Single Silicon Nanowires Research Articles

E-beam Lithography Technology for Quantum Device Fabrication and Nanoscale Patterning

Currently nanotechnology becoming more important with the implementation of nano devices including quantum devices. In this paper, we will briefly introduce the JEOL JBX-8100FS e-beam lithography tool which was recently installed in Hallym University and the current status of the exposure conditions set up. As applications using e-beam lithography tool, we will introduce Schottky barrier single hole transistor and silicon nanowire thermoelectric device, respectively. We are under researching plasmonic and quantum devices as basic research.

Thermoelectric performance of high aspect ratio double-sided silicon nanowire arrays

Roughly, 50% of primary energy worldwide is rejected as waste heat over a wide range of temperatures. Waste heat above 573 K has the highest Carnot potential (>50%) to be converted to electricity due to higher Carnot efficiency. Thermoelectric (TE) materials have gained significant attention as potential candidates for efficient thermal energy conversion devices. Silicon nanowires (SiNWs) are promising materials for TE devices due to their unique electrical and thermal properties. In this study, we report the successful fabrication of high-quality double-sided SiNW arrays using advanced techniques. We engineered the double-sided structure to increase the surface area and the number of TE junctions, enhancing TE energy conversion efficiency. We also employed non-agglomeration wire tip engineering to ensure uniformity of the SiNWs and designed effective Ohmic contacts to improve overall TE efficiency. Additionally, we post-doped the double-sided SiNW arrays to achieve high electrical conductivity. Our results showed a significant improvement in the TE performance of the SiNW array devices, with a maximum figure-of-merit (ZT) value of 0.24 at 700 K, fabricated from the single SiNW with ZT of 0.71 at 700 K in our previous work [Yang et al., Nat. Commun. 12(1), 3926(2021)].

Selective sensing of DNA/RNA nucleobases by metal-functionalized silicon nanowires: A DFT approach

Ultrasensitive chemical sensors based on silicon nanowires (SiNW) are optimal for detection of biological species, since they are fast and non-invasive, their fabrication is compatible with current semiconductor technology, and silicon is a biocompatible material. SiNW-based DNA sensors are well known, but there are few studies regarding the interaction of SiNWs with the single DNA/RNA nucleobases: Guanine (G), Cytosine (C), Adenine (A), Thymine (T), and Uracil (U). This work uses Density Functional Theory to study the interaction between the single nucleobases and SiNWs decorated with Cu, Ag and Au atoms, to determine their potential use as nucleobase detectors or carriers, or even to use nucleobase-functionalized SiNWs as sensing platform for other chemical species. Numerical results show remarkable changes of the nanowire's band gap upon adsorption of nucleobases. Likewise, the adsorption energies of the nucleobases on the functionalized SiNW follow the trend C > G > A > T > U. Cu-functionalized nanowires are suitable for the electrical detection of cytosine, while Au-functionalized nanowires may detect thymine and uracil. On the other hand, large variations of the nanowire work function were found when guanine and adenine are adsorbed on Cu-functionalized nanowires.

Neural oscillation of single silicon nanowire neuron device with no external bias voltage

In this study, we perform simulations to demonstrate neural oscillations in a single silicon nanowire neuron device comprising a gated p–n–p–n diode structure with no external bias lines. The neuron device emulates a biological neuron using interlinked positive and negative feedback loops, enabling neural oscillations with a high firing frequency of ~ 8 MHz and a low energy consumption of ~ 4.5 × 10−15 J. The neuron device provides a high integration density and low energy consumption for neuromorphic hardware. The periodic and aperiodic patterns of the neural oscillations depend on the amplitudes of the analog and digital input signals. Furthermore, the device characteristics, energy band diagram, and leaky integrate-and-fire operation of the neuron device are discussed.

New Electrochemically Protective Layer Based on Nanometric Dielectric Coating for Silicon Based Micro Supercapacitors

Dielectric materials have been used for decades for micro and nanoelectronics where their insulation and polarizability properties are critical. However, in the energy storage field, material scientists tends to consider high-k dielectric layers in contact with an active material only as an insulating passivation layer. In microelectronics, this conception has been modified with the study of dielectrics at nanoscale level [1-2] revealing interesting properties scarcely known by other fields [3]. We propose to reconsider the vision of high-k dielectric materials for energy at nanoscale specifically.Based on microelectronic techniques [4], a nanometric-scale thick layer of dielectric is deposited by Atomic Layer Deposition (ALD). Allowing us to create an ultra-thin, pinhole-free alumina (Al2O3) nanometric layers on complex architectures as the entanglement of Silicon nanowires.[5] Microelectronics measurements on a single silicon nanowire (SiNW) is shown to display thickness dependent tunneling electrical conduction. This result brings a new light on this material class in the energy field and allows original approaches : achieving scientific leaps by using thin layers of dielectric to protect the active materials and enhance their lifetime in new environments. As an illustrative application, a silicon based micro-supercapacitor (µSC) protected by a 3 nm alumina layer exhibits Electrical Double Layer Capacitance (EDLC) by means of tunneling current in aqueous electrolyte. This result is an unprecedented for this material, allowing an outstanding lifetime capacity and retaining 99% of its initial capacitance after 2 million cycles. Extended to multiple energy materials, such method could lead to notable progresses [6].

Compact Biomimetic Hair Sensors Based on Single Silicon Nanowires for Ultrafast and Highly-Sensitive Airflow Detection.

Wearable sensors that can mimic functionalities of human bodies have attracted intense recent attention. However, research on wearable airflow sensors is still lagging behind. Herein, we report a biomimetic hair sensor based on a single ultralong silicon nanowire (SiNW-BHS) for airflow detection. In our device, the SiNW can provide both mechanical and electrical responses in airflow, which enables a simple and compact design. The SiNW-BHSs can detect airflow with a low detection limit (<0.15 m/s) and a record-high response speed (response time <40 ms). The compact design of the SiNW-BHSs also enables easy integration of an array of devices onto a flexible substrate to mimic human skin to provide comprehensive airflow information including wind speed, incident position, incident angle, and so forth. This work provides novel-designed BHSs for ultrafast and highly sensitive airflow detection, showing great potential for applications such as e-skins, wearable electronics, and robotics.

Enhanced Light-Harvesting in Single Rectangular Silicon Nanowires

Light-harvesting of single nanowires is very crucial to enhance conversion efficency of solar cells. Here, we systematically examined light-harvesting of single rectangular nanowires and found that light-harvesting of rectangular nanowires is increased contrasted with that of square nanowires, which is because decreasing the horizontal side can strengthen the leaky mode resonances and increasing the vertical side can increase the length of the light path. Numerical results showed that the photocurrent of single rectangular silicon nanowires is dramatically enhanced by 82.9% or 276.5% in comparison with that of square nanowires with the same vertical side (1000 nm) or horizontal side (100 nm), respectively. This work indicates that light-harvesting of single nanowires can be improved by decreasing the symmetry from the square to rectangular nanowires.

Third optical harmonic generation reveals circular anisotropy in tilted silicon nanowire array.

In this Letter, we report on the circular anisotropy of third-harmonic (TH) generation in an array of silicon nanowires (SiNWs) of approximately 100 nm in diameter tilted to the crystalline silicon substrate at an angle of 45°. Numerical simulations of the scattering at the fundamental and TH frequencies of circularly polarized light by a single SiNW and an ansatz structure composed of 13 SiNWs used as a geometrical approximation of the real SiNW array indicate asymmetric scattering diagrams, which is a manifestation of the photonic spin Hall effect mediated by the synthetic gauge field arising due to the special guided-like mode structure in each SiNW. Despite strong light scattering in the SiNW array, the experimentally measured TH signal demonstrated significant dependence on the polarization state of incident radiation and the SiNW array spacial orientation in regard to the wave vector direction.

Development of a robust fabrication process for single silicon nanowire-based omega gate transistors on polyamide substrate

Single silicon nanowire (SiNW) omega-gate field-effect transistors have been fabricated using a standard photolithography method on a Kapton flexible polyamide thin film attached to a sacrificial silicon substrate. SiNWs have been grown by the chemical vapor deposition method using a vapor–liquid–solid mechanism and gold as the catalyst. A key step for proper SiNW integration, Kapton surface flattening, was performed via an innovative method based on soap. Contrary to a previously reported integration process on flexible substrates, this flexible/rigid hybrid substrate is compatible with temperature as high as , allowing the formation of low-resistive nickel silicide at the source/drain contacts. As a consequence, our devices can exhibit excellent electrical properties such as hole mobility, 105 ratio and subthreshold slope of about . These parameters can compete with those of organic transistors or in some aspects even exceeding electrical parameters of similar single SiNW transistors fabricated onto flexible substrates. In addition, after separation from the rigid silicon substrate, devices on Kapton experience a significant improvement in their performance, such as two orders of magnitude for ratio and halving the subthreshold slope. This flexible/rigid hybrid substrate, offering high chemical and thermal stability, as well as preserving good electrical features and even improving them, after detaching and transfering the polyamide layer to a plastic substrate, which opens up a new route for the integration of further nanostructures.

Hall Effect Measurements in Rotating Magnetic Field on Sub-30-nm Silicon Nanowires Fabricated by a Top–Down Approach

We present the nanofabrication and transport properties of single silicon nanowires (NWs) having mean widths in the range from sub-30 to 500 nm. Hall effect measurements are undertaken in the magnetic fields of 14 T at 300 K. The NWs are defined by electron-beam lithography (EBL) using the negative tone resist hydrogen silsesquioxane (HSQ) as a mask for reactive ion etching (RIE). Silicon NWs are patterned on nonuniform highly doped n-type silicon-on-insulator (SOI) substrates. The doping profile has been observed to show a significant effect on the NW electrostatics, which in turn influences the contact and transport properties of the NWs. For the formation of Hall electrodes, we have employed an angled substrate evaporation technique, where the NW itself is used as a shadow mask and an intimate sidewall contact has been formed. The Hall electrodes are not opposite to each other in this case; therefore, the longitudinal resistance pickup had to be considered when extracting the Hall signal of the NW. The mobility of these NWs is discussed. For the narrowest 40-nm-wide silicon NW, the obtained value of mobility is 292 ± 6 cm2/Vs and, for the blanket, nonpatterned device layer, it is 100 ± 0.1 cm2/Vs. The effective mobility increases as the width of the NWs decreases. This is attributed to the reduced dimensionality of the electron transport in the NWs. Both the electrical and effective thicknesses of the NW change at small physical width, which results in enhanced electron transport within the channel and enhances the value of the measured Hall signal.

Light Trapping in Single Elliptical Silicon Nanowires.

Light trapping in single nanowires (NWs) is of vital importance for photovoltaic applications. However, circular NWs (CNWs) can limit their light-trapping ability due to high geometrical symmetry. In this work, we present a detailed study of light trapping in single silicon NWs with an elliptical cross-section (ENWs). We demonstrate that the ENWs exhibit significantly enhanced light trapping compared with the CNWs, which can be ascribed to the symmetry-broken structure that can orthogonalize the direction of light illumination and the leaky mode resonances (LMRs). That is, the elliptical cross-section can simultaneously increase the light path length by increasing the vertical axis and reshape the LMR modes by decreasing the horizontal axis. We found that the light absorption can be engineered via tuning the horizontal and vertical axes, the photocurrent is significantly enhanced by 374.0% (150.3%, 74.1%) or 146.1% (61.0%, 35.3%) in comparison with that of the CNWs with the same diameter as the horizontal axis of 100 (200, 400) nm or the vertical axis of 1000 nm, respectively. This work advances our understanding of how to improve light trapping based on the symmetry breaking from the CNWs to ENWs and provides a rational way for designing high-efficiency single NW photovoltaic devices.

Room temperature terahertz detector based on single silicon nanowire junctionless transistor with high detectivity

In this work, the n-type single silicon nanowire (NW) based junctionless field-effect transistor (FET) is demonstrated as an efficient terahertz (THz) detector. For the effective coupling of the THz radiations with NW junctionless FET, the lobes of the rounded bow-tie antenna are connected to the gate and source terminals of the device. The antenna design is optimized with proper impedance matching conditions to achieve maximum power transfer between antenna and detector. The simulated antenna resonates at 0.43 THz frequency with 19 GHz bandwidth. Further simulations have been done on Lumerical finite difference time domain software to analyze the electric field distribution profile. To investigate the optical response of this optimized antenna design, an array of the simulated antenna has been fabricated and its transmission spectra are measured. Finally, the simulated antenna has been integrated with the n-type NW junctionless transistor. A maximum responsivity of 468 V W−1 at 0.425 THz frequency and noise-equivalent-power of ∼ 10−9W/Hz1/2 is obtained at room temperature. The complementary metal-oxide-semiconductor’s compatibility, ease of integration on chips, possibility to realize multiple pixel arrays, andscalability to higher frequencies, make this device promising for THz electronics.

Channel Length-Dependent Operation of Ambipolar Schottky-Barrier Transistors on a Single Si Nanowire.

For use in flexible, printable, wearable electronics, Schottky-barrier field-effect transistors (SB-FETs) with various channel materials including low-dimensional nanomaterials have been considered so far due to their comparatively simple and cost-effective integration scheme free of junction and channel dopants. However, the electric conduction mechanism and the scaling properties underlying their performance differ significantly from those of conventional metal-oxide-semiconductor (MOS) field-effect transistors. Indeed, an understanding of channel length scaling and drain bias impact has not been elucidated sufficiently. Here, multiple ambipolar SB-FETs with different channel lengths have been fabricated on a single silicon nanowire ensuring a constant nanowire diameter. Their length scaling behavior is analyzed through drain current and transconductance contour maps, each depending on the drain and gate bias. The reduced gate control and extended drain field effect on Schottky junctions were observed in short channels. Activation energy measurements showed lower sensitive behavior of the Schottky barrier to gate bias in the short-channel device and confirmed the thinning of Schottky barrier width for electrons at the source interface with drain bias.

Towards the fabrication of third generation solar cells on amorphous, flexible and transparent substrates with well-ordered and disordered Si-nanowires/pillars

Abstract Si Nanowires (NWs) are typically synthesized on limited substrates that lack essential characteristics, such as mechanical flexibility and optical transparency. Most of the synthesis processes are also costly and inhibit widespread applications enabled by NWs. Throughout this study, therefore, we have shown that ordered and disordered single crystalline silicon nanowires can be grown and transferred from Si wafer to a broad range of foreign substrates while maintaining their original order on the mother substrates. Vertically-aligned Si NWs have been successfully transferred to Ag-pre-coated glasses, transparent-conductive-oxides and metal foils that ensure ohmic contacts between Si NWs and the transferred substrates, which are critical for scalable manufacturing of electronics and opto-electronic devices. This strategy presents an opportunity to develop low-cost device manufacturing with highly crystalline semiconductor materials, and is a critical leap towards the next generation high performance core-shell Si-NWs solar cells. In order to demonstrate devices based on the transferred NWs, the NWs are coated with a thin layer of CZTS to fabricate a third generation solar cell. The devices were characterized and exhibited the highest power conversion efficiency of 1.31% reported to date, for such transferred NWs and material combinations.

Effect of Silicon Wafer Resistivity on Morphology and Wettability of Silicon Nanowires Arrays

Herein, we prepare vertical and single crystalline silicon nanowires (SiNWs) via a one-step metal-assisted chemical etching method in aqueous NH4HF2/AgNO3 solution. The effects of silicon substrate resistivity and concentrations of NH4HF2 and AgNO3 on the etching process were examined. Two properties were studied, the morphology and the wettability of etched layers. The morphology of the silicon nanowire (SiNW) layers was investigated by scanning electron microscopy (SEM) while the wettability was studied by contact angle measurement system. It was established that the morphology is strongly influenced by etching parameters and their wettability changes from superhydrophilic to hydrophobic.

A Single Silicon Nanowire-Based Ratiometric Biosensor for Ca2+ at Various Locations in a Neuron.

Ionic calcium (Ca2+) is an important second messenger in cells, particularly in the neuron. A deficiency or excess of Ca2+ would lead to neuronal apoptosis and further injury to the brain. For accurate analysis of intracellular Ca2+, a single silicon nanowire (SiNW)-based ratiometric biosensor was constructed by simultaneously anchoring Ru(bpy)2(mcbpy-O-Su-ester)(PF6)2, as a reference molecule, and Fluo-3, as a response molecule, onto the surface of a single SiNW. The SiNW-based biosensor exhibits high sensitivity and favorable selectivity for detecting Ca2+. With the assistance of a micromanipulator and laser scanning confocal microscope, two single SiNW sensors were placed in the body and the neurites of an individual neuron to detect Ca2+. The difference between the concentrations of Ca2+ in the body and neurites was identified. The results from the present study provide new insights into Ca2+ in neurons at a high spatial resolution, and the strategy used in this study provides a new opportunity to investigate cellular metabolism by combining the advantages of a single-cell detection technique and physiology.

A Unique Ionization Gas Sensor With Extraordinary Susceptibility of Sub-1-Volt

In this study, an ionization gas sensor device assembled by a nanoneedle array and a single nanowire is reported. Each nanoneedle is hybridized and consists of the Si nanorod with platinum nanocrystallites on the top. In the device, nanoneedle arrays serve as one electrode and the single silicon nanowire as the counter electrode to form a unique asymmetric discharge space. We believe that gas between this electrode pair is polarized and directly ionized in an extremely high electrical field, which is confirmed by the microstructure characterization, gas-sensing test and theoretic calculation. The advantage of ultralow operation voltage, power consumption with trace sensing ability renders the device an extraordinary ionization gas sensor.

Ultraminiaturized Stretchable Strain Sensors Based on Single Silicon Nanowires for Imperceptible Electronic Skins.

Miniaturized stretchable strain sensors are key components in E-skins for applications such as personalized health-monitoring, body motion perception, and human-machine interfaces. However, it remains a big challenge to fabricate miniaturized stretchable strain sensors with high imperceptibility. Here, we reported for the first time novel ultraminiaturized stretchable strain sensors based on single centimeter-long silicon nanowires (cm-SiNWs). With the diameter of the active materials even smaller than that of spider silks, these sensors are highly imperceptible. They exhibit a large strain sensing range (>45%) and a high durability (>10 000 cycles). Their optimum strain sensing ranges could be modulated by controlling the prestrains of the stretchable cm-SiNWs. On the basis of this capability, sensors with appropriate sensing ranges were chosen to respectively monitor large and subtle human motions including joint motion, swallow, and touch. The strategy of applying single cm-SiNWs in stretchable sensors would open new doors to fabricate ultraminiaturized stretchable devices.

Highly Sensitive and Fast Detection of C-Reactive Protein and Troponin Biomarkers Using Liquidgated Single Silicon Nanowire Biosensors

ABSTRACTC-reactive protein (CRP) and cardiac troponin I (cTnI) biomolecules represent the earliest enzymes that appear in the blood when a cardiac injury occurs. Real-time and selective detection of these biomarkers is essential for the prediction and detection of cardiovascular diseases at an early stage. Here we report on the label-free specific detection of both proteins at picomolar concentrations using fabricated nanowire-based biosensors. We demonstrate a novel functionalization technique based on the attachment of dibenzocyclooctyne (DBCO)-linked troponin-specific aptamers to azide-functionalized silicon (Si) nanowire (NW) surface. Due to the fast and reliable immobilization of cTnI-specific aptamers and CRP-specific antibodies on the Si NWs, the fabricated devices can rapidly detect target biomolecules demonstrating high sensitivity. We confirm the attachment of proteins to the surface of Si NWs by atomic force microscopy (AFM). Moreover, we demonstrate that nanowire structures of different sizes enable the detection of biomarkers in a wide concentration range (from 1 pg/ml to 1 µg/ml), corresponding to CRP and cTnI elevation levels during the early stage of disease formation.

A Novel Top-Down Fabrication Process for Vertically-Stacked Silicon-Nanowire Array

Silicon nanowires are widely used for sensing applications due to their outstanding mechanical, electrical, and optical properties. However, one of the major challenges involves introducing silicon-nanowire arrays to a specific layout location with reproducible and controllable dimensions. Indeed, for integration with microscale structures and circuits, a monolithic wafer-level process based on a top-down silicon-nanowire array fabrication method is essential. For sensors in various electromechanical and photoelectric applications, the need for silicon nanowires (as a functional building block) is increasing, and thus monolithic integration is highly required. In this paper, a novel top-down method for fabricating vertically-stacked silicon-nanowire arrays is presented. This method enables the fabrication of lateral silicon-nanowire arrays in a vertical direction, as well as the fabrication of an increased number of silicon nanowires on a finite dimension. The proposed fabrication method uses a number of processes: photolithography, deep reactive-ion etching, and wet oxidation. In applying the proposed method, a vertically-aligned silicon-nanowire array, in which a single layer consists of three vertical layers with 20 silicon nanowires, is fabricated and analyzed. The diamond-shaped cross-sectional dimension of a single silicon nanowire is approximately 300 nm in width and 20 μm in length. The developed method is expected to result in highly-sensitive, reproducible, and low-cost silicon-nanowire sensors for various biomedical applications.