Search

Photonic films based on cellulose nanocrystals (CNCs) are sustainable candidates for sensors, structurally colored radiative cooling, and iridescent coatings. Such CNC-based films possess a helicoidal nanoarchitecture, which gives selective reflection with the polarization of the incident light. However, due to the hygroscopic nature of CNCs, the structural colored material changes and may be irreversibly damaged at high relative humidity. Thus, moisture protection is essential in such settings. In this work, hygroscopic CNC-based films are protected with a bioinspired synthetic plant cuticle; a strategy already adopted by real plants. The protective cuticle layers altered the reflected colors to some extent, but more importantly, they significantly reduced the water vapor permeance by more than two orders of magnitude, from 2.1 x 10(7) (pristine CNC/GLU film) to 12.3 x 10(4) g mu m m(-2) day(-1) atm(-1) (protected CNC/GLU film). This expands significantly the time window of operation for CNC/GLU films at high relative humidity. Funding Agencies|Olle Byggmaestare [194-0679]; Knut and Alice Wallenberg Foundation (WWSC); Linkoeping University; Wallenberg Wood Science Center; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoeping University [2009 00971]

In this letter, we report the theoretical study on phonon transport in monocrystalline silicon thin-films having unfilled or metal-filled circular holes (i.e., phononic crystals, PnCs) and show that the thermal conductivity, κ, at 1 K can be maximally reduced by using a multiscale structure, which allows us control over the porosity of the structure. The circular scatterers are placed in the square (SQ) and hexagonal (HX) pattern with a fixed 100 nm interhole spacing, and the pit diameter is varied between 10 and 90 nm. Each of the corresponding silicon PnCs shows reduced κ compared to the unpatterned film. The SQ-PnC having tungsten-filled pits shows the greatest reduction in κ when we consider only the effects of coherent scattering. Furthermore, we have computed κ for the PnC where the unit cell, of 100 nm and 500 nm sizes, comprises the Sierpinski gasket (SG) with circular holes of different diameters (depending on the fractal order) in the same cell. It is observed that the κ for the 2nd (100 nm cell) and 3rd order (500 nm cell) SG-PnC is comparable to the SQ- and HX-PnC with a pit diameter of 90 nm. When we add the effect of the diffuse boundary scattering in κ, there is a lowering in κ compared to that when only the coherent effects are considered. The additional κ-reduction due to boundary scattering for the SQ-PnC and HX-PnC (both with 90 nm diam) as well as the 2nd and 3rd order SG-PnCs is 47%, 40%, 80%, and 60%, respectively.In this letter, we report the theoretical study on phonon transport in monocrystalline silicon thin-films having unfilled or metal-filled circular holes (i.e., phononic crystals, PnCs) and show that the thermal conductivity, κ, at 1 K can be maximally reduced by using a multiscale structure, which allows us control over the porosity of the structure. The circular scatterers are placed in the square (SQ) and hexagonal (HX) pattern with a fixed 100 nm interhole spacing, and the pit diameter is varied between 10 and 90 nm. Each of the corresponding silicon PnCs shows reduced κ compared to the unpatterned film. The SQ-PnC having tungsten-filled pits shows the greatest reduction in κ when we consider only the effects of coherent scattering. Furthermore, we have computed κ for the PnC where the unit cell, of 100 nm and 500 nm sizes, comprises the Sierpinski gasket (SG) with circular holes of different diameters (depending on the fractal order) in the same cell. It is observed that the κ for the 2nd (1...

We have demonstrated that deep level traps created by B implantation can reduce the contact resistance by forming an additional path for electron transport via trap assisted tunneling in GaN and AlGaN/GaN heterostructures. B implantation by plasma-immersion ion implantation creates deep level traps 0.36 eV below the conduction band edge to a shallow depth (10–25 nm) in the structure. These traps act as efficient percolation path for electrons between the TiN Ohmic contact and the active region, which can be bulk GaN or a two-dimensional electron gas (2DEG) formed at the AlGaN/GaN heterostructure. The improved Ohmic behavior is manifested as reduced specific contact resistivity and normalized contact resistance. The specific contact resistance and the normalized contact resistance are found to decrease by 59% (30%) and 86% (51%), respectively, for bulk GaN (AlGaN/GaN). The effect of B implantation on the sheet resistance of the 2DEG is insignificant when the implantation energy and post-implantation annealing time are controlled optimally.

We have demonstrated a type-II band-aligned heterostructure between pulsed laser deposited topological insulator bismuth telluride and metal organic-chemical-vapour deposited GaN on a sapphire substrate. The heterostructure shows a large valence band-offset of 3.27 eV as determined from x-ray photoelectron spectroscopy, which is close to the bandgap of GaN (3.4 eV). Further investigation using x-ray diffraction, Raman spectroscopy, and energy-dispersive x-ray spectrum reveals the stoichiometric and material properties of bismuth telluride on GaN. Steady state photon emission from GaN is found to be modulated by the charge transfer process due to diffusion across the junction. The time constant involved with the charge transfer process is found to be 0.6 ns by transient absorption spectroscopy. The heterostructure can be used for designing devices with different functionalities and improving the performance of the existing devices on GaN. (C) 2015 AIP Publishing LLC.

We have investigated Schottky contacts on GaN and observed that Fermi level pinning is dominant at the metal/GaN interface with a pinning factor of 0.23. A methodology to solve the problem by introducing a thin layer of MgO between the metal and the semiconductor is demonstrated here. It is observed that the insertion of a thin layer of the insulator prevents the metal wave-function penetration into the semiconductor band gap which in turn helps in the Fermi level depinning for GaN. We have particularly demonstrated the Fermi level depinning for ferromagnetic Schottky contact Fe and shown its usefulness for electrical spin injection and detection. The resistance-area product of an as deposited Fe/GaN contact is found to be too high for efficient spin injection and detection. It is improved considerably by using a 3 nm layer of MgO and the effective barrier height is reduced to 0.4 eV. We have further investigated the influence of low work function metal Gd and found it is possible to do barrier height engineering when deposited in conjunction with other metals. (C) 2013 Elsevier B.V. All rights reserved.

We have demonstrated electrical spin-injection from GaCrN dilute magnetic semiconductor (DMS) in a GaN-based spin light emitting diode (spin-LED). The remanent in-plane magnetization of the thin-film semiconducting ferromagnet has been used for introducing the spin polarized electrons into the non-magnetic InGaN quantum well. The output circular polarization obtained from the spin-LED closely follows the normalized in-plane magnetization curve of the DMS. A saturation circular polarization of similar to 2.5% is obtained at 200 K. (C) 2013 AIP Publishing LLC.

We have theoretically designed and experimentally demonstrated a multiterminal lateral magnetoresistive device using electrical spin injection and detection in semiconductor, which can act as a memory array. The memory state is associated with the direction of the magnetization state. The state is read out from clear transition in current both in magnitude and direction depending on the relative magnetization direction. The current shows a plateau in varying magnetic field regions indicating stable magnetization direction due to differences in coercivity. The device characteristics are well explained in the framework of two-dimensional spin transport and spin-dependent tunneling. (C) 2013 The Japan Society of Applied Physics

We report room temperature ferromagnetism in crystalline GaCrN prepared by Cr deposition and drive-in diffusion with Curie temperature much above 300 K. The Curie temperature increases with increasing active Cr concentration. Cr doped GaN acts as an n-type material with significant increase in electron carrier concentration due to the presence of Cr. Optical property of GaCrN is found to be very similar to GaN with an additional peak at 3.29 eV due to Cr. The hysteresis measurements show that the ferromagnetic ordering is maintained up to 300 K with no significant change in saturation magnetization. Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4799716]