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The interaction of bovine serum albumin (BSA) with sulfated, carboxylated, and pyridinium-grafted cellulose nanocrystals (CNCs) was studied as a function of the degree of substitution by determining the adsorption isotherm and by directly measuring the thermodynamics of interaction. The adsorption of BSA onto positively charged pyridinium-grafted cellulose nanocrystals followed Langmuirian adsorption with the maximum amount of adsorbed protein increasing linearly with increasing degree of substitution. The binding mechanism between the positively charged pyridinum-grafted cellulose nanocrystals and BSA was found to be endothermic and based on charge neutralization. A positive entropy of adsorption associated with an increase of the degree of disorder upon addition of BSA compensated for the unfavorable endothermic enthalpy and enabled formation of pyridinium-g-CNC-BSA complexes. The endothermic enthalpy of adsorption was further found to decrease as a function of increasing degree of substitution. Negatively charged cellulose nanocrystals bearing sulfate and/or carboxylic functionalities were found to not interact significantly with the BSA protein. To investigate in more detail the role of single amino acids in the adsorption of proteins onto cellulose nanocrystals, we also studied the interaction of different types of amino acids with CNCs, i.e., charged (lysine, aspartic acid), aromatic (tryptophan, tyrosine), and polar (serine) amino acids. We found that none of the single amino acids bound with CNCs irrespective of surface charge and that therefore the binding of proteins with CNCs appears to require larger amino acid sequences that induce a greater entropic contribution to stabilize binding. Single amino acids are thus not adsorbed onto cellulose nanocrystals. [ABSTRACT FROM AUTHOR]

The improvement of tandem hydrogenated amorphous/microcrystalline Si solar cells under prolonged exposure to reverse bias direct current electric fields and illumination has been investigated. In this work, the authors show that the application of reverse bias stress in the presence of illumination slows down the solar cell ageing kinetics (caused mainly by the Staebler-Wronski effect and by the increase in the series resistance) and, in suitable conditions, it produces an improvement of the solar cell characteristic parameters as a function of stress time. The authors discuss the effect of temperature, electric field intensity, and illumination level. [ABSTRACT FROM AUTHOR]

In this paper, we report a purposely designed instrumentation and a jump detection procedure for the measurement of single-electron phenomena in solid-state non- volatile memories based on a silicon nanocrystal floating gate metal-oxide-semiconductor field-effect transistor. The stepwise evolution of the drain current of a memory cell after a "write" operation is monitored by means of a purposely designed low-noise acquisition system with a bandwidth of up to 10 kHz. The advantage of the measurement system background noise and bandwidth over a traditional semiconductor parameter analyzer performance is evident in the detection and classification of single-electron events. [ABSTRACT FROM AUTHOR]

We report on the full process integration of nano- crystal (NC) memory cells in a stand-alone 16-Mb NOR Flash device. The Si NCs are deposited by chemical vapor deposition on a thin tunnel oxide, whose surface is treated with a low thermal budget process, which increases NC density and minimizes oxide degradation. The device fabrication has been obtained by means of conventional Flash technology, which is integrated with the CMOS periphery with high- and low-voltage transistors and charge pump capacitors. The memory program and erase threshold voltage distributions are well separated and narrow. The voltage distribution widths are related to NC sizes and dispersion, and bigger NCs can induce a cell reliability weakness. An endurance issue is also related to the use of an oxide/nitride/oxide dielectric which acts as a charge trapping layer, causing a shift in the program/erase window and a distribution broadening during cycling. [ABSTRACT FROM AUTHOR]

Abstract: Si nanocrystal memory cells have been integrated in Flash-like stand-alone devices of 16Mb along with high and low voltage CMOS logic circuitry. Process integration drawbacks such as nanocrystal residuals in the circuitry region have been eliminated by optimizing etching processes. The program/erase threshold voltage distributions of the memory sectors are well separated and narrow. The voltage distribution width is related to NC sizes, and bigger NCs induce cell reliability problems. Some reliability issues for endurance are also related to the use of ONO dielectric which acts as charge trapping layer, mainly causing program/erase window shift and threshold voltage distribution broadening during endurance. [Copyright &y& Elsevier]

Nanocrystals memory cells, in which the conventional polysilicon floating gate is replaced by an array of silicon nanocrystals, have been fabricated and characterized. Single cells and cell arrays of 1 Mb and 10 k have been realized by using a conventional 0.15 μm FLASH technology. Si nanocrystals are deposited on top of tunnel oxide by chemical vapor deposition. Properties of the memory cell have been investigated both for NAND and NOR applications in terms of program/erase window and programming times. Suitable program/erase threshold voltage window can be achieved with fast voltage pulses by adequate choice of tunnel and control dielectric.The feasibility of dual bit storage is also proven showing that the nanocrystals are separated and the inter-dot tunneling is inhibited. Good endurance and retention behaviors are demonstrated even after long cycling. [Copyright &y& Elsevier]