Nanostructured silver substrates with stable and universal sers properties: Application to organic molecules and semiconductor nanoparticles

Nanostructured silver films have been prepared by thermal deposition on silicon, and their properties as SERS substrates investigated. The optimal conditions of the post-growth annealing of the substrates were established. Atomic force microscopy study revealed that the silver films with relatively dense and homogeneous arrays of 60-80-nm high pyramidal nanoislands are the most efficient for SERS of both organic dye and inorganic nanoparticles analytes. The noticeable enhancement of the Raman signal from colloidal nanoparticles with the help of silver island films is reported for the first time. © 2009 The Author(s)

Investigation of electron-phonon interaction in bulk and nanostructured semiconductors

In this paper, the problem of electron-phonon interaction (EPI) innsemiconductor crystals and quantum dots (QDs) is considered. It is shown that the model of strong EPI developed for organic molecular crystals can be successfully applied to bulk and nanosized semiconductors. The idea of the approach proposed here is to describe the experimental Raman (or absorption) spectra containing the phonon replicas theoretically by varying the EPI constant. The main parameter of the theoretical expression describing the experimental spectrum is the ratio of EPI constant to the frequency of the corresponding phonon mode. Based on the experimental and theoretical results, we have found that decreasing the size of CdSxSe₁₋x QDs embedded in borosilicate glass matrix results in some enhancement of electron-phonon interaction

Physical properties of nanocrystaline PbS synthesized by electrolytic method

The possibility of obtaining nanocrystaline lead sulfide by an electrolytic method using lead electrodes is demonstrated, and the influence of temperature on the synthesis process is investigated. Based on the results of X-ray diffraction studies, the chemical and phase composition of the obtained samples is determined, as well as the parameters of the unit cell of the crystals lattice. The size of the nanocrystallites and the magnitude of residual mechanical strain in them is determined using the methods of Debye-Scherrer and Williamson-Hall. The results of X-ray diffraction are in agreement with the results of the Raman scattering on phonons

Facile SERS substrates from Ag nanostructures chemically synthesized on glass surfaces

A quick one-step fabrication of efficient SERS substrates by a modified approach based on a silver-mirror reaction (using Tollens’ reagent) is reported. Commercially available microscope slides or cover glass (coverslips) were used as-received, without special surface treatment. In contrast to the commonly used two-step process, the composition of the Tollens reagent was modified to use a single-step process. The obtained rather homogeneous films of densely packed nanoislands are promising for application as substrates for Surface-Enhanced Raman Scattering (SERS), as demonstrated by several different kinds of molecules as analytes. In particular, the achieved level of detection of a standard dye analyte, down to 10-14 M of Rhodamine 6G, is in the range of best values reported in the literature. Low concentrations of some biomolecules are also detected, such as lysozyme (10-4 M), adenine (10-4 M), and salicylic acid (10-5 M). For some analytes, stronger SERS was observed in the drop, and for others after the solvent was dried. The possible reasons for this effect are described. By applying thermal annealing in the inert gas atmosphere, the Ag film morphology can be partially converted into a coral-like 3D structure that may be advantageous for the localization of the analyte in the “hot spots” and allow additional spectral tunability of the plasmon resonance

SERS of Rhodamine 6G on substrates with laterally ordered and random gold nanoislands

Preparation and study of laterally ordered and disordered arrays of Au nanoislands as SERS substrates are reported. Developed technology allows obtaining SERS substrates with long-term stability (up to six months), efficient (up to 10⁴) and laterally homogenous enhancement of the Raman signal from molecular analyte. The substrates developed are suitable for Raman bio-diagnostics, because their plasmon resonance can be tuned within the range 700-900 nm that falls into the transparency window of human tissues. The dependence of optical and enhancement properties of the substrates on their morphology has been studied. The morphology of the Au island film and their plasmon resonance spectrum depend noticeably on the nominal Au thickness and post-annealing temperature, while the duration of annealing is of minor importance. Formation of nanoholes in the case of Au substrates on holographically pre-patterned polymer film opens up the possibility of additional Raman enhancement via the "hot spot"-effect

Optical and acoustical phonon modes in superlattices with SiGe QDs

Multilayers with SiGe nanoislands grown in a broad temperature range (300-600 °C) are studied using Raman spectroscopy, HRXRD and AFM. It is shown that the islands are fully strained when obtained at 300 °C and gradually relax with the growth temperature increase. The main contribution to the Raman peaks caused by scattering on folded acoustic phonons in multilayers (n ≤ 10) with nanoislands is due to the islands themselves. The enhancement of the scattering intensity due to resonance of the exciting light with the electronic transitions inside the islands is shown to play a significant role

Optically Induced Structural Transformation in Disordered Kesterite Cu2ZnSnS4

The kesterite structured semiconductor Cu2ZnSnS4is one of the most promising compound for earth abundant low cost solar cells. One of the complex problem on this way deals with its stoichiometry. In this work Raman spectra of Cu rich Cu2ZnSnS4 crystals are discussed in connection with the non stoichiometric composition and disordering within the cat ion sublattice of the kesterite. The shift of the main A peak from 338 to 331 cm 1 and its broadening are attributed here to transition from the kesterite I 4symmetry to the disordered kesterite structure I 2m symmetry . It is shown that this transition may also be driven by an intense light, which could stimulate transformation of Cu ion to Cu2 ions and facilitates generation of CuZn defects on 2d crystalographic position

Influence of the dispersion medium on the properties of CdTe micro- and nanocrystals in a colloidal solution

Surface and optical properties of CdTe nanoparticles obtained by grinding (40-150 nm, microcrystals) and colloidal synthesis (1-4 nm, nanocrystals) methods are investigated. It is shown that the most intensive adsorption of stabilizer molecules on the CdTe surface occurs when solvents are better wetting the surface of CdTe particles. It is found that the best stabilization of both the micro- and nanocrystals of CdTe is provided by using methyl and ethyl alcohol as the dispersion medium. The basic characteristics of photoluminescence of CdTe nanocrystals stabilized with thioglycolic acid in deionized water, methanol and ethanol of various concentrations are reported

Thin films of Cu₂ZnSnS₄ for solar cells: optical and structural properties

The structure of Cu₂ZnSnS₄ films was investigated by Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, optical reflectance and photoluminescence. The films were formed by thermal annealing layers of copper, zinc and tin sulfides on glass substrates at different substrate temperature and ambient atmosphere. It was revealed that the films have the dominant structure of kesterite with possible inclusions of stannite Cu₂ZnSnS₄ structure. Under certain growth conditions, however, segregation of Cu₂₋xS occurs, as proved by registering the characteristic peak in Raman spectra. No traces of secondary phases of zinc or tin sulphides are found

Strain relaxation in thin Si₁-ₓ-yGeₓCy layers on Si substrates

The possibility to obtain a heterosystem consisting of the upper partially strained and lower relaxed layers by gradient in situ doping of SiGe layers with carbon is considered. The properties of the as-grown and annealed (600 to 1000℃) samples have been studied by Raman spectroscopy and atomic force microscopy. The strain relaxation degree in the as-grown layers as estimated from the Raman spectra amounts 50 % for Si₀.₇-ʸGe₀.₃Сʸ and 0 % for Si₀.₉-ʸGe₀.₁Сʸ. During the annealing, the strain has been found to be relaxed not homogeneously over the whole structure but in a layer-by-layer way. The segregation of carbon atoms is observed for both types of as-grown Si₁-ₓ-ʸGeₓСʸ layers in the near-substrate regions.Розглянуто можливiсть отримання вiдрелаксованих sige шарiв на кремнiєвiй пiдкладцi, що градiєнтно in situ легувалися вуглецем у процесi епiтаксiї. Використовуючи спектроскопiю комбiнацiйного розсiювання свiтла (КРС) та атомну силову мiкроскопiю, дослiджено властивостi вихiдних зразкiв та зразкiв пiсля термiчних обробок у дiапазонi температур 600-1000℃. Iз спектрiв КРС оцiнено ступiнь пластичної релаксацiї у вихiдному Si₀.₇-ʸGe₀.₃Сʸ (50 %) та Si₀.₉-yGe₀.₁Сʸ (0 %) шарах. Встановлено, що при вiдпалах релаксацiя напружень вiдбувається не однаково по всьому об'єму, а пошарово. В обох типах Si₁-ₓ-ʸGeₓСʸ шарiв на їх iнтерфейсах з Si пiдкладками вiдбувається сегрегацiя вуглецю.Рассмотрена возможность получения отрелаксированных sige слоев на кремниевой подложке, градиентно in situ легированных углеродом в процессе эпитаксии. Используя спектроскопию комбинационного рассеяния света (КРС) и атомную силовую микроскопию, исследованы свойства исходных образцов и образцов после термических обработок в диапазоне температур 600-1000℃. Из спектров КРС оценена степень пластической релаксации в исходном Si₀.₇-ʸGe₀.₃Сʸ (50 %) и Si₀.₉-ʸGe₀.₁Сʸ (0 %) слоях. Установлено, что релаксация напряжений при отжигах происходит не однородно по всему объему, а послойно. В обоих типах Si₁-ₓ-ʸGeₓСʸ слоев происходит сегрегация углерода на интерфейсах с Si подложками