Red organic light-emitting diodes with high efficiency,low driving voltage and saturated red color realized via two step energy transfer based on ADN and Alq3 co-host system

We demonstrated efficient red organic light-emitting diodes based on a wide band gap material 9,10-bis(2-naphthyl)anthracene (ADN) doped with 4-(dicyano-methylene)-2-t-butyle-6-(1,1,7,7-tetramethyl-julolidyl-9-enyl)-4H-pyran (DCJTB) as a red dopant and 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10(2-benzothiazolyl)quinolizine-[9,9a,1gh]coumarin (C545T) as an assistant dopant. The typical device structure was glass substrate/ITO/4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA)/N,N′-bis(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB)/[ADN:Alq₃]:DCJTB:C545T/Alq₃/LiF/Al. It was found that C545T dopant did not by itself emit but did assist the energy transfer from the host (ADN) to the red emitting dopant via cascade energy transfer mechanism. The OLEDs realized by this approach significantly improved the EL efficiency. We achieved a significant improvement regarding saturated red color when a polar co-host emitter (Alq₃) was incorporated in the matrix of [ADN:Alq₃]. Since ADN possesses a considerable high electron mobility of 3.1 × 10⁻⁴ cm²  V⁻¹ s⁻¹, co-host devices with high concentration of ADN (>70%) exhibited low driving voltage and high current efficiency as compared to the devices without ADN. We obtained a device with a current efficiency of 3.6 cd/A, Commission International d’Eclairage coordinates of [0.618, 0.373] and peak λ_max = 620 nm at a current density of 20 mA/cm². This is a promising way of utilizing wide band gap material as the host to make red OLEDs, which will be useful in improving the electroluminescent performance of devices and simplifying the process of fabricating full color OLEDs.     

Efficient red light phosphorescence emission in simple bi-layered structure organic devices with fluorescent host-phosphorescent guest system

Highly efficient red phosphorescent devices comprising a simple bi-layered structure using tris(1-phenylisoquinoline)iridium (Ir(piq)₃) doped in a narrow band-gap fluorescent host material, bis(10-hydroxybenzo [h] quinolinato)beryllium complex (Bebq₂) are reported. The driving voltage to reach 1000 cd/m² is 3.5 V in Bebq₂:Ir(piq)₃ red phosphorescent device. With a dopant concentration of as low as 4%, the current and power efficiency values of 8.41 cd/A and 7.34 lm/W are obtained in this PHOLEDs, respectively. External quantum efficiency (EQE) of 14.5% is noticed in this red phosphorescent device, promising to high brightness applications.     

Synthesis,crystal growth and characterization of a semiorganic material: Calcium dibromide bis(glycine) tetrahydrate

Single crystals of semiorganic material calcium dibromide bis(glycine) tetrahydrate were grown from aqueous solution. The crystal belongs to monoclinic system, with a = 13.261(5) Å, b = 6.792(2) Å, c = 15.671(9) Å and β = 91.68(4)°. The presence of the elements in the title compound was confirmed by energy dispersive X-ray analysis. The solubility and metastable zone width were found. The grown crystals were tested by powder XRD, FTIR, Thermo Gravimetric and Differential Thermal Analysis, UV–vis–NIR analysis, dielectrical and mechanical studies. The transmittance of calcium dibromide bis(glycine) tetrahydrate crystal has been used to calculate the refractive index n, the extinction coefficient K and both the real ɛ_r and imaginary ɛ_i components of the dielectric constant as functions of wavelength. The optical band gap of calcium dibromide bis(glycine) tetrahydrate is 3.23 eV.     

An organic electroluminescent device made from a gadolinium complex

A gadolinium ternary complex, tris(1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone) (phenanthroline) gadolinium [Gd(PMIP)₃(Phen)] was synthesized and used as a light emitting material in the organic electroluminescent (EL) devices. The triple layer device with a structure of indium tin oxide (ITO)/N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) (20 nm)/Gd(PMIP)₃(Phen) (80 nm)/2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (bathocuproine or BCP) (20 nm)/Mg: Ag(200 nm)/Ag(100 nm) exhibited green emission peaking at 535 nm. A maximum luminance of 230 cd/m² at 17 V and a peak power efficiency of 0.02 lm/w at 9 V were obtained.     

High-efficiency organic light-emitting diodes (OLEDs) with a mixed layer structure

Improved performance of organic light-emitting diodes (OLEDs) as obtained by a mixed layer was investigated. The OLEDs with a mixed layer which were composed of N,N′-diphenyl-N,N′-bis(1-napthyl-phenyl)-1,1′-biphenyl-4,4′-diamine (NPB), tris-(8-hydroxyquinolato) aluminum (Alq₃) and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) showed the highest brightness and efficiency, which reached 19048 cd/m² at 17 V and 4.3 cd/A at 10 mA/cm², respectively. The turn-on voltage of the device is 2.6 V. Its Commission Internationale del’Eclairage (CIE) coordinate is (0.497, 0.456) at 17 V, and the CIE coordinates of the device are largely insensitive to the driving voltages, which depicts stabilized yellow color.     

Solution-processed white organic light-emitting diodes with mixed-host structures

Efficient white light-emitting diodes (WOLEDs) were fabricated with a solution-processed single emission layer composed of a molecular and polymeric material mixed-host (MH). The main host used was a blue-emitting molecular material of 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) and the assisting host used was a hole-transport-type polymer of poly(9-vinylcarbazole) (PVK). By co-doping 4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl and 5,6,11,12-tetraphenylnaphacene into the MH, the performances of the fabricated devices made with different mixing ratio of host materials were investigated, and were to depend on the mixing ratios. Under the optimal PVK:DPVBi ratio (3:7), we achieved a maximum luminance of 14 110 cd/m² and a maximum current efficiency of 9.5 cd/A. These improvements were attributed to the MH structure, which effectively improved the thermal stability of spin-coated film and enhanced the hole-injection/transporting properties of WOLEDs.     

High temperature protonic conduction in Sr-doped LaP3O9

Electrical conduction of Sr-doped LaP₃O₉ ([Sr]/{[La] + [Sr]} = 2–10 mol%) was investigated under 0.4–5 kPa of p(H₂O) and 0.01–100 kPa of p(O₂) or 0.3–3 kPa of p(H₂) at 573–973 K. Sr-doped LaP₃O₉ showed apparent H/D isotope effect on conductivity regardless of the Sr-doping level under both H₂O/O₂ oxidizing and H₂/H₂O reducing conditions at investigated temperatures. Conductivities of the material were almost independent of p(O₂) and p(H₂O). These results demonstrated that the Sr-doped LaP₃O₉ exhibited protonic conduction under wide ranges of p(O₂), p(H₂O) and temperature. The conductivity of the Sr-doped LaP₃O₉ increased with increasing Sr concentration up to its solubility limit, ca. 3 mol%, while the further Sr-doping slightly degraded the conductivity. These indicate that Sr²⁺ substitution for La³⁺ leads to proton dissolution into the material and induced protonic conduction. Conductivities of the 3 mol% Sr-doped sample were 2 × 10^- 6–5 × 10^− 4 S cm^− 1 at 573–973 K.     

Synthesis,measurements, and theoretical analysis of carbazole derivatives with high-triplet-energy

In order to obtain the blue light-emitting organic materials with high triplet state energy, two 3,5-diphenyl-4H-1,2,4-triazole (Tz) containing carbazole (Cz) derivatives of 9-(4-(3,5-diphenyl-4H-1,2,4-triazol-4-yl)phenyl)-9H-carbazole (TzCz1) and 3,6-di-tert-butyl-9-(4-(3,5-diphenyl-4H-1,2,4-triazol-4-yl)phenyl)-9H-carbazole (TzCz2) are synthesized using Cz acting as the starting material, as well as characterized by the ¹H NMR spectra, ultraviolet–visible (UV–vis) absorption spectra, and the IR absorption spectra. The luminescence quantum yields (LQYs) of TzCz1 and TzCz2 are measured in CH₂Cl₂ solution to be 32.1% and 47.5%, respectively. The electrochemical analysis and the photophysical measurements suggest that the triplet energy levels and the energy gaps of the highest-occupied orbital and the lowest-unoccupied orbital are 2.83 eV and 3.59 eV for TzCz1, and 2.80 eV and 3.43 eV for TzCz2. At last, the theoretical analyses of their ground state geometries and the simulated UV–vis absorption spectra are carried out at B3LYP1/6-31G? level. The studies mentioned above indicate that both TzCz1 and TzCz2 are suitable for the host materials of blue light-emitting diodes.     

Influence of thickness of functional layer on performance of organic salt-doped OLED with ITO/PVK:PBD:TBAPF6/Al structure

The effect of thickness of functional layer on the electrical and electroluminescence (EL) properties of single-layer OLED with ITO/PVK:PBD:TBAPF₆/Al structure were investigated where indium tin oxide (ITO) was used as anode, poly(9-vinylcarbazole) (PVK) as polymeric host, 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as electron-transporting molecule, tetrabutylammonium hexafluorophosphate (TBAPF₆) as organic salt dopant and aluminium (Al) as cathode. A unique transition phenomenon at high bias voltage in the devices was observed and the transition was reversible. The transition voltage and turn on voltage decreased with the decrease of functional layer thickness. The turn on voltage was approximately 5.5 V and 6.5 V for 55-nm-thick and 95-nm-thick devices, respectively. However, the current efficiency of 95-nm-thick device was higher than the 55-nm-thick device. More interestingly, the Commission Internationale d’Eclairage (C.I.E.) coordinates of EL spectra of 95-nm-thick device at bias voltage ranging from 7 V to 13 V located in the white light region even without any dye doping. The PL and EL spectra were found completely different. PBD electromer was proposed to dominate the EL spectrum, but the contribution from PVK–PBD electroplex cannot be completely ruled out.     

Structural,optical and electrical properties of europium picrate tetraethylene glycol complex as emissive material for OLED

A new europium complex [Eu(Pic)₂(H₂O)(EO4)](Pic)·0.75H₂O was synthesized and used as the emission material for the single layer device structure of ITO/EO4–Eu–Pic/Al, using a spin-coating technique. Study on the optical properties of the [Eu(Pic)₂(H₂O)(EO4)](Pic)·0.75H₂O complex where EO4=tetraethylene glycol and Pic=picrate anion, had to be undertaken before being applicable to the study of an organic light emitting diode (OLED). The electrical property of an OLED using current–voltage (I–V) measurement was also studied. In complex, the Eu(III) ion was coordinated with the EO4 ligand as a pentadentate mode, one water molecule, and with two Pic anions as bidentate and monodentate modes, forming a nine-coordination number. The photoluminescence (PL) spectra of the crystalline complex in the solid state and its thin film showed a hypersensitive peak at 613.5–614.9 nm that assigned to the ⁵D₀→⁷F₂ transition. A narrow band emission from the thin film EO4–Eu–Pic was obtained. The typical semiconductor I–V curve of device ITO/EO4–Eu–Pic/Al showed the threshold and turn on voltages at 1.08 and 4.6 V, respectively. The energy transfer process from the ligand to the Eu(III) ion was discussed by investigating the excitation and PL characteristics. Effect of the picrate anion on the device performance was also studied.     

Study of EVOH based single ion polymer electrolyte: Composition and microstructure effects on the proton conductivity

A comb-like EVOH based single ion polymer electrolyte (EVOH-g-SPEG) was synthesized by sulfonification of EVOH grafts 2-(2-chloroethoxy) ethanol (C₄H₉O₂Cl)/2-[2-(2-chloroethxy) ethoxy] ethanol (C₆H₁₃O₃Cl) with 1, 3-propane sultone. The main chain of the comb-like polymer is hydrophobic polyethylene segments; the side chain is hydrophilic poly (ethylene glycol) (PEG) segment, which can solubilize large amounts of inorganic salts. The sulfonic acid group was introduced onto the end of the PEG side chain. The acid form of SPE was successfully obtained by being dialyzed from the products with acid solution. The saturation water sorption of EVOH-g-SPEG membrane increased with the side chain length and the immersion time. The XRD results indicate that the water in SPE membrane region can destroy the membrane crystalline structure and the water absorption membranes are nearly amorphous. AFM phase images of the hydration membranes clearly show the hydrophilic domains, with sizes increasing from 10 to 35 nm as a function of the side chain length. A phase inversion could be observed when n ≥ 5, which was consistent with a rapid increase in water absorption. And the ion conductivity is also measured by AC impedance. The conductivity is greatly influenced by ion exchange capacity and water sorption. The comb-like EVOH-g-SPEG polymer electrolyte grafts with 2 PEG side chain provides the highest ionic conductivity (1.65 × 10^− 3 S cm^− 1). The comb-like polymer could be a candidate as new polymeric electrolyte material for fuel cells and other electrochemical devices.     

Cavitation milling of natural cellulose to nanofibrils

Cavitation holds the promise of a new and exciting approach to fabricate both top down and bottom up nanostructures. Cavitation bubbles are created when a liquid boils under less than atmospheric pressure. The collapse process occurs supersonically and generates a host of physical and chemical effects. We have made an attempt to fabricate natural cellulose material using hydrodynamic as well as acoustic cavitation. The cellulose material having initial size of 63 micron was used for the experiments. 1% (w/v) slurry of cellulose sample was circulated through the hydrodynamic cavitation device or devices (orifice) for 6 h. The average velocity of the fluid through the device was 10.81 m/s while average pressure applied was 7.8 kg/cm². Cavitation number was found to be 2.61. The average particle size obtained after treatment was 1.36 micron. This hydrodynamically processed sample was sonicated for 1 h 50 min. The average size of ultrasonically processed particles was found to be 301 nm. Further, the cellulose particles were characterized with X-ray diffraction (XRD) and differential scanning calorimetry (DSC) to see the effect of cavitation on crystallinity (X_c) as well as on melting temperature (T_m). Cellulose structures consist of amorphous as well as crystalline regions. The initial raw sample was 86.56% crystalline but due to the effect of cavitation, the crystallinity reduced to 37.76%. Also the melting temperature (T_m) was found to be reduced from 101.78 °C of the original to 60.13 °C of the processed sample. SEM images for the cellulose (processed and unprocessed) shows the status and fiber–fiber alignment and its orientation with each other. Finally cavitation has proved to be very efficient tool for reduction in size from millimeter to nano scale for highly crystalline materials.     

Deposition of device quality amorphous silicon and solar cell from argon dilution of silane

In our present study hydrogenated amorphous silicon (a-Si:H) thin films and solar cells have been prepared in a conventional single chamber rf-PECVD unit from silane–argon mixture by varying radio frequency (rf) power densities from 6 mW/cm² to 50 mW/cm². By optimizing the properties of the intrinsic material we have chosen a material which is deposited at 6 mW/cm² rf power density, 0.2 Torr pressure, 175 ^oC substrate temperature and by 97% argon dilution. For this material minority carriers (holes) diffusion length (L_d) measured in the as deposited state is 180 nm and it degrades by 15% after light soaking. This high L_d value indicates that the material is of device quality. We have fabricated a single junction solar cell having the structure p-a-SiC:H/i-a-Si:H/n-a-Si:H without optimizing the doped layers. This set exhibits a mean open circuit voltage of 0.8 V and conversion efficiency of 7.7%. After light soaking conversion efficiency decreases by 15% which demonstrates that it is possible to deposit device grade material and solar cells from silane–argon mixture.     

Synthesis and electroluminescent characterization of a symmetric starburst orange-red light material

A new symmetric starburst orange-red light material, tris(4-(2-(N-butyl-1,8-naphthalimide)ethynyl)phenyl)amine (TNGT), was designed and synthesized. It shows a high fluorescence quantum yield and a slight concentration-quenching effect. A high brightness (6600 cd/m²) and a high current efficiency [4.57 cd/A (at 420 cd/m²)] with CIE (0.59, 0.40) were achieved at a relatively high doping concentration (20 wt%) in a TNGT-based OLED.     

Multi-species time-history measurements during n-hexadecane oxidation behind reflected shock waves

Species concentration time-histories were measured during oxidation for the large, normal-alkane, diesel-surrogate component n-hexadecane. Measurements were performed behind reflected shock waves in an aerosol shock tube, which allowed for high fuel loading without pre-test heating and possible decomposition and oxidation. Experiments were conducted using near-stoichiometric mixtures of n-hexadecane and 4% oxygen in argon at temperatures of 1165–1352 K and pressures near 2 atm. Concentration time-histories were recorded for five species: C₂H₄, CH₄, OH, CO₂, and H₂O. Methane was monitored using DFG laser absorption near 3.4 μm; OH was monitored using UV laser absorption at 306.5 nm; C₂H₄ was monitored using a CO₂ gas laser at 10.5 μm; and CO₂ and H₂O were monitored using tunable DFB diode laser absorption at 2.7 and 2.5 μm, respectively. These time-histories provide critically needed kinetic targets to test and refine large reaction mechanisms. Comparisons were made with the predictions of two diesel-surrogate reaction mechanisms (Westbrook et al. [1]; Ranzi et al. [9]) that include n-hexadecane, and areas of needed improvement in the mechanisms were identified. Comparisons of the intermediate product yields of ethylene for n-hexadecane with those found for other smaller n-alkanes, show that an n-hexadecane mechanism derived from a simple hierarchical extrapolation from a smaller n-alkane mechanism does not properly simulate the experimental measurements.     

Structural,vibrational study and superprotonic behavior of a new mixed dipotassium hydrogenselenate dihydrogenphosphate K2(HSeO4)1.5(H2PO4)0.5

Ongoing studies of the KHSeO₄–KH₂PO₄ system aiming at developing novel proton conducting solids resulted in the new compound K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (dipotassium hydrogenselenate dihydrogenphosphate). The crystals were prepared by a slow evaporation of an aqueous solution at room temperature. The structural properties of the crystals were characterized by single-crystal X-ray analysis: K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (denoted KHSeP) crystallizes in the space group P 1¯ with the lattice parameters: a = 7.417(3) Å, b = 7.668(2) Å, c = 7.744(5) Å, α = 71.59(3)°, β = 87.71(4)° and γ = 86.04(6)°. This structure is characterized by HSeO₄⁻ and disordered (H_xSe/P)O₄⁻ tetrahedra connected to dimers via hydrogen bridges. These dimers are linked and stabilized by additional hydrogen bonds (O–H–O) and hydrogen bridges (O–H…O) to build chains of dimers which are parallel to the [0, 1, 0] direction at the position x = 0.5.The differential scanning calorimetry diagram showed two anomalies at 493 and 563 K. These transitions were also characterized by optical birefringence, impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of the proton conductors in this compound were determined in a wide temperature range. The transport properties in this material are assumed to be due to H⁺ protons hopping mechanism.     

Current transport mechanism and photovoltaic properties of photoelectrochemical cells of ITO/TiO2/PVC–LiClO4/graphite

This paper deals with the current transport mechanism of solid state photoelectrochemical cells of ITO/TiO₂/PVC–LiClO₄/graphite as well as the physical properties of a component of a device affecting its performance. The principle of operation and a schematic energy level diagram for the materials used in the photoelectrochemical cells are presented. The device makes use of ITO films, TiO₂ films, PVC–LiClO₄ and graphite films as photoanode, photovoltaic material, solid electrolyte and counter electrode, respectively. The device shows rectification. The J_sc and V_oc obtained at 100 mW cm⁻² were 0.95 μAcm⁻² and 180 mV, respectively.     

The VUV–vis luminescent properties of NaYFPO4: Dy3+ phosphor

Dy³⁺-doped monoclinic NaYFPO₄ phosphor has been synthesized by solid-state reaction technique. Its photoluminescence in the vacuum ultraviolet (VUV)-visible region was investigated. The most intensity broadband emission centered at about 171 nm was the host-related absorption. Another broadband at 153 nm could be related to the O₂→Dy³⁺ charge transfer band (CTB) absorption. The excitation peaks located at 178 nm and 256 nm were the spin-allowed (SA) and spin-forbidden (SF) f–d transitions of Dy³⁺, respectively. Some sharp lines in the range of 280–500 nm were due to the f–f transitions of Dy³⁺ within its 4f⁹ configuration. Under the VUV–vis excitation, the Dy³⁺-doped NaYFPO₄ phosphor showed the characteristic emissions of Dy³⁺ (⁴F_9/2→⁶H_15/2 transitions and ⁴F_9/2→⁶H_13/2 transitions) with a stronger blue emission peaking at about 485 nm. All the chromaticity coordinates of the sample were in the near cold-white region. It can be predicted that this phosphor can be applied in both mercury-free luminescence lamps and white LED.     

Superior performance characteristics for the poly(2,5-dimethoxyaniline)–poly(styrene sulfonic acid)-based electrochromic device

We have fabricated an electrochromic (EC) device with poly(2,5-dimethoxyaniline), PDMA, entrapped in poly(styrene sulfonic acid) (PSS) as an electrochromic layer. The device showed improved performances like stability, optical contrast, etc., over the device with a PDMA layer doped by H₂SO₄. In the process of fabrication of the EC device with a sandwich configuration, indium tin oxide (ITO)/PDMA–PSS||poly(ethyleneimine) (PEI)/orthophosphoric acid (H₃PO₄)/WO₃/ITO, electrochemical polymerization of 2,5-dimethoxyaniline (DMA) was performed with PSS as electrolyte and ITO coated glass as working electrode. The performance characteristics of EC device, like optical contrast, stability, switching time, etc., were followed by cyclic voltammetry, double potential step chronoamperometry and in-situ spectroelectrochemistry. The device was operated in between − 1 V and + 1 V, and absorption characteristics were followed by in-situ UV–visible spectroscopy. A visible contrast in color upon switching the potential from − 1 V to + 1 V was noticed for the device. The device was pale yellow at − 1 V and dark green at + 1 V. Incorporation of PSS into PDMA resulted enhancement in the performance of the complementary electrochromic device. The optical contrast of the device was improved by incorporating PSS into PDMA matrix. The device retained nearly 50% of their optical contrast after 10,000 double steps informing the superior performance of PDMA–PSS in the EC device.     

Adsorption of thiophene on silica-supported Mo clusters

The adsorption/decomposition kinetics/dynamics of thiophene has been studied on silica-supported Mo and MoS_x clusters. Two-dimensional cluster formation at small Mo exposures and three-dimensional cluster growth at larger exposures would be consistent with the Auger electron spectroscopy (AES) data. Thermal desorption spectroscopy (TDS) indicates two reaction pathways. H₄C₄S desorbs molecularly at 190–400 K. Two TDS features were evident and could be assigned to molecularly on Mo sites, and S sites adsorbed thiophene. Assuming a standard preexponential factor (ν = 1 × 10¹³/s) for first-order kinetics, the binding energies for adsorption on Mo (sulfur) sites amount to 90 (65) kJ/mol for 0.4 ML Mo exposure and 76 (63) kJ/mol for 2 ML Mo. Thus, smaller clusters are more reactive than larger clusters for molecular adsorption of H₄C₄S. The second reaction pathway, the decomposition of thiophene, starts at 250 K. Utilizing multimass TDS, H₂, H₂S, and mostly alkynes are detected in the gas phase as decomposition products. H₄C₄S bond activation results in partially sulfided Mo clusters as well as S and C residuals on the surface. S and C poison the catalyst. As a result, with an increasing number of H₄C₄S adsorption/desorption cycles, the uptake of molecular thiophene decreases as well as the H₂ and H₂S production ceases. Thus, silica-supported sulfided Mo clusters are less reactive than metallic clusters. The poisoned catalyst can be partially reactivated by annealing in O₂. However, Mo oxides also appear to form, which passivate the catalyst further. On the other hand, while annealing a used catalyst in H/H₂, it is poisoned even more (i.e., the S AES signal increases). By means of adsorption transients, the initial adsorption probability, S₀, of C₄H₄S has been determined. At thermal impact energies (E_i = 0.04 eV), S₀ for molecular adsorption amounts to 0.43 ± 0.03 for a surface temperature of 200 K. S₀ increases with Mo cluster size, obeying the capture zone model. The temperature dependence of S₀(T_s) consists of two regions consistent with molecular adsorption of thiophene at low temperatures and its decomposition above 250 K. Fitting S₀(T_s) curves allows one to determine the bond activation energy for the first elementary decomposition step of C₄H₄S, which amounts to (79 ± 2) kJ/mol and (52 ± 4) kJ/mol for small and large Mo clusters, respectively. Thus, larger clusters are more active for decomposing C₄H₄S than are smaller clusters.