| 1. |
- Bao, Jiming, et al.
(author)
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Nanowire-induced Wurtzite InAs Thin Film on Zinc-Blende InAs Substrate
- 2009
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In: Advanced Materials. - : Wiley. - 1521-4095 .- 0935-9648. ; 21:36, s. 3654-3654
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Journal article (peer-reviewed)abstract
- InAs pyramids and platelets on a zinc-blende InAs substrate are found to exhibit a wurtzite crystal structure. induced by wurtzite InAs nanowires, wurtzite InAs thin film and its associated zinc-blende/wurtzite heterocrystalline heterostructures may open up new opportunities in band-gap engineering and related device applications.
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| 2. |
- Björk, Mikael, et al.
(author)
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Tunable effective g factor in InAs nanowire quantum dots
- 2005
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:20
-
Journal article (peer-reviewed)abstract
- We report tunneling spectroscopy measurements of the Zeeman spin splitting in InAs few-electron quantum dots. The dots are formed between two InP barriers in InAs nanowires with a wurtzite crystal structure grown using chemical beam epitaxy. The values of the electron g factors of the first few electrons entering the dot are found to strongly depend on dot size. They range from close to the InAs bulk value in large dots vertical bar g(*)vertical bar=13 down to vertical bar g(*)vertical bar=2.3 for the smallest dots.
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| 3. |
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| 4. |
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| 5. |
- Bleszynski-Jayich, Ania C., et al.
(author)
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Imaging a one-electron InAs quantum dot in an InAs/InP nanowire
- 2008
-
In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 77:24
-
Journal article (peer-reviewed)abstract
- Nanowire heterostructures define high-quality few-electron quantum dots for nanoelectronics, spintronics, and quantum information processing. We use a cooled scanning probe microscope (SPM) to image and control an InAs quantum dot in an InAs/InP nanowire using the tip as a movable gate. Images of dot conductance vs tip position at T=4.2 K show concentric rings as electrons are added, starting with the first electron. The SPM can locate a dot along a nanowire and individually tune its charge, abilities that will be very useful for the control of coupled nanowire dots.
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| 6. |
- Bordag, Michael, et al.
(author)
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Shear stress measurements on InAs nanowires by AFM manipulation
- 2007
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In: Small. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 3:8, s. 1398-1401
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Journal article (peer-reviewed)abstract
- On an upward curve? The curvature of an elastically deformed nanowire pinned to a flat surface contains information about the maximum static friction force, and hence the shear stress, between the nanowire and the surface. Here, InAs nanowires are bent in a controlled manner using the tip of an atomic force microscope (see image). The shear stress can be obtained from a simple analysis according to the standard theory of elasticity.
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| 7. |
- Bryllert, Tomas, et al.
(author)
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Vertical high-mobility wrap-gated InAs nanowire transistor
- 2006
-
In: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 27:5, s. 323-325
-
Journal article (peer-reviewed)abstract
- In this letter, the authors demonstrate a vertical wrap-gated field-effect transistor based on InAs nanowires [Proc. DRC, 2005, p. 157]. The nanowires have a diameter of 80 nm and are grown using selective epitaxy; a matrix of typically 10 x 10 vertically standing wires is used as channel in the transistor. The authors measure current saturation at V-ds = 0.15 V (V-g = 0 V), and a high mobility, compared to the previous nanowire transistors, is deduced.
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| 8. |
- Conache, Gabriela, et al.
(author)
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AFM-based manipulation of InAs nanowires
- 2008
-
In: Proceedings of the IVC-17 (17th International Vacuum Congress) [also] ICSS-13 (13th International Conference on Surface Science) [also] ICN+T-2007 (International Conference on Nanoscience and Technology). - Bristol : Institute of Physics (IOP). ; 100, s. 052051-052051
-
Conference paper (peer-reviewed)abstract
- A controlled method of manipulation of nanowires was found using the tip of an Atomic Force Microscope (AFM). Manipulation is done in the ‘Retrace Lift’ mode, where feedback is turned off for the reverse scan and the tip follows a nominal path. The effective manipulation force during the reverse scan can be changed by varying an offset in the height of the tip over the surface. Using this method, we have studied InAs nanowires on different substrates. We have also investigated interactions between wires and with gold features patterned onto the substrates.
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| 9. |
- Conache, Gabriela, et al.
(author)
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Bias-controlled friction of InAs nanowires on a silicon nitride layer studied by atomic force microscopy
- 2010
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In: Physical Review B Condensed Matter. - College Park, Md. : American Physical Society. - 0163-1829 .- 1095-3795. ; 82:3
-
Journal article (peer-reviewed)abstract
- By studying how nanowires lying on a surface bend when pushed by an atomic force microscopy tip we are able to measure the friction between them and the substrate. Here, we show how the friction between InAs nanowires and an insulating silicon nitride layer varies when a dc voltage is applied to the tip during manipulation. The bias charges the capacitor formed by the wire and the grounded silicon back contact. Electrostatic forces increase the contact pressure and allow us to tune the friction between the wire and the silicon nitride surface. Using nanowires of about 40-70 nm diameter and a few microns in length we have applied biases in the range +12 to -12 V. A monotonic increase of the sliding friction with voltage was observed. This increase in friction with the normal force implies that the mesoscopic nanowire-surface system behaves like a macroscopic contact, despite the nanometer size of the contact in the direction of motion. The demonstrated bias-controlled friction has potential applications in MEMS/NEMS devices.
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| 10. |
- Conache, Gabriela, et al.
(author)
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Comparative friction measurements of InAs nanowires on three substrates
- 2010
-
In: Journal of Applied Physics. - College Park, MD : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 108:9
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Journal article (peer-reviewed)abstract
- We have investigated friction between InAs nanowires and three different substrates: SiO2, fluorosilanized SiO2, and Si3N4. The nanowires were pushed laterally with the tip of an atomic force microscope and the friction force per unit length for both static and sliding friction was deduced from the equilibrium shape of the bent wires. On all three substrates, thick wires showed a difference between sliding and static friction of up to three orders of magnitude. Furthermore, all substrates display a transition to stick-slip motion for nanowires with a diameter of less than about 40 nm. Hydrophobic and hydrophilic substrates display similar friction behavior suggesting that a condensed water layer does not strongly influence our results. The patterns and trends in the friction data are similar for all three substrates, which indicates that they are more fundamental in character and not specific to a single substrate. ©2010 American Institute of Physics.
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| 11. |
- Conache, Gabriela, et al.
(author)
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Friction measurements of InAs nanowires on Silicon nitride by AFM manipulation
- 2009
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In: Small. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 5:2, s. 203-207
-
Journal article (peer-reviewed)abstract
- A study was conducted to perform friction measurements of InAs nanowires (NW) on silicon nitride (Si 3N 4) through atomic force microscopy (AFM) manipulation. The investigations revealed the friction force per unit length for sliding and static friction over a range of nanowire diameters. It was found that there is a significant difference between the coefficients of the two sliding modes for large wires. It was also found that the difference between the two sliding modes disappears at smaller diameters and the sliding friction becomes equal with the static friction. The AFM investigations were performed on a Nanoscope IIIa Dimension 3100, using rectangular cantilevers, with a nominal spring constant of 30 N m -1. The nanowires were manipulated, using the 'Retrace Lift' mode of the AFM controller. The friction force per unit length was gathered from the local curvature of the NWs, using standard elasticity theory.
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| 12. |
- Conache, Gabriela, 1977-, et al.
(author)
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Nanowire friction with an applied bias
- 2009
-
Conference paper (peer-reviewed)abstract
- Recently, we have shown how the friction acting on nanowires pushed across a surface by an AFM tip can be determined by measuring the radius of curvature of the bent wire aŸer manipulation. This technique allows us to study the friction properties of an extended mesoscale contact. Our main focus has been to determine whether such contacts behave like macroscopic objects, in which dišerences between the 'true' and 'apparent' contact areas play a key role and friction varies linearly with the applied normal force, or whether they are more like atomic-scale point contacts, wheremore fundamental processes dominate and friction oŸen is independent of the normal force. In this work we show how the friction between InAs nanowires and an insulating silicon nitride layer on a conductive silicon substrate varies when a DC voltage is applied to the AFM tip during manipulation. e tip charges the capacitor formed by the wire and the grounded silicon back contact, giving rise to attractive Coulomb forces and thus increasing the contact pressure between the wire and the silicon nitride. In this way we can vary the normal force on the sliding surfaces using a single wire, with a constant structure and contact geometry. Using nanowires of about 40-50 nm diameter and a few microns in length we have applied tip voltages in the range +12 to -12 V. Simplemodeling indicates that these voltages su›ce to give similar levels of band-lling and depletion to when the same wires are used in working wrap-gate or back-gate devices. A monotonic increase of the sliding friction with the voltage applied on the tip was observed. is implies that the friction increases with the normal force and that this mesoscopic system behaves more like a macroscopic contact, despite the nanometer size of the contact in the direction of motion.
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| 13. |
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| 14. |
- Eymery, Joel, et al.
(author)
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Strain and shape of epitaxial InAs/InP nanowire superlattice measured by grazing incidence X-ray techniques
- 2007
-
In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 7:9, s. 2596-2601
-
Journal article (peer-reviewed)abstract
- Quantitative structural information about epitaxial arrays of nanowires are reported for a InAs/InP longitudinal heterostructure grown by chemical beam epitaxy on an InAs (111)(B) substrate. Grazing incidence X-ray diffraction allows the separation of the nanowire contribution from the substrate overgrowth and gives averaged information about crystallographic phases, epitaxial relationships (with orientation distribution), and strain. In-plane strain in homogeneities, intrinsic to the nanowires geometry, are measured and compared to atomistic simulations. Small-angle X-ray scattering evidences the hexagonal symmetry of the nanowire cross-section and provides a rough estimate of size fluctuations.
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| 15. |
- Eymery, J., et al.
(author)
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X-ray measurements of the strain and shape of dielectric/metallic wrap-gated InAs nanowires
- 2009
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:13
-
Journal article (peer-reviewed)abstract
- Wrap-gate (111) InAs nanowires (NWs) were studied after HfO2 dielectric coating and Cr metallic deposition by a combination of grazing incidence x-ray techniques. In-plane and out-of-plane x-ray diffraction (crystal truncation rod analysis) allow determining the strain tensor. The longitudinal contraction, increasing with HfO2 and Cr deposition, is significantly larger than the radial dilatation. For the Cr coating, the contraction along the growth axis is quite large (-0.95%), and the longitudinal/radial deformation ratio is >10, which may play a role on the NW transport properties. Small angle x-ray scattering shows a smoothening of the initial hexagonal bare InAs NW shape and gives the respective core/shell thicknesses, which are compared to flat surface values.
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| 16. |
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| 17. |
- Fröberg, Andreas, 1985, et al.
(author)
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Effects of an Empowerment-Based Health-Promotion School Intervention on Physical Activity and Sedentary Time among Adolescents in a Multicultural Area
- 2018
-
In: International Journal of Environmental Research and Public Health. - Basel : MDPI. - 1661-7827 .- 1660-4601. ; 15:11
-
Journal article (peer-reviewed)abstract
- Physical activity (PA) decreases with age, and interventions are needed to promote PA during adolescence, especially, among those in low-socioeconomic status (SES) areas. The aim of this study was to investigate whether a two-year, empowerment-based health-promotion school intervention had any effects on changes in (a) moderate-to-vigorous PA (MVPA), (b) sedentary time (SED), (c) exercise training (ET) frequency, and (d) ET duration, among adolescents. Participants (aged 12-13 years at baseline) from one intervention school and two control schools, were recruited from a multicultural area of Sweden, characterized by low-SES. During the course of the two-year intervention, a total of 135 participants (43% boys) were included in the study. The intervention was developed and implemented as a result of cooperation and shared decision-making among the researchers and the participants. MVPA and SED were measured with accelerometers, and ET frequency and duration was self-reported at the beginning of the seventh, eighth, and ninth grade, respectively. There were no significant effects of the two-year, empowerment-based health-promotion school intervention on changes in the accelerometer-measured MVPA and SED, or the self-reported ET frequency and duration, among the adolescents. Overall, the intervention was unsuccessful at promoting PA and reducing SED. Several possible explanations for the intervention's lack of effects are discussed.
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| 18. |
- Fröberg, Andreas, 1985, et al.
(author)
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Exploring reasons to attend formal teaching sessions among students: A self-determination theory perspective
- 2021
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In: Högre Utbildning. - : Cappelen Damm AS - Cappelen Damm Akademisk. - 2000-7558. ; 11:2, s. 70-83
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Journal article (peer-reviewed)abstract
- Among students in higher education, attending formal teaching sessions might be important not only for academic achievement but also to foster human values. Despite this, the low and declining attendance rate is a growing concern in higher education. This study aimed to explore what students believe teachers could do to facilitate attendance at formal teaching sessions in the physical education part of the teacher education program in Sweden. Three focus group interviews were conducted among students aged 20 to 35 who attended the teacher education programme. The self-determination theory was used as a theoretical framework, and data were analysed and categorised using qualitative content analysis. The analysis of the interviews formed an overarching theme that intersected with four categories. The results show that teachers might facilitate attendance during formal teaching sessions by providing opportunities for students to interact with each other; match challenges with skills; be engaged, enthusiastic, and caring; and outline the value and rationale. The study’s implications for teachers are discussed in the paper.
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| 19. |
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| 20. |
- Fröberg, Linus, et al.
(author)
-
Diameter-dependent growth rate of InAs nanowires
- 2007
-
In: Physical Review B. Condensed Matter and Materials Physics. ; 76
-
Journal article (peer-reviewed)abstract
- We have grown Au seeded InAs nanowires using chemical beam epitaxy and report on the growth rate dependence on nanowire diameter. We find a maximum of the growth rate at a nanowire diameter of 25 nm, below which the growth rate decreases due to the Gibbs-Thomson effect. Above the maximum, the growth rate decreases with increasing diameter due to the effect of material diffusion to the growth point. A unified model, which accounts for both the Gibbs-Thomson effect and material diffusion, is presented and successfully compared to the experiments. From the comparison, we extract the diffusion length on the substrate surface and a critical diameter, below which nanowire growth ceases, and show that these physical parameters can be tuned by controlling the supersaturation.
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| 21. |
- Fröberg, Linus
(author)
-
Growth, Physics, and Device Applications of InAs-based Nanowires
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- This thesis is based on three different projects: 1) the epitaxial growth of nanowires using chemical beam epitaxy, 2) the study of electron transport through quantum dots and multiple quantum dots in nanowires at low temperature, and 3) the development of wrap gated nanowire field effect transistors. In the first part, a method of studying the diffusion of the source material on the substrate surface was developed. Nanowires were positioned in a triangular pattern on the substrate and, depending on the density of the nanowires in the arrays, the growth rate changes due to competition for available source material on the surface. A model was developed that could be fitted to experimental data using the diffusion length as one of the fitting parameters. The growth rate dependence on nanowire diameter was also studied and was satisfactorily explained by a model that takes both substrate diffusion and the Gibbs–Thomson effect into account. Nanowire heterostructures in the InAs/InP system were studied and the importance of seed particle alloying was demonstrated. The nanowires were grown from Au seed particles which alloy with indium, forming a Au–In seed particle. The composition of the particle is different during InAs and InP growth, and for each heterostructure interface the seed particle composition has to change. This affects the initial growth of InAs and InP segments. By growing two thin segments of InP in an InAs nanowire, a quantum dot was formed between the InP tunnel barriers. At low temperature (4.2 K), the electron transport through these quantum dots is governed by Coulomb interactions. In a thin quantum dot, the energy levels are raised up in energy, which allows transport through the lowest level. This transport was investigated by scanning gate microscopy to map out the electrostatic environment of the quantum dot. Furthermore, double quantum dots were studied, where the characteristics of two single quantum dots were combined to form a more complex transport system. The final part of the thesis is devoted to the development of vertical nanowire transistors with a gate that wraps around the nanowire channel. This allows enhanced control of the potential in the channel compared to conventional planar devices. Three different devices were studied: 1) an InAs device with a ~1 µm gate length, 2) an InAs device with 50 nm gate length, and 3) a heterostructure device with an InAsP segment in the channel. The InAs devices showed good current saturation and subthreshold characteristics for drive voltages around 0.5 V. The InAsP device showed a reduced off current and lower inverse subthreshold slope in comparison to similarly processed InAs reference devices.
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| 22. |
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| 23. |
- Fröberg, Linus, et al.
(author)
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Transients in the Formation of Nanowire Heterostructures.
- 2008
-
In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 8:11, s. 3815-3818
-
Journal article (peer-reviewed)abstract
- We present results on the effect of seed particle reconfiguration on the growth of short InAs and InP nanowire segments. The reconfiguration originates in two different steady state alloy compositions of the Au/In seed particle during growth of InAs and InP. From compositional analysis of the seed particle, the In content in the seed particle is determined to be 34 and 44% during InAs and InP growth, respectively. When switching between growing InAs and InP, transient effects dominate during the time period of seed particle reconfiguration. We developed a model that quantitatively explains the effect and with the added understanding we are now able to grow short period (<10 nm) nanowire superlattices.
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| 24. |
- Fröberg, Linus, et al.
(author)
-
Vertical InAs nanowire wrap-gate FETs
- 2006
-
In: Book of abstracts: Semicond Nanowires Symp, Eindhoven, The Netherlands (2006).
-
Conference paper (peer-reviewed)
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| 25. |
- Fuhrer, Andreas, et al.
(author)
-
Few electron double quantum dots in InAs/InP nanowire heterostructures
- 2007
-
In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 7:2, s. 243-246
-
Journal article (peer-reviewed)abstract
- We report on fabrication of double quantum dots in catalytically grown InAs/InP nanowire heterostructures. In the few-electron regime, starting with both dots empty, our low-temperature transport measurements reveal a clear shell structure for sequential charging of the larger of the two dots with up to 12 electrons. The resonant current through the double dot is found to depend on the orbital coupling between states of different radial symmetry. The charging energies are well described by a capacitance model if next-neighbor capacitances are taken into account.
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| 26. |
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| 27. |
- Hilner, Emelie, et al.
(author)
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Direct Atomic Scale Imaging of III-V Nanowire Surfaces.
- 2008
-
In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 8:11, s. 3978-3982
-
Journal article (peer-reviewed)abstract
- We have succeeded in direct atomic scale imaging of the exterior surfaces of III-V nanowires by scanning tunneling microscopy (STM). By using atomic hydrogen, we expose the crystalline surfaces of InAs nanowires with regular InP segments in vacuum while retaining the wire morphology. We show images with atomic resolution of the two major types of InAs wurtzite nanowire surface facets and scanning tunneling spectroscopy (STS) data. Ab initio calculations of the lowest energy surface structures and simulated STM images, agree very well with experiments.
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| 28. |
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| 29. |
- Holmberg, Christopher, 1984, et al.
(author)
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Empowering aspects for healthy food and physical activity habits : adolescents’ experiences of a school-based intervention in a disadvantaged urban community
- 2018
-
In: International Journal of Qualitative Studies on Health and Well-being. - Abingdon : Taylor & Francis. - 1748-2623 .- 1748-2631. ; 13:sup1: Equal Health
-
Journal article (peer-reviewed)abstract
- Purpose:This study aimed to describe adolescents’ experiences of participating in a health-promoting school-based intervention regarding food and physical activity, with a focus on empowering aspects. Method:The school was located in a urban disadvantaged community in Sweden, characterized by poorer self-reported health and lower life expectancy than the municipality average. Focus group interviews with adolescents (29 girls, 20 boys, 14–15 years) and their teachers (n = 4) were conducted two years after intervention. Data were categorized using qualitative content analysis. Results: A theme was generated, intersecting with all the categories: Gaining control over one’s health: deciding, trying, and practicing together, in new ways, using reflective tools. The adolescents appreciated influencing the components of the intervention and collaborating with peers in active learning activities such as practicing sports and preparing meals. They also reported acquiring new health information, that trying new activities was inspiring, and the use of pedometers and photo-food diaries helped them reflect on their health behaviours. The adolescents’ experiences were also echoed by their teachers. Conclusions: To facilitate empowerment and stimulate learning, health-promotion interventions targeting adolescents could enable active learning activities in groups, by using visualizing tools to facilitate self-reflection, and allowing adolescents to influence intervention activities.
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| 30. |
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| 31. |
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| 32. |
- Jonsson, Linus, et al.
(author)
-
Possibilities and Challenges in Developing and Implementing an Empowerment-based School-Intervention in a Swedish Disadvantaged Community
- 2020
-
In: Health Promotion International. - Oxford : Oxford University Press. - 0957-4824 .- 1460-2245. ; 35:2, s. 232-243
-
Journal article (peer-reviewed)abstract
- In this paper, we describe and critically reflect on the possibilities and challenges of developing and implementing an empowerment-based school intervention regarding healthy food and physical activity (PA), involving participants from a Swedish multicultural area characterized by low socioeconomic status. The 2-year intervention was continually developed and implemented, as a result of cooperation and shared decision making among researchers and the participants. All 54 participants were seventh graders, and the intervention comprised health coaching, health promotion sessions and a Facebook group. We experienced that participants valued collaborating with peers, and that they took responsibility in codeveloping and implementing the intervention. Participants expressed feeling listened to, being treated with respect and taken seriously. However, we also experienced a number of barriers that challenged our initial intentions of aiding participation and ambition to support empowerment. Moreover, it was challenging to use structured group health coaching and to work with goal-setting in groups of participants with shared, and sometimes competing, goals, wishes and needs related to food and PA. Successful experiences from this intervention was the importance of acquiring a broad and deep understanding of the context and participants, being open to negotiating, as well as adjusting the intervention. © The Author(s) 2019. Published by Oxford University Press. All rights reserved.
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| 33. |
- Jonsson, Linus, 1986, et al.
(author)
-
Possibilities and challenges in developing and implementing an empowerment-based school-intervention in a Swedish disadvantaged community
- 2020
-
In: Health Promotion International. - 0957-4824 .- 1460-2245. ; 35:2, s. 232-243
-
Journal article (peer-reviewed)abstract
- In this paper, we describe and critically reflect on the possibilities and challenges of developing and implementing an empowerment-based school intervention regarding healthy food and physical activity (PA), involving participants from a Swedish multicultural area characterized by low socioeconomic status. The 2-year intervention was continually developed and implemented, as a result of cooperation and shared decision making among researchers and the participants. All 54 participants were seventh graders, and the intervention comprised health coaching, health promotion sessions and a Facebook group. We experienced that participants valued collaborating with peers, and that they took responsibility in codeveloping and implementing the intervention. Participants expressed feeling listened to, being treated with respect and taken seriously. However, we also experienced a number of barriers that challenged our initial intentions of aiding participation and ambition to support empowerment. Moreover, it was challenging to use structured group health coaching and to work with goal-setting in groups of participants with shared, and sometimes competing, goals, wishes and needs related to food and PA. Successful experiences from this intervention was the importance of acquiring a broad and deep understanding of the context and participants, being open to negotiating, as well as adjusting the intervention.
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| 34. |
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| 35. |
- Larsson, Magnus, et al.
(author)
-
Strain mapping in free-standing heterostructured wurtzite InAs/InP nanowires
- 2007
-
In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:1
-
Journal article (peer-reviewed)abstract
- The strain distribution in heterostructured wurtzite InAs/InP nanowires is measured by a peak finding technique using high resolution transmission electron microscopy images. We find that nanowires with a diameter of about 20 nm show a 10 nm strained area over the InAs/InP interface and the rest of the wire has a relaxed lattice structure. The lattice parameters and elastic properties for the wurtzite structure of InAs and InP are calculated and a nanowire interface is simulated using finite element calculations. Both the method and the experimental results are validated using a combination of finite element calculations and image simulations.
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| 36. |
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| 37. |
- Nilsson, Henrik, et al.
(author)
-
Nanowire-based multiple quantum dot memory
- 2006
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:16
-
Journal article (peer-reviewed)abstract
- The authors propose and demonstrate an alternative memory concept in which a storage island is connected to a nanowire containing a stack of nine InAs quantum dots, each separated by thin InP tunnel barriers. Transport through the quantum dot structure is suppressed for a particular biasing window due to misalignment of the energy levels. This leads to hysteresis in the charging/discharging of the storage island. The memory operates for temperatures up to around 150 K and has write times down to at least 15 ns. A comparison is made to a nanowire memory based on a single, thick InP barrier.
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| 38. |
- Persson, A. I., et al.
(author)
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The fabrication of dense and uniform InAs nanowire arrays
- 2009
-
In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 20:22
-
Journal article (peer-reviewed)abstract
- Nanowires are important candidates for use in future electronics, photonics and thermoelectrics applications. We focus here in particular on nanowires for use in thermoelectric power generation and present a method of fabricating dense uniform InAs nanowire arrays amenable to future incorporation of advanced heterostructures that could further increase the thermoelectric performance of these nanowires. In these applications it will be important to have the nanowires densely packed in order to give an appreciable amount of power output. Here we present the fabrication of such dense arrays, using metal-particle seeded growth and chemical beam epitaxy, where the metal particles are defined by electron beam lithography, metal evaporation and lift-off. We evaluate the potential of chemical beam epitaxy for the growth of dense, freestanding InAs nanowire arrays and describe the process that enabled us to achieve areal packing densities of up to 19% with a variation of only a few per cent in nanowire diameter and height. We close by discussing how even higher areal packing densities can be achieved.
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| 39. |
- Persson, Ann, et al.
(author)
-
Surface diffusion effects on growth of nanowires by chemical beam epitaxy
- 2007
-
In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101
-
Journal article (peer-reviewed)abstract
- Surface processes play a large role in the growth of semiconductor nanowires by chemical beam epitaxy. In particular, for III-V nanowires the surface diffusion of group-III species is important to understand in order to control the nanowire growth. In this paper, we have grown InAs-based nanowires positioned by electron beam lithography and have investigated the dependence of the diffusion of In species on temperature, group-III and -V source pressure and group-V source combinations by measuring nanowire growth rate for different nanowire spacings. We present a model which relates the nanowire growth rate to the migration length of In species. The model is fitted to the experimental data for different growth conditions, using the migration length as fitting parameter. The results show that the migration length increases with decreasing temperature and increasing group-V/group-III source pressure ratio. This will most often lead to an increase in growth rate, but deviations will occur due to incomplete decomposition and changes in sticking coefficient for group-III species. The results also show that the introduction of phosphorous precursor for growth of InAs1−xPx nanowires decreases the migration length of the In species followed by a decrease in nanowire growth rate.
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| 40. |
- Pettersson, Håkan, et al.
(author)
-
Friction measurements on InAs NWs by AFM manipulation
- 2008
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Conference paper (peer-reviewed)abstract
- We discuss a new approach to measure the friction force between elastically deformed nanowires and a surface. The wires are bent, using an AFM, into an equilibrium shape determined by elastic restoring forces within the wire and friction between the wire and the surface. From measurements of the radius of curvature of the bent wires, elasticity theory allows the friction force per unit length to be calculated. We have studied friction properties of InAs nanowires deposited on SiO2, silanized SiO2 and Si3N4 substrates. The wires were typically from 0.5 to a few microns long, with diameters varying between 20 and 80 nm. Manipulation is done in a `Retrace Lift' mode, where feedback is turned off for the reverse scan and the tip follows a nominal path. The effective manipulation force during the reverse scan can be changed by varying an offset in the height of the tip over the surface. We will report on interesting static- and sliding friction experiments with nanowires on the different substrates, including how the friction force per unit length varies with the diameter of the wires.
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| 41. |
- Pettersson, Håkan, 1962-, et al.
(author)
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Nanowire friction with an applied bias
- 2010
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In: Bulletin of the American Physical Society. - : American Physical Society.
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Conference paper (peer-reviewed)abstract
- Recently, we have shown how the friction experienced by nanowires pushed by an AFM tip can be determined by measuring their radius of curvature after manipulation [1]. It is of fundamental interest to know whether the wires behave like macroscopic objects, or if they are more like true atomic-scale point contacts where friction becomes independent of the applied normal force. Here we study how the friction between InAs nanowires and a SiN layer on conductive silicon varies when a DC voltage is applied. The tip charges the capacitor formed by the wire and the silicon back contact, causing attractive Coulomb forces and so increasing the contact pressure. A monotonic increase of the sliding friction with voltage was observed. This implies that the friction increases with the normal force and that this mesoscopic system behaves more like a macroscopic contact, despite being only nanometers in size in the direction of motion.
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| 42. |
- Pettersson, Håkan, 1962-, et al.
(author)
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Shear stress measurements on InAs nanowires by AFM manipulation
- 2007
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In: Bulletin of the American Physical Society. - New York : American Physical Society. - 0003-0503. ; 52:1
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Journal article (peer-reviewed)abstract
- In this paper, we report on a novel approach to measure shear stress between elastic nanowires and a SiO2 surface. The method is based on the fact that the curvature of an elastically deformed nanowire pinned to a flat surface contains information about the maximal static friction force, i.e., the shear stress between the wire and the surface. At rest, the deformed wire is kept in equilibrium by counterbalancing static friction forces and restoring elastic forces. In the present work, InAs nanowires are bent in a controlled manner using the tip of an atomic force microscope (AFM). After the manipulation, the curvature of the most bent state can be determined from AFM micrographs. Assuming bulk values for the Young’s modulus, the shear stress can be obtained from straight- forward analyses according to standard theory of elasticity.
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| 43. |
- Rehnstedt, Carl, et al.
(author)
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Drive current and threshold voltage control in vertical InAs wrap-gate transistors
- 2008
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In: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 44:3, s. 236-237
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Journal article (peer-reviewed)abstract
- Results on fabrication and DC-characterisation of vertical InAs nanowire wrap-gate field-effect transistor arrays with a gate length of 50 nm are presented. Each nanowire array was processed into a transistor with a systematic variation in a number of wires and wire diameter over the sample. Extensive studies have been performed on the influence of wire number and diameter on the transistor characteristics due to a high device yield (84%). In particular it is shown that the threshold voltage depends on the wire diameter, with a change in the order of 5 mV/nm. These results show the possibility of changing the transistor characteristics on the sample by altering the wire dimensions, still using only one patterning and growth sequence.
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| 44. |
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| 45. |
- Roddaro, Stefano, et al.
(author)
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Growth of vertical InAs nanowires on heterostructured substrates
- 2009
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 20:28
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Journal article (peer-reviewed)abstract
- We investigate the Au-assisted growth of InAs nanowires on two different kinds of heterostructured substrates: GaAs/AlGaAs structures capped by a 50 nm thick InAs layer grown by molecular beam epitaxy and a 2 mu m thick InAs buffer layer on Si(111) obtained by vapor phase epitaxy. Morphological and structural properties of substrates and nanowires are analyzed by atomic force and transmission electron microscopy. Our results indicate a promising direction for the integration of III-V nanostructures on Si-based electronics as well as for the development of novel micromechanical structures incorporating nanowires as their active elements.
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| 46. |
- Suyatin, Dmitry, et al.
(author)
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Electrical properties of self-assembled branched InAs nanowire junctions
- 2008
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 8:4, s. 1100-1104
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Journal article (peer-reviewed)abstract
- We investigate electrical properties of self-assembled branched InAs nanowires. The branched nanowires are catalytically grown using chemical beam epitaxy, and three-terminal nanoelectronic devices are fabricated from the branched nanowires using electron-beam lithography. We demonstrate that, in difference from conventional macroscopic junctions, the fabricated self-assembled nanowire junction devices exhibit tunable nonlinear electrical characteristics and a signature of ballistic electron transport. As an example of applications, we demonstrate that the self-assembled three-terminal nanowire junctions can be used to implement the functions of frequency mixing, multiplication, and phase-difference detection of input electrical signals at room temperature. Our results suggest a wide range of potential applications of branched semiconductor nanostructures in nanoelectronics.
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| 47. |
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| 48. |
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| 49. |
- Thelander, Claes, et al.
(author)
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The electrical and structural properties of n-type InAs nanowires grown from metal-organic precursors.
- 2010
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 21:20
-
Journal article (peer-reviewed)abstract
- The electrical and structural properties of 111B-oriented InAs nanowires grown using metal-organic precursors have been studied. On the basis of electrical measurements it was found that the trends in carbon incorporation are similar to those observed in the layer growth, where an increased As/In precursor ratio and growth temperature result in a decrease in carbon-related impurities. Our results also show that the effect of non-intentional carbon doping is weaker in InAs nanowires compared to bulk, which may be explained by lower carbon incorporation in the nanowire core. We determine that differences in crystal quality, here quantified as the stacking fault density, are not the primary cause for variations in resistivity of the material studied. The effects of some n-dopant precursors (S, Se, Si, Sn) on InAs nanowire morphology, crystal structure and resistivity were also investigated. All precursors result in n-doped nanowires, but high precursor flows of Si and Sn also lead to enhanced radial overgrowth. Use of the Se precursor increases the stacking fault density in wurtzite nanowires, ultimately at high flows leading to a zinc blende crystal structure with strong overgrowth and very low resistivity.
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| 50. |
- Thelander, Claes, et al.
(author)
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Vertical enhancement-mode InAs nanowire field-effect transistor with 50-nm wrap gate
- 2008
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In: IEEE Electron Device Letters. - 0741-3106. ; 29:3, s. 206-208
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Journal article (peer-reviewed)abstract
- We present results on fabrication and de characterization of vertical InAs nanowire wrap-gate field-effect transistor arrays with a gate length of 50 nm. The wrap gate is defined by evaporation of 50-nm Cr onto a 10-nm-thick HfO2 gate dielectric, where the gate is also separated from the source contact with a 100-nm SiOx spacer layer. For a drain voltage of 0.5 V, we observe a normalized transconductance of 0.5 S/mm, a subthreshold slope around 90 mV/dec, and a threshold voltage just above 0 V. The highest observed normalized on current is 0.2 A/mm, with an off current of 0.2 mA/mm. These devices show a considerable improvement compared to previously reported vertical InAs devices with SiNx gate dielectrics.
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