionscm−2.The effect of nitrogen ion implantation has been examined in transparent surfaces of CR-39 polymer. Samples were implanted with 100keV N+ ions to various doses ranging from 1014to1017cm−2. The chemical and structural changes in the implanted specimens were performed using Raman spectroscopy and glancing angle x-ray diffraction. Ultraviolet-visible absorption analysis indicates a drastic decline in optical band gap from 3.50eV in virgin sample to 0.80eV at an implantation dose of 1017ionscm−2.

Synthesis of buried SiC using an energetic ion beam

Buried silicon carbide (SiC) was synthesized at room temperature using implantation of 150u2009keV C+ ions in n-type Si (100) and Si (111) substrates. The dose of implanted C+ was varied from 4 × 1017 to 8 × 1017u2009cm−2. Post-implantation annealing at 1000°u2009C for 30u2009min was carried out in inert ambience. Rutherford backscattering spectroscopy, x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy were employed to characterize the samples. FTIR and Raman spectroscopic techniques in combination with the XRD analysis confirmed the development of the β-SiC phase in the samples. The average size of the SiC precipitates was estimated to be 9u2009nm from XRD analysis.

Temperature-dependent barrier characteristics of swift heavy ion irradiated Au∕n-Si Schottky structure

The electrical behavior of Au∕n-Si(100) structure, irradiated with 120MeV Ag8+107, has been investigated in a wide temperature range (50–300K). The forward bias current-voltage (I-V) and reverse bias capacitance-voltage (C-V) measurements have been used to extract the diode parameters. The variations in various parameters of the irradiated Schottky structure have been systematically studied as a function of temperature. It is found that the flatband barrier height is almost independent of the change in temperature. The ionized-donor concentration decreases while the ideality factor increases with decreasing temperatures. The behavior of Schottky parameters is explained by taking into account the role of the swift heavy ion irradiation induced defects at metal-semiconductor junction. The results are interpreted on the basis of recent models of Fermi level pinning.

Self-organization of 6H‐SiC (0001) surface under keV ion irradiation

In the present study, we have investigated the temporal evolution of 6H‐SiC (0001) surface under 100keV Ar+ ion irradiation at oblique incidence (θ=60°). The topographical changes introduced by ion beam were examined using scanning force microscopy, and it is demonstrated that while at short time scales, surface morphology is dominated by dots with average diameter of 30nm, periodic height modulations or ripples emerge at the later time scales. Existing theories of ripple formation have been invoked to explain various features of the observed ripples. Ripple structures developed on a physically stable material such as SiC are expected to show very small time degradation and therefore, would be more advantageous for various technological applications as compared to those grown on conventional semiconductors such as Si, GaAs, InP, etc.

Thermoluminescence and photoluminescence characteristics of sol–gel prepared pure and europium doped silica glasses

Thermoluminescence (TL) and photoluminescence (PL) measurements have been performed on gamma-irradiated amorphous SiO 2 and SiO 2 : Eu glass samples prepared by the sol-gel technique. In this type of silica the basic TL feature i.e. a prominent glow peak at 60 < T m < 120°C is similar to that already studied in several such amorphous SiO 2 samples. The temperature of the glow peak also shifts to higher values as a result of partial pre-heating treatments as has been reported earlier for other silica glasses. In the europium doped silica a prominent TL peak is obtained at around 170°C with a small shoulder at around 115°C. Significantly, a partial pre-heating for even up to 100°C simply removes the 170°C peak from the glow curve and a new peak of very low intensity is found above 300°C. An explanation for such strange results has been provided in this paper. Moreover, PL studies performed on the europium doped material show the presence of europium as both Eu 2+ and Eu 3+ in the material.

Embedded Ge nanocrystals in SiO2 synthesized by ion implantation

200u2009nm thick SiO2 layers grown on Si substrates were implanted with 150u2009keV Ge ions at three different fluences. As-implanted samples were characterized with time-of-flight secondary ion mass spectrometry and Rutherford backscattering spectrometry to obtain depth profiles and concentration of Ge ions. As-implanted samples were annealed at 950u2009°C for 30 min. Crystalline quality of pristine, as-implanted, and annealed samples was investigated using Raman scattering measurements and the results were compared. Crystalline structure of as-implanted and annealed samples of embedded Ge into SiO2 matrix was studied using x-ray diffraction. No secondary phase or alloy formation of Ge was detected with x-ray diffraction or Raman measurements. Scanning transmission electron microscope measurements were done to get the nanocrystal size and localized information. The results confirmed that fluence dependent Ge nanocrystals of different sizes are formed in the annealed samples. It is also observed that Ge is slowly dif...

Substrate dependence in the formation of TiO2 nanophases by dense electronic excitation

Irradiation by swift heavy ion (SHI) is an excellent tool for the nanostructuring of thin films. During SHI irradiation, the energy of the projectile is transferred to the target mainly via electronic energy loss (Se). If the value of Se is more than a threshold value Seth, then latent tracks are formed in the target and a large amount of deposited energy gets confined in narrow dimensions. This leads the system to a non-equilibrium state and it then relaxes dynamically by inducing nucleation of nanocrystallites along the latent tracks. In the present investigation, amorphous thin films of TiO2 are deposited on substrates of fused silica and that of single crystal sapphire. The films are then irradiated by a 100 MeV Au ion beam. Atomic force microscopy is employed for the surface study. The structural phase change induced by SHI irradiation is identified by glancing angle x-ray diffraction. Optical characterization is carried out by UV?vis absorption spectroscopy. Defects created during irradiation are studied by electron spin resonance spectroscopy studies. The role of a substrate in the SHI-induced nanocrystallization process is studied.

Effect of swift heavy ion irradiation on deep levels in Au∕n-Si (100) Schottky diode studied by deep level transient spectroscopy

In situ deep level transient spectroscopy has been applied to investigate the influence of 100MeV Si7+ ion irradiation on the deep levels present in Au∕n-Si (100) Schottky structure in a wide fluence range from 5×109to1×1012ionscm−2. The swift heavy ion irradiation introduces a deep level at Ec−0.32eV. It is found that initially, trap level concentration of the energy level at Ec−0.40eV increases with irradiation up to a fluence value of 1×1010cm−2 while the deep level concentration decreases as irradiation fluence increases beyond the fluence value of 5×1010cm−2. These results are discussed, taking into account the role of energy transfer mechanism of high energy ions in material.