Single-hole Tunneling Research Articles

Research on a Grading Evaluation System for Water Inflow in Three-Hole Parallel Subsea Tunnels Considering Inter-Tunnel Influence

Water inflow analysis is critical for subsea tunnel construction. However, existing studies largely concentrate on the inflow issues pertaining to single-hole tunnels. To address current practical engineering problems, a three-hole parallel configuration is common for subsea tunnels, which may alter water inflow patterns due to the influence of their seepage fields. Herein, numerical simulations are conducted to investigate the water inflow characteristics of a three-hole parallel subsea tunnel. Specifically, the impact of various factors on the water inflow phenomenon, including the permeability coefficient of the surrounding rock, the depth of the seawater, the depth of the tunnel, the spacing between tunnels, and the relative size of the tunnels, are comprehensively studied. Furthermore, based on the principles of the analytic hierarchy process and fuzzy mathematics, an exhaustive assessment framework is developed to evaluate the water inflow of three-hole parallel subsea tunnels. The results indicate that there is a mutual influence between the three parallel tunnels, differing from the predicted water inflow, which is overestimated in a single-hole tunnel model. Therefore, the water inflow assessment for a three-hole parallel subsea tunnel system should account for the inter-tunnel influences. The findings of this study offer valuable insights for the design of waterproofing and drainage systems in three-hole subsea tunnels.

Numerical study on gas temperature and smoke control in blind roadway fires

In this study, smoke movement characteristics and smoke temperature in the blind roadway and the connected main roadway were mainly investigated numerically. The outcomings indicate that as the fire source gradually moves away from the heading face, the flame tilts from the heading face to the portal of the blind roadway. The gas temperature in the blind roadway and the downstream of the main roadway during ventilation is higher than that in the situation without ventilation, and it depends only on the fire location. The high-temperature smoke will generate energy loss as it passed through the bifurcation structure, resulting in a sudden decline in the longitudinal temperature attenuation curve. In addition, blind roadway fires require a higher critical velocity than single-hole tunnel fires. For a given heat release rate, the critical velocity gradually decreases as the fire source approaches the heading face. Besides, the line of L*=1.5 divides the variation of the dimensionless variable Q˙*2/3/v*2 with the dimensionless backlayering length (L*) into two regions with different slopes. Moreover, prediction models take into account the fire location to predict the dimensionless backlayering length and dimensionless critical velocity of the blind roadway are proposed.

Transport Characteristics of Silicon Multi-Quantum-Dot Transistor Analyzed by Means of Experimental Parametrization Based on Single-Hole Tunneling Model.

The transport characteristics of a gate-all-around Si multiple-quantum-dot (QD) transistor were studied by means of experimental parametrization using theoretical models. The device was fabricated by using the e-beam lithographically patterned Si nanowire channel, in which the ultrasmall QDs were self-created along the Si nanowire due to its volumetric undulation. Owing to the large quantum-level spacings of the self-formed ultrasmall QDs, the device clearly exhibited both Coulomb blockade oscillation (CBO) and negative differential conductance (NDC) characteristics at room temperature. Furthermore, it was also observed that both CBO and NDC could evolve along the extended blockade region within wide gate and drain bias voltage ranges. By analyzing the experimental device parameters using the simple theoretical single-hole-tunneling models, the fabricated QD transistor was confirmed as comprising the double-dot system. Consequently, based on the analytical energy-band diagram, we found that the formation of ultrasmall QDs with imbalanced energetic natures (i.e., imbalanced quantum energy states and their imbalanced capacitive-coupling strengths between the two dots) could lead to effective CBO/NDC evolution in wide bias voltage ranges.

Smoke movement and control in longitudinal ventilated tunnel fires with cross-passages

This paper studies the characteristics of smoke movement and control in longitudinal ventilated tunnel fires with cross-passages through numerical modeling. Previous reports mainly focused on fires in single-hole tunnel, however, tunnels with cross-passages have been widely applied in real life, the cross-passages between main tunnels provide additional path for air and fire smoke, and significantly affect smoke temperature and back-layering length, which has not been studied in the past. Hence, full-scale simulations were conducted considering different heat release rates, fire locations, longitudinal ventilation velocities, and cross-passage intervals in this study. It shows that the smoke temperature distribution with or without cross-passages is almost the same under natural ventilation condition, while the temperature gradually increases with the decrease of interval of cross-passages under longitudinal ventilation condition. Due to the more air leakage, the smoke back-layering length increases with decreasing interval of cross-passage. The air leakage mass through the cross-passage was then characterized by the interval of cross-passages and fire location. Considering fire position and interval of cross-passages, the actual ventilation velocity is used to establish a new smoke back-layering length model. A basic understanding was provided by new findings in this study for smoke movement and control in tunnel fires with cross-passages.

Numerical study on the smoke movement and control in main roadway for mine fires occurred in branch

Mine exogenous fire is the main disaster in coal mines. Owing to the complicated structure and the ventilation network, the smoke movement and control in branched roadway fires of coal mines is more complicated than that in traffic tunnel fires. In this study, the smoke backlayering length and critical velocity in a main roadway for fires that occurred in a branch were studied with varying fire locations. The results suggest that the smoke from the branch does not spread along the width centerline of the main roadway, but forms an early “snake-shaped” structure. The variation of dimensionless backlayering length with the dimensionless variable ln(Q˙*1/3/V*) is divided into two regions with different slopes by the line of L* = 1.6. Besides, branched roadway fires have a lower backlayering length and critical velocity compared to single-hole tunnel fires. These two parameters increase with decreasing the fire-node distance. Combined with dimensionless analysis and simulation results, calculation models considering fire location were proposed to estimate the smoke backlayering length and critical velocity. The credibility of prediction models is validated by comparing them with simulation results. The outcomes of the current study guide smoke control in similar-structured mine roadways and traffic tunnels.

Analytical study on seepage field of subsea twin tunnels constructed by NATM

When two tunnels are close to each other, there will be serious mutual interference in the seepage fields. It may result in errors of more than 30% to use an independent single-hole tunnel model for seepage field analysis. An analytical model for the seepage field of subsea twin tunnels is proposed, and an analytical solution of the seepage field is obtained based on the superposition principle. The analytical solution is verified by degradation analysis, a numerical test and an engineering case. It is shown that: (1) The optimal net distance of twin tunnels is 1 times the tunnel diameter. At this time, the water inflow into one of the twin tunnels is the lowest, which is about 70% of the water inflow into the independent single-hole tunnel. (2) When the diameter of the drainage tunnel is reduced by 75% (the excavation area is reduced by 94%, and the project cost is greatly reduced), the water inflow into the main tunnel increases by only 18%. Therefore, small diameter drainage tunnel is the priority strategy. (3) The drainage tunnel should preferably be arranged at 45° obliquely below the main tunnel.

Theoretical and numerical study on critical velocity and driving force for preventing smoke backlayering in a connection roadway fire of coal mines

H-shape tunnel is a common roadway structure in the coal mine. When a fire occurs in the connection roadway, the characteristics of smoke movement and control are different from those in the traditional single-hole tunnel. This paper studies the critical ventilation velocity and driving force for preventing smoke backlayering in a mine connection roadway fire by numerical modeling. Results indicate that when the dimensionless heat release rate (Q̇*) is less than 0.28, the dimensionless critical ventilation velocity (Vc*) varies as the 1/8 power of the dimensionless heat release rate. Beyond 0.28, Vc* remains almost constant, independent of the heat release rate. For a certain heat release rate, the critical velocity in the connection roadway is lower than that in the single-hole tunnel, which is probably attributed to the smaller ventilation resistance or the effect of the downstream flow field on the smoke backlayering front. The current study prefers to use the ventilation resistance for further analysis. Besides, a calculation model of driving force for preventing smoke backlayering in the connection roadway fire is put forward by theoretical analysis. The predictions by the proposed model are found to comply well with the numerical simulation data. The outcomings of the current study are of guiding significance for the fire prevention and smoke control in the tunnel with a similar structure.

Development and Application of Model Test System for Reconstruction and Expansion of Existing Shallow Single-Hole Tunnel into Twin-Arch Tunnel

In this study, we developed a tunnel excavation model test system to investigate the deformation and mechanical response of the surrounding rocks and tunnel structure during the reconstruction and expansion of an existing shallow single-hole tunnel into a twin-arch tunnel. A model test was conducted to study the variation in the ground surface settlement characteristics, surrounding rock pressure, and internal stresses of the supporting structure and midwall during the construction process. The influence of the excavation distance on displacements and structural stress between the faces of the left and right tunnels was analysed using numerical software. A comparison between the model test results and the monitoring and measurement construction results revealed a fairly consistent ground surface settlement, indicating that the system is stable and reliable and can be widely applied to laboratory model test research on tunnel excavation. Results show that the excavation of the first tunnel had a significant effect on the stability of the surrounding rock within the distance of a single-tunnel span behind the tunnel face. When the excavation distance between the two tunnels exceeded twice the length of the single-tunnel span, its effect on the stresses and deformation of the reconstructed twin-arch tunnel was negligible.

A Suspended Silicon Single-Hole Transistor as an Extremely Scaled Gigahertz Nanoelectromechanical Beam Resonator.

Suspended single-hole transistors (SHTs) can also serve as nanoelectromechanical resonators, providing an ideal platform for investigating interactions between mechanical vibrations and charge carriers. Demonstrating such a device in silicon (Si) is of particular interest, due to the strong piezoresistive effect of Si and potential applications in Si-based quantum computation. Here, a suspended Si SHT also acting as a nanoelectromechanical beam resonator is demonstrated. The resonant frequency and zero-point motion of the device are ≈3GHz and 0.2pm, respectively, reaching the best level among similar devices demonstrated with Si-containing materials. The mechanical vibration is transduced to electrical readout by the SHT. The signal transduction mechanism is dominated by the piezoresistive effect. A giant apparent effective piezoresistive gauge factor with strong correlation to single-hole tunneling is extracted in this device. The results show the great potential of the device in interfacing charge carriers with mechanical vibrations, as well as investigating potential quantum behavior of the vibration phonon mode.

Resonant tunneling and hole transport behavior in low noise silicon tri-gate junctionless single hole transistor

The fabrication of p-type silicon junctionless tri-gate transistors and their temperature dependent transport studies are reported in this work. The fabricated transistors have shown a good transfer characteristic down to a low temperature of ∼ 80 K with an ON/OFF ratio of 106. The threshold voltage and the subthreshold slope were found to be dependent on temperature. In particular, the threshold voltage and the flat band voltage have positive slopes of 2.24 and 1.19 mV K−1, respectively, with temperature. Channel resistance was found to be increasing with decreasing temperature. The devices have shown a typical 1/f noise behavior in the frequency range of (1–50) Hz and 1/f2 type behavior in the frequency range of (50–100 Hz). At a temperature of 4.2 K, current vs. gate voltage characteristic at a fixed source drain bias shows clear coulomb peaks with different intervals for different gate bias voltages and the observed spikes were consistent within the sub-bands. We relate this to the single hole tunneling, mediated by the charged acceptors available in the channel region. Coupling strength of the dopants was also studied.

Numerical simulation of fire smoke in extra-long river-crossing subway tunnels

With the gradually increasing number of river-crossing tunnels in recent years, the risk of tunnel fires continues to rise. Therefore, the fire-smoke control effects of different tunnel structures and ventilation and smoke exhaust systems should be studied. The Fire Dynamics Simulator was used to simulate fires in segments with different slopes in Nanjing Metro Line 10 by considering single-hole single-track and single-hole double-track structures. Moreover, variations in temperature, CO concentration, visibility, and the settling height of the smoke layer were analyzed in detail. The results show that, in terms of temperature, CO concentration, and visibility in the −28‰, +8.9‰, +28‰ tunnels, the single-hole double-track tunnel structure has certain advantages. However, in the −7.5‰ tunnel, the single-hole single-track tunnel slightly presents lower risks than the single-hole two-track structure, whereas the settling height of the smoke layer is higher. In general, the fire risk closely associated with the gradients, and results show that the hazard for the section with positive gradient (+8.9‰, +28‰) after a fire were lower than those for the section with negative gradient (−28‰, −7.5‰). Simultaneously, the fire risk is related to the location of the fire due to different serious consequences under different fire scenarios. Comparatively, the damage caused by fire in section −7.5‰ tunnel is the greatest. In terms of the tunnel's own structure and internal facilities, the single-hole double-track tunnel contains an evacuation platform, fireproof doors, and other emergency facilities, so it is a safer choice from the viewpoint of personnel evacuation. In short, combining related parameters after the fire revealed that the single-hole double-track structure is more suitable in the actual design and application processes.

Dynamic Response of Shallow-Buried Tunnels under Asymmetrical Pressure Distributions

Abstract Based on the similarity theory, two physical testing models (double-hole tunnel and single-hole tunnel) with a scale of 1:10 were designed and manufactured. A series of shaking table tests followed by numerical simulations was carried out to obtain the dynamic response characteristics of shallow-buried tunnels with asymmetrical pressure distributions. The similarities and differences in the dynamic response laws between double-hole tunnel and single-hole tunnel were studied. The effects of types of seismic wave (Wenchuan wave, Darui artificial wave, and Kobe wave), peaks acceleration excitation (0.1 g, 0.2 g, 0.4 g, and 0.6 g), excitation directions (horizontal and vertical directions), and excitation modes (unidirection and bidirection) on dynamic response laws of the tunnels were studied. The results show that the variation of acceleration multiplying factor (AMF) shows a nonlinear trend. The AMFs are different at different monitoring points. The type of seismic wave has a significant effect on the acceleration response, with Kobe wave being the most serious, followed by the Darui artificial wave and the Wenchuan wave. In bidirectional excitation, the AMFs are relatively larger than those of unidirectional excitation. A comparison between the numerical simulation and the shaking table tests in both acceleration time history and peaks acceleration shows that the results of the shaking table tests and numerical simulations are credible. The acceleration response of monitoring points near the existing slope is generally magnified. The residual strains are generated at the monitoring points. The variation trends of both tensile strain and compressive strain are opposite. The tensile strains are generally larger than the compressive strains. Many factors, such as the type of seismic wave, peaks of acceleration excitation, excitation direction, and excitation mode, have a significant influence on the dynamic strain response and acceleration response of the tunnels. The research results could promote the understanding of dynamic response characteristics of the tunnels.

Transport studies of electron-hole and spin-orbit interaction in GaSb/InAsSb core-shell nanowire quantum dots

We report low-temperature transport studies of parallel double quantum dots formed in GaSb/InAsSb core-shell nanowires. At negative gate voltages, regular patterns of Coulomb diamonds are observed in the charge stability diagrams, which we ascribe to single-hole tunneling through a quantum dot in the GaSb core. As the gate voltage increases, the measured charge stability diagram indicates the appearance of an additional quantum dot, which we suggest is an electron quantum dot formed in the InAsSb shell. We find that an electron-hole interaction induces shifts of transport resonances in the source-drain voltage from which an average electron-hole interaction strength of $2.9\ifmmode\pm\else\textpm\fi{}0.3\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$ is extracted. We also carry out magnetotransport measurements of a hole quantum dot in the GaSb core and extract level-dependent $g$ factors and a spin-orbit interaction.

Modulation of peak-to-valley current ratio of Coulomb blockade oscillations in Si single hole transistors

We demonstrate a method to modulate the peak-to-valley current ratio of Coulomb blockade oscillation peaks in room temperature-operating Si single-hole tunnel transistors. By connecting the extra p+in+ junction (i.e., a current effluence path) to the drain reservoir, we effectively deplete the leakage current (i.e., valley current) that stem from the diffusion current of the parasitic field-effect transistor within the device. The addition of the extra current-effluence path significantly improves the Coulomb blockade characteristics in comparison to the original Coulomb blockade oscillations. We believe the method is advantageous for designing high performance Si single electron/hole tunnel devices.

Single-hole tunneling through a two-dimensional hole gas in intrinsic silicon

In this letter we report single-hole tunneling through a quantum dot in a two-dimensional hole gas, situated in a narrow-channel field-effect transistor in intrinsic silicon. Two layers of aluminum gate electrodes are defined on Si/SiO2 using electron-beam lithography. Fabrication and subsequent electrical characterization of different devices yield reproducible results, such as typical MOSFET turn-on and pinch-off characteristics. Additionally, linear transport measurements at 4 K result in regularly spaced Coulomb oscillations, corresponding to single-hole tunneling through individual Coulomb islands. These Coulomb peaks are visible over a broad range in gate voltage, indicating very stable device operation. Energy spectroscopy measurements show closed Coulomb diamonds with single-hole charging energies of 5–10 meV and lines of increased conductance as a result of resonant tunneling through additional available hole states.

Possibility of Transport Through a Single Acceptor in a Gate-All-Around Silicon Nanowire PMOSFET

Temperature-dependent electrical transport measurements of cylindrical shaped gate-all-around silicon nanowire p-channel MOSFET were performed. At 4.2 K, they show current oscillations, which can be analyzed by single hole tunneling originated from nanowire quantum dots. In addition to this single hole tunneling, one device exhibited strong current peaks, surviving even at room temperature. The separations between these current peaks corresponded to the energy of 25 and 26 meV. These values were consistent with the sum of the bound-state energy spacing and the charging energy of a single boron atom. The radius calculated from the obtained single-atom charging energy was also comparable to the light-hole Bohr radius.

Detection of field-induced single-acceptor ionization in Si by single-hole-tunneling transistor

The authors have detected the ionization of single-acceptors in the underlying p on p+ substrate of a silicon-on-insulator (SOI) wafer using a single-hole-tunneling (SHT) transistor fabricated in the top Si layer of the SOI at low temperatures. It was found that freeze-out boron atoms in the substrate are sequentially ionized from near the buried SiO2∕p-Si substrate interface to deeper positions by application of a vertical electric field, creating steplike features in the time-dependent SHT current.

Superconductivity in silicon nanostructures

We present the findings of single-hole and pair-hole tunneling into the negative-U centres at the quantum well—δ-barrier interfaces that seems to give rise to the superconductivity observed in the silicon nanostructures prepared by short time diffusion of boron on the n-type Si(100) surface. These Si-based nanostructures represent the p-type ultra-narrow self-assembled silicon quantum wells, 2nm, confined by the δ-barriers heavily doped with boron, 3nm. The EPR and the thermo-emf studies show that the δ-barriers appear to consist of the trigonal dipole centres, B+–B−, which are caused by the negative-U reconstruction of the shallow boron acceptors, 2B0→B++B−. Using the CV and thermo-emf techniques, the transport of two-dimensional holes inside SQW is demonstrated to be accompanied by single-hole tunneling through these negative-U centres that results in the superconductivity of the δ-barriers, which seems to be in frameworks of the mechanism suggested by E. Simanek and C.S. Ting (Sol. St. Commun. 32 (1979) 731; Phys. Rev. Lett. 45 (1980) 1213). The values of the correlation gaps obtained from these measurements are in a good agreement with the data derived from the temperature and magnetic field dependencies of the magnetic susceptibility, which reveal a strong diamagnetism and additionally identify the superconductor gap value.

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H-shape tunnel is a common roadway structure in the coal mine. When a fire occurs in the connection roadway, the characteristics of smoke movement and control are different from those in the traditional single-hole tunnel. This paper studies the critical ventilation velocity and driving force for preventing smoke backlayering in a mine connection roadway fire by numerical modeling. Results indicate that when the dimensionless heat release rate (Q̇*) is less than 0.28, the dimensionless critical ventilation velocity (Vc*) varies as the 1/8 power of the dimensionless heat release rate. Beyond 0.28, Vc* remains almost constant, independent of the heat release rate. For a certain heat release rate, the critical velocity in the connection roadway is lower than that in the single-hole tunnel, which is probably attributed to the smaller ventilation resistance or the effect of the downstream flow field on the smoke backlayering front. The current study prefers to use the ventilation resistance for further analysis. Besides, a calculation model of driving force for preventing smoke backlayering in the connection roadway fire is put forward by theoretical analysis. The predictions by the proposed model are found to comply well with the numerical simulation data. The outcomings of the current study are of guiding significance for the fire prevention and smoke control in the tunnel with a similar structure.

Single-hole tunneling into a strain-induced SiGe quantum ring

We have observed single-hole tunneling and Coulomb blockade in the resonant tunneling characteristics of an ultrasmall Si/SiGe strained vertical quantum dot. The current steps near the tunneling threshold are due to tunneling of the holes from the emitter to the doubly degenerate ground state of the strain-induced quantum ring in the vertical quantum dot, and the spacing of the steps gives the charging energy of the quantum ring. When a magnetic field is applied parallel to the tunneling direction, the evolution of the single-hole tunneling features reveals a cusp arising from the angular-momentum transition of the single-particle ground state of the quantum ring in the magnetic field.