Shiu-Ming Huang

Extremely high-performance visible light photodetector in the Sb 2 SeTe 2 nanoflake

The photocurrent was performed in the Sb2SeTe2 topological insulator at a wavelength of 532 nm. It exhibits extremely high performance that the responsivity and the photoconductive gain reach 2293 AW−1 and 5344 at 1 V. This high photoresponse is orders of magnitude higher than most reported values in topological insulators and two-dimensional transitional metal dichalcogenides. This finding suggests that the Sb2SeTe2 nanoflake has great potential for future optoelectronic device applications.

The linear magnetoresistance from surface state of the Sb2SeTe2 topological insulator

A non-saturating linear magnetoresistance (MR) is observed in Sb2SeTe2 topological insulator. The results show that the MR slope and the critical magnetic field of the linear MR are proportional to the carrier mobility and inverse mobility, respectively. These are consistent with the prediction of a model, which is constructed by Parish and Littlewood [Nature 426, 162 (2003)], in the weak mobility fluctuation condition. The Kohler plot of the magnetoresistance does not collapse onto a single curve that supports the multi-carriers scattering mechanisms.

Observation of surface oxidation resistant Shubnikov-de Haas oscillations in Sb2SeTe2 topological insulator

The robustness of Sb2SeTe2 topological insulators against surface oxidation has been comparatively investigated through their magneto-transport and X-ray photoelectron spectroscopic properties with samples freshly cleaved or exposed to air over various timeframes. The magnetoresistance data exhibit Shubnikov-de Haas oscillations with the same period of oscillations for all samples regardless of surface oxidation, whereas the core-level electron binding energies of the constituent elements vary. That there is no shift in Fermi levels and no smearing-out in the amplitude of oscillations suggests that the surface states of the studied topological insulators are impervious to surface oxidation.

Two-carrier transport-induced extremely large magnetoresistance in high mobility Sb2Se3

Large magnetoresistance (MR) has been widely reported in the A2B3 (A = Sb or Bi; B = Se or Te) family of topological insulators (TIs). Sb2Se3 is not a TI that was confirmed by the extracted zero Berry phase and the X-ray diffraction. An extremely large MR was observed in the Sb2Se3 crystals. This large MR increased quadratically with the magnetic field applied. The observed MR ratio was 830% at 10 K and 9 T, which was larger than that previously reported for all A2B3 family TIs. This large MR originated from two carriers with high mobility. The inversely square root of the MR ratio was proportional to the resistance.

Thickness-dependent conductance in Sb 2 SeTe 2 topological insulator nanosheets

The conductivity increases as thickness decreases in a series of Sb2SeTe2 topological insulator nanosheets with thickness ranging from 80 to 200 nm, where the sheet conductance is proportional to the thickness. The corresponding sheet conductance of the surface state is 8.7 e2/h which is consistent with the values extracted from the temperature dependent Shubnikov-de Haas oscillations at high magnetic fields. The extracted Fermi momentum is the same as the results from the ARPES value, and the Berry phase is π. These support that the thickness dependent sheet conductance originates from the combination of the surface state and the bulk state.

The temperature dependence of the crossover magnetic field of linear magnetoresistance in the Cu0.1Bi2Se3

A non-saturating linear magnetoresistance (MR) is observed in Cu0.1Bi2Se3 in a wide range of temperatures. The crossover magnetic field, B*, deviating from the linear MR, increases as the temperature increases. The experimental results show that the normalized B*, inverse MR slope and mobility follow the same temperature dependence that is consistent with the model constructed by Parich and Littlewood (PL model). The mechanism of the T 2 dependent B* is systematically and comprehensively discussed through existing theories, and might be due to the electron−electron scattering in a highly uniform system with a few low mobility defects.

Gas detection using large-size graphene with defects

A macroscopic graphene is thermally annealed in oxygen gas, and Raman spectroscopy shows that the number of structural defects increases after thermal annealing. The temperature dependence of resistance is studied in macroscopic graphene with different numbers of structural defects in various gas environments. The temperature dependent slope of normalized resistance is independent of the number of structural defects and is small in the gas environment of heavier molecules. Following the temperature dependent slopes of normalized resistance, one can identify the molecule mass of the environmental gas. The temperature dependence of thermal electric power is sensitive to the quantity of the structural defects.

Enhancement of carrier transport characteristic in the Sb 2 Se 2 Te topological insulators by N 2 adsorption

The carrier transport characteristics of Sb2Se2Te topological insulators were investigated, after exposure to different levels of nitrogen gas. The magnetoresistance (MR) slope for the Sb2Se2Te crystal increased by approximately 100% at 10 K after 2-days of exposure. The Shubnikov-de Haas (SdH) oscillation amplitude increased by 30% while oscillation frequencies remained the same. MR slopes and the mobilities had the same dependency on temperature over a wide temperature range. All measured data conformed to a linear correlation between MR slope and mobility, supporting our hypothesis that the MR increase and the SdH oscillation enhancement might be caused by mobility enhancement induced by adsorbed N2 molecular.

Highly responsive photoconductance in a Sb2SeTe2 topological insulator nanosheet at room temperature

A photocurrent was applied to a Sb2SeTe2 topological insulator nanosheet at a wavelength of 325 nm, and it exhibited extremely high performance such that the responsivity and photoconductive gain are 354 A W−1 and 1531, respectively, at a bias of 0.1 V. This photoresponse is orders of magnitude higher than most reported values for topological insulators and two-dimensional transitional metal dichalcogenides. The photoresponse is linear with the applied voltage. Responsivity and gain under vacuum are higher than that in air by a factor of 2.5. This finding suggests that the Sb2SeTe2 topological insulator nanosheet has great potential for ultraviolet optoelectronic device applications.

Effects of molecular adsorption on carrier transport properties of large-size graphene

The temperature dependent resistance and thermoelectric power of macroscopic graphenes are studied in various gas environments. The temperature dependent slope of resistance is weaker in gas environments with heavier molecules. Following the temperature dependent slopes of normalized resistance, one can identify the molecular mass of the environmental gas. This is relative to the atomically sharp potential modification due to adsorbed gas molecules on the graphene. The temperature dependent thermopower increases as the mass of the gas molecules increases. A universal relationship between resistance and thermoelectric power in various gas environments further confirms that the transport mechanism is dominated by the adsorbed gas molecules on the graphene surface.