Electroluminescence (EL) from the monolayer of a network of a one-dimensional (1D) necklace of 10 nm Au particles (nano)cemented by CdS is imaged. The EL and photoluminescence (PL) spectra confirm the emission from CdS. The EL emission blinks and is highly specular. The position of the speckles from individual CdS cement sites is independent of magnitude and polarity of the applied bias. The EL is explained by field-assisted ionization of the cement due to high internal fields in the array caused by stationary local charging that also leads to robust single electron effect at room temperature.
About a 100 nm thick multilayer film of nanoparticle monolayers and polymer layers is shown to behave like cellular-foam with a modulus below 100 KPa. The 1.25 cm radius film adhered to a rigid surface can be compressed reversibly to 60% strain. The more than 4 orders of magnitude lower modulus compared to its constituents is explained by considering local bending in the (nano)cellular structure, similar to cork and wings of beetles. As the rigidity of the polymer backbone is increased in just four monolayers, the modulus of the composite increases by over 70%. Electro-optical map of the strain distribution over the area of compression and increase in modulus with thickness indicates the films have zero Poisson's ratio.
Apart
from texture, the human finger can sense palpation. The detection
of an imbedded structure is a fine balance between the relative stiffness
of the matrix, the object, and the device. If the device is too soft,
its high responsiveness will limit the depth to which the imbedded
structure can be detected. The sensation of palpation is an effective
procedure for a physician to examine irregularities. In a clinical
breast examination (CBE), by pressing over 1 cm2 area,
at a contact pressure in the 70–90 kPa range, the physician
feels cancerous lumps that are 8- to 18-fold stiffer than surrounding
tissue. Early detection of a lump in the 5–10 mm range leads
to an excellent prognosis. We describe a thin-film tactile device
that emulates human touch to quantify CBE by imaging the size and
shape of 5–10 mm objects at 20 mm depth in a breast model using
∼80 kPa pressure. The linear response of the device allows
quantification where the greyscale corresponds to the relative local
stiffness. The (background) signal from <2.5-fold stiffer objects
at a size below 2 mm is minimal.
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