Tuning the cross-gap transition energy of a quantum dot by uniaxial stress

We show that a piezoelectric actuator can be used to apply uniaxial stress to a layer of self-assembled quantum dots. The applied stress leads to a change of the quantum dot's ground state exciton energy by up to a few hundred μeV. This approach allows the possibility of an in situ and continuous tuning of the stress at temperatures down to 4 K and offers an alternative to tuning by temperature and Stark effect. We measure the relative change in the charging energy to the n-doped back contact by capacitance and the change in the exciton energy by photoluminescence. By tuning the uniaxial stress we are able to perform reflection spectroscopy on a single dot.     

Corrugated single layer templates for molecules: From h-BN nanomesh to graphene based quantum dot arrays

Functional nano-templates enable self-assembly of otherwise impossible arrangements of molecules. A particular class of such templates is that of sp² hybridized single layers of hexagonal boron nitride or carbon (graphene) on metal supports. If the substrate and the single layer have a lattice mismatch, superstructures are formed. On substrates like rhodium or ruthenium these superstructures have unit cells with ~3-nm lattice constant. They are corrugated and contain sub-units, which behave like traps for molecules or quantum dots, which are small enough to become operational at room temperature. For graphene on Rh(111) we emphasize a new structural element of small extra hills within the corrugation landscape. For the case of molecules like water it is shown that new phases assemble on such templates, and that they can be used as “nano-laboratories” where many individual processes are studied in parallel. Furthermore, it is shown that the h-BN/Rh(111) nanomesh displays a strong scanning tunneling microscopy-induced luminescence contrast within the 3 nm unit cell which is a way to address trapped molecules and/or quantum dots.     

Corrugated single layer templates for molecules: From h-BN nanomesh to graphene based quantum dot arrays

Functional nano-templates enable self-assembly of otherwise impossible arrangements of molecules. A particular class of such templates is that of sp ² hybridized single layers of hexagonal boron nitride or carbon (graphene) on metal supports. If the substrate and the single layer have a lattice mismatch, superstructures are formed. On substrates like rhodium or ruthenium these superstructures have unit cells with ∼3-nm lattice constant. They are corrugated and contain sub-units, which behave like traps for molecules or quantum dots, which are small enough to become operational at room temperature. For graphene on Rh(111) we emphasize a new structural element of small extra hills within the corrugation landscape. For the case of molecules like water it is shown that new phases assemble on such templates, and that they can be used as “nano-laboratories” where many individual processes are studied in parallel. Furthermore, it is shown that the h-BN/Rh(111) nanomesh displays a strong scanning tunneling microscopy-induced luminescence contrast within the 3 nm unit cell which is a way to address trapped molecules and/or quantum dots.     

Design of graphene coupling enhanced quantum dot infrared photodetector

Optical Review - The conventional quantum dot infrared photodetector (QDIP) has a weak ability to capture light, which limits the further improvement of absorptivity. In this paper, the graphene...     

Surface quantum oscillations in (100) inversion layers under uniaxial stress

Surface quantum oscillations have been measured with uniaxially stressed (100) n-type inversion layers. A relation between mechanical stress and cyclotron mass m_c has been observed. In the quantum limit the two-fold valley degeneracy is lifted by about 1 meV with compression.     

graphene量子点的起伏效应对尺寸的敏感性研究

用第一原理研究了graphene量子点器件在不同尺寸时的输运特性,以得到起伏效应所引起的输运特性的变化,以及对尺寸的敏感性.研究结果表明无论电极与锯齿型边界的graphene量子点相连还是与扶手椅型边界的graphene量子点相连,都会受起伏效应较大的影响,并且随尺寸的不同影响程度也不同.加偏压后得到的电流也受较大影响,但两种连法受到的影响随尺寸的增加效果不同. 关键词： graphene 量子点 起伏效应     

Exciton polarization, fine-structure splitting, and the asymmetry of quantum dots under uniaxial stress

We derive a general relation between the fine-structure splitting (FSS) and the exciton polarization angle of self-assembled quantum dots under uniaxial stress. We show that the FSS lower bound under external stress can be predicted by the exciton polarization angle and FSS under zero stress. The critical stress can also be determined by monitoring the change in exciton polarization angle. We confirm the theory by performing atomistic pseudopotential calculations for the InAs/GaAs quantum dots. The work provides deep insight into the dot asymmetry and their optical properties and a useful guide in selecting quantum dots with the smallest FSS, which are crucial in entangled photon source applications.     

Silica-covered Au nanoresonators for fluorescence modulating of a graphene quantum dot

We synthesize Au@SiO2composite particles with a core-shell structure, and utilize the Au@SiO2nanoparticles to modulate the fluorescence emission of the graphene quantum dot(GQD) through varying the silica shell thickness. The silica shell thickness can be easily controlled by varying the coating time. After silica coating, we investigate the influence of the silica thickness on the fluorescence emission of the GQD and find that the fluorescence property of the GQD can be changed as expected by varying the thickness of the silica shell. We propose an optimized coating time for the silica shell under the interaction of fluorescence quenching and enhancement.     

Electronic properties of Z-shaped graphene nanoribbon under uniaxial strain

Based on tight-binding approximation and a generalized Green's function method, the effect of uniaxial strain on the electron transport properties of Z-shaped graphene nanoribbon (GNR) composed of an armchair GNR sandwiched between two semi-infinite metallic armchair GNR electrodes is numerically investigated. Our results show that the increase of uniaxial strain enhances the band gap and leads to a metal-to-semiconductor transition for Z-shaped GNR. Furthermore, in the Landauer–Büttiker formalism, the current–voltage characteristics, the noise power resulting from the current fluctuations and Fano factor of strained Z-shaped GNR are explored. It is found the threshold voltage for the current and the noise power increased so that with reinforcement of the uniaxial strain parameter strength, the noise power goes from the Poisson limit to sub-Poisson region at higher bias voltages.     

Conductivity of heavily doped Si:P under uniaxial stress

Barely insulating, uncompensated Si:P samples have been tuned through the metal‐insulator transition applying uniaxial stress along the [100] direction. We find a critical exponent μ ≈︂ 1 of the electrical conductivity extrapolated to temperature T = 0, i.e. σ(T → 0,S) ∼ |S — S_c|^μ, in disagreement with earlier stress tuning studies along [123‐] where μ ≈︂ 0.5 was reported. Varying the stress or the concentration leads to a different T dependence of σ(T). Our stress‐tuning measurements obey finite‐T scaling with a dynamic exponent z = 3.     

Dielectric function due to carrier confinement in semiconducting quantum well systems

The real peart of the dielectric function is calculated in quasi-one and two dimensional semiconducting structures using the Kramers-Kronig dispersion relations. At photon frequencies above the threshold for interband transitions, new structure in the index of refraction is found while below the threshold frequency, the index of refraction is reduced below its value in the bulk.     

Magnetic sub-band structure of HgTe under uniaxial stress

The magnetic sub-band structure of HgTe is calculated for the strain-splitting Γ₈ bands, and the lowest Landau levels of the conduction and valence bands at k_H = 0 are shown to cross each other as the magnetic field is increased. It is demonstrated that the crossing means the band inversion for the case of the compressional stress and the semimetal—semiconductor transition for the case of the tensile stress.