13 research outputs found
Detection beyond the Debye Screening Length in a High-Frequency Nanoelectronic Biosensor
Nanosensors based on the unique electronic properties
of nanotubes and nanowires offer high sensitivity and have the potential
to revolutionize the field of Point-of-Care (POC) medical diagnosis.
The direct current (dc) detection of a wide array of organic and inorganic
molecules has been demonstrated on these devices. However, sensing
mechanism based on measuring changes in dc conductance fails at high
background salt concentrations, where the sensitivity of the devices
suffers from the ionic screening due to mobile ions present in the
solution. Here, we successfully demonstrate that the fundamental ionic
screening effect can be mitigated by operating single-walled carbon
nanotube field effect transistor as a high-frequency biosensor. The
nonlinear mixing between the alternating current excitation field
and the molecular dipole field can generate mixing current sensitive
to the surface-bound biomolecules. Electrical detection of monolayer
streptavidin binding to biotin in 100 mM buffer solution is achieved
at a frequency beyond 1 MHz. Theoretical modeling confirms improved
sensitivity at high frequency through mitigation of the ionic screening
effect. The results should promise a new biosensing platform for POC
detection, where biosensors functioning directly in physiologically
relevant condition are desired
Graphene Ambipolar Nanoelectronics for High Noise Rejection Amplification
In a modern wireless communication
system, signal amplification is critical for overcoming losses during
multiple data transformations/processes and long-distance transmission.
Common mode and differential mode are two fundamental amplification
mechanisms, and they utilize totally different circuit configurations.
In this paper, we report a new type of dual-gate graphene ambipolar
device with capability of operating under both common and differential
modes to realize signal amplification. The signal goes through two
stages of modulation where the phase of signal can be individually
modulated to be either in-phase or out-of-phase at two stages by exploiting
the ambipolarity of graphene. As a result, both common and differential
mode amplifications can be achieved within one single device, which
is not possible in the conventional circuit configuration. In addition,
a common-mode rejection ratio as high as 80 dB can be achieved, making
it possible for low noise circuit application. These results open
up new directions of graphene-based ambipolar electronics that greatly
simplify the RF circuit complexity and the design of multifunction
device operation
Evidence for Extraction of Photoexcited Hot Carriers from Graphene
We report evidence of nonequilibrium hot carrier extraction from graphene by gate-dependent photocurrent study. Scanning photocurrent excited by femtosecond pulse laser shows unusual gate dependence compared with continuous wave (CW) laser excitation. Power dependence studies further confirm that the photocarriers extracted at the metal/graphene contact are nonequilibrium hot carriers. Hot carrier extraction is found to be most efficient near the Dirac point where carrier lifetime reaches a maximum. These observations not only provide evidence of hot carrier extraction from graphene but also open the door for graphene-based hot carrier optoelectronics
Patient, stone demographics and operative characteristics.
<p>ESWL: extracorporeal shock wave lithotripsy.</p><p>PCNL: percutaneous nephrolithotomy.</p><p>GFR: glomerular filtration rate.</p><p>SD: standard deviation.</p
Ultrafast Lateral Photo-Dember Effect in Graphene Induced by Nonequilibrium Hot Carrier Dynamics
The
photo-Dember effect arises from the asymmetric diffusivity
of photoexcited electrons and holes, which creates a transient spatial
charge distribution and hence the buildup of a voltage. Conventionally,
a strong photo-Dember effect is only observed in semiconductors with
a large asymmetry between the electron and hole mobilities, such as
in GaAs or InAs, and is considered negligible in graphene due to its
electron–hole symmetry. Here, we report the observation of
a strong lateral photo-Dember effect induced by nonequilibrium hot
carrier dynamics when exciting a graphene–metal interface with
a femtosecond laser. Scanning photocurrent measurements reveal the
extraction of photoexcited hot carriers is driven by the transient
photo-Dember field, and the polarity of the photocurrent is determined
by the device’s mobility asymmetry. Furthermore, ultrafast
pump–probe measurements indicate the magnitude of photocurrent
is related to the hot carrier cooling rate. Our simulations also suggest
that the lateral photo-Dember effect originates from graphene’s
2D nature combined with its unique electrical and optical properties.
Taken together, these results not only reveal a new ultrafast photocurrent
generation mechanism in graphene but also suggest new types of terahertz
sources based on 2D nanomaterials
Associations between types and intensity of physical activity and prostate cancer risk in the South and East China case control study on prostate and bladder cancer (SEARCH).
<p>Associations between types and intensity of physical activity and prostate cancer risk in the South and East China case control study on prostate and bladder cancer (SEARCH).</p
Characteristics of prostate and bladder cancer cases and controls in the South and East China case control study on prostate and bladder cancer (SEARCH).
<p>Characteristics of prostate and bladder cancer cases and controls in the South and East China case control study on prostate and bladder cancer (SEARCH).</p