Photon emission from adsorbed C60 molecules with sub-nanometer lateral resolution

We present the first experimental demonstration of spatially resolved photon emission of individual molecules on a surface. A scanning tunneling microscope (STM) was used as a local electron source to excite photon emission from hexagonal arrays of C₆₀ molecules on Au(110) surfaces. Specifically, we show that in maps of photon emission intensities, C₆₀ fullerenes appear as arrays of individual light emitters 4 Å in diameter and separated by 10 Å. Comparison with simultaneously recorded STM images reveals, that most intense emission is detected when the STM tip is centered above a molecule. The results demonstrate the highest spatial resolution of light emission to date using a scanning probe technique.     

用扫描隧道显微镜观察石墨被Au离子轰击后的表面损伤

用扫描隧道显微镜研究石墨被Au离子轰击后的表面损伤。实验结果表明:用低剂量(1×10¹²ion/cm²)530keV的Au⁺和4.5MeV的Au⁺⁺均匀轰击石墨。在石墨表面所产生的最显著的损伤是单个入射Au离子造成的小丘,小丘的横向平均线度约为1.8nm。从高分辨的扫描隧道显微镜图象可以看出,这种损伤往往伴有多种形式的3^1/2×3^1/2R 30°的超结构(R为石墨的晶格常数)     

A Sensitive “Optical Nose” for Detection of Volatile Organic Molecules Based on Au@MOFs Nanoparticle Arrays through Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is an effective technique for detecting toxic gas and volatile organic molecules (VOMs); however, recent SERS-based gas sensors have disadvantages and lack an effective approach to capture toxic gas and insufficient reproducibility of SERS substrates. Herein, a facile strategy is developed to integrate metal-organic frameworks with Au nanoparticle (NP) arrays to form Au@ZIF-8 NP arrays, which can be used as an “optical nose” based on SERS to detect toxic VOMs with good reproducibility and sensitivity. Toluene as a target molecule is recognized at ppm levels by the Au@ZIF-8 NP arrays in situ. And the analytical enhancement factor of Au@ZIF-8 NP arrays for toluene is about 1.2 × 10⁵. Importantly, this SERS substrate can also detect the 1-butanol molecule, which provides an idea for designing a universal VOM sensor. In addition, the coating method of the ZIF-8 shell can be extended to synthetize various NPs@ZIF-8 core–shell composites, such as Au nanospheres@ZIF-8, Au@Ag nanorods@ZIF-8, PS microspheres@ZIF-8, and Fe₂O₃ microellipsoids@ZIF-8 composites.     

Pt-chain induced formation of Ge nanowires on the Ge(001) surface

A new reconstructed Pt/Ge(001)–4 × 2 surface structure of 0.25 ML Pt deposition is suggested based on density functional theory. The Ge dimers form nanowire arrays on a Pt-chain modified Ge(001) surface in which the chain is located between the two quasi-dimer rows and below the Ge nanowire. The simulated scanning tunneling microscope (STM) images of the surface are in excellent agreement with the previously observed STM features and sample bias dependence. It is the nanowire Ge dimers and not the Pt atoms that contribute to the STM images for occupied states at high sample biases, contrary to what has always been assumed in experiments. The surface bands of the Pt chain and quasi-dimer rows exhibit quasi-one-dimensional metallic behavior in the direction of the nanowire. When changing from the 4 × 2 to the 4 × 4 structure, there are likely pseudogaps opened at the new surface Brillouin zone boundary, which simultaneously reduce the metallicity. This may be related to the Peierls instability. The interaction between the Pt chain and the quasi-dimer row, as well as the inter-quasi-dimer row interaction, is of essential importance for stabilization.     

STM and HREELS investigation of gas phase silanization on hydroxylated Si(100)

The gas phase anhydrous reaction of glycidoxypropyldimethylethoxysilane (GPDMES) with a model hydroxylated surface has been investigated using high-resolution electron energy loss spectroscopy (HREELS) and scanning tunneling microscopy (STM). Water dissociation on the clean reconstructed (2 × 1)-Si(100) surface was used to create an atomically flat surface with ~ 0.5 ML of hydroxyl groups. Exposure of this surface to GPDMES at room temperature under vacuum was found to lead to formation of covalent Si–O–Si bonds although high exposures (6 × 10⁸ L) were required for saturation. STM images at the early stages of reaction indicate that the reaction occurs randomly on the surface with no apparent clustering. The STM images together with semi-empirical (AM1) calculations provide evidence for hydrogen bonding interactions between the oxygen atoms in the molecule and surface hydroxyl groups at low coverage.     

STM investigation of the reaction of AgO added rows with CO2 on a Ag(110) surface

The formation of carbonate species by a reaction of AgO added rows with CO₂ was investigated by scanning tunneling microscopy (STM). STM observation during the reaction revealed that the AgO added rows were compressed from a (4 × 1) to a (2 × 1) phase, according to the growth of carbonate domains. Though the carbonate domains give a (1 × 2) diffraction pattern, STM images of this domain do not show a (1 × 2) structure, which indicates that the Ag substrate reconstructs to a (1 × 2) structure. Though the CO₃ species thermally decompose at a lower temperature than AgO added rows, the AgO added rows can be selectively decomposed by ultraviolet irradiation.     

Scanning tunneling microscopy/spectroscopy study of adsorption of C<Subscript>60</Subscript>F<Subscript>36</Subscript> molecules on the 7 × 7-Si(111) surface

Spatially resolved images of an individual C₆₀F₃₆ fluorofullerene molecules on Si(111)-7 × 7 surface have been obtained by means of scanning tunneling microscopy/spectroscopy (STM/STS). The presence of isomers with different symmetry (T, C ₃, C ₁) has been revealed in STM investigation of initial adsorption stage of C₆₀F₃₆ on silicon surface Si(111)-(7 × 7). The adsorbed fluorofullerene molecule can occupy any adsorption site of silicon surface (corner site, faulted half, unfaulted half) that indicates for strong molecule-substrate interaction. The HOMO-LUMO gap of the adsorbed C₆₀F₃₆ molecules have been estimated from current image tunneling spectroscopy (CITS) and z(V) with engaged feedback measurements. The value of HOMO-LUMO gap observed experimentally was 3 eV. The C₆₀F₃₆ molecules adsorption on Si(111)-(7 × 7) surface was stable and kept equilibrium configuration during several hours.     

Monolayered adatom aggregation induced by metallofullerene molecules on Cu(100)

The adsorption and self-assembly of Gd@C₈₂ molecules on Cu(100) surface have been investigated using scanning tunneling microscopy (STM). The metallofullerene molecules in the assemblies showed two characteristic apparent heights in the STM images. STM manipulation and spectroscopy was performed and revealed the formation of Cu adatom islands underneath the Gd@C₈₂ molecules. The monolayered Cu aggregates were resulted from the adatom–molecule complexation, which is supported by density functional theory (DFT) calculations that show charge transfer and electrostatic interactions between Gd@C₈₂ and adatoms. In addition, sub-molecularly resolved STM images demonstrated the structural and orientational ordering of Gd@C₈₂ assemblies upon thermal annealing. DFT calculations demonstrated that Gd atom located at the lower part of the carbon cage is a favored adsorption configuration for Gd@C₈₂ molecules adsorbed on Cu(100).     

甘氨酸在Cu(001)表面的吸附结构

结合低能电子衍射(LEED)及其消失斑点规律和扫描隧道显微镜(STM)手段确定了室温下甘氨酸在Cu(001)表面能形成c(2×4)和两种(2×4)吸附结构((2×4)₁和(2×4)₂),并推断出在两种(2×4)结构单胞中两甘氨酸分子的羧基相对于衬底的吸附取向一致,而它们的氨基则不同.实验中还观察到c(2×4)与(2×4)₂结构能相互转变成窄条相互穿插共存,这说明几种吸附结构能量相近. 关键词：     

X-ray observations of tungsten wire array Z-pinch implosions on QiangGuang-1 facility

Z-pinch experiments with two arrays consisting, respectively, of 32 4-μm- and 6-μm-diameter tungsten wires have been carried out on QiangGuang-1 facility with a current rising up to 1.5MA in 80ns. At early time of implosion, x-ray framing images show that the initial emission comes from the central part of arrays, and double clear emission rings, drifting to the anode and the cathode at 5×10⁶cm/s and 2.4×10⁷cm/s respectively, are often produced near the electrodes. Later, in a 4-μm-diameter tungsten wire array, filamentation caused by ohmic heating is prominent, and more than ten filaments have been observed. A radial inward shift of arrays starts at about 30\,ns earlier than the occurrence of the x-ray peak power for both kinds of arrays, and the shrinkage rate of emission region is as high as 1.7×10⁷cm/s in a 4-μm-diameter tungsten wire array, which is two times higher than that in a 6-μm one. Emission from precursor plasmas is observed in implosion of 6-μm-diameter tungsten wire arrays, but not in implosion of a 4-μm-diameter tungsten wire array. Whereas, in a 4-μm-diameter tungsten wire array, the soft x-ray emission shows the growth of m=1 instability in the plasma column, which is caused by current. The reasons for the discrepancy between implosions of 4-μm- and 6-μm-diameter tungsten wire arrays are explained.     

Effects of Immersion Temperature on Self-Assembled Monolayers of Octanethiol on Au(111)

Self-assembled monolayers (SAMs) of 1-octanethiol (OT) on Au(111) surfaces, prepared at immersion temperatures between 300 K and 363 K in a sealed stainless steel chamber, were studied by scanning tunneling microscopy (STM). An oblique (√3 × √3)R30° OT-SAM structure was observed below 348 K, whereas a superstructure (3×√7)R11° covered the gold surfaces at 363 K. The highly resolved STM images permitted assignment of four symmetry-inequivalent OT molecules per 8.7 × 7.6 Å² unit cell at 363 K. Differences in the topographical heights of the molecules were attributed to the binding of OT sulfur head groups at different adsorption sites on Au(111). This structure was not observed in stirring reflux at a high temperature, which indicates a higher pressure (> 1 atm) in the chamber may be one of crucial factors for structural transition. As the immersion temperature increased, a lower density of vacancy islands and a higher fraction of island area were observed.     

Relaxation of vibrationally excited reaction products in a crystal lattice

The relaxation of vibrationally excited nitrogen molecules in the matrix of silver azide is studied. The effective rate constants for the interaction of an excited nitrogen molecule with free charge carriers (1.7 × 10^–10 cm³ s–1) and for the generation a hole from the level of the produced defect at the expense of the vibrational energy of the molecule (3 × 10¹⁰ s^–1) are estimated. An associative–dissociative mechanism of the deactivation is proposed, which consists in the capture of an electron onto the level of the produced defect with the subsequent emission of an electron into the conduction band at the expense of the vibrational energy of the excited molecule. The effective rate constants for electron emission from the excited level of a hydrogen-like defect at values of the principal quantum number of 3 and 4 are estimated as 1.8 × 10⁹ and 2.8 × 10⁹ s^–1, respectively. Based on the processes considered, an expression for the probability of chain propagation is obtained.     

Scanning tunneling microscopy on self-assembled calix[4]resorcinarene monolayer adsorbates on Au(111)

Self-assembled Monolayers of calix[4]resorcinarene receptor molecules on Au(111) were studied by UHV scanning tunneling microscopy and X-ray photoelectron spectroscopy. Highly ordered monolayers were observed with domains oriented at an angle of 60° relative to each other. Molecularly resolved images were investigated and lattice constants found which depended on the preparation solvent. The STM images of two samples, one prepared in 1 mM chloroform/ethyl alcohol adsorbate solution and one in 1 mM hexane adsorbate solution are consistent with having a ×2 and 4×2 lattice, respectively. Received: 22 September 1999 / Accepted: 28 March 2000 / Published online: 11 May 2000     

Optimizing surface-enhanced Raman scattering by template guided assembling of closely spaced silver nanocluster arrays

We present an easy approach to synthesize closely spaced regular arrays of silver nanoclusters, which are self-assembled by depositing gas-phase synthesized metal nanoclusters onto pre-patterned triblock copolymer templates. The array has a high particle density of about 2 ×10³ particles per μm², and an average interparticle space of about 20 nm. The surface plasmon resonance wavelength of the array is tuned due to the interparticle plasmon coupling. High SERS sensitivity for less than one layer trans-1,2-bi-(4-pyridyl) ethylene (BPE) molecule detection, with an enhancement factor of 2.6 ×10⁶, has been demonstrated for a substrate with this array. The enhanced Raman signal was found to be 5 times higher than that measured from the substrate with randomly distributed silver nanoparticles.     

LEED and STM studies of the stability of the MoO2(100) surface

Atomic scale images and low energy electron diffraction pattern of a MoO₂(100) single crystal surface are presented, which show different structural modifications depending on surface preparation. A short in-situ heat treatment of the as-grown single crystal results in an atomically ordered surface whose diffraction pattern and STM images are consistent with those expected from the bulk structure. The symmetry of the STM images suggests an oxygen termination of the surface. A significantly longer heat treatment causes a thermodynamically stable (4 × 1) reconstruction which is interpreted to be due to a loss of oxygen chains. The (4 × 1) reconstruction vanishes after Ar-ion-sputtering and subsequent annealing. Additional long sputtering cycles result in a (2 × 1) reconstruction. The observed surface reconstructions can be transformed into each other by heating or sputtering cycles.     

ESDIAD and LEED studies of the clean TiO2(100) surface

Electron-stimulated desorption ion angular distribution (ESDIAD) and LEED were used to investigate the structure changes at the TiO₂(100) surface. The angular distribution of O⁺ ions from the (1 × 3) reconstructed surface is consistent with the microfacet model proposed from X-ray diffraction and STM studies. The (1 × 3) reconstructed surface can be transferred back to the (1 × 1) surface after annealing at 950 K in oxygen, through a stage where the surface consists of (1 × 1) and (1 × 3) domains which are smaller than the coherent width of the LEED electron beam. Evidence for surface reconstruction on the (1 × 1) surface is also found.     

第一过渡金属酞菁分子的电子结构的第一性原理计算

对第一过渡金属酞菁化合物(Metal Phthalocyanine,MPc,M=Sc,Ti,V,Cr,Mn,Fe,Co,Ni和Cu)的电子结构和基本物理化学性质进行了第一性原理计算.理论模拟出来的STM图像表现出亚分子结构,与已有的实验观察结果相当吻合,且跟金属原子的d电子组态明显有关.在小偏压条件下,第一过渡金属首尾端ScPc,NiPc和CuPc分子的中央金属离子在STM图像表现为空洞,其他所有金属酞菁分子的中央金属离子均为亮斑.同时还研究了ScPc和NiPc分子的STM图像与偏压的关系,当针尖偏压分别 关键词： STM图像模拟 金属酞菁 电子结构     

液晶分子的抗弯刚度与分子间位致排斥势

定义了反映分子刚性的物理量，称为抗弯刚度Ｋ．给出了用具体的化学键结构和键的力常数计算Ｋ的方法．计算得ＰＡＡ，ａｎｉｓａｌｄｅｈｙｄｅ ａｚｉｎｅ和ＢＡ的Ｋ分别为３．１７×１０⁴，２．９３×１０⁴，４．１７×１０⁴ｎｍｋ_BＫ．导出了分子间位致弹性排斥势．提出了处理弹性棒分子体系的统计物理方法．对ＰＡＡ作了具体的数值计算，并讨论了向列序形成的微观机制：吸引势是主要的，但位致排斥势起十分重要的作用． 关键词：     

The adsorption of a substituted benzene,the ethynyl-trifluoro-toluene on Si(100)-2 × 1

The adsorption of 3-ethynyl-trifluoro-toluene (ETFT) on Si(100)-2 × 1 surface in ultra high vacuum is studied in the low coverage regime, through a joint experimental and theoretical approach. The STM images of both filled and empty states revealed few distinct adsorption configurations. On the basis of Density Functional Theory (DFT) calculations the STM images were simulated and three main adsorption configurations were identified, with a predominance of di-sigma bonded species that leave the benzene ring unreacted. A discussion of the reactivity of the reconstructed silicon surface towards benzene derivatives is proposed by comparing the adsorption of ETFT close related molecules, like styrene and phenylacetylene.     

The chemisorption of pentacene on Si(0 0 1)-2 × 1

Adsorption structures of the pentacene (C₂₂H₁₄) molecule on the clean Si(0 0 1)-2 × 1 surface were investigated by scanning tunneling microscopy (STM) in conjunction with density functional theory calculations and STM image simulations. The pentacene molecules were found to adsorb on four major sites and four minor sites. The adsorption structures of the pentacene molecules at the four major sites were determined by comparison between the experimental and the simulated STM images. Three out of the four theoretically identified adsorption structures are different from the previously proposed adsorption structures. They involve six to eight Si-C covalent chemical bonds. The adsorption energies of the major four structures are calculated to be in the range 67-128 kcal/mol. It was also found that the pentacene molecule hardly hopped on the surface when applying pulse bias voltages on the molecule, but was mostly decomposed.