CONTROL OF AVERAGE SPACING OF OMCVD GROWN GOLD NANOPARTICLES

Metallic nanostructures and their applications is a rapidly expanding field. Nobel metals such as silver and gold have historically been used to demonstrate plasmon effects due to their strong resonances, which occur in the visible part of the electromagnetic spectrum. Localized surface plasmon resonance (LSPR) produces an enhanced electromagnetic field at the interface between a gold nanoparticle (Au NP) and the surrounding dielectric. This enhanced field can be used for metal-dielectric interface- sensitive optical interactions that form a powerful basis for optical sensing. In addition to the surrounding material, the LSPR spectral position and width depend on the size, shape, and average spacing between these particles. Au NP LSPR based sensors depict their highest sensitivity with optimized parameters and usually operate by investigating absorption peak shifts. The absorption peak of randomly deposited Au NPs on surfaces is mostly broad. As a result, the absorption peak shifts, upon binding of a material onto Au NPs might not be very clear for further analysis. Therefore, novel methods based on three well-known techniques, self-assembly, ion irradiation, and organo-metallic chemical vapour deposition (OMCVD) are introduced to control the average-spacing between Au NPs. In addition to covalently binding and other advantages of OMCVD grown Au NPs, interesting optical features due to their non- spherical shapes are presented. The first step towards the average-spacing control is to uniformly form self- assembled monolayers (SAMs) of octadecyltrichlorosilane (OTS) as resists for OMCVD Au NPs. The formation and optimization of the OTS SAMs are extensively studied. The optimized resist SAMs are ion-irradiated by a focused ion beam (FIB) and ions generated by a Tandem accelerator. The irradiated areas are refilled with 3-mercaptopropyl- trimethoxysilane (MPTS) to provide nucleation sites for the OMCVD Au NP growth. Each step during sample preparation is monitored by using surface characterization methods such as contact angle measurements, ellipsometry, X-ray photoelectron iii spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), Rutherford backscattering spectroscopy (RBS), UV-Visible spectroscopy, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS)

Binary Mixtures of SH- and CH3-Terminated Self-Assembled Monolayers to Control the Average Spacing Between Aligned Gold Nanoparticles

This paper presents a method to control the average spacing between organometallic chemical vapor deposition (OMCVD) grown gold nanoparticles (Au NPs) in a line. Focused ion beam patterned CH3-terminated self-assembled monolayers are refilled systematically with different mixtures of SH- and CH3-terminated silanes. The average spacing between OMCVD Au NPs is demonstrated systematically to decrease by increasing the v/v% ratio of the thiols in the binary silane mixtures with SH- and CH3-terminated groups

Systemic Model Of Developing Agricultural Advisory Services In Iran

Functionality, agricultural extension, particularly advisory services have been and still are being criticized for ineffectiveness, supply-drivenness, lack of sustainability and inability to offer appropriate services which benefit the poor. Nevertheless, agricultural advisory services remain crucial to improving the livelihoods of rural poor people as well as facilitating sustainable agricultural development. Even the best policy environment will not result in pro-poor agricultural growth if the concerned rural people do not have access to adequate services be they knowledge services, or more tangible services such as farm inputs, credit, land, water, appropriate technology or marketing. Hence, agricultural advisory services must continually adapt to the changing agricultural environment and to changes in farm family circumstances in order to remain relevant. The purpose of this paper was to outline the agricultural advisory services in Iran from beginning to the present based on conceptualizing expert’s opinions and empirical evidences. The processes and approaches used in the implementation of the advisory services need as much as focus as the actual conditions and programs or products around which the changes are centered. This paper explains a systemic model for institutional developing agricultural advisory services in Iran and identifies related institutional challenges and opportunities