Langmuir-Blodgett Films

Petty, Michael C.

doi:10.1017/cbo9780511622519

Cited by 709 publications

(242 citation statements)

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“…The spectra found in our study are essentially the same as those found in the literature for the CR [14]. There is not observed spectrum shift as the solid phase UV-vis is compared to spectra of the solution phase, indicating that the molecular H or J-aggregation does not occur for these systems [15]. As shown in Figure 2, a linear increase in the absorbance at 500 nm was observed, suggesting that the same amount of material was adsorbed in each deposition step (each layer).…”

Section: Resultssupporting

confidence: 88%

Roughness Control of Layer-by-Layer and Alternative Spray Films from Congo Red and PAH via Laser Light Irradiation

Cardoso¹,

Silva²,

Maciel³

et al. 2012

MSA

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Films from congo red (CR) alternated with poly(allylamine hydrochloride), PAH, were prepared by layer-by-layer and alternative spray techniques. In order to investigate the change of roughness induced by laser light irradiation (532 nm), both kinds of films were characterized by using UV-visible spectroscopy and atomic force microscopy (AFM). At different irradiation times, layer-by-layer, LbL, films showed small changes in the roughness and irregular behavior, whereas spray films exhibited higher and a regular decreasing of roughness with increasing irradiation time. The higher roughness of spray films as compared with the LbL ones was attributed to different formation mechanisms of the films. The decreasing of the roughness as a function of the irradiation time (exhibited by the spray films) was associated to surface relaxation due to the interplay between photoisomerization of congo red dye and the heating of the sample during the laser light irradiation. The results suggested that the alternative spray technique is the best choose to control of roughness of the films by using light irradiation.

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Section: Resultssupporting

confidence: 88%

Roughness Control of Layer-by-Layer and Alternative Spray Films from Congo Red and PAH via Laser Light Irradiation

Cardoso¹,

Silva²,

Maciel³

et al. 2012

MSA

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“…This differs from the well-known gasϪliquidϪsolid phase transition model. 29 In this context, to scrutinize the exact packing of the tetrapods, LB depositions were conducted at various pressures, specifically 1, 10, 22, and 39 mN m . This morphology would create the increase in pressure at a larger packing area due to the presence of voids in the monolayer.…”

Section: Resultsmentioning

confidence: 99%

Self-Assembly of CdTe Tetrapods into Network Monolayers at the Air/Water Interface

Goodman

Zhao²,

DeRocher³

et al. 2010

ACS Nano

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Cadmium telluride (CdTe) tetrapods are synthesized with varying aspect ratios through multiple injections of the Te precursor, which provides an excellent means of controlling and tailoring the optical properties of the tetrapods. The self-assembly of CdTe tetrapods at the air/water interface is explored using the LangmuirBlodgett (LB) technique due to potential use in solar cells arising from the intriguing tetrapod shape that improves charge transport and the optimum band gap energy of CdTe that enhances light absorption. Interestingly, the Langmuir isotherm shows two pressure plateau regions: one at âˆ¼10 mN/m with the other at the high surface pressure of âˆ¼39 mN/m. LB deposition at various pressures allows the discernment of the unique two-dimensional packing alluded in the isotherm. By placing CdTe at the air/water interface, it is revealed in the deposition that the tetrapods experienced a dewetting phenomenon, forming a ribbon structure at the onset of surface pressure with a height corresponding to the length of one tetrapod arm. With the increase of surface pressure, the ribbons widen to an eventual large-scale percolated network pattern. The packing density of tetrapods is successfully manipulated by controlling the surface pressure, which may find promising applications in optoelectronic devices. KeywordsMaterials Science and Engineering, CdTe, Langmuir-Blodgett, network, self-assembly, tetrapod Disciplines Biochemical and Biomolecular Engineering | Chemical Engineering | Materials Science and Engineering CommentsReprinted with permission from ACS Nano 4 (2010) Semiconductor nanocrystals with various shapes have been synthesized, with quantum dot (QD), quantum rod (QR; i.e., nanorod), tetrapod, and nanowire synthesis being the most refined and controlled. While QDs are relatively easy to synthesize, properties that are more advantageous can be realized with the unique shapes. For example, the ability to manipulate the shape of nanocrystals has led to QRs with diameters ranging from 2 to 10 nm and lengths ranging from 5 to 100 nm. 17,18 Because of their intrinsic structural anisotropy, QRs possess many unique properties that make them potentially better nanocrystals for photovoltaic cells and biomedical applications than QDs. They possess the polarized emission and their Stokes shift is dependent upon their aspect ratio. 17,18 Photovoltaic cells made of QRs and conjugated polymers show an improved optical absorption in the red and near-infrared ranges originating from the QRs.3 Moreover, the long axis of the QRs provides continuous paths for transporting electrons. The performance of photovoltaic cells can be further improved if the QRs are vertically aligned between two electrodes to minimize the carrier transport pathways. 3 The elongated nanorods and branched nanocrystals (i.e., tetrapods) enable more effective charge transport.To date, there are few reports of nanocrystal assembly at the air/water interface.19,20 By contrast, studies have been conducted at the fluid/fluid interface, with ...

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“…Prior to deposition, the TOPO ligand was exchanged for pentamethylene sulfide (PMS) offering a short and rigid capping. To deposit these nanocrystals onto the SOI wafer, the Langmuir-Blodgett method [7] was used ( Figure 1): a SOI sample is placed into water container, after which the nanocrystals are added. The Q-InP|PMS particles spread on the water surface and can be forced into a close packed film by compressing the surface area.…”

Section: Fabricationmentioning

confidence: 99%