Solid State Phenomena Vol. 201

Abstract: Moores law predicts the reduction of the device elements size and the advancement of physics with time for the next generation microelectronic industries. Materials and devices sizes and enriched physics are strongly correlated phenomena. Everyday physics moves a step forward from microscale classical physics toward nanoscale quantum phenomenon. Similarly, the vast micro/nanoelectronics needs advancement in growth and characterization techniques and unexplored physics to cope with the 21^st century market demands. The continuous size reduction of devices stimulates the researchers and technocrats to work on nanomaterials and devices for the next generation technology. The semiconductor industry is also facing the problem of size limitation and has followed Moores law which predicts 16 nm nodes for next generation microelectronic industries. Nanometer is known as the 10 times of an Angstrom unit, where it is common consensus among the scientists that any materials and devices having physical dimensions less than 1000 times of an Angstrom will come under the umbrella of Nanotechnology. This review article focuses on the fundamental aspects of nanoscale materials and devices: (i) definitions and different categories of nanomaterials, (ii) quantum scale physics and technology, (iii) self-assembed nanostructures, (iv) growth conditions and techniques of 0D, 1D, 2D, and 3D dimensional materials, (v) understanding of the multifunctionalities of the nanomaterials, (vi) nanoscale devices for low energy consumption and fast response, (vii) integration of nanoscale materials with Si-based systems, and (viii) major technical challenges.

Abstract: One-dimensional nanowires (NWs) have attracted considerable attention in recent years because of their novel physical properties and potential applications as interconnects in nanometre-scale electronics. NWs have potential applications in nanoscale electronics, optoelectronics, photonics, sensors, and solar cells due to their unique electrical, chemical, and optical properties. Several chemical and physical methods are commonly used to produce NWs. Among them, electrochemical synthesis and vapour-liquid-solid (VLS) methods to produce NWs have become popular among scientific workers due to a number of advantages. Synthesis of NWs using anodic alumina and polymer templates in an electrochemical cell has been described in detail as investigated in our laboratory. Characterization of metal and semiconductor NWs has been accomplished using scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), high resolution transmission microscope (HRTEM), X-ray diffraction (XRD), and energy dispersive X-ray analysis (EDAX). Morphology of NWs has been revealed by SEM, structure by TEM, crystallinity by XRD and chemical composition by EDAX. I-V characteristics of copper and semiconductor NWs were recorded in-situ, as grown in pores of anodic alumina template, using Dual Source Meter (Keithley Model 4200 SCS) with platinum probes for contacts. Resonating tunneling diode (RTD) characteristics of fabricated NWs have been investigated. Bulk production of Copper NWs has been described by seed growth technique. Applications of NWs are not covered in any detail under this review. Table of Contents

Abstract: VI semiconductors are promising nanomaterials for applications as window layers in low-cost and high-efficiency thin film solar cells. These nanoparticles are considered to be the model systems for investigating the unique optical and electronic properties of quantum-confined semiconductors. The electrical and optical properties of polymers are improved by doping with semiconductor materials and metal ions. In particular, nanoparticle-doped polymers are considered to be a new class of organic materials due to their considerable modification of physical properties. In this paper, I review the present status of these types of Inorganic/Organic hybrid nanocomposite materials. CdSe nanorods dispersed in polyvinyl alcohol (PVA) matrix have been prepared by chemical routes. Different characterization techniques like structural, optical and electrical have been used to characterize these nanocomposites. The devices like Schottky diodes and MOS structures have been fabricated and the results have been discussed in this review. The results have been compared with the reported literature by other groups also. Table of Contents

Abstract: Nanomaterials have fascinated researchers in recent years because these materials exhibit unusual optical, magnetic and electrical properties as compared to their bulk counterparts. Incorporating impurity ions into a semiconducting host to extend its properties has been one of the most important techniques that paved the way for the modern technology based on spintronic devices. Over the past few years, oxide based dilute magnetic semiconductors (DMSs) have gained remarkable interest due to the possibility of inducing room temperature ferromagnetism. This review describes the experimental developments and optical properties of oxide based DMSs, including the recent results on ZnO, CdO and In₂O₃ based systems. Optical properties of transition metal (TM)-doped ZnO, CdO and In₂O₃ dilute magnetic semiconductor nanoparticles show red shift in energy band gaps. Such types of phenomena are attributed to sp-d exchange interactions between band electrons and localized d-electrons of the substituted transition metal ions. Table of Contents

Abstract: Gas detection instruments are increasingly needed for industrial health and safety, environmental monitoring, and process control. To meet this demand, considerable research into new sensors is underway, including efforts to enhance the performance of traditional devices, such as resistive metal oxide sensors, through nanoengineering. The resistance of semiconductors is affected by the gaseous ambient. The semiconducting metal oxides based gas sensors exploit this phenomenon. Physical chemistry of solid metal surfaces plays a dominant role in controlling the gas sensing characteristics. Metal oxide sensors have been utilized for several decades for low-cost detection of combustible and toxic gases. Recent advances in nanomaterials provide the opportunity to dramatically increase the response of these materials, as their performance is directly related to exposed surface volume. Proper control of grain size remains a key challenge for high sensor performance. Nanoparticles of SnO₂ have been synthesized through chemical route at 5, 25 and 50°C. The synthesized particles were sintered at 400, 600 and 800°C and their structural and morphological analysis was carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The reaction temperature is found to be playing a critical role in controlling nanostructure sizes as well as agglomeration. It has been observed that particle synthesized at 5 and 50°C are smaller and less agglomerated as compared to the particles prepared at 25°C. The studies revealed that particle size and agglomeration increases with increase in sintering temperature. Thick films gas sensors were fabricated using synthesized tin dioxide powder and sensing response of all the sensors to ethanol vapors was investigated at different temperatures and concentrations. The investigations revealed that sensing response of SnO₂ nanoparticles is size dependent and smaller particles display higher sensitivity. Table of Contents

Abstract: A wide variety of metallic and metal oxide nanoflowers and other exotic patterns have been fabricated using different techniques. We have created copper and cupric oxide nanoflowers using two different techniques: electro-deposition of copper in polymer and anodic alumina templates, and cytyltrimethal ammonium bromide (CTAB)-assisted hydrothermal method, respectively. Zinc oxide and manganese oxide nanoflowers have been synthesized by thermal treatment. Characterization of nanoflowers is done in the same way as for nanowires using XRD, SEM, TEM and FESEM. Scanning Electron Microscope (SEM) images record some interesting morphologies of metallic copper nanoflowers. Field Emission Scanning Electron Microscope (FESEM) has been used to determine morphology and composition of copper oxide nanoflowers. X-ray diffraction (XRD) pattern reveals the monoclinic phase of CuO in the crystallographic structure of copper oxide nanoflowers. Nanoflowers find interesting applications in industry. There is an element of random artistic design of nature, rather than science, in exotic patterns of nanoflowers fabricated in our laboratory.

Abstract: Copper doped Zinc Sulfide (ZnS:Cu)) is a known green light emitter. Present paper reports luminescence of ZnS:Cu nanoparticles and nanocomposites. Three different nanostructures: mercaptoethanol capped ZnS:Cu nanoparticles, polyvinyl alcohol (PVA) capped ZnS:Cu nanoparticles and ZnS:Cu/PVA nanocomposites have been prepared by chemical route. X-ray diffraction (XRD) revealed cubic zinc blende structure of ZnS:Cu nanocrystals of size below 20 nm. The particle size is found to decrease with increasing capping agent concentration or ZnS loading in PVA matrix. Optical absorption spectra show blue shift in the absorption edge indicating quantum size effect. Photoluminescence (PL) of all the samples was studied by exciting with 212 nm light. The PL spectra of ZnS:Cu/ PVA nanocomposite films show quite broad emission peak at 415 nm where as the PL spectra of mercaptoethanol capped and PVA capped nanoparticles show a very narrow peak at 426 nm and 403 nm respectively. It seems that the nature of passivation of surface states affects the position of surface states. Electroluminescence (EL) studies have shown that light emission starts at a threshold and then increases with voltage. Higher EL intensity and lower threshold voltage is obtained in case of smaller particles. The EL spectra of all the samples are found to be broad with peak at about 420 nm. The EL intensity of ZnS:Cu/PVA nanocomposites is much larger than the ZnS:Cu nanoparticles. The high efficiency EL devices for display and lighting can be fabricated using ZnS:Cu nanocomposites with PVA matrix giving violet emission.

Abstract: Multiwalled Carbon Nanotubes (MWCNTs) have been synthesized using a low cost arc discharge method without using metal catalyst and vacuum devices. Effect of magnetic field on the synthesis of MWCNTs and their purity has been scrutinized. A magnetic field of 310 gauss has been found to give better purity of carbon nanotubes as confirmed by Raman spectroscopy. However, the removal of amorphous carbon from the surface of so prepared multiwalled carbon nanotubes has been achieved by different oxidizing conditions. It has been observed that the maximum removal of amorphous carbon found by using the strong oxidizing agent HNO₃/H₂O₂. This strong oxidizing agent HNO₃/H₂O₂ removes most of the carbonaceous impurities leading to thermal stability of carbon nanotubes suggested by thermo gravimetric analysis. X-ray diffraction show the formation of carbon nanotubes having a peak indexed at (002) as the fingerprint for multiwalled carbon nanotubes. Fourier Transform Infrared (FTIR) spectra confirmed the formation of the multiwalled carbon nanotubes showing a characteristic stretching band at 1615 cm^-1 corresponding to the C=C bonds of tubular carbon. Raman spectroscopy revealed invaluable insights into the purification of nanotubes. G-band (1577 cm^-1) corresponds to the confirmation of MWCNTs. Defect induced D-band (1355 cm^-1) has been minimized after purifying CNTs with HNO₃/H₂O₂ for 24 hrs. Transmission Electron microscopic (TEM) studies indicate the formation of CNTs with controlled alignment having diameter in the range 2-8 nm.

Abstract: Recently the utilization of prokaryotic cells (such as bacteria, algae) and plants have emerged as novel methods for the synthesis of nanoparticles intracellularly. Therefore the applications on living organisms have recently attracted the attention of biologists towards nanobiotechnology. In the present study, Silver, Gold and bimetallic alloy Ag-Au nanoparticles were synthesized from marine red alga, Gracilaria sp., of Gulf of Mannar with different molar concentrations of 100%Ag, 100% Au and Ag:Au (1:1, 1:3 and 3:1). The reduction of Ag, Au and Ag:Au NPs was confirmed by change of colour (i.e. from transparent to dark brown for silver NPs, to ruby red for gold NPs and pale pink for bimetallic NPs) as well as by peak absorption spectra. The absorption peak of the Gracilaria sp., for 100% Ag occurred at 419nm, for 100% Au at 536nm, for Ag: Au (1:1) concentrations at 504 nm for Ag: Au (1:3) at 526 nm and for Ag: Au (3:1) at 501nm. The size of Ag, Au and bimetallic Ag-Au NPs was measured by SEM analysis, proved that the synthesized nanoparticles were colloidal in nature. The bimetallic nanoparticles exhibited good antibacterial activity against Gram positive bacteria Staphylococcus aureus and Gram negative bacteria Klebsiella pneumoniae. The above results revealed that Salmonella typhii and Escherichia coli have no activity. However, bimetallic NPs of 1:3 concentration showed zones of inhibition against the pathogenic bacteria such as Staphylococcus aureus and Klebsiella pneumoniae rather than Ag NPs and Au NPs. This process of the nanoparticles production is eco-friendly as it is free from any solvent or toxic chemicals, and is also easily amenable for large-scale production.