A. Kovalskiy

Chalcogenide glass e-beam and photoresists for ultrathin grayscale patterning

The advantages and applications of chalcogenide glass ChG thin film photoresists for grayscale lithography are demonstrated. It is shown that the ChG films can be used to make ultrathin 600 nm, high-resolution grayscale patterns, which can find their ap- plication, for example, in IR optics. Unlike polymer photoresists, the IR transparent ChG patterns can be useful as such on the surface or can be used to transfer the etched pattern into silicon or other substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater etch selectivity than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR region. The optical functionality of the Fresnel lenses is confirmed. Application of silver pho- todissolution in grayscale lithography for microelectromechanical sys- tems MEMS applications is also shown. A substrate to ChG/silver thick- ness etching ratio of 10 is obtained for the transfer of patterns into silicon using reactive ion etching RIE, more than a fivefold increase compared to traditional polymer photoresist.

Structural paradigm of Se-rich Ge–Se glasses by high-resolution x-ray photoelectron spectroscopy

The structure of binary GexSe100−x chalcogenide glass family (0≤x≤30) is determined by high-resolution x-ray photoelectron spectroscopy (XPS). On the basis of compositional dependences of fitting parameters for Ge and Se core level XPS spectra, the ratio between edge- and corner-shared tetrahedra is determined. We find that this ratio for glasses with 20≤x≤30 is almost constant with a value same as for the high-temperature crystalline form of GeSe2.

Structural model of homogeneous As–S glasses derived from Raman spectroscopy and high-resolution XPS

The structure of homogeneous bulk As x S100− x (25 ≤ x ≤ 42) glasses, prepared by the conventional rocking–melting–quenching method, was investigated using high-resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. It is shown that the main building blocks of their glass networks are regular AsS3/2 pyramids and sulfur chains. In the S-rich domain, the existence of quasi-tetrahedral (QT) S = As(S1/2)3 units is deduced from XPS data, but with a concentration not exceeding ∼3–5% of total atomic sites. Therefore, QT units do not appear as primary building blocks of the glass backbone in these materials, and an optimally-constrained network may not be an appropriate description for glasses when x < 40. It is shown that, in contrast to Se-based glasses, the ‘chain-crossing’ model is only partially applicable to sulfide glasses.

Long-Term Physical Ageing in As-Se Glasses with Short Chalcogen Chains

Long-term physical ageing of chalcogenide glasses, which occurs over tens of years, is much less understood than the short-term ageing. With Se-rich underconstrained As30Se70 glass as a model composition (consisting of Sen chains with n≤3 on average), a microscopic model is developed for this phenomenon by combining information from differential scanning calorimetry, extended x-ray absorption fine structure, Raman, and 77Se solid state nuclear magnetic resonance spectroscopies. The accompanying changes in the electronic structure of these glasses are investigated by x-ray photoelectron spectroscopy. The data suggest ageing from cooperative relaxation, presumably involving bond switching or reconfiguration of As–Se–Se–As fragments.

Technological modification of spinel-based CuxNi1–x–yCo2yMn2–yO4 ceramics

Abstract The peculiarities of electroceramics formation in Cu x Ni 1– x – y Co 2 y Mn 2– y O 4 (0.1⩽ x ⩽0.8; 0.1⩽ y ⩽0.9– x ) system under different sintering conditions are studied by the methods of X-ray diffraction, optical microscopy, electron-probe microanalysis and electrical measurements. Structure-properties relations for these ceramic semiconducting materials, obtained at different sintering temperatures are discussed. The electrical conductivity and activation energy show strong dependence on sintering temperature. Two groups of investigated ceramics with a different character of electrical conductivity dependences on the temperature of sintering are distinguished. Obtained results are explained in the framework of the model of thermally induced cation rearrangement in octahedral and tetrahedral sites of electroceramics.

Structure of Se-rich As-Se glasses by high-resolution x-ray photoelectron spectroscopy

To establish the validity of various proposed structural models, we have investigated the structure of the binary As{sub x}Se{sub 100-x} chalcogenide glass family (x{<=}40) by high-resolution x-ray photoelectron spectroscopy. From the composition dependence of the valence band, the contributions to the density of states from the 4p lone pair electrons of Se and the 4p bonding states and 4s electrons of Se and As are identified in the top part of the band. The analysis of Se 3d and As 3d core-level spectra supports the so-called chain crossing model for the atomic structure of Se-rich As{sub x}Se{sub 100-x} bulk glasses. The results also indicate small deviations ({approx}3-8%) from this model, especially for glass compositions with short Se chains (25<x{<=}40). For example, the presence of As-As homopolar defect bonds in the stoichiometric As{sub 40}Se{sub 60} and of Se-Se-Se fragments in a glass with composition x=30 is established.

In search of energy landscape for network glasses

Quick scanning extended x-ray absorption fine-structure spectroscopy is used to obtain in situ structural information on the real-time response of network glasses at the nanoscale level of atomic organization to the temperature ramp through the glass transition range. The results testify nonlinear, real-time temperature response indicative of nanoscale dynamic heterogeneity in disordered systems with intermediate fragility, related to the intermetabasin transitions within potential energy/enthalpy landscape.

IR impurity absorption in Sb2S3–GeS2(Ge2S3) chalcogenide glasses

Abstract The IR optical transmission spectra in the 4000–1000 cm −1 (2.5–10 μm) region in the chalcogenide glasses (ChG) of the ternary Ge–Sb–S system of stoichiometric Sb 2 S 3 –GeS 2 and non-stoichiometric Sb 2 S 3 –Ge 2 S 3 compositions are studied. The compositional dependences of the measured IR spectra connected with influence of O-, H- and C-based absorbed impurites are analyzed.

Effect of Co60 γ-irradiation on the optical properties of As-Ge-S glasses

Abstract The influence of Co 60 γ-irradiation on the optical properties of chalcogenide semiconducting glasses from As 2 S 3 –Ge 2 S 3 cut-section is analyzed taking into account the accompanying spontaneous thermal annealing of the samples in the irradiation chamber. It is established that essential thermal heating of the investigated glasses during high-doses irradiation leads to the rough changes in compositional dependences of radiation-induced total (unrelaxed) and static (relaxed) optical effects. An attempt to describe dose dependence of the observed optical changes is made on the basis of stretched–exponential relaxation function.

Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary AsxSe100 − x, AsxS100 − x, GexSe100 − x and GexS100 − x chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.