6 research outputs found
Black Phosphorus Gas Sensors
The utilization of black phosphorus and its monolayer (phosphorene) and few-layers in field-effect transistors has attracted a lot of attention to this elemental two-dimensional material. Various studies on optimization of black phosphorus field-effect transistors, PN junctions, photodetectors, and other applications have been demonstrated. Although chemical sensing based on black phosphorus devices was theoretically predicted, there is still no experimental verification of such an important study of this material. In this article, we report on chemical sensing of nitrogen dioxide (NO<sub>2</sub>) using field-effect transistors based on multilayer black phosphorus. Black phosphorus sensors exhibited increased conduction upon NO<sub>2</sub> exposure and excellent sensitivity for detection of NO<sub>2</sub> down to 5 ppb. Moreover, when the multilayer black phosphorus field-effect transistor was exposed to NO<sub>2</sub> concentrations of 5, 10, 20, and 40 ppb, its relative conduction change followed the Langmuir isotherm for molecules adsorbed on a surface. Additionally, on the basis of an exponential conductance change, the rate constants for adsorption and desorption of NO<sub>2</sub> on black phosphorus were extracted for different NO<sub>2</sub> concentrations, and they were in the range of 130ā840 s. These results shed light on important electronic and sensing characteristics of black phosphorus, which can be utilized in future studies and applications
Tandem Solar Cells Using GaAs Nanowires on Si: Design, Fabrication, and Observation of Voltage Addition
Multijunction solar cells provide
us a viable approach
to achieve efficiencies higher than the ShockleyāQueisser limit.
Due to their unique optical, electrical, and crystallographic features,
semiconductor nanowires are good candidates to achieve monolithic
integration of solar cell materials that are not lattice-matched.
Here, we report the first realization of nanowire-on-Si tandem cells
with the observation of voltage addition of the GaAs nanowire top
cell and the Si bottom cell with an open circuit voltage of 0.956
V and an efficiency of 11.4%. Our simulation showed that the current-matching
condition plays an important role in the overall efficiency. Furthermore,
we characterized GaAs nanowire arrays grown on lattice-mismatched
Si substrates and estimated the carrier density using photoluminescence.
A low-resistance connecting junction was obtained using n<sup>+</sup>-GaAs/p<sup>+</sup>-Si heterojunction. Finally, we demonstrated tandem
solar cells based on top GaAs nanowire array solar cells grown on
bottom planar Si solar cells. The reported nanowire-on-Si tandem cell
opens up great opportunities for high-efficiency, low-cost multijunction
solar cells
Highly Sensitive and Quick Detection of Acute Myocardial Infarction Biomarkers Using In<sub>2</sub>O<sub>3</sub> Nanoribbon Biosensors Fabricated Using Shadow Masks
We demonstrate a scalable and facile
lithography-free method for
fabricating highly uniform and sensitive In<sub>2</sub>O<sub>3</sub> nanoribbon biosensor arrays. Fabrication with shadow masks as the
patterning method instead of conventional lithography provides low-cost,
time-efficient, and high-throughput In<sub>2</sub>O<sub>3</sub> nanoribbon
biosensors without photoresist contamination. Combined with electronic
enzyme-linked immunosorbent assay for signal amplification, the In<sub>2</sub>O<sub>3</sub> nanoribbon biosensor arrays are optimized for
early, quick, and quantitative detection of cardiac biomarkers in
diagnosis of acute myocardial infarction (AMI). Cardiac troponin I
(cTnI), creatine kinase MB (CK-MB), and B-type natriuretic peptide
(BNP) are commonly associated with heart attack and heart failure
and have been selected as the target biomarkers here. Our approach
can detect label-free biomarkers for concentrations down to 1 pg/mL
(cTnI), 0.1 ng/mL (CK-MB), and 10 pg/mL (BNP), all of which are much
lower than clinically relevant cutoff concentrations. The sample collection
to result time is only 45 min, and we have further demonstrated the
reusability of the sensors. With the demonstrated sensitivity, quick
turnaround time, and reusability, the In<sub>2</sub>O<sub>3</sub> nanoribbon
biosensors have shown great potential toward clinical tests for early
and quick diagnosis of AMI
Carbon Nanotube Macroelectronics for Active Matrix Polymer-Dispersed Liquid Crystal Displays
Active
matrix liquid crystal display (AMLCD) is the most widely
used display technology nowadays. Transparent display is one of the
emerging technologies to provide people with more features such as
displaying images on transparent substrates and simultaneously enabling
people to see the scenery behind the panel. Polymer-dispersed liquid
crystal (PDLC) is a possible active matrix transparent display technology
due to its high transparency, good visibility, and low power consumption.
Carbon nanotubes (CNTs) with excellent mobility, high transparency,
and room-temperature processing compatibility are ideal materials
for the driver circuit of the PDLC display. Here, we report the monolithic
integration of CNT thin-film transistor driver circuit with PDLC pixels.
We studied the transmission properties of the PDLC pixels and characterized
the performance of CNT thin-film transistors. Furthermore, we successfully
demonstrated active matrix seven-segment PDLC displays using CNT driver
transistors. Our achievements open up opportunities for future nanotube-based,
flexible thin-film transparent display electronics
GaAs Nanowire Array Solar Cells with Axial pāiān Junctions
Because of unique structural, optical,
and electrical properties,
solar cells based on semiconductor nanowires are a rapidly evolving
scientific enterprise. Various approaches employing IIIāV nanowires
have emerged, among which GaAs, especially, is under intense research
and development. Most reported GaAs nanowire solar cells form pān
junctions in the radial direction; however, nanowires using axial
junction may enable the attainment of high open circuit voltage (<i>V</i><sub>oc</sub>) and integration into multijunction solar
cells. Here, we report GaAs nanowire solar cells with axial pāiān
junctions that achieve 7.58% efficiency. Simulations show that axial
junctions are more tolerant to doping variation than radial junctions
and lead to higher <i>V</i><sub>oc</sub> under certain conditions.
We further study the effect of wire diameter and junction depth using
electrical characterization and cathodoluminescence. The results show
that large diameter and shallow junctions are essential for a high
extraction efficiency. Our approach opens up great opportunity for
future low-cost, high-efficiency photovoltaics
High-Performance Sub-Micrometer Channel WSe<sub>2</sub> Field-Effect Transistors Prepared Using a FloodāDike Printing Method
Printing technology has potential
to offer a cost-effective and
scalable way to fabricate electronic devices based on two-dimensional
(2D) transition metal dichalcogenides (TMDCs). However, limited by
the registration accuracy and resolution of printing, the previously
reported printed TMDC field-effect transistors (FETs) have relatively
long channel lengths (13ā200 Ī¼m), thus suffering low
current-driving capabilities (ā¤0.02 Ī¼A/Ī¼m). Here,
we report a āfloodādikeā self-aligned printing
technique that allows the formation of source/drain metal contacts
on TMDC materials with sub-micrometer channel lengths in a reliable
way. This self-aligned printing technique involves three steps: (i)
printing of gold ink on a WSe<sub>2</sub> flake to form the first
gold electrode, (ii) modifying the surface of the first gold electrode
with a self-assembled monolayer (SAM) to lower the surface tension
and render the surface hydrophobic, and (iii) printing of gold ink
close to the SAM-treated first electrode at a certain distance. During
the third step, the gold ink would first spread toward the edge of
the first electrode and then get stopped by the hydrophobic SAM coating,
ending up forming a sub-micrometer channel. With this printing technique,
we have successfully downscaled the channel length to ā¼750
nm and achieved enhanced on-state current densities of ā¼0.64
Ī¼A/Ī¼m (average) and high on/off current ratios of ā¼3
Ć 10<sup>5</sup> (average). Furthermore, with our high-performance
printed WSe<sub>2</sub> FETs, driving capabilities for quantum-dot
light-emitting diodes (LEDs), inorganic LEDs, and organic LEDs have
been demonstrated, which reveals the potential of using printed TMDC
electronics for display backplane applications