Surface Transport Properties of Pb-Intercalated Graphene

Intercalation experiments on epitaxial graphene are attracting a lot of attention at present as a tool to further boost the electronic properties of 2D graphene. In this work, we studied the intercalation of Pb using buffer layers on 6H-SiC(0001) by means of electron diffraction, scanning tunneling microscopy, photoelectron spectroscopy and in situ surface transport. Large-area intercalation of a few Pb monolayers succeeded via surface defects. The intercalated Pb forms a characteristic striped phase and leads to formation of almost charge neutral graphene in proximity to a Pb layer. The Pb intercalated layer consists of 2 ML and shows a strong structural corrugation. The epitaxial heterostructure provides an extremely high conductivity of σ=100 mS/□. However, at low temperatures (70 K), we found a metal-insulator transition that we assign to the formation of minigaps in epitaxial graphene, possibly induced by a static distortion of graphene following the corrugation of the interface layer.

Detection of Reproductive Hormones in Females by Using 1D Photonic Crystal-Based Simple Reconfigurable Biosensing Design

In this manuscript, we have explored the photonic biosensing application of the 1D photonic crystal (PhC) (AB)NCDC(AB)N, which is capable of detecting reproductive progesterone and estradiol hormones of different concentration levels in blood samples of females. The proposed structure is composed of an air cavity surrounded by two buffer layers of material MgF2, which is sandwiched between two identical 1D sub PhCs (AB)N. Both sub PhCs are made up of alternate layers of materials, SiO2 and Si, of period 5. MATLAB software has been used to obtain transmission characteristics of the structure corresponding TE wave, only with the help of the transfer matrix method. The mainstay of this research is focused on the dependence of the intensity and position of the defect mode inside the photonic bandgap with respect to reproductive hormone concentrations in blood samples, change in the thickness of the cavity region and change in angle of incidence corresponding to TE wave only. The proposed design shows high sensitivity of 98.92 nm/nmol/L and 96.58 nm/nmol/L when the cavity of a thickness of 340 nm is loaded with progesterone and estradiol hormones of concentrations of 80 nmol/L and 11 nmol/L, respectively, at an incident angle of 20°. Apart from sensitivity, other parameters such as quality factor and figure of merit have also been computed to gain deep insight about the sensing capabilities of the proposed design. These findings may pave the path for the design and development of various sensing devices capable of detecting gynecological problems pertaining to reproductive hormones in females. Thus, the simple design and excellent performance makes our design most efficient and suitable for sensing applications in industrial and biomedical fields.

Defect characterization of heavy-ion irradiated AlInN/GaN on Si high-electron-mobility transistors

The characteristic energies of traps in InAlN/AlN/GaN high-electron mobility transistor structures on Si(111) substrates formed after irradiation with 75 MeV S-ions is studied by means of c-lattice parameter analysis, vertical IV-characteristics, micro-photoluminescence (µ-PL), photocurrent (PC) and thermally stimulated current (TSC) spectroscopy. From the lattice parameter analysis, point defect formation is concluded as the dominant source of defects upon irradiation. A strong compensation effect mani-fests itself through enhanced resistivity of the devices as found in vertical IV- measure-ments. The defect formation is detected optically by an additional PL-band within the green spectral region while defect states with threshold energies at 2.9 eV and 2.65 eV were observed by PC spectroscopy. TSC spectra exhibit two defect-related emissions between 300 K and 400 K with thermal activation energies of 0.78-0.82 eV and 0.91-0.98 eV, respectively. The data further supports the formation of Ga vacancies (VGa) and related complexes acting mainly as acceptors compensating the originally undoped n-type GaN buffer layers after irradiation.

Separation of AlN layers from silicon substrates by KOH etching

In this work, the AlN/Si(111) epitaxial structures grown consistently by plasma assisted molecular beam epitaxy (PA MBE) and hydride vapour phase epitaxy (HVPE) methods were studied. The PA MBE AlN buffer layers were synthesized via coalescence overgrowth of self-catalyzed AlN nanocolumns on Si(111) substrates and were used as templates for further HVPE growth of thick AlN layer. It was shown that described approaches can be used to obtain AlN layers with sufficiently smooth morphology. It was found that HVPE AlN inherited crystallographic polarity of the AlN layer grown by PA MBE. It was demonstrated that the etching of such AlN/Si(111) epitaxial structures results in partial separation of the AlN epilayers from the Si(111) substrate and allows to form suspended structures. Moreover, the avoidance of surface damage and backside overetching was achieved by use thin Cr film as surface protective coating and by increasing the layer thickness accordingly.

1D reconfigurable bistable photonic device composed of phase change material for detection of reproductive female hormones

In this manuscript one-dimensional (1D) photonic biosensor (PQ) N GDG(PQ) N composed of phase change material (PCM) germanium antimony telluride (GST) has been studied in visible region of electromagnetic spectrum. This design is capable of label free recognition of reproductive hormones of female which are significant during reproductive process such as menstruation and parturition. The proposed structure is composed of an air cavity separated by two buffer layers of GST material. The GST buffer layers have been used to improve the sensing performance of the structure. The modified cavity associated with buffer GST layers is sandwiched between two 1D photonic structures (PS) (PQ) N . Both 1D PS are consisted of alternate material layers of SiO2 and Si of period 5. The transmission spectra of proposed design have been obtained by using transfer matrix method and MATLAB software. In this work the performance of the devise has been investigated for normal and oblique incidence corresponding to TE wave only under the influence of change of phases of GST. The mainstay of this research is focused on the tunable performance of proposed bio-sensing design due to switching between amorphous phase (aGST) and crystalline phase (cGST) of GST. Moreover how the change in the thickness of cavity region as well as angle of incidence corresponding to TE wave affects the performance of the design has also been studied. The sensitivity, quality factor and figure of merit values of the design have also been studied to get deep insight about the sensing capabilities of the proposed design under the influence of crystalline and amorphous phases of GST. Thus due to simple architecture and excellent switchable and reconfigurable characteristics, our structure works efficiently in industrial and biomedical refractive index based sensing applications.