Linear and nonlinear optical properties of transfer ribonucleic acid (tRNA) thin solid films

The denaturation of double-stranded deoxyribonucleic acid (ds-DNA) has been well known to break nucleobase bonds, resulting in single-stranded deoxyribonucleic acid (ss-DNA) in solutions, which can recombine to form ds-DNA in a reversible manner. We developed an efficient process to irreversibly maintain various DNA denaturation levels in thin solid films in order to investigate the impacts of the denaturation on the optical properties of DNA films. By adding NaOH in an aqueous solution of salmon testis DNA, we flexibly controlled the level of denaturation in the solution, which was then spin-coated on Si and silica substrates to irreversibly bind ss-DNAs in a thin solid film. The denaturation of DNA in thin solid films was experimentally confirmed by ultraviolet-visible and Fourier transform infrared spectroscopic investigations, whose level could be controlled by the NaOH content in the aqueous solution precursor. By this irreversible denaturation process, we developed a new method to flexibly vary the refractive index of DNA thin solid films in a wide range of Δn>0.02 in the visible to near-infrared range. Thermo-optic coefficients dn/dT of the films were also experimentally measured in the temperature range from 40°C to 90°C to confirm the significant impacts of denaturation. Detailed thin film processes and optical characterizations are discussed.

The first-order unified linear instability analysis (LISA) of the governing equation for the evolution of surfaces and interfaces under capillary, electromigration (EM), and elastostatic forces is developed. A formal treatment of the thermomigration (Soret effect) driven by the nonuniform temperature distribution caused by exothermic phase transformation (growth) at the surface and interfacial layers is presented and its apparent influence on the capillary force in connection with the stability is also established in a concise analytical form. This unified approach, which relies on a rigorous theory of irreversible thermodynamics of surfaces and interfaces, seriously considers the anisotropies associated with the generalized growth mobility, the interfacial specific Gibbs free energy (i.e., the surface stiffness), and the surface diffusivity in thin solid films. The singularity in the surface stiffness at the cusp regions of the Wulff construction of the surface Gibbs free energy is fully elaborated by using a modified cycloid-curtate function as a basis for generating the Dirac $\ensuremath{\delta}$ distribution, which shows an unusually strong anomalous effect on the surface morphological instability even in the absence of EM forces, as illustrated clearly by the graphical representation of the EM-induced instability threshold level as a function of tilt angle and wave number, in a three-dimensional plot for various intrinsic and normalized system parameters. In the development of LISA theory special attention is paid to the origin of the elastostatic forces, which include not only the elastic strain energy density, but also the elastic dipole tensor interaction between mobile atomic species and the applied stress field. The profound influence of the anomalous surface stiffness anisotropy on the surface morphological evolution under the applied stress system is demonstrated by three-dimensional computer graphics applied for copper and silicon thin single-crystal solid films having, respectively, sixfold {111}- and fourfold {100}-symmetric singular (vicinal) planes as the top surfaces, which reveal the fine features of the theory and give insight into some controversial issues related to LISA in the literature. This unified approach also considers the stress dependence of the generalized growth mobility and its profound influence on the stability of the interface displacement and roughening in thin solid films. As a special application of the theory, the effects of uniaxial and biaxial applied stresses on the recrystallization and the interfacial morphological evolution of amorphous Si deposited on silicon substrates are thoroughly analyzed and excellent quantitative agreement is found with the published experimental data in the literature.

Biomaterials based on deoxyribonucleic acid (DNA) have shown notable potential in optoelectronic and photonic devices. In order to further investigate the optical properties of a DNA-based lipid complex such as DNA-cetyltrimethylammonium (CTMA), which is widely used in current DNA thin film research, a new refinement process was developed to minimize the relative bound water content and control binding of CTMA onto the DNA backbone. The water contents and CTMA binding in the DNA-CTMA precipitates were identified by spectrometric measurements to quantify effects of our refinement process. Dissolving these refined DNA-CTMAs in organic solvents, thin solid films were deposited on Si and quartz substrate using the spin coating process. Their refractive indices and absorbance were measured to quantitatively assess the impact of our refinement process on the optical properties of the DNA-CTMA films. In addition, thermo-optic coefficients, dn/dT, were also measured in a temperature range from 30 to 100°C to observe differences among refined DNA-CTMAs. Detailed quantitative spectroscopic analyses and optical measurements are reported.

Generation of a coherent electromagnetic radiation in the far IR (THz) spectral range upon excitation of a semiconductor InAs crystal by 70-fs Ti: sapphire laser pulses is studied. The effect of a magnetic field of different orientation on generation in the submillimeter-wavelength range is analyzed. Placing the crystal into the magnetic field of an optimized permanent magnet with a strength of 5 kOe aligned along the surface of the semiconductor increased the power of generated radiation by a factor of six compared with that in the absence of the field. For the average pump-laser output power of 150 mW and repetition rate of 80 MHz, the average power of the THz radiation reached 100 nW. For detection of ultrashort pulses of the THz radiation, we used, for the first time, a highly sensitive uncooled optoacoustic detector, which detected signals with a power lower than 1 nW.

Investigation of the mechanism of the UV-induced palladium deposition process from thin solid palladium acetate films

Multilayers (MLs) of 31 bi-layers and a 10-nm layer thickness each of Si/SiC were deposited on silicon, quartz and mullite substrates using a high-speed, ion-beam sputter deposition process. The samples deposited on the silicon substrates were used for imaging purposes and structural verification as they did not allow for accurate electrical measurement of the material. The Seebeck coefficient and the electrical resistivity on the mullite and the quartz substrates were reported as a function of temperature and used to compare the film performance. The thermal conductivity measurement was performed for ML samples grown on Si, and an average value of the thermal conductivity was used to find the figure of merit, zT, for all samples tested. X-ray diffraction (XRD) spectra showed an amorphous nature of the thin films. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the film morphology and verify the nature of the crystallinity. The mobility of the multilayer films was measured to be only 0.039 to 1.0 cm2/Vs at room temperature. The samples were tested three times in the temperature range of 300 K to 900 K to document the changes in the films with temperature cycling. The highest Seebeck coefficient is measured for a Si/SiC multilayer system on quartz and mullite substrates and were observed at 870 K to be roughly −2600 μV/K due to a strain-induced redistribution of the states’ effect. The highest figure of merit, zT, calculated for the multilayers in this study was 0.08 at 870 K.

Femtosecond laser micromachining has been used to write bulk waveguides and photonic devices in glasses, polymers, and crystalline silicon (Gattass and Mazur, Nat Photonics 2:219–225, 2008). Refractive index changes in these materials tend to be less than a percent, which sets limitations on applications due to low light confinement. Hydrogenated amorphous silicon (a-Si:H) presents a unique, versatile material platform with incredible potential. Variations in the hydrogen content can produce refractive index changes as high as 40–80 % (Fortmann et al. Thin Solid Films 395:142–146, 2001). There is potential for integration on a silicon platform. We use femtosecond laser micromachining to locally reduce the hydrogen content of the material, with the goal of increasing the refractive index. We will use this method to directly write three-dimensional (3D) photonic devices in a-Si:H. This novel, simple method for photonic device fabrication in a-Si:H will facilitate many applications and device integration. Femtosecond laser processing enables 3D fabrication through nonlinear interactions. An ultrafast pulsed laser is focused inside the bulk of a transparent material. Due to tight focusing, material modifications only occur at the focal point of the laser. Complex patterns can by written by translating the sample with respect to the laser focus using x-, y- and z-translation. Intensity dependence of nonlinear processes enables fabrication of features with dimensions below the diffraction limit of light through careful selection of laser exposure. 3D fabrication allows greater versatility in devices and can increase device density, which is critical for modern optics and electronics where space is at a premium. Waveguide fabrication through variations in hydrogen content has been demonstrated in 2D using traditional micro- and nano-fabrication techniques (Fortmann et al. Thin Solid Films 430:278–282, 2003; 501:350–353, 2006). This process requires many steps, including ion implantation to locally control hydrogen content. The waveguides consist of regions with low hydrogen content. Fabrication of 3D photonic devices would require stacking many 2D layers. We are developing femtosecond laser processing to directly write complex 3D patterns in a single-step process, introducing greater versatility and processing speed. We have succeeded in lowering the hydrogen concentration in 2D patterns within a 1-μm film of a-Si:H using a near infrared (1,050 nm) femtosecond laser. Contrast is visible between unaltered and laser processed material under optical microscopy, suggesting index changes due to a reduction in hydrogen content. Contrast increase with laser fluence or a greater number of incident laser pulses. AFM measurements verify that regions with reduced hydrogen content do not exhibit changes in surface topography. We used Raman spectroscopy to verify the reduction in hydrogen content by examining the intensity ratio of Si-H bonding peaks (2,000 and 2,100 cm−1) to Si-Si bonding around 480 cm−1 (Fig. 58.1). A reduction in the Si-H intensity corresponds to reduced hydrogen content (Brodsky et al. Phys Rev B 16:3556–3571, 1977). These initial results provide a proof of concept and valuable knowledge for the fabrication of devices.

In this study, we investigated the magnetic and magneto-optical properties of Bi1.5Y1.5Fe5O12 (Bi:YIG) films prepared on quartz and silicon substrates, respectively, by radio frequency magnetron sputtering and disposed by microwave annealing. The results indicated that the lattice constant and magnetic properties were significantly different on different substrates. First, the lattice constant of film on quartz substrate was found to be 9% greater than that on silicon substrate because of larger residual stress. Second, the grain size of film on silicon substrate was smaller than that on quartz substrate at same annealing temperature, which led to its magnetization being 70% smaller than that on quartz substrate and coercive force was 50% less. Finally, the transmittance of the Bi:YIG film and pure YIG was studied and the Faraday angle of Bi1.5Y1.5Fe5O12 film on quartz substrate was found to be − 8°/µm at λ = 544 nm and − 1.8°/µm at λ = 677 nm.

Defect transformations in nitrogen-doped CVD diamond during irradiation and annealing

We compared the heating and cooling theoretical and experimental transient times of DyPO4 nanoparticles as a result of their heating by themultiphonon relaxation after femtosecond laser excitation in the near IR spectral range into different absorption spectral lines of the Dy3+ ion. We have shown that the relaxation of the heat flux to a stationary value occurs according to an exponential law. Depending on the value of the Biot number, two different relaxation mechanisms can be realized, in one of which the relaxation time depends on the thermal conductance of the interface, and in the other on the thermal diffusivity. It is shown that, after averaging over the ensemble of nanoparticles, the kinetics of the relaxation of the heat flux in these limiting cases has a substantially different character. The results might be helpful for assessing the prospects of the dielectric crystalline nanoparticles doped with rare-earth ions in the local hyperthermia treatment of cancer cells.

The smooth surface of the amorphous Al2O3 film on either silicon or quartz, coated by atomic layer deposition (ALD), was changed to rough surface by annealing in either air or hydrogen at high temperature (745°C) due to the formation of nanosized pinholes and micrometre pimples during the crystallisation of the amorphous Al2O3. The rough surface makes the growth of long carbon nanotubes (CNTs) by chemical vapour deposition impossible. Nevertheless, we were able to develop new catalyst recipes for successful growth of vertically aligned CNTs on ALD-Al2O3 coated silicon and quartz substrates. The lengths of the CNTs reached 90 µm on silicon substrates and 180 µm on quartz substrates. Furthermore, it is observed that the adhesion of CNTs on silicon substrates is much stronger than that on quartz substrates.

Though fullerenes have been revolutionizing photovoltaic technology over the last decades,20, 188190 they are being replaced by nonfullerene acceptors.28, 191 Albeit many upsides of fullerenes ranging from multiple charge acceptance to isotropic charge mobility are commendable; downsides like low visible light absorption and poor tunability of electronic energy levels and high cost are limiting their usability. Some earlier research was targeted towards the synthesis of structurally elegant and functional fullerene assemblies bound by multiple noncovalent interactions.48, 192 However, just a few research on van der Waals (vdW) dimers and photopolymerized fullerenes unveiled presence of charge traps149 and high electron affinities67 which are detrimental for photovoltaic performance. This early research has initiated the development of a holistic framework to understand how supramolecular structure determines optoelectronic properties. This has been the prime scientific challenge in fullerene electronics in the recent years.192 This thesis not only ddresses the above mentioned challenge and bridges the gap between single molecule and device level, but strives to reach the grand target of alleviating the fundamental limitations of fullerenes (also see Figure 11 and Figure 12). This is done by tailoring the optoelectronic properties of the amphiphilic fullerene derivative MPEGC60, by supramolecular structural control on thin solid films.

Carbon-rich amorphous silicon carbide and silicon carbonitride films for silicon-based photoelectric devices and optical elements: Application from UV to mid-IR spectral range

Optical limiting properties in copper oxide thin films under a high-repetition-rate femtosecond laser

Vertically aligned N-doped carbon nanotubes by spray pyrolysis of turpentine oil and pyridine derivative with dissolved ferrocene