High-quality n-Si/i-p+-i SiGe/n-Si structure grown by ultra high vacuum chemical molecular epitaxy

The n-Si/i-p⁺-i SiGe/n-Si structure was grown by ultra high vacuum chemical molecular epitaxy, and analysed by high resolution X-ray diffraction, cross-sectional transmission electron microscopy, and secondary ion mass spectroscopy. A high-quality SiGe base layer with an abrupt interface to the Si was obtained. No defects were observed in the n-Si/i-p⁺-i SiGe/n-Si structure. Both the Ge and boron atoms are uniformly distributed in the p⁺-SiGe layer, and the changes of profile of both boron and Ge atoms are abrupt from the n-Si to the SiGe layer. A high-performance microwave power SiGe heterojunction bipolar transistor (HBT) was made from the n-Si/i-p⁺-i SiGe/n-Si structure. Therefore, device-quality n-Si/i-p⁺-i SiGe/n-Si structures can be grown by ultra high vacuum chemical molecular epitaxy.     

Investigation of P3HT/n-Si heterojunction using surface photovoltage spectroscopy

Surface photovoltage spectroscopy (SPS) was used to investigate the interactions of the interface between regioregular poly(3-hexylthiophene) (P3HT) and n-type single crystalline silicon. The SPS responses of silicon and the P3HT/n-Si heterojunction caused by band to band transition of silicon are 30 mV and 160 mV respectively. The band-bending in the silicon side of the P3HT/n-Si structure is larger than that of bare n-Si. The density of the interface states of the P3HT/n-Si heterojunction increased significantly after the deposition of P3HT. Based on the contact potential difference (CPD) transient results, charge transport and separation processes are fast in the silicon substrate and slow in the P3HT layer respectively.     

Analysis of current conduction mechanism in CZTSSe/n-Si structure

In this study, Cu₂ZnSn(S,Se)₄ (CZTSSe) thin films were deposited by the single step thermal evaporation process using the sintered powder of CZTSSe on soda lime glass (SLG) and Si wafer substrates. The structural, optical, and electrical properties of deposited films were investigated. Current–voltage (I–V) in the temperature range of 250–350 K, capacitance–voltage(C–V) and conductance–voltage (G/w–V) measurements at room temperature were carried out to determine electrical properties of CZTSSe/n-Si structure. The forward bias I–V analysis based on thermionic emission (TE) showed barrier height inhomogeneity at the interface and thus, the conduction mechanism was modeled under the assumption of Gaussian distribution of barrier height. The mean barrier height \(({\bar {\Phi }_{B0}})\) and standard deviation \(({\sigma _0})\) at zero bias were obtained as 1.27 eV and 0.18 V, respectively. Moreover, Richardson constant was obtained as 120.46 A cm^?2 K^?2 via modified Richardson plot and the density of interface states (D_it) profile was determined using the data obtained from forward bias I–V measurements. In addition, by the results of frequency dependent C–V measurements, characteristics of the interface state density were calculated applying high-low frequency capacitance (C_HF ? C_LF) and Hill–Coleman methods.     

Photoelectron spectroscopy of discontinuous nickel films

Photoelectron spectroscopy was used to investigate the formation of the energy band structure in nickel films when the mean thickness and consequently the island dimensions in the discontinuous region are increased. The photoelectron spectrum shows groups of electrons with different spin polarizations which are characterized by different potential barrier transmission probabilities (escape functions) at the same kinetic energy. The photoelectron spectra show that electrons of both groups are present in films with mean thicknesses η ranging from 6 to 300 Å, i.e. with mean island dimensions D ranging from 30 to 40 Å, and that a marked qualitative change in the photoelectron energy distribution which can be ascribed to changes in the nickel energy band structure occurs for $\text{η ? 3}\text{A}\text{?}$, i.e. for D in the range 20-12 Å.     

Photoelectron spectroscopy—principles and applications

The photoemission process and principles are briefly reviewed. The electron spectrometer, the specimen preparation chamber and, in particular, the associated ultra-high vacuum system and the technique for obtaining the ultimate vacuum, as well as the in situ preparation techniques, are described in detail. Some applications and their results are given.     

Photoelectron spectroscopy characterization of diamond-like carbon films

The electronic states of diamond-like hydrogenated carbon (DLC) films were studied by synchrotron radiation photoelectron spectroscopy. The valence band spectra measured at different excitation energies show the gradual emergence of the p-pi band in relation to the sample annealing and ion bombardment amorphization. The p-pi band of the annealed DLC was characterized by localized p(z) states, while the formation of the amorphous carbon surface was accompanied by appearance of the delocalized p(z) states, which reduce the optical gap. A simple approach permitting the extraction of the 2p band shape from the photoelectron spectra is proposed.     

Photoelectron spectroscopy of ion-irradiated B-doped CVD diamond surfaces

Chemical vapour deposition (CVD) diamond films were irradiated by 1 keV argon ions at room temperature with doses ranging from 3.6 × 10¹² to 1.1 × 10¹⁶ Ar⁺ cm². The influence of sputtering on the valence band density of states of a boron-doped CVD diamond film was investigated by ultraviolet photoelectron spectroscopy and the changes in the plasmon features were observed by X-ray photoelectron spectroscopy of the carbon Is core level and its loss region. A gradual change from typical diamond features to amorphous carbon was observed after prolonged bombardment times. Above a critical dose D_crit of 5.8 × 10¹⁴ Ar⁺ cm² the damaged surface layer is characterized by a splitting of the C Is bulk peak into two components: a bulk-like diamond peak at 285.3 eV binding energy and a defect peak with 1 eV lower binding energy, which is attributed to the production of an amorphous sp²-rich carbon matrix. Moreover additional occupied states in the range of 0–4 eV binding energy, completely different to those observed on reconstructed diamond surfaces, were observed in the valence band spectra of the ion-irradiated diamond surface. These filled states can also be attributed to the amorphous carbon matrix which is formed at high doses. At very low doses (< 3 × 10¹⁴ ions cm²) only a band bending of the C Is diamond core level peak, along with the formation of some occupied states in the band structure at around 3.8 eV binding energy was observed. A comparison with annealed hydrogen-free CVD diamond surfaces shows some similarities concerning these filled states. The obtained spectra are compared with other crystalline and amorphous forms of carbon and the results are discussed in terms of an irradiation-induced change in the atomic structure of the surface. A comparison of ion bombarded and annealed diamond samples clearly shows that no graphitization takes place in the latter case.     

A comparative study regarding effects of interfacial ferroelectric Bi4Ti3O12 (BTO) layer on electrical characteristics of Au/n-Si structures

Present study focuses on the effects of interfacial ferroelectric BTO layer on the electrical characteristics of Au/n-Si structures, hence Au/n-Si (MS) and Au/BTO/n–Si (MFS) structures were fabricated and admittance measurements (capacitance–voltage: C–V and conductance–voltage: G/ω–V) of both structures were conducted between 10 kHz and 1 MHz at room temperature. Results showed that C–V and G/ω–V characteristics were affected not only by frequency but also through deposition of BTO layer. Some effects can be listed as sharper peaks in C–V plots, higher capacitance and conductance values. Structure’s series resistance (R _s) also decreased due to BTO layer. Interface states (N _ss) profiles of the structures were obtained using Hill–Coleman and high-low frequency capacitance (C _HF–C _LF). Some of the main electrical parameters were extracted from C ^?2–V plots using depletion capacitance approach. Furthermore, current–voltage characteristics of MS and MFS structures were presented.     

A study on interfacial mechanisms and structure of poly(ethylene-co-methacrylic acid)/copper with reflection–absorption infrared spectroscopy

The interfacial mechanism and structure of poly(ethylene-co-methacrylic acid)/copper were investigated using reflection-absorption infrared spectroscopy (RAIR). Based on IR spectrum of EMAA/copper, a strong absorption peak appearing at approximate 1,600 cm⁻¹ is attributed to the asymmetric stretching vibration of COO^― (υCOO_as^―) and a relatively weak absorption band at 1,375 cm⁻¹ is assigned to the symmetric stretching vibration of COO^― (υCOO_s^―). Therefore, it can be determined that copper interacts with EMAA through a strong ionic interaction and carboxylate structure is formed in the interfacial regions. And, according to the band intensities of carboxylate stretching modes and different sensitivities of RAIR to perpendicular and parallel transition moments, it can be concluded that EMAA is absorbed onto a copper substrate with a configuration in which the twofold axis of the C_2υ point group for carboxylate group inclines certain degree from the normal to the surface. In addition, the interfacial carboxylate structure of EMAA/copper is confirmed to be a monodentate one through calculating the difference (Δυ)between the asymmetric carboxylate stretch (υCOO_as^―) and the symmetric stretch (υCOO_s^―).     

rGO-AuNPs/n-Si的肖特基接触特性研究

通过水热法制备了还原氧化石墨烯负载Au纳米复合材料(rGO-AuNPs),结合旋涂法,将其涂覆在单晶硅表面,制备出rGO-AuNPs/n-Si肖特基接触。结果表明,rGO-AuNPs的衍射峰以单质Au为主,存在较弱的石墨烯衍射峰,同时纳米Au粒子(Au nanoparticles, AuNPs)较均匀分布在石墨烯表面,表明成功合成了负载Au的还原氧化石墨烯。从电流-电压(Current-voltage,I-V)曲线可以看出rGO-AuNPs/n-Si肖特基接触具有整流特性。在负载量下,随着Au含量的递增,肖特基势垒高度增加,理想因子减小,但漏电流增大,可能是由于氧化石墨烯在还原过程中缺陷的存在,产生了隧道电流和镜像力,降低了肖特基势垒的横向均匀性。     

Investigation of interfacial structure of Mg/Al vacuum diffusion-bonded joint

The interfacial structure of the Mg/Al diffusion-bonded joint was studied by means of SEM, EPMA and TEM. The test results indicated that the interface zone of Mg/Al diffusion-bonded joint included the transition region on Mg side, the mid-diffusion region and the transition region on Al side. The concentration distribution of Mg and Al atoms in the diffusion zone includes three different regions. The three regions are intermetallic compounds Mg₂Al₃, Mg₃Al₂ and MgAl, respectively. The location of Mg₂Al₃, Mg₃Al₂ and MgAl phases in the diffusion zone can be determined. The Mg₃Al₂ phases were observed in the transition region on Mg side by means of TEM.     

Auger electron spectroscopy study on the interfacial chemical reactions and drive-out diffusion of thin Au/Cr bilayers on GaAs

The contact reaction and drive-out diffusion between a GaAs substrate and a bilayer of thin films of gold and chromium were studied. The interdiffusion and drive-out diffusion were analyzed by Auger electron spectroscopy. Drive-out diffusion of gallium, arsenic and chromium atoms was observed. The arsenic and gallium concentrations close to the surface depend on the thickness of the chromium layer. The thickness of the arsenic-rich surface layer shows a linear dependence on the chromium layer thickness.     

Polytypism of SiC and interfacial structure in SiCp/Al composites

In the present work, the polytypism of SiC and the interfacial structure between SiC and Al were investigated using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HREM). It was approved that 15R could be juxtaposed with 6H stacking sequences in the same SiC reinforcement and a structural transformation zone was also observed. The Al₄C₃ compound can nucleate on SiC at the SiC/Al interface with the growth orientation parallel to the C axis of SiC. Mechanisms for the observed phenomena were also discussed in detail.     

DLTS study of annihilation of oxidation induced deep-level defects in Ni/SiO2/n-Si MOS structures

This paper describes the fabrication of MOS capacitor and DLTS study of annihilation of deeplevel defects upon thermal annealing. Ni/SiO₂/n-Si MOS structures fabricated on n-type Si wafers were investigated for process-induced deep-level defects. The deep-level traps in Si substrates induced during the processing of Ni/SiO₂/n-Si have been investigated using deep-level transient spectroscopy (DLTS). A characteristic deep-level defect at E _C = 0·49 eV which was introduced during high-temperature thermal oxidation process was detected. The trap position was found to shift to different energy levels (E _C = 0·43, 0·46 and 0·34 eV) during thermal annealing process. The deep-level trap completely anneals at 350°C. Significant reduction in trap density with an increase in recombination life time and substrate doping concentration as a function of isochronal annealing were observed.     

Synthesis and characteristics of p-CuAlO2/n-Si heterostructure

In this paper the CuAlO₂/Si heterostructure was synthesized by the radio-frequency magnetron sputtering. The CuAlO₂ thin film tends to be oriented on the (001) surface. The positive Hall coefficient confirms p-type nature of the film and the value of hole concentration is found to be around 3.6 × 10¹⁵ cm⁻³. The contact between the n- and p-type semiconductors was found to be rectifying within the measured temperature range from 320 to 120 K, and the diffusion potential increases with decreasing temperature. The ratio of forward current over the reverse current exceeds 35 within the range of applied voltages of −1.5 to +1.5 V and the turn-on voltage is about 0.5 V.     

Photoelectron spectroscopy and secondary ion mass spectrometry characterization of diamond-like carbon films

Photoelectron spectroscopy at different photon energies was used to optimize the photoexcitation cross section for valence band study of diamond-like hydrogenated carbon films. The electronic states of diamond-like carbon (DLC) were studied by synchrotron radiation photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The valence band spectra measured at different excitation energies show the gradual emergence of the p-π band in relation to the sample annealing and ion bombardment amorphization. The p-π band of the annealed DLC was characterized by localized p_z states whilst the formation of the amorphous carbon surface was accompanied by appearance of the delocalized p_z states in the gap. Secondary ion mass spectrometry and thermal desorption spectroscopy showed that sample annealing was accompanied by hydrogen content decrease.     

Correlation between interfacial molecular structure and mechanics in CNT/epoxy nano-composites

We study the effect of the molecular nature of the interface between an epoxy matrix and multi-walled carbon nanotubes (CNTs) on the mechanical properties of the resultant nano-composites, with emphasis on toughness. A number of samples based on variously functionalized CNTs, namely, pristine, carboxylated, and aminated CNTs are examined, with different qualities of dispersion. Nano-composite toughness is found to increase with enhanced interfacial adhesion, an effect that is opposite to what is usually observed in traditional fiber-based composites. The classical pull-out energy model is shown to effectively explain this result. It is thus possible to tune the toughness of a nano-composite by adjusting the molecular nature of its interface and the CNT characteristics, namely its strength and its length relative to its critical length.     

Studying natural oxide on the surface of n-Si(111), n-Si(100), and p-Si(111) single crystal wafers by X-ray reflection spectroscopy

The state of the surface of standard phosphorus-doped n-Si(111) and n-Si(100) (KEF grade) and boron-doped p-Si(111) (KDB grade) single-crystal wafers treated in a 50% HF–70% HNO₃ (1: 3, v/v) polishing solution has been studied using soft X-ray reflection spectroscopy. The fine structure of the reflection spectra in the region of the Si L _2,3 ionization threshold has been analyzed. The dependence of the natural oxide thickness on the orientation of a silicon single crystal surface is established.