Nanometric diamond delta doping with boron

Diamond is desired for active semiconducting device because of it high carrier mobility, high voltage breakdown resistance, and high thermal diffusivity. Exploiting diamond as a semiconductor is hampered by the lack of shallow dopants to create sufficient electronic carriers at room temperature. In this work, nanometer thick, heavily boron doped epitaxial diamond ‘delta doped’ layers have been grown on ultra smooth diamond surfaces which demonstrate p type conduction with enhanced Hall mobilities of up to 120 cm²/Vs and sheet carrier concentrations to 6 × 10¹³ cm^–2, thus enabling a new class of active diamond electronic devices. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Ultra‐sharp boron interfaces for delta doped diamond structures

Delta doping of diamond constitutes a very promising route to fabricate novel generation of high power and high frequency electronic devices. However, the achievement of abrupt interfaces between highly boron doped and undoped layers requires the shortest residence times of reactive species in the substrate vicinity. We report here on an innovative gas injection system especially designed to reduce this residence time. This technique was applied to fabricate sharp rising and decaying boron interfaces. According to SIMS profiles, the sharpest profiles were obtained on decaying interfaces exhibiting doping gradients close to 1.5 nm per decade over five decades of boron concentrations, namely from 10¹⁶ to 10²¹ atoms/cm³. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High‐order Stokes and anti‐Stokes Raman generation in monoisotopic CVD 12C‐diamond

We determined, for the first time, the room temperature phonon energy related to the F_2g vibration mode (ω_SRS(12C) ～ 1333.2 cm^–1) in a mono‐crystalline single‐isotope CVD ¹²C‐diamond crystal by means of stimulated Raman scattering (SRS) spectroscopy. Picosecond one‐micron excitation using a Nd³⁺:Y₃Al₅O₁₂‐laser generates a nearly two‐octave spanning SRS frequency comb (～12000 cm^–1) consisting of higher‐order Stokes and anti‐Stokes components. The spacing of the spectral lines was found to differ by Δω_SRS ～ 0.9 cm^–1 from the comb spacing (ω_SRS(natC) ～ 1332.3 cm^–1) when pumping a conventional CVD diamond crystal with a natural composition of the two stable carbon isotopes ¹²C (98.93%) and ¹³C (1.07%). (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Delta‐layer doping profile in diamond providing high carrier mobility

We show that the nano‐scale delta‐layer doping profile in diamond can significantly influence both the carrier mobility and two‐dimensional conductivity. We numerically considered and compared a simple boron doping profile with one maximum at the delta‐layer center and a more complicated profile with two maxima inside the delta layer and a minimum at its center. As a result we concluded that in the last case the hole mobility and the two‐dimensional conductivity are higher by more than 3 times and 60% respectively than in the first case. The physical reason for the improvement is that for the two‐maxima doping profile the peaks of the carrier and ionized dopant densities are spatially separated, whereas for the simple one‐maximum doping profile they coincide. So, the carrier scattering on ionized dopants for the two‐maxima profile significantly decreases in comparison with the simple one‐maximum profile. The proposed two‐maxima delta‐layer doping profile can be used for the creation of diamond‐based micro‐ and nanoelectronics devices, e.g. high‐frequency field effect transistors.

     

Comparative study of single and multi domain CVD graphene using large‐area Raman mapping and electrical transport characterization

We systematically investigate the impact of granularity in CVD graphene films by performing Raman mapping and electrical characterization of single (SD) and multi domain (MD) graphene. In order to elucidate the quality of the graphene film, we study its regional variations using large‐area Raman mapping and compare the G and 2D peak positions of as‐transferred chemical vapor deposited (CVD) graphene on SiO₂ substrate. We find a similar upshift in wavenumber in both SD and MD graphene in comparison to freshly exfoliated graphene. In our case, doping could play the dominant role behind the observation of such upshifts rather than the influence due to strain. Interestingly, the impact of the polymer‐assisted wet transfer process is the same in both the CVD graphene types. The electrical characterization shows that SD graphene exhibits a substantially higher (a factor 5) field‐effect mobility when compared to MD graphene. We attribute the low sheet resistance and mobility enhancement to a decrease in charge carrier scattering thanks to a reduction of the number of grain boundaries and defects in SD graphene.     

CuNi binary alloy catalyst for growth of nitrogen‐doped graphene by low pressure chemical vapor deposition

The CuNi binary alloy can be significant as a catalyst for nitrogen‐doped (N‐doped) graphene growth considering controllable solubility of both carbon and nitrogen atoms. Here, we report for the first time the possibility of synthesizing substitutional N‐doped bilayer graphene on the binary alloy catalyst. Raman spectroscopy, atomic force microscopy and transmission electron microscopy analysis confirm the growth of bilayer and few‐layer graphene domains. X‐ray photoelectron spectroscopy analysis shows the presence of around 5.8 at% of nitrogen. Our finding shows that large N‐doped bilayer graphene domains can be synthesized on the CuNi binary alloy.

     

Chromatographic paper embedded with silver nanostructure as a disposable substrate for surface‐enhanced Raman spectroscopy and catalytic reactor

The high cost of regular diagnostic kits severely impeded its uses for routine clinical assay and fieldworks. A cost‐effective chromatography paper is chemically modified with Ag nanostructures using the simple electroless silver deposition, producing a scalable and disposable substrate for surface‐enhanced Raman spectroscopy, as well as a large scale of catalytic active sites over many chemical reactions. Synergetic measurement including surface‐enhanced Raman spectroscopy and laser desorption ionization‐mass spectrometry is performed on Ag decorated filter paper using a thiol containing compound as indicator, allowing for the acquisition of spatially correlated spectroscopy in the tandem mode. In addition, hydrophilic porous cellulose network that contains a certain amount of liquid naturally served as a chemical reactor for molecular transport and reaction. Positive results from catalytic reaction on metallized paper convincingly demonstrated that total microanalysis system on paper (μ‐TASoP), as a compelling alternative would find a wide breadth of applications in developing disposable medical devices and customary laboratory assays. Copyright © 2015 John Wiley & Sons, Ltd.     

Investigation of optical emission spectroscopy in diamond chemical vapor deposition by Monte Carlo simulation

The optical emission spectra(atomic hydrogen(Hα,Hβ,Hγ),atomic carbon C(2p3s→2p2:λ=165.7 nm) and radical CH(A2△→X2П:λ=420-440 nm))in the gas phase process of the diamond film growth from a gas mixture of CH4 and H2 by the technology of electron-assisted chemical vapor deposition (EACVD)have been investigated by using Monte Carlo simulation.The results show that the growth rate may be enhanced by the substrate bias due to the increase of atomic hydrogen concentration and the mean temperature of electrons.And a method of determining the mean temperature of electrons in the plasma in-situ iS given.The strong dependence on substrate temperature of the quality of diamond film mainly attributes to the change of gas phase process near the substrate surface.