Abstract
Negative differential resistance behavior in oxide memristors, especially those using NbO
2
, is gaining renewed interest because of its potential utility in neuromorphic computing. However, ...there has been a decade-long controversy over whether the negative differential resistance is caused by a relatively low-temperature non-linear transport mechanism or a high-temperature Mott transition. Resolving this issue will enable consistent and robust predictive modeling of this phenomenon for different applications. Here we examine NbO
2
memristors that exhibit both a current-controlled and a temperature-controlled negative differential resistance. Through thermal and chemical spectromicroscopy and numerical simulations, we confirm that the former is caused by a ~400 K non-linear-transport-driven instability and the latter is caused by the ~1000 K Mott metal-insulator transition, for which the thermal conductance counter-intuitively decreases in the metallic state relative to the insulating state.
Highly reproducible bipolar resistance switching was recently demonstrated in a composite material of Pt nanoparticles dispersed in silicon dioxide. Here, we examine the electrical performance and ...scalability of this system and demonstrate devices with ultrafast (<100 ps) switching, long state retention (no measurable relaxation after 6 months), and high endurance (>3 × 107 cycles). A possible switching mechanism based on ion motion in the film is discussed based on these observations.
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•Fabricated flexible single, double, and quadruple stacked Si thermoelectric modules.•Measured an enhanced power production of 27%, showing vertical stacking is scalable.•Vertically ...scalable thermoelectric module design of semiconducting nanowires.•Design can utilize either p or n-type semiconductors, both types are not required.•ΔT increases with thickness therefore power/area can increase as modules are stacked.
We present the fabrication and characterization of single, double, and quadruple stacked flexible silicon nanowire network based thermoelectric modules. From double to quadruple stacked modules, power production increased 27%, demonstrating that stacking multiple nanowire thermoelectric devices in series is a scalable method to generate power by supplying larger temperature gradient. We present a vertically scalable multi-stage thermoelectric module design using semiconducting nanowires, eliminating the need for both n-type and p-type semiconductors for modules.
Abstract
Niobium dioxide can exhibit negative differential resistance (NDR) in metal-insulator-metal (MIM) devices, which has recently attracted significant interest for its potential applications as ...a highly non-linear selector element in emerging nonvolatile memory (NVM) and as a locally-active element in neuromorphic circuits. In order to further understand the processing of this material system, we studied the effect of thermal annealing on a 15 nm thick NbO
2
thin film sandwiched inside a nanoscale MIM device and compared it with 180 nm thick blanket NbO
x
(x = 2 and 2.5) films deposited on a silicon dioxide surface as references. A systematic transmission electron microscope (TEM) study revealed a similar structural transition from amorphous to a distorted rutile structure in both cases, with a transition temperature of 700 °C for the NbO
2
inside the MIM device and a slightly higher transition temperature of 750 °C for the reference NbO
2
film. Quantitative composition analysis from electron energy loss spectroscopy (EELS) showed the stoichiometry of the nominal 15 nm NbO
2
layer in the as-fabricated MIM device deviated from the target 1:2 ratio because of an interaction with the electrode materials, which was more prominent at elevated annealing temperature.
We demonstrate a promising new material system for ionic resistive switches: nitride memristors. The switching material is an AlN film, deposited using atomic layer deposition (ALD), and the ...electrodes can be TiN, Pt or Al. A variety of materials characterizations were performed to determine the structure, composition and impurities of the AlN films.
Selective area growth (SAG) of single crystalline indium phosphide (InP) nanopillars was demonstrated on an array of template segments composed of a stack of gold and amorphous silicon. The template ...segments were patterned by UV nanoimprint lithography on a silicon substrate covered with a natural oxide, and the SAG was achieved by metal organic chemical vapor deposition. Our SAG is different from conventional SAG in one critical aspect. In our SAG, growth of InP takes place selectively on a pre-defined array of template segments made of non-single crystal materials on a foreign substrate. The grown InP nanopillars were studied for their structural, chemical and optical properties. The new SAG process is not limited to the specific materials such as InP nanopillars and silicon substrate used in this demonstration; our approach enables flexible and scalable nanofabrication using industrially proven tools and a wide range of semiconductors on various non-semiconductor substrates.
•The Selectrive Area Growth (SAG) process demonstrated in this paper is not limited to the specific materials utilized here.•The SAG process demonstrated in this work utilizes UV nanoimprint lithography.•A-Si/Au template segments served as catalysts and nucleation sites for single-crystalline nanopillars on various non-single crystalline substrates.•Metal organic chemical vapor deposition (MOCVD) was used to deposit the single crystal semiconductor pillars in a patterned array.•The SAG process described in this paper is not the conventional process utilized today.
Two types of semiconductors, indium phosphide (InP) and silicon (Si), were separately grown on polycrystalline copper foils with the presence of gold colloidal particles. InP was grown with and ...without carbon deposition by metal organic chemical vapor deposition, and Si was grown with and without plasma enhanced chemical vapor deposition of carbon. While InP and Si grew as films on untreated copper foils, they were found to grow in the form of nanowires when copper foils were pre-treated with carbon. Structural analysis revealed that the grown InP nanowires were polycrystalline. In contrast, the grown Si nanowires were found to have core–shell structures with a monocrystalline core and a polycrystalline shell. Further analysis suggested that graphene was formed on the copper foils during the carbon deposition. Therefore, we concluded that the presence of graphene promoted the growth of InP and Si in the form of nanowires. The demonstration of growing semiconductor nanowires on copper foils could be a new path to integrate semiconductor and metal to provide a unique material platform for a wide range of devices.
•A intermediate layer allows growth on dissimilar materials, not limited to the materials here.•Two new designs are demonstrated in this work and utilizes only industrially proven methods.•Graphene allowed growth on large area, non-single crystalline, flexible Cu foil.•MOCVD was used to deposit the semiconductor nanowires on Cu foils.•The method described in this paper is not a conventional process utilized in industry today.
Thermoelectric (TE) devices that produce electric power from heat are driven by a temperature gradient (
Δ
T
=
T
hot
-
T
cold
,
T
hot
: hot side temperature,
T
cold
: cold side temperature) with ...respect to the average temperature (
T
). While the resistance of TE devices changes as
Δ
T
and/or
T
change, the current–voltage (
I
–
V
) characteristics have consistently been shown to remain linear, which clips generated electric power (
P
gen
) within the given open-circuit voltage (
V
OC
) and short-circuit current (
I
SC
). This
P
gen
clipping is altered when an appropriate nonlinearity is introduced to the
I
–
V
characteristics—increasing
P
gen
. By analogy, photovoltaic cells with a large fill factor exhibit nonlinear
I
–
V
characteristics. In this paper, the concept of a unique TE device with nonlinear
I
–
V
characteristics is proposed and experimentally demonstrated. A single TE device with nonlinear
I
–
V
characteristics is fabricated by combining indium phosphide (InP) and silicon (Si) semiconductor nanowire networks. These TE devices show
P
gen
that is more than 25 times larger than those of comparable devices with linear
I
–
V
characteristics. The plausible causes of the nonlinear
I
–
V
characteristics are discussed. The demonstrated concept suggests that there exists a new pathway to increase
P
gen
of TE devices made of semiconductors.
The growth of indium phosphide (InP) nanowires on transparent conductive aluminum-doped zinc oxide (AZO) thin films on polycrystalline copper (Cu) foils was proposed and demonstrated. AZO thin films ...and zinc oxide (ZnO) thin films, as comparison, were deposited on Cu foils by radio frequency magnetron sputtering. Subsequently, InP was grown by metal organic chemical vapor deposition with gold catalysts. InP nanowire networks formed on the AZO thin films, while no InP nanowires grew on the ZnO thin films. Morphological, crystalline, and optical properties of the InP nanowires on AZO thin films were compared with those of InP nanowires grown on silicon (Si) substrates. Zinc diffusion from AZO thin films into InP nanowire networks was suggested as the cause of substantial modifications on the optical properties of the InP nanowires on AZO thin films; redshift in photoluminescence spectra and a larger relative TO/LO intensity ratio in Raman spectra were observed, in comparison to those of the InP nanowires grown on Si substrates. In this paper, we proposed and demonstrated a new route to grow semiconductor nanowires on metals that potentially provide low-cost and mechanically flexible substrates and establish a reliable electrical contact by utilizing conductive oxide thin films as a template, which could offer a new material platform for such applications as sensors and thermoelectric devices.
Enhanced Raman signal of the longitudinal optical phonon mode in indium phosphide nanowire networks with gold coating of up to 5 nm thickness was observed experimentally to further study the phonon ...spectrum of nanowire networks. Indium phosphide nanowire networks coated with different nominal thicknesses of gold were prepared and optically studied. Scanning electron microscopy, photoluminescence spectroscopy and Raman spectroscopy were used to study the dependence of surface morphology and phonon modes of the nanowire networks on the nominal thickness of the gold coating. The Raman peak of longitudinal optical phonon mode for as grown sample was negligible, while the peak intensity for 1 and 5 nm gold coated sample reached to 1,379 and 792 a.u. respectively. Electromagnetic enhancement and extinction coefficient are discussed to qualitatively assess the role of the gold coating on indium phosphide nanowire networks.
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